Reactions of the Dirhenium(II) Complexes Re(2)X(4)(dppm)(2) (X = Cl, Br; dppm = Ph(2)PCH(2)PPh(2)) with Isocyanides. 10.(1) Synthesis and Characterization of the Complex [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) and Several Isomeric Forms of [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]Y (Y = PF(6), O(3)SCF(3))

The reactions of the unsymmetrical, coordinatively unsaturated dirhenium(II) complexes [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y = O(3)SCF(3) (3a), PF(6) (3b)) with XylNC afford at least three isomeric forms of the complex cation [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+). Two forms have very similar bis(&mgr;-halo)-bridged edge-sharing bioctahedral structures of the type [(CO)BrRe(&mgr;-Br)(2)(&mgr;-dppm)(2)Re(CNXyl)(2)]Y (Y = O(3)SCF(3) (4a/4a'), PF(6) (4b/4b')), while the third is an open bioctahedron [(XylNC)(2)BrRe(&mgr;-dppm)(2)ReBr(2)(CO)]Y (Y = O(3)SCF(3) (5a), PF(6) (5b)). While the analogous chloro complex cation [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+) was previously shown to exist in three isomeric forms, only one of these has been found to be structurally similar to the bromo complexes (i.e. the isomer analogous to 5a and 5b). The reaction of 3a with CO gives the salt [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) (7), in which the edge-sharing bioctahedral cation [(XylNC)BrRe(&mgr;-Br)(&mgr;-CO)(&mgr;-dppm)(2)ReBr(CO)](+) has an all-cis arrangement of pi-acceptor ligands. The Re-Re distances in the structures of 4b', 5a, and 7 are 3.0456(8), 2.3792(7), and 2.5853(13) ?, respectively, and accord with formal Re-Re bond orders of 1, 3, and 2, respectively. Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](PF(6))(0.78)(ReO(4))(0.22).CH(2)Cl(2) (4b') at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 19.845(4) ?, b = 16.945(5) ?, c = 21.759(3) ?, beta = 105.856(13) degrees, V = 7038(5) ?(3), and Z = 4. The structure was refined to R = 0.060 (R(w) = 0.145) for 14 245 data (F(o)(2) > 2sigma(F(o)(2))). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3).C(6)H(6) (5a) at 173 K: monoclinic space group P2(1)/n (No. 14) with a = 14.785(3) ?, b = 15.289(4) ?, c = 32.067(5) ?, beta = 100.87(2) degrees, V=7118(5) ?(3), and Z = 4. The structure was refined to R = 0.046 (R(w) = 0.055) for 6962 data (I > 3.0sigma(I)). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3).Me(2)CHC(O)Me (7) at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 14.951(2) ?, b = 12.4180(19) ?, c = 40.600(5) ?, beta = 89.993(11) degrees, V = 7537(3) ?(3), and Z = 4. The structure was refined to R = 0.074 (R(w) = 0.088) for 6595 data (I > 3.0sigma(I)).     

Preparation, Molecular and Electronic Structures, and Magnetic Properties of Face-Sharing Bioctahedral Titanium(III) Compounds: [PPh(4)][Ti(2)(&mgr;-Cl)(3)Cl(4)(PR(3))(2)

Reduction of TiCl(4) with 1 equiv of HSnBu(3) followed by addition of [PPh(4)]Cl and then PR(3) leads to two new dinuclear titanium(III) compounds, [PPh(4)][Ti(2)(&mgr;-Cl)(3)Cl(4)(PR(3))(2)] (R = Et and R(3) = Me(2)Ph), both of which contain an anion with the face-sharing bioctahedral type structure. Their crystal structures are reported. [PPh(4)][Ti(2)(&mgr;-Cl)(3)Cl(4)(PEt(3))(2)].2CH(2)Cl(2) crystallized in the triclinic space group P&onemacr;. Cell dimensions: a = 12.461(1) ?, b = 20.301(8) ?, c = 11.507(5) ?, alpha = 91.44 degrees, beta = 113.27(1) degrees, gamma = 104.27(2) degrees, and Z = 2. The distance between titanium atoms is 3.031(2) ?. [PPh(4)][Ti(2)(&mgr;-Cl)(3)Cl(4)(PMe(2)Ph)(2)].CH(2)Cl(2) also crystallized in the triclinic space group P&onemacr; with cell dimensitions a = 11.635(4) ?, b = 19.544(3) ?, c = 11.480(3) ?, alpha = 100.69(2) degrees, beta = 109.70(1) degrees, gamma = 95.08(2) degrees, and Z = 2. The distance between titanium atoms in this compound is 2.942(1) ?. Variable temperature magnetic susceptibilities were measured for [PPh(4)][Ti(2)(&mgr;-Cl)(3)Cl(4)(PEt(3))(2)]. Electronic structure calculations were carried out for a model ion, [Ti(2)(&mgr;-Cl)(3)Cl(4)(PH(3))(2)](-), and another well-known anion, [Ti(2)(&mgr;-Cl)(3)Cl(6)](3)(-), by employing an ab initio configuration interaction method. The results of the calculations reveal that the metal-metal interaction in these Ti(III) face-sharing compounds can be best described by strong antiferromagnetic coulping that leads to a singlet ground state and a thermally accessible triplet first excited state. Accordingly the measured magnetic data were satisfactorily fitted to a spin-only formula.     

Metal Binding of Polyalcohols. 4. Structure and Magnetism of the Hexanuclear, &mgr;(6)-Oxo-Centered [OFe(6)(H(-)(3)thme)(3)(OCH(3))(3)Cl(6)](2)(-) (thme = 1,1,1-Tris(hydroxymethyl)ethane)

The addition of [N(CH(3))(4)]OH to a methanolic solution of FeCl(3) and thme (thme = 1,1,1-tris(hydroxymethyl)ethane) yielded [N(CH(3))(4)](2)[OFe(6)(H(-)(3)thme)(3)(OCH(3))(3)Cl(6)].2H(2)O (1). Crystal data: C(26)H(64)Cl(6)Fe(6)N(2)O(15), trigonal space group P31c, a = 12.459(2) ?, c = 18.077(4) ?, Z = 2. The complex anion exhibits the well-known &mgr;(6)-O-Fe(6)-(&mgr;(2)-OR)(12) structure with three &mgr;(2)-methoxo bridges, three triply deprotonated H(-)(3)thme ligands, where each alkoxo group bridges two Fe(III) centers, and six terminally coordinating Cl(-) ligands. In contrast to two previously described ferric complexes with an analogous structure of the complex core, compound 1 is stable in air. Variable-temperature magnetic susceptibility measurements established antiferromagnetic exchange coupling interactions with J(trans)(Fe-&mgr;(6)-O-Fe) = 24.5 cm(-)(1), J(cis)(Fe-&mgr;(2)-O(thme)-Fe) = 11.5 cm(-)(1), and J(cis)'(Fe-&mgr;(2)-OCH(3)-Fe) = 19.5 cm(-)(1). The unexpectedly high value for J(trans) is explained by means of a superexchange pathway and is discussed for a simplified model by using MO calculations at the extended Hückel level.     

An Approach to Heterometallic Complexes with Selenolate and Tellurolate Ligands: Crystal Structures of cis-[Mn(CO)(4)(SePh)(2)](-), [(CO)(3)Mn(&mgr;-SeMe)(3)Mn(CO)(3)](-), (CO)(4)Mn(&mgr;-TePh)(2)Co(CO)(&mgr;-SePh)(3)Mn(CO)(3), and (CO)(3)Mn(&mgr;-SePh)(3)Fe(CO)(3)

Oxidative addition of diorganyl diselenides to the coordinatively unsaturated, low-valent transition-metal-carbonyl fragment [Mn(CO)(5)](-) produced cis-[Mn(CO)(4)(SeR)(2)](-). The complex cis-[PPN][Mn(CO)(4)(SePh)(2)] crystallized in triclinic space group P&onemacr; with a = 10.892(8) ?, b = 10.992(7) ?, c = 27.021(4) ?, alpha = 101.93(4) degrees, beta = 89.79(5) degrees, gamma = 116.94(5) degrees, V = 2807(3) ?(3), and Z = 2; final R = 0.085 and R(w) = 0.094. Thermolytic transformation of cis-[Mn(CO)(4)(SeMe)(2)](-) to [(CO)(3)Mn(&mgr;-SeMe)(3)Mn(CO)(3)](-) was accomplished in high yield in THF at room temperature. Crystal data for [Na-18-crown-6-ether][(CO)(3)Mn(&mgr;-SeMe)(3)Mn(CO)(3)]: trigonal space group R&thremacr;, a = 13.533(3) ?, c = 32.292(8) ?, V = 5122(2) ?(3), Z = 6, R = 0.042, R(w) = 0.041. Oxidation of Co(2+) to Co(3+) by diphenyl diselenide in the presence of chelating metallo ligands cis-[Mn(CO)(4)(SePh)(2)](-) and cis-[Mn(CO)(4)(TePh)(2)](-), followed by a bezenselenolate ligand rearranging to bridge two metals and a labile carbonyl shift from Mn to Co, led directly to [(CO)(4)Mn(&mgr;-TePh)(2)Co(CO)(&mgr;-SePh)(3)Mn(CO)(3)]. Crystal data: triclinic space group P&onemacr;, a = 11.712(3) ?, b = 12.197(3) ?, c = 15.754(3) ?, alpha = 83.56(2) degrees, beta = 76.13(2) degrees, gamma = 72.69(2) degrees, V = 2083.8(7) ?(3), Z = 2, R = 0.040, R(w) = 0.040. Addition of fac-[Fe(CO)(3)(SePh)(3)](-) to fac-[Mn(CO)(3)(CH(3)CN)(3)](+) resulted in formation of (CO)(3)Mn(&mgr;-SePh)(3)Fe(CO)(3). This neutral heterometallic complex crystallized in monoclinic space group P2(1)/n with a = 8.707(2) ?, b = 17.413(4) ?, c = 17.541(4) ?, beta = 99.72(2) degrees, V = 2621(1) ?(3), and Z = 4; final R = 0.033 and R(w) = 0.030.     

Synthesis, Characterization, and Comparative Properties of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)

The reaction of [PPN](2)[Re(6)C(CO)(19)] with Mo(CO)(6) and Ru(3)(CO)(12) under sunlamp irradiation provided the new mixed-metal clusters [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)], which were isolated in yields of 85% and 61%, respectively. The compound [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] crystallizes in the monoclinic space group P2(1)/c with a = 20.190 (7) ?, b = 16.489 (7) ?, c = 27.778 (7) ?, beta = 101.48 (2) degrees, and Z = 4 (at T = -75 degrees C). The cluster anion is composed of a Re(6)C octahedral core with a face capped by a Mo(CO)(4) fragment. There are three terminal carbonyl ligands coordinated to each rhenium atom. The four carbonyl ligands on the molybdenum center are essentially terminal, with one pair of carbonyl ligands (C72-O72 and C74-O74) subtending a relatively large angle at molybdenum (C72-Mo-C74 = 147.2(9) degrees ), whereas the remaining pair of carbonyl ligands (C71-O71 and C73-O73) subtend a much smaller angle (C71-Mo-C73 = 100.5(9) degrees ). The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows signals for four sets of carbonyl ligands at -40 degrees C, consistent with the solid state structure, but the carbonyl ligands undergo complete scrambling at ambient temperature. The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] at 20 degrees C is consistent with the expected structure of an octahedral Re(6)C(CO)(18) core capped by a Ru(CO)(3) fragment. The visible spectrum of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows a broad, strong band at 670 nm (epsilon = 8100), whereas all of the absorptions of [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] are at higher energy. An irreversible oxidation wave with E(p) at 0.34 V is observed for [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)], whereas two quasi-reversible oxidation waves with E(1/2) values of 0.21 and 0.61 V (vs Ag/AgCl) are observed for [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)]. The molybdenum cap in [Re(6)C(CO)(18)Mo(CO(4))](2-) is cleaved by heating in donor solvents, and by treatment with H(2), to give largely [H(2)Re(6)C(CO)(18)](2-). In contrast, [Re(6)C(CO)(18)Ru(CO)(3)](2-) shows no tendency to react under similar conditions.     

Magnetic Susceptibility Trends in Oxo-Bridged, Dinuclear Chromium(III) Complexes. Crystal Structure of [(tmpa)Cr(&mgr;-O)(&mgr;-CO(3))Cr(tmpa)](ClO(4))(2).2H(2)O

The synthesis and physical characterization of oxo-bridged [Cr(2)(tmpa)(2)(&mgr;-O)(X)](n)()(+) complexes (tmpa = tris(2-pyridylmethyl)amine) containing a variety of complementary ligands (X = CO(3)(2)(-), PhPO(4)(2)(-), HS(-)) are described, with the objective of understanding factors underlying variations in the antiferromagnetic coupling constant J. We also present the crystal structure of [(tmpa)Cr(&mgr;-O)(&mgr;-CO(3))Cr(tmpa)](ClO(4))(2).2H(2)O, for comparison with previous findings on [(tmpa)Cr(&mgr;-O)(&mgr;-CH(3)CO(2))Cr(tmpa)](ClO(4))(3). The carbonate-bridged complex crystallizes in the monoclinic space group P2(1)/c with a = 11.286(10) ?, b = 18.12(2) ?, c = 20.592(12) ?, beta = 95.99(5) degrees, and V = 4190 ?(3) and Z = 4. Asymmetric tmpa ligation pertains, with apical N atoms situated trans to bridging oxo and acido O atoms. Key structural parameters include Cr-O(b) bond lengths of 1.818(6) and 1.838(6) ?, Cr-OCO(2) distances of 1.924(7) and 1.934(7) ?, and a bridging bond angle of 128.3(3) degrees. Several attempts to prepare oxo, amido-bridged dimers were unsuccessful, but the nearlinear [Cr(tmpa)(N(CN)(2))](2)O(ClO(4))(2).3H(2)O complex was isolated from the reaction of dicyanamide ion with [Cr(tmpa)(OH)](2)(4+). In contrast to the behavior of analogous diiron(III) complexes, antiferromagnetic coupling constants of [Cr(2)(tmpa)(2)(&mgr;-O)(X)](n)()(+) dinuclear species are highly responsive to the X group. Considering the complexes with X = CO(3)(2)(-), PhPO(4)(2)(-), HS(-), SO(4)(2)(-), and RCO(2)(-) (10 R substituents), we find a reasonably linear, empirical relationship between J and oxo bridge basicity, as measured by pK(a) (Cr(OH)Cr) values in aqueous solution. While there is no theoretical basis for such a correlation between solid-state and solution-phase properties, this relationship demonstrates that CrOCr pi-bonding contributes significantly to antiferromagnetic exchange. Thus, J tends to become less negative with increasing &mgr;-O(2)(-) basicity, showing that greater availability of a bridging oxo group lone pair toward the proton, with decreasing CrOCr pi-interaction, reduces the singlet-triplet gap.     

Isolation of a Bismuth Chloride-Iron Carbonyl Adduct: Synthesis and Structural Characterization of [PhCH(2)NMe(3)](2)[Bi(2)Cl(4)(&mgr;-Cl)(2){&mgr;-Fe(CO)(4)}

The reaction of bismuth(III) chloride with [PhCH(2)NMe(3)](2)[Fe(CO)(4)] at a ratio of 2:1 in acetonitrile yields the iron carbonyl-bismuth chloride adduct [PhCH(2)NMe(3)](2)[Bi(2)Cl(4)(&mgr;-Cl)(2){&mgr;-Fe(CO)(4)}] cleanly in high yield. The complex consists of two BiCl(3) groups bridged by an [Fe(CO)(4)](2)(-) unit. Two chloride ligands are shared between the Bi atoms, producing square-pyramidal coordination at bismuth and octahedral coordination at the iron center. The production of this complex represents the synthesis of a stable adduct of a highly nucleophilic metal carbonyl anion with a strongly Lewis acidic main group halide. The compound C(24)H(32)N(2)O(4)Bi(2)Cl(6)Fe crystallizes in the orthorhombic space group Pba2 (No. 32) with cell parameters a = 14.624(3) ?, b = 17.010(3) ?, c = 7.1990(10) ?, V = 1790.8(5) ?(3), and Z = 2.     

Tetranuclear and Pentanuclear Vanadium(IV/V) Carboxylate Complexes: [V(4)O(8)(NO(3))(O(2)CR)(4)](2-) and [V(5)O(9)X(O(2)CR)(4)](2-) (X = Cl(-), Br(-)) Salts

The syntheses and properties of tetra- and pentanuclear vanadium(IV,V) carboxylate complexes are reported. Reaction of (NBzEt(3))(2)[VOCl(4)] (1a) with NaO(2)CPh and atmospheric H(2)O/O(2) in MeCN leads to formation of (NBzEt(3))(2)[V(5)O(9)Cl(O(2)CPh)(4)] 4a; a similar reaction employing (NEt(4))(2)[VOCl(4)] (1b) gives (NEt(4))(2)[V(5)O(9)Cl(O(2)CPh)(4)] (4b). Complex 4a.MeCN crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -148 degrees C: a = 13.863(13) ?, b = 34.009(43) ?, c = 12.773(11) ?, and Z = 4. The reaction between (NEt(4))(2)[VOBr(4)] (2a) and NaO(2)CPh under similar conditions gives (NEt(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6a), and the use of (PPh(4))(2)[VOBr(4)] (2b) likewise gives (PPh(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6b). Complex 6b crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -139 degrees C: a = 18.638(3) ?, b = 23.557(4) ?, c = 12.731(2) ?, and Z = 4. The anions of 4a and 6b consist of a V(5) square pyramid with each vertical face bridged by a &mgr;(3)-O(2)(-) ion, the basal face bridged by a &mgr;(4)-X(-) (X = Cl, Br) ion, and a terminal, multiply-bonded O(2)(-) ion on each metal. The RCO(2)(-) groups bridge each basal edge to give C(4)(v)() virtual symmetry. The apical and basal metals are V(V) and V(IV), respectively (i.e., the anions are trapped-valence). The reaction of 1b with AgNO(3) and Na(tca) (tca = thiophene-2-carboxylate) in MeCN under anaerobic conditions gives (NEt(4))(2)[V(4)O(8)(NO(3))(tca)(4)] (7). Complex 7.H(2)O crystallizes in space group C2/c with the following unit cell dimensions at -170 degrees C: a = 23.606(4) ?, b = 15.211(3) ?, c = 23.999(5) ?, and Z = 4. The anion of 7 is similar to those of 4a and 6b except that the apical [VO] unit is absent, leaving a V(4) square unit, and the &mgr;(4)-X(-) ion is replaced with a &mgr;(4),eta(1)-NO(3)(-) ion. The four metal centers are now at the V(IV), 3V(V) oxidation level, but the structure indicates four equivalent V centers, suggesting an electronically delocalized system. Variable-temperature magnetic susceptibility data were collected on powdered samples of 4b, 6a, and 7 in the 2.00-300 K range in a 10 kG applied field. 4b and 6a both show a slow increase in effective magnetic moment (&mgr;(eff)) from approximately 3.6-3.7 &mgr;(B) at 320 K to approximately 4.5-4.6 &mgr;(B) at 11.0 K and then a slight decrease to approximately 4.2 &mgr;(B) at 2.00 K. The data were fit to the theoretical expression for a V(IV)(4) square with two exchange parameters J = J(cis)() and J' = J(trans)() (H = -2JS(i)()S(j)()): fitting of the data gave, in the format 4b/6a, J= +39.7/+46.4 cm(-)(1), J' = -11.1/-18.2 cm(-)(1) and g = 1.83/1.90, with the complexes possessing S(T) = 2 ground states. The latter were confirmed by magnetization vs field studies in the 2.00-30.0 K and 0.500-50.0 kG ranges: fitting of the data gave S(T) = 2 and D = 0.00 cm(-)(1) for both complexes, where D is the axial zero-field splitting parameter. Complex 7 shows a nearly temperature-independent &mgr;(eff) (1.6-2.0 &mgr;(B)) consistent with a single d electron per V(4) unit. The (1)H NMR spectra of 4b and 6a in CD(3)CN are consistent with retention of their pentanuclear structure on dissolution. The EPR spectrum of 7 in a toluene/MeCN (1:2) solution at approximately 25 degrees C yields an isotropic signal with a 29-line hyperfine pattern assignable to hyperfine interactions with four equivalent I = (7)/(2) (51)V nuclei.     

Tetranuclear and Octanuclear Manganese Carboxylate Clusters: Preparation and Reactivity of (NBu(n)(4))[Mn(4)O(2)(O(2)CPh)(9)(H(2)O)] and Synthesis of (NBu(n)(4))(2)[Mn(8)O(4)(O(2)CPh)(12)(Et(2)mal)(2)(H(2)O)(2)] with a "Linked-Butterfly" Structure

The reaction of Mn(O(2)CPh)(2).2H(2)O and PhCO(2)H in EtOH/MeCN with NBu(n)(4)MnO(4) gives (NBu(n)(4))[Mn(4)O(2)(O(2)CPh)(9)(H(2)O)] (4) in high yield (85-95%). Complex 4 crystallizes in monoclinic space group P2(1)/c with the following unit cell parameters at -129 degrees C: a = 17.394(3) ?, b = 19.040(3) ?, c = 25.660(5) ?, beta = 103.51(1) degrees, V = 8262.7 ?(3), Z = 4; the structure was refined on F to R (R(w)) = 9.11% (9.26%) using 4590 unique reflections with F > 2.33sigma(F). The anion of 4 consists of a [Mn(4)(&mgr;(3)-O)(2)](8+) core with a "butterfly" disposition of four Mn(III) atoms. In addition to seven bridging PhCO(2)(-) groups, there is a chelating PhCO(2)(-) group at one "wingtip" Mn atom and terminal PhCO(2)(-) and H(2)O groups at the other. Complex 4 is an excellent steppingstone to other [Mn(4)O(2)]-containing species. Treatment of 4 with 2,2-diethylmalonate (2 equiv) leads to isolation of (NBu(n)(4))(2)[Mn(8)O(4)(O(2)CPh)(12)(Et(2)mal)(2)(H(2)O)(2)] (5) in 45% yield after recrystallization. Complex 5 is mixed-valent (2Mn(II),6Mn(III)) and contains an [Mn(8)O(4)](14+) core that consists of two [Mn(4)O(2)](7+) (Mn(II),3Mn(III)) butterfly units linked together by one of the &mgr;(3)-O(2)(-) ions in each unit bridging to one of the body Mn atoms in the other unit, and thus converting to &mgr;(4)-O(2)(-) modes. The Mn(II) ions are in wingtip positions. The Et(2)mal(2)(-) groups each bridge two wingtip Mn atoms from different butterfly units, providing additional linkage between the halves of the molecule. Complex 5.4CH(2)Cl(2) crystallizes in monoclinic space group P2(1)/c with the following unit cell parameters at -165 degrees C: a = 16.247(5) ?, b = 27.190(8) ?, c = 17.715(5) ?, beta = 113.95(1) degrees, V = 7152.0 ?(3), Z = 4; the structure was refined on F to R (R(w)) = 8.36 (8.61%) using 4133 unique reflections with F > 3sigma(F). The reaction of 4 with 2 equiv of bpy or picolinic acid (picH) yields the known complex Mn(4)O(2)(O(2)CPh)(7)(bpy)(2) (2), containing Mn(II),3Mn(III), or (NBu(n)(4))[Mn(4)O(2)(O(2)CPh)(7)(pic)(2)] (6), containing 4Mn(III). Treatment of 4 with dibenzoylmethane (dbmH, 2 equiv) gives the mono-chelate product (NBu(n)(4))[Mn(4)O(2)(O(2)CPh)(8)(dbm)] (7); ligation of a second chelate group requires treatment of 7 with Na(dbm), which yields (NBu(n)(4))[Mn(4)O(2)(O(2)CPh)(7)(dbm)(2)] (8). Complexes 7 and 8 both contain a [Mn(4)O(2)](8+) (4Mn(III)) butterfly unit. Complex 7 contains chelating dbm(-) and chelating PhCO(2)(-) at the two wingtip positions, whereas 8 contains two chelating dbm(-) groups at these positions, as in 2 and 6. Complex 7.2CH(2)Cl(2) crystallizes in monoclinic space group P2(1) with the following unit cell parameters at -170 degrees C: a = 18.169(3) ?, b = 19.678(4) ?, c = 25.036(4) ?, beta = 101.49(1) degrees, V = 8771.7 ?(3), Z = 4; the structure was refined on F to R (R(w)) = 7.36% (7.59%) using 10 782 unique reflections with F > 3sigma(F). Variable-temperature magnetic susceptibility studies have been carried out on powdered samples of complexes 2 and 5 in a 10.0 kG field in the 5.0-320.0 K range. The effective magnetic moment (&mgr;(eff)) for 2 gradually decreases from 8.61 &mgr;(B) per molecule at 320.0 K to 5.71 &mgr;(B) at 13.0 K and then increases slightly to 5.91 &mgr;(B) at 5.0 K. For 5, &mgr;(eff) gradually decreases from 10.54 &mgr;(B) per molecule at 320.0 K to 8.42 &mgr;(B) at 40.0 K, followed by a more rapid decrease to 6.02 &mgr;(B) at 5.0 K. On the basis of the crystal structure of 5 showing the single Mn(II) ion in each [Mn(4)O(2)](7+) subcore to be at a wingtip position, the Mn(II) ion in 2 was concluded to be at a wingtip position also. Employing the reasonable approximation that J(w)(b)(Mn(II)/Mn(III)) = J(w)(b)(Mn(III)/M(III)), where J(w)(b) is the magnetic exchange interaction between wingtip (w) and body (b) Mn ions of the indicated oxidation state, a theoretical chi(M) vs T expression was derived and used to fit the experimental molar magnetic susceptibility (chi(M)) vs T data. The obtained fitting parameters were J(w)(b) = -3.9 cm(-)(1), J(b)(b) = -9.2 cm(-)(1), and g = 1.80. These values suggest a S(T) = (5)/(2) ground state spin for 2, which was confirmed by magnetization vs field measurements in the 0.5-50.0 kG magnetic field range and 2.0-30.0 K temperature range. For complex 5, since the two bonds connecting the two [Mn(4)O(2)](7+) units are Jahn-Teller elongated and weak, it was assumed that complex 5 could be treated, to a first approximation, as consisting of weakly-interacting halves; the magnetic susceptibility data for 5 at temperatures >/=40 K were therefore fit to the same theoretical expression as used for 2, and the fitting parameters were J(w)(b) = -14.0 cm(-)(1) and J(b)(b) = -30.5 cm(-)(1), with g = 1.93 (held constant). These values suggest an S(T) = (5)/(2) ground state spin for each [Mn(4)O(2)](7+) unit of 5, as found for 2. The interactions between the subunits are difficult to incorporate into this model, and the true ground state spin value of the entire Mn(8) anion was therefore determined by magnetization vs field studies, which showed the ground state of 5 to be S(T) = 3. The results of the studies on 2 and 5 are considered with respect to spin frustration effects within the [Mn(4)O(2)](7+) units. Complexes 2 and 5 are EPR-active and -silent, respectively, consistent with their S(T) = (5)/(2) and S(T) = 3 ground states, respectively.     

Synthesis and structural characterization of trinuclear Cu(II)-pyrazolato complexes containing mu(3)-OH, mu(3)-O, and mu(3)-Cl ligands. Magnetic susceptibility study of [PPN](2)[(mu(3)-O)Cu(3)(mu-pz)(3)Cl(3)

The nine-membered [-Cu(II)-N-N-](3) ring of trimeric copper-pyrazolato complexes provides a sturdy framework on which water is twice deprotonated in consecutive steps, forming mu(3)-OH and mu(3)-O species. In the presence of excess chlorides the mu(3)-O(H) ligand is replaced by two mu(3)-Cl ions. The interconversion of mu(3)-OH and mu(3)-O and the exchange of mu(3)-O(H) and mu(3)-Cl are reversible, and the three species involved have been structurally characterized: [PPN][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(thf)].CH(2)Cl(2) (1a), monoclinic P2(1)/n, a = 10.055(2) A, b = 35.428(5) A, c = 15.153(2) A, beta = 93.802(3) degrees, V = 5386(1) A(3), Z = 4; [Bu(4)N][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)] (1b), triclinic P-1, a = 9.135(2) A, b = 13.631(2) A, c = 14.510(2) A, alpha = 67.393(2) degrees, beta = 87.979(2) degrees, gamma = 80.268(3) degrees, V = 1643.2(4) A(3), Z = 2; [PPN](2)[Cu(3)(mu(3)-O)(mu-pz)(3)Cl(3)] (2), monoclinic P2/c, a = 12.807(2) A, b = 13.093(2) A, c = 23.139(4) A, beta = 105.391(3) degrees, V = 3741(1) A(3), Z = 2; [PPN](2)[Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3)].0.75H(2)O.0.5CH(2)Cl(2) (3a), triclinic P-1, a = 14.042(2) A, b = 23.978(4) A, c = 25.195(4) A, alpha = 76.796(3) degrees, beta = 79.506(3) degrees, gamma = 77.629(3) degrees, V = 7988(2) A(3), Z = 4; [Bu(4)N](2)[Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3)] (3b), monoclinic C2/c, a = 17.220(2) A, b = 15.606(2) A, c = 20.133(2) A, beta = 103.057(2) degrees, V = 5270(1) A(3), Z = 4; [Et(3)NH][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(pzH)] (4), triclinic P-1, a = 11.498(2) A, b = 11.499(2) A, c = 12.186(2) A, alpha = 66.475(3) degrees, beta = 64.279(3) degrees, gamma = 80.183(3) degrees, V = 1331.0(5) A(3), Z = 2. Magnetic susceptibility measurements show that the three copper centers of 2 are strongly antiferromagnetically coupled with J(Cu-Cu) = -500 cm(-1).     

Synthesis and Reactivity of (Pentafluorophenyl)platinate(II) Complexes with Bridging 1,8-Naphthyridine (napy) and X Ligands (X = C(6)F(5), OH, Cl, Br, I, SPh). Crystal Structure of [NBu(4)][Pt(2)(&mgr;-napy)(&mgr;-OH)(C(6)F(5))(4)].CHCl(3)

By reaction of [NBu(4)](2)[Pt(2)(&mgr;-C(6)F(5))(2)(C(6)F(5))(4)] with 1,8-naphthyridine (napy), [NBu(4)][Pt(C(6)F(5))(3)(napy)] (1) is obtained. This compound reacts with cis-[Pt(C(6)F(5))(2)(THF)(2)] to give the dinuclear derivative [NBu(4)][Pt(2)(&mgr;-napy)(&mgr;-C(6)F(5))(C(6)F(5))(4)] (2). The reaction of several HX species with 2 results in the substitution of the bridging C(6)F(5) by other ligands (X) such as OH (3), Cl (4), Br (5), I (6), and SPh (7), maintaining in all cases the naphthyridine bridging ligand. The structure of 3 was determined by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic system, space group P2(1)/n, with a = 12.022(2) ?, b = 16.677(3) ?, c = 27.154(5) ?, beta = 98.58(3) degrees, V = 5383.2(16) ?(3), and Z = 4. The structure was refined to residuals of R = 0.0488 and R(w) = 0.0547. The complex consists of two square-planar platinum(II) fragments sharing a naphthyridine and OH bridging ligands, which are in cis positions. The short Pt-Pt distance [3.008(1) ?] seems to be a consequence of the bridging ligands.     

Coordination Chemistry of 2,2'-Dipyridyl Diselenide: X-ray Crystal Structures of PySeSePy, [Zn(PySeSePy)Cl(2)], [(PySeSePy)Hg(C(6)F(5))(2)], [Mo(SePy)(2)(CO)(3)], [W(SePy)(2)(CO)(3)], and [Fe(SePy)(2)(CO)(2)] (PySeSePy = C(5)H(4)NSeSeC(5)H(4)N; SePy = [C(5)H(4)N(2-Se)-N,Se])

The coordination chemistry of 2,2'-dipyridyl diselenide (PySeSePy) (2) (C(10)H(8)N(2)Se(2)) has been investigated and its crystal structure has been determined (monoclinic, P2(1)/c, a = 10.129(2) ?, b = 5.7332(12) ?, c = 19.173(3) ?, beta = 101.493(8) degrees, Z = 4). In metal complexes the ligand was found to coordinate in three different modes, as also confirmed by X-ray structure determination. N,N'-coordination was found in the zinc complex [Zn(PySeSePy)Cl(2)] (3) (C(10)H(8)Cl(2)N(2)Se(2)Zn, triclinic, P&onemacr;, a = 7.9430(10) ?, b = 8.147(2) ?, c = 11.999(2) ?, alpha = 93.685(10) degrees, beta = 107.763(10) degrees, gamma = 115.440(10) degrees, Z = 2) and Se,Se'-coordination in the adduct of the ligand with bis(pentafluorophenyl)mercury(II) [PySeSePyHg(C(6)F(5))(2)] (5) (C(10)H(8)F(10)HgN(2)Se(2), monoclinic, P2(1)/n, a = 7.7325(10) ?, b = 5.9974(14) ?, c = 25.573, beta = 98.037(10) degrees, Z = 2), which however displays only weak interactions between selenium and mercury. The reaction of the ligand with norbornadiene carbonyl complexes of molybdenum and tungsten leads to reductive cleavage of the selenium-selenium bond with oxidation of the metal center and concomitant addition of the resulting selenolate to the metal carbonyl fragment. Thus the 7-coordinate complexes [Mo(SePy)(2)(CO)(3)] (6) (C(13)H(8)MoN(2)O(3)Se(2), monoclinic, P2(1)/n, a = 9.319(3) ?, b = 12.886(5) ?, c = 13.231(6) ?, beta = 109.23(3) degrees, Z = 4) and [W(SePy)(2)(CO)(3)] (7) (C(13)H(8)N(2)O(3)Se(2)W, monoclinic, P2(1)/n, a = 9.303(2) ?, b = 12.853(2) ?, c = 13.232(2) ?, beta = 109.270(10) degrees, Z = 4) were obtained. The same N,Se-coordination pattern emerges from the reaction of [Fe(2)(CO)(9)] with (2) leading to [Fe(SePy)(2)(CO)(2)] (8) (C(12)H(8)FeN(2)O(2)Se(2), monoclinic, P&onemacr;, a = 8.6691(14) ?, b = 12.443(2) ?, c = 14.085(2) ?, alpha = 105.811(10) degrees, beta = 107.533(8) degrees, gamma = 92.075(10) degrees, Z = 4).     

Synthesis, Characterization, and Crystal Structure of a (&mgr;-Oxo)bis(&mgr;-acetato)diiron(III) Complex with a Dinucleating Hexapyridine Ligand, 1,2-Bis[2-(bis(2-pyridyl)methyl)-6-pyridyl]ethane. The First Example of a Discrete (&mgr;-Oxo)bis(&mgr;-acetato)diiron(III) Complex with a Dinucleating Ligand

A mononucleating tripyridine ligand, 2-(bis(2-pyridyl)methyl)-6-methylpyridine (L(1)), and a dinucleating hexapyridine ligand, 1,2-bis[2-(bis(2-pyridyl)methyl)-6-pyridyl]ethane (L(2)), have been prepared. The reaction of a carbanion of 2,6-lutidine with 2-bromopyridine affords L(1) which is converted to L(2) quantitatively by treating with tert-butyllithium and 1,2-dibromoethane. (&mgr;-Oxo)bis(&mgr;-acetato)diiron(III) complexes [Fe(2)(O)(OAc)(2)(L(1))(2)](ClO(4))(2) (1) and [Fe(2)(O)(OAc)(2)L(2)](ClO(4))(2) (2) have been synthesized and characterized by means of infrared, UV/vis, mass, and M?ssbauer spectroscopies and by measuring magnetic susceptibility and cyclic voltammograms. All the spectral data are consistent with the (&mgr;-oxo)bis(&mgr;-acetato)diiron(III) core structure in both 1 and 2. A relatively strong molecular ion peak at m/z 865 corresponding to [{Fe(2)O(OAc)(2)L(2)}(ClO(4))](+) in a FAB mass spectrum of 2 suggests the stabilization of the (&mgr;-oxo)bis(&mgr;-acetato)diiron(III) core structure by L(2) in a solution state. The compound 2.DMF.2-PrOH.H(2)O, chemical formula C(44)Cl(2)Fe(2)H(51)N(7)O(16), crystallizes in the monoclinic space group C2/c with a = 22.034(6) ?, b = 12.595(5) ?, c = 20.651(7) ?, beta = 121.49(2) degrees, and Z = 4. The cation has 2-fold symmetry with the bridging oxygen atom on the 2-fold axis: Fe-(&mgr;-O) = 1.782(5) ?, Fe-O-Fe = 123.6(6) degrees, and Fe.Fe = 3.142(3) ?. The diiron(III) core structure of 2 seems to be stabilized by encapsulation of the ligand. Compound 2 is the first example of a discrete (&mgr;-oxo)bis(&mgr;-acetato)diiron(III) complex with a dinucleating ligand.     

Linear Trinuclear Pt.Mo-Mo Complexes [Mo(2)PtX(2)(pyphos)(2)(O(2)CR)(2)](2) (X = Cl, Br, I; R = CH(3), C(CH(3))(3); pyphos = 6-(Diphenylphosphino)-2-pyridonate) with an Axial Interaction between the Quadruply Bonded Mo(2) Moiety and the Platinum Atom

An example of a direct axial interaction of a platinum(II) atom with a Mo(2) core through a uniquely designed tridentate ligand 6-(diphenylphosphino)-2-pyridonate (abbreviated as pyphos) is described. Treatment of PtX(2)(pyphosH)(2) (2a, X = Cl; 2b, X = Br; 2c, X = I) with a 1:1 mixture of Mo(2)(O(2)CCH(3))(4) and [Mo(2)(O(2)CCH(3))(2)(NCCH(3))(6)](2+) (3a) in dichloromethane afforded the linear trinuclear complexes [Mo(2)PtX(2)(pyphos)(2)(O(2)CCH(3))(2)](2) (4a, X = Cl; 4b, X = Br; 4c, X = I). The reaction of [Mo(2)(O(2)CCMe(3))(2)(NCCH(3))(4)](2+) (3b) with 2a-c in dichloromethane afforded the corresponding pivalato complexes [Mo(2)PtX(2)(pyphos)(2)(O(2)CCMe(3))(2)](2) (5a, X = Cl; 5b, X = Br; 5c, X = I), whose bonding nature is discussed on the basis of the data from Raman and electronic spectra as well as cyclic voltammograms. The linear trinuclear structures in 4b and 5a-c were confirmed by NMR studies and X-ray analyses: 4b, monoclinic, space group C2/c, a = 34.733(4) ?, b = 17.81(1) ?, c = 22.530(5) ?, beta = 124.444(8) degrees, V = 11498(5) ?(3), Z = 8, R = 0.060 for 8659 reflections with I > 3sigma(I) and 588 parameters; 5a, triclinic, space group P&onemacr;, a = 13.541(3) ?, b = 17.029(3) ?, c = 12.896(3) ?, alpha = 101.20(2) degrees, beta = 117.00(1) degrees, gamma = 85.47(2) degrees, V = 2599(1) ?(3), Z = 2, R = 0.050 for 8148 reflections with I > 3sigma(I) and 604 parameters; 5b, triclinic, space group P&onemacr;, a = 12.211(2) ?, b = 20.859(3) ?, c = 10.478(2) ?, alpha = 98.88(1) degrees, beta = 112.55(2) degrees, gamma = 84.56(1) degrees, V = 2433.3(8) ?(3), Z = 2, R = 0.042 for 8935 reflections with I > 3sigma(I) and 560 parameters; 5c, monoclinic, space group P2(1)/n, a = 13.359(4) ?, b = 19.686(3) ?, c = 20.392(4) ?, beta = 107.92(2) degrees, V = 5101(2) ?(3), Z = 4, R = 0.039 for 8432 reflections with I > 3sigma(I) and 560 parameters.     

X-ray Crystallographic Study of the Ruthenium Blue Complexes [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2): Steric Interactions and the Ru-Ru "Bond Length"

X-ray crystal structures are reported for the following complexes: [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O (tacn = 1,4,7-triazacyclononane), monoclinic P2(1)/n, Z = 4, a = 14.418(8) ?, b = 11.577(3) ?, c = 18.471(1) ?, beta = 91.08(5) degrees, V = 3082 ?(3), R(R(w)) = 0.039 (0.043) using 4067 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, monoclinic P2(1)/a, Z = 4, a = 13.638(4) ?, b = 12.283(4) ?, c = 18.679(6) ?, beta = 109.19(2) degrees, V = 3069.5 ?(3), R(R(w)) = 0.052 (0.054) using 3668 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)I(3)(tacn)(2)](PF(6))(2), cubic P2(1)/3, Z = 3, a = 14.03(4) ?, beta = 90.0 degrees, V = 2763.1(1) ?(3), R (R(w)) = 0.022 (0.025) using 896 unique data with I > 2.5sigma(I) at 293 K. All of the cations have cofacial bioctahedral geometries, although [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2) are not isomorphous. Average bond lengths and angles for the cofacial bioctahedral cores, [N(3)Ru(&mgr;-X)(3)RuN(3)](2+), are compared to those for the analogous ammine complexes [Ru(2)Cl(3)(NH(3))(6)](BPh(4))(2) and [Ru(2)Br(3)(NH(3))(6)](ZnBr(4)). The Ru-Ru distances in the tacn complexes are longer than those in the equivalent ammine complexes, probably as a result of steric interactions.     

Structural, Spectroscopic, and Magnetochemical Characterization of the Trinuclear Vanadium(III) Carboxylates [V(3)O(O(2)CR)(6)L(3)](ClO(4)) (R = Various Groups; L = Pyridine, 4-Picoline, 3,5-Lutidine)

Synthetic procedures are described that allow access to the [V(3)O(O(2)CR)(6)L(3)](ClO(4)) (R = various groups; L = pyridine (py), 4-picoline (pic) or 3,5-lutidine (lut)) family of complexes. Treatment of VCl(3)(THF)(3) with NaO(2)CR (R = Me, Et) in RCO(2)H/py, pic/MeCN, or CH(2)Cl(2) solution followed by addition of NBu(n)(4)ClO(4) leads to isolation of [V(3)O(O(2)CR)(6)L(3)](ClO(4)) salts in 47-95% yields. A similar procedure for R = C(6)H(5), C(6)H(4)-p-OMe, C(6)H(3)-m-Me(2), and C(6)H(4)-p-Cl but omitting addition of NaO(2)CR provides the corresponding benzoate or substituted-benzoate derivatives in 24-56% yields. The X-ray structure of [V(3)O(O(2)CEt)(6)(pic)(3)](ClO(4)) (4) shows the anion to consist of a [V(3)O](7+) triangular fragment with a &mgr;(3)-O(2)(-) ion in the V(3) plane; each triangular edge is bridged by two EtCO(2)(-) groups in their familiar syn,syn modes, and there is a terminal pic group on each V(III) completing distorted octahedral geometries at the metal atoms. The cation has imposed C(2) symmetry (isosceles V(3) triangle), the C(2) axis passing through one V atom and the central &mgr;(3)-O atom, but has D(3)(h)() virtual symmetry (equilateral V(3) triangle). Complex 4 crystallizes in monoclinic space group C2/c with the following unit cell dimensions at -171 degrees C: a = 13.935(2) ?, b = 18.323(2) ?, c = 17.470(2) ?, beta = 95.55(1) degrees, V = 4439.7 ?(3), Z = 4. The structure was solved using 2657 unique reflections with F > 3sigma(F) and refined on F to conventional R (R(w)) values of 0.058 (0.066). Variable-temperature, solid-state magnetic susceptibility measurements were made on complex 1 in the 5.01-280 K region in a 1 kG magnetic field. The effective magnetic moment (&mgr;(eff)) per V(3) unit decreases gradually from 4.64 &mgr;(B) at 280 K to 1.76 &mgr;(B) at 5.01 K. The data were fit to the theoretical expression for an isosceles V(III)(3) complex, and the fitting parameters were J = -18.0(7) cm(-)(1), J' = -10.4(4) cm(-)(1), and g = 1.985, with TIP held constant at 600 x 10(-)(6) cm(3) mol(-)(1); J' refers to the unique exchange interaction within the isosceles triangle. The ground state of complex 1 thus has S = 0.     

Reactions of the Dirhenium(II) Complexes Re(2)X(4)(&mgr;-dppm)(2) (X = Cl, Br; dppm = Ph(2)PCH(2)PPh(2)) with Isocyanides. 11.(1) A Triply Bonded Dirhenium Complex Containing a Labile Acetonitrile Ligand. Synthesis, Structural Characterization, and Reactivity of [(XylNC)(CH(3)CN)ClRe(&mgr;-dppm)(2)ReCl(2)(CO)]O(3)SCF(3)

The reaction of the open bioctahedral form of Re(2)Cl(4)(&mgr;-dppm)(2)(CO)(CNXyl) (1), where XylNC = 2,6-dimethylphenyl isocyanide, with TlO(3)SCF(3) in the presence of acetonitrile proceeds with retention of stereochemistry at the dirhenium unit to afford the complex [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(NCCH(3))]O(3)SCF(3) (3). The single-crystal X-ray structure determination of 3 shows that a Re&tbd1;Re bond is retained (the Re-Re distance is 2.378(3) ?) and that it is the chloride ligand trans to the XylNC ligand of 1 which is labilized. Complex 1 reacts with TlO(3)SCF(3) in a noncoordinating solvent to produce the unsymmetrical complex [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)]O(3)SCF(3) (2), through loss of this same chloride ligand of 1 and CO transfer from the adjacent Re center. The acetonitrile ligand of 3 is very labile and is readily displaced by XylNC and t-BuNC, with retention of stereochemistry, to produce complexes of stoichiometry [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(CNR)]O(3)SCF(3) (R = Xyl, 4a; R = t-Bu, 4b). In a noncoordinating solvent, the nitrile ligand of 3 is lost and 2 is formed following CO transfer; this conversion is reversed upon the reaction of 2 with acetonitrile. When 3 is treated with CO, the acetonitrile ligand is again displaced, but in this instance the reaction is accompanied by a structure change to produce an edge-sharing bioctahedral complex of the type [Re(2)(&mgr;-CO)(&mgr;-Cl)(&mgr;-dppm)(2)Cl(2)(CO)(CNXyl)]O(3)SCF(3) (5).     

Magnetochemical Properties and Reactions of Vanadium(III) Thiolate Complexes: Preparation of (NEt(4))(3)[V(3)Cl(6)(edt)(3)] and Mixed-Valence (NEt(4))[V(2)(edt)(4)] (edt = Ethane-1,2-dithiolate)

Reactions of the previously reported dinuclear vanadium(III) thiolate anion [V(2)(edt)(4)](2)(-) (edtH(2) = ethane-1,2-dithiol) are described. Treatment of (NEt(4))(2)[V(2)(edt)(4)] (1) in MeCN with equimolar (C(12)H(8)S(2))BF(4) (C(12)H(8)S(2)(+) = the thianthrenium radical cation) results in a one-electron oxidation and isolation of the V(III),V(IV) complex (NEt(4))[V(2)(edt)(4)] (2). The same product can also be obtained by controlled-potential electrolysis of 1 at -0.20 V vs Ag/AgCl. Treatment of 1 in CH(2)Cl(2) with py gives no reaction, but addition of Me(3)SiCl leads to formation of the known V(2)OCl(4)(py)(6) (3). The latter is also formed by the reduction of a 1:1 mixture of VOCl(3) and VCl(3)(THF)(3) in CH(2)Cl(2)/py and by the reaction in CH(2)Cl(2) of VCl(3)(THF)(3) and py with edt(2)(-). Treatment of 1 in MeCN with bpy (2,2'-bipyridine) gives no reaction, but addition of Me(3)SiCl results in formation and isolation of [V(2)OCl(2)(bpy)(4)]Cl(2) (4) identified by spectroscopic comparison with literature data. The reaction of 1 in MeCN with equimolar VCl(3)(THF)(3) and NEt(4)Cl gives (NEt(4))(3)[V(3)Cl(6)(edt)(3)] (5). A more convenient procedure to 5 is the reaction in MeCN of VCl(3)(THF)(3), Na(2)edt, and NEt(4)Cl in a 1:1:1 molar ratio. Complex 5.MeCN crystallizes in triclinic space group P&onemacr; with (at -154 degrees C) a = 14.918(3) ?, b = 17.142(5) ?, c = 11.276(3) ?, alpha = 106.78(1) degrees, beta = 95.03(1) degrees, gamma = 106.18(1) degrees, and Z = 2. The anion contains a near-linear V(3) unit with a face-sharing trioctahedral structure: the three edt(2)(-) groups provide the six bridging S atoms; two edt(2)(-) groups are in a &mgr;-eta(2):eta(2) mode (as in 1), but the third is in a &mgr;(3)-eta(1):eta(2):eta(1) mode. The V.V separations (>3.1 ?) preclude V-V bonding. Variable-temperature solid-state magnetic susceptibility studies have been performed on complexes 1, 2, and 5 in a 1.0 kG field and 5.00-300 K temperature range. For 1, the effective magnetic moment (&mgr;(eff)) gradually decreases from 1.09 &mgr;(B) at 300 K to 0.26 &mgr;(B) at 5.00 K. The data were fit to the Bleaney-Bowers equation, and the fitting parameters were J = -419(11) cm(-)(1) and g = 2.05. The singlet-triplet gap is thus 838 cm(-)(1). For 2, &mgr;(eff) is essentially temperature-independent, slowly decreasing from 1.90 &mgr;(B) at 300 K to 1.86 &mgr;(B) at 55 K and then to 1.63 &mgr;(B) at 5.00 K. The complex thus is S = (1)/(2) with no thermally accessible S = (3)/(2) state. The combined data on 1 and 2, together with the results of EHT calculations, show that 1 and 2 contain a V-V single bond tying up two of the d electrons and that the remaining two d electrons in 1 are antiferromagnetically coupled to give an S = 0 ground state and S = 1 excited state; for 2, the one remaining d electron gives an S = (1)/(2) state. For 5, &mgr;(eff) increases from 5.17 &mgr;(B) at 320 K to a maximum of 6.14 &mgr;(B) at 30.0 K and then decreases slightly to 6.08 &mgr;(B) at 5.00 K. The data were fit to the appropriate theoretical expression to give J = +42.5(6) cm(-)(1), J' = -1.8(5) cm(-)(1), and g = 1.77, where J and J' gauge the interactions between adjacent and terminal V(III) atoms, respectively. The complex has an S = 3 ground state and represents a very rare example of ferromagnetic coupling between V(III) centers.     

Molecular Assemblies Containing Unsupported [Fe(III)-(&mgr;(2):eta(2)-RCO(2))-Cu(II)] Bridges

Formate is an inhibitor of cytochrome oxidases and also effects conversion of the bovine heart enzyme from the "fast" to the "slow" cyanide-binding form. The molecular basis of these effects is unknown; one possibility is that formate inserts as a bridge into the binuclear heme a(3)-Cu(B) site, impeding the binding of dioxygen or cyanide. Consequently, Fe-Cu-carboxylate interactions are a matter of current interest. We have initiated an examination of such interactions by the synthesis of the first examples of [Fe(III)-(&mgr;(2):eta(2)-RCO(2))-Cu(II)] bridges, minimally represented by Fe(III)-L + Cu(II)-O(2)CR --> [Fe(III)-(RCO(2))-Cu(II)] + L. A series of Cu(II) precursor complexes and solvate forms have been prepared and their structures determined, including [Cu(Me(5)dien)(O(2)CH)](+) (3), [Cu(Me(5)dien)(O(2)CH)(MeOH)](+) (4), [Cu(Me(6)tren)(O(2)CH)](+) (5), and [Cu(Me(5)dien)(OAc)](+) (6). [4](ClO(4)) was obtained in monoclinic space group P2(1)/n with a = 8.166(3) ?, b = 15.119(5) ?, c = 15.070(4) ?, beta = 104.65(2) degrees, and Z = 4. [5](ClO(4))/[6](ClO(4)) crystallize in orthorhombic space groups Pnma/Pna2(1) with a = 16.788(2)/14.928(5) ?, b = 9.542(1)/9.341(4) ?, c = 12.911(1)/12.554(4) ?, and Z = 4/4. In all cases, the carboxylate ligand is terminal and is bound in a syn orientation. Also prepared for the purpose of structural comparison was [Fe(OEP)(O(2)CH)], which occurred in monoclinic space group P2(1)/c with a = 13.342(2) ?, b = 13.621(2) ?, c = 19.333(2) ?, beta = 106.12(2) degrees, and Z = 4. The desired bridges were stabilized in the assemblies [(OEP)Fe(O(2)CH)Cu(Me(5)dien)(OClO(3))](+) (9), [(OEP)Fe(OAc)Cu(Me(5)dien)](2+) (10), and {(OEP)Fe[(O(2)CH)Cu(Me(6)tren)](2)}(3+) (11), which were prepared by the reaction of 3, 6, and 5, respectively, with [Fe(OEP)(OClO(3))] in acetone or dichloromethane. [9](ClO(4))/[10](ClO(4))(2).CH(2)Cl(2) crystallize in triclinic space group P&onemacr; with a = 9.016(3)/13.777(3) ?, b = 15.377(5)/13.847(3) ?, c = 19.253(5)/17.608(4) ?, alpha = 78.12(3)/96.82(3) degrees, beta = 86.30(4)/108.06(3) degrees, gamma = 76.23(3)/114.32(3) degrees, and Z = 2/2. Each assembly contains a [Fe(III)-(RCO(2))-Cu(II)] bridge but with the differing orientations anti-anti (9) and syn-anti (10, 11). The compound [11](ClO(4))(2)(SbF(6)) occurs in orthorhombic space group Pbcn with a = 12.517(6) ?, b = 29.45(1) ?, c = 21.569(8) ?, and Z = 4. Complex 11 is trinuclear; the Fe(III) site has two axial formate ligands with bond distances indicative of a high-spin configuration. Structural features of 9-11 are discussed and are considered in relation to the possible insertion of formate into the binuclear sites of two oxidases whose structures were recently determined. The present results contribute to the series of molecular assemblies with the bridge groups [Fe(III)-X-Cu(II)], X = O(2)(-), OH(-), and RCO(2)(-), all with a common high-spin heme, thereby allowing an examination of electronic structure as dependent on the bridging atom or group and bridge structure. (Me(5)dien = 1,1,4,7,7-pentamethyldiethylenetriamine; Me(6)tren = tris(2-(dimethylamino)ethyl)amine; OEP = octaethylporphyrinate(2-).)     

Synthesis, NMR Study, and Reactivity of Isomeric Early-Late Heterobimetallic Dihydrides. X-ray Crystal Structure of (PPh(3))HRu(&mgr;-H)(&mgr;-PMe(2)C(5)Me(4))(2)(&mgr;-Cl)ZrCl

The new isomeric ruthenium/zirconium dihydrides of the formula (PPh(3))HRuH(&mgr;-PMe(2)Cp)(2)ClZrCl (1, 2) (Cp = C(5)Me(4)) have been characterized by elemental analysis and NMR ((1)H, (31)P and (1)H relaxation data). Complex 1, stabilized by Cl and H bridges, has been isolated from the room temperature reaction between RuH(2)(H(2))(PPh(3))(3) and (PMe(2)Cp)(2)ZrCl(2). The X-ray crystallographic study of 1 revealed a bimetallic complex. The six-coordinate Ru atom and the five-coordinate Zr atom are held together by two bifunctional phosphinocyclopentadienyl ligands and by H and Cl bridges. Crystal data for 1: monoclinic space group P2(1)/c, a = 13.901(2) ?, b = 18.205(6) ?, c = 16.633(3) ?, beta = 92.43(1) degrees, V = 4206 ?(3), Z = 4, d(calc) = 1.472 g cm(-)(3), R(F) = 0.056, R(w)(F) = 0.058. Complex 2 with two H bridges and terminal Cl ligands at Ru and Zr has been obtained by an irreversible isomerization of 1 in the presence of HNEt(3)BPh(4). This transformation has been proposed to occur through slow protonation of one of the phosphorus ligands with the five-coordinate Ru center formed by undergoing rapid pseudorotation. Complexes 1 and 2 do not react with H(2), N(2), or 3,3-dimethyl-but-1-ene. Treatment of 1 with 1 equiv of NaHBEt(3) in C(6)D(6) gives a mixture of new trihydrides (PPh(3))HRu(&mgr;-Cl)(&mgr;-H)(&mgr;-PMe(2)Cp)(2)ZrH (3) and (PPh(3))HRu(&mgr;-H)(2)(&mgr;-PMe(2)Cp)(2)ZrCl (4). Complex 3 transforms to 4 upon standing in solution for a period of several days. Under the same conditions, complex 2 leads smoothly to trihydride 4. Both trihydrides are new and have been characterized by (1)H, (31)P NMR, and (1)H NMR relaxation data. Complexes 1 and 4 are fluxional in solution at room temperature, showing hydride exchange between the terminal and bridging positions. The variable-temperature (1)H NMR spectra allowed determinations of the DeltaG() values of 16.4 (313 K, THF-d(8)) and 13.5 kcal/mol (295 K, toluene-d(8)) for the exchange in complexes 1 and 4, respectively. Possible exchange mechanisms have been discussed. Complex 2 is rigid on the NMR time scale.