Importance of out-of-state spin-orbit coupling for slow magnetic relaxation in mononuclear Fe(II) complexes

Two mononuclear high-spin Fe(II) complexes with trigonal planar ([Fe(II)(N(TMS)(2))(2)(PCy(3))] (1) and distorted tetrahedral ([Fe(II)(N(TMS)(2))(2)(depe)] (2) geometries are reported (TMS = SiMe(3), Cy = cyclohexyl, depe = 1,2-bis(diethylphosphino)ethane). The magnetic properties of 1 and 2 reveal the profound effect of out-of-state spin-orbit coupling (SOC) on slow magnetic relaxation. Complex 1 exhibits slow relaxation of the magnetization under an applied optimal dc field of 600 Oe due to the presence of low-lying electronic excited states that mix with the ground electronic state. This mixing re-introduces orbital angular momentum into the electronic ground state via SOC, and 1 thus behaves as a field-induced single-molecule magnet. In complex 2, the lowest-energy excited states have higher energy due to the ligand field of the distorted tetrahedral geometry. This higher energy gap minimizes out-of-state SOC mixing and zero-field splitting, thus precluding slow relaxation of the magnetization for 2.     

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.     

The Dinitramide Anion, N(NO(2))(2)(-)

The infrared and Raman spectra of the NH(4)(+), K(+), and Cs(+) salts of N(NO(2))(2)(-) in the solid state and in solution have been measured and are assigned with the help of ab initio calculations at the HF/6-31G and MP2/6-31+G levels of theory. In agreement with the variations observed in the crystal structures, the vibrational spectra of the N(NO(2))(2)(-) anion are also strongly influenced by the counterions and the physical state. Whereas the ab initio calculations for the free N(NO(2))(2)(-) ion indicate a minimum energy structure of C(2) symmetry, Raman polarization measurements on solutions of the N(NO(2))(2)(-) anion suggest point group C(1) (i.e., no symmetry). This is attributed to the very small (<3 kcal/mol) N-NO(2) rotational barrier in N(NO(2))(2)(-) which allows for easy deformation.     

Spectroelectrochemical Studies of Copper(I) Complexes with Binaphthyridine and Biquinoline Ligands. Crystal Structure Determination of Bis(6,7-dihydrodipyrido[2,3-b:3',2'-j][1,10]phenanthroline)copper(I) Tetrafluoroborate

The electrochemical and spectral properties of some copper(I) polypyridyl complexes based on 6,7-dihydrodibenzo[b,j][1,10]phenanthroline, dmbiq, and 6,7-dihydrodipyrido[2,3-b:3',2'-j][1,10]phenanthroline, dmbinap, are reported. These complexes are [Cu(dmbiq)(2)](+), 1; [Cu(dmbiq)(PPh(3))(2)](+), 2; [Cu(dmbinap)(2)](+), 3; and [Cu(dmbinap)(PPh(3))(2)](+), 4. 3 and 4 may be reduced to form ligand-based radical anion species. The resonance Raman spectra of 3(*)()(-)() and 4(*)()(-)() are almost identical and correspond closely to the spectrum of dmbinap(*)()(-)() and the reported spectra of complexes containing 2,2'-biquinoline radical anion moieties. Reduction processes for 1 and 2 are irreversible. For 1 the electronic spectral changes arising from reduction suggest demetallation of the complex. The structure of [Cu(C(18)H(12)N(4))(2)][BF(4)].CH(2)Cl(2) (3[BF(4)].CH(2)Cl(2)) was determined by single-crystal X-ray diffraction. It crystallized in the monoclinic space group P2(1)/c with cell dimensions a = 14.059(7) ?, b = 15.058(6) ?, c = 16.834(9) ?, beta = 111.56(5) degrees, Z = 4, rho(calcd) = 1.611 g/cm(3), and R(F(o)) = 0.0497.     

Benzoannelation stabilizes the d(xy)1 state of low-spin iron(III) porphyrinates

A series of low-spin, six-coordinate complexes [Fe(TBzTArP)L(2)]X (1) and [Fe(TBuTArP)L(2)]X (2) (X = Cl(-), BF(4)(-), or Bu(4)N(+)), where the axial ligands (L) are HIm, 1-MeIm, DMAP, 4-MeOPy, 4-MePy, Py, and CN(-), were prepared. The electronic structures of these complexes were examined by (1)H NMR and electron paramagnetic resonance (EPR) spectroscopy as well as density functional theory (DFT) calculations. In spite of the fact that almost all of the bis(HIm), bis(1-MeIm), and bis(DMAP) complexes reported previously (including 2) adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state, the corresponding complexes of 1 show the (d(xz), d(yz))(4)(d(xy))(1) ground state at ambient temperature. At lower temperature, the electronic ground state of the HIm, 1-MeIm, and DMAP complexes of 1 changes to the common (d(xy))(2)(d(xz), d(yz))(3) ground state. All of the other complexes of 1 and 2 carrying 4-MeOPy, 4-MePy, Py, and CN(-) maintain the (d(xz), d(yz))(4)(d(xy))(1) ground state in the NMR temperature range, i.e., 298-173 K. The EPR spectra taken at 4.2 K are fully consistent with the NMR results because the HIm and 1-MeIm complexes of 1 and 2 adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state, as revealed by the rhombic-type spectra. The DMAP complex of 1 exists as a mixture of two electron-configurational isomers. All of the other complexes adopt the (d(xz), d(yz))(4)(d(xy))(1) ground state, as revealed by the axial-type spectra. Among the complexes adopting the (d(xz), d(yz))(4)(d(xy))(1) ground state, the energy gap between the d(xy) and d(π) orbitals in 1 is always larger than that of the corresponding complex of 2. Thus, it is clear that the benzoannelation of the porphyrin ring stabilizes the (d(xz), d(yz))(4)(d(xy))(1) ground state. The DFT calculation of the bis(Py) complex of analogous iron(III) porphyrinate, [Fe(TPTBzP)(Py)(2)](+), suggests that the (d(xz), d(yz))(4)(d(xy))(1) state is more stable than the (d(xy))(2)(d(xz), d(yz))(3) state in both ruffled and saddled conformations. The lowest-energy states in the two conformers are so close in energy that their ordering is reversed depending on the calculation methods applied. On the basis of the spectroscopic and theoretical results, we concluded that 1, having 4-MeOPy, 4-MePy, and Py as axial ligands, exists as an equilibrium mixture of saddled and ruffled isomers both of which adopt the (d(xz), d(yz))(4)(d(xy))(1) ground state. The stability of the (d(xz), d(yz))(4)(d(xy))(1) ground state is ascribed to the strong bonding interaction between the iron d(xy) and porphyrin a(1u) orbitals in the saddled conformer caused by the high energy of the a(1u) highest occupied molecular orbital in TBzTArP. Similarly, a bonding interaction occurs between the d(xy) and a(2u) orbitals in the ruffled conformer. In addition, the bonding interaction of the d(π) orbitals with the low-lying lowest unoccupied molecular orbital, which is an inherent characteristic of TBzTArP, can also contribute to stabilization of the (d(xz), d(yz))(4)(d(xy))(1) ground state.     

Synthesis and characterization of Mo(6) chalcobromides and cyano-substituted compounds built from a novel [(Mo(6)Br(i)(6)Y(i)(2))L(a)(6)](n)()(-) discrete cluster unit (Y(i) = S or Se and L(a) = Br or CN)

The syntheses, crystal structures determined by single-crystal X-ray diffraction, and characterizations of new Mo(6) cluster chalcobromides and cyano-substituted compounds with 24 valence electrons per Mo(6) cluster (VEC = 24), are presented in this work. The structures of Cs(4)Mo(6)Br(12)S(2) and Cs(4)Mo(6)Br(12)Se(2) prepared by solid state routes are based on the novel [(Mo(6)Br(i)(6)Y(i)(2))Br(a)(6)](4)(-) (Y = S, Se) discrete units in which two chalcogen and six bromine ligands randomly occupy the inner positions, while the six apical ones are fully occupied by bromine atoms. The interaction of these two compounds with aqueous KCN solution results in apical ligand exchange giving the two first Mo(6) cyano-chalcohalides: Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O and Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O. Their crystal structures, built from the original [(Mo(6)Br(i)(6)Y(i)(2))(CN)(a)(6)](4)(-) discrete units, will be compared to those of the two solid state precursors and other previously reported Mo(6) cluster compounds. Their redox properties and (77)Se NMR characterizations will be presented. Crystal data: Cs(4)Mo(6)Br(12)S(2), orthorhombic, Pbca (No. 61), a = 11.511(5) A, b = 18.772(5) A, c = 28.381 A (5), Z = 8; Cs(4)Mo(6)Br(12)Se(2), Pbca (No. 61), a = 11.6237(1) A, b = 18.9447(1) A, c = 28.4874(1) A, Z = 8; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.1969(4) A, Z = 1; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.235(5) A, Z = 1.     

Molecular and electronic structures of iron(II)/(III) complexes containing N,S-coordinated,closed-shell o-aminothiophenolato(1-) and o-iminothiophenolato(2-) ligands

The coordination chemistry of the ligands o-aminothiophenol, H(abt), 4,6-di-tert-butyl-2-aminothiophenol, H[L(AP)], and 1,2-ethanediamine-N,N'-bis(2-benzenethiol), H(4)('N(2)S(2')), with FeCl(2) under strictly anaerobic and increasingly aerobic conditions has been systematically investigated. Using strictly anaerobic conditions, the neutral, air-sensitive, yellow complexes (mu-S,S)[Fe(II)(abt)(2)](2) (1), (mu-S,S)[Fe(II)(L(AP))(2)](2).8CH(3)OH (2), and (mu-S,S)[Fe(II)('H(2)N(2)S(2'))](2).CH(3)CN (3) containing high spin ferrous ions have been isolated where (abt)(1-), (L(AP))(1-), and ('H(2)N(2)S(2'))(2-) represent the respective N,S-coordinated, aromatic o-aminothiophenolate derivative of these ligands. When the described reaction was carried out in the presence of trace amounts of O(2) and [PPh(4)]Br, light-green crystals of [PPh(4)][Fe(II)(abt)(2)(itbs)].[PPh(4)]Br (4) were isolated. The anion [Fe(II)(abt)(2)(itbs)](-) contains a high spin ferrous ion, two N,S-coordinated o-aminophenolate(1-) ligands, and an S-bound, monoanionic o-iminothionebenzosemiquinonate(1-) pi radical, (itbs)(-). Complex 4 possesses an S(t) = 3/2 ground state. In the absence of [PPh(4)]Br and presence of a base NEt(3) and a little O(2), the ferric dimer (mu-NH,NH)[Fe(III)(L(AP))(L(IP))](2) (5a) and its isomer (mu-S,S)[Fe(III)(L(AP))(L(IP))](2) (5b) formed. (L(IP))(2-) represents the aromatic o-iminothiophenolate(2-) dianion of H[L(AP)]. The structures of compounds 2, 4, and 5a have been determined by X-ray crystallography at 100(2) K. Zero-field M?ssbauer spectroscopy of 1, 2, 3, and 4 unambiguously shows the presence of high spin ferrous ions: The isomer shift at 80 K is in the narrow range 0.85-0.92 mm s(-1), and a large quadrupole splitting, |DeltaE(Q)|, in the range 3.24-4.10 mm s(-1), is observed. In contrast, 5a and 5b comprise both intermediate spin ferric ions (S(Fe) = 3/2) which couple antiferromagnetically in the dinuclear molecules yielding an S(t) = 0 ground state.     

Photodissociation dynamics of IBr(-)(CO(2))(n), n<15

We report the ionic photoproducts produced following photoexcitation of mass selected IBr(-)(CO(2))(n), n=0-14, cluster ions at 790 and 355 nm. These wavelengths provide single state excitation to two dissociative states, corresponding to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states of the IBr(-) chromophore. Excitation of these states in IBr(-) leads to production of I(-)+Br and Br(-)+I( *), respectively. Potential energy curves for the six lowest electronic states of IBr(-) are calculated, together with structures for IBr(-)(CO(2))(n), n=1-14. Translational energy release measurements on photodissociated IBr(-) determine the I-Br(-) bond strength to be 1.10+/-0.04 eV; related measurements characterize the A(') (2)Pi(1/2)<--X (2)Sigma(1/2) (+) absorption band. Photodissociation product distributions are measured as a function of cluster size following excitation to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states. The solvent is shown to drive processes such as spin-orbit relaxation, charge transfer, recombination, and vibrational relaxation on the ground electronic state. Following excitation to the A(') (2)Pi(1/2) electronic state, IBr(-)(CO(2))(n) exhibits size-dependent cage fractions remarkably similar to those observed for I(2) (-)(CO(2))(n). In contrast, excitation to the B 2 (2)Sigma(1/2) (+) state shows extensive trapping in excited states that dominates the recombination behavior for all cluster sizes we investigated. Finally, a pump-probe experiment on IBr(-)(CO(2))(8) determines the time required for recombination on the ground state following excitation to the A(') state. While the photofragmentation experiments establish 100% recombination in the ground electronic state for this and larger IBr(-) cluster ions, the time required for recombination is found to be approximately 5 ns, some three orders of magnitude longer than observed for the analogous I(2) (-) cluster ion. Comparisons are made with similar experiments carried out on I(2) (-)(CO(2))(n) and ICl(-)(CO(2))(n) cluster ions.     

Electronic structure of highly ruffled low-spin iron(III) porphyrinates with electron withdrawing heptafluoropropyl groups at the meso positions

Bis(pyridine)[meso-tetrakis(heptafluoropropyl)porphyrinato]iron(III), [Fe(THFPrP)Py(2)](+), was reported to be the low-spin complex that adopts the purest (d(xz), d(yz))(4)(d(xy))(1) ground state where the energy gap between the iron d(xy) and d(π)(d(xz), d(yz)) orbitals is larger than the corresponding energy gaps of any other complexes reported previously (Moore, K. T.; Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 1999, 121, 5196-5209). Although the highly ruffled porphyrin core expected for this complex contributes to the stabilization of the (d(xz), d(yz))(4)(d(xy))(1) ground state, the strongly electron withdrawing C(3)F(7) groups at the meso positions should stabilize the (d(xy))(2)(d(xz), d(yz))(3) ground state. Thus, we have reexamined the electronic structure of [Fe(THFPrP)Py(2)](+) by means of (1)H NMR, (19)F NMR, and electron paramagnetic resonance (EPR) spectroscopy. The CD(2)Cl(2) solution of [Fe(THFPrP)Py(2)](+) shows the pyrrole-H signal at -10.25 ppm (298 K) in (1)H NMR, the CF(2)(α) signal at -74.6 ppm (298 K) in (19)F NMR, and the large g(max) type signal at g = 3.16 (4.2 K) in the EPR. Thus, contrary to the previous report, the complex is unambiguously shown to adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state. Comparison of the spectroscopic data of a series of [Fe(THFPrP)L(2)](+) with those of the corresponding meso-tetrapropylporphyrin complexes [Fe(TPrP)L(2)](+) with various axial ligands (L) has shown that the meso-C(3)F(7) groups stabilize the (d(xy))(2)(d(xz), d(yz))(3) ground state. Therefore, it is clear that the less common (d(xz), d(yz))(4)(d(xy))(1) ground state can be stabilized by the three major factors: (i) axial ligand with low-lying π* orbitals, (ii) ruffled porphyrin ring, and (iii) electron donating substituent at the meso position.     

Formation and characterization of a six-coordinate iron(III) complex with the most ruffled porphyrin ring

The six-coordinate iron(III) porphyrin complex, [Fe(T(i)PrP)(2-MeBzIm)(2)](+), having the most ruffled porphyrin ring shows some unusual properties; the complex adopts the pure (d(xz), d(yz))(4)(d(xy))(1) ground state below 200 K in spite of the coordination of an imidazole ligand and exhibits the rare spin transition to the (d(xz), d(yz))(3)(d(xy))(1)(d(z2))(1) state at higher temperature.     

Unusual electronic structure of bis-isocyanide complexes of iron(III) porphyrinoids

A series of isocyanide complexes, [Fe(Porphyrinoid)((t)BuNC)(2)](+), were synthesized and examined for their physicochemical properties. The molecular structure of the bis((t)BuNC) adduct of the iron(III) porphycene (1) and corrphycene (2) adopting the (d(xy))(2)(d(xz), d(yz))(3) ground state were determined for the first time. Furthermore, 1 and 2 showed unusual crossover phenomena between different electron configurations, (d(xy))(2)(d(xz), d(yz))(3) ground state and (d(xz), d(yz))(4)(d(xy))(1) ground state, by the addition of the external stimuli.     

Valence and spin situations in isomeric [(bpy)Ru(Q')2]n (Q' = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine). An experimental and DFT analysis

The article deals with the ruthenium complexes, [(bpy)Ru(Q')(2)] (1-3) incorporating two unsymmetrical redox-noninnocent iminoquinone moieties [bpy = 2,2'-bipyridine; Q' = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, aryl = C(6)H(5) (Q'(1)), 1; m-Cl(2)C(6)H(3) (Q'(2)), 2; m-(OCH(3))(2)C(6)H(3) (Q'(3)), 3]. 1 and 3 have been preferentially stabilised in the cc-isomeric form while both the ct- and cc-isomeric forms of 2 are isolated [ct: cis and trans and cc: cis and cis with respect to the mutual orientations of O and N donors of two Q']. The isomeric identities of 1-3 have been authenticated by their single-crystal X-ray structures. The collective consideration of crystallographic and DFT data along with other analytical events reveals that 1-3 exhibit the valence configuration of [(bpy)Ru(II)(Q'(Sq))(2)]. The magnetization studies reveal a ferromagnetic response at 300 K and virtual diamagnetic behaviour at 2 K. DFT calculations on representative 2a and 2b predict that the excited triplet (S = 1) state is lying close to the singlet (S = 0) ground state with singlet-triplet separation of 0.038 eV and 0.075 eV, respectively. In corroboration with the paramagnetic features the complexes exhibit free radical EPR signals with g～2 and (1)HNMR spectra with broad aromatic proton signals associated with the Q' at 300 K. Experimental results in conjunction with the DFT (for representative 2a and 2b) reveal iminoquinone based preferential electron-transfer processes leaving the ruthenium(ii) ion mostly as a redox insensitive entity: [(bpy)Ru(II)(Q'(Q))(2)](2+) (1(2+)-3(2+)) ? [(bpy)Ru(II)(Q(')(Sq))(Q(')(Q))](+) (1(+)-3(+)) ? [(bpy)Ru(II)(Q(')(Sq))(2)] (1-3) ? [(bpy)Ru(II)(Q(')(Sq))(Q(')(Cat))](-)/[(bpy)Ru(III)(Q(')(Cat))(2)](-) (1(-)-3(-)). The diamagnetic doubly oxidised state, [(bpy)Ru(II)(Q'(Q))(2)](2+) in 1(2+)-3(2+) has been authenticated further by the crystal structure determination of the representative [(bpy)Ru(II)(Q'(3))(2)](ClO(4))(2) [3](ClO(4))(2) as well as by its sharp (1)H NMR spectrum. The key electronic transitions in each redox state of 1(n)-3(n) have been assigned by TD-DFT calculations on representative 2a and 2b.     

Structure and reactivity of bis(silyl) dihydride complexes (PMe(3))(3)Ru(SiR(3))(2)(H)(2): model compounds and real intermediates in a dehydrogenative C-Si bond forming reaction

A series of stable complexes, (PMe(3))(3)Ru(SiR(3))(2)(H)(2) ((SiR(3))(2) = (SiH(2)Ph)(2), 3a; (SiHPh(2))(2), 3b; (SiMe(2)CH(2)CH(2)SiMe(2)), 3c), has been synthesized by the reaction of hydridosilanes with (PMe(3))(3)Ru(SiMe(3))H(3) or (PMe(3))(4)Ru(SiMe(3))H. Compounds 3a and 3c adopt overall pentagonal bipyramidal geometries in solution and the solid state, with phosphine and silyl ligands defining trigonal bipyramids and ruthenium hydrides arranged in the equatorial plane. Compound 3a exhibits meridional phosphines, with both silyl ligands equatorial, whereas the constraints of the chelate in 3c result in both axial and equatorial silyl environments and facial phosphines. Although there is no evidence for agostic Si-H interactions in 3a and 3b, the equatorial silyl group in 3c is in close contact with one hydride (1.81(4) A) and is moderately close to the other hydride (2.15(3) A) in the solid state and solution (nu(Ru.H.Si) = 1740 cm(-)(1) and nu(RuH) = 1940 cm(-)(1)). The analogous bis(silyl) dihydride, (PMe(3))(3)Ru(SiMe(3))(2)(H)(2) (3d), is not stable at room temperature, but can be generated in situ at low temperature from the 16e(-) complex (PMe(3))(3)Ru(SiMe(3))H (1) and HSiMe(3). Complexes 3b and 3d have been characterized by multinuclear, variable temperature NMR and appear to be isostructural with 3a. All four complexes exhibit dynamic NMR spectra, but the slow exchange limit could not be observed for 3c. Treatment of 1 with HSiMe(3) at room temperature leads to formation of (PMe(3))(3)Ru(SiMe(2)CH(2)SiMe(3))H(3) (4b) via a CH functionalization process critical to catalytic dehydrocoupling of HSiMe(3) at higher temperatures. Closer inspection of this reaction between -110 and -10 degrees C by NMR reveals a plethora of silyl hydride phosphine complexes formed by ligand redistribution prior to CH activation. Above ca. 0 degrees C this mixture converts cleanly via silane dehydrogenation to the very stable tris(phosphine) trihydride carbosilyl complex 4b. The structure of 4b was determined crystallographically and exhibits a tetrahedral P(3)Si environment around the metal with the three hydrides adjacent to silicon and capping the P(2)Si faces. Although strong Si.HRu interactions are not indicated in the structure or by IR, the HSi distances (2.00(4) - 2.09(4) A) and average coupling constant (J(SiH) = 25 Hz) suggest some degree of nonclassical SiH bonding in the RuH(3)Si moiety. The least hindered complex, 3a, reacts with carbon monoxide principally via an H(2) elimination pathway to yield mer-(PMe(3))(3)(CO)Ru(SiH(2)Ph)(2), with SiH elimination as a minor process. However, only SiH elimination and formation of (PMe(3))(3)(CO)Ru(SiR(3))H is observed for 3b-d. The most hindered bis(silyl) complex, 3d, is extremely labile and even in the absence of CO undergoes SiH reductive elimination to generate the 16e(-) species 1 (DeltaH(SiH)(-)(elim) = 11.0 +/- 0.6 kcal x mol(-)(1) and DeltaS(SiH)(-)(elim) = 40 +/- 2 cal x mol(-)(1) x K(-)(1); Delta = 9.2 +/- 0.8 kcal x mol(-)(1) and Delta = 9 +/- 3 cal x mol(-)(1).K(-)(1)). The minimum barrier for the H(2) reductive elimination can be estimated, and is higher than that for silane elimination at temperatures above ca. -50 degrees C. The thermodynamic preferences for oxidative additions to 1 are dominated by entropy contributions and steric effects. Addition of H(2) is by far most favorable, whereas the relative aptitudes for intramolecular silyl CH activation and intermolecular SiH addition are strongly dependent on temperature (DeltaH(SiH)(-)(add) = -11.0 +/- 0.6 kcal x mol(-)(1) and DeltaS(SiH)(-)(add) = -40 +/- 2 cal.mol(-)(1) x K(-)(1); DeltaH(beta)(-CH)(-)(add) = -2.7 +/- 0.3 kcal x mol(-)(1) and DeltaS(beta)(-CH)(-)(add) = -6 +/- 1 cal x mol(-)(1) x K(-)(1)). Kinetic preferences for oxidative additions to 1 - intermolecular SiH and intramolecular CH - have been also quantified: Delta = -1.8 +/- 0.8 kcal x mol(-)(1) and Delta = -31 +/- 3 cal x mol(-)(1).K(-)(1); Delta = 16.4 +/- 0.6 kcal x mol(-)(1) and Delta = -13 +/- 6 cal x mol(-)(1).K(-)(1). The relative enthalpies of activation (-)(1) x K(-)(1)). Kinetic preferences for oxidative additions to 1 - intermolecular SiH and intramolecular CH - have been also quantified: Delta (H)SiH(add) = 1.8 +/- 0.8 kcal x mol(-)(1) and Delta S((SiH-add) =31+/- 3 cal x mol(-)(1) x K(-)(1); Delta S (SiH -add) = 16.4 +/- 0.6 kcal x mol(-)(1) and =Delta S (SiH -CH -add) =13+/- 6 cal x mol(-)(1) x K(-)(1). The relative enthalpies of activation are interpreted in terms of strong SiH sigma-complex formation - and much weaker CH coordination - in the transition state for oxidative addition.     

A novel series of materials composed of arrays of vanadium oxide container molecules, [V18O42(X)] (X = H2O,Cl-, Br-): synthesis and characterization of [M2(H2N(CH2)2NH2)5][(M(H2N(CH2)2NH2)2]2V18O42(X)]. 9H2O (M = Zn,Cd)

The synthesis and characterization of the novel systems [Zn(2)(H(2)N(CH(2))(2)NH(2))(5)][(Zn(H(2)N(CH(2))(2)NH(2))(2))(2)V(18)O(42)(H(2)O)].9H(2)O (1), [Cd(2)(H(2)N(CH(2))(2)NH(2))(5)][(Cd(H(2)N(CH(2))(2)NH(2))(2))(2)V(18)O(42)(Br)].9H(2)O (2), and [Zn(2)(H(2)N(CH(2))(2)NH(2))(5)][(Zn(H(2)N(CH(2))(2)NH(2))(2))(2)V(18)O(42)(Cl)].9H(2)O (3) have been described. These materials represent a new class of solids that have been prepared by combining conventional coordination compounds with spherical polyoxovanadate clusters. The isomorphous structures of these hybrid solids consist of two-dimensional arrays of container cluster molecules [V(18)O(42)(X)] (X = H(2)O, Br-, Cl-) interlinked by the transition metal complex moieties [M(H(2)N(CH(2))(2)NH(2))(2)] (M = Zn, Cd). These compounds contain an unprecedented complex cation, [M(2)(H(2)N(CH(2))(2)NH(2))(5)](4+). Crystal data for 1: C(9)H(46)N(9)O(26)V(9)Zn(2), monoclinic space group P2(1)/m (No. 11), a = 12.3723(7) A, b = 20.9837(11) A, c = 15.8379(8) A, beta = 97.3320(10) degrees, Z = 4.     

Variable coordination modes of NO2(-) in a series of Ag(I) complexes containing triorganophosphines, -arsines,and -stibines. Syntheses,spectroscopic characterization (IR, 1H and 31P NMR,electrospray ionization mass), and structures of [AgNO2(R(3)E)(x)] adducts (E = P,As, Sb,x = 1-3)

Adducts of triorganophosphine, triphenylarsine, and triphenylstibine with silver(I) nitrite have been synthesized and characterized both in solution ((1)H, (31)P NMR) and in the solid state (IR, single-crystal X-ray structure analysis). In addition aggregates of AgNO(2) and ER(3) (E = P, As, Sb) have been identified in solution by electrospray ionization mass spectrometry (ESI-MS). The topology of the structures in the solid state was found to depend on the nature of ER(3) and on the stoichiometric ratio AgNO(2):ER(3). The adducts AgNO(2):EPh(3) (1:1) (E = P or Sb) are one-dimensional polymers, the role of NO(2)(-) being to bridge successive metal atoms by coordination of the two oxygens to one silver atom and the nitrogen lone pair to a successive Ag. The adduct AgNO(2):P(o-tolyl)(3) (1:1) is mononuclear, due to steric hindrance of the phosphine, the nitrite being O,O'-bidentate, a rare example of a quasi-linear P-Ag-X array. AgNO(2):P(p-F-C(6)H(4))(3) (1:1) is a dimer, the nitrite being coordinated through both oxygens, the first unidentate, the second bridging bidentate. P(o-tolyl)(3) and Pcy(3) form 1:2 adducts, also mononuclear, the nitrite still an O,O'-chelate. In contrast, the adduct AgNO(2):AsPh(3) (1:2) is a centrosymmetric dimer, essentially an aggregate of a pair of [Ag(O(2)N)(AsPh(3))(2)] arrays with one nitrite oxygen being the bridging atom. The adducts AgNO(2):EPh(3) (1:3) (E = As, Sb) are mononuclear, the nitrite behaving as a consistently strong O,O'-chelate. The E = As adduct is a triclinic solvated form, whereas the unsolvated E = Sb species is monoclinic. ESI-MS spectra of acetonitrile solutions of these complexes show the existence of [Ag(ER(3))](+), [Ag(CH(3)CN)](+), [Ag(CH(3)CN)(2)](+), [AgCl(2)](-), [Ag(NO(2))(2)](-), [Ag(ER(3))(CH(3)CN)](+), and [Ag(ER(3))(2)](+) as well as higher aggregates [Ag(2)(NO(2))(ER(3))(2)](+), [Ag(2)(NO(2))(3)](-) and [Ag(2)Cl(2)(NO(2))](-), which are less prevalent.     

Aggregation of [(tBu3SiS)MX]: structures of {[Br2Fe(mu-SSitBu3)2)FeBr(THF)]Na(THF)4}infinity, cis-[(THF)FeI]2(mu-SSitBu3)2, [(tBu3SiS)Fe]2(mu-SSitBu3)2, and comparative structure and magnetism studies of [(tBu3SiS)MX]n (M = Fe, Co, X = Cl, n = 12; M = Fe, Ni, X = Br, n = 12; M = Fe, X = I, n = 14)

A convenient synthesis of (t)Bu(3)SiSH and (t)Bu(3)SiSNa(THF)(x)() led to the exploration of "(t)Bu(3)SiSMX" aggregation. The dimer, [((t)Bu(3)SiS)Fe](2)(mu-SSi(t)Bu(3))(2) (1(2)), was formed from [{(Me(3)Si)(2)N}Fe](2)(mu-N(SiMe(3))(2))(2) and the thiol, and its dissolution in THF generated ((t)Bu(3)SiS)(2)Fe(THF)(2) (1-(THF)(2)). Metathetical procedures with the thiolate yielded aggregate precursors [X(2)Fe](mu-SSi(t)Bu(3))(2)[FeX(THF)]Na(THF)(4) (3-X, X = Cl, Br) and cis-[(THF)IFe](2)(mu-SSi(t)Bu(3))(2) (4). Thermal desolvations of 3-Cl, 3-Br and 4 afforded molecular wheels [Fe(mu-X)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-FeX, X = Cl, Br) and the ellipse [Fe(mu-I)(mu-SSi(t)Bu(3))](14)(C(6)H(6))(n) (6-FeI). Related metathesis and desolvation sequences led to wheels [Co(mu-Cl)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-CoCl) and [Ni(mu-Br)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-NiBr). The nickel wheel disproportionated to give, in part, [((t)Bu(3)SiS)Ni](2)(mu-SSi(t)Bu(3))(2) (7), which was also synthesized via salt metathesis. X-ray structural studies of 1(2) revealed a roughly planar Fe(2)S(4) core, while 1-(THF)(2), 3-Br, and 4 possessed simple distorted tetrahedral and edge-shared tetrahedral structures. X-ray structural studies revealed 5-MX (MX = FeCl, FeBr, CoCl, NiBr) to be wheels based on edge-shared tetrahedra, but while the pseudo-D(6)(d) wheels of 5-FeCl, 5-CoCl, and 5-FeBr pack in a body-centered arrangement, those of pseudo-C(6)(v)() 5-NiBr exhibit hexagonal packing and two distinct trans-annular d(Br...Br). Variable-temperature magnetic susceptibility measurements were conducted on 5-FeCl, 5-CoCl, 5-FeBr, and 6-FeI, and the latter three are best construed as weakly antiferromagnetic, while 5-FeCl exhibited modest ferromagnetic coupling. Features suggesting molecular magnetism are most likely affiliated with phase changes at low temperatures.     

Linear NiII-MnIII2-NiII tetramers: an oligomeric component of the MnIII2NiII single-chain magnets

Heterometallic linear tetramers [Mn(5-R-saltmen)Ni(pao)(bpy)(2)](2)(ClO(4))(4) (5-R-saltmen(2-) = N,N'-1,1,2,2-tetramethylethylene bis(5-R-salicylideneiminate); pao(-) = pyridine-2-aldoximate; bpy = 2,2'-bipyridine, R = H, 1; Cl, 2; Br, 3; MeO, 4) have been synthesized and structurally characterized. These compounds exhibit a [Ni(II)-NO-Mn(III)-(O)(2)-Mn(III)-ON-Ni(II)] skeleton where -ON- is an oximate bridge between Mn(III) and Ni(II) ions and -(O)(2)- is a bi-phenolate bridge between Mn(III) ions. These tetramers can be seen as oligomeric units of the heterometallic Mn(III)(2)-Ni(II) chain observed in a family of single-chain magnets (Clérac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837. Miyasaka, H.; Clérac, R.; Mizushima, K.; Sugiura, K.; Yamashita, M.; Wernsdorfer, W.; Coulon, C. Inorg. Chem. 2003, 42, 8203.). Magnetic measurements on these tetramers confirm the nature of the magnetic interactions reported for the Mn(III)(2)-Ni(II) chains: a strong antiferromagnetic Mn(III)/Ni(II) coupling via the oximate bridge (J(Ni-Mn) ranges from -23.7 to -26.1 K) and a weak ferromagnetic Mn(III)/Mn(III) coupling through the bi-phenolate bridge (J(Mn-Mn) ranges from +0.4 to +0.9 K). These magnetic interactions lead to tetramers with an S = 2 ground state.     

Theoretical study of rhodium(III)-catalyzed hydrogenation of carbon dioxide into formic acid. Significant differences in reactivity among rhodium(III), rhodium(I), and ruthenium(II) complexes

The title reaction was theoretically investigated, where cis-[RhH(2)(PH(3))(3)](+) and cis-[RhH(2)(PH(3))(2)(H(2)O)](+) were adopted as models of the catalyst. The first step of the catalytic cycle is the CO(2) insertion into the Rh(III)-H bond, of which the activation barrier (E(a)) is 47.2 and 28.4 kcal/mol in cis-[RhH(2)(PH(3))(3)](+) and cis-[RhH(2)(PH(3))(2)(H(2)O)](+), respectively, where DFT(B3LYP)-calculated E(a) values (kcal/mol unit) are given hereafter. These results indicate that an active species is not cis-[RhH(2)(PH(3))(3)](+) but cis-[RhH(2)(PH(3))(2)(H(2)O)](+). After the CO(2) insertion, two reaction courses are possible. In one course, the reaction proceeds through isomerization (E(a) = 2.8) of [RhH(eta(1)- OCOH)(PH(3))(2)(H(2)O)(2)](+), five-centered H-OCOH reductive elimination (E(a) = 2.7), and oxidative addition of H(2) to [Rh(PH(3))(2)(H(2)O)(2)](+) (E(a) = 5.8). In the other one, the reaction proceeds through isomerization of [RhH(eta(1)-OCOH)(PH(3))(2)(H(2)O)(H(2))](+) (E(a) = 5.9) and six-centered sigma-bond metathesis of [RhH(eta(1)-OCOH)(PH(3))(2)(H(2)O)](+) with H(2) (no barrier). RhH(PH(3))(2)-catalyzed hydrogenation of CO(2) proceeds through CO(2) insertion (E(a) = 1.6) and either the isomerization of Rh(eta(1)-OCOH)(PH(3))(2)(H(2)) (E(a) = 6.1) followed by the six-centered sigma-bond metathesis (E(a) = 0.3) or H(2) oxidative addition to Rh(eta(1)-OCOH)(PH(3))(2) (E(a) = 7.3) followed by isomerization of RhH(2)(eta(1)-OCOH)(PH(3))(2) (E(a) = 6.2) and the five-centered H-OCOH reductive elimination (E(a) = 1.9). From these results and our previous results of RuH(2)(PH(3))(4)-catalyzed hydrogenation of CO(2) (J. Am. Chem. Soc. 2000, 122, 3867), detailed discussion is presented concerning differences among Rh(III), Rh(I), and Ru(II) complexes.     

Theoretical Study of Metal-Tetrahydroborato Ligand Interactions in [Y(THF)(4)(BH(4))(2)](+)

Ab initio calculations for the [Y(H(2)O)(4)(BH(4))(2)](+) complex, a model of [Y(THF)(4)(BH(4))(2)](+), have been carried out to study the metal-BH(4)(-) ligand interactions. Our calculations for various isomers with different BH(4)(-) coordination modes allow us to explore the electronic and electrostatic interactions in details. It is found that both electronic and electrostatic effects are of almost equal importance.