High-nuclearity metal-cyanide clusters: synthesis,magnetic properties,and inclusion behavior of open-cage species incorporating [(tach)M(CN)3] (M = Cr,Fe, Co) complexes

The use of 1,3,5-triaminocyclohexane (tach) as a capping ligand in generating metal-cyanide cage clusters with accessible cavities is demonstrated. The precursor complexes [(tach)M(CN)(3)] (M = Cr, Fe, Co) are synthesized by methods similar to those employed in preparing the analogous 1,4,7-triazacyclononane (tacn) complexes. Along with [(tach)Fe(CN)(3)](1)(-), the latter two species are found to adopt low-spin electron configurations. Assembly reactions between [(tach)M(CN)(3)] (M = Fe, Co) and [M'(H(2)O)(6)](2+) (M' = Ni, Co) in aqueous solution afford the clusters [(tach)(4)(H(2)O)(12)Ni(4)Co(4)(CN)(12)](8+), [(tach)(4)(H(2)O)(12)Co(8)(CN)(12)](8+), and [(tach)(4)(H(2)O)(12)Ni(4)Fe(4)(CN)(12)](8+), each possessing a cubic arrangement of eight metal ions linked through edge-spanning cyanide bridges. This geometry is stabilized by hydrogen-bonding interactions between tach and water ligands through an intervening solvate water molecule or bromide counteranion. The magnetic behavior of the Ni(4)Fe(4) cluster indicates weak ferromagnetic coupling (J = 5.5 cm(-)(1)) between the Ni(II) and Fe(III) centers, leading to an S = 6 ground state. Solutions containing [(tach)Fe(CN)(3)] and a large excess of [Ni(H(2)O)(6)](2+) instead yield a trigonal pyramidal [(tach)(H(2)O)(15)Ni(3)Fe(CN)(3)](6+) cluster, in which even weaker ferromagnetic coupling (J = 1.2 cm(-)(1)) gives rise to an S = (7)/(2) ground state. Paralleling reactions previously performed with [(Me(3)tacn)Cr(CN)(3)], [(tach)Cr(CN)(3)] reacts with [Ni(H(2)O)(6)](2+) in aqueous solution to produce [(tach)(8)Cr(8)Ni(6)(CN)(24)](12+), featuring a structure based on a cube of Cr(III) ions with each face centered by a square planar [Ni(CN)(4)](2)(-) unit. The metal-cyanide cage differs somewhat from that of the analogous Me(3)tacn-ligated cluster, however, in that it is distorted via compression along a body diagonal of the cube. Additionally, the compact tach capping ligands do not hinder access to the sizable interior cavity of the molecule, permitting host-guest chemistry. Mass spectrometry experiments indicate a 1:1 association of the intact cluster with tetrahydrofuran (THF) in aqueous solution, and a crystal structure shows the THF molecule to be suspended in the middle of the cluster cavity. Addition of THF to an aqueous solution containing [(tach)Co(CN)(3)] and [Cu(H(2)O)(6)](2+) templates the formation of a closely related cluster, [(tach)(8)(H(2)O)(6)Cu(6)Co(8)(CN)(24) superset THF](12+), in which paramagnetic Cu(II) ions with square pyramidal coordination are situated on the face-centering sites. Reactions intended to produce the cubic [(tach)(4)(H(2)O)(12)Co(8)(CN)(12)](8+) cluster frequently led to an isomeric two-dimensional framework, [(tach)(H(2)O)(3)Co(2)(CN)(3)](2+), exhibiting mer rather than fac stereochemistry at the [Co(H(2)O)(3)](2+) subunits. Attempts to assemble larger edge-bridged cubic clusters by reacting [(tach)Cr(CN)(3)] with [Ni(cyclam)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) complexes instead generated extended one- or two-dimensional solids. The magnetic properties of one of these solids, two-dimensional [(tach)(2)(cyclam)(3)Ni(3)Cr(2)(CN)(6)]I(2), suggest metamagnetic behavior, with ferromagnetic intralayer coupling and weak antiferromagnetic interactions between layers.     

Giant metal-cyanide coordination clusters: tetracapped edge-bridged cubic Cr(12)Ni(12)(CN)(48) and double face-centered cubic Cr(14)Ni(13)(CN)(48) species

The crystal structures of two new metal-cyanide clusters with record high nuclearities are reported. A direct assembly reaction involving [(Me(3)tacn)Cr(CN)(3)] (Me(3)tacn = N,N',N"-trimethyl-1,4,7-triazacyclononane), NiI(2), and KCN in aqueous solution affords [(Me(3)tacn)(12)Cr(12)Ni(12)(CN)(48)](12+). The structure of this 24-metal cluster features a cube of eight Cr(III) centers linked along the edges by 12 trans-coordinated [Ni(CN)(4)](2)(-) units, and capped on four faces by [(Me(3)tacn)Cr](3+) moieties. Its metal-cyanide cage encloses a 900 A(3) cavity that is accessible through the two noncapped cube faces. A still larger cluster, [(Me(3)tacn)(14)Cr(14)Ni(13)(CN)(48)](20+), was obtained from a related reaction excluding the addition of KCN. This 27-metal species possesses a highly anisotropic geometry in which two face-centered cubic units are fused through a common Ni(II) vertex.     

A cyano-bridged single-molecule magnet: slow magnetic relaxation in a trigonal prismatic MnMo(6)(CN)(18) cluster

We report the synthesis of the first well-documented example of a cyano-bridged single-molecule magnet. An assembly reaction parallel to that employed in producing the trigonal prismatic [(Me(3)tacn)(6)MnCr(6)(CN)(18)](2+) (Me(3)tacn = N,N',N"-trimethyl-1,4,7-triazacyclononane) cluster affords K[(Me(3)tacn)(6)MnMo(6)(CN)(18)](ClO(4))(3) (1), containing an analogous molybdenum(III)-substituted cluster. Fits to the DC magnetic susceptibility and magnetization data for 1 show that the MnMo(6) cluster possesses weak antiferromagnetic coupling (J = -6.7 cm(-1)), leading to an S = (13)/(2) ground state with significantly enhanced magnetic anisotropy (D = -0.33 cm(-1) and E = -0.018 cm(-1)). Consistent with these results, AC magnetic susceptibility measurements show the molecule to exhibit slow magnetic relaxation indicative of a single-molecule magnet with an energy barrier of 10 cm(-1) for spin reversal.     

Syntheses, structures, and magnetic properties of low-dimensional heterometallic complexes based on the versatile building block [(Tp)Cr(CN)3]-

Using the tricyano precursor (Bu(4)N)[(Tp)Cr(CN)(3)] (Bu(4)N(+) = tetrabutylammonium cation; Tp = tris(pyrazolyl)hydroborate), a pentanuclear heterometallic cluster [(Tp)(2)Cr(2)(CN)(6)Cu(3)(Me(3)tacn)(3)][(Tp)Cr(CN)(3)](ClO(4))(3)·5H(2)O (1, Me(3)tacn = N,N',N'-trimethyl-1,4,7-triazacyclononane), three tetranuclear heterometallic clusters [(Tp)(2)Cr(2)(CN)(6)Cu(2)(L(OEt))(2)]·2.5CH(3)CN (2, L(OEt) = [(Cp)Co(P(O)(OEt)(2))(3)], Cp = cyclopentadiene), [(Tp)(2)Cr(2)(CN)(6)Mn(2)(L(OEt))(2)]·4H(2)O (3), and [(Tp)(2)Cr(2)(CN)(6)Mn(2)(phen)(4)](ClO(4))(2) (4, phen = phenanthroline), and a one-dimensional (1D) chain polymer [(Tp)(2)Cr(2)(CN)(6)Mn(bpy)](n) (5, bpy = 2,2'-bipyridine) have been synthesized and structurally characterized. Complex 1 shows a trigonal bipyramidal geometry in which [(Tp)Cr(CN)(3)](-) units occupy the apical positions and are linked through cyanide to [Cu(Me(3)tacn)](2+) units situated in the equatorial plane. Complexes 2-4 show similar square structures, where Cr(III) and M(II) (M = Cu(II) or Mn(II)) ions are alternatively located on the rectangle corners. Complex 5 consists of a 4,2-ribbon-like bimetallic chain. Ferromagnetic interactions between Cr(III) and Cu(II) ions bridged by cyanides are observed in complexes 1 and 2. Antiferromagnetic interactions are presented between Cr(III) and Mn(II) ions bridged by cyanides in complexes 3-5. Complex 5 shows metamagnetic behavior with a critical field of about 22.5 kOe at 1.8 K.     

Cyano-bridged bimetallic assemblies from hexacyanometalate, [M(CN)6](3-) (M = Mn(III) and Fe(III)), and [M(N4-macrocycle)]2+ (M=Fe(III), Ni(II) and Zn(II)) building blocks. Syntheses, multidimensional structures, and magnetic properties

Reactions between [M(N(4)-macrocycle)](2+) (M = Zn(II) and Ni(II); macrocycle ligands are either CTH = d,l-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane or cyclam = 1,4, 8, 11-tetrazaazaciclotetradecane) and [M(CN)(6)](3-) (M = Fe(III) and Mn(III)) give rise to cyano-bridged assemblies with 1D linear chain and 2D honeycomblike structures. The magnetic measurements on the 1D linear chain complex [Fe(cyclam)][Fe(CN)(6)].6H(2)O 1 points out its metamagnetic behavior, where the ferromagnetic interaction operates within the chain and the antiferromagnetic one between chains. The Neel temperature, T(N), is 5.5 K and the critical field at 2 K is 1 T. The unexpected ferromagnetic intrachain interaction can be rationalized on the basis of the axially elongated octahedral geometry of the low spin Fe(III) ion of the [Fe(cyclam)](3+) unit. The isostructural substitution of [Fe(CN)(6)](3-) by [Mn(CN)(6)](3-) in the previously reported complex [Ni(cyclam)](3)[Fe(CN)(6)](2).12H(2)O 2 leads to [Ni(cyclam)](3)[Mn(CN)(6)](2).16 H(2)O 3, which exhibits a corrugated 2D honeycomblike structure and a metamagnetic behavior with T(N) = 16 K and a critical field of 1 T. In the ferromagnetic phase (H > 1 T) this compound shows a very important coercitive field of 2900 G at 2 K. Compound [Ni(CTH)](3)[Fe(CN)(6)](2).13H(2)O 4, C(60)H(116)Fe(2)N(24)Ni(3)O(13), monoclinic, A 2/n, a = 20.462(7), b = 16.292(4), c = 27.262(7) A, beta = 101.29(4) degrees, Z = 4, also has a corrugated 2D honeycomblike structure and a ferromagnetic intralayer interaction, but, in contrast to 2 and 3, does not exhibit any magnetic ordering. This fact is likely due to the increase of the interlayer separation in this compound. ([Zn(cyclam)Fe(CN)(6)Zn(cyclam)] [Zn(cyclam)Fe(CN)(6)].22H(2)O.EtOH) 5, C(44)H(122)Fe(2)N(24)O(23)Zn(3), monoclinic, A 2/n, a = 14.5474(11), b = 37.056(2), c = 14.7173(13) A, beta = 93.94(1) degrees, Z = 4, presents an unique structure made of anionic linear chains containing alternating [Zn(cyclam)](2+) and [Fe(CN)(6)](3)(-) units and cationic trinuclear units [Zn(cyclam)Fe(CN)(6)Zn(cyclam)](+). Their magnetic properties agree well with those expected for two [Fe(CN)(6)](3-) units with spin-orbit coupling effect of the low spin iron(III) ions.     

Nucleophilic reactivity and oxo/sulfido substitution reactions of MVIO3 Groups (M = Mo, W)

The nucleophilic reactivity of oxo ligands in the groups M(VI)O(3) in the trigonal complexes [(Me(3)tacn)MO(3)] (M = Mo (1), W (10)) and [(Bu(t)(3)tach)MO(3)] (M = Mo (5), W (14)) has been investigated. Complexes 1/10 can be alkylated with MeOTf to give [(Me(3)tacn)MO(2)(OMe)](1+) (2/11), silylated with Pr(i)(3)SiOTf to form [(Me(3)tacn)MO(2)(OSiPr(i)(3))](+) (3/12), and protonated with HOTf to yield [(Me(3)tacn)MoO(2)(OH)](+) (4). Similarly, complexes 5/14 can be silylated to [(Bu(t)(3)tach)MO(2)(OSiPr(i)(3))](+) (6/15) and protonated to [(Bu(t)(3)tach)MO(2)(OH)](+) (7/16). Products were isolated as triflate salts in yields exceeding 70%. When excess acid was used, the dinuclear mu-oxo species [(Bu(t)(3)tach)(2)M(2)O(5)](2+) (8/17) were obtained. X-ray structures are reported for 2-4, 6-8, 12, and 15-17. All mononuclear complexes have dominant trigonal symmetry with a rhombic distortion owing to a M[bond]OR bond (R = Me, SiPr(i)(3), H), which is longer than M[double bond]O oxo interactions; the latter exert a substantial trans influence on M[bond]N bond lengths. Oxo ligands in 5/14 undergo replacement with sulfide. Lawesson's reagent effects formation of [(Bu(t)(3)tach)MS(3)] (9/18), 14 with excess B(2)S(3) yields incompletely substituted [(Bu(t)(3)tach)WOS(2)] (20), and 5 with excess B(2)S(3) yields [(Bu(t)(3)tach)Mo(IV)O(S(4))] (19). The structures of 9, 19, and 20 are reported. Precedents for M(VI)S(3) groups in five- and six-coordinate molecules are limited. This investigation is the first detailed study of the behavior of M(VI)O(3) groups in nucleophilic and oxo/sulfido substitution reactions and should be useful in synthetic approaches to the active sites of the xanthine oxidase enzyme family and of certain tungstoenzymes. (Bu(t)(3)tach = 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane, Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclonane; OTf = triflate).     

Osmium Complexes of 1,4,7-Triazacyclononane (tacn) and 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me(3)tacn) and the X-ray Crystal Structure of [(Me(3)tacn)Os(eta(6)-C(6)H(5)BPh(3))]BPh(4).CH(3)CN

The complexes of osmium with tacn (1,4,7-triazacyclononane) and Me(3)tacn (1,4,7-trimethyl-1,4,7-triazacyclononane), [LOs (eta(6)-C(6)H(6))](PF(6))(2) (L = tacn) and LOsCl(3) (L = tacn, Me(3)tacn), have been prepared by substitution of L on [Os(eta(6)-C(6)H(6))Cl(2)](2) or [Os(2)Cl(8)](2)(-), respectively. Reaction of LOsCl(3) with neat triflic acid leads to partial replacement of chloride and formation of the binuclear Os(III)-Os(III) complexes [LOs(&mgr;-Cl(3))OsL](PF(6))(3) (L = tacn, Me(3)tacn). The binuclear nature was established by NMR spectroscopy and elemental analysis and, for L = tacn, a partially refined X-ray crystal structure which shows the Os-Os separation to be 2.667 ?, indicative of significant metal-metal bonding. Reduction of [LOs(&mgr;-Cl(3))OsL](3+) over zinc amalgam in either aqueous or non-aqueous solution yields the intensely colored Os(II)-Os(III) mixed-valence ions [LOs(&mgr;-Cl(3))OsL](2+). Electrochemical measurements on [LOs(&mgr;-Cl(3))OsL](3+) in CH(3)CN reveal the reversible formation of the mixed valence ions. These are further reduced at lower potential to the Os(II)-Os(II) binuclear species, reversibly for L = Me(3)tacn. (Me(3)tacn)OsCl(3) is oxidized by persulfate ion to give [(Me(3)tacn)OsCl(3)](+); zinc amalgam reduction in an aqueous solution at high concentration produces the binuclear complex [(Me(3)tacn)Os(&mgr;-Cl(3))Os(Me(3)tacn)](3+) or, at low concentration, a solution containing an air sensitive osmium(II) species. Addition of BPh(4)(-) results in the eta(6)-arene zwitterion [(Me(3)tacn)Os(eta(6)-C(6)H(5)BPh(3))](+), which was characterized by X-ray diffraction on the BPh(4)(-) salt. The compound crystallizes in the triclinic space group P1 with a = 11.829(2) ?, b = 12.480(3) ?, c = 17.155(4) ?, alpha = 84.42(2) degrees, beta = 83.52(2) degrees, gamma = 71.45(2) degrees, V = 2380(2) ?(3), Z = 2, and R = 7.62%, and R(w) = 7.39%.     

Cyanide-limited complexation of molybdenum(III): synthesis of octahedral [Mo(CN)(6)](3-) and cyano-bridged [Mo(2)(CN)(11)](5-)

Octahedral coordination of molybdenum(III) is achieved by limiting the amount of cyanide available upon complex formation. Reaction of Mo(CF(3)SO(3))(3) with LiCN in DMF affords Li(3)[Mo(CN)(6)] x 6DMF (1), featuring the previously unknown octahedral complex [Mo(CN)(6)](3-). The complex exhibits a room-temperature moment of mu(eff) = 3.80 mu(B), and assignment of its absorption bands leads to the ligand field parameters Delta(o) = 24800 cm(-1) and B = 247 cm(-1). Further restricting the available cyanide in a reaction between Mo(CF(3)SO(3))(3) and (Et(4)N)CN in DMF, followed by recrystallization from DMF/MeOH, yields (Et(4)N)(5)[Mo(2)(CN)(11)] x 2DMF x 2MeOH (2). The dinuclear [Mo(2)(CN)(11)](5-) complex featured therein contains two octahedrally coordinated Mo(III) centers spanned by a bridging cyanide ligand. A fit to the magnetic susceptibility data for 2, gives J = -113 cm(-1) and g = 2.33, representing the strongest antiferromagnetic coupling yet observed through a cyanide bridge. Efforts to incorporate these new complexes in magnetic Prussian blue-type solids are ongoing.     

Cluster-to-metal magnetic coupling: synthesis and characterization of 25-electron [Re6-nOsnSe8(CN)6](5-n)-(n = 1, 2) clusters and (Re6-nOsnSe8[CNCu(Me6tren)]6)9+(n = 0, 1, 2) assemblies

The first face-capped octahedral clusters with 25 metal-based valence electrons are shown to provide versatile building units capable of engaging in magnetic exchange coupling. Reactions of [Re(5)OsSe(8)Cl(6)](3-) and [Re(4)Os(2)Se(8)Cl(6)](2-) with NaCN in a melt of NaNO(3) or KCF(3)SO(3) afford the 24-electron clusters [Re(5)OsSe(8)(CN)(6)](3-) and [Re(4)Os(2)Se(8)(CN)(6)](2-). The 13C NMR spectrum of a 13C-labeled version of the latter species indicates a 1:2 mixture of cis and trans isomers. Cyclic voltammograms of the clusters in acetonitrile display reversible [Re(5)OsSe(8)(CN)(6)](3-/4-), cis-[Re(4)Os(2)Se(8)(CN)(6)](2-/3-), and trans-[Re(4)Os(2)Se(8)(CN)(6)](2-/3-) couples at E(1/2) = -1.843, -0.760, and -1.031 V vs FeCp(2)(0/+), respectively, in addition to other redox processes. Accordingly, reduction of [Re(5)OsSe(8)(CN)(6)](3-) with sodium amalgam and [Re(4)Os(2)Se(8)(CN)(6)](2-) with cobaltocene produces the 25-electron clusters [Re(5)OsSe(8)(CN)(6)](4-) and [Re(4)Os(2)Se(8)(CN)(6)](3-). EPR spectra of these S = 1/2 species in frozen DMF solutions exhibit isotropic signals with g = 1.46 for the monoosmium cluster and g = 1.74 and 1.09 for the respective cis and trans isomers of the diosmium cluster. In each case, results from DFT calculations show the unpaired spin to delocalize to some extent into the pi* orbitals of the cyanide ligands, suggesting the possibility of magnetic superexchange. Reaction of [Re(5)OsSe(8)(CN)(6)](3-) with [Ni(H(2)O)(6)](2+) in aqueous solution generates the porous Prussian blue analogue Ni(3)[Re(5)OsSe(8)(CN)(6)](2).32H(2)O; however, the tendency of the 25-electron clusters to oxidize in water prohibits their use in reactions of this type. Instead, a series of cyano-bridged assemblies, [Re(6-n)Os(n)Se(8)[CNCu(Me(6)tren)](6)](9+) (n = 0, 1, 2; Me(6)tren = tris(2-(dimethylamino)ethyl)amine), were synthesized to permit comparison of the exchange coupling abilities of clusters with 23-25 electrons. As expected, the results of magnetic susceptibility measurements show no evidence for exchange coupling in the assemblies containing the 23- and 24-electron clusters, but reveal the presence of weak ferromagnetic coupling in [Re(4)Os(2)Se(8)[CNCu(Me(6)tren)](6)](9+). Assuming all cluster-Cu(II) exchange interactions to be equivalent, the data were fit to give an estimated coupling strength of J = 0.4 cm(-1). To our knowledge, the ability of such clusters to participate in magnetic exchange coupling has never previously been demonstrated.     

Tetracyanide-bridged divanadium complexes: redox switching between strong antiferromagnetic and strong ferromagnetic coupling

Reaction of [(Me3tacn)V(CF3SO3)3] (Me3tacn = N,N',N'-trimethyl-1,4,7-triazacyclononane) with LiCN in DMF results in oligomerization of cyanide to form [(Me3tacn)2V2(CN)4(mu-C4N4)]. The structure of this binuclear complex features a planar tetracyanide unit bridging two VIV centers via imido type linkages. The conjugated pathway provided by the bridging ligand leads to strong antiferromagnetic coupling (J = -112 cm-1) and an S = 0 ground state. Reduction of the complex with cobaltocene generates the Class III mixed-valence anion [(Me3tacn)2V2(CN)4(mu-C4N4)]1-, wherein resonance exchange induces strong ferromagnetic coupling to give a well-isolated S = 3/2 ground state.     

One-dimensional octacyanomolybdate-based Cu(II)--Mo(V) bimetallic assembly with a novel rope-ladder chain structure

A new type of one-dimensional cyanide-bridged Cu(II)--Mo(V) bimetallic assembly, [Cu(cyclam)](3)[Mo(CN)(8)](2)x5H(2)O (cyclam = 1,4,8,11-tetraazacyclotetradecane), was prepared by self-assembling Mo(CN)(8)(3)(-) and Cu(cyclam)(2+) ions in a 2:3 stoichiometric ratio. The overall molecular view is delineated as a novel rope-ladder chain structure. It displays a dominant ferromagnetic behavior within a pentanuclear Cu(3)Mo(2) unit (J(p) = 3.88 cm(-)(1)). Interunit ferromagnetic interactions (J(c) = -0.03 cm(-)(1)) through a longer magnetic pathway of Cu--Mo and weak antiferromagnetic couplings (zJ' = -0.46 cm(-)(1)) resulting from interchain interactions are obtained.     

Encapsulation of cyanometalates by a tris-macrocyclic ligand tricopper(II) complex: syntheses, structural variation, and magnetic exchange coupling pathways

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.     

From one-dimensional chain to pentanuclear molecule. Magnetism of cyano-bridged Fe(III)-Ni(II) complexes

Two cyano-bridged Ni(II)-Fe(III) complexes [(H(3)O)[Ni(H(2)L)](2)[Fe(CN)(6)](2).[Fe(CN)(6)].6H(2)O](n) (1) and [K(18-C-6)(H(2)O)(2)][Ni(H(2)L)](2)[Fe(CN)(6)](3).4(18-C-6).20H(2)O (2) (L = 3,10-bis(2-aminoethyl)-1,3,6,8,10,12-hexaazacyclotetradecane, 18-C-6 = 18-crown-6-ether) have been synthesized and characterized structurally and magnetically. Complex 1 has a zigzag one-dimensional structure, in which two trans-CN(-) ligands of each [Fe(CN)(6)](3)(-) link two trans-[Ni(H(2)L)](4+) groups, and in turn, each trans-[Ni(H(2)L)](4+) links two [Fe(CN)(6)](3)(-) in a trans fashion. Complex 2 is composed of cyano-bridged pentanuclear molecules with moieties connected by the trans-CN(-) ligands of [Fe(CN)(6)](3)(-). Magnetic studies show the existence of ferromagnetic Ni(II)-Fe(III) interactions in both complexes. The intermetallic magnetic coupling constant of both complexes was analyzed by using an approximate model on the basis of the structural features.     

Cyano-bridged FeIII2CuII3 and FeIII4NiII4 complexes: syntheses, structures, and magnetic properties

Two tricyanometallate precursors, (Bu4N)[(Tp4Bo)Fe(CN)3].H2O.2MeCN (1) and (Bu4N)[(pzTp)Fe(CN)3] (2) [Bu4N+ = tetrabutylammonium cation; Tp4Bo = tris(indazolyl)hydroborate; pzTp = tetrakis(pyrazolyl)borate], with a low-spin FeIII center have been synthesized and characterized. The reactions of 1 or 2 with [Cu(Me3tacn)(H2O)2](ClO4)2 (Me3tacn = N,N',N' '-trimethyl-1,4,7-triazacyclononane) afford two pentanuclear cyano-bridged clusters, [(Tp4Bo)2(Me3tacn)3Cu3Fe2(CN)6](ClO4)4.5H2O (3) and [(pzTp)2(Me3tacn)3Cu3Fe2(CN)6](ClO4)4.4H2O (4), respectively. Assembly reactions between 2 and [Ni(phen)(CH3OH)4](ClO4)2 (phen = 1,10-phenanthroline) or Zn(OAc)2.2H2O afford a molecular box [(pzTp)4(phen)4Ni4Fe4(CH3OH)4(CN)12](ClO4)4.4H2O (5) and a rectangular cluster [(pzTp)2Zn2Fe2(OAc)2(H2O)2(CN)6] (6). Their molecular structures were determined by single-crystal X-ray diffraction. In complexes 1 and 2, the central FeIII ions are coordinated by three cyanide carbon atoms and three nitrogen atoms of Tp4Bo- or pzTp-. Both complexes 3 and 4 show a trigonal-bipyramidal geometry, in which [(L)Fe(CN)3]- units occupy the apical positions and are linked through cyanide to [Cu(Me3tacn)]2+ units situated in the equatorial plane. Complex 5 possesses a cubic arrangement of eight metal irons linked through edge-spanning cyanide bridges, while complex 6 shows Zn2Fe2(CN)4 rectangular structure, in which FeIII and ZnII ions are alternately bridged by the cyanide groups. Intramolecular ferromagnetic couplings are observed for complexes 3-5, and they have S = 5/2, 5/2, and 6 ground states and appreciable magnetic anisotropies with negative D values equal to -0.49, -2.39, and -0.39 cm-1, respectively.     

Heterobimetallic coordination polymers incorporating [M(CN)(2)](-) (M = Cu,Ag) and [Ag(2)(CN)(3)](-) units: increasing structural dimensionality via M-M' and M...NC interactions

A series of new heterometallic coordination polymers has been prepared from the reaction of metal-ligand cations and KAg(CN)(2) units. Many of these contain silver-silver (argentophilic) interactions, analogous to gold-gold interactions, which serve to increase supramolecular structural dimensionality. Compared to [Au(CN)(2)](-) analogues, these polymers display new trends specific to [Ag(CN)(2)](-), including the formation of [Ag(2)(CN)(3)](-) and the presence of Ag...N interactions. [Cu(en)(2)][Ag(2)(CN)(3)][Ag(CN)(2)] (1, en = ethylenediamine) forms 1-D chains of alternating [Ag(CN)(2)](-) and [Ag(2)(CN)(3)](-) units via argentophilic interactions of 3.102(1) A. These chains are connected into a 2-D array by strong cyano(N)-Ag interactions of 2.572(3) A. [Cu(dien)Ag(CN)(2)](2)[Ag(2)(CN)(3)][Ag(CN)(2)] (2, dien = diethylenetriamine) forms a 1-D chain of alternating [Cu(dien)](2+) and [Ag(CN)(2)](-) ions with the Cu(II) atoms connected in an apical/equatorial fashion. These chains are cross-linked by [Ag(2)(CN)(3)](-) units via argentophilic interactions of 3.1718(8) A and held weakly in a 3-D array by argentophilic interactions of 3.2889(5) A between the [Ag(CN)(2)](-) in the 2-D array and the remaining free [Ag(CN)(2)](-). [Ni(en)][Ni(CN)(4)].2.5H(2)O (4) was identified as a byproduct in the reaction to prepare the previously reported [Ni(en)(2)Ag(2)(CN)(3)][Ag(CN)(2)] (3). In [Ni(tren)Ag(CN)(2)][Ag(CN)(2)] (5, tren = tris(2-aminoethyl)amine), [Ni(tren)](2+) cations are linked in a cis fashion by [Ag(CN)(2)](-) anions to form a 1-D chain similar to the [Au(CN)(2)](-) analogue. [Cu(en)Cu(CN)(2)Ag(CN)(2)] (6) is a trimetallic polymer consisting of interpenetrating (6,3) nets stabilized by d(10)-d(10) interactions between Cu(I)-Ag(I) (3.1000(4) A). Weak antiferromagnetic coupling has been observed in 2, and a slightly stronger exchange has been observed in 6. The Ni(II) complexes, 4 and 5, display weak antiferromagnetic interactions as indicated by their relatively larger D values compared to that of 3. Magnetic measurements on isostructural [Ni(tren)M(CN)(2)][M(CN)(2)] (M = Ag, Au) show that Ag(I) is a more efficient mediator of magnetic exchange as compared to Au(I). The formation of [Ni(CN)(4)](2)(-), [Ag(2)(CN)(3)](-), and [Cu(CN)(2)](-) are all attributed to secondary reactions of the dissociation products of the labile KAg(CN)(2).     

Single- and double-cubane clusters in the multiple oxidation states [VFe(3)S(4)](3+,2+,1+)

A new series of cubane-type [VFe(3)S(4)](z)() clusters (z = 1+, 2+, 3+) has been prepared as possible precursor species for clusters related to those present in vanadium-containing nitrogenase. Treatment of [(HBpz(3))VFe(3)S(4)Cl(3)](2)(-) (2, z = 2+), protected from further reaction at the vanadium site by the tris(pyrazolyl)hydroborate ligand, with ferrocenium ion affords the oxidized cluster [(HBpz(3))VFe(3)S(4)Cl(3)](1)(-) (3, z = 3+). Reaction of 2 with Et(3)P results in chloride substitution to give [(HBpz(3))VFe(3)S(4)(PEt(3))(3)](1+) (4, z = 2+). Reaction of 4 with cobaltocene reduced the cluster with formation of the edge-bridged double-cubane [(HBpz(3))(2)V(2)Fe(6)S(8)(PEt(3))(4)] (5, z = 1+, 1+), which with excess chloride underwent ligand substitution to afford [(HBpz(3))(2)V(2)Fe(6)S(8)Cl(4)](4)(-) (6, z = 1+, 1+). X-ray structures of (Me(4)N)[3], [4](PF(6)), 5, and (Et(4)N)(4)[6] x 2MeCN are described. Cluster 5 is isostructural with previously reported [(Cl(4)cat)(2)(Et(3)P)(2)Mo(2)Fe(6)S(8)(PEt(3))(4)] and contains two VFe(3)S(4) cubanes connected across edges by a Fe(2)S(2) rhomb in which the bridging Fe-S distances are shorter than intracubane Fe-S distances. M?ssbauer (2-5), magnetic (2-5), and EPR (2, 4) data are reported and demonstrate an S = 3/2 ground state for 2 and 4 and a diamagnetic ground state for 3. Analysis of (57)Fe isomer shifts based on an empirical correlation between shift and oxidation state and appropriate reference shifts results in two conclusions. (i) The oxidation 2 --> 3 + e(-) results in a change in electron density localized largely or completely on the Fe(3) subcluster and associated sulfur atoms. (ii) The most appropriate charge distributions are [V(3+)Fe(3+)Fe(2+)(2)S(4)](2+) (Fe(2.33+)) for 1, 2, and 4 and [V(3+)Fe(3+)(2)Fe(2+)S(4)](3+) (Fe(2.67+)) for 3 and [V(2)Fe(6)S(8)(SEt)(9)](3+). Conclusion i applies to every MFe(3)S(4) cubane-type cluster thus far examined in different redox states at parity of cluster ligation. The formalistic charge distributions are regarded as the best current approximations to electron distributions in these delocalized species. The isomer shifts require that iron atoms are mixed-valence in each cluster.     

Synthesis and alkali metal ion-binding properties of a chromium(III) triacetylide complex

A simple triacetylide complex of chromium(III) is synthesized for use as a potential precursor to metal-dicarbide clusters. Reaction of Me(3)SiCCLi with [(Me(3)tacn)Cr(CF(3)SO(3))(3)] (Me(3)tacn = N,N',N"-trimethyl-1,4,7-triazacyclononane) in THF generates [(Me(3)tacn)Cr(CCSiMe(3))(3)], which subsequently reacts with Bu(4)NF to supply [(Me(3)tacn)Cr(CCH)(3)] as an air-stable orange solid. The crystal structure of this unprecedented triacetylide complex reveals octahedral coordination of the chromium center, with linear Cr-C(triple bond)C bond angles and C(triple bond)C bond distances essentially identical to the corresponding distance in acetylene. Crystallization of the complex from a DMF solution containing K(CF(3)SO(3)) leads to the sandwich complex ([(Me(3)tacn)Cr(CCH)(3)](2)K)(+), in which the K(+) ion is coordinated in a side-on fashion by each of the six C(triple bond)C units. With the larger Cs(+) cation, a triangular ([(Me(3)tacn)Cr(CCH)(3)](3)Cs)(+) complex is instead observed. The magnetic properties of these alkali metal complexes are indicative of weak antiferromagnetic exchange between Cr(III) centers, with J = -0.8 and -0.3 cm(-1), respectively.     

Symmetry-based magnetic anisotropy in the trigonal bipyramidal cluster [Tp2(Me3tacn)3Cu3Fe2(CN)6]4+

Reaction of [(Me3tacn)Cu(H2O)2]2+ (Me3tacn = N,N',N' '-trimethyl-1,4,7-triazacyclononane) with [TpFe(CN)3]- (Tp- = hydrotris(pyrazolyl)borate) in a mixture of ethanol and acetonitrile affords the pentanuclear cluster [Tp2(Me3tacn)3Cu3Fe2(CN)6]4+. Single-crystal X-ray analysis reveals a trigonal bipyramidal structure featuring a D3h-symmetry core in which two opposing FeIII (S = 1/2) centers are linked through cyanide bridges to an equatorial triangle of three CuII (S = 1/2) centers. Fits to variable-temperature dc magnetic susceptibility data are consistent with ferromagnetic coupling to give an S = 5/2 ground state, while fits to low-temperature magnetization data indicate the presence of a large axial zero-field splitting (D = -5.7 cm-1). Frequency dependence observed in the ac magnetic susceptibility data confirms single-molecule magnet behavior, with an effective spin reversal barrier of Ueff = 16 cm-1. When compared with the much lower anisotropy barrier previously observed for the face-centered cubic cluster [Tp8(H2O)6Cu6Fe8(CN)6]4+, the results demonstrate the enormous influence of the geometry in which a given set of metal ions are arranged.     

Octahedral niobium chloride clusters as building blocks of templated prussian blue framework analogues

The preparation, structure, and magnetic properties of the first three-dimensional framework containing octahedral niobium cyanochloride clusters as building units are reported. Reactions of aqueous solutions of (Me(4)N)(2)K(2)[Nb(6)Cl(12)(CN)(6)] (2) with aqueous solutions of MnCl(2) result in the precipitation of the compound (Me(4)N)(2)[MnNb(6)Cl(12)(CN)(6)] (3). The structure of 3 was determined from single-crystal X-ray diffraction study (crystal data: cubic, Fm3macrom(No. 225), a = 15.513(4) A, V = 3733.2(12) A(3), Z = 4). Its 3D framework is based on edge-bridged [Nb(6)Cl(12)](2+) clusters and Mn(2+) ions bridged by cyanide ligands to form a cfc lattice [MnNb(6)Cl(12)(CN)(6)](2)(-) in which all tetrahedral sites are occupied by the cations (Me(4)N)(+) which act as charge compensating template. The structure of 3 can be considered as an expansion of the Prussian blue framework in which [Fe(CN)(6)](4)(-) is replaced by the cluster [Nb(6)Cl(12)(CN)(6)](4)(-). Magnetic susceptibility measurements indicate that Mn(2+) is present in a high spin d(5) configuration. No magnetic ordering is observed.     

Reactions of Ph3Sb═S with copper(I) complexes supported by N-donor ligands: formation of stable adducts and S-transfer reactivity

In the exploration of sulfur-delivery reagents useful for synthesizing models of the tetracopper-sulfide cluster of nitrous oxide reductase, reactions of Ph(3)Sb═S with Cu(I) complexes of N,N,N',N'-tetramethyl-2R,3R-cyclohexanediamine (TMCHD) and 1,4,7-trialkyltriazacyclononanes (R(3)tacn; R = Me, Et, iPr) were studied. Treatment of [(R(3)tacn)Cu(NCCH(3))]SbF(6) (R = Me, Et, or iPr) with 1 equiv of S═SbPh(3) in CH(2)Cl(2) yielded adducts [(R(3)tacn)Cu(S═SbPh(3))]SbF(6) (1-3), which were fully characterized, including by X-ray crystallography. The adducts slowly decayed to [(R(3)tacn)(2)Cu(2)(μ-η(2):η(2)-S(2))](2+) species (4-6) and SbPh(3), or more quickly in the presence of additional [(R(3)tacn)Cu(NCCH(3))]SbF(6) to 4-6 and [(R(3)tacn)Cu(SbPh(3))]SbF(6) (7-9). The results of mechanistic studies of the latter process were consistent with rapid intermolecular exchange of S═SbPh(3) between 1-3 and added [(R(3)tacn)Cu(NCCH(3))]SbF(6), followed by conversion to product via a dicopper intermediate formed in a rapid pre-equilibrium step. Key evidence supporting this step came from the observation of saturation behavior in a plot of the initial rate of loss of 1 versus the initial concentration of [(Me(3)tacn)Cu(NCCH(3))]SbF(6). Also, treatment of [(TMCHD)Cu(CH(3)CN)]PF(6) with S═SbPh(3) led to the known tricopper cluster [(TMCHD)(3)Cu(3)(μ(3)-S)(2)](PF(6))(3) in good yield (79%), a synthetic procedure superior to that previously reported (Brown, E. C.; York, J. T.; Antholine, W. E.; Ruiz, E.; Alvarez, S.; Tolman, W. B. J. Am. Chem. Soc. 2005, 127, 13752-13753).