Synthesis, crystal structures, and magnetic properties of a new family of heterometallic cyanide-bridged Fe(III)2M(II)2 (M=Mn, Ni, and Co) square complexes

New heterobimetallic tetranuclear complexes of formula [Fe(III){B(pz)(4)}(CN)(2)(μ-CN)Mn(II)(bpy)(2)](2)(ClO(4))(2)·CH(3)CN (1), [Fe(III){HB(pz)(3)}(CN)(2)(μ-CN)Ni(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (2a), [Fe(III){B(pz)(4)}(CN)(2)(μ-CN)Ni(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (2b), [Fe(III){HB(pz)(3)}(CN)(2)(μ-CN)Co(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (3a), and [Fe(III){B(pz)(4)}(CN)(2)(μ-CN)Co(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (3b), [HB(pz)(3)(-) = hydrotris(1-pyrazolyl)borate, B(Pz)(4)(-) = tetrakis(1-pyrazolyl)borate, dmphen = 2,9-dimethyl-1,10-phenanthroline, bpy = 2,2'-bipyridine] have been synthesized and structurally and magnetically characterized. Complexes 1-3b have been prepared by following a rational route based on the self-assembly of the tricyanometalate precursor fac-[Fe(III)(L)(CN)(3)](-) (L = tridentate anionic ligand) and cationic preformed complexes [M(II)(L')(2)(H(2)O)(2)](2+) (L' = bidentate α-diimine type ligand), this last species having four blocked coordination sites and two labile ones located in cis positions. The structures of 1-3b consist of cationic tetranuclear Fe(III)(2)M(II)(2) square complexes [M = Mn (1), Ni (2a and 2b), Co (3a and 3b)] where corners are defined by the metal ions and the edges by the Fe-CN-M units. The charge is balanced by free perchlorate anions. The [Fe(L)(CN)(3)](-) complex in 1-3b acts as a ligand through two cyanide groups toward two divalent metal complexes. The magnetic properties of 1-3b have been investigated in the temperature range 2-300 K. A moderately strong antiferromagnetic interaction between the low-spin Fe(III) (S = 1/2) and high-spin Mn(II) (S = 5/2) ions has been found for 1 leading to an S = 4 ground state (J(1) = -6.2 and J(2) = -2.7 cm(-1)), whereas a moderately strong ferromagnetic interaction between the low-spin Fe(III) (S = 1/2) and high-spin Ni(II) (S = 1) and Co(II) (S = 3/2) ions has been found for complexes 2a-3b with S = 3 (2a and 2b) and S = 4 (3a and 3b) ground spin states [J(1) = +21.4 cm(-1) and J(2) = +19.4 cm(-1) (2a); J(1) = +17.0 cm(-1) and J(2) = +12.5 cm(-1) (2b); J(1) = +5.4 cm(-1) and J(2) = +11.1 cm(-1) (3a); J(1) = +8.1 cm(-1) and J(2) = +11.0 cm(-1) (3b)] [the exchange Hamiltonian being of the type H? = -J(S?(i)·S?(j))]. Density functional theory (DFT) calculations have been used to substantiate the nature and magnitude of the exchange magnetic coupling observed in 1-3b and also to analyze the dependence of the exchange magnetic coupling on the structural parameters of the Fe-C-N-M skeleton.     

Photomagnetic studies on spin-crossover solid solutions containing two different metal complexes, [Fe(1-bpp)(2)](x)[M(terpy)2](1-x)[BF4]2 (M = Ru or Co)

The photomagnetic properties of two series of spin-crossover solid solutions, [Fe(1-bpp)(2)](x)[Ru(terpy)(2)](1-x)(BF(4))(2) and [Fe(1-bpp)(2)](x)[Co(terpy)(2)](1-x)(BF(4))(2) (1-bpp = 2,6-bis[pyrazol-1-yl]pyridine), have been investigated. For all the materials, the evolution of the T(LIESST) value, the high-spin → low-spin relaxation parameters and the LITH loops were thoroughly studied. Interestingly in the Fe:Co series, along the photo-excitation, cobalt ions are concomitantly converted from low-spin to high-spin states with the iron centres, and also fully relax after light excitation.     

Synthesis, structure, and magnetic properties of three 1D chain complexes based on high-spin metal-cyanide clusters: [Mn(III)6M(III)] (M = Cr, Fe, Co)

On the basis of high-spin metal-cyanide clusters of Mn(III)(6)M(III) (M = Cr, Fe, Co), three one-dimensional (1D) chain complexes, [Mn(salen)](6)[Cr(CN)(6)](2)·6CH(3)OH·H(2)O (1), [Mn(5-CH(3))salen)](6)[Fe(CN)(6)](2)·2CH(3)CN·10H(2)O (2), and [Mn(5-CH(3))salen)](6)[Co(CN)(6)](2)·2CH(3)CN·10H(2)O (3) [salen = N,N'-ethylenebis(salicylideneiminato) dianion], have been synthesized and characterized structurally as well as magnetically. Complexes 2 and 3 are isomorphic but slightly different from complex 1. All three complexes contain a 1D chain structure which is comprised of alternating high-spin metal-cyanide clusters of [Mn(6)M](3+) and a bridging group [M(CN)(6)](3-) in the trans mode. Furthermore, the three complexes all exhibit extended 3D supramolecular networks originating from short intermolecular contacts. Magnetic investigation indicates that the coupling mechanisms are intrachain antiferromagnetic interactions for 1 and ferromagnetic interactions for 2, respectively. Complex 3 is a magnetic dilute system due to the diamagnetic nature of Co(III). Further magnetic investigations show that complexes 1 and 2 are dominated by the 3D antiferromagnetic ordering with T(N) = 7.2 K for 1 and 9.5 K for 2. It is worth noting that the weak frequency-dependent phenomenon of AC susceptibilities was observed in the low-temperature region in both 1 and 2, suggesting the presence of slow magnetic relaxations.     

Metal Cyanide Ions Mx(CN)y]+,- in the gas phase: M = Fe,Co, Ni,Zn, Cd,Hg, Fe + Ag,Co + Ag

The generation of metal cyanide ions in the gas phase by laser ablation of M(CN)(2) (M = Co, Ni, Zn, Cd, Hg), Fe(III)[Fe(III)(CN)(6)] x xH(2)O, Ag(3)[M(CN)(6)] (M = Fe, Co), and Ag(2)[Fe(CN)(5)(NO)] has been investigated using Fourier transform ion cyclotron resonance mass spectrometry. Irradiation of Zn(CN)(2) and Cd(CN)(2) produced extensive series of anions, [Zn(n)(CN)(2n+1)](-) (1 < or = n < or = 27) and [Cd(n)(CN)(2n+1)](-) (n = 1, 2, 8-27, and possibly 29, 30). Cations Hg(CN)(+) and [Hg(2)(CN)(x)](+) (x = 1-3), and anions [Hg(CN)(x)](-) (x = 2, 3), are produced from Hg(CN)(2). Irradiation of Fe(III)[Fe(III)(CN)(6)] x xH(2)O gives the anions [Fe(CN)(2)](-), [Fe(CN)(3)](-), [Fe(2)(CN)(3)](-), [Fe(2)(CN)(4)](-), and [Fe(2)(CN)(5)](-). When Ag(3)[Fe(CN)(6)] is ablated, [AgFe(CN)(4)](-) and [Ag(2)Fe(CN)(5)](-) are observed together with homoleptic anions of Fe and Ag. The additional heterometallic complexes [AgFe(2)(CN)(6)](-), [AgFe(3)(CN)(8)](-), [Ag(2)Fe(2)(CN)(7)](-), and [Ag(3)Fe(CN)(6)](-) are observed on ablation of Ag(2)[Fe(CN)(5)(NO)]. Homoleptic anions [Co(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n+2)](-) (n = 1-3), [Co(2)(CN)(4)](-), and [Co(3)(CN)(5)](-) are formed when anhydrous Co(CN)(2) is the target. Ablation of Ag(3)[Co(CN)(6)] yields cations [Ag(n)(CN)(n-1)](+) (n = 1-4) and [Ag(n)Co(CN)(n)](+) (n = 1, 2) and anions [Ag(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n-1)](-) (n = 1, 2), [Ag(n)Co(CN)(n+2)](-) (n = 1, 2), and [Ag(n)Co(CN)(n+3)](-) (n = 0-2). The Ni(I) species [Ni(n)(CN)(n-1)](+) (n = 1-4) and [Ni(n)(CN)(n+1)](-) (n = 1-3) are produced when anhydrous Ni(CN)(2) is irradiated. In all cases, CN(-) and polyatomic carbon nitride ions C(x)N(y)(-) are formed concurrently. On the basis of density functional calculations, probable structures are proposed for most of the newly observed species. General structural features are low coordination numbers, regular trigonal coordination stereochemistry for d(10) metals but distorted trigonal stereochemistry for transition metals, the occurrence of M-CN-M and M(-CN-)(2)M bridges, addition of AgCN to terminal CN ligands, and the occurrence of high spin ground states for linear [M(n)(CN)(n+1)](-) complexes of Co and Ni.     

Photomagnetic K(0.25)Ni(1-x)Co(x)[Fe(CN)6]·nH2O and K(0.25)Co[Fe(CN)6](0.75y)[Cr(CN)6](0.75(1-y))·nH2O Prussian blue analogue solid solutions

Magnetically bistable solid solutions of Prussian blue analogues with chemical formulas of K(α)Ni(1-x)Co(x)[Fe(CN)(6)](β)·nH(2)O (Ni(1-x)Co(x)Fe) and K(α)Co(γ)[Fe(CN)(6)](y)[Cr(CN)(6)](1-y)·nH(2)O (CoFe(y)Cr(1-y)) have been synthesized and studied using mass spectrometry, M?ssbauer spectroscopy, X-ray diffraction, temperature-dependent infrared spectroscopy, and dc magnetometry. These compounds provide insight into interfaces between the photomagnetic Co-Fe Prussian blue analogue and the high-T(C) Ni-Cr Prussian blue analogue that exist in high-T(C) photomagnetic heterostructures. This investigation shows that the bistability of Co-Fe is strongly modified by metal substitution, with Ni(1-x)Co(x)Fe stabilizing high-spin cobalt-iron pairs and CoFe(y)Cr(1-y) stabilizing low-spin cobalt-iron pairs, while both types of substitution cause a dramatic decrease in the bistability of the material.     

Density functional investigation of metal-metal interactions in d4d4 face-shared [M2Cl9]3 - (M = Mn, Tc, Re) systems

The molecular and electronic structures of the d(4)d(4) face-shared [M(2)Cl(9)](3)(-) (M = Mn, Tc, Re) dimers have been calculated by density functional methods in order to investigate metal-metal bonding in this series. The electronic structures of these systems have been analyzed using potential energy curves for the broken-symmetry and other spin states arising from the various d(4)d(4) coupling modes, and closed energy cycles have been utilized to identify and quantify the parameters which are most important in determining the preference for electron localization or delocalization and for high-spin or low-spin configurations. In [Tc(2)Cl(9)](3)(-) and [Re(2)Cl(9)](3)(-), the global minimum has been found to be a spin-triplet state arising from the coupling of metal centers with low-spin configurations, and characterized by delocalization of the metal-based electrons in a double (sigma and delta(pi)) bond with a metal-metal separation of 2.57 A. In contrast, high-spin configurations and electron localization are favored in [Mn(2)Cl(9)](3)(-), the global minimum for this species being the ferromagnetic S = 4 state with a rather long metal-metal separation of 3.43 A. These results are consistent with metal-metal overlap and ligand-field effects prevailing over spin polarization effects in the Tc and Re systems, but with the opposite trend being observed in the Mn complex. The ground states and metal-metal bonding observed for the d(4)d(4) systems in this study parallel those previously found for the analogous d(2)d(2) complexes of V, Nb, and Ta, and can be rationalized on the basis that the d(4)d(4) dimer configuration is the hole equivalent of the d(2)d(2) configuration.     

Systematic investigation of trigonal-bipyramidal cyanide-bridged clusters of the first-row transition metals

Reactions between [M'(III)(CN)(6)](3-) anions (M' = Co, Cr, or Fe) and mononuclear complexes of M(II) ions (M = Cr, Mn, Co, Ni, or Zn) produce a family of pentanuclear clusters {[M(tmphen)(2)](3)[M'(CN)(6)](2)]}. The core of the clusters is formed by five metal ions that are bridged through six CN- linkers into a trigonal bipyramid, with M and M' ions occupying equatorial and axial positions of the bipyramid, respectively. Three of the CN- ligands from each M' center remain terminal and point toward the outside of the cluster, along the trigonal axes. Studies of magnetic coupling in the {[M(tmphen)(2)](3)[M'(CN)(6)](2)]} family of clusters revealed a similarity between the observed magnetic exchange constants and the values estimated for the molecule-based magnets of the Prussian blue family. The type of the magnetic exchange varies across the series, changing from antiferromagnetic for M = Cr and Mn to ferromagnetic for M = Co and Ni. Complexes {[M(tmphen)(2)](3)[M'(CN)(6)](2)]}, which contain diamagnetic Co(III) ions in the axial positions, serve as convenient model compounds for an accurate assessment of the magnetic parameters for the equatorial M ions in the absence of magnetic interactions. The {[Co(tmphen)(2)](3)[Cr(CN)(6)](2)]} cluster exhibits cyanide linkage isomerism, the relative amount of which depends on the synthetic conditions.     

Synthesis, structure and DFT study of dinuclear iron, cobalt and nickel complexes with cyclopentadienyl-metal moieties

Reactions of 1,1'-bis(dipheny1phosphino)cobaltocene with Co(PMe(3))(4), Ni(PMe(3))(4), Fe(PMe(3))(4), Ni(COD)(2), FeMe(2)(PMe(3))(4) or NiMe(2)(PMe(3))(3) afford a series of novel dinuclear complexes [((Me(3)P)[lower bond 1 start]Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)M[upper bond 1 end](η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (M = Co(1), Ni(2) and Fe(3)) [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](COD)](4), [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](PMe(3))(2)] (5) and [((Me(3)P)[lower bond 1 start]Co(Me)(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)Fe[upper bond 1 end](Me)(η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (6). Reactions of 1,1'-bis(dipheny1phosphino)ferrocene with Ni(PMe(3))(4), NiMe(2)(PMe(3))(3), or Co(PMe(3))(4) gives rise to complexes [Fe(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)M[upper bond 1 end](PMe(3))(2)] (M = Ni (7), Co (8)). The complexes 1-8 were spectroscopically investigated and studied by X-ray single crystal diffraction. The possible reaction mechanisms and structural characteristics are discussed. Density functional theory (DFT) calculations strongly support the deductions.     

Solid-state structural and magnetic investigations of [M[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) (M = Fe,Co, Ni,Cu): observation of a thermally induced solid-state phase change controlling an iron(II) spin-state crossover

The reaction of M(BF(4))(2).xH(2)O (M = Co, Ni, and Cu) and HC(3,5-Me(2)pz)(3) in a 1:2 ratio yields [Co[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) (2), [Ni[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) (3), and [Cu[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) (4). Over the temperature range from 5 to 350, 345, or 320 K, Curie law behavior is observed for microcrystalline samples of all three compounds showing them to have three, two, and one unpaired electrons, respectively, with no spin-crossover observed for 2. Crystalline samples of these compounds torque in the applied magnetic field the first time the sample is cooled to 5 K. The solid-state structures of all three are isomorphous at 220 K, monoclinic in the space group C2/c. The metal is located on a unique crystallographic site and has a trigonally distorted octahedral structure, with 4 showing the expected Jahn-Teller distortions. Cooling crystals of all three to low temperatures leads to the observation of the same phase change to triclinic in the new space group P(-)1 with nonmerohedral twinning. This change is reversible and yields two crystallographically unique metal sites at low temperature. The bond angles and distances for the two different metal sites for each compound in the low temperature structures are very similar to each other and to those in the 220 K structures. The same phase change, monoclinic to triclinic, has been observed previously for [Fe[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) (1), except in this case, the phase change results in half of the cations changing over from the high-spin state to the low-spin state while the other half of the cations remain high-spin, with the low-spin form decreasing its Fe-N bond distances by 0.19 A. The new results with 2-4 show that it is the phase transition, which occurs in complexes of the type [M[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) with first row transition metals, that is driving the unusual spin-crossover behavior of [Fe[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2).     

Dinuclear cyano complexes of cobalt(III) and Iron(III) containing noninnocent 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene bridging ligands

Two new dinucleating ligands 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene, H(4)(tpb), and 1,2,4,5-tetrakis(4-tert-butyl-2-pyridinecarboxamido)benzene, H(4)(tbpb), have been synthesized, and the following dinuclear cyano complexes of cobalt(III) and iron(III) have been isolated: Na(2)[Co(III)(2)(tpb)(CN)(4)] (1); [N(n-Bu)(4)](2)[Co(III)(2)(tbpb)(CN)(4)] (2); [Co(III)(2)(tbpb(ox2))(CN)(4)] (3); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(N(3))(4)] (4); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(CN)(4)] (5); [N(n-Bu)(4)](2)[Fe(III)(2)(tbpb)(CN)(4)] (6). Complexes 2-4 and 6 have been structurally characterized by X-ray crystallography at 100 K. From electrochemical and spectroscopic (UV-vis, IR, EPR, M?ssbauer) and magnetochemical investigations it is established that the coordinated central 1,2,4,5-tetraamidobenzene entity in the cyano complexes can be oxidized in two successive one-electron steps yielding paramagnetic (tbpb(ox1))(3)(-) and diamagnetic (tbpb(ox2))(2)(-) anions. Thus, complex 6 exists in five characterized oxidation levels: [Fe(III)(2)(tbpb(ox2))(CN)(4)](0) (S = 0); [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Fe(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Fe(III)Fe(II)(tbpb)(CN)(4)](3)(-) (S = (1)/(2)); [Fe(II)(2)(tbpb)(CN)(4)](4)(-) (S = 0). The iron(II) and (III) ions are always low-spin configurated. The electronic structure of the paramagnetic iron(III) ions and the exchange interaction of the three-spin system [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) are characterized in detail. Similarly, for 2 three oxidation levels have been identified and fully characterized: [Co(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Co(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Co(III)(2)(tbpb(ox2))(CN)(4)](0). The crystal structures of 2 and 3 clearly show that the two electron oxidation of 2 yielding 3 affects only the central tetraamidobenzene part of the ligand.     

mer-[Fe(pcq)(CN)3]-: a novel cyanide-containing building block and its application to assembling cyanide-bridged trinuclear FeIII2MnII complexes [pcq- = 8-(pyridine-2-carboxamido)quinoline anion

A new cyanide-containing building block K[Fe(pcq)(CN)(3)] [1; pcq(-) = 8-(pyridine-2-carboxamido)quinoline anion] containing a low-spin Fe(III) center with three cyanide groups in a meridional arrangement has been successfully designed and synthesized. Three cyanide-bridged trinuclear Fe(III)(2)Mn(II) complexes, [Fe(pcq)(CN)(3)](2)[Mn(CH(3)OH)(2)(H(2)O)(2)].2H(2)O (2), [Fe(pcq)(CN)(3)](2)[Mn(bipy)(2)].CH(3)OH.2H(2)O (3), and [Fe(pcq)(CN)(3)](2)[Mn(phen)(2)].CH(3)OH.2H(2)O (4), have been synthesized and structurally characterized. The magnetic susceptibilities of the three heterometallic complexes have been investigated.     

Synthesis and reactions of triphenylsilanethiolato complexes of manganese(II), iron(II), cobalt(II), and nickel(II)

Reactions of Fe[N(SiMe(3))(2)](2) with 1 and 2 equiv of Ph(3)SiSH in hexane afforded dinuclear silanethiolato complexes, [Fe(N(SiMe(3))(2))(mu-SSiPh(3))](2) (1) and [Fe(SSiPh(3))(mu-SSiPh(3))](2) (2), respectively. Various Lewis bases were readily added to 2, generating mononuclear adducts, Fe(SSiPh(3))(2)(L)(2) [L = CH(3)CN (3a), 4-(t)BuC(5)H(4)N (3b), PEt(3) (3c), (LL) = tmeda (3d)]. From the analogous reactions of M[N(SiMe(3))(2)](2) (M = Mn, Co) and [Ni(NPh(2))(2)](2) with Ph(3)SiSH in the presence of TMEDA, the corresponding silanethiolato complexes, M(SSiPh(3))(2)(tmeda) [M = Mn (4), Co (5), Ni (6)], were isolated. Treatment of 3a with (PPh(4))(2)[MoS(4)] or (NEt(4))(2)[FeCl(4)] resulted in formation of a linear trinuclear Fe-Mo-Fe cluster (PPh(4))(2)[MoS(4)(Fe(SSiPh(3))(2))(2)] (7) or a dinuclear complex (NEt(4))(2)[Fe(2)(SSiPh(3))(2)Cl(4)] (8). On the other hand, the reaction of 3a with [Cu(CH(3)CN)(4)](PF(6)) gave a cyclic tetranuclear copper cluster Cu(4)(SSiPh(3))(4) (9), where silanethiolato ligands were transferred from iron to copper. Silicon-sulfur bond cleavage was found to occur when the cobalt complex 5 was treated with (NBu(4))F in THF, and a cobalt-sulfido cluster Co(6)(mu(3)-S)(8)(PPh(3))(6) (10) was isolated upon addition of PPh(3) to the reaction system. The silanethiolato complexes reported here are expected to serve as convenient precursors for sulfido cluster synthesis.     

Substituent effect on formation of heterometallic molecular wheels: synthesis, crystal structure, and magnetic properties

The reaction of manganese(III) Schiff bases of the type salen(2-) (N,N'-ethylenebis(salicylideneaminato)) with X-substituted (X = CH(3), Cl) pyridinecarboxamide dicyanoferrite(III) [Fe(X-bpb)(CN)(2)](-) gave rise to a series of cyanide-bridged Mn(6)Fe(6) molecular wheels, [Mn(III)(salen)](6)[Fe(III)(bpmb)(CN)(2)](6) x 7H(2)O (1), [Mn(salen)](6)[Fe(bpClb)(CN)(2)](6) x 4H(2)O x 2CH(3)OH (2), [Mn(salen)](6)[Fe(bpdmb)(CN)(2)](6) x 10H(2)O x 5CH(3)OH (3), [Mn(5-Br(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 24H(2)O x 8CH(3)CN (4), and [Mn(5-Cl(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 25H(2)O x 5CH(3)CN (5). Compared with [Fe(bpb)(CN)(2)](-), which always gives rise to 1D or polynuclear species when reacting with Mn(III) Schiff bases, the introduction of substituents (X) to the bpb(2-) ligand has a driving force in formation of the novel wheel structure. Magnetic studies reveal that high-spin ground state S = 15 is present in the wheel compounds originated from the ferromagnetic Mn(III)-Fe(III) coupling. For the first time, the quantum Monte Carlo study has been used to modulate the magnetic susceptibility of the huge Mn(6)Fe(6) metallomacrocycles, showing that the magnetic coupling constants J range from 3.0 to 8.0 K on the basis of the spin Hamiltonian [Formula: see text]. Hysteresis loops for 1 have been observed below 0.8 K, indicative of a single-molecule magnet with a blocking temperature (TB) of 0.8 K. Molecular wheels 2-5 exhibit frequency dependence of alternating-current magnetic susceptibility under zero direct-current magnetic field, signifying the slow magnetization relaxation similar to that of 1. Significantly, an unprecedented archlike Mn(2)Fe(2) cluster, [Mn(5-Cl(salpn))](2)[Fe(bpmb)(CN)(2)](2) x 3H(2)O x CH(3)CN (6), has been isolated as an intermediate of the Mn(6)Fe(6) wheel 5. Ferromagnetic Mn(III)-Fe(III) coupling results in a high-spin S = 5 ground state. Combination of the high-spin state and a negative magnetic anisotropy (D) results in the observation of slow magnetization relaxation in 6.     

Periodic trends within a series of five-coordinate thiolate-ligated [MII(SMe2N4(tren))]+ (M = Mn, Fe, Co, Ni, Cu, Zn) complexes, including a rare example of a stable CuII-thiolate

A series of five-coordinate thiolate-ligated complexes [M(II)(tren)N4S(Me2)]+ (M = Mn, Fe, Co, Ni, Cu, Zn; tren = tris(2-aminoethyl)amine) are reported, and their structural, electronic, and magnetic properties are compared. Isolation of dimeric [Ni(II)(SN4(tren)-RS(dang))]2 ("dang"= dangling, uncoordinated thiolate supported by H bonds), using the less bulky [(tren)N4S](1-) ligand, pointed to the need for gem-dimethyls adjacent to the sulfur to sterically prevent dimerization. All of the gem-dimethyl derivatized complexes are monomeric and, with the exception of [Ni(II)(S(Me2)N4(tren)]+, are isostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. The nickel complex uniquely adopts an approximately ideal square pyramidal geometry and resembles the active site of Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structures are observed. The MII-S thiolate bonds systematically decrease in length across the series (Mn-S > Fe-S > Co-S > Ni-S approximately Cu-S < Zn-S) with exceptions occurring upon the occupation of sigma* orbitals. The copper complex, [Cu(II)(S(Me2)N4(tren)]+, represents a rare example of a stable CuII-thiolate, and models the perturbed "green" copper site of nitrite reductase. In contrast to the intensely colored, low-spin Fe(III)-thiolates, the M(II)-thiolates described herein are colorless to moderately colored and high-spin (in cases where more than one spin-state is possible), reflecting the poorer energy match between the metal d- and sulfur orbitals upon reduction of the metal ion. As the d-orbitals drop in energy proceeding across the across the series M(2+) (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metal charge-transfer transition moves into the visible region, and the redox potentials cathodically shift. The reduced M(+1) oxidation state is only accessible with copper, and the more oxidized M(+4) oxidation state is only accessible for manganese.     

Extended network thiocyanate- and tetracyanoethanide-based first-row transition metal complexes

Linear chain thiocyanate complexes of M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn, Cr) composition have been prepared and structurally, chemically, and magnetically characterized. Fe(NCS)(2)(OCMe(2))(2) exhibits metamagnetic-like behavior, and orders as an antiferromagnet at 6 K. The Mn and Cr compounds are antiferromagnets with T(c) of 30 and 50 K, respectively, with J/k(B) = -3.5 (-2.4 cm(-1)) and -9.9 K (-6.9 cm(-1)), respectively, when fit to one-dimensional (1-D) Fisher chain model (H = -2JS(i)·S(j)). Co(NCS)(2) was prepared by a new synthetic route, and powder diffraction was used to determine its structure to be a two-dimensional (2-D) layer with μ(N,S,S)-NCS motif, and it is an antiferromagnet (T(c) = 22 K; θ = -33 K for T > 25 K). M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn) and Co(NCS)(2) react with (NBu(4))(TCNE) in dichloromethane to form M(TCNE)[C(4)(CN)(8)](1/2), and in acetone to form M[C(4)(CN)(8)](OCMe(2))(2) (M = Fe, Mn, Co). These materials possess μ(4)-[C(4)(CN)(8)](2-) that form 2-D layered structural motifs, which exhibit weak antiferromagnetic coupling. Co(TCNE)[C(4)(CN)(8)](1/2) behaves as a paramagnet with strong antiferromagnetic coupling (θ = -50 K).     

Synthesis, characterization and thermal properties of trimetallic N3-Cr[quadruple bond]Cr···M-N3 azide complexes with M = Cr, Mn, Fe, and Co

We report here two novel synthetic pathways toward the preparation of a family of trimetallic diazide compounds of the type Cr(2)M(dpa)(4)(N(3))(2), with M = Cr (10), Mn (4), Fe (5), and Co (11). Reaction of either Cr(2)M(dpa)(4)(OTf)(2) (for M = Mn and Fe) or [Cr(2)M(dpa)(4)(MeCN)(2)](PF(6))(2) (for M = Cr and Co) with sodium azide in methanol leads to the formation of the corresponding diazide compounds, and single crystal X-ray diffraction measurements confirm the predicted structures. Compounds 4, 5, and 10 are all high-spin compounds, but 11 is a spin-crossover compound exhibiting low-spin behavior at low temperatures (~100 K). Thermolytic characterization by DSC and TGA reveals an exothermic reaction corresponding to the loss of two dinitrogen molecules from compounds 5, 10, and 11. Further characterization by solution NMR measurements and cyclic voltammetry are also presented.     

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.     

Magnetic properties of isostructural M(H2O)4[Au(CN)4]2-based coordination polymers (M = Mn, Co, Ni, Cu, Zn) by SQUID and μSR studies

A series of isomorphous M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Mn, Co, Ni, Zn; Cu is similar) coordination polymers was synthesized from the reaction of M(II) with KAu(CN)(4); they consist of octahedrally coordinated metal centres with four equatorial water molecules and trans-axial N-cyano ligands from [Au(CN)(4)](-) moieties, generating a linear 1-D chain of M(H(2)O)(4)[Au(CN)(4)]-units. An additional interstitial [Au(CN)(4)](-) unit forms AuN and hydrogen bonds with adjacent chains. The Cu(II) system readily loses water to yield Cu[Au(CN)(4)](2)(H(2)O)(4), which was not structurally characterized. The magnetic properties of these polymers were investigated by a combination of SQUID magnetometry and zero-field muon spin relaxation (ZF-μSR). Only weak antiferromagnetic interactions along the chains are mediated by the [Au(CN)(4)]-units, but the ZF-μSR data indicates that interchain interactions yield a phase transition to a magnetically ordered state for Cu[Au(CN)(4)](2)(H(2)O)(4) below 0.6 K, while for M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Co), depopulation of zero-field split Kramer's doublets to an effective "S = 1/2" ground state yields a transition to a spin-frozen magnetic state below 0.26 K. On the other hand, only a simple slowing-down of spins above 0.02 K is observed for the more weakly zero-field split M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Mn, Ni) complexes.     

Hydrothermal synthesis, structures and magnetic studies of transition metal sulfates containing hydrazine

By employing hydrothermal method, six transition metal sulfates containing hydrazine (N(2)H(4)) have been obtained: [M(SO(4))(2)(N(2)H(5))(2)](n) (M = Mn(1), Co(2), Ni(3)) and [M(N(2)H(4))SO(4)](n) (M = Mn(4), Co(5), Ni(6)). Their crystal structures and magnetic properties have been investigated experimentally and theoretically. Compounds 1-3 consist of one-dimensional sulfate bridged homometallic chains with protonated hydrazine molecule as terminal ligand, and compounds 4-6 are hydrazing-sulfate mixed bridged homometallic three-dimensional frameworks. Compounds 1-6 exhibit antiferromagnetic coupling between M(2+) ions, but their magnetic properties differ at low temperatures because of the different single-ion anisotropy and crystal structures. The magnetostructural correlations and the magnetic coupling mechanism are analyzed by density functional theory calculations (DFT).     

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.