Ln(terpy)]3+ (Ln = Sm, Gd) entity forms isolated magnetic chains with [W(CN)8]3-

The reaction between Ln(NO3)3*xH2O, Cs3[W(V)(CN)8]*H2O and 2,2':6',2'-terpyridine (terpy) leads to the original isomorphous cyano-bridged [Ln(III)(terpy)(DMF)4][W(V)(CN)8] *6H2O [Ln = Gd (1), Sm (2)] 1-D chains. The crystal structures of {Ln(III)W(V)} chains and consist of alternating {[W(CN)8]} and {[Ln(terpy)]} building blocks. The neighbouring 1-D chains are weakly linked through pi-pi stacking interactions of the aromatic rings leading to 2-D supramolecular layers. The layers are linked through hydrogen bonds between H2O molecules and terminal cyano ligands. Magnetic studies revealed a weak antiferromagnetic coupling (J = -2.3(2) K) within the {Gd(III)W(V)} chains in . The positive effective coupling constant J = +2.0(5) K between the total angular momentum of the Sm(III) centre and the spin of the W(v) ion is equivalent to an antiferromagnetic character of the spin coupling between both centres in the {Sm(III)W(V)} chains of 2. The magnetic measurements suggest that they display an isolated magnetic chain behaviour.     

Cyanide-bridged tetradecanuclear RuII3MII11 clusters (MII=ZnII and CuII) based on the high connectivity building block [Ru3(HAT)(CN)12]6-: structural and photophysical properties

Reaction of the anionic cyanometallate chromophore [{Ru(CN)4}3(micro3-HAT)]6- with [MII(tren)]2+ complexes (M=ZnII, CuII) provides discrete tetradecanuclear clusters of formula [{MII(tren)(micro-CN)}11{Ru3(HAT)(CN)}]16+; the weak luminescence of the Ru3 chromophore is substantially enhanced in the presence of ZnII ions, whereas it is completely quenched when CuII centers are present.     

Grid-type two-dimensional magnetic multinuclear metal complex: strands of ([CuII(mu-4,4'-bpy)]2+)n cross-linked by octacyanotungstate(V) ions

Reaction of the preorganized strands of ([Cu(II)(mu-4,4'-bpy)](2+))n (4,4'-bpy = 4,4'-bipyridine) with [W(V)(CN)(8)](3)(-) leads to a novel cyano-bridged Cu(II)(3)W(V)(2) complex [Cu(mu-4,4'-bpy)(DMF)(2)][Cu(mu-4,4'-bpy)(DMF)](2)[W(V)(CN)(8)](2).2DMF. 2H(2)O 1. The structure of 1 consists of the expected 2-dimensional grid-type network which is built of infinite ([Cu(II)(mu-4,4'-bpy)](2+))n chains cross-linked by octacyanotungstate units. The Cu(II)-NC-W(V)-CN-Cu(II) linkage exhibits the topology of a 3,2-chain. The skeleton of the layer is additionally stabilized by a hydrogen bond network formed by terminal cyano ligands of the [W(CN)(8)](3-) moiety and water molecules. The distance between the adjacent Cu(3)(II)W(2)(V) chains within the layer is 11.12 A along the a axis. The layers are connected by H-bonds of NCN-NDMF-NCN linkages into 3-D supramolecular architecture. The magnetic properties correspond to a dominant ferromagnetic coupling within the Cu(II)(3)W(V)(2) pentamer units (J = +35(4) cm(-1)) and much weaker effective AF interunit coupling which include both intra- and inter-3,2-chain interactions between pentamers (J' = -0.05(1) cm(-1)).     

Two WV-MnIII bimetallic assemblies built by octacyanotungstate(v) and MnIII Schiff bases: molecular structures and a spin-flop transition

Two W(V)-Mn(III) bimetallic compounds, [Mn(Cl-salmen)(H(2)O)2]{[Mn(5-Clsalmen)(H(2)O)]2[W(CN)8].2H(2)O (1.2H(2)O) [5-Clsalmen = N,N'-(1-methylethylene)bis(5-chlorosalicylideneiminato) dianion], which contains trinuclear Mn(2)W and isolated Mn(III) moieties, and [Mn(3-MeOsalcy)(H(2)O)2]3[W(CN)(8)].2H(2)O (2.2H(2)O) [3-MeOsalcy = N,N'-(trans-1,2-cyclohexanediylethylene)bis(3-methoxysalicylideneiminato) dianion] molecules were prepared in redox processes and characterized using X-ray analysis and magnetic measurements. Compound 1 is composed of the {[Mn(5-Clsalmen)(H(2)O)]2[W(CN)8]}- trimer, in which two CN groups among eight in [W(CN)8](3-) bridge W(5+) and two Mn(3+) ions and the remaining CN ligands are hydrogen-bonded to water molecules or unbound, and the [Mn(Cl-salmen)(H(2)O)2]+ cation. Subsequently, two water molecules of the isolated cation are subject to hydrogen bonds. For 2, there are no covalent bonds among the subunits and six serial stacks of [Mn(3-MeOsalcy)(H(2)O)2]+ units are all hydrogen-bonded. The many hydrogen bonds found in both complexes eventually lead to three-dimensional networks. The magnetic studies for 1 reveal that antiferromagnetic interactions (J = -5.4 cm(-1)) between W(V) and Mn(III) centers within the trimer are transmitted via the bridging CN groups. Intermolecular antiferromagnetic couplings (zJ' = -0.2 cm(-1)) are also observed. The static and dynamic magnetic data of 1 demonstrate the existence of a field-induced spin-flop transition occurring among the clusters and monomeric molecules.     

Tuning of magnetic properties of polynuclear lanthanide(III)-octacyanotungstate(V) systems: determination of ligand-field parameters and exchange interaction

The self-assembly reaction between trivalent lanthanide ions, 2,2':6',2' '-terpyridine (terpy) ligand, and octacyanotungstate(V) leads to the formation of two series of isomorphous cyano-bridged compounds: (i) one-dimensional (1-D) chains [Ln(terpy)(DMF)(4)][W(CN)(8)].6H(2)O.C(2)H(5)OH (Ln = Ce-Dy) and (ii) dinuclear molecules [Ln(terpy)(DMF)(2)(H(2)O)(2)][W(CN)(8)].3H(2)O (Ln = Ho, Er, Yb) and the ionic [Tm(III)(terpy)(DMF)(2)(H(2)O)(3)][WV(CN)(8)].4H(2)O.DMF (DMF = N,N-dimethylformamide) system. The crystal structures of 1-D chains consist of alternating {[W(CN)(8)]} and {[Ln(terpy)]} building blocks. The neighboring chains are weakly linked through the pi-pi stacking interactions of the aromatic rings, leading to two-dimensional supramolecular layers. The dinuclear species are weakly linked through the hydrogen bonds between H2O molecules and terminal cyano ligands resulting in a columnlike arrangement of dimers. Taking into account the ligand-field splitting and the exchange interaction, we have estimated the magnetic couplings between the Ln(III) and WV centers in a series of polycrystalline 1-D chains and in dimeric systems. The corresponding exchange constants have been shown to change the sign along the series of chains. The coupling is antiferromagnetic for 1 (J = -0.24 cm(-1)) and 2 (J = -0.07 cm(-1)), whereas 3 (J = +0.47 cm(-1)), 7 (J = +0.28 cm(-1)), and 8 (J = +0.23 cm(-1)) have ferromagnetic character. In the case of dimeric systems, the coupling constants seem to be independent of the lanthanide center. The splitting structures of the ground-state multiplets of the Ln(III) centers have been shown to explain the temperature dependences of the magnetic susceptibilities.     

Preparation and oxygenation of (flavonolato)copper isoindoline complexes with relevance to quercetin dioxygenase

Mesitylcopper reacts with flavonol (flaH) in the presence of 1,3-bis(2-pyridylimino)isoindoline (indH) to yield the diamagnetic complex CuI(fla)(indH), which on reaction with molecular oxygen undergoes oxidative splitting of the C2-C3 bond of the pyranone ring of the flavonolate ligand to give CuI(indH)(O-bs) (O-bs = O-benzoylsalicylate) (orthorhombic, P1, a = 8.048(7) A, b = 8.969(9) A, c = 19.240(2) A, alpha = 85.69 degrees, beta = 80.24(7) degrees, gamma = 77.87(7) degrees, V = 1337(2) A3, Z = 2) and carbon monoxide. The reaction of [CuI(CH3CN)4]ClO4, flaH, and indH with dioxygen at room temperature affords the paramagnetic complex [CuII(fla)(indH)]ClO4 (mu = 2.10 mu B), and after elimination of HClO4, CuII(fla)(ind) (orthorhombic, Pbca, a = 8.888(2) A, b = 19.169(7) A, c = 33.614(10) A, alpha = beta = gamma = 90 degrees, V = 5727(3) A3, Z = 8) with mu = 1.86 mu B is formed. The latter undergoes cleavage of the pyranone ring on oxygenation at 80 degrees C to give CuII(ind)(O-bs) (mu = 1.87 mu B, nu(CO) = 1742 cm-1, and nu(CO2) = 1581, 1387 cm-1) and carbon monoxide. CuII(fla)(ind) and [CuII(fla)(indH)]ClO4 serve as good catalysts for the oxygenation of flavonol to O-benzoylsalicyclic acid.     

2-D soft ferromagnet based on [Wv(CN)8]3- and CuII with a Tc of 34 K

Self-assembly of [Cu(tetren)]2+ (tetren = tetraethylenepentamine) and [W(CN)8]3- in acidic aqueous solution yields the double-layered square grid cyanide-bridged polymer of ((tetrenH5)0.8CuII4[Wv(CN)8](4).7.2H2O)n with Cu(II) centres of square pyramidal geometry coordinatively saturated solely by CN bridges supplied by five [W(CN)8]3- ions; it exhibits soft ferromagnetic behaviour with an ordering temperature Tc of 34 K.     

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.     

A two-dimensional octacyanomolybdate(V)-based ferrimagnet: {[Mn(II)(DMF)4]3[Mo(V)(CN)8]2}n

Treatment of [HNBu3]3[Mo(V)(CN)8] with manganese(II) p-toluenesulfonate in N,N'-dimethylformamide (DMF) affords {[Mn(II)(DMF)4]3[Mo(V)(CN)8]2}n (1) as a two-dimensional network. The structure of 1 consists of [cis-Mn(II)(DMF)4(mu-NC)2]2+ and [trans-Mn(II)(DMF)4(mu-NC)2]2+ units that are linked via cyanides to three-connected [Mo(V)(CN)5(mu-CN)3]3- centers in a 4:2:6 ratio, forming 12-membered rings. Magnetic measurements indicate that 1 is a ferrimagnet (TN = 8 K) that exhibits frequency-dependent behavior in chi". Heating of 1 affords an additional magnetic phase (TN = 21 K) that is absent of linkage isomerism.     

PPh4]3[W(CN)7(O2)].4H2O as the representative of the [M(L)7(LL)] class for nine-coordinate complexes

The photoinduced dissociation of a W-CN bond in [W(CN)8]4- in an aqueous solution under ambient conditions, in conjunction with the uptake of molecular oxygen, affords the W(VI) mixed-ligand complex anion [W(CN)(7)(eta2-O2)]3-, conveniently isolable as its [PPh4+] salt. Although research into the chemistry of cyanomolybdates and cyanotungstates has been pursued with great interest and vigor over several decades, there is a paucity of structurally characterized cyano-peroxo complexes of Mo and W. The side-on coordination mode of the peroxo moiety in [W(CN)7(eta2-O2)]3- has been ascertained with X-ray crystal structure determination [d(O-O) = 1.41 A; peroxo bite angle: 41.0 degrees ] and corroborated with vibrational spectroscopy [nu(O-O) = 915 cm(-1)]. The complex ion exhibits trapezoidal tridecahedral geometry and represents the new class of nine-coordinate complexes with one bidentate and seven monodentate ligands. Cyclic voltammetry shows a reversible redox behavior of [W(CN)7(eta2-O2)]3- in CH3CN with its standard reduction potential equal to 1.130 V. Generally, interest in atmospheric oxygen derives from the versatility of this molecule as a ligand and oxidant and extends to the physicochemical features it imparts to transition metals such as copper and iron in biological oxygen carriers.     

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).     

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.     

Microwave-assisted construction of ferromagnetic coordination polymers of [W(V)(CN)8]3- with Cu(II)-pyrazole synthons

The microwave-mediated self-assembly of [W(V)(CN)(8)](3-) with Cu(II) in the presence of pyrazole ligand resulted in the formation of three novel assemblies: Cu(II)(2)(Hpyr)(5)(H(2)O)[W(V)(CN)(8)](NO(3))·H(2)O (1), {Cu(II)(5)(Hpyr)(18)[W(V)(CN)(8)](4)}·[Cu(II)(Hpyr)(4)(H(2)O)(2)]·9H(2)O (2), and Cu(II)(4)(Hpyr)(10)(H(2)O)[W(V)(CN)(8)](2)(HCOO)(2)·4.5H(2)O (3) (Hpyr =1H-pyrazole). Single-crystal X-ray structure of 1 consists of cyanido-bridged 1-D chains of vertex-sharing squares topology. The structure of 2 reveals 2-D hybrid inorganic layer topology with large coordination spaces occupied by {Cu(Hpyr)(2)(H(2)O)(4)}(2+) ions. Compound 3 contains two types of cyanido-bridged 1-D chains of vertex-sharing squares linked together by formate ions in two directions forming hybrid inorganic-organic 3-D framework (I(1)O(2)). The magnetic measurements for 1-3 reveal a weak ferromagnetic coupling through Cu(II)-NC-W(V) bridges.     

W-knotted chain {[Cu(II)(dien)]4[W(V)(CN)8]}(5+)∞: synthesis, crystal structure, magnetism, and theory

The self-assembly of [Cu(II)(dien)(H(2)O)(2)](2+) and [W(V)(CN)(8)](3-) in aqueous solution leads to the formation (H(3)O){[Cu(II)(dien)](4)[W(V)(CN)(8)]}[W(V)(CN)(8)](2)·6.5H(2)O (1). The crystal structure of 1 consists of an unprecedented {[Cu(II)(dien)](4)[W(V)(CN)(8)]}(5+)(∞) chain of (2,8) topology, nonbridging [W(CN)(8)](3-) anions, and crystallization water molecules. The analysis of magnetic behavior of 1 was performed by the density functional theory (DFT) method and magnetic susceptibility measurements. The DFT broken symmetry approach gave two J(CuW) coupling constants: J(ax) = +2.9 cm(-1) assigned to long and strongly bent W-CN-Cu linkage, and the J(eq) = +1.5 cm(-1) assigned to short and less bent W-CN-Cu linkage, located at the axial and the equatorial positions of square pyramidal Cu(II) centers, respectively, in the hexanuclear {W(2)Cu(4)} chain subunit. The dominance of weak-to-moderate ferromagnetic coupling within the chain was confirmed by magnetic calculations. Zero-field susceptibility of the full chain segment {WCu(4)}(n) was calculated by a semiclassical analytical approach assuming that only one W(V) out of five ? spins of the chain unit WCu(4) is treated as a classical commuting variable. The calculation of the field dependence of the magnetization was performed separately by replacing the same spin with the Ising variable and applying the standard transfer matrix technique. The intermolecular coupling between the chain segments and off-chain [W(CN)(8)](3-) entities was resolved using the mean-field approximation set to be of antiferromagnetic character. The magnetic coupling parameters are compared with those of other low dimensional {Cu(II)-[M(V)(CN)(8)]} systems.     

Synthesis, characterization, and photoresponsive properties of a series of Mo(IV)-Cu(II) complexes

Six Mo(IV)-Cu(II) complexes, [Cu(tpa)](2)[Mo(CN)(8)]·15H(2)O (1, tpa = tris(2-pyridylmethyl)amine), [Cu(tren)](2)[Mo(CN)(8)]·5.25H(2)O (2, tren = tris(2-aminoethyl)amine), [Cu(en)(2)][Cu(0.5)(en)][Cu(0.5)(en)(H(2)O)][Mo(CN)(8)]·4H(2)O (3, en = ethylenediamine), [Cu(bapa)](3)[Mo(CN)(8)](1.5)·12.5H(2)O (4, bapa = bis(3-aminopropyl)amine), [Cu(bapen)](2)[Mo(CN)(8)]·4H(2)O (5, bapen = N,N'-bis(3-aminopropyl)ethylenediamine), and [Cu(pn)(2)][Cu(pn)][Mo(CN)(8)]·3.5H(2)O (6, pn = 1,3-diaminopropane), were synthesized and characterized. Single-crystal X-ray diffraction analyses show that 1-6 have different structures varying from trinuclear clusters (1-2), a one-dimensional belt (3), two-dimensional grids (4-5), to a three-dimensional structure (6). Magnetic and ESR measurements suggest that 1-6 exhibit thermally reversible photoresponsive properties on UV light irradiation through a Mo(IV)-to-Cu(II) charge transfer mechanism. A trinuclear compound [Cu(II)(tpa)](2)[Mo(V)(CN)(8)](ClO(4)) (7) was synthesized as a model of the photoinduced intermediate.     

Structural and magnetic studies on cyano-bridged rectangular Fe2M2 (M = Cu, Ni) clusters

Using the tricyano precursor, (Bu4N)[(Tp)Fe(CN)3] (Tp = Tris(pyrazolyl) hydroborate) (1), four new tetranuclear clusters, [(Tp)Fe(CN)3Cu(Tp)]2.2H2O (2), [(Tp)Fe(CN)3Cu(bpca)]2.4H2O (3) (bpca = bis(2-pyridylcarbonyl)amidate anion), [(Tp)Fe(CN)3Ni(tren)]2(ClO4)2.2H2O (4) (tren = tris(2-amino)ethylamine), and [(Tp)Fe(CN)3Ni(bipy)2]2[(Tp)Fe(CN)3]2.6H2O (5) (bipy = 2,2'-bipyridine), have been synthesized and structurally characterized. The four clusters possess similar square structures, where FeIII and MII (M = CuII or NiII) ions alternate at the rectangle corners. There exist intermolecular - stacking interactions through pyrazolyl groups of Tp- ligands in complexes 2 and 4, which lead to 1D chain structures. Complex 5 shows a 3D network structure through the coexistence of - stacking effects and hydrogen-bonding interactions. Magnetic studies show intramolecular ferromagnetic interactions in all four clusters. The exchange parameters are +11.91 and +1.38 cm(-1) for clusters 2 and 3, respectively, while uniaxial molecular anisotropy can be detected in complex 3 due to the distorted core in its molecular structure. Complex 4 has a ground state of S = 3 and shows SMM behavior with an effective energy barrier of U = 18.9 cm(-1). Unusual spin-glass-like dynamic relaxations are observed for complex 5.     

Crystal structures and magnetic properties of two low-dimensional materials constructed from [Mn(III)(salen)H2O]+ and [M(CN)8](3-/4-) (M = Mo or W) precursors

The syntheses, X-ray structures, and magnetic behaviors of two new cyano-bridged assemblies, the molecular [Mn(III)(salen)H2O]3[W(V)(CN)8].H2O (1) and one-dimensional [Mn(salen)(H2O)2]2[[Mn(salen)(H2O)][Mn(salen)]2[Mo(CN)(8)]].0.5ClO4.0.5OH.4.5H2O (2), are presented. Compound 1 crystallizes in the monoclinic system, has space group P2(1)/c, and has unit cell constants a = 13.7210(2) A, b = 20.6840(4) A, c = 20.6370(2) A, and Z = 4. Compound 2 crystallizes in the triclinic system, has space group P, and has unit cell dimensions a = 18.428(4) A, b = 18.521(3) A, c = 18.567(4) A, and Z = 2. The structure of 1 consists of the asymmetric V-shaped Mn-NC-W-NC-Mn-O(phenolate)-Mn molecules, where W(V) coordinates with [Mn(salen)H2O] and singly phenolate-bridged [Mn(salen)H2O]2 moieties through the neighboring cyano bridges. The [W(V)(CN)8]3- ion displays distorted square-antiprism geometry. The structure of 2 consists of the cyano-bridged [Mn3(III)Mo(IV)]n- repeating units linked by double phenolate bridges into one-dimensional zigzag chains. The Mn(III) centers are bound to Mo(IV) of square-antiprism geometry through the neighboring cyano bridges. The magnetic studies of 1 reveal the antiferromagnetic intramolecular interactions through the CN and phenolate bridges and the relatively weak intermolecular interactions. Compound 1 becomes antiferromagnetically ordered below TN = 4.6 K. The presence of the magnetic anisotropy is documented with the MH measurements carried out for both polycrystalline and single-crystal samples. At T = 1.9 K, the spin-flop transition is observed in the field of 18 kOe applied parallel to the bc plane, which is the easy plane of magnetization. Field dependence of magnetization of 1 shows field-induced metamagnetic behavior from the antiferromagnetic ground state of ST = 3/2 to the state of ST = 5/2. The magnetic properties of 2 indicate a weak antiferromagnetic interaction between Mn(III) centers in double-phenolate-bridged [Mn(III)(salen)]2 dinuclear subunits and a very weak ferromagnetic interaction between them through the diamagnetic [Mo(IV)(CN)8]4- spacer.     

Assembly of azido- or cyano-bridged binuclear complexes containing the bulky [Mn(phen)2]2+ building block: syntheses, crystal structures, and magnetic properties

Two new cyano-bridged heterobinuclear complexes, [Mn(II)(phen)2Cl][Fe(III)(bpb)(CN)2] x 0.5CH3CH2OH x 1.5H2O (1) and [Mn(II)(phen)2Cl][Cr(III)(bpb)(CN)2] x 2H2O (2) [phen = 1,10-phenanthroline; bpb(2-) = 1,2-bis(pyridine-2-carboxamido)benzenate], and four novel azido-bridged Mn(II) dimeric complexes, [Mn2(phen)4(mu(1,1)-N3)2][M(III)(bpb)(CN)2]2 x H2O [M = Fe (3), Cr (4), Co (5)] and [Mn2(phen)4(mu(1,3)-N3)(N3)2]BPh4 x 0.5H2O (6), have been synthesized and characterized by single-crystal X-ray diffraction analysis and magnetic studies. Complexes 1 and 2 comprise [Mn(phen)2Cl]+ and [M(bpb)(CN)2]- units connected by one cyano ligand of [M(bpb)(CN)2]-. Complexes 3-5 are doubly end-on (EO) azido-bridged Mn(II) binuclear complexes with two [M(bpb)(CN)2]- molecules acting as charge-compensating anions. However, the Mn(II) ions in complex 6 are linked by a single end-to-end (EE) azido bridging ligand with one large free BPh4(-) group as the charge-balancing anion. The magnetic coupling between Mn(II) and Fe(III) or Cr(III) in complexes 1 and 2 was found to be antiferromagnetic with J(MnFe) = -2.68(3) cm(-1) and J(MnCr) = -4.55(1) cm(-1) on the basis of the Hamiltonian H = -JS(Mn)S(M) (M = Fe or Cr). The magnetic interactions between two Mn(II) ions in 3-5 are ferromagnetic in nature with the magnetic coupling constants of 1.15(3), 1.05(2), and 1.27(2) cm(-1) (H = -JS(Mn1)S(Mn2)), respectively. The single EE azido-bridged dimeric complex 6 manifests antiferromagnetic interaction with J = -2.29(4) cm(-1) (H = -JS(Mn1)S(Mn2)). Magneto-structural correlationship on the EO azido-bridged Mn(II) dimers has been investigated.     

Crystal structure and magnetic properties of an octacyanometalate-based three-dimensional tungstate(V)-manganese(II) bimetallic assembly

A single crystal of the title compound [MnII6(H2O)9[W(V)(CN)8]4 x 13H2O]n was synthesized in a hot aqueous solution containing octacyanotungstate, Na3[W(CN)8] x 3H2O, and Mn(ClO4)2 x 6H2O. The compound crystallized in the monoclinic system, space group P2(1)/c with cell constants a = 15.438(2) A, b = 14.691(2) A, c = 33.046(2) A, beta = 94.832(9) degrees, and Z = 4. The crystal consists of a W(V)-CN-MnII linked three-dimensional network [[MnII(H2O)]3[MnII(H2O)2]3[W(V)(CN)8]4]n and H2O molecules as crystal solvates. There are two kinds of W sites: one is close to a dodecahedron geometry with six bridging and two terminal CN ligands; the other is close to a bicapped trigonal prism with seven bridging and one terminal CN ligands. The field-cooled magnetization measurement showed that the compound exhibits a spontaneous magnetization below Tc = 54 K. Further magnetization measurements on the field dependence reveal it to be a ferrimagnet where all of the MnII ions are antiparallel to all the W(V) ions.     

Halogen exchange and scrambling between C-X and M-X' bonds in copper, nickel, and cobalt complexes of 6,6'-bis(bromo/chloromethyl)-2,2'-bipyridine. structural, electrochemical, and photochemical studies

The synthesis, reactivities, spectroscopic, electrochemical, and structural studies of copper(I), copper(II), nickel(II), and cobalt(II) complexes of 6,6'-bis(bromomethyl)-2,2'-bipyridine (bpy-Br2) and 6,6'-bis(chloromethyl)-2,2'-bipyridine (bpy-Cl2) have been reported. The copper(I) complex [CuI(bpy-Br2)2](ClO4) (1) has been obtained in two crystallographic modifications, in which the coordination geometry of the metal center has the D2d symmetry. The reaction between CuCl2.2H2O and bpy-Br2 has been followed spectrophotometrically at 45 degrees C over a period of 7 h, and a mechanism for the intramolecular halogen exchange and scrambling in the initially formed compound [CuII(bpy-Br2)Cl2] (5) has been proposed. Depending upon the reaction conditions, several halogen-exchanged products, namely [CuII(bpy-Br1.86Cl0.14)(Cl1.89Br0.11)] (2), [CuII(bpy-Br1.81Cl0.19)(Cl1.70Br0.30)(H2O)] (3), and [CuII(bpy-Br0.63Cl1.37)(Cl0.54Br1.46)] (4), have been isolated in crystalline form. The reaction between bpy-Cl2 and CuCl2.2H2O provides [CuII(bpy-Cl2)Cl2] (7) and [CuII(bpy-Cl2)Cl2(H2O)] (8), whereas CoCl2.6H2O and NiCl2.6H20 on reaction with bpy-Br2 under boiling condition produce [CoII(bpy-Br0.5Cl1.5)(ClBr)] (11) and [NiII(bpy-Br0.46Cl1.54)(Cl0.73Br1.27)(H2O)] (12), respectively. The X-ray structures determined for the 4-coordinate compounds 2, 4, and 7 show flattened tetrahedral geometry for the metal center with the D2 symmetry. Both 5-coordinate compounds 3 and 12 have square pyramidal geometry, and whereas the nickel(II) complex 12 has near-perfect geometry (tau = 0.015), considerable distortion is observed for the copper(II) complex 3 (tau = 0.25). Complexes [CuII(bpy-Cl2)Br2] (6) and [CuII(bpy-Br2)Br2] under boiling condition undergo photoreduction to produce the dimeric copper(I) complexes [{CuI(bpy-Cl1.30Br0.70)(mu-Br)}2](9) and [{CuI(bpy-Br2)(mu-Br)}2] (10), respectively. The fact that the photoreduction of [CuII(bpy-Cl2)Br2] (6) and [CuII(bpy-Br2)Br2] do not take place in absence of light has been established by spectrophotometric measurements. The crystal structures of 9 and 10 have been determined. The electrochemical behavior of all the copper complexes 1-10 has been studied in acetonitrile and dichloromethane. The E1/2 values for the CuI/CuII redox couples show strong solvent dependence and for a given system the E1/2 value is more positive in dichloromethane relative to that in acetonitrile. For the compounds [CuII(bpy-Br2-xClx)(Cl2-yBry)] (x = 0-2, y = 0-2), the E1/2 values become more positive with the increase of y value.