A variable Ag-Cr-Oxalate channel lattice: [M(x)Ag(0.5)(-)(x)(H(2)O)(3)]@[Ag(2.5)Cr(C(2)O(4))(3)], M = K, Cs, Ag

Reaction of aqueous AgNO(3) with aqueous M(3)[Cr(ox)(3)] in >or=3:1 molar ratio causes the rapid growth of large, cherry-black, light-stable crystals which are not Ag(3)[Cr(ox)(3)], but [M(0.5)(H(2)O)(3)]@[Ag(2.5)Cr(ox)(3)] (ox(2)(-) = oxalate, C(2)O(4)(2)(-); M = Na, K, Cs, Ag, or mixtures of Ag and a group 1 element). The structure of these crystals contains an invariant channeled framework, with composition [[Ag(2.5)Cr(ox)(3)](-)(0.5)]( infinity ), constructed with [Cr(ox)(3)] coordination units linked by Ag atoms through centrosymmetric [Cr-O(2)C(2)O(2)-Ag](2) double bridges. The framework composition [Ag(2.5)Cr(ox)(3)](-)(0.5) occurs because one Ag is located on a 2-fold axis. Within the channels there is a well-defined and ordered set of six water molecules, strongly hydrogen bonded to each other and some of the oxalate O atoms. This invariant channel plus water structure accommodates group 1 cations, and/or Ag cations, in different locations and in variable proportions, but always coordinated by channel water and some oxalate O atoms. The general formulation of these crystals is therefore [M(x)Ag(0.5-x)(H(2)O)(3)]@[Ag(2.5)Cr(ox)(3)]. Five different crystals with this structure are reported, with compositions 1 Ag(0.5)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 2 Cs(0.19)Ag(0.31)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 3 K(0.28)Ag(0.22)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 4 Cs(0.41)Ag(0.09)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), and 5 Cs(0.43)Ag(0.07) [Ag(2.5)Cr(ox)(3)](H(2)O)(3). All crystallize in space group C2/c, with a approximately 18.4, b approximately 14.6, c approximately 12.3 A, beta approximately 113 degrees. Pure Ag(3)[Cr(ox)(3)](H(2)O)(3), which has the same crystal structure (1), was obtained from water by treating Li(3)[Cr(ox)(3)] with excess AgNO(3). Complete dehydration of all of these compounds occurs between 30 and 100 degrees C, with loss of diffraction, but rehydration by exposure to H(2)O(g) at ambient temperature leads to recovery of the original diffraction pattern. In single crystals, this reversible dehydration-hydration occurs without visually evident crystal change, but with loss of mechanical strength. We postulate a general mechanism for transport of water molecules along the channels, associated with local partial collapses of the channel framework, with concomitant bending but little breaking of the host Ag-O and Cr-O bonds, which is readily reversed.     

Diruthenium tetraacetate monocation, [RuII/III2(O2CMe)4]+, building blocks for 3-D molecule-based magnets

Diruthenium tetracarboxylates monocations are utilized as building blocks for cubic 3-D network structured molecule-based magnets. [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] [M = Cr (1a), Fe (2), Co (3)] were prepared in aqueous solution. Powder X-ray diffraction indicates that they have body-centered cubic structures (space group = Imm, a = 13.34, 13.30, and 13.10 A for 1a, 2, and 3, respectively), which was confirmed for 1a by Reitveld analysis of the synchrotron powder data [a = 13.3756(5) A]. [Ru(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)].xMeCN [M = Cr, x = 1.8 (1b); M = Mn, x = 3.3 (4)] were prepared from acetonitrile. The magnetic ordering of 1a (33 K), 1b (34.5 K), 2 (2.1 K), and 4 (9.6 K) was determined from the temperature dependencies of the in-phase (chi') alternating current (AC) susceptibility. The field dependence of the magnetization, M(H), at 2 K for 1a showed an unusual constricted hysteresis loop with a coercive field, H(cr), of 470 Oe while the M(H) data for 1b, 2, and 4 showed a normal hysteresis loop with a coercive field of 1670, 10, and 990 Oe, respectively. The (57)Fe M?ssbauer spectrum of 2 is consistent with the presence of low spin Fe(III) (delta = -0.05 mm/s; DeltaE = 0.33 mm/s) at room temperature, and the onset of 3-D magnetic ordering at lower temperature (<2 K). The effects of M(III) in [M(III)(CN)(6)](3-), and the large zero-field splitting (D) of diruthenium tetracarboxylates are discussed. The increasing critical temperatures T(c), with increasing S could not be accounted for by mean field models without significantly different J values for 1a, 4, and 2. By fitting the T(c) data with mean field models [H = -2JS(Ru).(S(M) - micro(B)(g(Ru)S(Ru) + g(M)S(M))H], J/k(B) are 4.46, 1.90, and 0.70 K for 1a, 4, and 2, respectively.     

Kinetics of the iodate reduction by hydrogen peroxide and relation with the Briggs-Rauscher and Bray-Liebhafsky oscillating reactions

The iodate reduction by hydrogen peroxide in acidic solutions is part of the Bray-Liebhafsky and Briggs-Rauscher oscillating reactions. At low hydrogen peroxide concentrations, typical of the Bray-Liebhafsky reaction, its rate law is -d[IO(-)(3)]/dt = (k'(R) + k"(R)[H(+)])[IO(-)(3)][H(2)O(2)] with k'(R) = 1.3 × 10(-7)(20°), 7.8 × 10(-7) (39°), 1.4 × 10(-5) M(-1) s(-1) (60°) and k"(R) = 1.5 × 10(-5) (25°), 6.2 × 10(-5) (39°), 6.3 × 10(-4) M(-2) s(-1) (60°). It is explained by a non-radical mechanism. At high hydrogen peroxide concentrations, typical of the Briggs-Rauscher reaction, a new reaction pathway appears with a rate more than proportional to [H(2)O(2)](2) and nearly independent of [IO(3)(-)] > 0.01 M. This pathway is inhibited by scavengers of free radicals. We suggest that it has a radical mechanism starting with IOH + H(2)O(2)? IOOH + H(2)O and IOOH+H(2)O(2)→ IO˙ + H(2)O+HOO˙.     

Pendant macrocyclic metallic building blocks for the design of cyano-bridged heterometallic complexes with 1D chain and 2D layer structures

A series of cyano-bridged Ni(II)-Cr(I/III) complexes have been synthesized by the reactions of hexaazacyclic Ni(II) complexes with [Cr(CN)(6)](3-) or [Cr(CN)(5)(NO)](3-). Using the tetravalent Ni(II) complex [Ni(H(2)L(2))](4+) (L(2) = 3,10-bis(2-aminoethyl)-1,3,6,8,10,12-hexaazacyclotetradecane), one-dimensional chainlike complexes were produced and subject to magnetic studies, affording the intermetallic magnetic exchange constants of J(1) = +0.23 cm(-1) and J(2) = +8.4 cm(-1) for the complex [Ni(H(2)L(2))][Cr(CN)(5)(NO)]ClO(4).5H(2)O (1) and of J = +5.9 cm(-1) for the complex [Ni(H(2)L(2))](4)[Cr(CN)(6)](5)OH.15H(2)O (2). X-ray diffraction analysis shows that complex 1 has a zigzag chain structure, whereas complex 2 consists of a branched chain structure. Complex 2 exhibits antiferromagnetic ordering at 8.0 K (T(N)). When an octahedral Ni(II) complex cis-[NiL(3)(en)](2+) (en = 1,2-ethylenediamine, L(3) = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) was used for the synthesis, the common 2D honeycomb-layered complex [NiL(3)](3)[Cr(CN)(5)(NO)](2).8H(2)O (3) was obtained, which has a T(N) value of 3.3 K. Below T(N), a metamagnetic behavior was observed in complexes 2 and 3.     

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.     

Oxidative homolysis of a nitrosylchromium complex

Metal(III)-polypyridine complexes [M(NN)(3)](3+) (M = Ru or Fe; NN = bipyridine (bpy), phenanthroline (phen), or 4,7-dimethylphenanthroline (Me(2)-phen)) oxidize the nitrosylpentaaquachromium(III) ion, [Cr(aq)NO](2+), with an overall 4:1 stoichiometry, 4 [Ru(bpy)(3)](3+) + [Cr(aq)NO](2+) + 2 H(2)O --> 4 [Ru(bpy)(3)](2+) + [Cr(aq)](3+) + NO(3)(-) + 4 H(+). The kinetics follow a mixed second-order rate law, -d[[M(NN)(3)](3+)]/dt = nk[[M(NN)(3)](3+)][[Cr(aq)NO](2+)], in which k represents the rate constant for the initial one-electron transfer step, and n = 2-4 depending on reaction conditions and relative rates of the first and subsequent steps. With [Cr(aq)NO](2+) in excess, the values of nk are 283 M(-1) s(-1) ([Ru(bpy)(3)](3+)), 7.4 ([Ru(Me(2)-phen)(3)](3+)), and 5.8 ([Fe(phen)(3)](3+)). In the proposed mechanism, the one-electron oxidation of [Cr(aq)NO](2+) releases NO, which is further oxidized to nitrite, k = 1.04x10(6) M(-1) s(-1), 6.17x10(4), and 1.12x10(4) with the three respective oxidants. Further oxidation yields the observed nitrate. The kinetics of the first step show a strong correlation with thermodynamic driving force. Parallels were drawn with oxidative homolysis of a superoxochromium(III) ion, [Cr(aq)OO](2+), to gain insight into relative oxidizability of coordinated NO and O(2), and to address the question of the "oxidation state" of coordinated NO in [Cr(aq)NO](2+).     

Syntheses, structures, and magnetic properties of mixed-valent diruthenium(II,III) diphosphonates with discrete and one-dimensional structures

Four mixed-valent ruthenium diphosphonates, namely, Na(4)[Ru(2)(hedp)(2)X]x16H(2)O [X = Cl (1), Br (2)], K(3)[Ru(2)(hedp)(2)(H(2)O)(2)]x6H(2)O (3), and Na(7)[Ru(2)(hedp)(2)Fe(CN)(6)]x24H(2)O (4), where hedp represents 1-hydroxyethylidenediphosphonate [CH(3)C(OH)(PO(3))(2)](4-), were synthesized and structurally characterized. Compounds 1, 2, and 4 show linear chain structures in which the mixed-valent [Ru(2)(hedp)(2)](3-) dimers are linked by X(-) or [Fe(CN)(6)](4-) bridges. Compound 3 contains discrete species of [Ru(2)(hedp)(2)(H(2)O)(2)](3-) where the axial positions of [Ru(2)(hedp)(2)](3-) paddlewheel are terminated by water molecules. Magnetic studies show that significant antiferromagnetic exchanges are mediated between the [Ru(2)(hedp)(2)](3-) (S = 3/2) units through halide bridges in compounds 1 and 2.     

Deviation between the chemistry of Ce(IV) and Pu(IV) and routes to ordered and disordered heterobimetallic 4f/5f and 5f/5f phosphonates

The heterobimetallic actinide compound UO(2)Ce(H(2)O)[C(6)H(4)(PO(3)H)(2)](2)·H(2)O was prepared via the hydrothermal reaction of U(VI) and Ce(IV) in the presence of 1,2-phenylenediphosphonic acid. We demonstrate that this is a kinetic product that is not stable with respect to decomposition to the monometallic compounds. Similar reactions have been explored with U(VI) and Ce(III), resulting in the oxidation of Ce(III) to Ce(IV) and the formation of the Ce(IV) phosphonate, Ce[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O, UO(2)Ce(H(2)O)[C(6)H(4)(PO(3)H)(2)](2)·H(2)O, and UO(2)[C(6)H(4)(PO(3)H)(2)](H(2)O)·H(2)O. In comparison, the reaction of U(VI) with Np(VI) only yields Np[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O and aqueous U(VI), whereas the reaction of U(VI) with Pu(VI) yields the disordered U(VI)/Pu(VI) compound, (U(0.9)Pu(0.1))O(2)[C(6)H(4)(PO(3)H)(2)](H(2)O)·H(2)O, and the Pu(IV) phosphonate, Pu[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O. The reactions of Ce(IV) with Np(VI) yield disordered heterobimetallic phosphonates with both M[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (M = Ce, Np) and M[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O (M = Ce, Np) structures, as well as the Ce(IV) phosphonate Ce[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O. Ce(IV) reacts with Pu(IV) to yield the Pu(VI) compound, PuO(2)[C(6)H(4)(PO(3)H)(2)](H(2)O)·3H(2)O, and a disordered heterobimetallic Pu(IV)/Ce(IV) compound with the M[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (M = Ce, Pu) structure. Mixtures of Np(VI) and Pu(VI) yield disordered heterobimetallic Np(IV)/Pu(IV) phosphonates with both the An[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (M = Np, Pu) and An[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O (M = Np, Pu) formulas.     

Synthesis and magnetic properties of 3-D [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr,Fe, Co)

Three-dimensional network structures of [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr, Fe, Co) composition have been formed and their magnetic properties characterized. [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr, Fe, Co) have nu(CN) IR absorptions at 2138, 2116, and 2125 cm(-1) and have body-centered unit cells (a = 13.34, 13.30, and 13.10 A, respectively) with -M-Ctbd1;N-Ru=Ru-Ntbd1;C-M- linkages along all three Cartesian axes. [Ru(II/III)(2)(O(2)CMe)(4)](3)[Cr(III)(CN)(6)] magnetically orders as a ferrimagnet (T(c) = 33 K) and has an unusual constricted hysteresis loop.     

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.     

Modified polyoxometalates: Hydrothermal syntheses and crystal structures of three novel reduced and capped Keggin derivatives decorated by transition metal complexes

Three novel polyoxometalate derivatives decorated by transition metal complexes have been hydrothermally synthesized. Compound 1 consists of [PMo(VI)(6)Mo(V)(2)V(IV)(8)O(44)[Co (2,2'-bipy)(2)(H(2)O)](4)](3+) polyoxocations and [PMo(VI)(4-)Mo(V)(4)V(IV)(8)O(44)[Co(2,2'-bipy)(2)(H(2)O)](2)](3-) polyoxoanions, which are both built on mixed-metal tetracapped [PMo(8)V(8)O(44)] subunits covalently bonded to four or two [Co(2,2'-bpy)(2)(H(2)O)](2+) clusters via terminal oxo groups of the capping V atoms. Compound 2 is built on [PMo(VI)(8)V(IV)(6)O(42)[Cu(I)(phen)](2)](5-) clusters constructed from mixed-metal bicapped [PMo(VI)(8)V(IV)(6)O(42)](7-) subunits covalently bonded to two [Cu(phen)](+) fragments in the similar way to 1. The structure of 3 is composed of [PMo(VI)(9)Mo(V)(3)O(40)](6-) units capped by two divalent Ni atoms via four bridging oxo groups. The crystal data for these are the following: C(120)H(126)Co(6)Mo(16)N(24)O(103)P(2)V(16) (1), triclinic P1, a = 15.6727(2) A, b = 17.3155(3) A, c = 19.5445(2) A, alpha = 86.1520(1) degrees, beta = 81.2010(1) degrees, gamma = 63.5970(1) degrees, Z = 1; C(120)H(85)Cu(6-)Mo(8)N(20)O(44)PV(6) (2), triclinic P1, a = 14.565(4) A, b = 15.899(3) A, c = 16.246(4) A, alpha = 116.289(2) degrees, beta = 103.084(2) degrees, gamma = 94.796(2) degrees, Z = 1; C(60)H(40)Mo(12)N(10)Ni(3)O(40)P (3), monoclinic P2(1)/c, a = 14.804(3) A, b = 22.137(4) A, c = 25.162(5) A, alpha = 90 degrees, beta = 98.59(3) degrees, gamma = 90 degrees, Z = 4.     

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.     

Synthesis and characterization of iron(III)-substituted, dimeric polyoxotungstates, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](n-) (n = 6, X = As(III), Sb(III); n = 4, X = Se(IV), Te(IV))

Interaction of the lacunary [alpha-XW(9)O(33)](9-) (X = As(III), Sb(III)) with Fe(3+) ions in acidic, aqueous medium leads to the formation of dimeric polyoxoanions, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)) in high yield. X-ray single-crystal analyses were carried out on Na(6)[Fe(4)(H(2)O)(10)(beta-AsW(9)O(33))(2)] x 32H(2)O, which crystallizes in the monoclinic system, space group C2/m, with a = 20.2493(18) A, b = 15.2678(13) A, c = 16.0689(14) A, beta = 95.766(2) degrees, and Z = 2; Na(6)[Fe(4)(H(2)O)(10)(beta-SbW(9)O(33))(2)] x 32H(2)O is isomorphous with a = 20.1542(18) A, b = 15.2204(13) A, c = 16.1469(14) A, and beta = 95.795(2) degrees. The selenium and tellurium analogues are also reported, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](4-) (X = Se(IV), Te(IV)). They are synthesized from sodium tungstate and a source of the heteroatom as precursors. X-ray single-crystal analysis was carried out on Cs(4)[Fe(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)] x 21H(2)O, which crystallizes in the triclinic system, space group P macro 1, with a = 12.6648(10) A, b = 12.8247(10) A, c = 16.1588(13) A, alpha = 75.6540(10) degrees, beta = 87.9550(10) degrees, gamma = 64.3610(10) gamma, and Z = 1. All title polyanions consist of two (beta-XW(9)O(33)) units joined by a central pair and a peripheral pair of Fe(3+) ions leading to a structure with idealized C(2h) symmetry. It was also possible to synthesize the Cr(III) derivatives [Cr(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)), the tungstoselenates(IV) [M(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)]((16)(-)(4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), and Hg(2+)), and the tungstotellurates(IV) [M(4)(H(2)O)(10)(beta-TeW(9)O(33))(2)]((16-4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)), as determined by FTIR. The electrochemical properties of the iron-containing species were also studied. Cyclic voltammetry and controlled potential coulometry aided in distinguishing between Fe(3+) and W(6+) waves. By variation of pH and scan rate, it was possible to observe the stepwise reduction of the Fe(3+) centers.     

Rational synthesis and magnetic properties of a family of low-dimensional heterometallic Cr-Mn complexes based on the versatile building block [Cr(2,2'-bipyridine)(CN)4]-

Six heterometallic compounds based on the building block [Cr(bpy)(CN)4]- (bpy = 2,2'-bipyridine) with secondary and/or tertiary coligands as modulators, {Mn(H2O)2[Cr(bpy)(CN)4]2}n (1), {Mn(bpy)(H2O)[Cr(bpy)(CN)4]2 x H2O}n (2), [Mn(bpy)2][Cr(bpy)(CN)4]2 x 5H2O (3), {[Mn(dca)(bpy)(H2O)][Cr(bpy)(CN)4] x H2O}n (4) (dca = N(CN)2(-)), {Mn(N3)(CH3OH)[Cr(bpy)(CN)4] x 2H2O}n (5), and {Mn(bpy)(N3)(H2O)[Cr(bpy)(CN)4] x H2O}2 (6), have been prepared and characterized structurally and magnetically. X-ray crystallography reveals that the compounds 1, 2, 4, and 5 consist of one-dimensional (1D) chains with different structures: a 4,2-ribbon-like chain, a branched zigzag chain, a 2,2-CC zigzag chain, and a 3,3-ladder-like chain, respectively. It also reveals that compound 3 has a trinuclear [MnCr2] structure, and compound 6 has a tetranuclear [Mn2Cr2] square structure. Magnetic studies show antiferromagnetic interaction between Cr(III) and Mn(II) ions in all compounds. All of the chain compounds exhibit metamagnetic behaviors with different critical temperatures (Tc) and critical fields (Hc; at 1.8 K): 3.2 K and 3.0 kOe for 1; 2.3 K and 4.0 kOe for 2; 2.1 K and 1.0 kOe for 4; and 4.7 K and 5.0 kOe for 5, respectively. The noncentrosymmetric compound 2 is also a weak ferromagnet at low temperature because of spin canting. The magnetic analyses reveal Cr-Mn intermetallic magnetic exchange constants, J, of -4.7 to -9.4 cm(-1) (H = -JS(Cr) x S(Mn)). It is observed that the antiferromagnetic interaction through the Mn-N-C-Cr bridge increases as the Mn-N-C angle (theta) decreases to the range of 155-180 degrees, obeying an empirical relationship: J = -40 + 0.2theta. This result suggests that the best overlap between t(2g) (high-spin Mn(II)) and t(2g) (low-spin Cr(III)) occurs at an angle of approximately 155 degrees.     

Oxidation of thioglycolate by [Os(phen)3]3+: an unusual example of redox-mediated aromatic substitution

The aqueous oxidation of thioglycolic acid (TGA) by [Os(phen)(3)](3+) (phen = 1,10-phenanthroline) is catalyzed by traces of ubiquitous Cu(2+) and inhibited by the product [Os(phen)(3)](2+). In the presence of dipicolinic acid (dipic), which thoroughly masks trace Cu(2+) catalysis, and spin trap PBN, the kinetics under anaerobic conditions have been studied in the pH range 1.82-7.32. The rate law is -d[Os(phen)(3)(3+)]/dt = k[TGA](tot)[Os(phen)(3)(3+)], with k = 2{(k(b)K(a1) + k(c)K(a1)K(i))[H(+)] + k(d)K(a1)K(a2)}/{[H(+)](2) + K(a1)[H(+)] + K(a1)K(a2)}; K(a1) and K(a2) are the successive acid dissociation constants of TGA, and K(i) is the tautomerization constant of two TGA monoanions. k(b) + k(c)K(i) = (5.9 +/- 0.3) x 10(3) M(-)(1) s(-)(1), k(d) = (1.6 +/- 0.1) x 10(9) M(-)(1) s(-)(1) at mu = 0.1 M (NaCF(3)SO(3)) and 25 degrees C. The major products in the absence of spin traps are dithiodiglycolic acid, [Os(phen)(3)](2+), and [Os(phen)(2)(phen-tga)](2+), where phen-tga is phenanthroline with a TGA substituent. A mechanism is proposed in which neutral TGA is unreactive, the (minor) thiolate form of the TGA monoanion undergoes one-electron oxidation by [Os(phen)(3)](3+) (k(c)), and the dianion of TGA likewise undergoes one-electron oxidation by [Os(phen)(3)](3+) (k(d)). The Marcus cross relationship provides a good account for the magnitude of k(d) in this and related reactions of TGA. [Os(phen)(2)(phen-tga)](2+) is suggested to arise from a post-rate-limiting step involving attack of the TGA(*) radical on [Os(phen)(3)](3+).     

Polyoxomolybdenum(V/VI)-sulfite compounds: synthesis, structural, and physical studies

Reaction of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) in the mixed-solvent system H(2)O/CH(3)CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH(4))(4)[Mo(4)(VI)SO(16)] x H(2)O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH(4))(4)[Mo(5)(VI)S(2)O(21)] x 3H(2)O (2). Compound {(H(2)bipy)(2)[Mo(5)(VI)S(2)O(21)] x H(2)O}(x) (3) was obtained from the reaction of aqueous acidic solution of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) (pH = 2.5) and 4,4'-bipyridine (4,4'-bipy). The mixed metal/sulfite species (NH(4))(7)[Co(III)(Mo(2)(V)O(4))(NH(3))(SO(3))(6)] x 4H(2)O (4) was synthesized by reacting Na(2)Mo(VI)O(4) x 2H(2)O with CoCl(2) x 6H(2)O and (NH(4))(2)SO(3) with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing Mo(VI)O(6) octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo(4) ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo(5)(VI)S(2)O(21)](4-), and these coordinatively saturated clusters are joined by diprotonated 4,4'-H(2)bipy(2+) through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [Co(III)Mo(2)(V)SO(3)(2-)] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d(6) octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported.     

Synthesis and characterization of Prussian blue analogues incorporating the edge-bridged octahedral [Zr6BCl12]2+ cluster core

In attempts to produce a microporous magnet, two approaches were explored for expanding the Prussian blue structure type via incorporation of edge-bridged octahedral [Zr(6)ZCl(12)](2+) (Z = B, Be) cluster cores. Dissolution of Rb(5)Zr(6)BCl(18) and K(5)Zr(6)BeCl(15) in an acetonitrile solution of Et(4)N(CN) led to the isolation of (Et(4)N)(5)[Zr(6)BCl(12)(CN)(6)] (1) and (Et(4)N)(5)[Zr(6)BeCl(12)(CN)(6)].2MeCN.2THF (2), respectively. The crystal structure of 1.1.5MeCN revealed the expected cyano-terminated cluster complex with a trans-N...N span of 11.73(3) Angstroms. Unfortunately, both [Zr(6)ZCl(12)(CN)(6)](5-) clusters rapidly lose their cyanide ligands in aqueous solution making them ill-suited for solid-forming reactions with hydrated metal ions. Such outer-ligand exchange, however, allows the use of [Zr(6)BCl(18)](4-) in the synthesis of expanded Prussian blue-type solids through reactions with [Cr(CN)(6)](3-). The use of 2.2 M aqueous LiCl to stabilize the cluster during the reaction gave (Et(4)N)(2)[Zr(6)BCl(12)][Cr(CN)(6)]Cl.3H(2)O (3), while the use of 1 M acetic acid yielded (Et(4)N)(2)[Zr(6)BCl(12)][Cr(CN)(6)]Cl.2H(2)O.CH(3)CO(2)H (4). A Rietveld refinement against X-ray powder diffraction data collected for 3 confirmed the presence of a cubic Prussian blue framework structure, featuring alternating [Zr(6)BCl(12)](2+) cores and [Cr(CN)(6)](3-) anions. The temperature dependence of magnetization data obtained for 4 revealed activation of magnetic exchange interactions between the S = (1)/(2) cluster units and the S = (3)/(2) hexacyanochromate complexes below 10 K.     

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.     

A phosphorus supported multisite coordinating tris hydrazone P(S)[N(Me)N=CH-C6H4-o-OH]3 as an efficient ligand for the assembly of trinuclear metal complexes: synthesis, structure, and magnetism

A phosphorus supported multisite coordinating ligand P(S)[N(Me)N=CH-C(6)H(4)-o-OH](3) (2) was prepared by the condensation of the phosphorus tris hydrazide P(S)[N(Me)NH(2)](3) (1) with o-hydroxybenzaldehyde. The reaction of 2 with M(OAc)(2).xH(2)O (M = Mn, Co, Ni, x = 4; M = Zn, x = 2) afforded neutral trinuclear complexes [P(S)[N(Me)N=CH-C(6)H(4)-o-O](3)](2)M(3) [M = Mn (3), Co (4), Ni (5), and Zn (6)]. The X-ray crystal structures of compounds 2-6 have been determined. The structures of 3-6 reveal that the trinculear metal assemblies are nearly linear. The two terminal metal ions in a given assembly have an N(3)O(3) ligand environment in a distorted octahedral geometry while the central metal ion has an O(6) ligand environment also in a slightly distorted octahedral geometry. In all the complexes, ligand 2 coordinates to the metal ions through three imino nitrogens and three phenolate oxygens; the latter act as bridging ligands to connect the terminal and central metal ions. The compounds 2-6 also show intermolecular C-H...S=P contacts in the solid-state which lead to the formation of polymeric supramolecular architectures. The observed magnetic data for the (s = 5/2)3 L(2)(Mn(II))(3) derivative, 3, show an antiferromagnetic nearest- and next-nearest-neighbor exchange (J = -4.0 K and J' = -0.15 K; using the spin Hamiltonian H(HDvV) = -2J(S(1)S(2) + S(2)S(3)) - 2J'S(1)S(3)). In contrast, the (s = 1)(3) L(2)(Ni(II))(3) derivative, 5, displays ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions (J = 4.43 K and J' = -0.28 K; H = H(HDvV)+ S(1)DS(1) + S(2)DS(2)+ S(3)DS(3)). The magnetic behavior of the L(2)(Co(II))(3) derivative, 4, reveals only antiferromagnetic exchange analogous to 3 (J = -4.5, J' = -1.4; same Hamiltonian as for 3).     

Theoretical insights into the ferromagnetic coupling in oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear complexes with aromatic diimine ligands

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Cr(III)L(ox)(μ-ox)M(II)L'(H(2)O)(2)](+)[M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged Cr(III)M(II) dinuclear cationic entities of 1 and 2 result from the coordination of a [Cr(III)L(ox)(2)](-) unit through one of its two oxalato groups toward a [M(II)L'(H(2)O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr(III) ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin M(II) ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr(III) (S(Cr) = 3/2) ion and the high-spin Co(II) (S(Co) = 3/2) or Mn(II) (S(Mn) = 5/2) ions across the oxalato bridge within the Cr(III)M(II) dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -JS(Cr)·S(M)]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Cr(III)Co(II) and S = 4 Cr(III)Mn(II) ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x(2)-y(2))(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x(2)-y(2))(Cr)/d(x(2)-y(2))(M), d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.