Self-penetration--a structural compromise between single networks and interpenetration: magnetic properties and crystal structures of

The three-dimensional coordination polymers [Mn(dca)2(H2O)] (1) and [M(dca)(tcm)], M =Co (2), Ni (3), Cu (4), dca =dicyanamide, N(CN)2-, tcm = tricyanomethanide, C(CN)3-, have isomorphous structures. In 1 half the dca ligands coordinate directly (through all three nitrogen atoms) to three Mn atoms (all metal atoms are six-coordinate), while the other half coordinate to two Mn atoms (through the nitrile nitrogens) and hydrogen bond to water molecules coordinated to a third Mn atom (through the amide nitrogen). This dca. H2O structural moiety is disordered over a mirror plane, and is replaced by the structurally equivalent tcm ligand in compounds 2-4. The resulting structures display a new self-penetrating 3,6-connected (2:1) network topology that can be related to, but is different from, the rutile net. The self-penetrating [M(dca)(tcm)] network can be viewed as a structural compromise between the two interpenetrating rutile-like networks of [M(tcm)2] and the single rutile-like network of alpha-[M(dca)2]. The temperature and field dependence of the DC and AC magnetic susceptibilities and magnetisations has been measured for complexes 1-4. Compounds 1-3 exhibit long-range magnetic order with critical temperatures of 6.3 K for 1, 3.5 K for 2 and 8.0 K for 3. The Cu11 compound 4 does not order and is essentially a paramagnet. Hysteresis measurements of coercive field and remnant magnetisation show that 1, 2 and 3 are soft magnets, 1 being a canted-spin antiferromagnet (weak ferromagnet), while 2 and 3 are ferromagnets that display some unusual features in their high-field magnetisation isotherms in comparison to their related alpha-[M(dca)2] phases.

Supramolecular Complexation of Polynuclear Aqua Ions: A Crown Ether Adduct of a µ-Oxo-Bridged Iron(III) Aqua Dimer.

Hydrolysis and polymerization of [Fe(OH(2))(6)](3+) in aqueous solution leads, in the early stages, to the oxo-bridged binuclear aqua ion [(H(2)O)(5)Fe(µ-O)Fe(OH(2))(5)](4+), which could be obtained in crystalline form through the use of [18]crown-6. The complex exhibits an almost linear Fe-O-Fe moiety and antiferromagnetic coupling that is consistent with current descriptions of exchange coupling in mono oxo-bridged binuclear Fe(III) complexes.

Interconversion of a monomer and two coordination polymers of a copper(II)-reduced Schiff base ligand-1,10-phenanthroline complex based on hydrogen- and coordinative-bonding.

Two compounds, [Cu(3)(Sbal)(2)(phen)(H(2)O)(2)](ClO(4))(2)-3H(2)O (1) and [Cu(H(2)Sbal)(2)(phen)](ClO(4))(2) (2), were isolated in successive steps from the reaction mixture containing Cu(ClO(4))(2)-6H(2)O, 1,10-phenanthroline, N-(2-hydroxybenzyl)-beta-alanine (H(2)Sbal), and LiOH in the ratio of 1:1:1:1. When the ratio of the base was doubled, the neutral monomer [Cu(Sbal)(phen)]-2H(2)O (3) was obtained. The cation in 1 exists as a one-dimensional polymer in the solid state, while weak O--H...O hydrogen bonds in the cation of 2 generate Delta Lambda Delta Lambda. type one-dimensional spiral chains. Addition of HClO(4) to 3 furnished 1 and 2, and this mixture can be converted back to 3 by the addition of a base. This conversion of a monomer to two 1-D polymers was found to be reversible. Crystal data for 1: triclinic space group P one macro, a = 12.0353(5) A, b = 12.2848(5) A, c = 15.3185(6) A, alpha = 84.993(1) degrees, beta = 89.411(1) degrees, gamma = 67.414(1) degrees, V = 2082.5(2) A(3), Z = 2, rho(calcd) = 1.668 g cm(-3). Crystal data for 2: tetragonal space group P4(1)/a, a = 10.8095(1) A, c = 59.0159(4) A, V = 6895.7(1) A(3), Z = 8, rho(calcd) = 1.605 g cm(-3). Crystal data for 3: monoclinic space group Pn, a = 10.6344(3) A, b = 5.3953(1) A, c = 18.1983(1) A, V = 1029.26(4) A(3), Z = 2, rho(calcd) = 1.526 g cm(-3). When Cu(NO(3))(2) was used in the place of Cu(ClO(4))(2), [Cu(2)(Sbal)(phen)(3)](NO(3))(2)-2.5H(2)O (4) was the only isolable product for the 1:1:1:1 ratio, and 3 was the only isolable product for the 1:1:1:2 ratio. Crystal data for 4: triclinic space group P one macro, a = 10.8063(8) A, b = 13.919(1) A, c = 16.564(1) A, alpha = 88.957(2) degrees, beta = 71.008(1) degrees, gamma = 69.829(2) degrees, V = 2198.9(3) A(3), Z = 2, rho(calcd) = 1.556 g cm(-3). Variable temperature magnetic measurements showed that the polymeric structure in 1 behaves, magnetically, as a strongly coupled micro-phenoxo dimer (2J = -390 cm(-1)) plus an isolated monomer.

Electrochemical synthesis and structural and physical characterization of one- and two-electron-reduced forms of [SMo12O40]2-.

Isolation of a soluble [NHex4]+ salt has allowed a detailed electrochemical study of the anion alpha-[SMo12O40]2- to be undertaken. Four reversible one-electron-reduction processes are observed in CH2Cl2 solution. Controlled potential electrolysis led to isolation of tetraalkylammonium salts of the one-electron-reduced anion alpha-[SMo12O40]3- and the two-electron-reduced anion alpha-[SMo12O40].4- [SMo12O40]3- is stable to disproportionation in dry solvents (Kdis = 10(-7.4). EPR and magnetic susceptibility data indicate that [SMo12O40]3- is a simple paramagnet (S = 1/2) while [SMo12O40]4- is paramagnetic with the mu eff values decreasing at low temperatures. Solutions of the two-electron-reduced species are EPR silent, but microcrystalline powders show very weak signals. The crystal structure of alpha-[NBu4]3[SMo12O40] has been determined (triclinic P1; a = 13.840(3) A; b = 15.587(4) A; c = 19.370(3) A; alpha = 94.82(2) degrees; beta = 93.10(1) degrees; gamma = 91.05(2) degrees; Z = 2). There is disorder around the C2 axis of the central SO4(2-) tetrahedron. In the presence of aqueous HClO4 (0.045 M) in thf/H2O or MeCN/H2O (98/2 v/v), [SMo12O40]2- exhibits five two-electron-reduction processes. Under these conditions, [SMo12O40]3- protonates and disproportionates into [SMo12O40]2- and the (2e-, 2H+)-reduced anion [H2SMo12O40]2-.

A purple acid phosphatase from sweet potato contains an antiferromagnetically coupled binuclear Fe-Mn center.

A purple acid phosphatase from sweet potato is the first reported example of a protein containing an enzymatically active binuclear Fe-Mn center. Multifield saturation magnetization data over a temperature range of 2 to 200 K indicates that this center is strongly antiferromagnetically coupled. Metal ion analysis shows an excess of iron over manganese. Low temperature EPR spectra reveal only resonances characteristic of high spin Fe(III) centers (Fe(III)-apo and Fe(III)-Zn(II)) and adventitious Cu(II) centers. There were no resonances from either Mn(II) or binuclear Fe-Mn centers. Together with a comparison of spectral properties and sequence homologies between known purple acid phosphatases, the enzymatic and spectroscopic data strongly indicate the presence of catalytic Fe(III)-Mn(II) centers in the active site of the sweet potato enzyme. Because of the strong antiferromagnetism it is likely that the metal ions in the sweet potato enzyme are linked via a mu-oxo bridge, in contrast to other known purple acid phosphatases in which a mu-hydroxo bridge is present. Differences in metal ion composition and bridging may affect substrate specificities leading to the biological function of different purple acid phosphatases.

Syntheses, crystal structures, magnetic properties, and EPR spectra of tetranuclear copper(II) complexes featuring pairs of "roof-shaped" Cu2X2 dimers with hydroxide, methoxide, and azide bridges.

Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), have been prepared from [Cu4Ldur(H2O)8](ClO4)8.9H2O (1). Addition of base to an aqueous solution of 1 gave [Cu4Ldur(mu2-OH)4](ClO4)4 (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu2-OMe)4](ClO4)4.HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu2-N3)4](PF6)4.4H2O.6CH3CN (4), was produced by reaction of Ldur with 4 molar equiv of Cu(OAc)2.H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P1 (No. 2) with a = 10.248(1) A, b = 12.130(2) A, c = 14.353(2) A, alpha = 82.23(1) degrees, beta = 80.79(1) degrees, gamma = 65.71(1) degrees, and Z = 1 for 2, a = 10.2985(4) A, b = 12.1182(4) A, c = 13.9705(3) A, alpha = 89.978(2) degrees, beta = 82.038(2) degrees, gamma = 65.095(2) degrees, and Z = 1 for 3, and a = 12.059(2) A, b = 12.554(2) A, c = 14.051(2) A, alpha = 91.85(1) degrees, beta = 98.22(1) degrees, gamma = 105.62(1) degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu2-X)2 cores (X = OH-, OMe-, N3-), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu.Cu distances of 2.940(4) A for 2, 2.962(1) A for 3, and 3.006(5) A for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu2-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.