Alan Storr

Synthesis, structure and magnetic properties of 3D interpenetrating nets of M(pyrazine)[Au(CN)2]2 (M=Cu, Ni, Co) supported by aurophilic interactions

Abstract New inorganic coordination polymers of the form M(pyrazine)[Au(CN)2]2 (M=Cu (1); Ni (2); Co (3)) have been prepared and the copper(II) analogue structurally characterised. The X-ray analysis revealed two 3D interpenetrating α-polonium networks consisting of 1D chains of Cu–pyrazine units connected by [Au(CN)2] bridges. The two networks are connected via weak aurophilic interactions (AuAu: 3.4729(2) A). Thermogravimetric analysis of all three compounds indicated the robust nature of these 3D systems, with decomposition beginning at 260 (1), 406 (2) and 360°C (3). The magnetic susceptibility of 1 shows a maximum in χM at 5.0 K; these data could be fitted to the theoretical expressions for either a 1D or a 2D Heisenberg antiferromagnetic array (J=−2.74 cm−1, g=2.32 and J=−3.45 cm−1, g=2.33, respectively). The magnetic susceptibility versus temperature data for 2 and 3 showed effects primarily associated with single-ion zero-field splitting; any weak antiferromagnetic coupling in these systems is very weak and hence was not quantified. Although the aurophilic interactions between the [Au(CN)2] units may positively influence both the formation of an interpenetrating structure and its subsequent thermal stability, the incorporation of anionic [Au(CN)2] units into M(pyrazine) systems does not seem to significantly increase magnetic interactions.

μ4-Oxo-hexakis(μ-3,5-dimethylpyrazolato-N,N')tetracobalt(II)

The title compound [Co 4 O(C 5 H 7 N 2 ) 6 ], consits of a central O atom coordinated by four Co II atoms which are themselves bridged in a pairwise fashion by six exobidentate 3,5-dimethylpyrazolate ligands. The coordination geometry about each Co I I atom is that of a distorted tetrahedron

Synthesis of pyrazolyl-borate, -aluminate, -gallate, and -indate ligands, and their chelating properties towards cobalt(II), nickel(II), copper(II), and zinc(II)

The uninegative dimethylbis(pyrazol-1-yl)- and bis(3,5-dimethylpyrazol-1-yl)dimethyl-gallate ions have been isolated as their sodium and tetra-alkylammonium salts. The anions act as bidentate chelating agents towards transition-metal ions. The orange air-stable nickel complex [Ni{Me2Ga(pz)2}2](pz = pyrazolyl) has a square-planar arrangement of four nitrogens about the nickel atom, while the purple oxygen-sensitive cobalt complex [Co{Me2Ga(pz)2}2] exhibits the transition metal in a tetrahedral environment. Steric requirements of the two ligands are emphasised in the two copper complexes [Cu{Me2Ga(pz)2}2] and [Cu{Me2Ga(dmpz)2}2](dmpz = 3,5-dimethylpyrazolyl) which, respectively, display the copper atoms in square-planar and pseudo-tetrahedral environments. The [Me2B(pz)2]– ligand has been synthesized and utilized to prepare nickel(II), copper(II), and zinc(II) complexes for comparative purposes. Representative pyrazolyl-aluminate and -indate ligands have also been synthesized, but attempts to complex these with transition-metal ions have so far proved unsuccessful.

Complex magnetism of ferrous chains based on alternating FeN4 and FeS4 tetrahedra

Abstract A combination of nuclear gamma resonance (Mossbauer effect) spectroscopy and ac susceptometry are used to characterize polybis(1-methyl-2-thioimidazolate)iron(II), [Fe(1-Me-2-S-imid)2]0.5Fe(Cp) 2 (hereafter I ). An alternative explanation for the I s weak ferromagnetic ground state, namely the alternation of g values along the polymer chain, is qualitatively considered in the light of the ngr results, in particular the temperature dependence and limiting values of the quadrupole splittings of the paramagnetic tetrahedral ferrous sites of this system.

A cis-Dioxomolybdenum(VI) Complex, [Mo{N2C3H3C(Me)2O}2(O)2]

In the cis-dioxomolybdenum(VI) complex bis[1-methyl-1-(1-pyrazolyl)ethanolato-N2,O]dioxomolybdenum(VI), [Mo(O)2(C6H9N2O)2] or C12H18MoN4O4, the Mo atom has distorted octahedral coordination to two (cis) oxo ligands and two N and two O atoms of the two substituted pyrazole ligands. Mo—Ooxo bond distances [mean 1.698 (6) A] correspond to double bonds, Mo—Ooxy [mean 1.951 (2) A] to single bonds, and Mo—N bonds [mean 2.326 (3) A] are lengthened as a result of the effect of the oxo ligands, which are trans to the N atoms.

Crystal and molecular structure of bis[dimethylbis(pyrazol-1-yl)gallato]nickel(II)

Crystals of the title compound are monoclinic, a= 8·530(6), b= 17·939(10), c= 7·415(6)A, β= 106·88(7)°, space group P21/c, Z= 2. The structure was determined from diffractometer data by Patterson and Fourier syntheses, and refined by full-matrix least-squares methods to R 0·049 for 1352 observed reflexions. The whole molecule is in a pseudo-chair conformation with the two six-membered Ga–(N–N)2–Ni rings in boat conformations. The nickel atom lies on a crystallographic centre of symmetry in the middle of a planar arrangement of four nitrogen atoms. Mean dimensions are: Ga–N 1·977, Ni–N 1·895, Ga–C 1·944, N–N 1·355, C–N 1·333, C–C 1·377 A; N–Ga–N 91·6, Ga–N–N 120·5, C–Ga–C 126·9, N–Ni–N (chelate angle) 92·4, N–Ni–N (non-chelate angle) 87·6, Ni–N–N, 124°.

Dialkyl(2-methylimidazolyl)metal tetramers of Group III elements: crystal and molecular structure of tetrakis-µ-(2-methylimidazolyl)tetrakis(diethylgallium)

A series of compounds [R2ML]4(R = Me, M = B, Al, Ga, and In; R = Et, M = Ga; L = 2-methylimidazolyl) has been synthesized by reaction of Group III metal trialkyls with molar equivalents of 2-methylimidazole. The products have been characterized and the X-ray crystal structure of the Et2Ga derivative determined. Crystals are monoclinic, a= 15.31(2), b= 19.39(3), c= 14.21(2)A, β= 101.30(9)°, space group I2/a, Z= 4 (tetrameric units). The structure was determined from diffractometer data by Patterson and Fourier methods, and refined by full-matrix least-squares methods to R 0.101 for 1 182 observed reflexions. The molecule consists of four diethyl-gallium moieties linked by 2-methylimidazolyl rings to form a ‘square’ of side 6 A. The molecule has pseudo-D2d symmetry and crystallographic two-fold symmetry, the two-fold axis passing through two of the gallium atoms. Mean dimensions are: Ga–N 1.98, Ga–C 1.90, N–C 1.36, C–CH3 1.46 A; N–Ga–N 102, C–Ga–C 124, and N–Ga–C 107°.

The crystal and molecular structure of a dideuterio(pyrazol-1-yl)gallane dimer

Crystals of the title compound are orthorhombic, a= 11·518(2), b= 11·278(1), c= 8·267(1)A, space group Cmc21, Z= 4 (dimeric units). The structure was determined from diffractometer data by Patterson and Fourier syntheses, and refined by full-matrix least-squares methods to R0·049 for 491 observed reflexions. The molecule is V-shaped, the angle between the unique portion of the molecule and its crystallographic mirror image being 128·4°, and the six-membered Ga(N–N)2 Ga ring being in the boat conformation. Mean dimensions are: Ga–N 1·974, N–N 1·34, N–C 1·35, C–C 1·35 A N–Ga–N′ 96·6, Ga–N–N′123·6°.

SYNTHESIS AND CRYSTAL AND MOLECULAR STRUCTURE OF ETHANOLAMINOGALLIUM DIMETHYL H2NCH2CH2O.GAME2

K E N ~ E T H S. CHOVC;, STEVEY J. RETTIG, ALAU STORK, and JAMES TROTTER. Can. J . Chem. 57, 586 (1979). Details of the synthesis and physical properties of H,NCH,CH20.GaMe2 are given. The compound crystallizes in the tetragonal space group P4,, a = 12.2771(2), c = 9.7345(4) A, Z = 8. The structure was solved by Patterson and Fourier syntheses and was refined by fullmatrix least-squares procedures to a final R value of 0.028 and X,, of 0.036 for 1378 reilections bvith I r 3 r ~ ( I ) . The structure consists of monomeric niolecules containing tetrahedraliycoordinated g a l l i ~ ~ n i atoms. Molecules are linked by an extensive network of N-H ... 0 hydrogen bonds. Bond lengths (corrected for libration) are: Ga-0, 1.916(5) and l.917(4), Ga-N, 2.056(6) and 2.072(6), and Ga-C, 1.962-1.974(8-9) A.

Spectroscopic studies on pyrazolyl-gallate and -borate complexes of copper(II) and nickel(II)

Variable-temperature 1H n.m.r. data are presented for the square-planar NiII complexes, [{Me2M(pz)2}2Ni](M = Ga or B, and pz = pyrazolyl, N2C3H3), and stereochemical nonrigidity for the molecules in solution is invoked to account for the spectral changes observed. Activation energies obtained for the suggested interconversion processes are 46 for the gallium and 67 kJ mol–1for the boron complex. The CuII complexes, [{Me2M(pz)2}2Cu](M = Ga or B), and [{Me2Ga(dmpz)2}2Cu](dmpz = 3,5-dimethylpyrazolyl, N2C5H7), have been studied by electronic absorption spectroscopy, ESCA, and e.s.r. spectroscopy. Data have been interpreted to provide tentative one-electron orbital sequences for copper in these complexes. The colour change observed from solid to solution for square-planar [{Me2Ga(pz)2}2Cu] has been interpreted in terms of a tetrahedral distortion of the square-planar CuN4 chromophore in solution. The e.s.r. results for the pseudotetrahedral complex, [{Me2Ga(dmpz)2}2Cu], indicate substantial d–p mixing in the ground state.