Trinuclear zinc(II) complexes and polymeric cadmium(II) complexes with theligand 2,5-bis(2-pyridyl)pyrazine: Synthesis, spectral analysis, and single-crystal and powder X-ray analyses

Three zinc compounds, [ZnCl2(bppz)(dmf)] (1), [Zn-3(OAc)(6)(bppz)(2)](H2O) (2), and [Zn-3(Cl)(6)(bppz)(3)](H2O) (3), and two cadmium complexes, {[Cd(O Ac)(2)(bppz)](H2O)(5)}(n) (4) and [Cd(NO3)(2)(bppz)](n) (5), where bppz is 2,5-bis(2-pyridyl)pyrazine, have been synthesized and characterized spectro scopically and crystallographically. The mononuclear complex 1, C17H17Cl2N5 OZn, crystallizes in the monoclinic space group P2(1)/c, with a = 8.654(1) Br, b = 9.500(1) Angstrom, c = 22.997(1) Angstrom, beta = 97.99(1)degrees, and Z = 4; R1 for 2356 observed reflections [I > 2 sigma(I)] was 0.058. The zinc atom has a distorted square planar coordination sphere with the ligan d bppz connected in a mono-bidentate manner. The remaining coordination sit es are occupied by the chloride counterions and by an oxygen atom of a solv ent: molecule. The trinuclear zinc compound 2, C40H38N8O12Zn3. H2O, crystal lizes in the triclinic space group P (1) over bar, with a = 12.238(4) Angst rom, b = 12.986(3) Angstrom, c = 15.470(4) Angstrom, alpha = 75.65(1)degree s, beta = 97.99(1)degrees, gamma = 65.98(1)degrees, and Z = 2: R1 for 4511 observed reflections [I > 2 sigma(I)] was 0.07. This complex consists of a linear arrangement of three zinc atoms. The central zinc atom, located on a crystallographic inversion center, is connected by six bridging acetate gr oups to two symmetry-related zinc atoms. It has an almost perfect octahedra l coordination environment. The outer symmetry-related zinc atoms are in a square pyramidal environment, and they coordinate to three acetate groups a nd to one bppz molecule in a mono-bidentate manner. Compound 3, C42H30Cl6N1 2Zn3. 1.25H(2)O, a cyclic zinc(II) trimer,crystallizes in the cubic space g roup Ia (3) over bar d, with a = 26.311(1) Angstrom and Z = 16; R1 for 692 observed reflections [I > 2 sigma(I)] was 0.038. This trinuclear complex ha s a perfect triangular arrangement of the zinc atoms. Each zinc atom is con nected to the other two by a bppz molecule. The coordination about the meta l is best described as a distorted octahedral with four long distances in t he basal plane, to two chlorines and to two nitrogen atoms, and two shea di stances in the axial direction, to two nitrogen atoms. With Cd-II two polym eric complexes, 4 and 5 were obtained. Compound 4, C18N16N4O4Cd . 5H(2)O, c rystallizes in the triclinic space group P (1) over bar, a = 9.045(1) Angst rom, b = 10.438(1) Angstrom, c = 12.719(1) Angstrom, alpha = 100.48(1)degre es, beta = 95.05(1)degrees, gamma = 95.86(1)degrees, and Z = 2; R1 for 3694 observed reflections [I > 2 sigma(I)] was 0.029. The analogous Cd(NO3)(2) complex with bppz, 5, could only be obtained in microcrystalline form, and its structure was solved by the use of X-ray powder diffraction methods. Co mpound 5, C14H10N6O6Cd, crystallizes in the monoclinic space group C2/c, wi th a = 11.6601(3) Angstrom, b = 11.9870(3) Angstrom, c = 12.1453(3) Angstro m, beta = 103.348(2)degrees, and Z = 4. In both 4 and 5 the cadmium atoms a re bridged by the ligand bppz, so forming uniform one-dimensional coordinat ion polymers. The cadmium ions exhibit the rare coordination number of 8, w ith two coordinated ligand molecules and two chelating acetate (4) or nitra te (5) groups.