Synthesis, crystal structure, and magnetic properties of tetraphenylarsonium tetrachloro(oxalato)rhenate(IV) and bis (2,2 '-bipyridine)tetrachloro(mu-oxalato)copper(II)rhenium(IV)

Two new rhenium(IV) compounds of formula (AsPh4)(2)[ReCl4(ox)] (1) and [ReC l4(mu-ox)Cu(bipy)(2)] (2) (AsPh4 = tetraphenylarsonium cation, ox = oxalate anion, and bipy = 2,2'-bipyridine) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 and 2 crystal lize in the monoclinic system, space groups P2(1)/c and P2(1)/n, respective ly, with a = 22.250(5) Angstrom, b = 11.245(3) Angstrom, c = 19.089(4) Angs trom, beta = 96.59(2)degrees, and Z = 4 for 1 and a = 9.421(2) Angstrom, b = 16.909(4) Angstrom, c = 16.179(4) Angstrom, beta = 93.97(2)degrees, and Z = 4 for 2. The structure of 1 is made up of [ReCl4(ox)](2-) anions and AsP h4+ cations held united by electrostatic forces. Rhenium(IV) is hexacoordin ate, with two oxygens of a chelating ox and four chlorine atoms building a distorted octahedron around the metal atom. There is no contact between the [ReCl4(ox)](2-) anions, the shortest Re ... Re and Cl ... Cl distances bei ng 10.345 and 7.209 Angstrom, respectively. This anionic complex is coordin ated to a [Cu(bipy)(2)](2+) cation in 2, through one oxalate-oxygen, giving a neutral heterometallic dinuclear unit. The Cu(II) ion shows a very disto rted five-coordinated geometry, four bipy-nitrogens occuping the equatorial positions and the oxygen atom the apical one. The basal plane geometry is distorted toward the tetrahedron, the dihedral angle between the mean plane s of the two bipy ligands is 37.6(2)degrees. These [ReCl4(mu-ox)Cu(bipy)(2) ] units are arranged in such a way that a chlorine atom of one of them poin ts toward the copper atom of the neighboring one, forming helicoid chains. The intrachain Re Cu distances through chloro and oxalato bridges are 4.658 and 4.798 Angstrom, respectively. The magnetic behavior of 1 and 2 has bee n investigated over the temperature range 1.8-300 K. 1 is a magnetically di luted Re(IV) complex, the great value of zero-field splitting of the ground level (D = 60 cm(-1)) accounting for the variation of chi(M)T with T in th e low-temperature range. 2 behaves as a ferrimagnetic chain, with weak anti ferromagnetic interactions between Re(IV) and Cu(II) through oxalato and si ngle chloro bridges.