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Quinoxaline 1,4-dioxide complexes with transition metal chlorides [1]
Journal article   Peer reviewed

Quinoxaline 1,4-dioxide complexes with transition metal chlorides [1]

D.E. Chasan, L.L. Pytlewski, C. Owens and N.M. Karayannis
Inorganica Chimica Acta, v 24(C), pp 219-226
1977
DOI: https://doi.org/10.1016/S0020-1693(00)93878-7

Abstract

3d metal chloride complexes with quinoxaline 1,4-dioxide were prepared and characterized by means of spectral and magnetic studies. Cr(III) and Fe(III) chlorides formed monomeric complexes of the types[CrCl 3L(OH 2) 2]·H 2O and[FeCl 3L 2(OH 2)]·6H 2O, involving unidentate L, aqua ligands and lattice water, while NiCl 2 yielded the chloride-bridged dimer[(OH 2)ClL 2NiCl 2NiL 2Cl(OH 2)], which alsocomprises unidentate L groups, coordinated through one of the NO oxygens. The rest of the new complexes contain bridging L of two types, viz.:i) L o, with one of the NO oxygens acting as a bridge between adjacent metal ions; or ii) oL o, with L functioning as a bidentate bridging ligand (i.e., each NO oxygen is coordinated to a different metal ion). The former type of bridging leads to subnormal paramagnetism for the Co(II) and Cu(II) complexes, which appear to be of the types [Cl 2LCo(L o) 2CoLCl 2]·8H 2O and[Cu 4Cl 8(L o) 4( oL o) 2]·4H 2O (theCu(II) compound involves bridging L of both types). Spin-spin coupling occurs in the preceding complexes by a superexchange mechanism, operating through the orbitals of the bridging oxygen atoms of the L o bridging ligands. The new Mn(II) and Zn(II) complexes are polynuclear ([MCl 2L 2] n·nxH 2O; x = 0 for M = Mn; x = 1 for M = Zn), with bridging chloro and bidentate, oL o, ligands. The Cr(III), Mn(II) and Ni(II) complexes are magnetically normal high-spin compounds, but the Fe(III) complex is magnetically subnormal. This compound involves spin-state equilibria, as suggested by the variation of its magnetic susceptibility with temperature; two possible types of equilibria, i.e., high-intermediate (S = 5/2-S = 3/2) and high-low (S = 5/2-S = 1/2) spin, are discussed.

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