Influence of the Counterion on the Coordinating Properties of (2,2'-bipiridyl)bis(oxalato)chromate(III) anion: Crystal Structures and Magnetic properties of AsPh4[Cr(bipy)(ox)2]H2O and [NaCr(bipy)(ox)2(H2O)].2H2O

[EN] Two new chromium(III)-containing complexes of formula AsPh4[Cr(bipy)(ox)(2)]. H2O 1 and [NaCr(bipy)(ox)(2)(H2O)]. 2H(2)O 2 (bipy = 2,2'-bipyridine and ox = oxalate dianion) have been synthesized and characterized by single-crystal X-ray diffraction. The structure of 1 consists of discrete [Cr(bipy)(ox)(2)](-) mononuclear anions, tetraphenylarsonium cations and uncoordinated water molecules. The structure of 2 reveals a novel two-dimensional framework which is made up of oxalato-bridged bimetallic Cr-III-Na-I helical chains which are interconnected through centrosymmetric Na2O2 units. Within the chain, a regular alternation of the metal ions is observed, the oxalate group acting as a bis(chelating) ligand. In addition to this coordination mode, two oxalates each act as monodentate ligands towards a sodium atom of a neighbouring chain thus leading to a sheetlike polymeric structure. The chromium environment is distorted octahedral in both complexes: two nitrogen atoms from a bidentate bipy ligand and four oxygen atoms from either two chelating (1) or two bis(chelating) (2) oxalate groups build the coordination polyhedron around the chromium atom. The Cr-N bond lengths [values in the ranges 2.077(3)-2.057(3) (1) and 2.067(4)-2.058(4) Angstrom (2)] are somewhat longer than the Cr-O ones [values in the ranges 1.960(2)-1.946(2) (1) and 1.968(3)-1.949(3) Angstrom (2)]. The sodium atom in 2 is also six-coordinated: a coordinated water molecule [2.371(5) and 2.325(4) Angstrom for Na(1)-O(17) and Na(2)-O(18), respectively] and five oxygens from three oxalate groups [values of the Na-O (ox) bonds in the ranges 2.511(4)-2.331(4) and 2.481(4)-2.364(4) Angstrom around Na(1) and Na(2), respectively] build a distorted octahedral NaO6 environment. The intralayer chromium-sodium and sodium-sodium distances through bridging oxalate in 2 vary in the ranges 5.657(4)-5.579(2) and 3.534(3)-3.497(4) Angstrom, respectively. Variable-temperature magnetic susceptibility measurements of 1 and 2 reveal the occurrence of very weak antiferromagnetic interactions together with zero-field splitting effects in both compounds. The use of the [Cr(bipy)(ox)(2)](-) unit as a ligand towards different univalent and divalent metal ions aimed at designing new heterobimetallic systems is analysed and discussed in the light of available structural data.Financial support from the Spanish Dirección General de Investigación Científica y Técnica (DGICYT) (Project PB94- 1002), the Training and Mobility Research Program from the European Community (TMR Contract ERBFMRXCT980181) and the COST Program (Action 518) is gratefully acknowledged.Muñoz Roca, MDC.; Julve, M.; Lloret, F.; Faus, J.; Andruh, M. (1998). Influence of the Counterion on the Coordinating Properties of (2,2'-bipiridyl)bis(oxalato)chromate(III) anion: Crystal Structures and Magnetic properties of AsPh4[Cr(bipy)(ox)2]H2O and [NaCr(bipy)(ox)2(H2O)].2H2O. Journal of the Chemical Society. Dalton transactions. (18):3125-3131. https://doi.org/10.1039/a804990d312531311