Chromium binuclear compounds

Chromium(II) acetate monohydrate, discovered by Peligot in 1844, is the best known chromium(II) compound because it can be precipitated readily from aqueous Cr11 solutions by sodium acetate, is stable in air for short periods, and is used as a reducing agent and a source of other chromium(II) compounds (Table 9). Nonetheless, in its deep red colour, feeble paramagnetism and acetate-bridged, binuclear structure (24) (determined in 1953 and refined in 1971),154155 which are still not completely understood, it differs sharply from other chromium(II) salts (Section 35.3.5.1). 

A small number of oxo-alkoxides of chromium have been structurally characterized. The mononuclear chromium(vi) compounds [Cr(0)2Cl(0CPh3)] and [Cr(0)2(0CPh3)2] both involve tetrahedrally coordinated chromium. Chromium(v) is five-coordinated (tetragonal pyramidal) with the terminal oxo-ligand in the apical position in the mononuclear [Cr(0) 02C2(CF3)4 2] and binuclear [Cr2 (0)2 (m-0)2 02C2 (CF3 )4 2] auions. ... 

There are many examples today of polynuclear metal complexes yielding a parent ion in the mass spectra, but initially their observation for high molecular weight compounds, such as di[bis(pentafluorophenyl)-phosphidoirontricarbonyl] (I), having a molecular ion of mje 1010 (90) was considered unusual, as were the binuclear chromium complexes (II)... 

The complex of tartaric acid and antimony (emetic) was described three centuries ago. Nevertheless, the structure of this compound has been elucidated these last fifteen years by X-ray diffraction ( 1 ). In fact, emetic presents a binuclear cyclic structure. Many authors mentioned similar complex with transition metals (vanadium (2), chromium (3)) or metalloids (arsenic (4), bismuth (5)). Emetic with phosphorus was not mentioned. Nevertheless, tartaric acid or alkyl tartrates has been utilized in phosphorus chemistry tartaric acid reacts with trialkyl phosphites giving heterocyclic phosphites (6). Starting from alkyl tartrates, we prepared spirophosphoranes with a P-H bond and sixco-ordinated compounds (7). With unprotected tartaric acid, many possibilities appear condensation as a diol, as a di(oc-hydro-xyacid), or even as a 8-hydroxyacid. 

The mass spectra of binuclear cyclopentadienylmetal carbonyl derivatives of chromium and molybdenum provide useful indications of the relative strengths of the metal-metal bonds in various compound types. The mass spectrum of [C5H5Cr(CO)3]2 (S. M = Cr) exhibits no bimetallic ions but only monometallic ions such as CsHsC CO) (n = 3,... 

Very recently a similar comparison of two binuclear chromium compounds was reported 137). 

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