Oxalato Compounds

Oxalato-tetrammino-cobaltic Chloride, [Co(NH3)4(C204)]C1, is prepared by dissolving chloro-aquo-tetrammino-eobaltic chloride in an aqueous solution of oxalic acid and heating the mixture for some time. The oxalato-compound gradually crystallises from the warm solution, and the crystals are collected and washed on the filter with alcohol until the filtrate is free from chlorine and from oxalic acid. It crystallises in carmine-red six-sided plates if dissolved in concentrated sulphuric acid and concentrated hydrochloric acid is added to the liquid, it is transformed into dichloro-tetrammino-cobaltic chloride. Sodium nitrite and acetic acid convert it into dinitro-tetrammino-cobaltic chloride.1... 

There are also carboxylates15 (Section 17-E-10), phosphates, catecholates, and oxalates. Most of the divalent iron oxalato compounds have a chain structure but the product of photoreduction of mononuclear [bipyH] [Feni(ojc)2(H20)2] gives a three-dimensional anionic polymeric network of [Fe2I(ox)3]2 1 and [Fen(bipy)3]2+ ions.16 Magnetic exchange typically occurs through the oxalate bridges.17 Six-coordinate iron(II) a-amino acid complexes are readily obtained from the reaction of the 4-coordinate Fe(mes)2(phen) and the protic amino add, AH, in THF 18... 

Zirconium oxalates exist as compounds, double compounds, and mixed oxalato complexes (165,195,225—226). When the carboxylate ligand is a longer alkyl chain, the materials often are called zirconium soaps. 

Self-Test 16.3A (a) Name the compound Fe0H(H20)5]G2. (b) Write the formula of potassium diaquabis(oxalato)chromate(II). 

Spectra of a variety of chromium compoimds in the +3 valence state are included in Fig. 16. The principal peak is centered at about 22-25 ev. in all cases. The CrjOa spectrum is almost identical to that of Mn02 of Fig. 5. Spectra of the oxalato complex and the ammonia complex are almost identical to spectra of the corresponding cobalt compounds of Figs. 13 and 11. 

A series of optically active linear tetradentate ligands, which have been stereospeeifically synthesized, have been used to prepare complexes with a trans-[CoN Cl2] core and both five- and six-membered chelate rings, in an attempt to correlate the sign of the Cotton effect with the known chiralities of compounds. How ever, a complete correlation was not possible. The synthesis, resolution, and properties of some oxalato, malonato, and diacido complexes of Co " with the stereospecific flexible tetramine ligands 5-Me-3,2,3-tet and NA -bis-(2-picoyl)-l-methyl-1,2-diaminoethane (picpn) have been reported. The stereospecificity is demonstrated by comparison of the optical rotation of the ligand prepared via an asymmetric synthesis with that of the ligand isolated from a resolved complex. The stereochemistry of the complexes has been deduced. ... 

Also, on replacement of oxalato- or carbonato-group by nitro-, chloro-, or bromo-radicles, brown salts are obtained with acid and sodium nitrite, and violet salts on treatment with concentrated hydrochloric or hydro-bromic acid. The brown nitro-compounds are therefore given a formula with the nitro-groups in the 1-, 2-, or eis-position, and the violet halogen salts the formula with halogen in the m-position. The cis-form may be transformed into the /ra -modification by intramolecular rearrangement. Concentrated hydrochloric acid converts carbonato-tctrammino-cobaltie salts first into violo-salts, and on standing, or on rise of temperature, these pass into the prasco- or I-, 6-salts. 

After the resolution of 1-2-chloro-ammino-diethylenediamino-cobaltie chloride many analogous resolutions of optically active compounds of octahedral symmetry were carried out, and active isomers of substances containing central cobalt, chromium, platinum, rhodium, iron atoms are known. The asymmetry is not confined to ammines alone, but is found in salts of complex type for example, potassium tri-oxalato-chromium, [Cr(Ca04)3]K3, exists in two optically active forms. These forms were separated by Werner2 by means of the base strychnine. More than forty series of compounds possessing octahedral symmetry have been proved to exist in optically active forms, so that the spatial configuration for co-ordination number six is firmly established. 

The corresponding- diethylenediamino-series, [Cr en2(C204)]X, are of interest, as through these the cis- and traws-diaeido-diethylene-diamino-ehromic salts are distinguished. Pfeiffer showed that only those salts with acidic groups in the cis-position were likely to form ring compounds when replaced by one oxalato-radicle hence the diacido-salts formed from the oxalato-salts by treatment with halogen acids are m-salts. 

Tetrammino-salts arc also known in which a divalent acidic radicle takes the place of two monovalent acidic radicles in the diacido-tetram-mino-series, giving rise to efs-compounds such as the earbonato-tetram-mino- and the oxalato-tctrammino-cobaltic salts. 

Values for the formation constants of [V(C204)]+ and [V(C204)2] were respectively 1.6 x 107 and 3.5 x 1012.271 By irradiation of these solutions at 254 nm, there is a photodecomposition of the oxalate sensitized by the oxalato vanadium(III) complex the resulting products were equimolar amounts of CO and C02. K3[V(C204)3]-3H20 can be easily crystallized from aqueous solutions containing ammonium vanadium alum and potassium oxalate. The measured magnetic moment is 2.78 BM and this compound obeys the Curie law quite closely.272 The thermal decomposition has been studied.273... 

Chemistry in aqueous solution sulfato, oxalato and related compounds 666... 

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