Structure Forming Role of Alkaline Metal Cations in the Formation of Chromium(III) Complexes with Anions of Cyclopropane-1,1-Dicarboxylic Acid

The reactions of Cr(NO3)3·9H2O with potassium, sodium, and lithium salts of cyclopropane-1,1-dicarboxylic acid (H2Cpdc) in a ratio of 1 : 3 are studied in order to elucidate the chemical assembling processes of the coordination polymers with Cr3+ and alkaline metal ions. The nature of the reacted alkaline metal cation affects the compositions and structures of the formed compounds. The reaction of Cr(NO3)3·9H2O with K2(Cpdc) affords the 3D polymeric complex [KCr(Cpdc)2(H2O)2]n (I) formed by the bis-chelate anionic fragments [Cr(Cpdc)2(H2O)2]–. Under similar conditions, the use of Na2(Cpdc) and Li2(Cpdc) results in the formation of the 3D polymers [Na4Cr(Cpdc)3(H2O)6(NO3)]n (II) and {[Li8Cr2(Cpdc)8(H2O)5]·H2O}n (III), respectively, containing the tris-chelate anionic fragments [Cr(Cpdc)3]3–. A distinctive feature of compound III is the presence in its structure of the {Li(Cpdc)}– fragments in which the Cpdc2– anion forms a six-membered chelate cycle with the Li+ ion. The crystal structures of compounds I–III are determined by X-ray diffraction (CIF files CCDC nos. 2031258 (I), 2031260 (II), and 2031261 (III)).