Coordination Polymers Ca(II)–Cr(III) and Ba(II)–Cr(III) with Cyclobutane-1,1-dicarboxylic Acid Anions

The reactions of Cr(NO 3 ) 3 ·9H 2 O with barium and calcium salts of cyclobutane-1,1-dicarboxylic acid (H 2 Cbdc) in a ratio of 1 : 3 in an aqueous solution are studied. The reaction products isolated in the crystalline state are shown to be compounds formed by the binuclear tetraanionic units [Cr 2 (OH) 2 (Cbdc) 4 ] 4– , and the nature of the alkaline-earth metal ion introduced into the synthesis affects the dimensionality of the formed polymeric structure. The 2D polymeric compound {[Ba 2 Cr 2 (OH) 2 (Cbdc) 4 (H 2 O) 5 ]·3H 2 O} n ( I ) is formed in the reaction with Ba(Cbdc), and the replacement of Ba 2+ by Ca 2+ results in the formation of the 1D coordination polymer {[Ca 2 Cr 2 (OH)(Cbdc) 4 (H 2 O) 6 ]·8H 2 O} n ( II ). The crystal structures of compounds I and II are determined by single-crystal XRD (CIF files CCDC nos. 2344872 ( I ) and 2344873 ( II ), respectively).