Lamellar and three-dimensional hybrid compounds formed by cyclohexene- and cyclohexanedicarboxylates of Pb, La, and Cd

To establish factors that determine the formation of three-dimensional hybrid structures of metal dicarboxylates involving metal-oxygen-metal linkages, we have investigated metal dicarboxylates derived from 1,2-cyclohexene as well as 1,2-, 1,3-, and 1,4-cyclohexane dicarboxylic acids. Thus, we have synthesized a 1,2-cyclohexenedicarboxylate of Cd, [Cd(1,2CHeDC)(H2O)] (I), a 1,2-cyclohexane-dicarboxylate of Pb, [Pb(1,2-CHDC)] (II), and three 1,4-cyclohexanedicarboxylates of La [La2(1,4-CHDC)(3)- (H2O)(4)] (III), [La-3(1,4-HCHDQ)(2)(1,4CHDC)(5)(H2O)(2)](H2O)-H-. (IV) and [La-2- (1,4-CHDC)(3)H2O](.)2-5H(2)O (V) under hydrothermal conditions and determined their structures. A mixed dicar- boxylate involving both 1,3- and 1,4-cyclohexenedicarboxylates of Pb, [Pb3O(1,3-CHDC)(1,4-CHDC)](.)0.5H(2)O (VI) and a 1,4-cyclohexan edicarboxyl ate of Pb, [Pb6O2(1,4-CHDC)(3)(1,4HCHDC)(2)], have also been synthesized and characterized. While the 1,2-dicarboxylates have layered structures, the 1,4-dicarboxylates and the mixed dicarboxylates possess three-dimensional structures. Interestingly, both the 1,2 and 1,4-dicarboxylates are true hybrid compounds composed of infinite M-O-M linkages. The equatorial-equatorial (e,e) conformation is adopted commonly in all these compounds, although less stable conformations are encountered occasionally. The formation of the layered and the three-dimensional structures can be understood based on the relative disposition of the two carboxylic groups, the 1,4-isomer favoring the three-dimensional structure. Based on the results of the present study along with the available literature, we conclude that in order to obtain three-dimensional hybrid structures with metal-oxygen-metal networks, it appears necessary to make use of the 1,4-cyclohexanedicarboxylic acid.