Isotype 1D polymers of cobalt(II) or zinc(II) constructed with square-planar tetraaqua-metal(2+) units and the bis-zwitterionic form of the μ_2-O,O′-trans-1,4-dihydrogen- cyclohexanediaminotetraacetate(2-) ligand

摘要

An uncompleted reaction between equimolar amounts of Co_2CO_3(OH)_2·2H_2O and trans-1,4-H _4cyclohexanediaminotetraacetic acid in water affords the 'acid' complex {[Co~(II)(trans-1,4-H_2CDTA)(H_2O) 4]·6H_2O}_n (1). Its IR spectrum does not show the expected ν(CO) band of carboxylic groups. Reactions in aqueous solution between Na(trans-1,4-H_3CDTA) and Zn(AcO)_2· 2H_2O or Na_2(trans-1,4-H_2CDTA) and Zn(NO_3)_2·6H_2O yield {[Zn(trans-1,4-H _2CDTA)(H_2O)_4]·6H_2O} _n (2) and {[Zn_2(trans-1,4-CDTA)(H_2O) _2]·H_2O}_n (3) respectively. Crystal structures of compounds 1-3 and that of the trans-1,4-H_4CDTA· 2H_2O acid are reported. For steric reasons, in the four reported structures the 1,4-CDTA ligand has the two iminodiacetate moieties as equatorial groups in the 1,4-cyclohexanedi-yl chair. Compounds 1 and 2 are isotype 1D polymers constructed by square planar M~(II)(H_2O) _4~(2+) knots (M~(II) = Co~(II) or Zn~(II)) linked to bis-zwitterionic trans-1,4-H_2CDTA~(2-) ligands that play a typical μ_2-O,O′- dicarboxylate bridging role. These 1D polymeric structures seem to be favoured by the H-bonded intra-stabilization of the bis-zwitterionic trans-1,4-H _2CDTA~(2-) ligand. In the neutral complex (3), the trans-1,4-CDTA acts as a bridging bis-chelating ligand as well as a syn-anti carboxylate building a polymer where the zinc(II) centres exhibit a rough bipyramidal trigonal coordination.