Crystal structures of two- and three-dimensional polymeric complexes assembled by metal pseudohalides and 4-aminobenzoic acid via hydrogen bonds and covalent bonds

Four polymeric complexes [M(SCN)2(4-abaH)2]n [M=Co(II) (1) or Cd(II) (2), 4-abaH=4-aminobenzoic acid], [Zn(N3)(4-aba)]n (3) and [Cd(N3)(4-aba)(H2O)]n (4) were prepared from the reactions of 4-abaH with M(SCN)2 [M=Co(II) or Cd(II)] and M(N3)2 [M=Zn(II) or Cd(II)] at different pH values. Their crystal structures have been determined by single-crystal X-ray diffraction. Both 1 and 2 consist of one-dimensional chains [M(μ-1,3-SCN)2(4-abaH)2]n, in which each pair of the lateral carboxylic groups form double hydrogen bonds to furnish infinite two-dimensional sheets. In 3, the Zn(II) atoms are bridged by μ-1,1-azide groups and μ2-carboxylate-O,O′ groups into an infinite zigzag chain featuring six-membered (ZnNZnOCO)n rings, which are further connected by the 4-aba-N,O,O′ groups to generate a two-dimensional network. In 4, however, adjacent Cd(II) atoms are bridged by μ-1,1,3-azide groups to form an infinite chain with both four-membered Cd2(μ-1,1-N3)2 and eight-membered Cd2(μ-1,3-N3)2 rings. These chains are further connected by the 4-aba-N,O groups to generate a three-dimensional brickwall-like network. The results show significant effect of pH on the formation of the network structures.