Conformational isomerism and hydrogen-bonded motifs of anion assisted supramolecular self-assemblies using CuII/CoII salts and pyridine-4-acetamide

Six novel metal-organic complex assemblies constructed from a conformation-flexible ligand - pyridine-4-acetamide (PAT) and inorganic Cu-II and Co-II salts have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Crystal structure analysis reveals five types of architectures by variation of metal salts. In {[Cu(PAT)(2)Cl-2]}(n) (1) and {[Co(PAT)(2)Cl-2]}(n) (3), PAT ligands bridge metal centers to form one-dimensional chains. The chains are extended to three dimensions with the aid of two types of hydrogen bonded motifs (R-4(2) (8)) and R-2(2) (12)). {[Cu(PAT)(2)(NO3)](NO3)(THF)}(n) (5) which exhibits two-dimensional coordinating layers forms open channels filled with solvent molecules. In [Cu(PAT)(2)Cl-2] (2), [Co(PAT)(2)Cl-2] (4) and [Co(PAT)(4)(H2O)(2)](NO3)(2)(THF)(2) (6), PAT is observed as a monofunctional ligand. Complex 2 forms one-dimensional hydrogen bonded chains. Crystal structure of complex 4 has a two-dimensional infinite hydrogen-bonded network with R-4(2) (8) and R-2(2) (8) motifs formed by complementary amide-amide hydrogen bonds. [Co(PAT)(4)(H2O)(2)](NO3)(2)(THF)(2) (6) crystallizes in centrosymmetric I4(1)/a space group. Complex 6 forms chiral channels which are filled with twisted solvent helices and anion helices. Within each channel the solvent helix and the anion helix have the same handedness; and adjacent channels have opposite handedness. Complexes 1, 2 and complexes 3, 4 illustrate examples of conformational supramolecular isomerism in {[Cu(PAT)(2)Cl-2]}(1) and {[Co(PAT)(2)Cl-2]}(1), respectively. In these complexes, changes of PAT conformations and coordination geometry of metal center induced the structural versatility. (C) 2009 Elsevier B. V. All rights reserved.