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 CuII and CoII 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)2Cl2]}n (1) and {[Co(PAT)2Cl2]}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)2Cl2] (2), [Co(PAT)2Cl2] (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 I41/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)2Cl2]}∞ and {[Co(PAT)2Cl2]}∞, respectively. In these complexes, changes of PAT conformations and coordination geometry of metal center induced the structural versatility.