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

Abstract 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 (NO 3 )](NO 3 )(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 (H 2 O) 2 ](NO 3 ) 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 (H 2 O) 2 ](NO 3 ) 2 (THF) 2 ( 6 ) crystallizes in centrosymmetric I 4 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 ]} ∞ and {[Co(PAT) 2 Cl 2 ]} ∞ , respectively. In these complexes, changes of PAT conformations and coordination geometry of metal center induced the structural versatility.