Metal-Directed Assembly of Hexameric Ring, Dimeric Ring and 1D Chain from a Branched Tripodal Ligand

To explore the influencing effect of different transition metal ions on the coordination geometries and structural architectures of metal–organic complexes with the same ligand, 10 new coordination compounds of a monobranched tripodal ligand N-[N′-(carboxymethyl)benzimidazol-2-ylmethyl]-N,N-bis(benzimidazol-2-ylmethyl)amine (HAcNTB), namely, [Co6(AcNTB)6]·6ClO4·36H2O (Co-ClO4), [Co6(AcNTB)6]·6BF4·9H2O·3CHCl3 (Co-BF4), [Zn6(AcNTB)6]·6ClO4·2CHCl3·15H2O (Zn-ClO4), [Zn6(AcNTB)6]·6BF4·52H2O (Zn-BF4), [Ni2(AcNTB)2(H2O)2]·2ClO4·2CH3OH·2H2O (Ni-ClO4), [Ni2(AcNTB)2(H2O)2]·2BF4·4CH3OH (Ni-BF4), {[Mn(AcNTB)(CH3OH)]·ClO4·H2O}n (Mn-ClO4), {[Mn(AcNTB)(CH3OH)]·BF4·H2O}n (Mn-BF4), {[Cd(AcNTB)(CH3OH)]·ClO4·H2O}n] (Cd-ClO4), {[Cd(AcNTB)(CH3OH)]·BF4·H2O}n (Cd-BF4) have been synthesized and characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction, and single-crystal X-ray diffraction. In isomorphous complexes Co-ClO4, Co-BF4, Zn-ClO4, and Zn-BF4, the metal centers (Zn2+ and Co2+) are five-coordinated in a trigonal bipyramid geometry, leading to formation of hexameric rings through linkage of six metals and six ligands without coordination of anion and solvent molecules. In isomorphous complexes Ni-ClO4 and Ni-BF4, the metal centers (Ni2+) prefer a six-coordinated octahedral geometry, resulting in dinuclear rings through connection of two metals and two ligands with water molecule participating in coordination. While in the isomorphous complexes Mn-ClO4, Mn-BF4, Cd-ClO4, and Cd-BF4, the metal centers are seven-coordinated to form one-dimensional (1D) chain, showing an irregularly distorted geometry with water or methanol solvents entering coordination sphere. The coordination geometric preference of different metal ions with respect to the metal ionic radii and coordination numbers play an important role in determining the assembly fashions. Density functional theory (DFT) calculations have been performed to track the stability effects obtained by the metal ions in different coordination environments.