Structures and fluorescent properties of picolinato zinc(II) and cadmium(II) complexes based on tridentate and tetradentate benzimidazole ligands

<p>Five picolinato zinc(II) and cadmium(II) complexes, [Zn(ntb)(pic)]ClO₄·CH₃OH·2H₂O (<b>1</b>), [Zn(bbma)(pic)]NO₃·2CH₃OH (<b>2</b>), [Cd(ntb)(pic)]ClO₄·0.75CH₃OH·H₂O (<b>3</b>), [Cd₂(bbma)₂(pic)₂](ClO₄)₂ (<b>4</b>), and [Cd₂(bbp)(bbp_-H)(pic)₂(C₂H₅OH)]ClO₄ (<b>5</b>), have been synthesized, where pic is the anion of picolinic acid, ntb is tris(2-benzimidazolylmethyl)amine, bbma is bis(benzimidazol-2-yl-methyl)amine, and bbp is 2,6-bis(benzimidazol-2-yl)pyridine. All the complexes were characterized by X-ray single-crystal diffraction, elemental analysis, IR, fluorescence spectroscopy, and thermal gravimetric analysis. <b>1</b>–<b>3</b> are mononuclear complexes in which picolinate adopts a N,O-chelating mode. <b>4</b> is a symmetrical dinuclear complex bridged by two anti-parallel picolinates in a N,O,O-coordination mode. <b>5</b> is also a dinuclear complex in which only one picolinate is a bridge. A 1-D double chain is formed by extensive H-bonds and <i>π</i>–<i>π</i> stacking in <b>1</b>, while single zigzag chains are formed in <b>5</b>. Complexes <b>2</b>–<b>4</b> all exhibit 6³-hcb 2-D frameworks. They extend to form four-connected 6⁶-dia 3-D topological nets for <b>2</b> and <b>4</b> and five-connected 4⁶·6⁴-bnn 3-D topological nets for <b>3</b>. The five complexes show emission maxima in the blue region in the solid state.