Zinc and Cadmium Coordination Polymers with Bis(tetrazole) Ligands Bearing Flexible Spacers: Synthesis, Crystal Structures, and Properties

Abstract

Seven new metal complexes with the formulas, [Zn₂(<b>L</b>^<b>1</b>)₂(H₂O)]_<i>n</i> (<b>1</b>), [Cd₂(<b>L</b>^<b>1</b>)Cl₂(H₂O)]<i>_n</i> (<b>2</b>), [Cd₃(<b>L</b>^<b>1</b>)₃(H₂O)₁₂]_<i>n</i> (<b>3</b>), [Zn(<b>L</b>^<b>2</b>)]<i>_n</i> (<b>4</b>), [Cd₂(<b>L</b>^<b>2</b>)Cl₂]_<i>n</i> (<b>5</b>), {[Zn(<b>L</b>^<b>3</b>)(H₂O)₄]·(H₂O)₂}<i>_n</i> (<b>6</b>), and {[Cd₃(<b>L</b>^<b>3</b>)₂Cl₄]·(H₂O)₄}<i>_n</i> (<b>7</b>), have been synthesized by the reactions of Zn^II or Cd^II salts with three structurally related flexible bis(tetrazol-5-yl)alkanes, 1,2-bis(tetrazol-5-yl)ethane (H₂<b>L</b>¹), 1,3-bis(tetrazol-5-yl)propane (H₂<b>L</b>²), and 1,4-bis(tetrazol-5-yl)butane (H₂<b>L</b>³), and characterized by single crystal X-ray diffraction analysis, IR spectroscopy, and thermogravimetric (TG) analysis. Because of the geometrical requirements of different metal ions and the diverse coordination modes of the tetrazolate rings of flexible bis(tetrazole) ligands as well as the different reaction conditions, the obtained complexes show diverse structures from one-dimensional (1D) chain to three-dimensional (3D) coordination polymers. <b>1</b>, <b>4</b>, and <b>6</b> are Zn^II complexes in which the Zn^II ions show tetrahedral coordination geometries. <b>1</b> and <b>4</b> are 3D frameworks, while <b>6</b> is 1D chain structure. <b>2</b>, <b>3</b>, <b>5</b>, and <b>7</b> are Cd^II complexes, and the Cd^II ions show octahedral coordination geometries. <b>3</b> is a two-dimensional (2D) sheet and <b>2</b>, <b>5</b>, <b>7</b> are all 3D frameworks. The tetrazolate rings of the structurally related ligands adopt either μ₁-tetrazolyl, μ₂-tetrazolyl, μ₃-tetrazolyl, or μ₄-tetrazolyl modes in our obtained complexes. The fluorescent properties of these complexes have also been investigated in the solid state at room temperature.