Syntheses, Properties and Crystal Structures of One-dimensional Transition Metal-Azide Coordination Polymers via Hydrogen Bonds

Three novel mononuclear transition metal-azide compounds, Mn(PzBu-t)4(N3)2 (1), Co(PzBu-t)4(N3)2 (2) and Co(PzBu-t)3(N3)3 (3) (PzBu-t = 3-tert-butyl pyrazole), have been synthesized and characterized by elemental analysis, IR and UV-Vis spectra, and the crystal structures of compounds 1 and 3 have been determined. Crystal data for 1: triclinic, space group P1 with a = 8.0844(9), b = 10.1230(12), c = 12.1046(13) A, alfa = 91.854(3)°, beta = 108.495(2)°, gamma =101.598(2)°, V = 915.33(18) A3 and Z = 1. Crystal data for 3: monoclinic, space group P2(1) with a = 10.3286(9), b = 23.593(2), c = 12.7735(10) A,beta = 106.659(2)°, V = 2982.0(4) A3 and Z= 2. The azide ions in compound 1 are coordinated to manganese(II) ions in trans centrosymmetric octahedral configuration. However, compound 3 shows two unsymmetrical molecules with distorted octahedral geometry ligated by three azide anions and three 3-tert-butyl pyrazole ligands in crystal cell. The compounds are aggregated to form one-dimensional chain through (pyrazole)N-H...N(azide) hydrogen bonds, respectively. In aqueous solution, the reaction of compound 2 with azide excess (2 equivalents) and H2O2 was investigated, and the product was isolated and identified to be homogeneous as compound 3. The result suggests that the compound 3, as the oxidation product of compound 2, was formed by the change of the coordination geometry around cobalt ion in the reaction process, due to the binding of peroxides to the cobalt ion via the removal of the pyrazole ligand.