Influence of metal ions, coligands and reaction conditions on the structural versatility and properties of 5-pyrimidyl-tetrazolate containing complexes

Abstract

Eight new complexes containing the versatile multidentate ligand 5-pyrimidyl-tetrazolate (pmtz), namely [Cu(mu(3)-pmtz)](n) (1), [Pd(2)(mu-pmtz)(2)Cl(2)] (2), [Ni(pmtz)(en)(2)]Cl x 2 H(2)O (3), [Cu(tren)(pmtz)(ClO(4))] (4), [Co(2)(tren)(2)(mu-pmtz)(mu-O(2))](ClO(4))(3) x 3 H(2)O (5), [Fe(2)(pmtz)(4)(H(2)O)(2)(mu-O)] x 5 H(2)O (6), [(UO(2))(4)(mu-pmtz)(2)(mu-OH)(2)(mu(3)-O)(2)(H(2)O)(4)] x 6 H(2)O (7) and [Dy(2)(pmtz)(4)(mu-pmtz)(H(2)O)(6)](pmtz) x 6 H(2)O (8), have been prepared by either conventional solution or hydrothermal techniques and characterised by single-crystal X-ray diffraction. Those compounds prepared under hydrothermal conditions ((1), (2), (7) and (8)) exhibit chelating/bridging coordination modes that connect two or three metal ions generating polynuclear species. Thus, compound is a 2D polymer where the ligand exhibits a new chelating/bridging kappa(2)N(1),N(7):kappaN(2):kappaN(3) coordination mode, whereas complexes (2) and (7) are dinuclear and tetranuclear species, respectively, in which the ligand displays a kappa(2)N(1),N(7):kappaN(2) coordination mode. The increase of the metal size favours the adoption of the kappa(2)N(1),N(7):kappa(2)N(4),N(11) bis(chelating)bridging mode. This is the case of compound (8) that contains bulky Dy(III) metal ions. Despite the large size of the UO(2+) metal ion, the pmtz ligand in (7) does not adopt the expected bis(chelating)bridging mode because the uranyl cation hydrolyzes to the highly stable bis(mu(3)-oxo) tetranuclear unit. Conventional mild solution conditions lead to complexes containing monodentate or chelating coordination modes. Thus, compounds (3) and (6) are mononuclear and mu-oxo dinuclear species, respectively, which contain kappa(2)N(1),N(7) chelating pmtz ligands. Compound (4) is mononuclear with the ligand acting in a new monodentate form through the N(1) atom of the tetrazolato ring, whereas (5) is a dinuclear complex where pmtz adopts a new exo-bidentate N(2),N(3) bridging coordination mode. Variable-temperature magnetic measurements of (6) indicate that the oxo-bridge mediates a very strong antiferromagnetic interaction between the iron(III) ions with a J = -222.7 cm(-1). Luminescence measurements show that the pmtz ligands act as "antenna" for energy absorption and transfer to the uranyl emissive state.