Eight new complexes containing the versatile multidentate ligand 5-pyrimidyl-tetrazolate (pmtz), namely [Cu(μ3-pmtz)]n (1), [Pd2(μ-pmtz)2Cl2] (2), [Ni(pmtz)(en)2]Cl·2H2O (3), [Cu(tren)(pmtz)(ClO4)] (4), [Co2(tren)2(μ-pmtz)(μ-O2)](ClO4)3·3H2O (5), [Fe2(pmtz)4(H2O)2(μ-O)]·5H2O (6), [(UO2)4(μ-pmtz)2(μ-OH)2(μ3-O)2(H2O)4]·6H2O (7) and [Dy2(pmtz)4(μ-pmtz)(H2O)6](pmtz)·6H2O (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 1 is a 2D polymer where the ligand exhibits a new chelating/bridging κ2N1,N7:κN2:κN3 coordination mode, whereas complexes (2) and (7) are dinuclear and tetranuclear species, respectively, in which the ligand displays a κ2N1,N7:κN2 coordination mode. The increase of the metal size favours the adoption of the κ2N1,N7:κ2N4,N11 bis(chelating)bridging mode. This is the case of compound (8) that contains bulky DyIII metal ions. Despite the large size of the UO2+ 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(μ3-oxo) tetranuclear unit. Conventional mild solution conditions lead to complexes containing monodentate or chelating coordination modes. Thus, compounds (3) and (6) are mononuclear and μ-oxo dinuclear species, respectively, which contain κ2N1,N7 chelating pmtz ligands. Compound (4) is mononuclear with the ligand acting in a new monodentate form through the N1 atom of the tetrazolato ring, whereas (5) is a dinuclear complex where pmtz adopts a new exo-bidentate N2,N3 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.
