Solvothermal syntheses, crystal structures, optical and thermal properties of new selenidogermanate and polyselenidogermanate

New selenidogermanate salts [NH4](2)[H2N(CH3)(2)](2)Ge2Se6 (1) and [Ni(dien)2](2)Ge2Se5(Se-2) (2) (dien = diethylenetriamine), and a selenidogermanate complex [{Ni(tepa)}(2)(mu-Ge2Se6)] (3) (tepa = tetraethylenepentamine) were prepared by solvothermal reactions. Compounds 1 and 2 consist of discrete [Ge2Se6](4-) and [(GeSe7)-Se-2]4- anions, and NH4+, [H2N(CH3)(2)](2+) and [Ni(dien)(2)](2+) counter cations, respectively. The [Ge2Se6](4-) anion is constructed by two tetrahedral GeSe4 building units via edge-sharing. In 2, two tetrahedral GeSe4 units are linked by a corner and a Se-Se bond to form a polyselenidogermanate anion [Ge2Se7](4-) containing a five-membered ring Ge2Se3. The dimeric [Ge2Se6](4-) anion acts as a bridging ligand via the trans terminal Se atoms to link two [Ni(tepa)](2+) cations, resulting in neutral complex 3. The Ni2+ ion in 2 is coordinated by two tridentate dien ligands, while it is coordinated by a pentadentate tepa ligand and a selenidogermanate anion in 3. The different coordination environments of Ni2+ ions indicate the influence of the denticity of ethylene polyamines on the formation of selenidogermanates in the presence of transition metal ions. The compounds 1-3 exhibit optical band gaps between 2.06 and 2.35 eV.