New Selenidogermanates with Transition-Metal Complexes as Counterions: Solvothermal Synthesis, Crystal Structures, and Properties of [Mn(en)3]2Ge2Se6 and [Fe(dien)2]2Ge2Se6

Summary. New selenidogermanates Mn(en)₃]₂Ge₂Se₆ (en = ethylenediamine) and Fe(dien)₂]₂Ge₂Se₆ (dien= diethylenetriamine) were synthesized by the reaction of germanium dioxide, elemental selenium, and transition metal chlorides in respectively en and dien. Both compounds crystallize in the monoclinic space group P2₁/n with two formula units in the unit cell, and consist of discrete Ge₂Se₆]⁴⁻ anions with transition metal complex cations as counter ions. The Ge₂Se₆]⁴⁻ anion is formed by two GeSe₄ tetrahedra sharing a common edge to form a planar Ge₂Se₂ four-membered ring. The Mn(en)₃]²⁺ and Ni(dien)₂]²⁺ complex cations are in distorted octahedral geometry. In both selenidogermanates extensive N–H···Se hydrogen bonding contacts lead to 3-dimensional network structures. The band gaps of 2.36 and 2.25 eV were derived from optical absorption spectra. Thermogravimetric analysis shows that the first compound decomposes in two steps under the nitrogen stream, while the second exhibits a one-step decomposition process.