Sr(Mg_3Ge)N_4 and Sr(Mg_2Ga_2)N_4: New isostructural Mg-containing quaternary nitrides with nitridometallate anions of _propor.to~3 [(Mg_3Ge)N_4]~(2-) and _propor.to~3 [(Mg_2Ga_2)N_4]~(2-) in a 3D-network structure

摘要

Two new isostructural Mg-containing quaternary nitrides, Sr(Mg_3Ge)N_4 and Sr(Mg_2Ga_2)N_4, were obtained as single crystals from their constituent elements in molten Na. Sr(Mg_3Ge)N_4 and Sr(Mg_2Ga_2)N_4 both crystallize in space group 14/m (No. 87) with a=8.316(1), c=3.398(1) A, Z=2, and a =8.2925(7), c=3.3585(5) A, Z=2, respectively. The two compounds are isoelectronic, with two Ga~(3+) in Sr(Mg_2Ga_2)N_4 replaced by one Mg~(2+) and one Ge~(4+) in Sr(Mg_3Ge)N_4. Condensed nitridometallate anions, _propor.to~3, [(Mg_3Ge)N_4]~(2-) and _propor.to~3, [(Mg_2Ga_2)N_4] ~(2-), form a 3D-network structure with basket-shaped cavities, which are occupied by the Sr~(2+) counter-cations. Each Sr~(2+) coordinates to eight N in a symmetric, near cubic conformation, with all Sr-N bond lengths of 2.86 A.