Synthesis and Structure of One-, Two-, and Three-Dimensional Alkaline Earth Metal Gallium Nitrides: Sr(3)Ga(2)N(4), Ca(3)Ga(2)N(4), and Sr(3)Ga(3)N(5).

We report the structures of three new alkaline earth metal gallium nitrides synthesized as crystals from the elements in sealed Nb tubes at 760 degrees C using Na/Sr and Na/Ca melts as growth media. The materials are all transparent insulators. Yellow Sr(3)Ga(2)N(4) is isostructural with the previously reported Ba(3)Ga(2)N(4) and Sr(3)Al(2)N(4). It crystallizes in Pnna (No. 52) with a = 5.9552(6) Å, b = 10.2753(8) Å, c = 9.5595(9) Å, and Z = 4. It contains infinite chains, [GaN(4/2)(3)(-)], of trans-edge-shared tetrahedra extending along the b axis. Colorless Ca(3)Ga(2)N(4) is isostructural with Ca(3)Al(2)As(4) and gamma-Ca(3)Al(2)N(4). It crystallizes in C2/c (No. 15) with a = 10.6901(11) Å, b = 8.3655(7) Å, c = 5.5701(4) Å, beta = 91.194(6) degrees, and Z = 4. It contains infinite sheets, [GaN(4/2)(3)(-)], of edge- and corner-sharing tetrahedra in the bc plane. Orange-yellow Sr(3)Ga(3)N(5) has a new structure; it crystallizes in P&onemacr; (No. 2) with a = 5.9358(6) Å, b = 7.2383(8) Å, c = 8.6853(12) Å, alpha = 108.332(10) degrees, beta = 103.783(9) degrees, gamma = 95.326(8) degrees, and Z = 2. It is one of the few materials prepared from Na melts which has an infinite three-dimensional framework structure. It contains a [Ga(3)N(5)(6)(-)] framework of edge- and corner-sharing GaN(4) tetrahedra.