Structures of [(CH3)4P]2CoCl4, [(CH3)4Sb]2CuCl4 and [(CH3)4Sb]2ZnBr4 and a correlation of pseudo-antifluorite [(CH3)4Pn]2MX4 salts Original Research Article

The room temperature structure of three members of the A2MX4 cubic antifluorite family are reported. [(CH3)4P]2CoCl4 is orthorhombic, Pnma, a=18.385(2), b=25.134(3), c=12.758(3) Å, V=5895(2) Å3 with Z=12. [(CH3)4Sb]2CuCl4 is cubic, F3c, a=25.020(3) Å with V=15,663(3) Å3. [(CH3)4Sb]2ZnBr4 is also cubic, F3c, a=25.977(3) Å, V=17,529(4) Å3 with Z=32. The structures are composed of discrete (CH3)4P+ or (CH3)4Sb+ cations and tetrahedral CoCl42−, CuCl42− or ZnBr42− anions. All three are commensurately modulated and the superspace group is subsequently assigned to (TMSb)2CuCl4 and (TMSb)2ZnBr4. The structures are correlated by an ascent of symmetry diagram with a fictional, pseudo-antifluorite Fmm aristotype having ≈12.7 Å axes. The previously reported room temperature structures of [(CH3)4As]2ZnCl4 and [(CH3)4As]2CoCl4, as well as the structures of their estimated, higher temperature phases, are similarly correlated.