M2BN2X (M = CA, SR, X = F, CL) - NEW HALOGENIDE COMPOUNDS WITH ISOLATED BN23- UNITS

The compounds M2BN2X (M = Ca, Sr; X = F, Cl) were synthesized from sto ichiometric mixtures of the binary components M3N2, MX2, and BN in sea led steel ampoules at 1273 K, All four structures were refined from si ngle crystal data. The isotypic fluorides crystallize in the orthorhom bic space group Pnma (No. 62) with a = 9.182 (2) Angstrom, b = 3.649(1 ) Angstrom, c = 9.966(2) Angstrom, Z = 4, and V = 333.9(1) Angstrom(3) for Ca2BN2F and a = 9.891(2) Angstrom, b = 3.904(1) Angstrom, c = 10. 193(2) Angstrom, Z = 4, acid V = 393.6(2) Angstrom(3) for Sr2BN2F. The structures are built from isolated BN23- anions and [MM3/3F] units, T he chlorides, which are related but not isotypic, crystallize in the s pace group Pnma (No. 62) with a = 11.657(1) Angstrom, b = 3.891(1) Ang strom, c = 8.965(1) Angstrom, Z = 4, and V = 406.6(1) Angstrom(3) for Ca2BN2Cl and a = 12.408(1) Angstrom, b = 4.161(1) Angstrom, c = 9.170( 1) Angstrom, Z = 4, and V = 473.4(1) Angstrom(3) for Sr2BN2Cl. The str uctures are built from isolated BN23- anions and [M3/3M2/2Cl] units, C alculations of the Madelung parts of lattice energy (MAPLE) and vibrat ion spectra of the compounds are reported. (C) 1998 Academic Press.