Syntheses, crystal structures and Raman spectra of Ba(BF 4)(PF 6), Ba(BF 4)(AsF 6) and Ba 2(BF 4) 2(AsF 6)(H 3F 4); the first examples of metal salts containing simultaneously tetrahedral BF 4− and octahedral AF 6− anions

Abstract

In the system BaF 2/BF 3/PF 5/anhydrous hydrogen fluoride (aHF) a compound Ba(BF 4)(PF 6) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF 4)(PF 6) crystallizes in a hexagonal P 6 ¯ 2 m space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å 3 at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF 4 − and PF 6 − anions. In the analogous system with AsF 5 instead of PF 5 the compound Ba(BF 4)(AsF 6) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å 3 at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF 6 − and four F atoms from BF 4 − anions. When the system BaF 2/BF 3/AsF 5/aHF is made basic with an extra addition of BaF 2, the compound Ba 2(BF 4) 2(AsF 6)(H 3F 4) was obtained. It crystallizes in a hexagonal P6 3/ mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å 3 at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF 4 −, three AsF 6 − and three H 3F 4 − anions. All F atoms, except the central atom in H 3F 4 moiety, act as μ 2-bridges yielding a complex 3-D structural network.