Preparation and crystal structures of [As(CF3)2O(OH)]2, [As(CF3)-O(OH)Cl]2, and As4(CF3)6O6(OH)2; a novel cage structure containing four- and six-co-ordinated arsenic

Abstract

The compounds [As(CF₃)₂O(OH)]₂(1) and As₄(CF₃)₆O₆(OH)₂(3) have been prepared by oxidative hydrolysis of As(CF₃)₃, and a mixture of As(CF₃)l₂ and As(CF₃)₂l, respectively; [As(CF₃)O(OH)Cl]₂(2) was isolated from the reaction of compound (3) with SiMe₃Cl. Crystals of compound (1) are triclinic, space group P, a= 584.2(1), b= 703.7(1), c= 958.6(1) pm, α= 103.91(1), β= 103.10(1), γ= 107.90(1)°, and Z= 1. Crystals of compounds (2) and (3) are monoclinic, space group P2₁/n, with a= 554.3(1), b= 934.5(2), c= 1 149.6(2) pm, β= 92.70(1)°, and Z= 2 for (2), and a= 880.3(2), b= 1 011.4(2), c= 1 256.7(3) pm, β= 104.17(2)°, and Z= 2 for (3). The structures were refined to R= 0.036, 0.038, and 0.046 for 1 520, 749, and 1 328 unique observed diffractometer data for compounds (1), (2), and (3), respectively. All three molecules have centrosymmetric structures with four-membered (AsO)₂ rings. In compounds (1) and (2) the rings bridge equatorial and axial positions of the trigonal-bipyramidal co-ordinated arsenic atoms; the equatorial ring As–O bonds are much shorter than the axial ring As–O bonds. The structures may be interpreted as intermediate stages in a dimerisation reaction pathway. Compound (3) possesses a novel cage structure involving octahedrally and tetrahedrally co-ordinated arsenic, and an (AsO)₄ ring in which the As^III–O bonds are much shorter than As^V–O bonds.