Synthesis of Au(II) fluoro complexes and their structural and magnetic properties

Gold at similar to 20 degrees C with F-2 in anhydrous hydrogen fluoride (aHF) acidified with SbF5 dissolves to a red solution from which orange Au-II(SbF6)(2) crystallizes on removal of volatiles. Au(SbF6)(2) is triclinic with a=5.300(1) Angstrom, b=5.438(1) Angstrom, c=8.768(2) Angstrom, alpha=76.872(3)degrees, beta=88.736(3)degrees, gamma=68.109(3)degrees, V=227.79(7) Angstrom(3), and Z=1, space group <P(1)over bar>. Each Au(II) atom, at (1) over bar, is at the center of an elongated octahedron of F ligands; the four F's of the approximately square AuF4 unit are at 2.09(2) Angstrom x2 Angstrom and 2.15(2) Angstrom x2, each F provided by a different SbF6 species. The two long Au-F interatomic distances are at 2.64(2) Angstrom. The SbF6 are grossly distorted in their interactions with the Au. A cis pair of F ligands of each SbF6, make close approach to two different gold atoms, stretching Sb-F to 1.99(2) and 1.94(2) Angstrom. In each case the Sb-F distances trans to these stretched Sb-F bonds are short,being 1.85(2) and 1.84(2) Angstrom, respectively. Magnetic susceptibility measurements show antiferromagnetic coupling with a susceptibility decrease below 13 K. Solvolysis of Au-II(SbF6)(2) in aHF is accompanied by disproportionation: 4Au(SbF6)(2)-->Au+Au3F8+8SbF(5)(solv). Fluorination, at similar to 20 degrees C, of the solution of Au(SbF6)(2), in SbF5 acidified aHF, precipitates red crystals of triclinic Au-II{SbF6}Au-2(II){(AuF4)-F-III}(2) with a(o)=5.2345(2) Angstrom, b(o)=8.1218(1) Angstrom, c(o)=10.5977(3) Angstrom, alpha=100.090(2)degrees, beta=100.327(2)degrees, gamma=104.877(2)degrees, V=416.63(2) Angstrom(3), space group <P(1)over bar>, and Z=1. It is a simple paramagnet. The structure shows two different Au(II) environments, each approximately square-coordinated by F ligands, one being coordinated trans by an F ligand of each of two SbF6 and similarly by an F ligand from each of two (AuF4)-F-III species. The other Au(II) is approximately square-coordinated via bridging F ligands to four different (AuF4)-F-III species. Au-II{SbF6}Au-2(II){(AuF4)-F-III}(2) with KAuF4 in aHF yields Au3F8 free of metallic gold,the simple paramagnetism of which indicates the formulation Au-II{(AuF4)-F-III}(2).