SYNTHESES, CRYSTAL-STRUCTURES AND PROPERTIES OF [PPH4]2[SBFE3H(CO)12]AND [PPH4]2[ASFE3H(CO)12]

Reaction of Sb2O3 or As2O3 with methanolic solutions of Fe(CO)5-OH- ha ve resulted in the formation of the anionic species [SbFe3H (CO)12]2- or [AsFe3H (CO)12]2-, which may be precipitated as their PPh4+ salts. The anions have also been obtained as the NEt4+, NMe4+ or N (= PPh3)2 salts. The PPh4+ salts of the anions are not isomorphous, with [PPh4] 2[SbFe3H(CO)12] crystallizing in the monoclinic space group P2(1)/c, w ith a = 11.165(5), b = 49.223(9), c = 10.903(5) angstrom, beta = 108.1 3(2)degrees and Z = 4, while [PPh4]2-[AsFe3H(CO)12] is triclinic, spac e group P1BAR, with a = 12.088(5), b = 13.257(5), c = 19.389(8) angstr om, alpha = 80.43(3), beta = 83.55(3), gamma = 70.83(3)degrees and Z = 2. Each anion consists of a central antimony or arsenic atom surround ed by three Fe(CO)4 groups in a trigonal-pyramidal arrangement, togeth er with a hydrogen atom, although this was not crystallographically lo cated and is inferred on the basis of charge considerations and, more importantly, H-1 NMR data. The Sb-Fe and As-Fe bond distances average 2.596(1) and 2.459(2) angstrom, respectively. The H-1 NMR spectra exhi bit slightly broad singlets at delta -1.39 for [SbFe3H(CO)12]2- and de lta 1.34 for [AsFe3H(CO)12]2-, both with w1/2 of ca. 6 Hz, which are i ndicative of hydrogen attached to antimony and arsenic. Attempts to sy nthesize the corresponding bismuth species were unsuccessful, which ma y be attributed to the poor Lewis basicity of the lone pair on bismuth and to the lack of stability displayed by a Bi-H bond. The reaction i n this case generally results in the formation of [BiFe4(CO)16]3- and bismuth metal, likely involving the disproportionation of an anionic B i(III)-Fe(m)(CO)n intermediate such as [BiFe3(CO)12]3-, the deprotonat ed bismuth analogue of [SbFe3H(CO)12]2- and [AsFe3H(CO)12]2-.