NEW NONCENTERED ICOSAHEDRAL NICKEL-BISMUTH CARBONYL CLUSTERS - GEOMETRIC ANALYSIS OF THE HOMOLOGOUS [NI-10(EME)(2)(CO)(18)](2-) DIANIONS (E=P, AS, SB, BI) CONTAINING NONCENTERED 1,12-NI10E2 ICOSAHEDRAL CAGES

The designed reaction of [Ni-6(CO)(12)](2-) (1) with MeBiCl2 in THF at low temperature (-78 degrees C) has given rise to the desired [Ni-10( BiMe)(2)(CO)(18)](2-) dianion (2) as the major product (ca. 45% yield) . This sought-after (methylbismuthinidene)nickel carbonyl cluster cont aining a noncentered 1,12-Ni10Bi2 icosahedral cage is the missing memb er of the known homologous [Ni-10(EMe)(2)(CO)(18)](2-) series (E = P, As, Sb) whose members differ from one another only by the substitution of two bridging E atoms of the congeneric main-group V (15) elements into the two centrosymmetrically related (opposite) vertices of the ic osahedral cage. The formulation of 2 in the [NMe4](+) salt was establi shed unambiguously from X-ray crystallography and ascertained from a c omplete elemental analysis. This air-sensitive brown compound was also characterized by IR, cyclic voltammetry, negative-ion ESI mass spectr ometry, and low-temperature C-13{H-1} and H-1 NMR spectroscopy. The [N Me4](+) salt of the ethylbismuthinidene [Ni-10(BiEt)(2)(CO)(18)](2-) ( 3) was similarly prepared, isolated, and structurally determined via a single-crystal X-ray diffraction study. Solid-state magnetic suscepti bility measurements conclusively showed 2 (in the [NMe4](+) salt) to b e diamagnetic at room temperature in accordance with it (and the other homologous members) being electronically equivalent (isolobal) with t he classic regular icosahedral [B12H12](2-) dianion in likewise posses sing 13 skeletal electron pairs. A detailed comparison of the essentia lly identical molecular parameters of 2 and 3 with those of the three other isostructural [Ni-10(EMe)(2)(CO)(18)](2-) clusters (E = P, As, S b) provides illuminating information regarding particular geometric ch anges in the empty icosahedral 1,12-Ni10E2 cages arising from a system atic size variation in the two E atoms of the four congeneric group V (15) elements. Moreover, a comparative analysis of the molecular param eters of 2 with those of the previously reported [Ni11B12(CO)(18)](3-) trianion (4), which contains a Ni-centered (filled) 1,12-Ni10Bi2 icos ahedral cage, reveals marked geometric distortions upon the formal ins ertion of a centered (interior) Ni(i) into the icosahedral cage. Varia ble-temperature C-13{H-1} NMR spectra of 2 in acetone-d(6) show fast t erminal-bridge carbonyl exchange of the 18 COs at room temperature but limiting slow exchange at low temperature (-60 degrees C), as was als o found for [Ni-10(EMe)(2)(CO)(18)](2-) (E = P, Sb) previously.