Treatment of (MeCp)2V2S4 with PBu3 gives the electron-deficient (56e) cubane (MeCp)4V4S4 (1). Desulfurization of a 1:1 mixture of (MeCp)2V2S4 and Cp2V2S4 gave a mixture of ring-substituted cubanes (MeCp)4-xCpxV4S4 (x = 1-4) while (MeCp)2V2S4 and Cp2V react to give exclusively (MeCp)2Cp2V4S4. Compound 1 has a triplet (S = 1) ground state, exhibits Curie-Weiss magnetic behavior, and has a well-resolved isotropically shifted 1H NMR spectrum. Cyclic voltammetry (vs Ag/AgCl) established the following redox series: 1+/1 (772 mV), 1/1- (176 mV), and 1-/12- (-1281 mV). The salt (BF4) was prepared by the reaction of 1 and Ph3CBF4. The diamagnetic 52e cubanes (RCp)4Ti4S4 (R = Me (2), i-Pr) were prepared from (RCp)TiCl2(THF)x and (Me3Si)2S. The compounds 1, (BF4), and 2 were characterized by single-crystal X-ray diffraction. Compound 1 crystallized in the cubic space group P43n with a = 16.551 (3) Å with Z = 6; 671 unique reflections were processed to a final R(F) = 5.31 (Rw(F) = 5.80). Compound (BF4) crystallized in the tetragonal space group I4 with a = 10.600 (3) Å and c = 12.600 (3) Å with Z = 2; 463 unique reflections were processed to a final R = 6.40 (Rw(F) = 6.55). Compound 2 crystallized in the orthorhombic space group Cmca with a = 1.412 (5), b = 17.293 (6), c = 24.503 (9) Å with Z = 8; 558 unique reflections were processed to give R = 10.5 (Rw(F) = 12.6). 1 and + are extremely similar structurally; no bond distances differ by more than 0.03 Å. The structure of 2 revealed two sets of Ti-Ti distances, four distances of 3.00 Å and two of 2.93 Å. Electronic structure calculations of Cp4V4S4 and [Cp4V4S4]+ were performed by the scattered wave-Xα method. The ground-state configuration for the Cp4V4S4 metal bonding orbitals is a12e4t22. The t2 orbital is predicted to be nonbonding, consistent with the structural results. The bonding in 1, 1+, and 2 is discussed in light of recent results from other laboratories.
ASJC Scopus subject areas
- Colloid and Surface Chemistry