CLUSTERS CONTAINING THE [REFE3(MU-3-S)4] CORE - AN EXPANSION OF THE HETEROMETAL CUBANE-TYPE CLUSTER SERIES MFE3S4

From self-assembly systems containing (Et4N)[ReS4], FeCl2, and NaSEt in methanol, the three cluster complexes (Et4N)3-[Re2Fe6S8(SEt)9] (7), (Et4N)2[Re2Fe7S8(SEt)12] (8), and (Et4N)4[Re2Fe7S8(SEt)12] (9), containing [ReFe3(μ3-S)4] cubane-type units, have been isolated in 66-84% yields as black, air-sensitive, crystalline solids. Compound 7 crystallizes in hexagonal space group P63/m with a = 17.148 (5) Å, b = 17.148 (4) Å, c = 16.202 (2) Å, and Z = 2. Compound 8 was found in orthorhombic space group Pcab with a = 12.316 (6) Å, b = 15.951 (5) Å, c = 38.44 (1) Å, and Z = 4. Compound 9 as its DMF monosolvate crystallizes in triclinic space group [formula omitted] with α = 11.560 (3) Å, 6=11.691 (2) Å, c = 20.960 (8) Å, and Z = 1. The cluster structures consist of two terminal cubane-type ReFe3S4(SEt)3 subclusters bridged through the Re atom by three μ2-SEt sulfur atoms (7) or by a trigonal (μ2-SEt)3Fe(μ2-SEt)3 unit (8, 9). In all cases the subclusters are related by an imposed center of symmetry. Structural data establish the presence of Fe(II) in the bridge units of 8 and 9; consequently the subciuster core oxidation states are 2[ReFe3S4]4+ and 2[ReFe3S4]3+, respectively. Cluster 7 supports a five-member electron-transfer series and clusters 8 and 9 are part of a four-member series; in both, subcluster core oxidation states range from [ReFe3S4]4+ (51 e) to [ReFe3S4]2+ (53 e). Clusters 7 and 8 undergo stoichiometric terminal ligand substitution with 6 equiv of benzenethiol in acetonitrile solution to afford [Re2Fe6S8(SEt)3(SPh)6]3- and [Re2Fe7S8(SEt)6(SPh)6]2-. These and other clusters can be identified by their characteristic isotropically shifted 1H NMR spectra. Property comparisons are made with the previously reported Mo and W clusters [M2Fe6S8(SR)9]3_ and [M2Fe7S8(SR)12]3-,4-, which are congruent in structure with 7 and 8/9, respectively. These new compounds extend the set of MFe3S4 cubane-type clusters to those with M = V, Mo, W, and Re, which include the isoelectronic subset [VFe3S4]2+ = [MoFe3S4]3+ = [WFe3S4]3+ = [ReFe3S4]4+ (51 e). The clusters define a stability plateau associated with cores containing 50-53 e, with the 51-e species having special stability. © 1990, American Chemical Society. All rights reserved.