Mark A. Greaney

Synthesis and characterization of ‘double-cubane’ complexes containing MFe3Se4 cores (MMo, W)

Abstract The reaction system (Et4N)2MSe4 (MMo, W)/FeCl3/EtSH/Na in methanol or ethanol at ambient temperature has yielded three principal products: [M2Fe6Se8(SEt)9]3−, [M2Fe7Se8(SEt)12]3− (MMo, W); and [W2Fe7Se8(SEt)12]4− which are isolable as Et4N+ salts. The structure of (Et4N)3[Mo2Fe6Se8(SEt)9] has been determined by single-crystal X-ray diffraction. It crystallizes in the hexagonal space group P63/m with a=17.453(3), c=16.575(2) A and Z=2. Reaction of [Mo2Fe7Se8(SEt)12]3− with 6 equiv of acetyl chloride or arylthiol afforded new clusters with substitution of the terminal ethanethiolate ligands: [Mo2Fe7Se8(SEt)6Cl6]3− and [Mo2Fe7Se8(SEt)6(SC6H4X)6]3−, XH, Cl. The structure of (Et4N)3[Mo2Fe7Se8(SEt)6(SC6H4-Cl)6 has been determined by single crystal X-ray diffraction. It crystallizes in the space group P 1 (No. 2) with a=11.401(2), b=12.697(2), c=19.897(3) A, α=87.91(1), β=74.93(1), γ=89.14(2)° and Z=1. The anions in both structures are of the ‘double-cubane’ type containing trigonally distorted MoFe3Se4 subclusters which are linked through the Mo atoms. In the former, linkage is through three μ2-ethanethiolate ligands; whereas in the latter, the bridging is accomplished by a Fe(SEt)6 distorted trigonal anti-prismatic moiety. These complexes are structurally similar to the related sulfur double-cubanes. Incorporation of the larger selenide ion has a surprisingly small effect upon the M···Fe distances within the cubane subclusters. All products show the full stoichiometric amount of four selenium atoms per cubane unit, indicating that MSe42− can effectively deliver all four selenium atoms in the assembly process even though one is no longer covalently bound to M. All clusters exhibit isotropically shifted 1H NMR spectra, which are the result of both contact and dipolar shift mechanisms and are larger in magnitude than the shifts observed in the sulfur analogs. This is consistent with the larger solution magnetic moments of these selenium double-cubanes as determined by the Evans method. Electrochemical reduction potentials of these selenium double-cubanes were nearly identical to their sulfur analogs as determined by cyclic voltammetry. Full tabulation of 1H NMR isotropic shifts, electronic absorption maxima, electrochemical reduction potentials, room temperature solution magnetic susceptibilities, and representative cyclic voltammograms and 1H NMR spectra are presented.

Synthesis and reactivity of molybdenum-sulfur cubes

A series of tetranuclear Mo 4 S 4 (R 2 NCS 2 ) 6 complexes has been prepared by using the ‘self-assembly’ route as well as by synthesis from well-defined molecular building blocks. A variety of mononuclear, dinuclear and trinuclear building blocks have been successfully used to prepare the tetranuclear Mo 4 S 4 6+ complexes. These thiocubanes have been prepared with mono-anionic 1,1-dithiolate ligands, which provide each of the Mo atoms with a pseudo-octahedral coordination geometry and result in the formation of neutral species. Mo 4 S 4 L 6 complexes with dialkyldithiocarbamate (DTC), R 2 NCS 2 ; dialkyldithiophosphate (DDP), (RO) 2 PS 2 ; alkylxanthate (XAN), ROCS 2 ; and alkylthioxanthate (THIOXAN), RSCS 2 ligands have been prepared. The structure of the Mo 4 S 4 (DDP) 6 complex was determined by single crystal X-ray structure analysis and is compared with the structures of other known Mo 4 S 4 thiocubane complexes. The synthesis, electrochemistry, reactivity and bonding of the tetranuclear clusters are presented.

Analogous reactivity of MoS42– and WSe42–: preparation of WSe2(Bui2NCS2)3 by an induced internal redox reaction

Addition of tetreaalkylthiuram disulfides R2NC(S)S–SC(S)NR2(R = Et and Bui) to WSe42– yields the new complexes WvSe2(R2NCS2)3, revealing that WSe42– undergoes induced internal electron transfer similar to that of MoS42–, but different from the reactivity of WS42–, as predicted by comparison of the lowest energy charge transfer transitions of the reactants.

Novel bonding mode for WS42–: synthesis and structure of [Mo2(O2CPh)2(WS4)2]2–

The synthesis of (Et4N)2[Mo2(O2CPh)2(WS4)2] is reported; the structure reveals a novel bonding mode for the tetrathiotungstate ligands which bridge two quadruply-bonded molybdenum atoms.