Cluster Oxalate Complexes [M33-Q)(μ2-Q2)3(C2O4)3]2- and [Mo33-Q)(μ2-Q)3(C2O4)3(H2O)3]2- (M = Mo, W; Q = S, Se):  Mechanochemical Synthesis and Crystal Structure

Mechanochemical reaction of cluster coordination polymers 1[M3Q7Br4] (M = Mo, W; Q = S, Se) with solid K2C2O4 leads to cluster core excision with the formation of anionic complexes [M3Q7(C2O4)3]2-. Extraction of the reaction mixture with water followed by crystallization gives crystalline K2[M3Q7(C2O4)3]·0.5KBr·nH2O (M = Mo, Q = S, n = 3 (1); M = Mo, Q = Se, n = 4 (2); M = W, Q = S, n = 5 (3)). Cs2[Mo3S7(C2O4)3]·0.5CsCl·3.5H2O (4) and (Et4N)1.5H0.5K{[Mo3S7(C2O4)3]Br}·2H2O (5) were also prepared. Close Q···Br contacts result in the formation of ionic triples {[M3Q7(C2O4)3]2Br}5- in 14 and the 1:1 adduct {[Mo3S7(C2O4)3]Br}3- in 5. Treatment of 1 or 2 with PPh3 leads to chalcogen abstraction with the formation of [Mo33-Q)(μ2-Q)3(C2O4)3(H2O)3]2-, isolated as (Ph4P)2[Mo33-S)(μ2-S)3(C2O4)3(H2O)3]·11H2O (6) and (Ph4P)2[Mo33-Se)(μ2-Se)3(C2O4)3(H2O)3]·8.5H2O·0.5C2H5OH (7). All compounds were characterized by X-ray structure analysis. IR, Raman, electronic, and 77Se NMR spectra are also reported. Thermal decomposition of 13 was studied by thermogravimetry.