Mechanochemical reaction of cluster coordination polymers 1(infinity)[M(3)Q(7)Br(4)] (M = Mo, W; Q = S, Se) with solid K2C2O4 leads to cluster core excision with the formation of anionic complexes [M(3)Q(7)(C2O4)(3)](2-). Extraction of the reaction mixture with water followed by crystallization gives crystalline K-2[M(3)Q(7)(C2O4)(3)]center dot 0.5KBr center dot nH(2)O (M = MO, Q = S, n = 3 (1); M = Mo, Q = Se, n = 4 (2); M = W, Q = S, n = 5 (3)). Cs-2[Mo3S7(C2O4)(3)]center dot 0.5CsCl.3.5H(2)O (4) and (Et4N)(1.5)H0.5K{[Mo3S7(C2O4)(3)]Br}center dot 2H(2)O (5) were also prepared. Close Q(...)Br contacts result in the formation of ionic triples {[M(3)Q(7)(C2O4)(3)](2)Br}(5-) in 1-4 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 [Mo-3(mu(3)-Q)(mu(2)-Q)(3)(C2O4)(3)(H2O)(3)](2-), isolated as (Ph4P)(2)[Mo-3(mu(3)-S)(mu(2)-S)(3)(C2O4)(3)(H2O)(3)]center dot 11H(2)O (6) and (Ph4P)(2)[Mo-3(U-3-Se)(mu(2)-Se)(3)(C2O4)(3)(H2O)(3)]center dot 8.5H(2)O center dot 0.5C(2)H(5)OH (7). All compounds were characterized by X-ray structure analysis. IR, Raman, electronic, and Se-77 NMR spectra are also reported. Thermal decomposition of 1-3 was studied by thermogravimetry.