A seven-electron cluster [Mo-3(mu(3)-S) {mu(3)-SC(CO2CH3)=C(CO2CH3) S} {mu-SC(CO2CH3)=CH(CO2CH3)}(dtp)(3)(mu-OAc)] [2, S2P(OC2-H-5) (-)(2); dtp) diethyldithiophosphate] and an organometallic cluster [Mo-3(mu(3)-S) {mu(3)-SC(CO2CH3)=C(CO2CH3) S} {mu-SC(CO2CH3) CH( OCH3)(CO2)}(dtp)(2)(CH3OH)(mu-OAc)](Mo - C) ( 3) were obtained by reaction in methanol of the sulfur-bridged trinuclear complex [Mo-3( mu(3)-S)(mu-S)(3)(dtp)(3)(CH3CN)(mu-OAc)] ( 1) with dimethylacetylenedicarboxylate (DMAD). The X-ray structures of 2 and 3 revealed the adduct formation of two DMAD molecules to the respective Mo3S4 cores. 2 is paramagnetic and obeys the Curie - Weiss law: the mu(eff) value at 300 K is 1.90 mu(B). The electron spin resonance signal was observed at 173 K. The density functional theory calculation of 2 demonstrated that the main components of the singly occupied molecular orbitals of alpha and beta spins are Mo d electrons and the main components of lowest unoccupied molecular orbitals are of Mo and the olefin moiety with one C - S bond. A one-electron reversible oxidation process of 2 was observed at E-1/2 = - 0.11 V vs Fc/Fc(+). The electronic spectrum of 2 has a peak at 468 nm (epsilon = 2170 M-1 cm(-1)) and shoulders at 640 ( 918) and 797 ( 605) nm, and 3 has shoulders at 441 ( 1740) and 578 ( 625) nm and a distinct peak at 840 (467) nm. An intermediate [Mo-3(mu(3)-S) {mu(3)-SC( CO2CH3)=C(CO2CH3) S} {mu- SC(CO2CH3) =CH(CO2CH3)}(dtp)(3)( mu-OAc)](+) ( 4) is tentatively suggested: a one-electron reduction of 4 gives 2, and a nucleophilic conjugate addition of CH3O- to the alpha,beta-unsaturated carbonyl group of 4 gives 3.