The incorporation of the quadruply bonded dimolybdenum(II) unit into an unusual 2-D polymeric assembly through the use of the asymmetric [4-Ph2P(O)C6H4CO2]− ligand that provides both equatorial and axial donor sites

The complex K4Mo2Cl8 reacts with the substituted benzoic acids XC6H4CO2H (X=4-Ph2P, 2-Ph2P, 4-Ph2P(O) or 4-Ph2P(S)) to form the complexes Mo2(μ-O2CC6H4-4-PPh2)4 (1), Mo2(μ-O2CC6H4-2-PPh2)4(MeOH)2 (2), {Mo2[μ-O2CC6H4-4-P(O)Ph2]4·4EtOH}n (3) and Mo2[μ-O2CC6H4-4-P(S)Ph2]4(MeOH)2 (4). The presence of coordinated methanol molecules in 2 is confirmed by a single crystal X-ray structure determination, while the crystal structure of 3 reveals that a two-dimensional polymer is formed by the coordination of a trans pair of PO groups associated with each dimolybdenum unit to the axial sites of neighboring dimolybdenum [Mo2(μ-O2CR)4] units. The other trans pair of PO groups in 3 are hydrogen-bonded to ethanol.