The reactions of the binuclear oxomolybdenum(V) complex [Cl-2(O)Mo(mu-OEt)(2)(mu-HOEt)Mo(O)Cl-2] (1) with Me(3)Si(allyl) and SbF3 produce the compounds [Mo6O6Cl6(mu(3)-O)(2)(mu(2)-OEt)(6)(mu 2-Cl)(2)] (2) and [Mo8O8Cl6(mu(3)-O)(4)(OH)(2)(mu(2)-OH)(4)(mu(2)-OEt>(4)(HoEt>4] (3), respectively. Treatment of 1 with the Lewis base PMe(3) affords the tetrameric complex [Mo4O4Cl4(mu(2)-OEt)(4)(HOEt)(2)(mu(3)-O)(?)2] (4), which represents another link in the chain of clusters produced by the reactions of 1 and simulating the build-up of polymeric molybdenum oxides by sol-gel methods. The crystal structure of 4 has been determined [C12H32Cl4Mo4O12, triclinic, P (1) over bar, a = 7.376(2) Angstrom, b = 8.807(3) Angstrom, c = 11.467(4) Angstrom, alpha = 109.61(1)degrees, beta = 92.12(3)degrees, gamma = 103.75(2)degrees, Z = 1]. By contrast, reaction of 1 with the nitrogen base NEt(3), followed by treatment with [PPN]Cl . 2H(2)O ([PPN](+) = [Ph(3)P=N=PPh(3)](+)), gives the complex [PPN](+)[Et(3)NH](+)[Cl-2(O)Mo(mu(2)-O)(2)Mo(O)Cl-2](2-) (6) in 90% yield. Its crystal structure [C36H30Cl4MoNOP2, triclinic, Pna2(1), a = 21.470(6) Angstrom, b = 16.765(2) Angstrom, c = 9.6155(14) Angstrom, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, Z = 16] includes the anion [Cl-2(O)Mo(mu(2)-0)(2)Mo(O)Cl-2-](2-) which is a charged derivative of the species forming the gels in sol-gel processes starting from chloromolybdenum ethoxides. Futhermore, compound 1 is found to be catalytically active in esterification and dehydration reactions of alcohols.