Reaction of the molybdenum(III) complex Mo2Cl6(THF)(3) with diethylamine at room temperature causes reduction of the starting compound to produce the dimolybdenum(II) complex Mo2Cl4(NHEt2)(4) (1). It was shown that the Cl- anions released by the substitution with amine can react with more of the starting material to give side products of molybdenum(III). Four such products were isolated and characterized : [NH2Et2] [MoCl4(NHEt2)(2)] (2), [NH2Et2][Mo2Cl7(NHEt2)(2)] (3), [NH2Et2](2)[MoCl5(NHEt2)] (4), and [NH2Et2](3)[Mo2Cl8(NEt2)] (5). The crystal structures of all complexes 1-5 have been investigated by X-ray diffraction. The structure of 1 consists of two trans-MoCl2(NHEt2)(2) units joined by a quadruple Mo-Mo bond (2.1330(6) Angstrom). The crystallographic parameters for compounds 1-5 are as follows : for 1, monoclinic space group C2/c with a 20.846(1) Angstrom, b = 7.044(1) Angstrom, c = 19.868(3) Angstrom, beta = 118.72(2)degrees, and Z = 4; for 2, triclinic space group with a = 9.820(3) Angstrom, b = 10.305(1) Angstrom, c = 11.510(1) Angstrom, alpha = 95.779(8)degrees, beta = 97.80(2)degrees, gamma = 111.17(1)degrees, and Z = 2; for 3, monoclinic space group P2(1)/n with a 13.847(5) Angstrom, b = 10.448(4) Angstrom, c = 22.091(4) Angstrom, beta = 96.68(2)degrees, and Z = 4; for 4, monoclinic space group P2(1)/c with a = 11.710(2) Angstrom, b = 12.363(2) Angstrom, c = 30.272(7) Angstrom, beta = 95.87(2)degrees, and Z = 8; for 5, monoclinic space group P2(1)/n with a = 10.335(1) Angstrom, b = 18.061(1) Angstrom, c = 16.775(1) Angstrom, beta = 95.558(8)degrees, and Z = 4.