The mixed-valence Cu(I)/Cu(II) complexes (Ph3P)4CuI2CuII(O2CCH2CO2)2 (1) and (Cy3P)4CuI2CuII(O2CCH2-CO2)2 (2), have been prepared from the acid-base reaction of Cu(II)(acac)2 or Cu(II)(butyrate)2 with the respective copper(I) hydrogen dicarboxylate derivative and their solid-state structures determined crystallographically. The Cu(II) center in both derivatives is chelated by two malonate dianions in a square-planar geometry. In complex 1 the two bis(triphenylphosphine)copper(I) moieties are coordinated to the internal oxygen atoms of the Cu(II) malonate core at an average distance of 2.177 [4] angstrom, resulting in a Cu(I)...Cu(II) separation of 3.132(1) angstrom. On the other hand in complex 2 the two bis(tricyclohexylphosphine)copper(I) groups are appended asymmetrically to opposite ketonic oxygens of the malonate ligands, hence affording a larger Cu(I)...Cu(II) separation of 4.600(1) angstrom. That is, the Cu(I) center in complex 1 is four-coordinate and a distorted tetrahedron, whereas in complex 2 the Cu(I) center is three-coordinate and trigonal planar. These structural differences, which persist in dichloromethane solution, are ascribed to the steric requirements of the phosphine ligands. Crystal data for 1 : space group P2(1)/n, a = 9.978(2) angstrom, b = 23.365(5) angstrom, c= 16.703(10) angstrom, beta = 103.840(0)degrees, Z = 2, R = 6.04%. Crystal data for 2 : space group P1BAR, a = 9.7280(10) angstrom, b = 15.084(2) A, c = 17.198(2) angstrom, alpha = 103.910(10)degrees, beta = 98.680(10)degrees, gamma = 102.890(10)degrees, Z = 1, R = 5.89%.