Novel dinuclear copper(II) complexes with phosphinato bridging ligands, [Cu-2 (NO3)(bMP)(2)(5-dmbpy)(2)]NO3.H2O (1), [Cu-2 (bMp)(2)(5-dmbpy)(2)(MeOH)(2)](BF4)(2) (2) (Hbmp = bis(4-methoxyphenyl)phosphinic acid, 5-dmbpy = 5,5-dimethyl-2,2'-bipyridine), have been prepared and characterized. Crystal structures of I and 2 have revealed that two copper(II) ions in 1 are linked by two syn-syn bridging phosphinates, whereas 2 has two syn-anti bridging phosphinates. Magnetic susceptibility data for the present complexes are well represented by the dimer equation with the 2J values of -19.1 cm(-1) for 1 and -0.7 cm(-1) for 2, indicating that weak antiferromagnetic interactions are operative.