The copper complexes with the commercial auxin herbicides MCPA, 2,4-D, and 2,4,5-T in the presence of a nitrogen donor heterocyclic ligand, phen or bipyam, were prepared and characterized. The available evidence supports a dimeric structure for the 2,4-D complex in the presence of bipyam while phen leads to monomeric forms. The EPR spectrum of Cu2(2,4-D)4(bipyam)2 at 4 K in the solid state exhibits an axial signal which corresponds to almost isolated S = 1/2 magnetic ions. Magnetic data for the dimer show a weak antiferromagnetic interaction between the two metal ions with J = -08 cm-1. The crystal structures of tetrakis[(2,4-dichlorophenoxy)acetato]bis(2,2'-bipyridylamine)dicopper(II), 1, bis(1,10-phenanthroline)[(2,4,5-trichlorophenoxy)acetato]copper(II) chloride, 2, and aqua(1,10-phenanthroline)bis[((2-methyl-4-chlorophenoxyacetato]copper(II), 3, were determined and refined by least-squares methods using three-dimensional MoK alpha data. 1 crystallizes in space group P1, in a cell of dimensions a = 10813(1) A, b = 12138(1) A, c = 11909(1) A, alpha = 86448(3) degrees, beta = 80127(3) degrees, and gamma = 63982(3) degrees, and V = 13837(2) A3, with Z = 1 2 crystallizes in space group I2/a, in a cell of dimensions a = 29958(9) A, b = 11342(3) A, c = 21196(7) A, beta = 10794(1) degrees, and V = 68522(4) A3, with Z = 8 3 crystallizes in space group P1, in a cell of dimensions a = 87419(8) A, b = 12512(1) A, c = 14598(1) A, alpha = 110737(1) degrees, beta = 95742(2) degrees, gamma = 103286(2) degrees, V = 14241(2) A3, with Z = 2.