New Cu(II) complexes of sulfamethazine (4-amino-N-[4,6-dimethyl-2-pyrimidinyl]benzenesulfonamide, HL) [CU2(CH3COO)(2)(L)(2)]. 2dmf (1) and {[Cu(L)(2)]. 2H(2)O}(infinity) (2) were prepared and structurally characterized. Compound 1 crystallizes in the monoclinic system, space group P2(1)/n, with a 8.9486(9) Angstrom, b = 15.0956(12) Angstrom, c = 16.542(3) Angstrom, beta = 105.584(15)degrees, and Z = 2. Compound 2 crystallizes in the monoclinic system, space group P2(1)/c, with a 13.8097(8) Angstrom, b = 14.5765(4) Angstrom, c = 13.7853(15) Angstrom, beta = 96.033(9)degrees, and Z = 1. In compound 1 two copper ions are Linked by two syn-syn acetates and two nonlinear NCN bridging groups pertaining to the deprotonated sulfamethazine ligands. Each copper center presents a nearly square planar geometry. Magnetic susceptibility data for 1 show a strong antiferromagnetic coupling with 2J = -216.7 cm(-1). The EPR spectra at the X- and Q-band frequencies present the signals corresponding to the dinuclear entity, being the zero-field splitting parameter, D = 0.265 cm(-1). The antiferromagnetic exchange coupling is discussed using DFT calculations on some model compounds with NCN bridging ligands;and also on model structures with mixed mu -acetato and NCN bridges. The copper in the polymeric compound 2 is five coordinate. The CuN5 chromophore has a highly distorted square pyramidal geometry with small axial N-Cu-N angles of 65.53(14) and 59.90(13)degrees. In the structure a sulfamethazinate anion binds to one copper through the sulfonamido and pyrimidine N atoms and to an adjacent copper via the amino N atom.