Copper(II) Complexes with 4-Amino-N-[4,6-dimethyl-2-pyrimidinyl]benzenesulfonamide. Synthesis, Crystal Structure, Magnetic Properties, EPR, and Theoretical Studies of a Novel Mixed μ-Carboxylato, NCN-Bridged Dinuclear Copper Compound

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]·2H2O} (2) were prepared and structurally characterized. Compound 1 crystallizes in the monoclinic system, space group P21/n, with a = 8.9486(9) Å, b = 15.0956(12) Å, c = 16.542(3) Å, β = 105.584(15)°, and Z = 2. Compound 2 crystallizes in the monoclinic system, space group P21/c, with a = 13.8097(8) Å, b = 14.5765(4) Å, c = 13.7853(15) Å, β = 96.033(9)°, 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 μ-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)°. 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.