The reaction of Cu(II) with 2-(alpha-hydroxybenzyl)thiamine in methanolic solutions produces Cu(I) and thiochrome. The crystal structure of the Cu-II(thiochrome)Cl-2 complex, formed from the reaction media, comprises an infinite array of Cu(thiochrome)Cl-2 neutral units linked together through the N(4'a) and N(1') atoms of thiochrome, coordinated to Cu(II). The copper atom is tetracoordinated with a weak Cu ... N(3') interaction in a compressed tetrahedral environment. Crystallographic data : space group P2(1), a = 7.433(1) Angstrom, b = 11.826(6) Angstrom, c = 10.009(2) Angstrom, beta = 91.25(1)degrees, V = 879.7(5) Angstrom(3), Z = 2. Continuous wave EPR spectroscopy shows that this conformation is retained in frozen solution. Magnetic susceptibility data in the 2-300 K temperature range showed that the mu(eff)/Cu variation (1.68-1.74 mu(B)) was negligible, indicating the absence of magnetic interactions between the Cu(lI) ions. In Cu-II(thiochrome)Cl-2 the magnetic interaction between the N(3') nitrogen of the pyrimidine ring and the copper d(x2-y2) electron spin is detected by ESEEM spectroscopy. The ESEEM data show the existence of a weak magnetic interaction (A(x) = 1.6 MHz, A(y) = 1.4 MHz, A(z) = 1.0 MHz) between the Cu unpaired electron spin and the nucleus of the N-14(3') of the pyrimidine ring. The nuclear quadrupole parameters for the nitrogen (e(2)qQ/h = 3.1 MHz, eta = 0.25) differ from those in crystalline pyrimidine, and this is discussed in terms of the electron distribution on the pyrimidine ring in the Cu-II(thiochrome)Cl-2 complex. It is once more shown that the ESEEM technique can provide useful structural information on similar inorganic systems, in the absence of X-ray diffraction data.