The crystal and molecular structure of bis(mu-3-pyridin-2-yl-1,2,4-triazolato-N’N1,N2)(sulfato-O)aquacopper(II)-diaquacopper(II) trihydrate (Cu2C14H22NgO10S; [Cu(Pt)2(SO4)(H2O)3](H2O)3 (1), in which pt is 3-pyridin-2-yl-1,2,4-triazolato) was determined by X-ray diffraction methods. Crystal data for 1 : T = 298 K, monoclinic, space group = P2(1)/a, a = 13.0234(5) angstrom, b = 13.4212(6) angstrom, c = 14.1119(4) angstrom, beta = 116.462(3)-degrees, Z = 4 (dinuclear molecules), and V = 2208.2(2) angstrom3. The least-squares refinement based on 3260 significant reflections [I > 2.5sigma(I)] converged to R = 0.045 and R(W) = 0.068. The structure of 1 consists of asymmetric dinuclear units, in which two symmetry independent copper(II) ions are linked by two dehydronated Hpt ligands (i.e., ligands having lost H+) bridging via N1,N2 in the equatorial plane. Both copper(II) ions are in a distorted square pyramidal environment, of which the basal plane around Cu2 is completed by a monodentate coordinating sulfate (Cu2-O11 = 2.000(3) angstrom), whereas a water molecule is coordinated to Cu1 (Cu1-O2 = 2.004(3) angstrom). Water molecules occupy the apical positions of both copper ions (Cu1-O1 = 2.219(5) angstrom, Cu2-O3 = 2.223(5) angstrom). The Cu1-Cu2 distance within the dinuclear unit is 4.0265(8) angstrom. The dinuclear units are stacked in pairs in such a way as to form tetranuclear units with a shortest Cu1-Cu2" (-x, -y, -z) distance of 3.997(1) angstrom. The two ligand planes are above each other at a stacking distance of 3.34 A. The magnetic susceptibility data (10-293 K) are interpreted on the basis of the spin Hamiltonian H = -2J(S(Cu1).S(Cu2)), yielding J = -49 cm-1 and g = 2.00. The magnetic data are compared to those obtained for related double 1,2,4-triazole-N1,N2 bridged dinuclear copper(II) compounds, and magneto-structural correlations are presented for the first time for this type of dimer. The superexchange pathway involves the sigma orbitals of the diazine-N1,N2 moiety of the bridging triazole network. A relation between the bridging ligand geometry (reflected in the Cu-N-N angles) and the magnitude of the magnetic interaction has been derived. The X-band powder EPR spectra, recorded at various temperatures, are typical of a triplet spin state lying above the singlet ground state.