The crystal structure of the compound bis(mu-bromo)bis[bromobis(dmtp)copper(II)] dihydrate (where dmtp = 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine) has been determined from single-crystal X-ray diffraction methods. The crystal belongs to the triclinic system, space group P ($) over bar 1, with a = 9.614(4) Angstrom, b = 12.370(6) Angstrom, c = 9.645(4) Angstrom, alpha = 99.01(3)degrees, beta = 60.17(3)degrees, gamma = 79.61(4)degrees, Z = 2, D-calcd = 1.906 g.cm(-3), R = 0.053 for 2188 observed reflections. The structure of the complex consists of dimeric molecules [Cu(dmtP)(2)Br-2](2) in which copper atoms are bridged by bromine ligands. The geometry at copper is a distorted trigonal bipyramid with bromine atoms occupying equatorial positions and N3-coordinated dmtp ligands in apical posistions. The Cu-Cu separation is 3.603(3) Angstrom, and Cu-bridging Br distances are 2.588(2) and 2.706(2) Angstrom. The magnetic susceptibility of a powdered sample has been measured in the 4.1-250.5 K temperature range and the data have been fitted to the modified Bleany-Bowers equation for exchange coupled copper(II) dimers indicating an antiferromagnetic coupling with a singlet-triplet separation of approximately 20 cm(-1). A comparison to other bis(mu-bromine)-bridged five-coordinated copper dimers has been made, showing that the magnetic interaction strength can be correlated to the arrangement of bromine atoms around the copper.