The technetium(iii) compound (n-Bu4N)2[Tc 2Br8] was prepared by metathesis of (n-Bu 4N)2[Tc2Cl8] with concentrated aqueous HBr in acetone and recrystallized from acetone-diethyl ether solution (2: 1 v/v). The acetone solvate obtained, (n-Bu4N) 2[Tc2Br8]·4[(CH3) 2CO] (1), crystallizes in the monoclinic space group P21/n with a = 13.8959(8) , b = 15.2597(9) , c = 15.5741(9) , β = 109.107(1)°, R1 = 0.028, and Z = 4. The Tc-Tc distance (2.1625(9)) and the average Tc-Br distances (2.4734(7) ) are in excellent agreement with those previously determined by EXAFS spectroscopy. These and other experimental data on quadruply metal-metal bonded group 7 [M 2X8] 2- dimers (M = Tc, Re; X = Cl, Br) are compared to the results of a set of multi-configurational quantum chemical studies. The calculated molecular structures of the ground states are in very good agreement with the structures determined experimentally. The theory overestimates the δ→δ* transition energies by some 1000 cm-1, but mimics the trends in δ→δ* energies across the series.