The structures, electronic and magnetic properties of the TM(isq)2 (isq=o-diiminobenzosemiquinonate) clusters have been investigated by using the PBE functional. The lengths of TM-N bonds of the TM(isq)2 clusters are as follows: 3d<5d<4d. According to the binding energies per atom of the TM(isq)2 clusters, the 5d TM(isq)2 clusters are more structurally stable than the corresponding 3d TM(isq)2 and 4d TM(isq)2 clusters except for the Lu(isq)2 and Hg(isq)2 clusters. According to the HOMO–LUMO gaps of the TM(isq)2 clusters, the 5d TM(isq)2 clusters are more kinetically stable than corresponding 3d TM(isq)2 and 4d TM(isq)2 clusters except for the Lu(isq)2 and W(isq)2 clusters. As for the TM(isq)2 clusters, the TM atoms lose a small amount of electrons within the scope of 0.375|e|∼1.755|e|. Maximum Mülliken spin densities (3.228|e|,0.963|e|,2.560|e| and 2.266|e|) of TM atoms of the TM(isq)2 clusters occur at Cr, Co, Mo and W.