The question of the (N,S) vs. (S,S) coordination mode on M · (ACDA)2 complexes (ACDA=2-aminocyclopentene-1-dithiocarboxylic acid, M=Ni2+, Pd2+, Pt2+) was assessed through an extensive ab initio study, using the hybrid B3LYP density functional approach. The (S,S) coordination was found to be the most stable one, with an energy difference of ca. 50 kJ mol−1 relative to the (N,S) coordination mode. Detailed analysis of the ab initio results indicates that this preference is a result of the combined effect of geometry constraints and electron distribution within the complex.