Theoretical studies on conformational analysis, geometry optimizations and frequencies for citrate at the MP2/LAN-L2DZ level portrait it as a promising candidate for a complexing agent for cadmium (II) ion (Cd 2+) and cadmium sulfide (CdS). Natural Bond Orbital (NBO) charges, Delocalization Indices, HOMO/LUMO gaps and surfaces along with absolute electronegativity values were employed to analyze the interactions among the configurations obtained. The most stable structures involved the interaction between the LUMO of Cd 2+ /CdS and the most dense region of the HOMO of the citrate ion.