Substituent effects on cooperativity between N•••X and C•••X interactions are studied in the 4-Z-Py•••XH3(NC)•••XH3(NC) complexes, where X=C, Si; Z=H, F, OH, CH3, NH2, F, NC, CN, NO2 and Py=pyridine. All N•••X and C•••X binding distances in the ternary complexes are always shorter than those in the corresponding binary complex. This indicates that the formation of the N•••X interaction strengthens C•••X bond in these complexes and vice versa. Our results reveal that the strength of N•••X and C•••X interactions in the ternary complexes considerably depends on the nature of X and Z substituents. For a given aromatic system, the shortening of N•••X and C•••X distances is more important for SiH3(NC) complexes than CH3(NC) counterparts. The mechanism of cooperative effects in the ternary complexes is unveiled by electrostatic potential analyses and natural bond theory.
