Cooperativity of tetrel bonds tuned by substituent effects

Substituent effects on cooperativity between N center dot center dot center dot X and C center dot center dot center dot X interactions are studied in the 4-Z-Py center dot center dot center dot XH3(NC)center dot center dot center dot XH3 (NC) complexes, where X=C, Si; Z=H, F, OH, CH3, NH2, F, NC, CN, NO2 and Py= pyridine. All N center dot center dot center dot X and C center dot center dot center dot 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 center dot center dot center dot X interaction strengthens C center dot center dot center dot X bond in these complexes and vice versa. Our results reveal that the strength of N center dot center dot center dot X and C center dot center dot center dot 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 center dot center dot center dot X and C center dot center dot center dot 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. [GRAPHICS] . The ELF representation (isosurface value=0.75 au) of 4-HPy center dot center dot center dot SiH3(NC)center dot center dot center dot SiH3 (NC) complex.