Coordination Behavior of Ni²⁺, Cu²⁺, and Zn²⁺ in Tetrahedral 1-Methylimidazole Complexes: A DFT/CSD Study

Table 5

Second-order perturbation theory of the Fock matrix in the NBO basis for Ni-1MeIm.

Donor	Acceptor
Ni1	N2	E(2)	N9	E(2)	N16	E(2)	N23	E(2)
LP(1)	RY ∗ (1)	0.24	RY ∗ (1)	0.03	RY ∗ (2)	0.16	RY ∗ (1)	0.24
LP(2)	RY ∗ (1)	0.27	RY ∗ (2)	0.03	RY ∗ (1)	0.45	RY ∗ (2)	0.08
LP(3)	RY ∗ (2)	0.13	RY ∗ (3)	0.05	RY ∗ (1)	0.10	RY ∗ (1)	0.13
LP(4)	RY ∗ (1)	0.07	RY ∗ (1)	0.07	RY ∗ (1)	0.07	RY ∗ (1)	0.68
LP(5)	RY ∗ (2)	0.04	RY ∗ (1)	0.32	—	—	RY ∗ (3)	0.06

Notable interactions in Ni-1MeIm include LP(2)Ni1 → RY ∗ (1)N2 and LP(2)Ni1 → RY ∗ (1)N16 of energies 0.27 and 0.45 kcal/mol, respectively, and also LP(4)Ni1 → RY ∗ (1)N23 of energy 0.68 kcal/mol. This delocalization of d-electrons onto non-Lewis orbitals could contribute to the decrease in occupancy of the Ni²⁺ d-orbitals [31]. In the case of Cu-1MeIm, similar interaction energies were observed: LP(1)Cu49 → RY∗(1)N1, LP(1)Cu49 → RY ∗ (1)N22, LP(4)Cu49 → RY ∗ (1)N1, and LP(4)Cu49 → RY ∗ (1)N22 of energies 0.32, 0.32, 0.29, and 0.29 kcal/mol, respectively.