MII···Cl Interaction Supported Heterometallic {NiIISnII}{SnIV} and {NiIISnII}{SnII} Complex Salts: Possibility of Ion-Pair-Assisted Tetrel Bonds

Crystal structures and theoretical calculations on the ion pairs of two types of heterometallic {NiIISnII}{SnIV} (type I) and {NiIISnII}{SnII} (type II) complex salts synthesized from the self-assembly reaction of the Schiff base N,N′-ethylenebis(3-methoxysalicylaldimine) (H2L1), N,N′-ethylenebis(3-ethoxysalicylaldimine) (H2L2), or N,N’-bis(3-methoxysalicylidene)-1,2-cyclohexanediamine (H2L3) with an adequate mixture of NiCl2·6H2O, SnCl2, and SnCl4·5H2O are presented. The heterometallic cation [NiIISnIIL(Cl)]+ is neutralized and stabilized by half of the hexachlorostannate(IV) [SnIVCl6]2– [in type I: L = L1 (1), L2 (2)] or by the trichlorostannate(II) [SnIICl3]− [in type II: L = L1 (3), L2 (4), L3 (5)]. Ion pairs in the crystal structures of the 1–7 interact via a variety of MII···Cl interactions (M = Ni, Cu, Sn) along with H bonds. Hirshfeld surface analysis was carried out to discover any other weak interactions such as π···π. Detailed geometrical analysis reveals that SnII···Cl interactions are dependent on the oxidation state of the metal halide donor, being lengthened with a higher oxidation state (SnII to SnIV). Structural comparison of 4 with the previously reported {CuIISnII}{SnII} derivatives (6 and 7) of H2L1 and H2L2 reveals that the length of other MII···Cl interactions (MII = Ni, Cu), being dependent on the halide acceptor [NiII (d8) or CuII (d9) system], decreases from the d8 metal ion system to the d9 system and hence that interaction (NiII···Cl) in 4 converts virtually to a covalent bond (CuII–Cl) in 6 and 7. The nature of ion-pair interactions in 1 and 3 was further investigated by DFT calculations with application of the QTAIM, ESP, NBO, and NCI methods. Significant charge transfer from the Cl to Sn atoms allows the characterization of the Sn···Cl interactions in these complex salts as an uncommon ion-pair-assisted Sn···Cl tetrel bond. © 2021 American Chemical Society