The importance of tetrel bonding interactions with carbon in two arrestive iso-structural Cd(ii)–Salen coordination complexes: a comprehensive DFT overview in crystal engineering

In this article, we describe the serendipitous synthesis of two remarkable iso-structural Cd(ii)–Salen complexes [L2Cd4(OAc)2(NCS)2] in the presence of H2L and NaSCN {where L = L1 (N,N′-bis(3-methoxysalicylidene)-1,2-diaminopropane) and L = L2 (N,N′-bis(3-methoxysalicylidene)-ethylenediamine) in 1 and 2, respectively}. The complexes were characterized by using elemental analysis, SEM-EDX, PXRD, spectroscopy, and X-ray crystallography. The X-ray crystal structure revealed that both complexes crystallize in the orthorhombic space group Pbcn, with unit cell parameters: a = 20.758(6), b = 11.022(3), c = 21.396(6) Å, V = 4895(2) Å3, and Z = 4. The inner N2O2 and outer O4 compartments are essentially occupied by two different Cd(ii) metal ions resulting from the de-protonated form of the ligand (L2−) with the Cd(1) metal ions adopting a capped octahedral geometry. At the same time, Cd(2) assumes a distorted trigonal prismatic geometry. The solid-state crystal structure involves various non-covalent supramolecular interactions delineated by Hirshfeld Surface and 2D fingerprint plot analysis. Noteworthily, interesting S⋯H, O⋯H, and N⋯H contacts were observed, which have identical percentages in both complexes. The sparse tetrel bonding interactions in the complex, involving the CH3 group, were evaluated in a new dimension of DFT. We observed this privileged bonding landscape that leads to the formation of self-assembled dimers in the crystal complexes. DFT-based MEP, RDG surface, NBO, and QTAIM/NCI plot investigation quantified such unique tetrel bonding interactions.