Coordination versus spodium bonds in dinuclear Zn( ii ) and Cd( ii ) complexes with a dithiophosphate ligand

• Published in: New journal of chemistry 2021-10, Vol.45 (41), p.19402-19415
• Main Authors: Kumar, Pretam, Frontera, Antonio, Pandey, Sushil K.
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Cadmium compounds; Coordination compounds; Covalence; Crystal lattices; Crystallography; Ligands; Quantum theory; Sulfur; Zinc
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/D1NJ03165A

The important role of spodium bonding (SpB) in Zn( ii ) and Cd( ii ) complexes is highlighted in this feature article. SpB has been recommended to distinguish coordination bonds (high covalent character) from non-covalent contacts. Here, two new d 10 -metal dithiophosphate complexes, [M(L) 2 ] 2 {where M = Zn (1) and Cd (2); L = O , O ′-bis(4- tert -butylphenyl) phosphorodithioate} have been synthesized in purely aqueous media and characterized by elemental and spectral analyses. The X-ray crystallography analyses indicate that both complexes are dinuclear, in which each metal atom is coordinated with four sulfur atoms in a distorted tetrahedral environment containing two four-membered chelate rings joined to a central eight-membered ring through metal (Zn/Cd) atoms. In complex 1 the eight-membered ring possesses a “saddle” conformation located on a two-fold axis of symmetry, C 2 , while in complex 2 it possesses a centrosymmetric “twisted chair” conformation, C i . In addition, the oxygen and sulfur atoms belonging to the bridging ligands form intramolecular SpBs with Zn( ii ) in 1 and Cd( ii ) in 2. The existence of intramolecular SpBs in both complexes is evidenced by DFT calculations by using the Bader's Quantum Theory of Atoms-in-Molecules (QTAIM) combined with the non-covalent interaction plot (NCI plot) index that is based on the reduced density gradient (NCI-RDG) method. A Hirshfeld surface study has been carried out to understand the intermolecular contacts in the crystal lattice.