Experimental and Theoretical Survey of Intramolecular Spodium Bonds/σ/π-Holes and Noncovalent Interactions in Trinuclear Zn(II)-Salen Type Complex with OCN- Ions: A Holistic View in Crystal Engineering

Dhrubajyoti Majumdar; Antonio Frontera; Sourav Roy; Dipankar Sutradhar

doi:10.1021/acsomega.3c08422

Experimental and Theoretical Survey of Intramolecular Spodium Bonds/σ/π-Holes and Noncovalent Interactions in Trinuclear Zn(II)-Salen Type Complex with OCN^- Ions: A Holistic View in Crystal Engineering

ACS Omega. 2023 Dec 19;9(1):1786-1797. doi: 10.1021/acsomega.3c08422. eCollection 2024 Jan 9.

Authors

Dhrubajyoti Majumdar¹, Antonio Frontera², Sourav Roy³, Dipankar Sutradhar⁴

Affiliations

¹ Department of Chemistry, Tamralipta Mahavidyalaya, Tamluk, West Bengal 721636, India.
² Department de Quimica, Universitat de les Illes Balears, Cra. de Valldemossa km 7.5, Palma de Mallorca (Baleares) 07122, Spain.
³ Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India.
⁴ School of Advanced Sciences and Languages, VIT Bhopal University, Kothrikalan, Sehore, Madhya Pradesh 466114, India.

Abstract

In this work, one new centrosymmetric trinuclear Zn(II) complex 1, [{(OCN)Zn(L)}₂Zn], using a salen-type ligand (H₂L) in the presence of OCN^- was synthesized and characterized via elemental, spectral, SEM-EDX, and single-crystal X-ray diffraction (SCXRD) study. In 1, SCXRD reveals two different stereochemical environments of zinc metal ions; one terminal Zn(II) center adopts square pyramidal geometries with the Addison parameter (τ) 0.095, and the central Zn(II) is tetracoordinated tetrahedral geometry. This article provides evidence of the significance and presence of spodium bonds (SpBs) in solid-state crystal structures involving a pseudotetrahedral environment of the central Zn-atom. X-ray structures reveal intramolecular Zn···O SpBs caused by the methoxy (-OCH₃) substituent O-atom adjacent to the coordinated phenoxy O-atom. These noncovalent interactions have been thoroughly studied using density functional theory calculations at the RI-BP86[2]-D3[3]/def2-TZVP level of theory that characterizes the nature of SpBs, including the Baders quantum theory of atoms-in-molecules "QTAIM", molecular electrostatic potential (MEP) surface, and noncovalent index plot (NCI). In addition, a unique complex-isomer-based theoretical model has been vividly employed to estimate the SpBs energy in the complex. Natural bond orbital (NBO) analysis also tries to establish the differentiation between σ-hole and π-hole SpBs' natures more authentically. The complex energy frameworks were used to investigate noncovalent interactions. To better understand the different intermolecular interactions, we conducted a Hirshfeld surface, which revealed N···H (15.4%) and O···H (9.1%) contacts and Zn···O (5.1%) (SpBs).