Synthesis, structural characterization, and theoretical analysis of novel zinc(ii) schiff base complexes with halogen and hydrogen bonding interactions

In this article, we present the synthesis and characterization of three zinc(ii) complexes, [ZnII(HL1)2] (1), [ZnII(HL2)2]·2H2O (2) and [ZnII(HL3)2] (3), with three tridentate Schiff base ligands, H2L1, H2L2, and H2L3. The structures of the complexes were confirmed by single-crystal X-ray diffraction analysis. DFT calculations were performed to gain insights into the self-assembly of the complexes in their solid-state structures. Complex 1 exhibits dual halogen-bonding interactions (Br⋯Br and Br⋯O) in its solid-state structure, which have been thoroughly investigated through molecular electrostatic potential (MEP) surface calculations, alongside QTAIM and NCIPlot analyses. Furthermore, complex 2 features a fascinating hydrogen-bonding network involving lattice water molecules, which serves to link the [ZnII(HL2)2] units into a one-dimensional supramolecular polymer. This network has been meticulously examined using QTAIM and NCIplot analyses, allowing for an estimation of the hydrogen bond strengths. The significance of H-bonds and CH⋯π interactions in complex 3 was investigated, as these interactions are crucial for the formation of infinite 1D chains in the solid state.

An insight into the hydrogen bonding, halogen bonding and chalcogen bonding interactions in manganese(iii) complexes with N2O2donor salicylidine Schiff base ligands

Four manganese(iii) complexes, [MnL¹(H₂O)₂]ClO₄·H₂O (1), [MnL²(H₂O)₂]ClO₄ (2), [MnL³(DMSO)(H₂O)]ClO₄ (3) and [MnL⁴(DMSO)(H₂O)]ClO₄ (4), where H₂L¹ = N,N'-bis(5-bromosalicylidene)-1,3-diaminopropane, H₂L² = 2,2-dimethyl-N,N-bis(3-methyloxysalicylidene)-1,3-diaminopropane, H₂L³ = N,N'-bis(5-chlorosalicylidene)-2,2-dimethyl-1,3-diaminopropane and H₂L⁴ = 2-hydroxy-N,N'-bis(3-ethyloxysalicylidene)-1,3-diaminopropane are tetradentate N₂O₂-donor ligands and DMSO = dimethyl sulfoxide, have been synthesized and characterised by elemental analysis, IR and UV-vis spectroscopy and single-crystal X-ray diffraction studies. All are monomeric complexes. Complex 1 crystallises in orthorhombic space group P2₁2₁2₁, complex 3 crystallises in triclinic space group P-1, whereas complexes 2 and 4 crystallize in monoclinic space groups, C2/c and C2/m respectively. In all the complexes, manganese(iii) has a six-coordinated pseudo-octahedral geometry in which imine nitrogen atoms and phenolate oxygen atoms of the deprotonated di-Schiff base constitute the equatorial plane. In complexes 1 and 2, water molecules are present in the fifth and sixth coordination sites in the axial positions while in complexes 3 and 4 they are occupied by one water and one DMSO. The coordinated water molecules initiate hydrogen-bonded networks in all complexes. DFT calculations have been carried out to analyze two aspects of these complexes viz. the formation of halogen (HaB) and chalcogen bonding (ChB) interactions in complexes 1 and 3 where the electron donor is the perchlorate anion and the acceptor either bromine or chlorine atoms for the HaBs and the sulfur atom of the coordinated DMSO for the ChB. In addition, other intermolecular effects are discussed in the solid state for complexes 1, 2 and 4, where the hydrogen atoms of the coordinated water molecules interact with the electron rich cavities formed by the phenolate and alkyloxy oxygen atoms of the Schiff-base ligand.

Principles Guiding the Square Bonding Motif Containing a Pair of Chalcogen Bonds between Chalcogenadiazoles

The bonding motif adopted by a dimer of chalcogenadiazole molecules is characterized by a pair of equivalent Ch···N chalcogen bonds. Quantum calculations show that the interaction energy is substantial, varying between 4 kcal/mol for Ch = S and 17 kcal/mol for Te. The interaction is cooperative in that the total bond strength is greater than either chalcogen bond individually. Neither the addition of a phenyl ring nor the addition of a pair of cyano substituents to the diazole ring has much influence on this binding. Removal of one N from the diazole weakens the binding, and addition of two nitrogens has little effect. The largest perturbation arises with three N atoms in each ring, for which the binding energy increases by some 25%. The ring size plays a minor role in most cases, although a near doubling of bond strength occurs if there are two N atoms present on a four-membered ring.

Synthesis, spectroscopic findings and crystal engineering of Pb(ii)-Salen coordination polymers, and supramolecular architectures engineered by σ-hole/spodium/tetrel bonds: a combined experimental and theoretical investigation

Spontaneous self-assembly is one of the available synthetic routes to achieve structurally versatile and unique crystal complexes with selected metal-ligand combinations in the spirit of pseudohalides. In this endeavour, we designed a novel 1D coordination polymer (CP), [(Cd)(Pb)(L)(η¹-NCS)(η¹-SCN)] _n (1), using a compartmental Salen ligand (H₃L) in the presence of NaSCN. The characterization of the CP was accomplished using several spectroscopic techniques: MALDI-TOF, PXRD, SEM, EDX mapping, and single-crystal X-ray crystallography. The CP crystallizes in the monoclinic space group P2₁/c with Z = 4. SCXRD reveals Cd(ii) and Pb(ii) metal ions fulfilled distorted square pyramidal and hemi-directed coordination spheres. Cd(ii) is placed in the inner N₂O₂ and heavier Pb(ii) in the outer O₄ compartments of the de-protonated form of the ligand [L]^2-. Supramolecular interactions in the intricate crystal structure produced attractive molecular architectures of the compound. The flexible aliphatic -OH pendent group coordinates with the Pb(ii) ions. This unique binding further elevates the supramolecular crystal topographies. The supramolecular interactions were authenticated by Hirshfeld surface analysis (HSA). The observation of the recurring unconventional tetrel bonds was rationalized by DFT calculations and surface plots of molecular electrostatic potential (MEP). In the 1D polymeric chain in the complex, the O-atom of the -OH groups shows a tetrel bonding interaction with the Pb atom. We have found that the combination of QTAIM/NCI and QTAIM/ELF plots helps reveal the nature of these contacts. Moreover, the QTAIM/ELF plot determines the donor-acceptor interaction between the O-atom and the Pb atom, establishing the σ-hole. Agreeably, the σ-hole interaction also helps Pb(ii) serve as a Lewis acid in the complex. Finally, spodium and tetrel bonds are formed, possible thanks to a hemi-directional coordination sphere of the Pb atoms in the polymer described.

Se⋅⋅⋅O/S and S⋅⋅⋅O Chalcogen Bonds in Small Molecules and Proteins: A Combined CSD and PDB Study

The importance of selenium-centered noncovalent chalcogen bonds represented as Se⋅⋅⋅A (A=O/S) has been explored for short directional contacts in small molecules and proteins. In addition, S⋅⋅⋅O centered contacts have been analyzed. Computational analyses involving the quantitative assessment of the associated energetics, the molecular electrostatic potentials (MEP), and electron density derived topological parameters, namely, quantum theory of atom in molecules (QTAIM) analyses, and NBO (natural bond orbital) based calculations, have been performed to unequivocally establish the strength, stability, and attractive role of chalcogen bonds in the solid-state. This investigation has been performed in molecules from both the Cambridge Structural Database (CSD) and Protein Data Bank (PDB). Thus futuristic materials may be designed keeping in mind the significance of these interactions, including their relevance in biology.

Participation of S and Se in hydrogen and chalcogen bonds

The heavier chalcogen atoms S, Se, and Te can each participate in a range of different noncovalent interactions. They can serve as both proton donor and acceptor in H-bonds. Each atom can also act as electron acceptor in a chalcogen bond.