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) ų, 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 (L^2-) 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.

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.

An insight into the non-covalent Pb⋯S and S⋯S interactions in the solid-state structure of a hemidirected lead(ii) complex

A hemi-directed copper(ii)/lead(ii) complex has been synthesized and characterized. The energy of chalcogen–chalcogen and tetrel bonding interactions in this complex was analyzed by DFT calculations.

Supramolecular Assemblies in Pb(II) Complexes with Hydrazido-Based Ligands

Herein, we describe the synthesis and single crystal X-ray diffraction characterization of several Pb(II) complexes using Schiff base hydrazido-based ligands and different counterions (NO3−, I– and ClO4). In the three complexes reported in this work, the lead(II) metal exhibits a high coordination number (n > 8) and thus it is apparently not involved in tetrel bonding interactions. Moreover, the aromatic ligands participate in noncovalent interactions that play an important role in the formation of several supramolecular assemblies in the solid state of the three Pb(II) complexes. These assemblies have been analyzed by means of Hirshfeld surface analysis and DFT calculations.

A tetranuclear nickel/lead complex with a salen type Schiff base: synthesis, structure and exploration of photosensitive Schottky barrier diode behaviour

A tetranuclear nickel(ii)/lead(ii) complex has been synthesized and characterized. The complex based device behaves as a Schottky diode. The charge transfer kinetics of the complex is enhanced after light soaking.

Formation of a tetranuclear supramolecule via non-covalent Pb⋯Cl tetrel bonding interaction in a hemidirected lead(ii) complex with a nickel(ii) containing metaloligand

A hetero-nuclear nickel(ii)/lead(ii) complex has been synthesized and characterized. The tetrel bonding interactions established between the σ-hole at the hemi-coordinated lead(ii) and the electron rich chlorido ligand has been analyzed by DFT study.

Fabrication of an Active Electronic Device Using a Hetero-bimetallic Coordination Polymer

A nickel(II)/lead(II) coordination polymer [(NCS)Pb(H₂O)LNi(NCS)]_n {H₂L = N,N'-bis(3-methoxysalicylidene)propane-1,3-diamine} has been synthesized and characterized. The band gap (3.18 eV) calculated from Tauc's plot suggests the semiconducting nature of the complex. The material has a photosensitivity of 5.76, indicating its applicability in the fabrication of photosensitive devices. The complex has been successfully applied in a technologically challenging thin-film photosensitive Schottky device.

Non-covalent tetrel bonding interactions in hemidirectional lead(ii) complexes with nickel(ii)-salen type metalloligands

Tetrel bonding interactions have been investigated in hetero-dinuclear nickel(ii)/lead(ii) complexes using MEP and DFT calculations.

On the importance of Pb⋯X (X = O, N, S, Br) tetrel bonding interactions in a series of tetra- and hexa-coordinated Pb(ii) compounds

We study Pb⋯X (X = N, S, Br) tetrel bonding interactions in a series of tetra- and hexa-coordinated Pb(ii) compounds that exhibit hemidirectional coordination.

Lead(ii): Lewis acid and occasional base, as illustrated by its complex with 1,5-naphthalenedisulfonate and 5-methyl-1,10-phenanthroline

Hydrogen bonding to lead(ii) evidences the Lewis base character of this cation due to its valence shell lone pair.

Modulation of the Structure and Properties of Uranyl Ion Coordination Polymers Derived from 1,3,5-Benzenetriacetate by Incorporation of Ag(I) or Pb(II)

Reaction of uranyl nitrate with 1,3,5-benzenetriacetic acid (H3BTA) in the presence of additional species, either organic bases or their conjugate acids or metal cations, has provided 12 new crystalline complexes, all but one obtained under solvo-hydrothermal conditions. The complexes [C(NH2)3][UO2(BTA)]·H2O (1) and [H2NMe2][UO2(BTA)] (2) crystallize as one- or two-dimensional (1D or 2D) assemblies, respectively, both with uranyl tris-chelation by carboxylate groups and hydrogen-bonded counterions but different ligand conformations. One of the bound carboxylate units is replaced by chelating 1,10-phenanthroline (phen) or 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4phen) in the complexes [(UO2)3(BTA)2(phen)3]·4H2O (3) and [(UO2)3(BTA)2(Me4phen)3]·NMP·3H2O (4) (NMP = N-methyl-2-pyrrolidone), which are a 2D network with honeycomb topology and a 1D polymer, respectively. With silver(I) cations, [UO2Ag(BTA)] (5), a three-dimensional (3D) framework in which the ligand assumes various chelating/bridging coordination modes, and the aromatic ring is involved in Ag(I) bonding, is obtained. A series of seven heterometallic complexes results when lead(II) cations and N-chelating molecules are both present. The complexes [UO2Pb(BTA)(NO3)(bipy)] (6) and [UO2Pb2(BTA)2(bipy)2]·3H2O (7), where bipy is 2,2'-bipyridine, crystallize from the one solution, as 1D and 2D assemblies, respectively. The two 1D coordination polymers [UO2Pb(BTA)(HCOO)(phen)] (8 and 9), again obtained from the one synthesis, provide an example of coordination isomerism, with the formate anion bound either to lead(II) or to uranyl cations. Another 2D architecture is found in [(UO2)2Pb2(BTA)2(HBTA)(H2O)2(phen)2]·2H2O (10), which provides a possible example of a Pb-oxo(uranyl) "cation-cation" interaction. While [UO2Pb(BTA)(HCOO)0.5(NO3)0.5(Me2phen)] (11), where Me2phen is 5,6-dimethyl-1,10-phenanthroline, is a 1D assembly close to those in 6 and 8, [UO2Pb2(BTA)2(Me4phen)2] (12), obtained together with complex 4, crystallizes as a 2D network as a result of the high degree of connectivity provided by the chelating/bridging tricarboxylate ligand. Emission spectra measured in the solid state display vibronic fine structure attributable to uranyl luminescence (except for complex 5, in which emission is quenched), with variations in maxima positions associated with modifications of the uranyl ion environment.

Charge Localisation in Heavy Alkali Metal Ion Complexes of 4,4'-Biphenyldicarboxylate

Crystal structure determinations on the isomorphous RbI and CsI complexes of 4,4′-biphenyldicarboxylate have shown the carboxylate entities to be coordinated in an unusual fashion where both oxygen atoms are in a tetrahedral environment indicative of negative charge localisation on each. The metal ions also show a highly irregular form of six-coordination, while the biphenyl units are planar, seemingly as a result of attractive interactions between the ortho hydrogen atoms.