A Nanosized Porous Supramolecular Lead(II)-N'-phenyl(pyridin-2-yl)methylene-N-phenylthiosemicarbazide Aggregate, Obtained Under Electrochemical Conditions

A novel nanosized porous supramolecular nonanuclear complex [Pb9(HL)12Cl2(ClO4)](ClO4)3·15H2O·a(solvent) (1·15H2O·a(solvent)) is reported that was synthesized by electrochemical oxidation of a Pb anode under the ambient conditions in a CH3CN:MeOH solution of N'-phenyl(pyridin-2-yl)methylene-N-phenylthiosemicarbazide (H2L), containing [N(CH3)4]ClO4 as a current carrier. The supramolecular aggregate of 1 is enforced by a myriad of Pb···S tetrel bonds (TtBs) established with the thiocarbonyl sulfur atoms of adjacent species, which have been also analyzed by DFT calculations via 2D maps of ELF, Laplacian and RDG properties. Moreover, Pb···Cl TtBs with the central Cl- anion, and Pb···O TtBs with the three oxygen atoms of the ClO4- anion, were revealed. Notably, the molecular structure of 1 differs significantly from that recently reported by us [Pb2(HL)2(CH3CN)(ClO4)2]·2H2O (2·2H2O), which was obtained using a conventional synthetic procedure by reacting Pb(ClO4)2 with H2L in the same CH3CN:MeOH solution, thus highlighting a crucial role of the electrochemical conditions. The optical characteristics of the complex were investigated using UV-vis spectroscopy and spectrofluorimetry in methanol. The complex was found to be emissive when excited at 304 nm, producing a broad emission band ranging from approximately 420 to 600 nm with multiple peaks. The CIE-1931 chromaticity coordinates, calculated as (0.33, 0.24), suggest that the emission lies in the white region of the chromaticity diagram. Further investigation is needed to fully characterize the origin of this emission.

Static and Dynamical Quantum Studies of CX3-AlX2 and CSiX3-BX2 (X = F, Cl, Br) Complexes with Hydrocyanic Acid: Unusual Behavior of Strong π-Hole at Triel Center

The set of TX₃-TrX₂ (T = C, Si, Ge; Tr = B, Al, Ga; X = F, Cl, Br) molecules offers a rather unique opportunity to study both σ-hole and π-hole dimerization on the tetrel and triel ends, respectively. According to the molecular electrostatic potential (MEP) distribution, the π-hole extrema (acidic sites) were more intense than their σ-hole counterparts. The molecules owning the most (CX₃-AlX₂) and least (SiX₃-BX₂) intense π-holes were chosen to evaluate their capacities to attract one and two HCN molecules (Lewis bases). We discovered that the energetic characteristics of π-hole dimers severely conflict with the monomers MEP pattern since the weakest π-hole monomer forms a dimer characterized by interaction energy compared to those created by the monomers with noticeably greater power in the π-hole region. This outcome is due to the deformation of the weakest π-hole donor. Furthermore, the MEP analysis for monomers in the geometry of respective dimers revealed a "residual π-hole" site that was able to drive second ligand attachment, giving rise to the two "unusual trimers" examined further by the NCI and QTAIM analyses. Apart from them, the π-hole/π-hole and σ-hole/π-hole trimers have also been obtained throughout this study and described using energetic and geometric parameters. The SAPT approach revealed details of the bonding in one of the "unusual trimers". Finally, Born-Oppenheimer Molecular Dynamics (BOMD) simulations were carried out to investigate the time evolution of the interatomic distances of the studied complexes as well as their stability.

Effects of Lewis Basicity and Acidity on σ-Hole Interactions in Carbon-Bearing Complexes: A Comparative Ab Initio Study

The effects of Lewis basicity and acidity on σ-hole interactions were investigated using two sets of carbon-containing complexes. In Set I, the effect of Lewis basicity was studied by substituting the X3/X atom(s) of the NC-C6H2-X3 and NCX Lewis bases (LB) with F, Cl, Br, or I. In Set II, the W-C-F3 and F-C-X3 (where X and W = F, Cl, Br, and I) molecules were utilized as Lewis acid (LA) centers. Concerning the Lewis basicity effect, higher negative interaction energies (Eint) were observed for the F-C-F3∙∙∙NC-C6H2-X3 complexes compared with the F-C-F3∙∙∙NCX analogs. Moreover, significant Eint was recorded for Set I complexes, along with decreasing the electron-withdrawing power of the X3/X atom(s). Among Set I complexes, the highest negative Eint was ascribed to the F-C-F3∙∙∙NC-C6H2-I3 complex with a value of -1.23 kcal/mol. For Set II complexes, Eint values of F-C-X3 bearing complexes were noted within the -1.05 to -2.08 kcal/mol scope, while they ranged from -0.82 to -1.20 kcal/mol for the W-C-F3 analogs. However, Vs,max quantities exhibited higher values in the case of W-C-F3 molecules compared with F-C-X3; preferable negative Eint were ascribed to the F-C-X3 bearing complexes. These findings were delineated as a consequence of the promoted contributions of the X3 substituents. Dispersion forces (Edisp) were identified as the dominant forces for these interactions. The obtained results provide a foundation for fields such as crystal engineering and supramolecular chemistry studies that focus on understanding the characteristics of carbon-bearing complexes.

Synthesis, crystal structure, and properties of three lead(II) complexes based on the 1,10-phenanthroline ligand

Three new lead(II) complexes containing the 1,10-phenanthroline ligand, [Pb(phen)2(3,5-DNB)2] (1), [Pb(phen)2(3,5-DNB)(NO3)]2·H2O (2), and [Pb(phen)(HCOO)(NO3)(H2O)] n (3) (phen = 1,10-phenanthroline, 3,5-DNB = 3,5-dinitrobenzoate anion) have been synthesized and characterized by elemental analyses, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses (TGA), and single-crystal X-ray diffraction. The complexes 1 and 2 are monomeric species, whereas complex 3 is a one-dimensional polymer. In the three complexes, the ligand phen creates a number of π···π stacking interactions and hydrogen bonds, which play an important role in extending complexes 1–3 to supramolecular architectures. The Pb(II) ion of complexes 1 and 2 shows hemidirected geometry with noncovalent Pb···O/C tetrel bonds formed which further stabilize the supramolecular structures.

The tetrel bonding role in supramolecular aggregation of lead(II) acetate and a thiosemicarbazide derivative

A new Pb^II coordination complex [PbL(OAc)], which was readily synthesized from a mixture of Pb(OAc)₂·3H₂O and 1-(pyridin-2-yl)benzylidene-4-phenylthiosemicarbazide (HL) is reported. The crystal structure analysis of [PbL(OAc)] showed that the Pb^II cation is N,N',S-chelated by the tridentate pincer-type ligand L and by the oxygen atoms of the acetate anion. In addition, the metal centre forms Pb...O and Pb...S tetrel bonds with an adjacent complex molecule, yielding a 1D zigzag polymeric chain, which is reinforced by N-H...O hydrogen bonds and π...π interactions. These chains are interlinked by C-H...py non-covalent interactions, realized between one of the acetate hydrogen atoms and the pyridine rings. According to the Hirshfeld surface analysis, the crystal packing is mainly characterized by intermolecular H...H, H...C and H...O contacts, followed by H...N, H...S, C...C, C...N, Pb...H, Pb...O and Pb...S contacts. The FTIR and ¹H NMR spectra of [PbL(OAc)] testify to the deprotonation of the parent ligand HL, while the acetate ligand exhibits an anisobidentate coordination mode as established by means of single-crystal X-ray diffraction and FTIR spectroscopy. Lastly, theoretical calculations at the PBE0-D3/def2-TZVP level of theory have been used to analyze and characterize the Pb...O and Pb...S tetrel bonds observed in the crystal of [PbL(OAc)], using a combination of QTAIM (Quantum Theory of Atoms in Molecules) and NCIPlot (Non-Covalent Interaction Plot) computational tools.

Experimental and Theoretical Evidence of a Pb⋅⋅⋅Pb Ditetrel Bond Without a σ-Hole

The crystal structure of a newly synthesized compound, [PbL(Ac)]₂ , (where L=2 (amino(pyrazin-2-yl) methylene) hydrazinecarbothioamide, Ac=acetate anion) exhibits a close contact between pairs of Pb atoms, suggesting a ditetrel bond, in addition to two Pb⋅⋅⋅O tetrel bonds, and two C-H⋅⋅⋅O H-bonds. The presence of this ditetrel bond as an attractive component is confirmed by various quantum chemical methods. This novelty of this particular bond is its existence even in the absence of a σ-hole on the Pb atom, which is typically considered a prerequisite for a bond of this type. From a wider perspective, a survey of the Cambridge Structural Database suggests this bond may be more common than was hitherto thought, with 44 examples of Pb⋅⋅⋅Pb contacts amongst a total number of 219 examples of T⋅⋅⋅T interactions in general (T=Si, Ge, Sn, Pb).

Lead(ii) supramolecular structures formed through a cooperative influence of the hydrazinecarbothioamide derived and ancillary ligands

We report on tetrel bonding and other noncovalent interactions in the lead(ii)-derived complexes with the hydrazinecarbothioamide derived and ancillary ligands, which predominantly drive the formation of extended architectures.

Evaluation of the antitumor activity of a series of the pincer-type metallocomplexes produced from isonicotinohydrazide derivative

In this work we report on the antitumor properties of a series of pincer-type metallocomplexes [Hg₂(HL-keto)Cl₄]_n (1), [Hg(HL-keto)I₂] (2) and [Mn(HL-zwitterion)Cl₂]∙MeOH (3∙MeOH), derived from N'-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) and corresponding metal salts. The Hg(II) and Mn(II) salts are chelated by the keto (HL-keto) or zwitterionic (HL-zwitterion) form of HL, respectively. The cytotoxic effects of these compounds have been accessed against lung adenocarcinoma (A549) and hepatocellular carcinoma (HepG2 and Huh7) cell lines. Complexes 1 and 2 were found to be most efficient against the cell line Huh7 with IC₅₀ value of 2.56 and 9.90 μM, respectively, while they exhibit moderate activity towards cell lines A549 and HepG2, as evidenced from IC₅₀ values in the range 27.98-56.99 μM. Complex 3∙MeOH is less efficient towards all the three cell lines with relatively high IC₅₀ values. The mechanisms of the metallocomplexes killing the aforementioned cells were elucidated by flow cytometry, colony formation and polymerase chain reaction (PCR) analysis of apoptosis related expression of the genes. The results of the cytotoxic effects and antitumor activity on different cell lines are affected by the metal nature and the presence of the coordinated halide.

Competition between Inter and Intramolecular Tetrel Bonds: Theoretical Studies Complemented by CSD Survey

Crystal structures document the ability of a TF₃ group (T=Si, Ge, Sn, Pb) situated on a naphthalene system to engage in an intramolecular tetrel bond (TB) with an amino group on the adjoining ring. Ab initio calculations evaluate the strength of this bond and evaluate whether it can influence the ability of the T atom to engage in a second, intermolecular TB with another nucleophile. A very strong CN^- anionic base can approach the T either along the extension of a T-C or T-F bond and form a strong TB with an interaction energy approaching 100 kcal/mol, although this bond is weakened a bit by the presence of the internal T⋅⋅⋅N bond. The much less potent NCH base engages in a correspondingly longer and weaker TB, less than 10 kcal/mol. Such an intermolecular TB is weakened by the presence of the internal TB, to the point that it only occurs for the two heavier tetrel atoms Sn and Pb.

Experimental and Theoretical Studies of Dimers Stabilized by Two Chalcogen Bonds in the Presence of a N···N Pnicogen Bond

The structure of the 5,6-dichloro-2,1,3-benzoselenadiazole homodimer, obtained by adding the ligand, 4,5-dichloro-o-phenylenediamine, to the methanolic solution of SeCl₄, was determined by X-ray crystallography, augmented by Fourier transform infrared, Raman, and NMR spectroscopy. The binding motif involves a pair of Se···N chalcogen bonds, with a supplementary N···N pnicogen bond. Quantum calculations provide assessments of the strengths of the individual interactions as well as their contributing factors. All together, these three bonds compose a total interaction energy between 5.4 and 16.8 kcal/mol, with the larger chalcogen atom associated with the strongest interactions. Replacement of the Se atoms by S and Te analogues allows analysis of the dependence of these forces on the nature of the chalcogen atom. Calculations also measure the importance to the binding of the presence of a second N atom on each diazole unit as well as the substituted phenyl ring to which it is fused.

Tetrel Bonding and Other Non-Covalent Interactions Assisted Supramolecular Aggregation in a New Pb(II) Complex of an Isonicotinohydrazide

A new supramolecular Pb(II) complex [PbL(NO₂)]_n was synthesized from Pb(NO₃)₂, N’-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) and NaNO₂. [PbL(NO₂)]_n is constructed from discrete [PbL(NO₂)] units with an almost ideal N₂O₃ square pyramidal coordination environment around Pb(II). The ligand L⁻ is coordinated through the 2-pyridyl N-atom, one aza N-atom, and the carbonyl O-atom. The nitrite ligand binds in a κ²-O,O coordination mode through both O-atoms. The Pb(II) center exhibits a hemidirected coordination geometry with a pronounced coordination gap, which allows a close approach of two additional N-atoms arising from the N=C(O) N-atom of an adjacent molecule and from the 4-pyridyl N-atom from the another adjacent molecule, yielding a N₄O₃ coordination, constructed from two Pb–N and three Pb–O covalent bonds, and two Pb⋯N tetrel bonds. Dimeric units in the structure of [PbL(NO₂)]_n are formed by the Pb⋯N=C(O) tetrel bonds and intermolecular electrostatically enforced π⁺⋯π⁻ stacking interactions between the 2- and 4-pyridyl rings and further stabilized by C–H⋯π intermolecular interactions, formed by one of the methyl H-atoms and the 4-pyridyl ring. These dimers are embedded in a 2D network representing a simplified uninodal 3-connected fes (Shubnikov plane net) topology defined by the point symbol (4∙8²). The Hirshfeld surface analysis of [PbL(NO₂)] revealed that the intermolecular H⋯X (X = H, C, N, O) contacts occupy an overwhelming majority of the molecular surface of the [PbL(NO₂)] coordination unit. Furthermore, the structure is characterized by intermolecular C⋯C and C⋯N interactions, corresponding to the intermolecular π⋯π stacking interactions. Notably, intermolecular Pb⋯N and, most interestingly, Pb⋯H interactions are remarkable contributors to the molecular surface of [PbL(NO₂)]. While the former contacts are due to the Pb⋯N tetrel bonds, the latter contacts are mainly due to the interaction with the methyl H-atoms in the π⋯π stacked [PbL(NO₂)] molecules. Molecular electrostatic potential (MEP) surface calculations showed marked electrostatic contributions to both the Pb⋯N tetrel bonds and the dimer forming π⁺⋯π⁻ stacking interactions. Quantum theory of atoms in molecules (QTAIM) analyses underlined the tetrel bonding character of the Pb⋯N interactions. The manifold non-covalent interactions found in this supramolecular assembly are the result of the proper combination of the polyfunctional multidentate pyridine-hydrazide ligand and the small nitrito auxiliary ligand.

Exploring thiophene-2-acetate and thiophene-3-acetate binding modes towards the molecular and supramolecular structures and photoluminescence properties of Pb(ii) polymers

The isomeric ligands thiophene-2(3)-acetate as linkers were used to construct Pb(ii) coordination polymers with an intriguing structure, noncovalent interactions, topology and interesting photoluminescence properties.

On the importance of π-hole spodium bonding in tricoordinated HgII complexes

The synthesis and X-ray characterization of two new tri-coordinated Hg complexes where the planar Hg atom participates in π-hole spodium bonding.