A new coordination polymer constructed from Pb(NO3)2 and a benzylideneisonicotinohydrazide derivative: Coordination-induced generation of a π-hole towards a tetrel-bonding stabilized structure

Transition between the Noncovalency and Covalency of σ-Hole Bonds

The properties of the bond between a N-ligand and a Lewis acid containing a σ-hole are studied by quantum chemical methods. Interactions considered include pnicogen bonds involving SbX5, PX5, and PX3, where X represents any of the halogen atoms F, Cl, Br, or I. Also studied are the tetrel bonds of PbX4 and SiX4, as well as the chalcogen bond involving TeOX4. Both NH3 and NCH are applied as two possible bases of differing potency. Some of the bonds are very strong with interaction energies easily exceeding 25 kcal/mol and with AIM bond critical point densities much higher than 0.04 au, suggesting their classification as coordinate covalent bonds. The pentavalent SbX5 and PX5 fall into this category when combined with NH3, as does TeOX4. Although the tetrel bonds involving PbX4 are only slightly weaker, they are probably better viewed as a strong noncovalent bond on the cusp of covalency. Changing the internal bonding of hypervalent SbX5 to the more conventional SbX3 weakens the interaction to a classical noncovalent pnicogen bond. Reducing the base nucleophilicity from NH3 to NCH weakens the bonds so that they are clearly noncovalent.

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.

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.

Frustrated Lewis Pairs Based on Carbon⋅⋅⋅Carbon+ Tetrel Bonds: A DFT Study

The ability of Triangulenium (TA⁺ ) compounds to form Frustrated Lewis Pairs (FLPs) with N-HeteroCycle Carbenes (NHCs) is analysed in this manuscript at the PBE0-D3/def2-TZVP level of theory. We have used six TA⁺ -based moieties, three presenting similar bridging groups (O (trioxo), -CH₂ (triaryl) and -NH (triaza)) and another three mixing, O, -CH₂ and NH moieties. In addition, several aryl-substituted NHCs have been used as electron donor moieties to undergo carbon⋅⋅⋅carbon⁺ tetrel bonds with the TA⁺ derivatives. More precisely, -Me,-iPr, -tBu and -Ph groups were used. Finally, we have used Bader's quantum theory of "atoms in molecules" (QTAIM) and Natural Bonding Analysis (NBO) to characterize the carbon⋅⋅⋅carbon⁺ tetrel bonds described herein. We expect the results gathered herein will be useful for further exploitation of carbon⋅⋅⋅carbon⁺ bonds in the formation of FLPs as well as to expand the current knowledge of tetrel bonds to the fields of synthetic chemistry and catalysis.

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.