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This perpective delves into the emerging field of matere bonds, a novel type of noncovalent interaction involving group 7 elements such as manganese, technetium, and rhenium. Matere bonds, a new member of the σ-hole family where metal atoms act as electron acceptors, have been shown experimentally and theoretically to play significant roles in the self-assembly and stabilization of supramolecular structures both in solid-state and solution-phase environments. This perspective article explores the physical nature of these interactions, emphasizing their directionality and structural influence in various supramolecular architectures. Recent studies have expanded the understanding of matere bonds beyond classical metal-ligand coordination, highlighting their potential in crystal engineering and catalysis. This perspective article also examines the occurrence of matere bonds in biological systems, particularly within manganese-containing proteins, where they contribute to the structural integrity and catalytic activity. Theoretical and computational analyses, including molecular electrostatic potential surfaces and density functional theory, further elucidate the properties and applications of matere bonds, offering new insights for the design of advanced materials and biomimetic systems. This comprehensive overview underscores the versatility of matere bonds, paving the way for future innovations in supramolecular chemistry involving metals.

The first example of N-confused strapped calix[4]pyrrole 5 is presented. The structural integrity of 5 and its regular isomer 4 was unambiguously confirmed by single crystal X-ray diffraction analysis. Anion binding studies using 1 H NMR titration carried out in CDCl 3 revealed a small but detectable tendency of 5 to interact with an anion. Conversely, the isomeric regular strapped calix[4]pyrrole 4 displayed high selectivity for fluoride anions under similar experimental conditions. The high fluoride selectivity of 4 and unexpectedly low anion affinity of 5 were ascribed to the presence of intramolecular hydrogen bonds within strapping subunits.

The stability and hydrolytic behavior of squaramate esters in aqueous solutions have been investigated. The structure of squaramates and the nature of adjacent groups significantly influence their aqueous stability and reactivity towards nucleophiles. Squaramate esters, lacking or containing weakly basic neighboring group participation (NGP) substitutions, remain stable up to pH 9. Their hydrolysis rate ( k OH ≈ 10 -1 M -1 s -1 ) is 1000 times faster than that of squaramides, following a second-order rate law. Squaramate esters functionalized with basic NGP groups, such as amines, display a pH-dependent hydrolysis rate due to anchimeric assistance of the terminal amino group, reducing stability to pH 5. However, when the squaramate ester has a terminal nucleophilic group in the γ position of the alkyl chain, it undergoes rapid intramolecular cyclization, forming cyclic squaramides., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A robust method of hazardous metal ion removal from an aqueous environment involves the use of chelating agents, such as ethylenediaminetetraacetic acid (EDTA). Here, we focus on mercury (Hg 2+ ) uptake by EDTA using both molecular dynamics and density functional theory simulations. Our results indicate that the deprotonation of the EDTA carboxylate groups improves the localization of negative charge on the deprotonated sites. This mechanism facilitates charge transfer between the metal ions and EDTA, and provides a stronger and more stable EDTA-Hg 2+ complex formation improving the efficiency of the chelation process. The best metal removal conditions are achieved using the fully deprotonated form of EDTA, which naturally occurs at pH levels above 3.

In this article, we present the synthesis and characterization of three zinc(ii) complexes, [Zn II (HL 1 ) 2 ] (1), [Zn II (HL 2 ) 2 ]·2H 2 O (2) and [Zn II (HL 3 ) 2 ] (3), with three tridentate Schiff base ligands, H 2 L 1 , H 2 L 2 , and H 2 L 3 . 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 [Zn II (HL 2 ) 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Herein, we report the synthesis of a Pb(II) based three-dimensional coordination polymer (3D CP), [Pb(DCTP)] n (1) [H 2 DCTP = 2,5-dichloroterephthalic acid] with an unprecedented topology, which exhibits a photomechanical effect wherein crystals show jumping upon UV irradiation. The Pb(II) CP forms a type II Cl⋯Cl interaction, which weakens further upon UV irradiation to resolve the anisotropic mechanical strain. The work presented here could be a beacon to the nascent field of photoactuating smart materials.

( Cl Im Dipp )P-P(Dipp)˙ (1˙), a rare example of a neutral, mixed substituted diphosphene radical, has been prepared by reduction of ( Cl Im Dipp )PP(Dipp)[OTf] (2[OTf]) and ( Cl Im Dipp )PP(Cl)(Dipp) (3) with cobaltocene (CoCp 2 ) ( Cl Im Dipp = 4,5-dichloro-1,3-bis(1,3-diisopropylphenyl)-imidazol-2-yl, Dipp = 2,6-diisopropylphenyl). Radical compound 1˙ readily activates white phosphorus (P 4 ), resulting in the formation of an intriguing octaphosphane butterfly compound P 8 ( Cl Im Dipp ) 2 (Dipp) 2 (4).

Herein we have computationally evaluated the relationship between Ag and Au nanoparticle (Ag/AuNP) size and π-surface extension in the formation of noncovalent complexes at the PBE0-D3/def2-TZVP level of theory. The NP-π interaction is known in supramolecular chemistry as a Regium-π bond (Rg-π), and differentiates from classical coordination bonds in strength and type of metal orbitals involved. In this study, the Rg-π complexes involved small Ag/AuNPs composed by 1 to 5 atoms and benzene, naphthalene and anthracene as π-systems, being characterized using several molecular modeling tools, including molecular electrostatic potential (MEP) calculations, energy decomposition analysis (EDA), quantum theory of atoms in molecules (QTAIM), non covalent interaction plot (NCIplot) and natural bonding orbital (NBO) methodologies. We believe the results reported herein will be useful for those scientists working in catalysis, molecular recognition and materials science fields, where structural-energetic relationships of weak interactions are crucial to achieve product selectivity, a particular molecular recognition mode or a specific molecular assembly.

With the objective of gaining insight into the modulation of the reduction potential of the Ni(II/I) couple, we have synthesized two mononuclear nickel(II) complexes, NiL en (H 2 L en = N , N '-bis(3-methoxysalicylidene)-1,2-diamino-2-methylpropane) and NiL pn (H 2 L pn = N , N '-bis(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane) of two N 2 O 4 donor ligands and recorded their cyclic voltammograms. Both the nickel complexes show reversible reduction processes for the Ni(II/I) couple in acetonitrile solution but the reduction potential of NiL pn ( E 1/2 = -1.883 V) is 188 mV more positive than that of NiL en ( E 1/2 = -2.071 V). In the presence of redox inactive metal ions (Li + , Na + , K + , Mg 2+ , Ca 2+ and Ba 2+ ), the reduction potentials are shifted by 49-331 mV and 99-435 mV towards positive values compared to NiL en and NiL pn , respectively. The shift increases with the decrease of the p K a of the respective aqua-complexes of the metal ion but is poorly co-linear; however, better linearity is found when the shift of the mono- and bi-positive metal ion aqua complexes is plotted separately. Spectrophotometric titrations of these two nickel complexes with the guest metal ions in acetonitrile showed a well-anchored isosbestic point in all cases, confirming the adduct formation of NiL en and NiL pn with the metal ions. Structural analysis of single crystals, [(NiL en )Li(H 2 O) 2 ]·ClO 4 (1), [(NiL pn )Li(H 2 O)]·ClO 4 (2), [(NiL pn ) 2 Na]·BF 4 (3) and [(NiL pn ) 2 Ba(H 2 O)(ClO 4 )]·ClO 4 (4), also corroborates the heterometallic adduct formation. The orbital energies of the optimised heterometallic adducts from which electron transfers originated were calculated in order to explain the observed reduction process. A strong linear connection between the calculated orbital energies and the experimental E 1/2 values was observed. According to MEP and 2D vector field plots, the largest shift for divalent metal ions is most likely caused by the local electric field that they impose in addition to Lewis acidity.

A Protein Data Bank (PDB) survey has revealed noncovalent contacts involving Mn centres and protein residues. Their geometrical features are in line with the interaction between low electron density sites located along the Mn-O/N coordination bonds (σ-holes) and the lone pairs belonging to TYR, SER or HIS residues, known as a matere bond (MaB). Calculations at the PBE0-D3/def2-TZVP level of theory were used to investigate the strength and shed light on the physical nature of the interaction. We expect the results presented herein will be useful for those scientists working in the fields of bioinorganic chemistry, particulary in protein-metal docking, by providing new insights into transition metal⋯Lewis base interactions as well as a retrospective point of view to further understand the structural and functional implications of this key transition metal ion.

The structure-directing "key-to-lock" interaction of double σ-(I III )-hole donating iodonium cations with the O-flanked pseudo-lacune rims of [β-Mo 8 O 26 ] 4- gives halogen-bonded iodonium-beta-octamolybate supramolecular associates. In the occurrence of their tetragonal pyramidal motifs, deep and broad σ-(I III )-holes of a cation recognize the molybdate backbone, which provides an electronic pool localized around the two lacunae. The halogen-bonded I⋯O linkages in the structures were thoroughly studied computationally and classified as two-center, three-center bifurcated, and unconventional "orthogonal" I⋯O halogen bonds. In the latter, the O-atom approaches orthogonally the C-I III -C plane of an iodonium cation and this geometry diverge from the IUPAC criteria for the identification of the halogen bond., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Metallophilic interactions, specifically argentophilic (Ag⋯Ag) and aurophilic (Au⋯Au) interactions, play a crucial role in stabilizing various molecular and solid-state structures. In this manuscript, we present a convenient method to estimate the strength of argentophilic and aurophilic interactions based on quantum theory of atoms in molecules (QTAIM) parameters evaluated at the bond critical points connecting the metal centres. We employ density functional theory (DFT) calculations and the QTAIM parameters to develop this energy predictor. To validate the reliability and applicability of our method, we test it using a selection of X-ray crystal structures extracted from the cambridge structural database (CSD), where argentophilic and aurophilic interactions are known to be significant in their solid-state arrangements. This method offers a distinct advantage in systems where multiple interactions, beyond metallophilic interactions, contribute to the overall stability of the structure. By employing our approach, researchers can distinctly quantify the strength of argentophilic and aurophilic interactions, facilitating a deeper understanding of their impact on molecular and solid-state properties. This method fills a critical gap in the existing literature, offering a valuable tool to researchers seeking to unravel the intricate interactions in metal-containing compounds.

A new doubly carboxylato-bridged Co(II) dinuclear complex, [Co(bdtbpza)(NCS)] 2 (1), was obtained in a satisfactory yield by employing a 'scorpionate'-type precursor, bdtbpza {bis-(3,5-di- tert -butylpyrazol-1-yl)acetate}, and was then structurally characterized. Single-crystal X-ray diffraction analysis revealed that, in 1, each Co(II) is penta-coordinated, leading to a distorted trigonal-bipyramidal geometry within the coordination environment of N 3 O 2 . Weak antiferromagnetic coupling within the Co(II) ions in 1 was found based on the isotropic spin Hamiltonian H = - J ( S 1 · S 2 ) for the S i = 3/2 system. For evaluating the spin density distribution and the mechanism for the magnetic exchange coupling, DFT analysis was performed, with the calculated result agreeing the experimental magnetic data. A study into electrochemical H 2 evolution, involving cyclic voltammetry (CV), controlled potential electrolysis (CPE), and gas chromatographic (GC) analyses of the graphite electrode modified with the cobalt complex in a neutral aqueous solution revealed the high catalytic activity of the complex with a low overpotential toward H 2 O reduction. The faradaic efficiency of the catalyst was found to be 83.7% and the di-cobalt catalyst-modified electrode displayed quite an interesting H 2 -evolution activity compared with that of bare electrodes. These results are encouraging for the future potential application of 1 in water splitting.

In this manuscript we report the synthesis and characterization of two new polynuclear zinc(ii) complexes, [Zn 2 L 1 (μ-OAc) 3 ] n ·H 2 O (1) and [Zn 2 L 2 (μ-OAc) 3 ] n (2) using two tridentate ligands, HL 1 {4-chloro-2-(((2-(methylamino)ethyl)amino)methyl)phenol} and HL 2 {2,4-dibromo-6-(((3-(methylamino)propyl)amino)methyl)phenol}. The structures were confirmed by single-crystal X-ray diffraction analysis. Both complexes form 1D chains. The energy of H-bonding interaction in the solid state structures of the complexes has been estimated by DFT calculation and the crucial role of hydrogen bonding in shaping their structures has been highlighted., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A trinuclear linear mixed-valence centrosymmetric cobalt(iii)-cobalt(ii)-cobalt(iii) complex, [Co II {(μ-L)(μ-Hglu)Co III (OH 2 )} 2 ](ClO 4 ) 2 ·6H 2 O has been synthesized during tetradentate N 2 O 2 donor 'Schiff base' ligand, H 2 L { N , N '-bis(salicylidene)-1,3-diaminopropane} and glutaric acid (H 2 glu) as anionic co-ligand. The complex has been characterized by spectroscopic measurements and its solid state structure has been determined by single crystal X-ray diffraction analysis. The supra-molecular assembly formed by the hydrogen bonding interactions in the solid state of the complex has been analysed using DFT calculations., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Despite significant progress in immunotherapy and chimeric antigen receptor T cell therapy of leukemia, chemotherapy is the major treatment option for the disease. Therefore, the development of potent and safe drugs for standard and targeted chemotherapy of leukemia remains an important task for medicinal chemists. A library of 94 diverse 6-aryl-4-cycloamino-1,3,5-triazine-2-amines was prepared using a one-pot microwave-assisted protocol, which involves a three-component reaction of cyanoguanidine, aromatic aldehydes and cyclic amines, and subsequent dehydrogenative aromatization of the dihydrotriazine intermediates in the presence of alkali. The cytotoxic properties of prepared compounds were evaluated against the leukemic Jurkat T cell line and the selectivity of the 24 most active compounds was also assessed using a normal fibroblast MRC-5 cell line, indicating selective antiproliferative activity against leukemic cells. The structure-activity relationship was analysed, and the prepared 3D-QSAR model was found to predict the antileukemic activity of the compounds with reasonable accuracy. In the cell morphology study, both apoptosis and necrosis features were observed in Jurkat T cells after treatment with the most active compound., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Twelve (N^N^N)platinum pyridyl complexes, (N^N^N)Pt(pyF), were synthesised and investigated for their singlet oxygen generation and potential biological activities. They exhibited 1 IL and 1 MLCT absorption transitions at approximately 325 and 360 nm, identified through TD-DFT calculations. Luminescence was observed only in the L1-derived compounds in solution, with a dual emission with the main contribution of phosphorescence under deaerated conditions. Room temperature phosphorescence was detected in all solid-state cases. Electron-withdrawing substituents at specific positions (R1 and X) and the number of fluorine atoms in R2 were found to enhance the photosensitizing capabilities of these compounds. Biological assessments, including cytotoxicity and photocytotoxicity, were conducted to evaluate their potential as chemotherapeutic agents and photosensitizers. Complexes with chloro substitution in the N^N^N tridentate ligand of the central pyridine ring exhibited promising chemotherapeutic properties. Ancillary pyridine ring substitution became significant under irradiation conditions, with fluoromethylated substituents enhancing cytotoxicity. Complex 2-CF3 was the most efficient singlet oxygen producer and a highly effective photosensitizer. CHF 2 -substituted complexes also showed improved photosensitizing activity. DNA binding studies indicated moderate interactions with DNA, offering insights into potential biological applications.

Two 1,3,4-oxadiazole-2-thione- N -Mannich derivatives, specifically 5-(4-chlorophenyl)-3-[(2-trifluoromethylphenylamino)methyl]-1,3,4-oxadiazole-2(3 H )-thione (1) and 5-(4-chlorophenyl)-3-[(2,5-difluorophenylamino)methyl]-1,3,4-oxadiazole-2(3 H )-thione (2), were synthesized and then characterized by elemental analysis and NMR ( 1 H and 13 C) spectroscopy and the single crystal X-ray diffraction method. The formed weak intermolecular interactions in the solid-state structures of these derivatives were thoroughly investigated utilizing a variety of theoretical tools such as Hirshfeld surface analysis and quantum theory of atoms in molecules (QTAIM). Furthermore, the CLP-PIXEL and density functional theory calculations were used to study the energetics of molecular dimers. Numerous weak intermolecular interactions such as C-H⋯S/Cl/F/π interactions, a directional C-Cl⋯Cl halogen bond, π-stacking, type C-F⋯F-C contact and a short F⋯O interaction, help to stabilize the crystal structure of 1. Crystal structure 2 also stabilizes with several weak intermolecular contacts, including N-H⋯S, C-H⋯N//Cl/F interactions, a highly directional C1-Cl1⋯C(π) halogen bond and C(π)⋯C(π) interaction. In vitro antimicrobial potency of compounds 1 and 2 was assessed against various Gram-positive and Gram-negative bacterial strains and the pathogenic yeast-like Candida albicans . Both compounds showed marked activity against all tested Gram-positive bacteria and weak activity against Escherichia coli and lacked inhibitory activity against Pseudomonas aeruginosa . In addition, compounds 1 and 2 displayed good in vitro anti-proliferative activity against hepatocellular carcinoma (HepG-2) and mammary gland breast cancer (MCF-7) cancer cell lines. Molecular docking studies revealed the binding modes of title compounds at the active sites of prospective therapeutic targets., Competing Interests: The authors declare that they have no competing interests., (This journal is © The Royal Society of Chemistry.)

Computations at the PBE0-D3/def2-TZVP level of theory in conjunction with a Protein Data Bank (PDB) survey have provided first time evidence of favorable noncovalent interactions between ADP metavanadate (VO 4 ) and ADP orthovanadate (VO 5 ) and electron rich atoms. These involve a σ-hole present in the V atom and the lone pairs belonging to (i) protein residues ( e.g. , serine (SER), glutamate (GLU) or histidine (HIS)), (ii) backbone carbonyl groups and (iii) water molecules. A computational study has been carried out to rationalize the physical nature and directionality of the interaction in addition to its plausible biological role. The results reported herein are expected to have an impact in the fields of medicinal chemistry, bioinorganic chemistry and chemical biology.

In this manuscript we report the synthesis and X-ray characterization of two cyanidoaurate telluronium salts, namely (3-fluorophenyl)(methyl)(phenyl)telluronium dicyanidoaurate [(3-F-Ph)(Me)(Ph)Te][Au(CN) 2 ] (1) and methyldiphenyltelluronium dicyanidoaurate [(Me)(Ph) 2 Te][Au(CN) 2 ] (2). In the solid state, the tellurium atom establishes three concurrent and directional chalcogen bonds (ChBs) with the adjacent anions, in both compounds. These charge-assisted ChBs (CAChBs) have been analyzed using DFT calculations and several computational tools. The MEP surface analysis discloses the existence of three σ-holes at the Te-atoms capable of establishing strong CAChBs with the counter-ions. In addition, significant charge transfer from the lone pair orbital at the N-atom of the anion to the antibonding σ*(Te-C) orbital of the cation is observed in some cases.

A doubly-interlocked [2]catenane - or Solomon link - undergoes a complex conformational change upon addition of sulfate in methanol. This transformation generates a single pocket where two SO 4 2- anions bind through multiple hydrogen bonds and electrostatic interactions. Despite the close proximity of the two anions, binding is highly cooperative.

Combining computations and X-ray structure analysis we have demonstrated that [Pt(CN 4 )] 2- can behave as a Lewis acid inside an enzyme's cavity. The nature of a counterintuitive contact found between a catalytically active GLN residue belonging to a mitochondrial synthase and the Pt(II) center was investigated by combining molecular dynamics and quantum mechanics calculations. Results confirm the electron acceptor role of [Pt(CN 4 )] 2- , serving as an inspiration for the design of biomolecular cages able to tweak the nucleophilic/electrophilic character of an organometallic compound.

Three cobalt complexes, namely [Co III (HL 1 ) 2 (N 3 ) 2 ]ClO 4 (1), [Co III (L 2 )(HL 2 )(N 3 )]ClO 4 ·1.5H 2 O (2), and [Co III (L 3 )(HL 3 )(NCS)] 2 [Co II Cl 2 (NCS) 2 ] (3), where HL 1 = 2-(3-(dimethylamino)propyliminomethyl)-6-methoxyphenol, HL 2 = 2-(2-(dimethylamino)ethyliminomethyl)-4,6-dichlorophenol, and HL 3 = 2-(2-(dimethylamino)ethyliminomethyl)-6-methoxyphenol, as potential tridentate N 2 O-donor Schiff base ligands, were synthesized and characterized using elemental analysis, IR and UV-vis spectroscopy, and single-crystal X-ray diffraction studies. All three were found to be monomeric ionic complexes. Complex 1 crystallizes in the orthorhombic space group Pbcn , whereas both complexes 2 and 3 crystallize in triclinic space groups, P 1̄. Further, 1 and 2 are cationic complexes of octahedral cobalt(iii) with perchlorate anions, whereas complex 3 contains a cationic part of octahedral cobalt(iii) and an anionic part of tetrahedral cobalt(ii). Hydrogen-bonding interactions involving aromatic and aliphatic CH bonds as H-bond donors and the pseudo-halide co-ligands as H-bond acceptors were established, which are important aspects governing the X-ray packing. These interactions were analyzed theoretically using the quantum theory of atoms in molecules (QTAIM) and non-covalent interaction plot (NCI plot) analyses. Moreover, energy decomposition analysis (EDA) was performed to analyze the stabilization of the complexes in terms of the electrostatic, dispersion, and correlation forces., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Calix[4]pyrroles bearing hydroxyl (1) or urea (3) groups attached to the meso -positions with propyl linkers were synthesized as cis - and trans -isomers. The anion binding properties of cis -1 and cis -3 were screened with ion-mobility mass spectrometry, where cis -1 formed complexes with Cl - , Br - and H 2 PO 4 - , whereas cis -3 formed complexes with most of the investigated anions, including Cl - , Br - , I - , NO 3 - , ClO 4 - , OTf - , SCN - and PF 6 - . The structures of the chloride complexes were further elucidated with density functional theory calculations and a crystal structure obtained for cis -1. In solution, chloride and dihydrogenphosphate anion binding with cis -1 and cis -3 were compared using 1 H NMR titrations. To assess the suitability of two-armed calix[4]pyrroles as anion transporters, chloride transport studies of cis -1, cis -3 and trans -3 were performed using large unilamellar vesicles. The results revealed that cis -3 had the highest activity among the investigated calix[4]pyrroles, which was related to the improved affinity and isolation of chloride inside the binding cavity of cis -3 in comparison to cis -1. The results indicate that appending calix[4]pyrroles with two hydrogen bonding arms is a feasible strategy to obtain anion transporters and receptors with high anion affinity.

Despite debate on intramolecular N→P interactions in peri -substituted naphthalene derivatives their coordination chemistry has not yet been reported. Herein, we describe bonding in and reactivity of dichloro(8-dimethylamino-1-naphthyl)phosphane towards pentacarbonyltungsten(0) reagents. A 1-aza-2-phospha-acenaphthene complex was obtained via the unexpected elimination of chloromethane enabled through P-coordination. Theoretical DFT calculations provide insights into P⋯N pnictogen bonding interaction as well as the reaction pathway of the elimination reaction., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this study, the ability of CF 3 groups to bind to the electron-rich side chains and backbone groups of proteins has been investigated by combining a Protein Data Bank (PDB) survey and ab initio quantum mechanics calculations. More precisely, an inspection of the PDB involving organic ligands containing a CF 3 group and electron-rich atoms (A = N, O and S) in the vicinity revealed 419 X-ray structures exhibiting CF 3 ⋯A tetrel bonds (TtBs). In a posterior stage, those hits that exhibited the most relevant features in terms of directionality and intermolecular distance were selected for theoretical calculations at the RI-MP2/def2-TZVPD level of theory. Also, Hammett's regression plots of several TtB complexes involving meta - and para -substituted benzene derivatives were computed to shed light on the substituent effects. Moreover, the TtBs were characterized through several state-of-the-art computational techniques, such as the Quantum Theory of Atoms in Molecules (QTAIM) and Noncovalent Interactions plot (NCIplot) methodologies. We believe that the results gathered from our study will be useful for rational drug design and biological communities as well as for further expanding the role of this interaction to biomedical applications.

In recent years Pd(II) and Pt(II) cases have been reported wherein metals in square planar complexes were used as nucleophilic partners to construct supramolecular assemblies with electrophilic molecules like σ-hole and π-hole donors. The formation of such assemblies is based on the nucleophilicity and accessibility of the d z 2 orbital (in group-10 elements) in the square-planar complexes. This opens new avenues in inorganic chemistry and crystal engineering as it enriches the current toolbox of noncovalent interactions and supramolecular synthons thus allowing the design of new types of architectures in the solid state. This manuscript reports a comprehensive theoretical study characterizing π-hole⋯d z 2 [M II ] (M = group 10 element) interactions from an energetic point of view. Several computational tools based on the topology of the electron density are used. Examined systems had been identified by considering structures in the Cambridge Structural Database where this interaction was used to construct supramolecular assemblies. Several aromatic rings have been used, varying from π-basic to π-acid rings by adjusting the number of fluorine substituents. Moreover, the influence of metal⋯metal interactions on the nucleophilicity of the d z 2 orbital has been studied using MEP surface analysis. The π-hole energies are moderately strong (from -5 to -10 kcal mol -1 ) and the crucial role of dispersion forces is revealed.

The reactivity of biological or synthetic metalloenzymes is modulated in the presence of redox innocent Lewis acidic metal ions as they change the redox potential of the redox active metal ions present in the active site of metalloenzymes. To study this effect, we synthesised a mono-nuclear V(IV) complex (VOL, 1) with an N 2 O 4 donor bicompartmental ligand, characterized it by single-crystal X-ray crystallography and recorded its cyclic voltammogram in acetonitrile. The CV revealed a reversible redox process for the V(IV)/V(V) couple. The potential of the V(IV)/V(V) couple shifted to a more positive value when equivalent amounts of Li + , Na + , K + , Mg 2+ , Ca 2+ and Ba 2+ ions were added separately to its acetonitrile solution, but the extent of shift for Li + and Mg 2+ was much less than that of the other metal ions. The guest metal ions except Li + and Mg 2+ were accommodated in the outer compartment of VOL as confirmed by IR and UV-Vis spectral analysis. Single-crystal structural analysis of [(VOL)KPF 6 ] 2 , (1·K) and [(VOL)Ba(ClO 4 ) 2 (H 2 O)] n , (1·Ba) also confirmed the hetero-metallic adduct formation. The correlation of the shift of the V(IV/V) redox potential with the Lewis acidity of respective metal ions deviated appreciably from linearity. DFT calculations suggest that the shift in potential is probably controlled by local electric fields induced by those ions, as indicated by 2D vector electric field maps.

Methyltrioxorhenium(VII) (MTO) is a widely employed catalyst for metathesis, olefination, and most importantly, oxidation reactions. It is often preferred to other oxometal complexes due to its stability in air and higher efficiency. The seminal papers of K. B. Sharpless showed that when pyridine derivatives are used as co-catalysts, MTO-catalyzed olefin epoxidation with H 2 O 2 as oxidant, a particularly useful reaction, is accelerated, with pyridine speeding up catalytic turnover and increasing the lifetime of MTO under the reaction conditions. In this paper, combined experimental and theoretical results show that the occurrence of σ-hole interactions in catalytic systems extends to MTO. Four crystalline adducts between MTO and aliphatic and heteroaromatic bases are obtained, and their X-ray analyses display short Re⋯N/O contacts opposite to both O-Re and C-Re covalent bonds with geometries consistent with σ-hole interactions. Computational analyses support the attractive nature of these close contacts and confirm that their features are typical of σ-hole interactions. The understanding of the nature of Re⋯N/O interactions may help to optimize the ligand-acceleration effect of pyridine in the epoxidation of olefins under MTO catalysis.

This communication reports the synthesis and X-ray characterization of a new mononuclear aluminium compound exhibiting an intramolecular σ-hole triel bonding interaction. It is compared with a dinuclear aluminium compound, previously reported by us, where the aluminium atoms participate in two concurrent σ-hole triel bonding interactions. To our knowledge, such behaviour has not been previously described in the literature.

In this article, we describe the serendipitous synthesis of two remarkable iso-structural Cd(ii)-Salen complexes [L 2 Cd 4 (OAc) 2 (NCS) 2 ] in the presence of H 2 L and NaSCN {where L = L 1 ( N , N '-bis(3-methoxysalicylidene)-1,2-diaminopropane) and L = L 2 ( 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) Å 3 , and Z = 4. The inner N 2 O 2 and outer O 4 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 CH 3 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., Competing Interests: The authors indicate no competing interests or personal relationships that may have influenced the work described in this paper., (This journal is © The Royal Society of Chemistry.)

Identifying and characterizing new binding events between electron donor and acceptor counterparts represents a crucial step to complete the molecular recognition and aggregation picture, which is key to chemistry and biology. In this study we interrogated both the PDB (Protein Data Bank) and CSD (Cambridge Structural Database) for the presence of Cu and Ag regium-π (Rg-π) bonds (an attractive noncovalent force between elements from group 11 and π-systems). Concretely, we found evidence of the plausible biological role of the interaction in protein-DNA systems, bacterial Ag extrusion processes and Heme group redox functionality. Furthermore, we also highlighted the implications of Rg-π bonds in the crystal packing of two host-guest systems, where this interaction is key for the binding and recognition of small organic molecules as well as for the encapsulation of organometallic complexes. Theoretical models were used to analyse the strength of the interaction (RI-MP2/def2-TZVP level of theory) together with QTAIM (Quantum Theory of Atoms in Molecules), NBO (Natural Bonding Orbital) and NCIplot (Non Covalent Interactions plot) analyses, which further assisted in the characterization of the regium-π interactions described herein. We expect the results from this study will be useful to attract the attention of chemical biologists as well as to expand the potential of the interaction to the supramolecular chemistry and crystal engineering communities.

Cocrystallization of a bis[1-(4-pyridyl)butane-1,3-dionato]copper(II) (1) complex and 1,4-diiodoperfluorobenzene in the presence of pyridine yields a 1 : 1 cocrystal where both the σ and π-holes of 1,4-diiodoperfluorobenzene play a role. The crystal structure shows short arene CuO 4 ⋯π-hole stacking contacts, where the {d z 2 -Cu II O 4 } moiety functions as an integrated five-center π-hole acceptor. DFT calculations combined with quantum theory of atoms-in-molecules and noncovalent interaction plot analyses corroborated the structure-defining role of the {d z 2 -Cu II O 4 }⋯π-hole contacts.

Single crystal X-ray analyses show that iodine in pyridinium periodates acts as a halogen bond (HaB) donor forming short and almost linear contacts with neutral and anionic electron donors. A combination of QTAIM and NCIplot computational tools proves the attractive nature of these contacts.

The interaction of a [bis(pyridine)iodine(I)] + cation with a [bis(pyridine)silver(I)] + cation, in which an iodonium ion acts as a nucleophile by transferring electron density to the silver(I) cation, is reinvestigated herein. No measurable interaction is observed between the cationic species in solution by NMR; DFT reveals that if there is an attractive interaction between these complexes in solution, it is dominantly the π-π interaction of pyridines.

This manuscript shows that chalcogen bonding (ChB) interactions are enhanced by the coordination of the chalcogen atom to metal centers as evidenced using DFT calculations (PBE0-D3/def2-TZVP level of theory). X-ray structures retrieved from the Cambridge Structural Database (CSD) are used to support the enhanced ability of Se and Te-atoms coordinated to transition metals to participate in ChBs, eliminating the necessity to use strong electron-withdrawing groups bonded to the Ch atom. Orbital analysis performed using the natural bond orbital (NBO) technique discloses a large LP → σ* contribution, especially for anionic electron donors. In one example, the new σ-hole that is generated upon complexation (opposite to the Ch-M bond) plays a crucial role in the solid state, promoting the formation of infinite 1D polymers.

This manuscript reports four new gold(I)-silver(I) complexes with 2-(2-pyridyl)-1,8-naphthyridine (pyNP) and terpyridine (terpy) as ancillary ligands, having formulae [Ag(pyNP)(Au(CN) 2 )] 2 (1), [Ag 2 Au 2 (μ-CN) 2 (CN) 2 (pyNP) 2 ] (2), [Ag 2 Au(μ-CN) 2 (terpy) 2 ][Au(CN) 2 ] (3) and [Ag 4 Au 4 (μ-CN) 8 (terpy) 2 (py)] (4). Complexes 1 and 2 are structural isomers obtained from different solvents. The Au(CN) 2 - anion is not coordinated and establishes intramolecular Au⋯Ag,Ag interactions in 1. In contrast, it is monocoordinated to silver atoms via a CN fragment in compound 2 and no metallophilic interaction is observed. In compound 3, one Au(CN) 2 anion bridges two Ag(terpy) fragments. In this complex an infinite array of gold atoms is found, exhibiting aurophilic interactions of 3.415 Å. In complex 4 the 3D architecture observed in the crystal packing is driven by Au⋯Au and Au⋯Ag metallophilic interactions. All compounds have been structurally and vibrationally characterized to better understand the crystal forces. In addition, a solution chemistry study in different solvents by ESI-MS spectrometry was performed to comprehend the speciation and solvent effects. Finally, DFT calculations were carried out to analyze the Ag⋯Au interactions and also the π-stacking interactions that are relevant in the crystal packing of some structures. Special attention has been paid to the bifurcated nature of the Au⋯Ag,Ag interactions in compound 1 that has been analyzed theoretically using the quantum theory of atoms-in-molecules (QTAIM) and the Natural Bond Orbital (NBO) computational tools.

Porous architectures characterized by parallel channels arranged in honeycomb or rectangular patterns are identified in two polymorphic crystals of a zwitterionic 4-(aryliodonio)-benzenesulfonate. The channels are filled with disordered water molecules which can be reversibly removed on heating. Consistent with the remarkable strength and directionality of the halogen bonds (XBs) driving the crystal packing formation, the porous structure is stable and fully preserved on almost quantitative removal and readsorption of water. The porous systems described here are the first reported cases of one-component 3D organic frameworks whose assembly is driven by XB only (XOFs). These systems are a proof of concept for the ability of zwitterionic aryliodonium tectons in affording robust one-component 3D XOFs. The high directionality and strength of the XBs formed by these zwitterions and the geometrical constraints resulting from the tendency of their hypervalent iodine atoms to act as bidentate XB donors might be key factors in determining this ability., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A coordination polymer (1) and a trinuclear complex (2) have been synthesized using a compartmental N 2 O 2 O 2 ' donor Schiff base ligand. Both complexes are characterized using different spectroscopic techniques and their structures are determined using single crystal X-ray diffraction analyses. Energies associated with different non-covalent (S⋯O chalcogen bonds, C-H⋯H-C, C-H⋯I and C-H⋯π) interactions in the solid state of both complexes have been calculated using the Turbomole program. Investigations of electrical conductivity and photosensitivity of both complexes reveal that suitable Schottky diode devices could be fabricated from both complexes. The current vs. voltage plots of the complex based devices have been used to calculate the conductivity under dark and irradiation conditions. In both complexes the charge transportation mainly occurs through space which involves the hopping process. Standard band theory has been used to compare the experimental and theoretical results of optoelectronic measurements. The calculations confirm that both are direct band gap (2.78 and 3.30 eV) semiconductors and that complex 1 exhibits a lower band gap, in line with the experimental results (3.21 and 3.43 eV in 1 and 2, respectively).

The silver(i) and iodine(i) complexes of the 2-substituted pyridines 2-(diphenylmethyl)pyridine (1) and 2-(1,1-diphenylethyl)pyridine (2), along with their potential protonated side products, were synthesised to investigate the steric limitations of iodine(i) complex formation. The complexes were characterised by 1 H and 1 H- 15 N HMBC NMR, X-ray crystallography, and DFT calculations. The solid-state structures for the silver(i) and iodine(i) complexes were extensively compared to the literature and analysed by DFT to examine the influence of the sterically bulky pyridines and their anions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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)(η 1 -NCS)(η 1 -SCN)] n (1), using a compartmental Salen ligand (H 3 L) 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 P 2 1 / 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 N 2 O 2 and heavier Pb(ii) in the outer O 4 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., Competing Interests: The authors do not indicate any competing interests or personal relationships that may have influenced the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

We describe here a comparative study between two tripodal anion receptors based on selenophene as the binding motif. The receptors use benzene or perfluorobenzene as a spacer. The presence of the electron-withdrawing ring activates the selenium atom for anion recognition inducing the formation of self-assembled supramolecular structures in the presence of chloride or bromide anions, which are bonded by the cooperative action of hydrogen and chalcogen bonding interactions. DOSY NMR and DLS experiments provided evidence for the formation of the supramolecular structures only in the presence of a perfluorobenzene based anion receptor while the analogous benzene one shows the classical anion/receptor complex without the participation of the selenium atom. The energetic and geometric features of the complexes of both receptors with the Cl and Br anions have been studied in solution. These results combined with the molecular electrostatic potential (MEP) surface plots allow us to rationalize the quite different behaviors of both receptors observed experimentally.

Organometal halide perovskites are promising, high-performance absorbers in solar cells. However, the light-harvesting performance of these devices is still limited by excessive charge carrier recombination. Charge carrier management can be improved, taking into account the transport properties of layers surrounding the absorber. In particular, the choice of an appropriate hole-transport material (HTM) could provide a path towards increasing the device performance of perovskite solar cells (PSCs). The Lambertian reflection on the cell's back-surface reflector could increase the power conversion efficiency (PCE) of PSCs as well. Taking into account these facts, we analyse the absorptance and the PCE of a perovskite thin-film solar cell with the Lambertian reflection on the cell's back-surface reflector for various organic and inorganic HTMs. The analysis is done by means of the Monte-Carlo ray tracing simulations complemented by the transfer-matrix method to account for the interference phenomenon in the local generation rate G of carriers in a thin-film multilayer system. This function is employed further in the transport equations to calculate the current-voltage characteristics of the cell. We show that wide band gap HTMs, that possess negligible absorption, increase the photocurrent in the perovskite, passing reflected photons from the back reflector. In contrast, at the same perovskite thickness the PSC gains less photocurrent with narrow band gap HTMs, where an excessive non-radiative recombination takes place. Our analysis demonstrates that the optimal thickness of the solar cell with the typical absorber CH 3 NH 3 PbI 3 is ∼300 nm, providing the maximal efficiency ∼18.8% for the wide band gap HTM (CuSCN) at the moderate absorber purity (the diffusion length  D ∼ 1 μm).

Two new transition metal complexes with 1-methylimidazole (1-MeIm) and azide as ligands, namely, [Co(1-MeIm) 4 (N 3 ) 2 ] (1) and [Ni(1-MeIm) 4 (N 3 ) 2 ] (2), have been synthesized and characterized by IR, Raman, UV-Vis and XPS spectroscopy. Their crystal structures were solved by single-crystal X-ray diffraction. The supramolecular self-assembly of the two complexes is governed by non-classical C-H⋯N hydrogen bonds and C-H ⋯ π interactions. Lattice energies and intermolecular interaction energies for various molecular pairs are quantified using the PIXEL method. DFT computational studies to assess the binding energy through modern tools like non-covalent interaction (NCI plots) analysis and reduced density gradient (RDG) analysis have also been carried out. A detailed analysis of geometric descriptors revealed the existence of quasi-isostructural pairs or 'main-part' isostructuralism in a series formed by 1, 2, and a related cadmium complex, being more evident in the 1/2 pair. DFT studies using theoretical models have been used to disclose the relative importance of the H-bond and C-H⋯π noncovalent interactions. Magnetic measurements for compound 1 show weak ferrimagnetic coupling between adjacent M(II) centers, mediated by H-bonding and C-H⋯π non-covalent interactions.

This manuscript reports the synthesis, X-ray characterization and DFT study of three new [M(bipy) 3 ] 2 [Au(CN) 2 ] 3 (X) (M = Fe, Co, and Ni; bipy = 2,2'-bipyridine; X = anion) ionic compounds. These salts are composed of [M(bipy) 3 ] 2+ dications and [Au(CN) 2 ] - anions in a 2 : 3 ratio. The positive charge is compensated by X = Cl - anions in compounds 1 (M = Fe) and 2 (M = Co) and X = OH - in 3 (M = Ni). The three tridentate bipyridine ligands define the coordination of the M 2+ cation, resulting in a nearly octahedral coordination sphere. The linear dicyanoaurate(I) anions are completely surrounded by a cradle of aromatic rings with Au-ring centroid distances below the sum of van der Waals radii, evidencing the existence of a specific Au⋯π attraction. This interaction has been analyzed in terms of the role of the Au-atom (Lewis acid or Lewis base) using DFT calculations combined with the quantum theory of atoms in molecules (QTAIM), noncovalent interaction plot index (NCIplot) and natural bond orbital (NBO) computational tools. The NBO suggests that the Au⋯π interaction is an example of a coinage bond in spite of the anionic nature of the acceptor and the cationic nature of the donor.

New 1-2 nm macrocyclic iodine(I) complexes prepared VIA a simple ligand exchange reaction manifest rigid 0.5-1 nm cavities that bind the hexafluorophosphate anion in the gas phase. The size of the cavities and the electrostatic interactions with the iodine(I) cations influence the anion binding properties of these macrocyclic complexes.

We report here the design, synthesis, and antiproliferative activity of three coordination complexes [Mn 2 (pydco) 2 (bpy) 2 (H 2 O) 2 ]·2H 2 O (1), [Zn(bpy)(Hpydco) 2 ] (2), and [Zn(bpy)Cl(Hpydco)]·2H 2 O (3) (H 2 pydco = pyridine-2,5-dicarboxylic acid N -oxide, bpy = 2,2'-bipyridine). Molecular structures of these complexes have been characterized by elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and powder and single-crystal X-ray diffraction. According to the structural analysis, 1-3 are discrete complexes containing N - and O -donor ligands (bpy and pydco 2- ) in which pydco 2- can be coordinated to the metal centres via the N -oxide oxygen and one carboxylate oxygen to generate a six-membered chelate ring. Also, these structures benefit from extensive intermolecular interactions such as hydrogen bonds and π-interactions which are the major forces to make them more stable in the solid state. The energetic features of the π-stacking interactions observed in compounds 1-3 have been computed and compared to the H-bonds. The interactions in the solid state have been also studied using the independent gradient model approach (IGM plot). The IGM-δg approach uses a new descriptor (δg) that locally represents the difference between a virtual upper limit of the electron density gradient and the true electron density gradient. This newly developed IGM methodology automatically extracts the signature of interactions between two given fragments. Finally, the antiproliferative properties of these complexes were tested on several cancer cell lines by MTT assay and flow cytometry. Also, to compare the antiproliferative activities of these complexes with common chemotherapy drugs, the antiproliferative property of cisplatin was evaluated as a reference and positive control., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Through the combination of X-ray structure analysis and density functional theory (DFT) theoretical calculations at the B3LYP-D3/def2-TZVP level of theory, we designed and investigated two novel host units for the recognition of neutral ( e.g. halobenzenes) and charged ( e.g. chloride and nitrate) guests inspired by a glutamate carboxypeptidase II (GCPII) system and its inhibitors.