Ionic dioxidovanadium(V) complexes with Schiff-base ligands as potential insulin-mimetic agents : substituent effect on structure and stability

Four dioxidovanadium(V) complexes with Schiff-base ligands based on 2-hydroxybenzhydrazide with four different substituted salicylaldehydes (5-chlorosalicylaldehyde, 3,5-dichlorosalicylaldehyde, 5-nitrosalicylaldehyde, 3-bromo-5-chlorosalicylaldehyde) were synthesized and described, by using V(2)O(5) and triethylamine. The single crystal X-ray structure measurements as well as elemental analyses and IR spectra confirmed the formulas of the ionic complexes with a protonated triethylamine acting as counterion, HTEA[VO(2)(L)] (HL = Schiff-base ligand). The kinetic stability of the complexes at pH = 2 and 7 was discussed with respect to the neutral vanadium(V) complexes previously studied as potential insulin-mimetic agents. A correlation between the substituents in an aromatic ring of the Schiff-base ligands with crystal packing, and also with the stability of the compounds, was presented

Molecular and crystalline architectures based on HgI : from metallamacrocycles to coordination polymers

We report the synthesis and X-ray characterization of three metallamacrocycles and one coordination polymer obtained by using coordination driven self-assembly of the HgI2 salt with four different ligands

Solvent dependent nuclearity of manganese complexes with a polydentate hydrazone-based ligand and thiocyanate anions

The reaction of Mn(II) chloride with the 2-benzoylpyridyl-(2-picolyl)-hydrazone ligand (HL) and thiocyanate anions in different solvent systems affords mono- [Mn(HL)2(SCN)2] (1), di- [Mn2(HL)2(SCN)4] (2) and a tetra-nuclear complex [Mn4(L)4(SCN)4].2(CH3CN) (3) with concomitant different coordination modes of the ligands. Remarkably, the nuclearity of the complexes only depends on the solvent used, ethanol for 1, n-propanol for 2 and acetonitrile for 3. The complexes have been characterized by elemental analysis, IR spectroscopy technique and the molecular structures determined by single crystal X-ray analysis. In 1 and 2 the ligands are present in its neutral form, while they are deprotonated in 3, but more significantly in all structures a different denticity of ligands was detected: in complex 1 one molecule is tridentate coordinated though the N,N,O donor set, the other bidentate through N,O; in 2 the ligands is of N,N,O-tridentate; finally in 3 each ligand, acting as N,N,O,N-tetradentate species, bridges two metals to form a tetranuclear assembly. The crystal structures have been described using the Hirshfeld surface analysis. Finally, we have studied the ability of the thiocynato ligand to participate in H-bonding and C\u2013H/\u3c0 interactions by means of DFT calculations (B3LYP/6-31+G 17 17)

Anion-driven tetrel bond-induced engineering of lead(II) architectures with N′-(1-(2-pyridyl)ethylidene)nicotinohydrazide : experimental and theoretical findings

The evaluation of N′-(1-(2-pyridyl)ethylidene)nicotinohydrazide (HL) as a linker for the PbII tagged extended structures is described. The reaction of Pb(ClO4)2 or Pb(OAc)2 with HL in MeOH at 60 °C and room temperature, respectively, leads to heteroleptic complexes {[PbL]ClO4}n·nH2O and [PbL(OAc)]2, while the same reaction of Pb(ClO4)2 with HL at 60 °C in the presence of two equivalents of NaOAc or NaNO2 leads to heteroleptic complexes {[Pb(HL)(OAc)]ClO4}n and [PbL(NO2)]n, respectively. Using Pb(NO3)2 as a source of PbII in the same reaction with HL and two equivalents of NaN3 or NaNCS at room temperature yields [PbLN3]n and [Pb2(HL)2(NO3)2(NCS)2], respectively. The room temperature reaction of Pb(NO3)2 with HL in the presence of two equivalents of NaClO4 leads to the transformation of the parent ligand to its perchlorate salt [H2L]ClO4. In all the obtained PbII structures, HL or its deprotonated form L acts both as a chelating and a bridging ligand. The nature of the inorganic anion also influences the final structure. In all complexes the PbII center exhibits a hemidirected coordination geometry with all the covalent bonds being concentrated on one hemisphere of the coordination sphere with the closest approach of two atoms on the other side varying from 151° to 232°. The sterically available PbII ion participates in tetrel bonding as evidenced from the detailed structural analysis of the described complexes. As a result of tetrel bonding, the structures of all the six compounds can be extended to a higher dimensional framework, which is further stabilized by π⋯π stacking interactions between the aromatic rings. The DFT based charge and energy decomposition (ETS-NOCV) calculations are performed in order to shed light on the nature of non-covalent interactions that determine the stability of the obtained structures

Metal-organic and supramolecular lead(II) networks assembled from isomeric nicotinoylhydrazone blocks : the effects of ligand geometry and counter-ion on topology and supramolecular assembly

A new series of six structurally diverse lead(II) coordination compounds was assembled from two isomeric nicotinoylhydrazones as neutral ligands and three Pb(II) salts with different monoanions (chloride, nitrate and thiocyanate) as starting materials. The products were isolated in good yields and were fully characterized, including by single-crystal Xray diffraction and theoretical methods. Within the six compounds, three feature 2D metal-organic networks, two are 1D coordination polymers, and another one comprises discrete 0D dimeric units. The structures of the latter low dimensional compounds are extendable into 2D supramolecular networks. The topology of the coordination or supramolecular networks is primarily dictated by the geometry of the nicotinoylhydrazone used as a main building block. In contrast, supramolecular interactions are greatly influenced by the choice of the anion in the starting lead(II) salt, which is demonstrated by Hirshfeld surface analysis. In fact, the topological analysis and classification of metal-organic or supramolecular underlying networks in the obtained compounds was performed, disclosing the hcb, 2C1, gek1, SP 1-periodic net (4,4)(0,2) and 3,4L83 topological types; the latter topology was docummented for three compounds, including both coordination and supramolecular networks. In two compounds containing thiocyanate moieties there are supramolecular contacts between thiocyanate anions and lead centres. These were shown by DFT calculations to be strong tetrel bonds (–15.3 and –16.7 kcal/mol) between the σ-hole of the lead atom and the π-system of the thiocyanate S–C bond

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

Five new Pb(ii) complexes of hydrazone-based and Schiff-based ligands and three different anionic co-ligands (azide, thiocyanate and bromide) have been synthesized and characterized by structural, analytical and spectroscopic methods. This variety of ligands can coordinate to the Pb(ii) metal center in a tridentate or tetradentate fashion via a different combination of any of nitrogen, oxygen and sulphur donor atoms. Moreover, the organic ligands can be in mono-deprotonated or neutral forms. By using single-crystal X-ray crystallography, we show that the synthesized complexes aggregate into larger supramolecular entities due to the formation of noncovalent tetrel bonding interactions. The Pb(ii) center is hemidirectionally coordinated even in those complexes where the coordination number is six. Consequently, this is sterically ideal for establishing tetrel bonding interactions with electron-rich nitrogen, bromide or sulphur atoms. These contacts are significantly larger than the sums of the covalent radii. Hence, they can be described as non-covalent tetrel bonding interactions. They interconnect the covalently bonded units into supramolecular assemblies (dimers or tetramers). The contribution of contacts involving the Pb atom has been studied using Hirshfeld surface analysis and fingerprint plots. We have analysed the supramolecular assemblies observed in the solid state by means of DFT calculations and characterized them using Bader's theory of atoms-in-moleculesS. K. Seth is grateful to the SERB-DST (Govt. of India) for the Overseas Postdoctoral Fellowship (SB/OS/PDF-524/2015-16). G. M. is grateful to the University of Maragheh for the financial support of this research (Agreement number 95.1726). A. B. and A. F. thank the MINECO/AEI of Spain (projects CTQ2014-57393-C2-1-P and CTQ2017-85821-R). A. B. and A. F. thank the CTI (UIB) for computational facilitie

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

Structural versatility of the quasi-aromatic Möbius type zinc(II)-pseudohalide complexes : experimental and theoretical investigations

In this contribution we report for the first time fabrication, isolation, structural and theoretical characterization of the quasi-aromatic Mobius complexes [Zn(NCS)(2)L-I] (1), [Zn-2(mu(1,1)-N-3)(2)(L-I)(2)][ZnCl3(MeOH)](2)center dot 6MeOH (2) and [Zn(NCS)L-II](2)[Zn(NCS)(4)]center dot MeOH (3), constructed from 1,2-diphenyl-1,2-bis((phenyl(pyridin-2-yl)methylene)hydrazono)ethane (L-I) or benzilbis(acetylpyridin-2-yl)methylidenehydrazone (L-II), respectively, and ZnCl2 mixed with NH4NCS or NaN3. Structures 1-3 are dictated by both the bulkiness of the organic ligand and the nature of the inorganic counter ion. As evidenced from single crystal X-ray diffraction data species 1 has a neutral discrete heteroleptic mononuclear structure, whereas, complexes 2 and 3 exhibit a salt-like structure. Each structure contains a Zn-II atom chelated by one tetradentate twisted ligand L-I creating the unusual Mobius type topology. Theoretical investigations based on the EDDB method allowed us to determine that it constitutes the quasi-aromatic Mobius motif where a metal only induces the pi-delocalization solely within the ligand part: 2.44|e| in 3, 3.14|e| in 2 and 3.44|e| in 1. It is found, that the degree of quasi-aromatic pi-delocalization in the case of zinc species is significantly weaker (by similar to 50%) than the corresponding estimations for cadmium systems - it is associated with the Zn-N bonds being more polar than the related Cd-N connections. The ETS-NOCV showed, that the monomers in 1 are bonded primarily through London dispersion forces, whereas long-range electrostatic stabilization is crucial in 2 and 3. A number of non-covalent interactions are additionally identified in the lattices of 1-3

Modulation of coordination in pincer-type isonicotinohydrazone Schiff base ligands by proton transfer

We present here two different coordination polyhedra of pincer type N2O hydrazone based ligands supplemented with thiocyanate ions. The compounds namely [Hg(SCN)2(HL1)] (1) and [Hg(SCN)2(HL2)] (2) have a common isonicotinohydrazone fragment and have been prepared by using a coordination driven self-assembly of the Hg(SCN)2 with two different ligands including 2-benzoylpyridine-isonicotinoylhydrazone (HL1), and 2-acetylpyridineisonicotinoylhydrazone (HL2). In compound 1 the ligand coordinated to the mercury center in the keto form (=N–NH=C=O) whereas, in compound 2, the proton at the hydrazine group have been shifted to the uncoordinated pyridine ring and the ligand acted as a zwitterion. The structures provide a complementary system for proton transfer within the ligand molecule involving the keto-enol tautomerization of amide group and 4-pyridyl N protonation. As a result, the relative location of orbitals and ligands in the complexes are different as well as the bonding strength and the coordination polyhedra. We have also studied electrostatically enhanced π···π (either conventional or involving the chelate ring) interactions observed in the solid state of both compounds and analyzed them using DFT calculations, Molecular Electrostatic Potential surface and the Bader’s theory of atoms in molecules

Lead(II) coordination polymers driven by pyridine-hydrazine donors : from anion-guided self-assembly to structural features

In this work, we report extensive experimental and theoretical investigations on a new series of PbII coordination polymers exhibiting extended supramolecular architectures, namely [Pb2(LI)(NCS)4]n (1), [Pb(HLII)I2]n (2), [Pb(LIII)I]n (3) and [Pb(HLIV)(NO3)2]n·nMeOH (4), which were self-assembled from different PbII salts and various pyridine-hydrazine based linkers, namely 1,2-bis(pyridin-3-ylmethylene)hydrazine (LI), (pyridin-4-ylmethylene)isonicotinohydrazide (HLII), 1-(pyridin-2-yl)ethylidenenicotinohydrazide (HLIII) and phenyl(pyridin-2-yl)methylenenicotinohydrazide (HLIV), respectively. It is recognized that the origin of self-assembling is fundamentally rooted in a dual donor (6s2/6p0 hybridized lone electron pair) and electrophilic behaviour of PbII. This allows production of extended topologies from a 1D polymeric chain in 4 through a 2D layer in 2 to the 3D frameworks in 1 and 3, predominantly due to the cooperative action of both covalent and non-covalent tetrel interactions of the overall type Pb-X (X = O, N, S, I). Counterintuitively, the latter, seemingly weak interactions, have appeared to be even stronger than the typical covalent bonds due to the presence of a bunch of supportive London dispersion dominated contacts: ππ, Lpπ, C-HO, C-HI, C-HH-C as well as more typical mainly electrostatically driven N-HO or N/O-HO hydrogen bonds. It is revealed that the constituting generally strong tetrel type Pb-X (X = O, N, S, I) bonds, though dominated by a classic Coulomb term, are therefore characterized by a very important London dispersion constituent, extremely strong relativistic effects and the two way dative-covalent Pb ↔ X electron charge delocalization contribution as revealed by the Extended Transition State Natural Orbital for Chemical Valence (ETS-NOCV) charge and energy decomposition scheme. It unravels that the pyridine-hydrazine linkers are also excellent London dispersion donors, and that together with the donor-acceptor properties of the heavy (relativistic) PbII atoms and nucleophilic counterions lead to extended self-assembling of 1-4