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We report σ-hole interaction/spodium/tetrel bonding and other non-covalent interactions in a heteronuclear Pb(ii)–Salen coordination polymer using DFT, HSA, QTAIM/NCI, and QTAIM/ELF plots. The non-covalent interactions predominantly drive the formation of extended architectures.

Spontaneous self-assembly in the supramolecular entity is one of the enthralling synthetic routes. It produces disparate structure crystal complexes after selecting suitable M-L combinations in the pseudohalide sense. In this attempt, a novel cocrystal is synthesized from two independent components (0D + 1D), [PbCd(L1)(SCN)2]·[PbCd(L1)(SCN)2]n (1) using a Salen (H2L1) and NaSCN, which was characterized by spectroscopic, EDX, SEM, PXRD, and X-ray crystallography. The title complex crystallizes in the triclinic space group P1 with unit cell parameters: a = 8.5733(2), b = 11.3798(2), c = 27.105(5) Å, V = 2583.95(9) Å3, and Z = 4. X-ray structure divulges the de-protonated form of [L−2], comprising Cd(II)/Pb(II) ions placed in the inner N2O2 and outer O4 compartments. The Cd(II)/Pb(II) metal ions satisfy trigonal-prismatic and square pyramidal geometries. Crystal engineering and Hirshfeld surface approaches delineate the dominant interactions, e.g., H-bonding (36.4%), C⋯H (20.8%), and S⋯H (21.1%). The unique chalcogen (ChB)/tetrel bonds observed in its solid-state architecture were authenticated by DFT using the PBo-D3/def2-TZVP level of theory. The QTAIM/NCI plot reveals the nature of these contacts. The S···S distance is 2.499(4) Å, and the C–S···S angle is close to linearity (168.8°), confirming the typical ChB. The MEP surface explores the most nucleophilic part at the N-atom belonging to the bonding of Cd-NCS (– 42 kcal/mol). HOMO–LUMO energy gap and NLO parameters provide chemical reactivity and sensitive optical information about the molecules. Meanwhile, Molecular docking was conceded based on total energy with three bacterial proteins like Staphylococcus aureus (PDB ID: 1JIJ) and pseudomonas aeruginosa (PDB ID: 3JPU), and Escherichia coli (PDB ID: 5MMN). Docking and PLIP confirmed the bioactivity of the complex. The compound was screened in vitro against two-gram + ve and two-gram -ve bacteria. The complex had lower MIC (μg/mL) values (10.1) compared to the parent ligand (32.7), implying greater antimicrobial efficiencies. The time-kill kinetics led to the bactericidal activities of the complex.

Two new dicyanamide modulated zinc metal complexes [Zn4(LOMe)2(µ1-dca)2(µ1,5-dca)2] (1) and [Zn3(LOEt)2(H2O)(µ1-dca)(µ1,5-dca)] (2) have been synthesized using H2vanen-type compartmental ligands. Schiff base ligands and the complexes were characterized by means of elemental analyses, FT-IR, FT-Raman, UV–Visible, powder X-ray diffraction, TGA and fluorescence spectroscopy. Dicyanamide modulated Zn4/Zn3-nuclear metal complexes were structurally characterized by single crystal X-ray diffraction studies. In 1, the asymmetric Zn2-nuclear unit was ensembled with one fully deprotonated Schiff base ligand [LOMe]2− along with two dicyanamide ions where two structurally independent Zn(II) metal centers are found in the X-ray crystal structure. Single X-ray crystal structure confirmed the environment of Zn1 is distorted square pyramidal whereas Zn2 acquires distorted tetrahedral geometry. Unlike 1, in 2 three independent zinc metal centers have been identified as square pyramidal (Zn1), distorted trigonal bipyramidal (Zn2) and distorted tetrahedral (Zn3). 1 and 2 geometry were optimized using hybrid B3LYP functional with DGDZVP basis set to explain frontier molecular orbitals, molecular electrostatic potential and Hirshfeld surface (dnorm surfaces and 2D fingerprint plots). The electronic UV–Vis properties were determined by TD-DFT approach. The steady state and time-resolved fluorescence properties have been explored in DMSO solution. 1 and 2 exhibit bi-exponential decay and intra-ligand (π → π*) fluorescence behaviors with lifetimes in the range (2.45–5.71 ns). In addition, complexes solid-state and different solvent-dependent absorption and fluorescence spectra have been reported. Finally, the cytotoxic effect of the investigated dicyanamide complexes against breast cancer cell line (MCF7) shows promising results which makes them prospective complexes for anticancer medicament studies.

A novel tetranuclear heterometallic complex, [KZn(3-MeOsalpn) (μ1,1-NCS)]2(1) [3-MeOsalpn2- = N, N′-propylene bis(3-methoxysalicylideneiminate)] has been synthesized by the reaction of Zn(OAc)2・2H2O with the multidentate Schiff-base ligand, N, N’-bis(2-hydroxy-3-methoxybenzylidene)-propane-1,2-diamine (H2LOMe) in the presence of KSCN. 1 is characterized by elemental analysis, powder X-ray diffraction and different spectroscopic techniques along with single crystal X-ray crystallography. Crystal structure of 1 completely divulges a very intricate heterometallic environment of Zn(II) which is a centrosymmetric penta-coordinated distorted square pyramidal molecule possessing a basic tetranuclear structural core [KZn(OAr)2(μ1,1-NCS)]2 that consisting mainly two Zn atoms and two K atoms bridged by four μ2-OAr- (O1, O1*, O2 and O2*), and two [μ1,1-NCS]- groups. In the asymmetric unit of the binding action μ2-OAr- from one fully deprotonated [LOMe]2- enable to construct the four membered heterometallic ZnK(O)2 core. Complex 1 structure was optimized with the aid of density functional theory at B3LYP level hybrid functional and GAUSSIAN 16 programming package in presence of 6–31 + g(d, p) basis set. ESP study of Schiff base ligand further supported that polymerization is more favorable with potential border line Zn(II) metal ion. Hirshfeld surface and 2D fingerprint plots have been explored in 1 to find out different types of non-covalent supramolecular interactions. The solution and solid-state luminescent property of the title complex 1 was reported. Fluorescence life time study further indicates that excited state stabilities of 1 are smaller than Schiff base ligand. Finally, experimental UV–Vis electronic transitions of 1 were compared with those obtained theoretically from TD-DFT level of calculations.

Two new dicyanamide-interlaced tetranuclear Zn(II)-Schiff-base complexes [Zn2(LOMe)(µ-dca-κN1κN5)(µ-dca-κN1)]2 (1) and [Zn2(LOEt)(µ-dca-κN1κN5)(µ-dca-κN1)]2 (2) were synthesized by using salicylaldimino type Schiff bases (H2LOMe) and (H2LOEt) respectively. Schiff base ligands and the complexes were characterized by elemental analyses, powder X-ray diffraction, FT-IR, FT-Raman, 1H NMR, 13C NMR, UV–Vis, TGA and fluorescence spectroscopy. Dicyanamide modulated complexes were structurally characterized by single crystal X-ray diffraction studies. X-ray crystal structure divulges that the two complexes are isostructural. In both the complexes, the Zn1 metal centers fulfill 5-coordinated distorted square pyramidal geometry having ZnN3O2 chromospheres where Schiff bases are mainly trapped in their complete deprotonated dianionic forms[L]2−, whereas Zn2 metal center attained distorted octahedral geometry. In both complexes two asymmetric units are connected by double μ1,5-dicyanamide ion thus forming Zn4-nuclear metal complex. B3LYP/def2-TZVP level of theory (DFT) successfully applied in both complexes. The complexes (1–2) exhibit intraligand (π → π*) fluorescence in DMSO solvent with lifetimes in the range 0.66–0.82 ns. In vitro antibacterial, membrane damage assay and anti-biofilm properties of both complexes are evaluated against some important Gram-positive and Gram-negative bacterial strains. Finally, the UV–Vis experimental spectral findings are well rationalized with the electronic distribution of HOMO-LUMO through TD-DFT level of calculations.

In this work we have reported two novel tetranuclear Cd(II) complexes viz. [Cd4 (LOMe)2 (μ1,1-N3)3 (μ1,3-N3)]n (1) and [Cd4 (LOEt)2 (μ1,1-N3)3(OAc)]2 (2) where (H2LOMe) and (H2LOEt) are two important less explored salen-type Schiff base ligands. Both of the complexes have been characterized by using routine spectroscopic techniques, elemental analyses (C, H and N), X-ray powder diffraction pattern (PXRD) and thermal analysis by TGA along with single x-ray crystallography. The complete structural study discloses that in both cases the fully deprotonated ligand [LOMe]2- or [LOEt]2- utilized all potential coordination sites to accommodate four Cd(II) ions. Complex 1 is a one-dimensional polymer with azide (N3) linkage having both (μ1,1 end on) and (μ1,3 end-to-end) azido bridging but complex 2 is a discrete octanuclear ensamble where two [Cd4(O)4(N)2]2+ units bridged to each other showing μ1,1 end on end on azide bridging. Exploration of photo physical properties in DMSO solvent reveals that Cd(II) complexes enhance appreciably the fluorescence behavior over free Schiff base ligands (H2LOMe) and (H2LOEt). DFT calculations performed at B3LYP/def2-TZVP level of theory reveal both the energetics and composition of FMOs in these complexes and also show electrophilic and nucleophilic areas via molecular electrostatic maps [ESP] concept. The antibacterial, membrane damage assay and anti-biofilm properties of complexes 1 and 2 were investigated very carefully against some important Gram-positive and Gram-negative bacterial strains.

Two new dicyanamide bridged multinuclear Zn complexes, [Zn

A series of dinuclear Zn(II) complexes [Zn2 (L1) (CH3OH)2(SCN) (OAc)](1), [Zn2 (L1) (CH3OH)2(N3)2](2) and [Zn2 (L1) (Cl)2(CH3OH)]·CH3OH (3) have been synthesized by the reaction of compartmental Schiff base ligand (H2L1) [N,N′-Bis(3-ethoxysalicylidenimino)-1,3-diaminopropane] with Zn(OAc)2·2H2O in presence of coligand like KSCN, NaN3 and NaCl respectively. X-ray diffraction analysis revealed that all the complexes are neutral and possess a 4-membered Zn2 (μ2-O)2 ring fastened by the unified coordination action of a doubly deprotonated ligand. In addition, solid state structure of the complexes display extensive intermolecular interaction which has been supported theoretically by Hirshfeld surface analysis with 2D Fingerprint plots. The synthesized Zn(II) metal complexes observed enhancement of luminescence emission compared to the parent Schiff base due to emanating ligand based intraligand (π→π∗) fluorescence. Additionally, Zn(II) metal complexes exhibited considerable antimicrobial potency against some important Gram +ve and Gram -ve bacteria.

Two new dicyanamide bridged multinuclear Zn complexes, [Zn2(L1)(µ1,5-dca)2(µ1-dca)]n (1) and [Zn2(L2)(µ1,5-dca)2(µ1-dca)]n (2) have been synthesized using N2O4-based pro-ligands (H2L1 = N,N′-bis(5-bromo-3-methoxysalicylidenimino)-1,3-diaminopropane, H2L2 = N,N′-bis(3-ethoxysalicylidene)-2,2-dimethyl-1,3-propanediamine) and characterized by microanalytical and spectroscopic techniques. Both complexes are stable in solution and solid-state. Thermogravimetric analysis (TGA) findings showed that complexes are stable at room temperature. Single-crystal X-ray diffraction (SCXRD) has proven that complexes are identical structures where two zinc metal ions are crystallographically independent. The directional properties of dicyanamide co-ligands via µ1,5 bridging have resulted in different connectivity of zinc metal ions leading to 1D templates. SCXRD revealed some notable non-covalent interactions (π⋯π, C-H····π, and H-bonding) in their solid-state crystal structures. 1–2 have strong fluorescence behaviour over pro-ligands, which may be quenched in the presence of various electron-deficient explosive nitroaromatic compounds (epNACs). Complex 2 fluorescence intensity is sharper than 1; hence the former retained high sensitivity and selectivity for trinitrophenol (TNP). The enhancement of fluorescence mechanism, detection limit (LOD), and the quenching constant (KSV) have been calculated using the Stern-Volmer equation (SV), where the KSV value for TNP is found to be 1.542 × 104 M−1. The solution phase quenching mechanism has been rationalized by (a) electrostatic interactions through charge-transfer complex, (b) photo-induced electron transfer (PET) by the HOMO-LUMO energy gap via DFT, and (c) fluorescence resonance energy transfer (FRET). Finally, complex 2 is applied as a sensor by turn-off fluorescence response to detecting TNP nitroaromatics in the DMF medium.

A novel heteronuclear Salen complex, [NiHgCl2(L)] (1) (H2L = N,N′-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3-diamine) has been integrated using two different synthetic lines. The complex is characterized by various spectroscopic techniques, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and single-crystal X-ray diffraction (SC-XRD). Powder X-ray diffraction (PXRD) confirms complex phase purity and crystallinity. The scanning electron microscope and energy-dispersive X-ray analysis (SEM-EDX) identified the element’s chemical composition, morphology, and crystal size. X-ray diffraction revealed ligand released phenoxide-type deprotonated form [L]2− and had spent two pockets, N2O2 pocket occupied by Ni(II) comprises square planar geometry (NiN2O2). In contrast, Hg(II) occupies a large open O4 compartment accompanied by two chloride ions (HgO4Cl2), switching to achieve a trigonal prismatic structure. The close surveillance of the crystal structure discloses various non-covalent interactions like H-bonding, C H⋯π, and π⋯π. The complex’s geometry was fully optimized, employing the quantum chemistry method at the DFT/B3LYP with the 6-31G (d, p) basis set to divine the vibrational spectra, NMR chemical shifts, and solvent effect on the electronic properties. Natural Bond Orbital (NBO) dissected the stability of the molecular structure and the intermolecular orbital interactions. The highest stabilizing energy was 132.84 kcal/mol between the lone pair C12 and the antibonding of N7-C17 atoms. The Hirshfeld Surface (HS) is detectable that the H⋯N input is maximum than H⋯O. The electrophilic-nucleophilic sites, non-covalent interactions, and reactivity were investigated based on Molecular Electrostatic Potential (MESP), Reduced Density Gradient (RDG), atoms in a molecule (AIM), and the HOMO-LUMO difference. Eventually, a significant correlation was anticipated between theoretical and experimental spectroscopic criteria.

A new hetero-bimetallic Zn(II)/Ca(II) complex, [Zn2(LOMe-pn)2(ƞ1-NCS)2Ca] (1) has been synthesized using a potentially hexadentate N2O4 proligand, H2LOMe-pn = N,N-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3 diamine and structurally well characterized by different physicochemical techniques. Single crystal X-ray diffraction study of the complex revealed that, de-protonic form of the ligand utilizes two pockets, one is occupied by Zn(II) ion and other is housed by a Ca(II) ion. The Zn centres are fitted into the N2O2 compartment with distorted square pyramidal geometry while a large open O2O2' compartment is occupied by a Ca(II) ion in a octacoordinated environment. DFT studies were successfully carried out using DFT/M06 functional level and 6-31G * basis set (over all the atoms) to delineate the complex optimized structure, composition of the frontier molecular orbitals, global reactivity, total energy frameworks, MEP, total dipole moment, average polarizability and first hyperpolarizability. First hyperpolarizability value (59.62 × 10 −31 esu) suggests that complex is a good NLO material. Hirshfeld surface revealed the presence of many short intermolecular contacts like C⋯H/S⋯H/N⋯H/O⋯H/H⋯H/C⋯C and S⋯S in the crystal structure. The experimental absorption spectra are comparable with the electronic transitions assigned from TD-DFT studies. CHEF based (π→π*) luminescence property has been measured in DMSO solvent at room temperature. Concentration dependent antibacterial efficacy was investigated against gram-negative bacterial strains viz. Escherichia coli (ATCC 25922) & Pseudomonas aeruginosa (ATCC 27853) and gram-positive bacterial strains viz. Staphylococcus aureus (ATCC 25923) & Bacillus subtilis (ATCC 6633). The bacterial killing efficiency and solvent effect of the complex was compared with that of ligand. Finally, a docking study with the active site of DNA Gyrase and DNA Polymerase III proteins has been carried out to corroborate the experimental findings.

A linear Zn(II) complex, [Zn3(LOMe-pn)2(ƞ1-NCS)2] (1) containing a N2O2O′2 donor Schiff base, (H2LOMe-pn = N, N-bis(3-methoxysalicylidene)-2, 2-dimethylpropane-1, 3 diamine) has been synthesized and structurally well characterized. SCXRD study reveals that in 1, the asymmetric section contains two identical discrete unit and each discrete unit contains three zinc metal ions (Zn1, Zn2 and Zn3) which are crystallographic independent, two deprotonated ligands [LOMe-pn]2- and [SCN−] ions which are linked with only terminal zinc ion in a η1 mode where terminal zinc atoms (Zn1/Zn3) are distorted square pyramidal while Zn2 is square antiprismatic. All computational calculations were performed by the DFT/M06 functional level and the 6-31G * basis set in the ground state. Complex optimized structure, HOMO-LUMO energy gap, Hirshfeld surface, MEP and NLO property was nicely explained with the help of DFT. Total dipole moment, average polarizability and first hyperpolarizability were calculated where α and βhyp values are well demonstrate the NLO property of complex (1). In addition, Bader’s “atoms-in-molecules” was analysed to delineate complex non-covalent interactions using the same level of theory. Experimental electronic spectra were explained using TD-DFT level of calculations with an IEFPCM solvent model. DMF solvent explore complex (1) is a fluorescent material with maximum emission at 479 nm at an excitation wavelength of 300 nm. Finally, molecular docking was executed with cytochrome P450 from B. megaterium and M. tuberculosis. Results of molecular docking and HOMO-LUMO energy gap can provide new insights in the development of antimycobacterial drugs and next-generation semiconductor devices.

Gold and silver-gold alloy nanoparticles with mean diameter of 10nm and narrow size distribution were prepared by reduction of the correspondent metal precursors using aqueous dextran solution which acts as both a reducing and capping agent. The formation of nanoparticles was characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS). The silver and gold nanoparticles exhibited absorption maxima at 425 and 551 nm respectively; while for the bimetallic Ag-Au alloy appeared 520 nm in between them. TEM images showed monodispersed particles in the range of 8-10nm. The crystallinity of the nanoparticles was assured by XRD analysis. DLS data gave particle size distribution. The dextran stabilized Au nanoparticles used as a colorimetric sensor for detection and estimation of pesticide present in water. The dextran stabilized Ag-Au alloy nanoparticles exhibited interesting antimicrobial activity against bacteria at micromolar concentrations.

A di-nuclear azido-bridged Cd(II) 1-D coordination polymer [Cd2(H2LpentOMe)(µ1,1-N3)2]n (1) has been successfully synthesized using less explored bi-compartmental Schiff base ligand (H2LpentOMe) and characterized by elemental analysis, FT-IR, FT-Raman, UV–Visible, SEM-EDAX, powder X-ray diffraction and fluorescence spectroscopy. Solid-state X-ray single crystal study revealed two different geometrical environment of Cd metal centres with distorted square pyramidal (Cd1) and distorted pentagonal bipyramid (Cd2). Overall, small-sized azide ions in asymmetric unit act as µ1,1 bridging mode. Geometry is optimized in gas phase using ORCA 3.0.3 and B3LYP level TZVP basis set to explain frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) and global reactivity. The HOMO-LUMO energy gap (3.434 Ev) suggests that chemical reactivity of complex 1 is low but fairly stable. Moreover, molecular electrostatic potential map was drawn to identify reactive regions in terms of electrophilic and nucleophilic. The steady state and time-resolved fluorescence properties have been explored in DCM and solid-state condition at room temperature. Complex 1 exhibit bi and tri-exponential decay in DCM as well as solid-state. The fluorescence behaviours are predominantly intra-ligand in nature (π → π*) with lifetimes in the range (1.16–1.11 ns). Solvatochromism has been reported to show solvent dependent absorption and fluorescence spectral changes. Fascinatingly, red shifted solvatochromism was observed upon increasing solvent polarity. Finally, concentration dependent antimicrobial activity was investigated against two standard bacterial strains (Staphylococcus aureus (ATCC 25923) and Methicillin-resistant Staphylococcus aureus (MRSA) where 250 µg/ml concentration of complex 1 is sufficient to show the antimicrobial effect.

In this paper we reported preparation of methylcellulose-silver nanocomposite films by mixing of aqueous solution of methylcellulose with silver nitrate followed by casting. The silver nanoparticles were generated in methylcellulose matrix through reduction and stabilization by methylcellulose. The surface plasmon band at 412 nm indicated the formation of Ag nanoparticles. The MC-Ag nanocomposite films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). The X-ray diffraction analysis of synthesized MC-Ag nanocomposite films revealed that metallic silver was present in face centered cubic crystal structure. Average crystallite size of silver nanocrystal was 22.7 nm. The FTIR peaks of as-synthesized MC-Ag nanocomposite fully designated the strong interaction between Ag nanoparticles and MC matrix. Nano-sized silver modified methylcellulose showed enhanced mechanical properties i.e. the introduction of Ag leading to both strengthening and toughening of MC matrix. The methylcellulose-silver nanocomposite films offered excellent antimicrobial activity against various microorganisms.

A simple one-step rapid synthetic route is described for the preparation of silver nanoparticles by reduction of silver nitrate (AgNO3) using aqueous dextran solution which acts as both reducing and capping agent. The formation of silver nanoparticles is assured by characterization with UV-vis spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The absorbance of the silver nanoparticles is observed at 423 nm. The AFM image clearly shows the surface morphology of the well-dispersed silver nanoparticles with size range of 10-60 nm. TEM images show that the nanoparticles are spherical in shape with ∼5-10 nm dimensions. The crystallinity of Ag nanoparticles is assured by XRD analysis. The antimicrobial activity of as synthesized silver nanoparticles is tested against the bacteria, Bacillus subtilis, Bacillus cereus, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The bacterial growth is inhibited by gradual reduction of the concentration of the silver nanoparticles.

Silver nanoparticles were successfully synthesized from AgNO3 through a reliable, eco-friendly and simple green route using Paederia foetida L. leaf extract as a reducing cum stabilizing agent. UV-Visible Spectroscopy, dynamic light scattering, atomic force microscopy, transmission electron microscopy, and X-ray diffraction analysis were used for characterization of silver nanoparticles. The synthesized silver nanoparticles were spherical in shape with size range of 4–15 nm. The nanoparticles were face-centered cubic crystal structure. The adopted technique for silver nanoparticle synthesis is suitable for large-scale production. The as-prepared silver nanoparticles revealed excellent antibacterial activity against different gram classes of bacteria and would be a promising candidate for various pharmaceutical, biomedical, and environmental applications.

A facile one-pot approach for rapid synthesis of silver and gold nanoparticles (Ag NPs and Au NPs) with narrow size distribution and good stability was described by reducing silver nitrate and chloroauric acid with polysaccharide dextrin. Here, dextrin was used as both a reducing and stabilizing agent for synthesis of NPs. The as-synthesized Ag NPs and Au NPs were characterized by UV–visible absorption spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The Ag NPs and Au NPs exhibited an absorption maxima at 404 and 547 nm respectively. TEM images showed NPs in the range of 8–28 nm. The crystallinity of the NPs was measured by XRD analysis. Furthermore, the as-prepared Ag NPs revealed colorimetric sensor property for detection of Cu2+ ions based on changes in absorbance resulting from metal ion-induced aggregation of NPs or direct deposition of metal ions onto NPs. The as-prepared Au NPs exhibited a notable catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4.