Trigonal Bipyramidal Coordination Geometry Research Articles

An oxo‐acetato‐bridged trinuclear cobalt(III) cluster‐persuaded cobalt oxide active electrocatalyst for efficient hydrogen evolution activity

This study presents the synthesis and electrocatalytic performance of the cobalt(III) complex [Co3(μ1,1,1‐O)(μ1,3‐CH3CO2)(L)3]2(DMF)3 (Cotri), featuring a double deprotonated (N,O)‐donor ligand (L2‐), where the protonated form of it (H2L) is 2,2′‐(hydrazine‐1,2‐diylidenebis(ethan‐1‐yl‐1‐ylidene))diphenol. The X‐ray structure reveals a trinuclear cobalt cluster formed with three cobalt(III) centers interlinking through oxido (μ1,1,1‐O) and acetato (μ1,3‐O2CCH3) bridges in coupling with bis‐congregator‐type chelating ligands. Cotri adopts cobalt centers of octahedral and trigonal bipyramidal coordination geometries and bears a dominant Co(2)…H(DMF) agostic interactions appraised by lattice dimethyl formamide (DMF) molecules. Further, Cotri shows promising heterogeneous electrocatalytic hydrogen evolution activity in 1 M KOH, with an overpotential of 441 mV to achieve 10 mA/cm2 current density. Tafel slope analysis suggests the Volmer–Heyrovsky step as the rate‐determining step. The number of active sites and TOF for Cotri were estimated at 4.010 × 10−8 mol and 0.2467 s−1, respectively, ensuring its excellent hydrogen generation activity. Stability assessments through controlled potential electrolysis (CPE) and cyclic voltammetry (CV) for multiple cycles addressed the transformation of Cotri to Co2O3 nanoparticles, which turned out to be a more active Co2O3 electrocatalyst. The morphology and particle size of the in situ developed Co2O3 active catalyst under the electrochemical conditions attributes to the superior hydrogen evolution activity.

Solution structure, crystal structure, Hirshfeld surface analysis of copper(II) diamide species as an optical chemical sensor

Optical chemical sensors are promising tools for the detection of metal ions in various samples. Copper(II) has received significant attention among metal ions due to its toxic nature and widespread applications in various industrial processes. In recent years, several optical chemical sensors have been developed to detect copper(II) with high sensitivity and selectivity. This paper describes the spectrophotometric determination of trace amounts of copper(II) using N1-(2-aminoethyl)-N2-((pyridin-2-yl)methyl)oxalamide (H2(555)NH2) as an optical chemical sensor. The protonation and formation constants of the Cu(II)/(H2(555)NH2) system were determined at 25 °C and the ionic strength of 0.15 mol dm−3 using glass electrode potentiometry. The structures of the different species, present in solution at different pH values, were determined using UV–vis, 1H NMR, and EPR spectroscopic techniques. At pH 5, the [Cu(H2(555)NH2)]2+ species was formed with the Cu(II) coordinated to the pyridole nitrogen and the terminal amine. Above pH 8, [Cu(H2(555)NH2)H-2] is the most predominant species in solution. Here the Cu(II) coordinates to all four nitrogen atoms. In the solid state, a dinuclear complex, [Cu(H(55)NH3)Cl]2[Cu(H2O)2(NO3)2Cl2]H2O, was formed. Single crystal X-ray structure showed the Cu(II) to be coordinated to the pyridine and the amide N-atoms in addition to an O-atom from one of the two carbonyl groups. The coordination environment was completed by two bridged chloride ions to give a slightly distorted trigonal bipyramidal coordination geometry around the copper centre. The amine was not coordinated. The proposed sensor was successfully applied to determine copper(II) in real samples, with recoveries ranging from 10−5 to 10−3 mol/dm−3. Using H2(555)NH2 as an optical chemical sensor emerged as a powerful tool for detecting copper(II) ions in different aqueous samples.

Synthesis, characterizations, antitumor and antimicrobial evaluations of novel Mn(II) and Cu(II) complexes with NNN-tridentate s-Triazine-Schiff base ligand

The new s-triazine hydrazone, 2,4-bis(morpholin-4-yl)-6-[(E)-2-[1-(pyridin-2-yl)ethylidene]hydrazin-1-yl]-1,3,5-triazine, (L) ligand was used to synthesize three new metal complexes. Single-crystal X-ray diffraction analysis indicated that the [MnLCl2] (1) and [CuLCl2].H2O (2) complexes exhibit distorted trigonal bipyramidal coordination geometry with one NNN-tridentate ligand L and two chloride ions. The trigonality index (τ5) was calculated to be 0.332 and 0.235 Ǻ for complexes 1 and 2, respectively. In case of the [CuL(NO3)2] complex (3), the Cu(II) ion is hexa-coordinated with one NNN-tridentate ligand L, one bidentate nitrate and one monodentate nitrate. The supramolecular structure of complexes 1 and 3 was analyzed using Hirshfeld calculations; hydrogen bonding-based interactions have the largest contribution in their molecular packing. The anticancer and antimicrobial activities of the ligand and its complexes (1–3) were examined. The three complexes have higher anticancer activity against colon HCT-116 and lung A-549 cancer cell lines than the free ligand (L). The only exception is complex 1 which has less cytotoxic activity against lung A-549 cancer cell line than L. Interestingly, the Cu(II) complexes have higher cytotoxic activity than the Mn(II) complex, where complex 3 has the best anticancer activity against HCT-116 (IC50 = 7.78 ± 0.27 μg/mL) and A-549 (12.40 ± 0.54 μg/mL) cell lines. In addition, the three complexes showed greater activity against gram-positive bacteria (S. aureus and B. subtilis) than gram-negative bacteria (E. coli and P. vulgaris) where 3 has best antibacterial activity.

Asymmetrical Platinum and Rhodium Dinuclear Complex Strongly Bound to Filled d Complexes by Unbridged Pt-Metal Bonds: Toward Heterometallic-Extended Metal Atom Chains.

Heterometallic extended metal atom chains (EMACs) aligned with three types of metal were rationally synthesized by forming unbridged metal-metal bonds based on the interactions between highest occupied and lowest unoccupied molecular orbitals at the d orbital. These chains form pentanuclear structures aligned as Rh-Pt-M-Pt-Rh with relatively large formation constants of 5.0×1013 M-2 for M=Pt and 6.3×1011 M-2 for M=Pd, while retaining their backbones in solution. In the case of M=Cu, the original Cu(+2) atoms were reduced to Cu(+1) during the synthetic process. Cu(+1) has an unprecedented trigonal bipyramidal coordination geometry. The reported synthesis based on asymmetrical dinuclear complexes provides a guideline for the synthesis of hetero-EMACs to allow several analogs through judicious combinations realized by tuning the number of metal nuclei and metal species.

Synthesis and structural investigation of mononuclear penta- and hexa-coordinated Co complexes of 8-hydroxyquinoline derived ligands

This article describes the synthesis and structural property investigation of two new mononuclear Co(II) complexes of 8-hydroxyquinoline derived flexible tridentate N,O,N'- (LI) and tetradentate N,O,O',N'-ligands (LII). The reactions were carried out between CoCl2.6H2O and the respective ligands in methanol to obtain the complexes CoLICl2 and CoLIICl2 in good yields. The complexes are characterized by elemental analysis, mass, IR spectroscopy, and single-crystal X-ray diffraction. The molecular structure of CoLICl2 shows distorted trigonal bipyramidal coordination geometry with the structural index parameter τ = 0.83. The apical positions are occupied with the quinoline O- and one terminal Cl-atom, whereas the equatorial positions are held by the two N-atoms and the second Cl-atom. In contrast, CoLIICl2 has a slightly distorted octahedral structure with all the donor atoms of the chelating ligand LII holding the equatorial positions with the two-terminal Cl-atoms at the apical positions. Electronic structure calculations are used to evaluate the geometrical, electronic, and magnetic properties of these complexes. Non-periodic calculations used to simulate molecules indicate a strong dπ-pπ bonding between Co and ligands. The crystal packing from both the solid-state structures revealed further stability of the molecule via weak non-covalent interactions through π.…π stacking between quinoline rings and C–H.…Cl hydrogen bonding. A detailed comparison between the geometric parameters of CoL1Cl2 and CoLIICl2 are reported. In addition, the comparison of selected structural parameters between a range of transition metal quinolates from the literature are given. Periodic calculations to simulate crystals using B3LYP hybrid functional predicts both the crystalline structures to be magnetic insulators.

Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica

AbstractAl(OC(CF3)3)(PhF) reacts with silanols present on partially dehydroxylated silica to form well‐defined ≡SiOAl(OC(CF3)3)2(O(Si≡)2) (1). 27Al NMR and DFT calculations with a small cluster model to approximate the silica surface show that the aluminum in 1 adopts a distorted trigonal bipyramidal coordination geometry by coordinating to a nearby siloxane bridge and a fluorine from the alkoxide. Fluoride ion affinity (FIA) calculations follow experimental trends and show that 1 is a stronger Lewis acid than B(C6F5)3 and Al(OC(CF3)3)(PhF) but is weaker than Al(OC(CF3)3) and iPr3Si+. Cp2Zr(CH3)2 reacts with 1 to form [Cp2ZrCH3][≡SiOAl(OC(CF3)3)2(CH3)] (3) by methide abstraction. This reactivity pattern is similar to reactions of organometallics with the proposed strong Lewis acid sites present on Al2O3.

Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica.

Al(OC(CF3 )3 )(PhF) reacts with silanols present on partially dehydroxylated silica to form well-defined ≡SiOAl(OC(CF3 )3 )2 (O(Si≡)2 ) (1). 27 Al NMR and DFT calculations with a small cluster model to approximate the silica surface show that the aluminum in 1 adopts a distorted trigonal bipyramidal coordination geometry by coordinating to a nearby siloxane bridge and a fluorine from the alkoxide. Fluoride ion affinity (FIA) calculations follow experimental trends and show that 1 is a stronger Lewis acid than B(C6 F5 )3 and Al(OC(CF3 )3 )(PhF) but is weaker than Al(OC(CF3 )3 ) and i Pr3 Si+ . Cp2 Zr(CH3 )2 reacts with 1 to form [Cp2 ZrCH3 ][≡SiOAl(OC(CF3 )3 )2 (CH3 )] (3) by methide abstraction. This reactivity pattern is similar to reactions of organometallics with the proposed strong Lewis acid sites present on Al2 O3 .

Experimental and theoretical approaches on structural, spectroscopic (FT‐IR and UV‐Vis), nonlinear optical, and molecular docking analyses for Zn (II) and Cu (II) complexes of 6‐chloropyridine‐2‐carboxylic acid

AbstractNovel transition metal‐based complexes that may be of value as biological agents and/or nonlinear optical materials, Zn (II) and Cu (II) transition metal complexes of 6‐chloropyridine‐2‐carboxylic acid (LH), were successfully synthesized. The chemical structure of each complex was characterized using X‐ray diffraction (XRD) method and FT‐IR spectroscopy. XRD and FT‐IR demonstrated that L ligand coordinate to central metal ions through the donor N and O atoms. By coordinating two H2O ligand to Zn (II) ion, a distorted octahedral complex geometry was constructed for 1. As for 2, a distorted trigonal bipyramidal coordination geometry was obtained by a H2O ligand coordination to Cu (II) ion. Theoretical studies using B3LYP/6‐311++G(d,p)‐LanL2DZ were performed to further validate the proposed structures. The molecular docking of 1 to SARS‐CoV‐2 main protease (PDB: 6LU7) gives a binding energy of −5.24 kcal/mol and inhibition constant of 144.6 μM, demonstrating that 1 is a more promising candidate to biologically active complexes than 2. The first‐order hyperpolarizability (β) parameter for 1 and 2 was calculated as 0.88 × 10−30 and 10.40 × 10−30 esu, respectively. These β values also demonstrated that 2 exhibits more effective NLO character than 1 due to the electronic configuration and coordination geometry.

Three metal(II) complexes constructed using the 2-(1H-benzo[d]imidazol-2-yl)quinoline ligand

Abstract 2-(1H-benzo[d]imidazol-2-yl)quinoline (BQ) as ligand and three coordination compounds of formula {Zn(BQ)Cl2} (1), {Pb(BQ)Cl2} n (2) and {[Cu(BQ)2(OC(O)CH3)]OC(O)CH3 · CH3COOH} (3) have been synthesized and fully characterized. The complexes crystallize in triclinic space group P 1 ‾ $P‾{1}$ . In complexes 1 and 2, the coordination geometry is a distorted tetrahedral environment around the zinc center and a distorted sixfold coordination geometry around the lead center, respectively. In complex 3 the central Cu(II) center is in a trigonal bipyramidal coordination geometry. The Cu(II) ion is surrounded by two bidentate 2-(2′-quinolyl)benzimidazole (BQ) ligands and one coordinated acetate molecule. One further acetate anion associated by a strong hydrogen bond with a molecule of acetic acid balances the charge of the compound.

Synthesis, spectroscopy, and crystallography of mononuclear, five-coordinate aluminum complexes that act as cyclic ester polymerization initiators

Three ketoimines with pendant quinolyl moieties and a series of five-coordinate ketoiminate aluminum complexes were prepared and characterized spectroscopically and crystallographically. The synthesis of the ketoimines completed a series of ten regioisomers for which the product ratio varied between the product resulting from quinoline addition adjacent to the alkyl/aryl group or adjacent to the trifluoromethyl substituent. Quantitation of the ketoimine regioisomer ratios with 19F NMR demonstrated the role of steric encumbrance in the nucleophilic attack mechanistic step of the Schiff base condensation reaction and was further supported by linear free energy relationships with the Charton steric parameter and DFT calculations. Eight five-coordinate aluminum complexes were prepared in 57–92% yield from ketoimines and tris(2,6-dimethylphenoxide) aluminum dimer and characterized with 1H, 13C, 19F, and 27Al nuclear magnetic resonance spectroscopy, UV–visible absorbance spectroscopy, elemental analysis, and single-crystal X-ray crystallography. These mononuclear complexes differ from previously reported aluminum ion-pair complexes due to the symmetric cleavage of tris-dimethylphenoxide aluminum dimer by THF and were shown to have distorted trigonal bipyramidal coordination geometries (τ5 = 0.73–0.89). In a preliminary study, the aluminum complexes were demonstrated to be effective initiators for ring-opening polymerization of ε-caprolactone (εCL) to poly-caprolactone (PCL) and l-lactide (LA) to poly-lactic acid (PLA), reaching 77–99% conversion in 2 h for εCL and 10 h for LA at 100 °C.

A new phenolato-bridged dinuclear manganese(II) complex as a turn-on fluorosensor for Zn2+ ions via Mn2+ ion replacement

A new synthesized and structurally characterized phenolato bridged di-nuclear manganese(II) complex, formulated as [Mn2L(OAc)2(DMF)2]PF6 (1) (where HL = 4-methyl-2,6-bis-[(2-morpholin-4-yl-ethylimino)-methyl]-phenol and OAc = acetate anion), can act as a turn-on Zn2+ sensing probe through the in situ formation of the corresponding dinuclear Zn(II) complex, [Zn2L(OAc)2]PF6 (2) via direct Mn2+ ion replacement in MeOH/DMF (1/14) medium. The selective and specific fluorescent change due to addition of Zn2+ ions to a solution of 1 enables the detection of Zn2+ ions in dimethylformamide (DMF). The fluorescent dinuclear zinc(II) complex 2 has also been produced through the direct reaction between Zn2+ ions and HL. Both complexes 1 and 2 have been characterized by using physico-chemical and spectroscopic tools, and finally by single crystal X-ray crystallography for a detailed structural determination. The crystallographic investigation indicates that the Mn(II) and Zn(II) ions in the complexes exhibit a distorted octahedral and distorted trigonal bipyramidal coordination geometry, respectively. Interestingly, complex 1 showed very weak fluorescence in solution and no emission in the solid state, whereas complex 2 gave a strong bluish-green coloured fluorescence in both solution and in the solid state, which may be due to the distinct packing of complex 2 compared to 1, as well as to intermolecular hydrogen bonding and CH---π, CH---N and CH---O interactions in the crystal packing, likely playing crucial roles for the fluorescence behavior.

A New Phenolato-Bridged Dinuclear Manganese(II) Complex as a Turn-On Fluorosensor for Zn <sup>2</sup>+ Ions Via Mn <sup>2</sup>+ Ion Replacement

A new synthesized and structurally characterized phenolato bridged di-nuclear manganese(II) complex, formulated as [Mn2L(OAc)2(DMF)2]PF6 (1) (where HL = 4-methyl-2,6-bis-[(2-morpholin-4-yl-ethylimino)-methyl]-phenol, and OAc = acetate anion) can act as a turn-on Zn2+ sensing probe through in situ formation of the correspondent dinuclear Zn(II) complex, [Zn2L(OAc)2]PF6 (2) via direct Mn2+ ion replacement in in MeOH/DMF (1/14) medium. This selective and specific fluorescent change due to addition of Zn2+ ions to the solution of 1 enables to detect Zn2+ ion in dimethylformamide (DMF). The fluorescent dinuclear zinc(II) complex 2 has been achieved also through the direct reaction between Zn2+ ions and HL. Both the complexes 1 and 2 have been characterized using physico-chemical and spectroscopic tools, and finally by single crystal X-ray crystallography for a detailed structural determination. The crystallographic investigation indicates that the Mn(II) and Zn(II) in the complexes exhibit a distorted octahedral and distorted trigonal bipyramidal coordination geometry, respectively. Interestingly, complex 1 showed a very weak fluorescence in solution and no emission in solid state, whereas complex 2 gave a strong bluish-green coloured fluorescence in both solution and solid state, which may be due to the distinct packing of complex 2 compared to 1, as well as to the intermolecular hydrogen bonding and C–H---π, C–H---N, C–H---O interactions in the crystal packing, likely playing crucial roles for the fluorescence behavior.

Synthesis and structure of bis(tetraphenylantimony) malonate

Bis(tetraphenylantimony) malonate was synthesized by the reaction of tetraphenylantimony bromide with silver malonate (the molar ratio was 2:1) in toluene. According to the X-ray diffraction data, the tridentate carboxylate ligand is a chelate. The coordination number of the Sb(1) atom involved in a contact with the carbonyl oxygen atom increases to six (Sb(1)—O(1), 2.199(7) A; Sb(1)—O(3), 2.362(7) A). Another antimony atom remains five-coordinate (Sb(2)—O(4), 2.304(7) A). The antimony atoms Sb(1) and Sb(2) have distorted octahedral and trigonal-bipyramidal coordination geometry, respectively.

Coordination Dynamics of Zinc Triggers the Rate Determining Proton Transfer in Human Carbonic Anhydrase II.

We present, for the first time, how transient changes in the coordination number of zinc ion affects the rate determining step in the enzyme human carbonic anhydrase (HCA) II. The latter involves an intramolecular proton transfer between a zinc-bound water and a distant histidine residue (His-64). In the absence of time-resolved experiments, results from classical and QM-MM molecular dynamics and transition path sampling simulations are presented. The catalytic zinc ion is found to be present in two possible coordination states; viz. a stable tetra-coordinated state, T and a less stable penta-coordinated state, P with tetrahedral and trigonal bipyramidal coordination geometries, respectively. A fast dynamical inter-conversion occurs between T and P due to reorganization of active site water molecules making the zinc ion more positively charged in state P. When initiated from different coordination environments, the most probable mechanism of proton transfer is found to be deprotonation of the equatorial water molecule from state P and transfer of the excess proton via a short path formed by hydrogen bonded network of active site water molecules. We estimate the rate constant of proton transfer as from P and from T. A quantitative match of estimated kP with the experimental value, ( ) suggests that dynamics of Zn coordination triggers the rate determining proton transfer step in HCA II.

Synthesis, Solid State, Solution and ESI‐MS Studies of Zinc(II) Cluster Complexes with a Branched Mixed Donor Thiolate Ligand

Synthesis of the unusual spirobicyclic pentanuclear complex [Zn((ZnL)2(µ‐OH))2](ClO4)4·CH3CN·7H2O (1) (LH = N‐(2‐pyridylmethyl)‐N‐(2‐(methylthio)ethyl)‐N‐(2‐thioethyl)‐amine is described. Compound 1 was thoroughly characterized by a combination of X‐ray crystallography, XPRD, IR, variable temperature 1H NMR and ESI‐MS. The peripheral zinc ions of 1 have distorted trigonal bipyramidal coordination geometry provided by the NN′SS′ donor set of one L and a µ2‐hydroxido bridge to another peripheral zinc ion. The central zinc atom has a distorted tetrahedral Zn(SR)4 coordination environment provided by four µ2‐thiolate bridges from L. In crystalline form, the complex ions of 1 are largely insulated from contact by an elaborate hydrogen bond network involving µ2‐hydroxido bridges, perchlorate ions and all the solvent molecules. Dissociation of 1 in CD3CN solution and recombination to form other multinuclear complexes was investigated by variable temperature 1H NMR.

Nucleophilic reactivity of a copper(II)-hydroperoxo complex

Copper(II)-hydroperoxo species are often detected as key intermediates in metalloenzymes and biomimetic compounds containing copper. However, the only reactivity has previously been observed for the copper(II)-hydroperoxo complexes is electrophilic, occurring through O-O bond cleavage. Here we report that a mononuclear end-on copper(II)-hydroperoxo complex, which has been successfully characterized by various physicochemical methods including UV-vis, rRaman, CSI-MS and EPR, is a reactive oxidant that utilizes a nucleophilic mechanism. In addition, DFT calculations fully support the electronic structure of this complex as a copper(II)-hydroperoxo complex with trigonal bipyramidal coordination geometry. A positive Hammett ρ value (2.0(3)) is observed in the reaction of copper(II)-hydroperoxo complex with para-substituted acyl chlorides, which clearly indicates nucleophilic character for the copper(II)-hydroperoxo complex. The copper(II)-hydroperoxo complex is an especially reactive oxidant in aldehyde deformylation with 2-PPA and CCA relative to the other metal-bound reactive oxygen species reported so far. The observation of nucleophilic reactivity for a copper(II)-hydroperoxo species expands the known chemistry of metal-reactive oxygen species.

Crystal structure of chlorido-{tris-[2-(iso-propyl-sulfan-yl)phen-yl]phosphane-κ4 P,S,S',S''}nickel(II) tri-fluoro-methane-sulfonate.

The complex cation of the title compound, [NiCl{P(C6H4-2-S-i-Pr)3}](CF3SO3), has a slightly distorted trigonal-bipyramidal coordination geometry in which three S atoms are located in the equatorial plane, and one P and one Cl atom in the apical positions. In the cation, there are two intra-molecular C-H⋯S hydrogen bonds. In the crystal, there are some inter-molecular C-H⋯O and C-H⋯F hydrogen bonds formed between the cation and the anion. The tri-fluoro-methane-sulfonate anion and one of the methyl groups are both disordered over two sets of sites with occupancies of 0.629 (17):0.371 (17) and 0.786 (14):0.214 (14), respectively.

Crystal structure of a 1:1 adduct of tri-phenyl-tin chloride with 3-cyclo-hexhyl-2-phenyl-1,3-thia-zolidin-4-one.

In the centrosymmetric (racemic) title compound, chlorido-(3-cyclo-hexhyl-2-phenyl-1,3-thia-zolidin-4-one-κO)tri-phenyl-tin(IV), [Sn(C6H5)3Cl(C15H19NOS)], the tin(IV) atom exhibits a trigonal-bipyramidal coordination geometry with the three phenyl groups in equatorial positions and the chloride anion and ligand oxygen atom present at axial sites [O-Sn-Cl = 175.07 (14)°]. The thia-zolidinone ring of the ligand adopts an envelope conformation with the S atom as the flap. The dihedral angles between the heterocycle ring plane (all atoms) are 44.3 (9)° with respect to the pendant C-phenyl plane and 34.3 (11)° to the N-cyclo-hexyl ring (all atoms). The C-phenyl and N-cyclo-hexyl ring are close to orthogonal to each other, with a dihedral angle of 81.1 (4)° between them. In the crystal, mol-ecules are linked by weak C-H⋯Cl hydrogen bonds to generate [001] chains.

Luminescent Vapochromism Due to a Change of the Ligand Field in a One-Dimensional Manganese(II) Coordination Polymer.

The reactions of MnBr2 and ethane-1,2-diylbis(diphenylphosphine oxide) (dppeO2) in dichloromethane-methanol solutions gave colorless crystals with the general chemical formulas [MnBr2(dppeO2)] n (1), [MnBr2(dppeO2)(DMF)] n (1a), [Mn(dppeO2)3][MnBr4] (2), and Mn2Br4(dppeO2)2 (3) depending on the crystallization conditions. Compounds 1 and 1a display one-dimensional chain structures composed of Mn(II) ions linked by bridging dppeO2 to exhibit tetrahedral (1) or trigonal-bipyramidal (1a) coordination geometry, whereas 3 exhibits a cyclic dinuclear structure with two Mn(II) centers bridged by double dppeO2 to adopt tetrahedral geometry. Compound 2 consists of octahedrally coordinated cation [Mn(dppeO2)3]2+ and tetrahedrally arranged anion [MnBr4]2-. While 1 and 3 in crystalline and powder states are highly luminescent with green emission bands centered at ca. 510 nm, 2 shows intense orange luminescence peaking at 594 nm. Upon exposure of 1 to N, N-dimethylformamide vapor, the green emission centered at 510 nm is converted to red luminescence peaking at 630 nm, ascribed to the formation of DMF-coordinated compound 1a with a trigonal-bipyramidal ligand field, as demonstrated by X-ray crystallography. Red-emitting 1a could be reverted to the original green-emitting 1 with a tetrahedral ligand field upon heat at 160 °C, and such a reversible conversion could be perfectly repeated for several cycles. A new mechanism of luminescent vapochromism is thus proposed because of the reversible conversion of ligand fields in manganese(II) complexes.

Structural variations in zinc(II) complexes with N,N-di(4-fluorobenzyl)dithiocarbamate and imines: New precursor for zinc sulfide nanoparticles

Bis(N,N-di(4-fluorobenzyl)dithiocarbamato-κ2S,S′)zinc(II) (1), bis(N,N-di(4-fluorobenzyl)dithiocarbamato-κ2S,S′)(pyridine-κN)zinc(II) (2), (μ-4,4′-bipyridine-κ2N,N′)bis[bis(N,N-di(4-fluorobenzyl)dithiocarbamato-κ2S,S′)zinc(II)] (3) and (2,2′-bipyridine-κ2N,N′)bis(N,N-di(4-fluorobenzyl)dithiocarbamato-κS,S′)zinc(II) (4) were prepared and characterized by elemental analysis, spectroscopy (IR, 1H and 13C NMR) and their structures were elucidated by X-ray crystallography. The centrosymmetric dinuclear structure of 1 features both bridging and chelating dithiocarbamate ligands to that a distorted trigonal bipyramidal S5 coordination geometry results. The coordination geometry of zinc(II) in 2 and both zinc(II) in the dinuclear complex 3 is an intermediate between tetragonal pyramidal and trigonal bipyramidal. In complex 4, the resulting N2S4 donor set defines a distorted octahedral geometry. Addition of imines (pyridine, 4,4′-bipyridine and 2,2′-bipyridine) to the complex 1 affects the ZnS distances and SZnS angles. The optimized geometry, HOMO-LUMO in the ground state and MEP have been calculated for 1 and 2. MEP analysis support the substantial contribution of the resonance structure RR′-N+CS22− to the description of their structures on the complexes 1 and 2. Quantification of the intermolecular interactions present in 1–4 was realized by Hirshfeld surface analysis. Zinc sulfide nanoparticles were prepared from 1 and characterized by PXRD, SEM, TEM, EDAX and DRS. The PXRD study showed that the nanoparticles is composed of cubic phase of zinc sulfide. Photocatalytic activity of as-prepared ZnS was tested by examining the degradation of rhodamine-B in aqueous solution under UV light illumination.