Trigonal Bipyramidal Arrangement Research Articles

Synthesis, spectral, antibacterial and QSAR studies of tin and silicon complexes with Schiff base of amino acids

A series of main group metal and metalloid complexes of Sn(IV), Sn(II), and Si(IV) ions with bidentate Schif bases derived from condensation of animo acids (Tryptophan, Histidine, Alanine, Serine, Aspartic acid) and 4‑methoxy-benzaldehyde were synthesized and were well characterized by diferent analytical and spectroscopic (UV–Vis, FT-IR, and NMR) methods, molar conductance determinations, and elemental analysis. Spectroscopic evidence indicates that Schif bases coordinate via η2-N,O-donor atoms with tin and silicon centres in a 2:1 molar ratio, with a trigonal bipyramidal and octahedral geometrical arrangement for Si(IV) and Sn(IV), respectively, and a distrtorted tetrahedral structure for Sn(II) complexes. The antibacterial efficacy of the produced compounds was tested in vitro using four different gramme (+) and gramme (-) bacteria. The designed model produced statistically significant results with of R2 = 0.93, Q2= 0.0.87 and Rpred2 = 0.92. Most potent compound forms the hydrogen bond with most active amino acids Arg136 and Gly63. The R3Sn(IV) compounds were shown to be the most effective antibacterial agent among all the produced compounds confirmed by molecular docking. The findings imply that these compounds might serve as leading compounds in the quest for novel antibacterial agents.

Exploiting Strong {CrIII–DyIII} Ferromagnetic Exchange Coupling to Quench Quantum Tunneling of Magnetization in a Novel {CrIII2DyIII3} Single-Molecule Magnet

The {3d–4f} pentanuclear complexes with the formula [CrIII2LnIII3(PhCO2)7(OH)6 (iPrO)(NO3)(H2O)3] (iPrO = isopropoxide) (where Ln = Dy (1), Gd (2)) have been synthesized and characterized using magnetic and theoretical studies. The metal core of complexes 1 and 2 has a trigonal bipyramidal arrangement with three LnIII ions in the triangular plane and two CrIII ions occupying the axial positions. These ions are held together by six μ3-OH bridges and seven carboxylate bridges. The dc magnetic susceptibility data reveal ferromagnetic interactions presiding between CrIII and LnIII ions in 1 and 2. The fitting of the susceptibility curve employing the DFT calculated J (vide infra), yield JGdIII–GdIII = +0.008 cm–1, JCrIII–GdIII = +0.27 cm–1, and JCrIII–CrIII = −0.007 cm–1 for 2. The dynamic (ac) magnetic susceptibility studies on 1 indicate slow relaxation of magnetization with a Ueff value of 30.9 K (21.4 cm–1) and τ0 = 4.09 × 10–10 s. These extracted parameters are among the highest for any reported {CrIIIDyIII} complexes. DFT and ab initio CASSCF/RASSI–SO/SINGLE_ANISO/POLY_ANISO calculations were carried out to estimate the exchange interactions and their role in quenching the quantum tunneling of magnetization (QTM) behavior. Ab initio calculations on the DyIII ions reveal three asymmetric DyIII centers with the estimated single ion barrier in the range of 78–184 cm–1, however, with a large QTM probability. Despite a triangular {Dy3} motif, the gzz axes do not align in the triangular plane as observed in the {CrIIIDyIII6} single-molecule toroids (SMT) reported earlier by us. This is essentially due to the presence/absence of the iPrO–/carboxylate group that alters the charge distribution around the DyIII ion and hence the orientation of the corresponding gzz axis. The combination of DFT and ab initio CASSCF calculations yield JDyIII–DyIII = +0.012 cm–1, JCrIII–DyIII = +1.20 cm–1, and JCrIII–CrIII = −0.95 cm–1 for 1. The mechanism of magnetization relaxation developed for the {CrIII2DyIII3} cluster reveals that the relatively strong ferromagnetic CrIII–DyIII exchange interaction reduces the ground state QTM significantly yielding a Ueff of 38.6 cm–1, which agrees with the experimental value. Thus, our study iterates the importance of CrIII ion to enhance the exchange coupling in the {3d–4f} family of clusters.

Synthesis, characterization, crystal structures and electrochemical properties of heteroleptic Cu(II), Mn(II) and Zn(II) complexes of metronidazole with benzoic acid derivatives

Cu(II), Mn(II) and Zn(II) complexes of metronidazole with benzoic acid derivatives formulated as [Cu2(met)4(4-nba)4] (1), [Mn(met)2(2bba)2(H2O)2] (2) and [Zn(met)2(3,5-dnba)2] (3) [met = metronidazole, 4-nba = 4-nitrobenzoic acid, 2-bba = 2-bromobenzoic acid and 3,5-dnba = 3,5-dinitrobenzoic acid] were synthesized and characterized by elemental analysis and spectroscopic techniques and two of them by single crystal X-ray crystallography. Single crystal X-ray crystallography revealed a five-coordinate, trigonal bipyramidal arrangement in compound 1, while compound 2 is six coordinate octahedral geometry. The molar conductance indicates the complexes are non-electrolytes in solution. The EPR spectra of 1 and 2 showed broad signals centered on g = 2.125, 2.116 and 1.970, 2.005. A hyperfine quartet was observed in the solid state for 1 typical of Cu(II) ion, I = 3/2; while a hyperfine sextet characteristic of 55Mn nucleus, I = 5/2 was observed for 2. Cyclic voltammetry revealed a one-step redox couple for 1 at a potential range of −0.4 to +0.1 V assigned to the reduction peak of Cu(II)/Cu(I). The linearity of Randles-Sevcik plot (R2 = 0.999) suggests a diffusion-controlled redox couple.

Synthesis of Co(II) NNN-pyridine based complexes and their activity in the partial oxidation of n-octane

A series of four NNN-pyridine based ligands of the general form: pyCH2N(R)CH2py {R = propyl, tert-butyl, cyclohexyl and phenyl; py = pyridine} were synthesised and characterised. Complexation of each ligand to CoCl2·6H2O afforded new Co(II) complexes [Co{pyCH2N(R)CH2py}Cl2] (R = C3H7 (1), C(CH3)3 (2), C6H11 (3) and C6H5 (4)). Single crystal X-ray diffraction data confirmed that complex 1 crystallised as a mononuclear unit and was characterised by a distorted trigonal bipyramidal arrangement of ligands around Co. As catalysts in the oxidation of n-octane using t-BuOOH as oxidant,2 (10% product yield) was found to be most efficient and the selectivity over 1–4 was predominantly towards 2-octanol, after reduction of alkylhydroperoxides by PPh3. All catalysts were significantly more active in the activation of n-octane using hydrogen peroxide, with a yield of 45% observed over catalyst 3. Furthermore, with H2O2, all catalysts produced a high concentration of alkylhydroperoxides, with catalyst 4 giving up to 91% alcohols after workup. TONs of up to 1100 were achieved over the Co/H2O2 systems.

Synthesis, Spectroscopic and Antimicrobial Studies of Homo- and Heteronuclear Tin(IV)/Pd(II) Complexes of 2-Amino-6-(Dithiocarboxyamino)Hexanoic Acid

Homobimetallic organotin(IV) carboxylates dithiocarboxylates, Ph2SnLCS2Sn(Cl)Ph2 (1) and Ph3SnHLCS2SnPh3 (2) were synthesized by a room temperature reaction of l-lysine monohydrate (H2LH) with potassium hydroxide, carbon disulfide and Ph3SnCl/Ph2SnCl2 in methanol. Heterotrinuclear complexes (Bu2SnLCS2)2Pd (3) and (Bu2SnLCS2)2Pd (4) were also synthesized by a reaction of H2LH with KOH, CS2 and PdCl2(aq) in methanol followed by the treatment with n-Bu2SnCl2/Ph2SnCl2. The products were characterized by elemental analysis, FT-IR, multinuclear NMR (1H, 13C and 119Sn) and electron ionization mass spectroscopy (EIMS). The elemental analysis and mass spectrometry verified the molecular composition and structures of complexes. FT-IR spectroscopy demonstrated monodentate binding behavior of the carboxylate group and chelating mode of the dithiocarbamate moiety. The diorganotin(IV) derivatives 1, 3 and 4 convert their solid-state tetra-coordinated structures into trigonal bipyramidal arrangements in solution. However, triphenyltin(IV) derivative 2 exhibited penta-coordinated environment around Sn(IV) in the solid-state and tetrahedral configuration in the solution form. A square planar environment around Pd(II) was exhibited in the solid state. The investigated products displayed antibacterial/antifungal potential, and their minimal inhibitory concentrations (MIC) values were also demonstrated. The nature of the coordinated metals (Sn + Sn or Sn + Pd) and the substitution pattern at tin play a major role in biological actions of these products. The heterometallic (Pd, Sn) products possessed more potential against fungi than bacteria. The heterobimetallic dibutyltin(IV) complex 3 has shown the lowest hemolytic activity (10.76%), while its phenyltin(IV) counterpart 4 possessed the highest cytotoxicity (50.11%).

Electronic Structure Explanation for the Structure and Reactivity of di-n-Butyltin(IV) Derivative of Glycylphenylalanine

The density functional theory (DFT)-based quantum-chemical calculations have been performed on di-n-butyltin(IV) derivative of glycylphenylalanine (H2L) using the Gaussian 09 software package. The molecular geometry of n-Bu2SnL was optimized at B3LYP/6-31G(d,p)/LANL2DZ(Sn) level of theory without any symmetry constraint. The harmonic vibrational frequencies were computed at the same level of theory to find the true potential energy surface (PES) minima. The various geometrical and thermochemical parameters for the studied complex are obtained in the gas phase. The atomic charges at all the atoms were calculated using Mulliken Population Analysis, Hirshfeld Population Analysis and Natural Population Analysis. The charge distribution within the studied complex is explained on the basis of molecular electrostatic potential maps, the frontier molecular orbital analysis and conceptual-DFT-based reactivity (global as well as local) descriptors, using the finite difference approximation method. The nature of O–Sn, N–Sn, N → Sn and C–Sn bonds is discussed in terms of the conceptual-DFT-based reactivity descriptors. The structural analysis of the studied complex has been carried out in terms of the selected bond lengths and bond angles. The structural and atomic charge analysis suggests a distorted trigonal bipyramidal arrangement consisting of negatively charged centres around the positively charged central Sn atom.

Formations of unexpected chloro-bridged bis(macrocycle) dicopper(II) complexes via decomposition of dichloromethane as a source of chloro-ligands

Abstract The 20-membered N3O2-macrocycle L reacts with copper(II) salts (NO3, ClO4) in dichloromethane/methanol to yield unexpected isostructural chloro-bridged dinuclear bis(macrocycle) copper(II) complexes of type [LCuII-(μ-Cl)2-CuIIL]X2 (1: X = NO3, 2: X = ClO4). Each complex contains two five-coordinate copper(II) ions which are bridged by two chloro-ligands, (μ-Cl)2, and the remaining coordination sites are completed by three nitrogens from the macrocycle. Notably, the chloro-bridging ligands are derived from the partial decomposition of the dichloromethane solvent molecules. Analogous reaction employing copper(I) chloride also afforded a similar dimer complex, [LCuII-(μ-Cl)2-CuIIL]Cl2 (3), suggesting such type of the chloro-bridged dicopper(II) complexes are thermodynamically stable under the reaction conditions employed in this work. Considering the τ values (0.45–0.52) for the five-coordinated copper(II) centers, complexes 1–3 present an intermediate geometry between square planar and trigonal bipyramidal arrangements.

N-donor ligands-directed coordination of Zn- azido complexes

Two zinc (II) pseudo-halide complexes [Zn(L1)(N3)2]n (1L1: 1,2-diaminocyclohexane) and Zn(L2)2(N3)2 (2L2: 4,5-dimethy-2-(pyridine-2-yl) imidazole) have been synthesized and characterized. Single-crystal X-ray structural analysis revealed that the central ZnII atoms in 1 displays distorted trigonal bipyramidal arrangement with a 1D chain structure bridged by N3− anions, while in 2, the central ZnII atoms incorporating with two bidentate L2 ligands, and adopts an octahedral geometry and shows a “butterfly” coordination framework. Structural analysis demonstrated that the organic ligands play an important role in determining the resultant structure. In addition, both complexes were further characterized by thermal stability properties and Hirshfeld surface analysis.

Structure of a pentamanganese(II)-phenoxide cluster with a central five-coordinate oxide: MnII5(μ-OPh)6(μ3-OPh)2(μ5-O)(Py)6·Py (Py is pyridine).

Polynuclear metal clusters frequently feature geometric structural features not common in traditional coordination chemistry. These structures are of particular interest to bioinorganic chemists studying metallocluster enzymes, which frequently possess remarkably unusual inorganic structures. The structure of the manganese cluster μ5-oxido-di-μ3-phenoxido-hexa-μ-phenoxido-hexakis(pyridine-κN)hexamanganese(II) pyridine monosolvate, [Mn5(C6H5O)8O(C5H5N)6]·C5H5N or MnII5(μ-OPh)6(μ3-OPh)2(μ5-O)(Py)6·Py, containing an unusual trigonal bipyramidal central oxide, is described. The compound was isolated from a reaction mixture containing bis(trimethylsilylamido)manganese(II) and phenol. The central O atom is presumed to have originated as adventitious water. The molecule crystalizes in a primitive monoclinic crystal system and is presented in the centrosymetric P2/n space group. The molecule possesses crystallographically imposed twofold symmetry, with the central O atom centred on the twofold axis and surrounded by a distorted trigonal bipyramidal arrangement of Mn atoms, which are further bridged by phenoxide ligands, and terminally ligated by pyridine. A pyridine solvent molecule resides nearby, also situated on a crystallographic twofold axis. The cluster is compared to three closely related previously reported structures.

Structural Dependence of the Ising-type Magnetic Anisotropy and of the Relaxation Time in Mononuclear Trigonal Bipyramidal Co(II) Single Molecule Magnets.

This paper describes the correlation between Ising-type magnetic anisotropy and structure in trigonal bipyramidal Co(II) complexes. Three sulfur-containing trigonal bipyramidal Co(II) complexes were synthesized and characterized. It was shown that we can engineer the magnitude of the Ising anisotropy using ligand field theory arguments in conjunction with structural parameters. To prepare this series of compounds, we used, on the one hand, a tetradentate ligand containing three sulfur atoms and one amine (NS3tBu) and on the other hand three different axial ligands, namely, Cl-, Br-, and NCS-. The organic ligand imposes a trigonal bipyramidal arrangement with the three sulfur atoms lying in the trigonal plane with long Co-S bond distances. The magnetic properties of the compounds were measured, and ab initio calculations were used to analyze the anisotropy parameters and perform magneto-structural correlations. We demonstrate that a smaller axial zero-field splitting parameter leads to slower relaxation time when the symmetry is strictly axial, while the presence of very weak rhombicity decreases the energy barrier and speeds the relaxation of the magnetization.

Synthesis, spectroscopic characterization, X-ray crystal structure and biological activities of homo- and heterobimetallic complexes with potassium-1-dithiocarboxylatopiperidine-4-carboxylate

Six homobimetallic organotin(IV) carboxylates dithiocarboxylates of the general formula R2(Cl)SnSSCLCOOSn(Cl)R2 (R=Me: 1; n-Bu: 2; Ph: 3)/R3SnSSCLCOOSnR3 (R=Me: 4; n-Bu: 5; Ph: 6), a trinucleartin(IV) derivative [Ph2(Cl)SnSSCLCOO]2SnPh2 (7), three heterobimetallic (Sn, Pd) products of the type Cl2PdSSCLCOOSnR3 (R=Me: 8; Bu: 9; Ph: 10) and a palladium complex KOOCLCSSPdSSCLCOOK (11) were synthesized from potassium 1-dithiocarboxylatopiperidine-4-carboxylate (KSSCLCOOK) insitu. The structures of the complexes were verified by spectroscopic techniques (FT-IR, UV–Visible, 1H NMR, 13C NMR, EI-MS/ESI) and TGA. FT-IR data indicated a bidentate binding mode of the carboxylate/dithiocarbamate group, with tetra and penta-coordinated arrangements around Pd(II) and Sn(IV) centers in solid state. In solution state, a trigonal bipyramidal environment around Sn(IV) and a square planar geometry of Pd(II) was justified by NMR (1H and 13C) and UV–Vis spectroscopies. In heteronuclear products (8–10), the ligand develops linkage through oxygen and sulfur donor sites to Sn(IV) and Pd(II), respectively. The mass fragmentation and thermal degradation patterns were excellently agreed with the molecular composition of products. Single crystal XRD analysis of the complex 6 demonstrated that the geometry of sulfur bonded tin(IV) lies between tetrahedral and trigonal bipyramidal, while a distorted trigonal bipyramidal arrangement was verified for oxygen bonded Sn(IV). The synthesized complexes exhibited antimicrobial activities against various strains of bacteria and fungi by disc diffusion method and their minimal inhibitory concentrations were also found. The nature of the coordinated metal played a major role in biological actions of such complexes. While Pd(II) incorporation chiefly induces SS-DNA binding capacity and ALPs inhibition in complexes, the coordination with Sn(IV) stimulates the antibacterial and antifungal potentials. The complexes exhibited sufficiently lower hemolytic activities as compared to triton X-100 (positive control, 100% lysis) and higher than PBS (negative control, 0% lysis).

High-resolution photoelectron imaging spectroscopy of cryogenically cooled Fe4O(-) and Fe5O(.).

We report high-resolution photodetachment spectra of the cryogenically cooled iron monoxide clusters Fe4O(-) and Fe5O(-) obtained with slow photoelectron velocity-map imaging (cryo-SEVI). Well-resolved vibrational progressions are observed in both sets of spectra, and transitions to low-lying excited states of both species are seen. In order to identify the structural isomers, electronic states, and vibrational modes that contribute to the cryo-SEVI spectra of these clusters, experimental results are compared with density functional theory calculations and Franck-Condon simulations. The main bands observed in the SEVI spectra are assigned to the (15)A2←(16)B2 photodetachment transition of Fe4O(-) and the (17)A'←(18)A″ photodetachment transition of Fe5O(-). We report electron affinities of 1.6980(3) eV for Fe4O and 1.8616(3) eV for Fe5O, although there is some uncertainty as to whether the (15)A2 state is the true ground state of Fe4O. The iron atoms have a distorted tetrahedral geometry in Fe4O(0/-) and a distorted trigonal-bipyramidal arrangement in Fe5O(0/-). For both neutral and anionic species, the oxygen atom preferably binds in a μ2-oxo configuration along the cluster edge. This finding is in contrast to prior predictions that Fe5O(0/-) exhibits a μ3 face-bound structure.

A density functional theory insight into the structure and reactivity of diphenyltin(IV) derivative of glycylphenylalanine

Abstract The quantum-chemical calculations based on density functional theory (DFT) have been performed on the diphenyltin(IV) derivative of glycyl-phenylalanine (H2L) at the B3LYP/6-31G(d,p)/LANL2DZ(Sn) level of theory without any symmetry constraint. The harmonic vibrational frequencies were computed at the same level of theory to find the true potential energy surface minima. The various geometrical and thermochemical parameters for the studied complex are obtained in the gas phase. The atomic charges at all the atoms were calculated using the Mulliken population analysis, the Hirshfeld population analysis, and the natural population analysis. The charge distribution within the studied complex is explained on the basis of molecular electrostatic potential maps, frontier molecular orbital analysis, and conceptual DFT-based reactivity (global and local) descriptors, using the finite difference approximation method. The nature of O-Sn, N-Sn, N→Sn, and C-Sn bonds is discussed in terms of the conceptual DFT-based reactivity descriptors. The structural analysis of the studied complex has been conducted in terms of the selected bond lengths and bond angles. The structural and the atomic charge analyses suggest a distorted trigonal bipyramidal arrangement consisting of negatively charged centers around the positively charged central Sn atom.

Magnetic anisotropy in pentacoordinate 2,6-bis(arylazanylidene-1-chloromethyl)pyridine cobalt(II) complexes with chlorido co-ligands

Static and dynamic magnetic properties of a series of four pentacoordinate [CoII(L3A-D)Cl2] complexes 1–4 (1, L3A=N,N′-bis(2,4,6-trimethylphenyl)pyridine-2,6-dicarboximidoyl dichloride; 2, L3B=N,N′-bis(2,6-dimethylphenyl)pyridine-2,6-dicarboximidoyl dichloride; 3, L3C=N,N′-bis(4-chloro-2,6-dimethylphenyl)pyridine-2,6-dicarboximidoyl dichloride; and 4, L3D=N,N′-bis(2,6-diisopropyl)pyridine-2,6-dicarboximidoyl dichloride) were thoroughly studied. Irrespective of the sign of the zero-field splitting parameter D, all the compounds 1–4 showed the uniaxial type of magnetic anisotropy and also slow relaxation of magnetization, hence belong to the class of field-induced single-ion magnets. The values of the D parameter range from large and positive in 1 and 2 (45.8cm−1, and 38.4cm−1, respectively) to large and negative in 3 and 4 (−43.9cm−1, and −41.3cm−1, respectively). In the cases of complexes 1–3, a very large rhombicity was revealed (E/D=from 0.24 to 0.31). Only in compound 4, which possesses large negative axial and practically zero rhombic magnetic anisotropy (D=−41.3cm−1, E/D=0.0), the extraction of spin reversal barrier, U=22.8K, from Argand diagram was feasible. The experimental findings were also supported by ab initio multi-reference CASSCF/NEVPT2 calculations. Finally, the magneto-structural correlation of D vs. τ was proposed, showing that the square-pyramidal Co(II) complexes adopt large and negative D values, and moreover, that the sign of D is changed to positive on transition to the chromophore geometries closer to the trigonal bipyramidal arrangement, with a crossing point at τ≈0.29.

An intramolecular antiferromagnetically coupled pentanuclear Mn(II) cluster containing acetate and tetracarboxylate linkers: Synthesis, structure and magnetism

A new Mn(II) complex {[Mn5(CH3COO)2(L)2(DMF)8](DMF)}n (1), (H4L = 3,5-bis(3′,5′-dicarboxylphenyl)-1H-1,2,3-triazole), has been synthesized and structurally characterized. The complex 1 have pentanuclear Mn(II) core, where the two sides of metal centers (Mn2 and Mn3) have trigonal bipyramidal arrangement and the middle metal center (Mn1) have octahedral environment utilizing two O atoms from adjacent bridging bidentate carboxylate groups and four O atoms from four coordinated DMF molecules. The planar arrangement of pentanuclear Mn(II) atoms are linked by L linkage to generate two dimensional sheet. The magnetic property of the compound indicates χMT value for the five Mn(II) unit to be 21.3 cm3 K mol−1 at 300 K, which is close to the spin-only value (21.9 cm3 K mol−1) for the pentamer having S = 5/2. Also, the Hirshfeld surface analyses have been performed which indicated the absence of weak Mn···Mn interaction thereby corroborating the results of observed magnetic properties.

Syntheses, Structures and Spectral Properties of Mononuclear CuII and Dimeric ZnII Complexes Based on an Asymmetric Salamo‐type N2O2 Ligand

AbstractThe asymmetric Salamo‐type N2O2 ligand H2L and its corresponding CuII and ZnII complexes [CuL] and [{ZnL}2]·2CH3CN were synthesized and structurally characterized. Crystallographic data of the CuII complex revealed that the CuII ion is tetracoordinate with a slightly distorted square planar arrangement forming a 2D supramolecular plane structure by hydrogen bonding and π···π stacking interactions. In the ZnII complex, the ZnII ions are pentacoordinate in N2O2 tetradentate fashion and intermolecular contacts between ZnII and oxygen atoms result in a head‐to‐tail dimer. The ZnII ions were found to have slightly distorted square pyramidal and trigonal bipyramidal arrangements, respectively. Hydrogen bonding interactions stabilized the ZnII complex to facilitate self‐assembly to a 1D linear chain. The CuII and ZnII complexes show intense photoluminescence with maximum emissions at approx. 426 and 411 nm upon excitation at 360 and 350 nm, respectively.

Synthesis of Titanium and Zirconium Complexes with 2‐­Pyridonate and 2, 6‐Pyridinedithiolate Ligands

AbstractTreatment of complex [Cp2TiCl2] with the lithium salt of 2‐hydroxypyridine afforded complex [Cp2Ti(Opy)2] (1), whereas the same synthetic strategy applied to the analogous zirconium compound [Cp2ZrCl2] did not worked. However, the use of the metallocene [Cptt2ZrMe2] with protic ligands allowed directing the reactivity towards protonation of the methyl groups attached to zirconium. To check this approach we reacted [Cptt2ZrMe2] with methanol affording complex [Cptt2ZrMe(OMe)] (2), which was characterized in situ by NMR techniques. In the same line, the reaction of [Cptt2ZrMe2] with 2‐hydroxypyridine gave complex [Cptt2Zr(Me)(Opy)] (3); forcing the conditions of this reaction did not lead to the expected complex [Cptt2Zr(Opy)2], most probably due to the steric hindrance exerted by the bulky cyclopentadienyl ligands. Further reactions of complex 3 with ligands having acidic protons also led to the recovery of the starting complex. However, when shifting to the bifunctional ligand 2, 6‐dimercaptopyridine [py(SH)2] a double protonation of the methyl ligands in [Cptt2ZrMe2] occurred, allowing the isolation of mononuclear complex [Cptt2Zr(κS,κS,κN‐pyS2)] (4), upon evolution of methane. The molecular structure of complex 4 was determined by X‐ray methods, showing the zirconium atom in a highly distorted trigonal bipyramidal arrangement; structural parameters indicate a conventional Zr–N bond, but rather weak Zr–S interactions.

Pyridoxal based ONS and ONO vanadium(V) complexes: Structural analysis and catalytic application in organic solvent free epoxidation

A series of dinuclear and mononuclear oxovanadium(V) complexes containing tridentate Schiff base ligands derived from pyridoxal and appropriate thiosemicarbazide or hydrazide are reported. The compounds were characterised by elemental analysis, thermogravimetric analysis, IR and NMR spectroscopy. The molecular structure of the dioxido-vanadium(V) complex [VO2(HL5)]·MeOH·H2O (H2L5=pyridoxal benzhydrazido ligand), determined by X-ray crystallography, reveals an unexpected distorted trigonal bipyramidal arrangement of the VO2 moiety. A DFT study of this molecule and of the related [VO2(H2L5)] complex of VIV reveals a moderate effect of the oxidation state change on the bond distances and angles, pointing to solvation as the cause of the structural distortion. All complexes were tested as (pre) catalysts for olefin epoxidation by aqueous tert-butylhydroxyperoxide (TBHP) under solvent-free conditions. Low vanadium loadings (0.05% vs. olefin) resulted in good cyclooctene conversions and TOFs. The lifetime of one catalyst was explored through repeated runs with recovery/recycling. DFT calculations have also addressed the olefin epoxidation mechanism, which reveals the possible direct O atom transfer from the activated tert-butoxido (tBuOO–) ligand, without the need to generate a peroxido (O22–) ligand.

Spectrophotometric Determination of Equilibrium Constants of Dimethyl and Diethyltin(IV) Dichloride with 5,10,15,20-Tetrakis(4-trimethyl-ammonio-phenyl)-prophine Tetratosylate

The formation constant of dimethyl and diethyltin(IV) dichloride hydrolytic species and their complexation reactions with 5,10,15,20-tetrakis(4-trimethyl-ammonio-phenyl)-prophine tetratosylate (TTMAPP) were evaluated using potentiometric and spectrophotometric methods. 1H NMR spectra of dimethyl and diethyltin(IV) at different pHs have an octahedral structure in low pHs and a distorted trigonal bipyramidal structural arrangement at higher pH values. The compositions of the formed complexes were determined, and it was shown that they form a single mononuclear 1:1 species with the ligand. The results indicate that the formation constants are in the order Me2Sn(IV)–TTMAPP > Et2Sn(IV)–TTMAPP.

Tuning the Ising-type anisotropy in trigonal bipyramidal Co(II) complexes.

This paper demonstrates the engineering and tuning of Ising-type magnetic anisotropy in trigonal bipyramidal Co(II) complexes. Here, we predict that employing a ligand that forces a trigonal bipyramidal arrangement and has weak equatorial σ-donating atoms, increases (in absolute value) the negative zero field splitting parameter D. With these considerations in mind, we used a sulfur containing ligand (NS3(iPr)), which imposes a trigonal bipyramidal geometry to the central Co(II) ion with long equatorial Co-S bonds. The resulting complex exhibits a larger anisotropy barrier and a longer relaxation time in comparison to the complex prepared with a nitrogen containing ligand (Me6tren).