Pentagonal Bipyramidal Geometry Research Articles

Structural characterization and antileishmanial activity of newly synthesized organo-bismuth(V) carboxylates: experimental and molecular docking studies.

In a quest to discover new formulations for the treatment of various parasitic diseases, a series of heteroleptic triorganobismuth(V) biscarboxylates of type [BiR3(O2CR')2], where R=C6H5 for 1-4 and p-CH3C6H4 for 5-8, were synthesized, characterized and evaluated for their biological potential against L. tropica. All the synthesized complexes were fully characterized by elemental analysis, FT-IR, multinuclear (1H and 13C) NMR spectroscopy and X-ray crystallography. The crystal structures for [BiPh3(O2CC6H4(o-Br))2] (1), [BiPh3(O2CC2H2C6H4)2] (2), [BiPh3(O2CC6H4(m-NO2))2] (3) and [BiPh3(O2CC6H4(2-OH,3-CH3))2] (4) were determined and found to have a distorted pentagonal bipyramidal molecular geometry with seven coordinated bismuth center for 1-3 and for 4 distorted octahedral geometry, respectively. All the synthesized complexes demonstrated a moderate to significant activity against leishmania parasites. A broad analytical approach was followed to testify the stability for (1-8) in solid state as well as in solution and in leishmanial culture M199, ensuring them to be stable enough to exert a significant antileishmanial effect with promising results. Cytotoxicity profile suggests that tris(tolyl) derivatives show lower toxicity against isolated lymphocytes with higher antileishmanial potential. Molecular docking studies were carried out to reveal the binding modes for (1-8)targeting the active site of trypanothione reductase (TR) (PDB ID: 4APN) and Trypanothione Synthetase-Amidase structure (PDB ID 2vob).

Dihalo bismuth cations: unusual coordination properties and inverse solvent effects in Lewis acidity

Dihalo bismuth cations show an unusual pentagonal bipyramidal coordination geometry with a stereochemically inactive lone pair. Their relevance for the Lewis acidity of BiX3 is discussed.

Effective tuning of magnetic anisotropy in distorted pentagonal bipyramidal Ni(II) complexes via substitution of axial coligands.

A series of Ni(II) complexes with pyridine-based macrocyclic ligand L (3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1(18),14,16-triene) with general formula [Ni(L)(X)2]0/2+ (X = Br- (1), I- (2), CH3CN (3), NCS- (4), imidazole (5)) was prepared and thoroughly investigated. X-ray molecular structures confirmed pentagonal bipyramidal geometry for all studied complexes with a strong Jahn-Teller distortion in the pentagonal equatorial plane and significantly elongated Ni-O distance(s) with a decrease of this distortion by varying axial coligands (CH3CN > Br- > I- > NCS- > imidazole). Direct current magnetic measurements revealed the easy-axis type of magnetic anisotropy with negative as well as positive axial zero-field-splitting parameter D ranging from +6.8 to -14.5 cm-1, which remains not affected in the halogenido series Cl- → Br- → I-, but which increases in the series with N-axial ligands in order CH3CN → NCS- → imidazole. Theoretical calculations helped to elucidate (i) the final coordination numbers 6 + 1 for 1 and 2, and 5 + 2 for 2-5, (ii) the pattern of splitting of d-orbitals, contributions of excited states to the final D-values and their final signs, and (iii) the complexity in the variation of the D and E parameters with elongation of axial bond distances in such strongly distorted systems. The studied complexes did not show any alternating magnetic susceptibility signal, but it was clearly documented that the magnetic anisotropy of the pentagonal bipyramidal Ni(II) complexes can be modulated/tuned by variation of axial coligands. Nevertheless, great care has to be taken for symmetry of the equatorial ligand field.

Modulation of the magnetic dynamics of pentagonal-bipyramidal Co(II) complexes by fine-tuning the coordination microenvironment.

Four air-stable mononuclear Co(II) complexes, with the formulas [Co(dapbh)(H2O)(CH3OH)] (1), [Co(Hdapbh)(N3)(CH3OH)]·(CH3OH) (2), [Co(H2aapbh)(CH3OH)2]·(NO3)2 (3) and [Co(H2bapbh)(H2O)(NO3)]·(NO3) (4), have been synthesized and structurally characterized by single crystal X-ray diffraction. In all of the complexes, the Co(II) centers constrained by the rigid pentadentate ligand H2LR with two protonable hydrogens adopt a heptacoordinated pentagonal-bipyramidal geometry. The combined analyses of magnetic data and ab initio calculations unveil large easy-plane magnetic anisotropies for these complexes (D = +37.338, +37.273, +41.138 and +41.139 cm-1 for 1-4, respectively), which indicate that the chemical alterations of the equatorial ligand and the ligand field strength in the axial positions synergistically fine-tune the magnitude of the D values. Magnetic investigations demonstrate the field-induced single-ion magnetic behavior in complexes 1, 2 and 4 with diverse energy barriers (Ueff) of 12.25 for 1, 44.15 for 2 and 48.72 K for 4, corresponding to the geometrical distortion of the heptacoordinated Co(II) ion. That is, the greatest deviation from the ideal D5h symmetry in 4 is responsible for the highest barrier.

Oxoperoxovanadium Complexes of Hetero Ligands: X-Ray Crystal Structure, Density Functional Theory, and Investigations on DNA/BSA Interactions, Cytotoxic, and Molecular Docking Studies.

Oxoperoxovanadium (V) complexes [VO (O)2 (nf) (bp)] (1) and [VO (O)2 (ox) (bp)] (2) based on 5-nitro-2-furoic acid (nf), oxine (ox) and 2, 2′ bipyridine (bp) bidentate ligands have been synthesized and characterized by FT-IR, UV-visible, mass, and NMR spectroscopic techniques. The structure of complex 2 shows distorted pentagonal-bipyramidal geometry, as confirmed by a single-crystal XRD diffraction study. The interactions of complexes with bovine serum albumin (BSA) and calf thymus DNA (CT-DNA) are investigated using UV-visible and fluorescence spectroscopic techniques. It has been observed that CT-DNA interacts with complexes through groove binding mode and the binding constants for complexes 1 and 2 are 8.7 × 103 M−1 and 8.6 × 103 M−1, respectively, and BSA quenching constants for complexes 1 and 2 are 0.0628 × 106 M−1 and 0.0163 × 106 M−1, respectively. The ability of complexes to cleave DNA is investigated using the gel electrophoresis method with pBR322 plasmid DNA. Furthermore, the cytotoxic effect of the complexes is evaluated against the HeLa cell line using an MTT assay. The complexes are subjected to density functional theory calculations to gain insight into their molecular geometries and are in accordance with the results of docking studies. Furthermore, based on molecular docking studies, the intermolecular interactions responsible for the stronger binding affinities between metal complexes and DNA are discussed.

Metal-organic frameworks based on heterocyclic ligands and some transition metals as effective carbon steel corrosion inhibitors in aqueous environment

A variety of corrosion inhibitors, including inorganic salts and organic compounds containing heteroatoms and electron clouds, were utilized as corrosion inhibitors for metals in diverse corrosive environments”. The presence of Nano cages and hollow spheres in metal organic frameworks expands their applicability in the field of electrochemistry. Metal-organic frameworks (MOFs) containing 2,6-pydinedicarboxylic acid ligands (2,6-pydcH2) as well as Cd and Mn were synthesized to investigate their influence on C-steel corrosion inhibition in 1 M hydrochloric acid solution. 2-Asymmetric units of each MOFs1 and 2 represent a repeat structure which contains 2-metal cations coordinated to two 2,6-pydc ligands and 3-molecules of H2O with one free 2,6-pydcH2 as guest molecule. The network structures of 1 and 2, contains 2-similar Cd (II) or Mn (II) atoms surrounded by 7- atoms adopting unusual distorted pentagonal bipyramidal geometry. The prevention of C-steel corrosion was studied using weight loss (WL), “Tafel polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM)”. Inhibition efficacy rises with raising inhibitor concentration, decreases with rise in temperature and reached 91.42% at 25 °C for MOF (1) at 1 × 10-4 M. On the other hand, it increases with improvement of concentration and in rise in temperature and reached 85.98% at 45 °C for MOF (2) at 1 × 10-4 M. Polarization measurements revealed that these MOFs operated as a mixed kind of inhibitors. The activation and adsorption thermodynamic properties were estimated and discussed. The value of free energy of adsorption determined at 25 °C (ΔGoads = 16.96, 41.61 kJ mol−1 for MOFs 1 and 2, respectively), suggested a physisorption for MOF (1) and Chemisorption for MOF (2) compounds. The adsorption of these inhibitors was shown to follow the Langmuir adsorption isotherm. The surface morphology of a C-steel sample was done using scanning electron microscopy (SEM) technique. All tests conducted that MOFs 1 and 2 acted as good corrosion inhibitors.

Novel metal complexes with pyrano[3,2‐c]quinoline‐3‐carboxaldehyde: Synthesis, spectroscopic, molecular modeling, QSAR, antimicrobial, and antitumor studies

Reaction of 6‐ethyl‐4‐hydroxy‐2,5‐dioxo‐5,6‐dihydro‐2H‐pyrano[3,2‐c]quinoline‐3‐carboxaldehyde (HL) with some metal ions, namely, manganese (II), cobalt (II), nickel (II), zinc (II), cadmium (II), chromium (III), iron (III), cerium (III), oxovanadium (IV), and dioxouranium (VI), yielded a new series of metal complexes; with the general formula, [MHnLAm(H2O)x]Xy·zH2O, n = 0–1, A = NO3− or OAc−, m = 0–2, X = NO3− or SO42−, y = 0–1, and z = 0–3. The metal complexes were characterized by elemental analysis, molar conductance, magnetic moment, thermal analysis, and spectroscopic studies. The HL ligand coordinated with metal ions as monobasic or neutral bidentate via OO donor sites of aldehyde –O and phenolic –OH producing metal complexes with tetrahedral, octahedral, and pentagonal bipyramidal geometries. On the bases of PM3 level, molecular orbital calculations were performed for metal complexes using HyperChem 7.52 program, and the results were correlated with the experimental data. The biological activity of chelating agent and its metal complexes was screened towards Staphylococcus aureus and Bacillus subtilis as Gram‐positive bacteria; Salmonella typhimurium and Escherichia coli as Gram‐negative bacteria, as well as Candida albicans (yeast) and Aspergillus fumigatus (fungus). The antitumor activity of the HL ligand and its metal complexes was tested against Ehrlich Ascites Carcinoma cell line (EAC), which revealed promising IC50 values, comparable with that of cisplatin. Additional QSAR models were developed to predict the biodistribution of a smaller set of metal complexes and the calculated data correlated with antitumor results.

Deciphering the Role of Anions and Secondary Coordination Sphere in Tuning Anisotropy in Dy(III) Air-Stable D5h SIMs.

Precise control of the crystal field and symmetry around the paramagnetic spin centre has recently facilitated the engineering of high-temperature single-ion magnets (SIMs), the smallest possible units for future spin-based devices. In the present work, we report a series of air-stable seven coordinate Dy(III) SIMs {[L2 Dy(H2 O)5 ][X]3 ⋅L2 ⋅n(H2 O), n = 0, X = Cl (1), n=1, X = Br (2), I (3)} possessing pseudo-D5h symmetry or pentagonal bipyramidal coordination geometry with high anisotropy energy barrier (Ueff ) and blocking temperature (TB ). While the strong axial coordination from the sterically encumbered phosphonamide, t BuPO(NHi Pr)2 (L), increases the overall anisotropy of the system, the presence of high symmetry significantly quenches quantum tunnelling of magnetization, which is the prominent deactivating factor encountered in SIMs. The energy barrier (Ueff ) and the blocking temperature (TB ) decrease in the order 3>2>1 with the change of anions from larger iodide to smaller strongly hydrogen-bonded chloride in the secondary coordination sphere, albeit the local coordination geometry and the symmetry around the Dy(III) display only slight deviations. Ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations provide deeper insights into the dynamics of magnetic relaxation in addition to the role of the secondary coordination sphere in modulating the anisotropy of the D5h systems, using diverse models. Thus, in addition to the importance of the crystal field and the symmetry to obtain high-temperature SIMs, this study also probes the significance of the secondary coordination sphere that can be tailored to accomplish novel SIMs.

A Cd(II) Luminescent Coordination Grid as a Multiresponsive Fluorescence Sensor for Cr(VI) Oxyanions and Cr(III), Fe(III), and Al(III) in Aqueous Medium.

Hydro(solvo)thermal reactions of Cd(NO3)2, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H2bdc) afforded a luminescent coordination polymer, {[Cd(Br-1,3-bdc)(NI-mbpy-34)(H2O)]∙2H2O}n (1). Single-crystal X-ray diffraction analysis showed that 1 features a two-dimensional (2-D) gridlike sql layer with the point symbol of (44·62), where the Cd(II) center adopts a {CdO5N2} pentagonal bipyramidal geometry. Thermogravimetric (TG) analysis confirmed the thermal stability of 1 up to about 340 °C, whereas XRPD patterns proved the maintenance of crystallinity and framework integrity of 1 in CH2Cl2, H2O, CH3OH, and toluene. Photoluminescence studies indicated that 1 displayed intense blue fluorescence emissions in both solid-state and H2O suspension-phase. Owing to the good fluorescent properties, 1 could serve as an excellent turn-off fluorescence sensor for selective and sensitive Cr(VI) detection in water, with LOD = 15.15 μM for CrO42− and 14.91 μM for Cr2O72−, through energy competition absorption mechanism. In addition, 1 could also sensitively detect Cr3+, Fe3+, and Al3+ ions in aqueous medium via fluorescence-enhancement responses, with LOD = 2.81 μM for Cr3+, 3.82 μM for Fe3+, and 3.37 μM for Al3+, mainly through an absorbance-caused enhancement (ACE) mechanism.

Energetic features of antiparallel stacking and hydrogen bonding interactions in two coordination complexes bearing 1,10-phenanthroline-2,9-dicarboxylic acid

Two new metal–organic complexes, [Co(phen)(PDA)H2O]·CH3CN·H2O (1), (phen = 1,10-phenanthroline, PDA = 1,10-phenanthroline-2,9-dicarboxylate) and [Ce2(PDA)3(H2O)2]·3H2O (2) have been synthesized and characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray crystallography. Structural characterization by single-crystal X-ray diffraction shows that in 1 the cobalt ion forms a discrete seven-coordinated complex with a distorted pentagonal bipyramidal geometry around the metal centre. These discrete units are further packed into 3-D supramolecular assemblies by different kinds of the noncovalent interactions. Complex 2 consists of a 1D coordination polymeric structure with the cerium ion coordinated by PDA and water in the form of left-handed and right-handed helices. The extended aromatic systems of PDA and phen have a strong tendency to establish antiparallel π···π stacking interactions generating interesting assemblies in the solid state of 1. They have been studied theoretically using DFT calculations and characterized by means of the quantum theory of “atoms-in-molecules” (QTAIM) and the noncovalent interaction (NCI) plot methods. This study is useful to understand in more detail the energetic and structural stability of these categories of metal-organic complexes. The results reported herein suggest that the antiparallel π-stacking interactions involving the neutral and, in principle innocent, phen auxiliary ligand are energetically very relevant in the solid state of 1.

Magnetization Dynamics on Isotope-Isomorphic Holmium Single-Molecule Magnets.

Here we reported the deuteration of the metal-binding equatorial water molecules in a reported HoIII single-molecule magnet (SMM) with pentagonal-bipyramidal geometry, from [Ho(CyPh2 PO)2 (H2 O)5 ]3+ to [Ho(CyPh2 PO)2 (D2 O)5 ]3+ . The hyperfine structures originating from the nuclear spin of 165 HoIII can be clearly observed. Moreover, the resulting magnetization dynamics revealed the switch of the relative relaxation rates for the two isotope-isomorphic complexes-respectively faster/slower at low/high temperature. The noticeable isotope effect arises from not only the paramagnetic metal center but also the diamagnetic ligands, which can be explained by the ab initio calculated tunnel splitting and the involvement of the super-hyperfine interaction related to the difference in the nuclear spin number of protium (1 H, I=1 /2 ) and deuterium (2 H, I=1).

Synthesis and structures of tantalum chloride and tantalum aryloxide compounds bearing bidentate and tridentate pyrrole‐amine ligands

AbstractA series of mononuclear tantalum derivatives containing substituted pyrrole‐amine ligands are synthesized. Reacting TaCl5 with one equivalent of Li[C4H2N‐2,5‐(CH2NMe2)2] in toluene affords TaCl4[C4H2N‐2,5‐(CH2NMe2)2] (1), whereas TaCl4[C4H3N‐2‐(CH2NEt2)] (2) is generated between the combination of TaCl5 and Li[C4H3N‐2‐(CH2NEt2)] in moderate yield. Similarly, while subjecting Li[C4H2N‐2‐(CH2NMe2)‐5‐(CH2NHtBu)] with TaCl5 in diethyl ether, it affords TaCl3[C4H2N‐2‐(CH2NMe2)‐5‐(CH2NtBu)] (3) at moderate yield. Interestingly, the mixing of TaCl4[C4H2N‐2,5‐(CH2NMe2)2] (1) with excess Li[O‐Ph‐2,6‐iPr2] in tetrahydrofuran generates the tantalum aryloxide compound, Ta(O‐Ph‐2,6‐iPr2)Cl3[C4H2N‐2,5‐(CH2NMe2)2] (4). Single crystal X‐ray diffraction analysis reveals that compound 4 is hepta‐coordinated possessing a distorted pentagonal bipyramidal geometry. All the compounds are characterized by proton nuclear magnetic resonance and carbon‐13 nuclear magnetic resonance spectroscopy, and we highlight the structural variation of tantalum derivatives with bi‐ or tridentate (symmetric and asymmetric) pyrrole precursors.

New Volatile Tantalum Imido Precursors with Carboxamide Ligands.

A series of Ta(V) tBu-imido/N-alkoxy carboxamide complexes, TaCl2(NtBu)(pyridine)(edpa) (1), TaCl(NtBu)(edpa)2 (2), Ta(NtBu)(edpa)3 (3), TaCl2(NtBu)(pyridine)(mdpa) (4), and Ta(NtBu)(mdpa)3 (5), were successfully synthesized by metathesis reactions between Ta(NtBu)Cl3(py)2 and several equivalents of Na(edpa) (edpaH = N-ethoxy-2,2-dimethylpropanamide) and Na(mdpa) (mdpaH = N-methoxy-2,2-dimethylpropanamide). Furthermore, complexes 3 and 5 were simply transformed to new dimeric structures [Ta(μ2–O)(edpa)3]2 (6) and [Ta(μ2–O)(mdpa)3]2 (7) with the elimination of the NtBu imido group by air exposure. Compounds 1–7 were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that complexes 3 and 5 have a distorted pentagonal bipyramidal geometry around the central Ta atom, with three monoanionic bidentate N-alkoxy carboxamide ligands and one tBu imido ligand saturating the coordination of tantalum ions. TGA revealed that complexes 3 and 5 had superior thermal characteristics and stability. These complexes could potentially be applied as precursors for tantalum oxide thin films.

Coarse-Grained Modeling and Molecular Dynamics Simulations of Ca2+-Calmodulin.

Calmodulin (CaM) is a calcium-binding protein that transduces signals to downstream proteins through target binding upon calcium binding in a time-dependent manner. Understanding the target binding process that tunes CaM’s affinity for the calcium ions (Ca2+), or vice versa, may provide insight into how Ca2+-CaM selects its target binding proteins. However, modeling of Ca2+-CaM in molecular simulations is challenging because of the gross structural changes in its central linker regions while the two lobes are relatively rigid due to tight binding of the Ca2+ to the calcium-binding loops where the loop forms a pentagonal bipyramidal coordination geometry with Ca2+. This feature that underlies the reciprocal relation between Ca2+ binding and target binding of CaM, however, has yet to be considered in the structural modeling. Here, we presented a coarse-grained model based on the Associative memory, Water mediated, Structure, and Energy Model (AWSEM) protein force field, to investigate the salient features of CaM. Particularly, we optimized the force field of CaM and that of Ca2+ ions by using its coordination chemistry in the calcium-binding loops to match with experimental observations. We presented a “community model” of CaM that is capable of sampling various conformations of CaM, incorporating various calcium-binding states, and carrying the memory of binding with various targets, which sets the foundation of the reciprocal relation of target binding and Ca2+ binding in future studies.

Magneto-structural studies of a one dimensional Mn(II) coordination polymer derived from a flexible polydentate ligand

The polydentate ligand LHμ contains bipyridine, hydrazone and oxime functionalities and reacts with Mn(CH3COO)2·4H2O to afford an alternating one dimensional chain comprising Mn(II) ions, [{Mn2(LH)(CH3COO)3(CH3OH)2}·CH3OH]n(1). The structure of 1 contains two Mn(II) ions in the asymmetric unit; Mn1 adopts an unusual pentagonal bipyramidal coordination geometry comprising an [N3O4] donor set, while Mn2 adopts a more conventional octahedral geometry coordinated by an [NO5] donor set. The two manganese ions within the dinuclear unit are connected to each either via Ohydrazone and syn-syn Oacetate bridges. These dinuclear units are then linked by anti-anti Oacetate bridges, affording a magnetic 1-D alternating chain topology. Magnetic studies on 1 reveal the presence of weak antiferromagnetic interactions via Ohydrazone and acetate bridges. The magnetism of 1 was modelled using a dimer model [Ĥ = −2JŜ1Ŝ2], with inter-dimer exchange modelled using a mean field term (zJ’) to afford g = 2.046 ± 0.002, J/k = -1.03 ± 0.02 cm−1 and zJ’ = −0.06 ± 0.01 cm−1.

Triple M as Manganese: Medicine, magnetism and macrocycles. Seven-coordinate Mn(II) complexes with pyridine-based macrocyclic ligands

Manganese, or more accurately manganese(II) complexes, are extensively used in various scientific and research fields. In this work, we present the preparation and characterization of three manganese(II) complexes with three structurally-new pyridine-based macrocyclic ligands, which differ from each other by functional group in pendant arms. The ligands’ backbone consists of a parental 17-membered macrocycle (LdiProp) containing pyridine and piperazine rings, which are part of the macrocyclic scaffold. The original aliphatic NH groups in LdiProp were successively substituted with three different pendant arms – benzyl (bn2-LdiProp), 2-pyridylmethyl (py2-LdiProp) and 2-aminoethyl ((NH2et)2-LdiProp). A series of manganese(II) complexes with structural formulas [Mn(bn2-LdiProp)Cl2]·CH3OH (1), [Mn(py2-LdiProp)](ClO4)2·0.5CH3CN·0.35H2O (2) and [Mn((NH2et)2-LdiProp)](ClO4)2 (3) were subsequently prepared. In all cases, the presence of coordination number seven with a close to pentagonal bipyramid geometry was confirmed by X-ray diffraction analysis. The axial positions were occupied by chlorido coligands (1) or nitrogen atoms of the pendant arms (2 and 3). The pentagonal bipyramidal coordination sphere was distorted in case of all complexes 1–3 and axially compressed for 2 and 3. The equatorial Mn–Naliphatic bond distances were significantly lengthened up to 2.61 Å.

Synthesis of uranium complexes incorporating extended azo-imine ligands: Molecular and electronic structure

The new azo-imine ligands 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl)diazenyl) phenylimino)methyl)phenol, H2L1, 1a, and 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl) diazenyl)p-chlorophenylimino)phenol, H2L2, 1b, were prepared. Reaction of H2L1;1a, and H2L2;1b, with uranyl nitrate hexahydrate afforded the mononuclear complexes of compositions [U(O)2(L1)(H2O)]; 2a, and [U(O)2(L2)(H2O)]; 2b, complexes respectively. The newly synthesised ligands (1a and 1b) and the complexes (2a and 2b) were characterised unequivocally. The x-ray structure of 2a was determined. The tetradentate dianionic ligand (L1)2- coordinated the uranium ion equatorially with a water molecule in the same plane. Two axially coordinated oxo ligands completed the overall pentagonal bipyramid geometry around U(VI) ion. Structural pattern, electron transfer properties (oxidation near 1.32 ​V vs Ag/AgCl) and electronic transitions of [U(O)2(L1)(H2O)]; 2a, and [U(O)2(L2)(H2O)]; 2b have been rationalized by DFT calculations.

A novel family of hepta-coordinated Cr(III) complexes with a planar pentadentate N3O2 Schiff base ligand: synthesis, structure and magnetism

A series of seven-coordinate pentagonal-bipyramidal (PBP) Cr(III) complexes with pentadentate pyridine-based ligands, 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone), H2DAPMBH (H2LOCH3) or 2,6-diacetylpyridine bis(benzoylhydrazone), H2DAPBH (H2L) and different axial ligands have been prepared. The reaction of the H2LOCH3 with CrCl2·4H2O in methanol or CrCl3·6H2O in CH3CN led to a novel seven-coordinate pentagonal-bipyramidal (PBP) complex [Cr(HLOCH3)Cl2] (1) with the mono-deprotonated chelating ligand in the equatorial plane and two apical Cl atoms. Then, taking advantage of lability of the apical Cl ligands in 1, a number of PBP CrIII complexes with charged (viz. CH3O−, N3−, CN−, NCS−) and neutral (viz. CH3OH, H2O) apical ligands was obtained and characterized: [Cr(HLOCH3)Cl2]·4CHCl3 (1), [Cr(HLOCH3)Cl2]·CH3OH (1a), [Cr(HLOCH3)(H2O)Cl]PF6·CH3OH (2), [Cr(HL)(H2O)Cl]ClO4·0.25H2O (3), [Cr(HLOCH3)(H2O)2](NO3)2·H2O·C2H5OH (4), [Cr(LOCH3)(CH3OH)(OCH3)]·CH3OH (5), [Cr(HLOCH3)(NCS)2]·1.5H2O (6), [Cr(HLOCH3)(N3)2]·xH2O (7, x = 0.2, 8, x = 0, 9, x = 0, three phases in the same synthesis), [Cr(LOCH3)(N3)2][Na(CH3OH)2]·2CH3OH (10), [Cr(LOCH3)(CN)2][Na(H2O)(C2H5OH)] (11). Single crystal X-ray analysis reveals that all the complexes 1–11 have the PBP geometry with a pentadentate ligand in a form of [HLOCH3]− or [LOCH3]2− in the equatorial plane. The PBP complexes are prone to aggregate into dimers or polymers, either due to strong hydrogen bonds or due to the transformation of terminal ligands into bridging between different metallic centers. All complexes 1–11 exhibit considerable in-plane distortion of the CrN3O2 pentagon due to the shift of the CrIII ion from the central position, which is caused by the strong first-order Jahn-Teller (JT) effect for the high-spin 3d3 configuration in the PBP ligand field. The mechanism of JT distortions is rationalized in terms of DFT calculations. DC magnetic measurements indicate a high-spin (S = 3/2) ground state of complex [Cr(HLOCH3)Cl2]·4CHCl3 (1); theoretical analysis of its magnetic properties reveals negative zero-field splitting energy with the anisotropy parameter D = –1.8 cm−1 and weak dimer-like antiferromagnetic spin coupling J = –0.23 cm−1 between neighboring PBP units [CrIII(HLOCH3)Cl2] mediated by π-stacking of planar H2LOCH3 ligands.

Structural diversity in substituted aminosilyl‐aminopyridinate metal (Zr or Fe) complexes: Synthesis, structures, and ethylene polymerization

Seven examples of chlorozirconium N‐[(N,N‐dimethylamino)dimethylsilyl]‐2‐pyridylaminates, mononuclear monoligand Zr[(RC5H4N)NSiMe2NMe2]Cl3LiCl(Et2O)2 (R = 4‐Me, Zr1; R = 5‐Me, Zr2; R = 5‐Cl, Zr3), chloro‐bridged dinuclear diligand [Zr{(RC5H4N)NSiMe2NMe2}Cl3]2 (R = 5‐Cl, Zr4; R = 4‐Cl, Zr5), and mononuclear triligand Zr[(RC5H4N)NSiMe2NMe2]3Cl (R = 6‐Me, Zr6; R = H, Zr7), have been prepared by the individual reactions of zirconium tetrachloride with the corresponding lithium N‐[(N,N‐dimethylamino)dimethylsilyl]‐2‐pyridylaminates of (RC5H4N)NHSiMe2NMe2 (R = 4‐Me, 1a; 5‐Me, 1b; 5‐Cl, 1c; 4‐Cl, 1d; 6‐Me, 1e; H, 1f), respectively. Besides seven coordination around zirconium core, Zr1–Zr5 adopt a distorted pentagonal bipyramid geometry with the ligand acting as a monoanionic η2:η1‐tridentate fashion; Zr6–Zr7 present capped trigonal prism geometry with the ligand as η2‐coordination with a pendant N (CH3)2 free. Extensively, the reactions of FeCl2 with lithiated (RC5H4N)NHSiMe2NMe2 (R = 4‐Me, 1a; 5‐Cl, 1c; 6‐Me, 1e) afford the corresponding dimeric complexes (R = 4‐Me, Fe1; 5‐Cl, Fe2; 6‐Me, Fe3), in which Fe1 and Fe2 exhibit C2 symmetry with each iron unit as a distorted trigonal bipyramidal geometry, while Fe3 specially possesses a centrosymmetric hour‐glass‐shaped core with each iron center as a distorted tetrahedral geometry. Upon activation with methylaluminoxane (MAO), zirconium complexes exhibit moderate to good activities toward ethylene polymerization and produce the polyethylenes with high molecular weight and broad dispersity.

Synthesis of novel volatile niobium precursors containing carboxamide for Nb2O5 thin films

A series of novel Nb(V) tBu-imido/N-alkoxy carboxamide complexes, NbCl2(NtBu)(pyridine)(edpa) (1), NbCl2(NtBu)(pyridine)(mdpa) (2), and Nb(NtBu)(mdpa)3 (3), were successfully synthesized by metathesis reaction between Nb(NtBu)Cl3(py)2 and several equivalents of Na(edpa) (edpaH = Nethoxy-2,2-dimethylpropanamide) and Na(mdpa) (mdpaH = N-methoxy-2,2-dimethylpropanamide). These complexes could potentially serve as precursors for Nb-containing thin films. Compounds 1–3 were characterized by FT-IR and 1H and 13C NMR spectroscopies, elemental analysis, and thermogravimetric analysis (TGA). Single crystal X-ray diffraction analysis suggested that complex 3 has a distorted pentagonal bipyramidal geometry around the central Nb atom, with three bidentate mdpa ligands and one tBu imido group saturating the coordination. TGA analysis revealed that the thermal characteristics of 3 were superior to those of 1 and 2. All prepared complexes were able to be distilled or sublimed and expected potential precursors for the fabrication of thin films.