Dimeric pentacoordinate trivalent iron complexes of benzoyl hydrazones

Dimeric iron(III) complexes derived from benzhydrazide and salicylaldehyde (BSH), o-hydroxy-acetophenone (BAH), o-hydroxypropiophenone(BPH), o-hydroxybutyrophenone(BBH) and 2-hydroxy-1-naphthaldehyde(BNH), having general formula [Fe(L)X]₂, X  Cl, Br, or NO₃ and characterised by elemental analyses and by conductance, molecular weights, electronic, infrared spectral and magnetic measurements, are described. The dimeric nature of the complexes is revealed by infrared spectra which show that two monomeric units, each having square-pyramidal stereochemistry, are stacked together through phenolic oxygen acting as bridges. The anions are present as axial ligand and the ranges observed for ν(FeCl), ν(FeBr) and ν(FeONO₂) in the far IR spectra are consistent with the pentacoordinate stereochemistry. The lowering in magnetic moments (4.30 – 4.50 BM) from spin-only value has been explained by the presence of anti-ferromagnetic exchange which takes place via σ and π-bonding pathways. The electronic spectra have also been discussed.     

Thermal decomposition of pentacoordinate uranium(VI) complexes

The thermal decomposition of some mixed uranyl complexes with Schiff bases and DMSO, EtOH or (Ph)₃PO as neutral ligand, were investigated and the corresponding activation energy, E*_a, and enthalpy of dissociation, ΔH_d, values were calculated.

The results obtained indicate that for the same neutral ligand, the thermal stability of the uranyl complexes is influenced by the Schiff base used; for the same Schiff base, the presence of (Ph)₃PO results in a greater thermal stability of the mixed complexes than when the other two neutral ligands are present.     

New tetra- and pentacoordinate nickel(I) complexes

Summary The reduction of nickel(II) halides with NaBH₄ in ethanol has been studied in the presence of various tertiary phosphines and arsines. Complexes of the type XNiL₃ have been isolated in this way when X = Cl, Br, I and L = PPh₃, AsPh₃, no reaction being observed when L = PEt₃, PBu₃ and Ph₂P(CH₂)₂PPh₂.The reaction of XNiL₃ with CO gas at room temperature produces pentacoordinate carbonyl complexes XNi(CO)₂L₂ when L is triphenylphosphine. The lack of stability prevents the isolation of similar complexes when L is trip henylarsine.Structural data obtained by i.r. spectroscopy and susceptibility measurements as well as chemical behaviour of the new complexes are described.     

五配位有机锡络合物的合成和表征

制备并表征了十个新型五配位有机锡络合物,用X射线衍射测定了它们的单晶结构,它们被指认炎二环氮染锡二氧杂壬烯类化合物.     

Syntheses and characterization of pentacoordinate organo-tin(IV) complexes II

Nine substituted benzoyl hydrazonyl, three semicarbazonyl, and four thiosemicarbazonyl tridentate ligands were synthesized. They were used to coordinate with Bu₂SnCl₂ or (PhCH₂)₂SnCl₂ to form 18 novel tin complexes that contained pentacoordinate organotin(IV) in a heterobicyclic ring. All these complexes were characterized by MS, NMR, and IR spectroscopy elemental analyses. © 1995 John Wiley & Sons, Inc.     

Synthesis of benzo[h]quinoline-based neutral pentacoordinate organosilicon complexes

Reactions of 10-benzo[h]quinolyllithium with a series of organosilanes led to the formation of neutral pentacoordinate complexes. The diethynyl-substituted complex was able to be converted to di(arylethynyl)-substituted ones by the Sonogashira-Hagihara coupling reaction. Electronegative substituents shortened N-Si distances and enhanced fluorescence intensity from the complexes.     

Large magnetic anisotropy in pentacoordinate Ni(II) complexes

Pentacoordinate complexes in which Ni(II) is chelated by the tridentate macrocyclic ligand 1,4,7-triisopropyl-1,4,7-triazacyclononane (iPrtacn) of formula [Ni(iPrtacn)X(2)] (X=Cl, Br, NCS) have relatively large magnetic anisotropies, revealed by the large zero-field splitting (zfs) axial parameters |D| of around 15 cm(-1) measured by frequency-domain magnetic resonance spectroscopy (FDMRS) and high-field high-frequency electron paramagnetic resonance (HF-HFEPR). The spin Hamiltonian parameters for the three complexes were determined by analyzing the FDMRS spectra at different temperatures in zero applied magnetic field in an energy window between 0 and 40 cm(-1). The same parameters were determined from analysis of HF-HFEPR data measured at different frequencies (285, 380, and 475 GHz) and at 7 and 17 K. The spin Hamiltonian parameters D (axial) and E (rhombic) were calculated for the three complexes in the framework of the angular overlap model (AOM). The nature and magnitude of the magnetic anisotropy of the three complexes and the origin of the influence of the X atoms were analyzed by performing systematic calculations on model complexes.     

DFT calculations of isomer shifts and quadrupole splitting parameters in synthetic iron-oxo complexes: applications to methane monooxygenase and ribonucleotide reductase

To predict isomer shifts and quadrupole splitting parameters of Fe atoms in the protein active sites of methane monooxygenase and ribonucleotide reductase, a correlation between experimental isomer shifts ranging 0.1-1.5 mm s(-)(1) for Fe atoms in a training set with the corresponding density functional theory (DFT) calculated electron densities at the Fe nuclei in those complexes is established. The geometries of the species in the training set, consisting of synthetic polar monomeric and dimeric iron complexes, are taken from the Cambridge structural database. A comparison of calculated M?ssbauer parameters for Fe atoms from complexes in the training set with their corresponding experimental values shows very good agreement (standard deviation of 0.11 mm/s, correlation coefficient of -0.94). However, for the Fe atoms in the active sites of the structurally characterized proteins of methane monooxygenase and ribonucleotide reductase, the calculated M?ssbauer parameters deviate more from their experimentally measured values. The high correlation that exists between calculated and observed quadrupole splitting and isomer shift parameters for the synthetic complexes leads us to conclude that the main source of the error arising for the protein active sites is due to the differing degrees of atomic-level resolution for the protein structural data, compared to the synthetic complexes in the training set. Much lower X-ray resolutions associated with the former introduce uncertainty in the accuracy of several bond lengths. This is ultimately reflected in the calculated isomer shifts and quadrupole splitting parameters of the Fe sites in the proteins. For the proteins, the closest correspondence between predicted and observed M?ssbauer isomer shifts follows the order MMOH(red), RNR(red), MMOH(ox), and RNR(ox), with average deviations from experiment of 0.17, 0.17, 0.17-0.20, and 0.32 mm/s, but this requires DFT geometry optimization of the iron-oxo dimer complexes.     

Surface-immobilized single-site iridium complexes for electrocatalytic water splitting

Water into oxygen: Mono-iridium complexes (see picture; L=PO(3) H(2) or COOH) were immobilized on an indium tin oxide (ITO) surface to form a molecular electrocatalytic water oxidation assembly that mimics photosystem?II in producing molecular oxygen with high turnover numbers (TONs). The catalyst shows TONs for O(2) higher than 210?000 and turnover frequencies higher than 6.7?s(-1) during electrochemical catalytic water splitting.     

Correlation of isomer shift and quadrupole splitting and the sign of EFG

Mössbauer isomer shift // and quadrupole splitting /E_Q/ values in a series of isostructural compounds correlate well to give linear relationship provided the sign of electric field gradient /EFG/ is assigned to the E_Q. The correlation has been used in predicting the sign of EFG for some monosubstituted pentacyanoferrate/II/ complexes. Usefulness of such correlations and its limitations are presented.     

Interpretation of Mott–Schottky plots of photoanodes for water splitting

A large body of literature reports that both bismuth vanadate and haematite photoanodes are semiconductors with an extremely high doping density between 10¹⁸ and 10²¹ cm⁻³. Such values are obtained from Mott–Schottky plots by assuming that the measured capacitance is dominated by the capacitance of the depletion layer formed by the doping density within the photoanode. In this work, we show that such an assumption is erroneous in many cases because the injection of electrons from the collecting contact creates a ubiquitous capacitance step that is very difficult to distinguish from that of the depletion layer. Based on this reasoning, we derive an analytical resolution limit that is independent of the assumed active area and surface roughness of the photoanode, below which doping densities cannot be measured in a capacitance measurement. We find that the reported doping densities in the literature lie very close to this value and therefore conclude that there is no credible evidence from capacitance measurements that confirms that bismuth vanadate and haematite photoanodes contain high doping densities.

Electron injection from the contact dominates the Mott–Schottky plots of thin-film photoanodes, rather than the depletion capacitance.     

BN-analogues of vinylidene transition metal complexes: the borylnitrene isomer

Density functional computations using the BP86 functional within the resolution-of-identity approximation and polarized triple-zeta basis sets are employed for the study of the three isoelectronic (CO)(4)FeL (L = CCH(2) (5), BNH(2) (6), NBH(2) (7)) as well as (CO)(4)Fe(NBcat) (9) (cat = catecholato) complexes. In all complexes 5-7, the ligand L prefers the equatorial position of a pseudo trigonal bipyramid. The borylnitrene complex 7 has a linear Fe-N-B arrangement; its Fe-L bond dissociation energy is similar to that of the vinylidene complex 5 and only slightly lower than that of 6. Nonetheless, 7 is less stable thermodynamically than 6 by 40 kcal mol(-1). Complexes of type 7 are expected to be reactive on the basis of the following findings: the HOMO-LUMO energy gap is small, the rearrangement from 7 to 6 via an iminoborane intermediate involves barriers of 15 and 28 kcal mol(-1), and the dissociation of a CO molecule to give (CO)(3)FeNBH(2) is only slightly endergonic (+7 kcal mol(-1) at 298.15 K). The catecholate bridge in 9 results in significant changes: the bipyramidal complex is no longer a minimum, but an isocycanato complex is obtained instead computationally.     

The reactivity of areneseleninato complexes. New pentacoordinate nickel(II) complexes with benzeneseleninato ions and ethylenediamine as ligands

Summary Five-coordinate bis(Se-benzeneseleninato)tris(ethylenediamine)nickel(II) complexes are obtained by reaction of the Ni(H₂O)₂(XC₆H₄SeO₂)₂ complexes (X = H,p-Cl,m-Cl,m-Br orp-Me) with ethylenediamine. All the diaquo complexes react with three moles of ethylenediamine to form Se-seleninato derivatives. The compounds are characterized on the basis of far i.r. and near i.r. spectroscopy, electronic spectra and magnetochemical investigations. The most attainable geometry is the square pyramidal, probably slightly distorted; tentative assignments for the electronic spectra are proposed. Conductivity data indicate that these new complexes are nonelectrolytes; both areneseleninato and ethylenediamine behave as monodentate ligands. The magnetic moments show that all the complexes are of high-spin type, the values lying within the ranges observed for other high-spin five-coordinate nickel(II) complexes.