Extended network thiocyanate- and tetracyanoethanide-based first-row transition metal complexes

Linear chain thiocyanate complexes of M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn, Cr) composition have been prepared and structurally, chemically, and magnetically characterized. Fe(NCS)(2)(OCMe(2))(2) exhibits metamagnetic-like behavior, and orders as an antiferromagnet at 6 K. The Mn and Cr compounds are antiferromagnets with T(c) of 30 and 50 K, respectively, with J/k(B) = -3.5 (-2.4 cm(-1)) and -9.9 K (-6.9 cm(-1)), respectively, when fit to one-dimensional (1-D) Fisher chain model (H = -2JS(i)·S(j)). Co(NCS)(2) was prepared by a new synthetic route, and powder diffraction was used to determine its structure to be a two-dimensional (2-D) layer with μ(N,S,S)-NCS motif, and it is an antiferromagnet (T(c) = 22 K; θ = -33 K for T > 25 K). M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn) and Co(NCS)(2) react with (NBu(4))(TCNE) in dichloromethane to form M(TCNE)[C(4)(CN)(8)](1/2), and in acetone to form M[C(4)(CN)(8)](OCMe(2))(2) (M = Fe, Mn, Co). These materials possess μ(4)-[C(4)(CN)(8)](2-) that form 2-D layered structural motifs, which exhibit weak antiferromagnetic coupling. Co(TCNE)[C(4)(CN)(8)](1/2) behaves as a paramagnet with strong antiferromagnetic coupling (θ = -50 K).     

The hapticity of octafluorocyclooctatetraene in its first-row mononuclear transition metal carbonyl complexes: effect of perfluorination

The iron tricarbonyl complex of octafluorocyclooctatetraene was synthesized by Hughes and co-workers and shown by X-ray crystallography to have a trihapto–monohapto structure (η^3,1-C₈F₈)Fe(CO)₃ in contrast to the tetrahapto structure (η⁴-C₈H₈)Fe(CO)₃ formed by the non-fluorinated cyclooctatetraene. This difference has stimulated a comprehensive density functional theoretical study of the octafluorocyclooctatetraene metal carbonyl complexes (C₈F₈)M(CO) _n (n = 4, 3, 2, 1 for M = Ti, V, Cr, Mn, and Fe; n = 3, 2, 1 for M = Co, Ni) for comparison with their hydrogen analogues (C₈H₈)M(CO) _n . In most such systems, the substitution of fluorine for hydrogen leads to relatively small changes in the preferred structures. However, for the iron carbonyl derivatives (C₈X₈)Fe(CO)₃ (X = H, F), the difference observed experimentally has been confirmed by theory with (η^3,1-C₈F₈)Fe(CO)₃ and (η⁴-C₈H₈)Fe(CO)₃ being the lowest energy structures by 4 and 14 kcal/mol, respectively. The ligand exchange reactions C₈H₈ + (C₈F₈)M(CO) _n  → C₈F₈ + (C₈H₈)M(CO) _n are predicted to be exothermic for almost all of the systems considered, with the (η^3,1-C₈X₈)Fe(CO)₃ system being the main exception. This suggests that the C₈F₈ ligand generally bonds more weakly to transition metals than the C₈H₈ ligand in accord with the electron-withdrawing effect of the ligand fluorine atoms.     

UV photoelectron spectra of first-row transition metal hydridocarbonyl and hydridotrifluorophosphine complexes

The He(I) photoelectron spectrum of FeH₂(PF₃)₄ is reported, and the bands are assigned and compared with those of the analogous carbonyl complex. Molecular obrital energies for the MH σ-bonding orbitals, metal-3 d orbitals and metal-phosphorus σ-bonding orbitals for the hydridocarbonyl and hydridotrifluorophosphine complexes MnHL₅, FeH₂L₄ and CoHL₄ (L CO and PF₃) are compared and correlations discussed.     

Pyridazine- versus pyridine-based tridentate ligands in first-row transition metal complexes

A series of first-row transition metal complexes with the unsymmetrically disubstituted pyridazine ligand picolinaldehyde (6-chloro-3-pyridazinyl)hydrazone (PIPYH), featuring an easily abstractable proton in the backbone, was prepared. Ligand design was inspired by literature-known picolinaldehyde 2-pyridylhydrazone (PAPYH). Reaction of PIPYH with divalent nickel, copper, and zinc nitrates in ethanol led to complexes of the type [Cu(II)(PIPYH)(NO(3))(2)] (1) or [M(PIPYH)(2)](NO(3))(2) [M = Ni(II) (2) or Zn(II) (3)]. Complex synthesis in the presence of triethylamine yielded fully- or semideprotonated complexes [Cu(II)(PIPY)(NO(3))] (4), [Ni(II)(PIPYH)(PIPY)](NO(3)) (5), and [Zn(II)(PIPY)(2)] (6), respectively. Cobalt(II) nitrate is quantitatively oxidized under the reaction conditions to [Co(III)(PIPY)(2)](NO(3)) (7) in both neutral and basic media. X-ray diffraction analyses reveal a penta- (1) or hexa-coordinated (2, 3, and 7) metal center surrounded by one or two tridentate ligands and, eventually, κ-O,O' nitrate ions. The solid-state stoichiometry was confirmed by electron impact (EI) and electrospray ionization (ESI) mass spectrometry. The diamagnetic complexes 5 and 6 were subjected to (1)H NMR spectroscopy, suggesting that the ligand to metal ratio remains constant in solution. Electronic properties were analyzed by means of cyclic voltammetry and, in case of copper complexes 1 and 4, also by electron paramagnetic resonance (EPR) spectroscopy, showing increased symmetry upon deprotonation for the latter, which is in accordance with the proposed stoichiometry [Cu(II)(PIPY)(NO(3))]. Protic behavior of the nickel complexes 2 and 5 was investigated by UV/vis spectroscopy, revealing high π-backbonding ability of the PIPYH ligand resulting in an unexpected low acidity of the hydrazone proton in nickel complex 2.     

Polarizability effect in transition metal carbonyl complexes

The literature date on substituent influence on the carbonyl stretching frequencies (ν), CO stretching force constants (k), as well as ¹³C NMR carbonyl chemical shifts (δ) have been analyzed for 19 series of the transition metal carbonyl complexes. It was established for the first time that the ν, k and δ values depend not only on the inductive and resonance effects but also on the polarizability of substituents. The polarizability contribution ranges up to 37%.     

Hydrogen bonding in transition metal carbonyl complexes

Conclusions The formation of a previously unknown type of hydrogen bonding OH...OC-M involving the oxygen atom of the CO group at the metal atom was observed upon the interaction of CpMn(CO)₂-P(i-Pr)₃ with (CF₃)₃COH in liquid xenon solution at low temperatures.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2605–2608, November, 1986.     

Thermal degradation of the transition metal carbonyl complexes

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅(dppm) (whereM=Cr, Mo and W;dppm=Bis-(diphenylphosphino)-methane) has been studied using TG and DSC technics and their results reported. All the complexes facilely lose a carbonyl ligand (CO) below 200 °C. The kinetic analysis on the molybdenum complex suggested a first order dissociation pathway for this decarbonylation process. Dephosphination occurred at high temperature, followed by further decarbonylations. The enthalpy changes associated with the first decarbonylation are reported. The measured kinetic parameters are in good agreement with the literature values on similar systems obtained from solution studies.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonyl-Komplexen des Typs M(CO)₅(dppm) (M=Cr, Mo oder W; dppm=Bis-(diphenylphosphino)-methan) wurden mittels TG und DSC untersucht. Alle diese Komplexe geben unterhalb 200 °C leicht einen Carbonylliganden (CO) ab. Die für den Molybdänkomplex ausgeführte kinetische Analyse deutet auf einen Dissoziationsverlauf erster Ordnung für diesen Decarbonylierungsprozeß hin. Bei hohen Temperaturen erfolgt Dephosphinierung, gefolgt von weiterer Decarbonylierung. Die sich auf den ersten Decarbonylierungsschritt beziehenden Enthalpieänderungen werden angegeben. Die gemessenen kinetischen Parameter stimmen gut mit Literaturwerten ähnlicher Systeme überein.

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M(CO)₅(dppm), M=Cr, W;dppm=-. 200° . . , . , . , .

     

Chirp-driven vibrational distribution in transition metal carbonyl complexes

In this theoretical study vibrational ladder climbing in transition metal carbonyl complexes, as a possible means to initialize chemical ground state reactions, and the resulting vibrational population distribution using chirped mid-infrared femtosecond laser pulses is investigated. Our model system is MnBr(CO)(5), a strong IR-absorber within an experimentally easily accessible wavelength region. Special emphasis is put on the perturbation due to additional vibrational modes, especially on one, which allows dissociation at low energies. The related potential energy surface for the three representative modes is calculated, whereon quantum dynamics calculations, including the laser-molecule interaction, are performed. No significant coupling could be detected, neither in the bound, nor in the dissociative region. Contrarily, we found a dynamical barrier even for energies high above the dissociation limit. Different vibrational population distributions after the laser excitation of the CO stretching mode could be generated in dependence of the chirp parameters. Based on these findings we simulated the laser excitation corresponding to an experiment by M. Joffre et al., Proc. Natl. Acad. Ssi. U. S. A., 2004, 101(36), 13216-13220, where coherent vibrational ladder climbing in carboxyhemoglobin was demonstrated and we could offer an explanation for an open question, concerning the interpretation of the spectroscopic data.     

Absorption spectra of first-row transition metal complexes of bacteriochlorins: a theoretical analysis

A theoretical study on a family of divalent transition metal bacteriochlorin complexes (M-BC, where M = Mn, Fe, Co, Ni Cu, and Zn) has been carried out to elucidate their potentialities as active molecules in photodynamic therapy (PDT). To draw a complete picture of their electronic properties, both for the ground and excited states, these complexes have been studied by the means of density functional theory (DFT). The time-dependent DFT (TDDFT) approach was used to interpret the electronic spectra, while solvent effects were taken into account by explicitly considering both two water molecules coordinated to the central metal atom and the contribution from the solvent bulk. Particular attention has been devoted to the analysis of the so-called Q bands, since these can be particularly important for medical applications. Metal substitution and environment (solvent) effects have been analyzed, and good agreement is found between computed and available UV-vis spectra. These theoretical data, especially those relative to the metallobacteriochlorins not yet completely characterized at the experimental level, could give some hints for future medical applications.     

多核过渡金属配合物自旋阻挫的理论研究

区别于双核配合物，自旋阻挫是多核配合物重要的磁现象之一．在分子磁体系中，自旋阻挫引起体系基态的多变和简并以及可能的基态自旋中间值等特征．简要地介绍多核配合物磁耦合竞争自旋阻挫的理论研究进展．     

Absorption spectroscopy and binding constants for first-row transition metal complexes of a DOPA-containing peptide

A diverse array of biological systems incorporate 3,4-dihydroxyphenlyalanine (DOPA) into proteins and small molecules for cross-linking and material generation. Marine worm eggshells, sea squirt wound plugs, and marine mussel adhesives may all be formed by combining DOPA-containing molecules with high levels of metals. In order to provide model systems for characterizing these biomaterials, we carried out a study on metal binding to a DOPA-containing peptide. Ultraviolet-visible absorption spectra are presented for the AdopaTP peptide binding to Fe3+, V3+, VO2+, Mn3+, Ti4+, Cu2+, Co2+, and Ni2+ in mono, bis, and where applicable, tris coordination modes. Association constants were determined for selected metal ions binding to the peptide. In general, the spectroscopic and binding properties of this DOPA-containing peptide were found to be similar to those of catechol.     

具有不同长度碳链的不对称四苯基卟啉及其金属配合物的合成

叶绿素、血红素、维生素B_(12)等都是不对称的金属卟啉类化合物叫,1975年Anton等首次合成了几种不对称取代四苯基卟啉及其金属配合物.其后,Leznoff,Molinaro等也发表了有关工作.我们模拟叶绿素的结构合成了三个系列13个具有不同长度碳链的单取代四苯基卟啉及其铜、锌、钴、镍等金属配合物(图1).用元素分析、红外光谱、可见吸收光谱和核磁共振谱等表征了它们的可能结构.     

几种卟啉及其配合物合成方法的改进

本文首先改进了meso位有强推电子基团的四-[4-(N,N-二甲基)苯胺基]卟啉(TDMAPPH~2)的合成方法.在此基础上, 改进了最近报道的一种新型水溶性卟啉四-[4-(N,N,N-二甲基, 丙磺酸基)苯胺基]卟啉(TDMAPPTPSH~2)的合成, 进而合成了系列水溶性金属卟啉(M'TDMAPPTPS, M'=Co,Cu,Zn,Mg,Mn,Ni).并由IR,UV-vis光谱法和元素分析得到确证.     

Thermal degradation of transition metal carbonyl complexes. Part II

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅py (where M=Cr, Mo, and W; py=pyridine) has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) and their results reported. It was found that for each of the three complexes studied, the starting material M(CO)₆ was formed which immediately sublimed unchanged with or without concomitant loss of carbonyl (CO) ligands to give the first large weight loss step. This was closely followed by the volatilisation of the pyridine ligands and at higher temperatures the loss of further CO ligands. The enthalpy changes associated with the above-mentioned steps are reported. The conversion of M(CO)₅py to M(CO)₆ and other products was confirmed by the analysis of residue after pyrolysis in a tube furnace under conditions similar to those observed in TG experiments.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonylkomplexen der allgemeinen Formel M(CO)₅py (mit M=Cr, Mo und W; py=Pyridin) wurden mittels TG und DSC untersucht. Von jeder der drei Komplexe wird die Ausgangssubstanz M(CO)₆ erhalten, die sofort unverändert mit oder ohne gleichzeitigem Verlust an Carbonyl (CO)-Liganden sublimiert und die erste große Gewichtsverluststufe ergibt. Diesem Schritt folgt gleich die Verflüchtigung des Pyridinliganden und bei höheren Temperaturen die Abgabe weiterer CO-Liganden. Die mit den genannten Schritten einhergehenden Enthalpieveränderungen werden mitgeteilt. Die Umwandlung von M(CO)₅py zu M(CO)₆ und anderen Produkten wurden durch Analyse des Rückstandes nach der Pyrolyse in einem Röhrenofen unter ähnlichen Bedingungen wie in den TG-Versuchen bestätigt.

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()₅, M=, , =. , , , . , . . , .

     

A Theoretical study of the interaction of ethylene with transition metal complexes

In order to be able to describe the ethylene molecule bonded to an active site of a Titanium- or Nickel fluoride crystal, we have used the Hartree-Fock-Slater model, implemented by a Discrete Variational Method, as introduced by Ellis and Painter. The study of the ethylene molecule at a crystal surface then gives a clear, easily interpreted picture of the electronic structure. The-back donation from metal to olefin is found to be extremely important, both in the Ti- and in the Ni-complex. This back donation is caused by a strong interaction of ad orbital of the central ion with a ^* as well as the ^* molecular orbital of ethylene. As a result of these interactions, the C-C bond of ethylene is weakened considerably.A comparison is made between the Ti-ethylene and the Ni-ethylene systems.

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Zusammenfassung Die Elektronenstruktur von Äthylen, das an ein aktives Zentrum eines Titan- bzw. Nickelfluoridkristalls gebunden ist, ist mittels der Hartree-Fock-Slater-Theorie kombiniert mit der sog. Discrete Variational Method theoretisch behandelt worden. Es zeigt sich, daß die-Backdonation sowohl im Nickel- als auch im Titankomplex außerordentlich wichtig ist; sie entsteht durch eine starke Wechselwirkung eines Metall-d-Orbitals sowohl mit einem ^* als auch einem ^*-Orbital des Äthylens. Dies führt zu einer erheblichen Schwächung der Doppelbindung.Außerdem werden die beiden Systeme (Titan und Nickel) miteinander verglichen.

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Alfred P. Sloan Research Fellow     

Density functional study of ammonia activation by late first-row transition metal cations

Density functional theory (DFT) in its B3LYP implementation is used to investigate the reaction of ammonia with the late (Co(+), Ni(+), and Cu(+)) first-row transition metal cations in both high- and low-spin states. The potential energy surfaces (PES's) leading to three different exit channels are closely examined. The binding energies for the reaction products are calculated and compared with the corresponding experimental values. A comparison with our earlier works covering the reactivity of the Sc-Fe series of cations is made in order to underline similarities and differences of the reaction mechanisms as well as to establish trends along the row.     

Basicity of transition metal carbonyl complexes: VIII. An infrared study of the reaction of aluminium chloride with some cyclopentadienyl and arenecarbonyl transition metal complexes

The interaction of cyclopentadienyl and arene derivatives of carbonyl complexes of Group V, VI and VII transition metals with AlCl₃ in benzene and CH₂Cl₂ solutions has been studied by IR spectroscopy.The formation of adducts involving the metal atom or the carbonyl oxygen atom was observed. The reaction path depends on the structure of the complex and on the nature of the solvent. In benzene the adduct formation at the CO ligand is more favourable than in CH₂Cl₂ solution. Introduction of a phosphine ligand in the place of the CO group or introduction of donor substituents into the π-ring increases the basicity of the central metal atom and makes adduct formation at the metal more probable.The basicity of the metal atom in complexes with the same ligands increases with increases of atomic number in the group. CpRe(CO)₂Br₂ forms adducts with AlCl₃ at the bromine atoms ($\text{1}\text{1}$ and $\text{sol1}\text{2}$). For Fe(CO)₄PPh₃ and Fe(CO)₃(PPh₃)₂ complex formation takes place at the iron atom.     

Synthesis, thermal and spectral studies of first-row transition metal complexes with Girard P reagent-based ligand

A new series of first-row transition metal complexes with 1-acetylpyridinium chloride-4-benzoyl thiosemicarbazide (H2GPBzIT) have been prepared and characterized by elemental analysis, spectroscopic and magnetic measurements. The proton-ligand ionization constants were determined potentiometrically using Irving-Rossotti technique. The stability constants of complexes were also calculated and were found in agreement with the sequence of stability constants of Irving and Williams. Thermal stability and degradation kinetics have been measured using thermogravimetric analyzer. Kinetic parameters were obtained for each stage of thermal degradation of complexes using Coats-Redfern method.