The spectrochemical properties of noncubic transition metal complexes in solutions. Part I. Mixed tetragonal distorted nickel(II) pyridine complexes in chloroform

Summary The electronic spectra of tetragonal nickel(II) complexestrans-[Ni(Py)₄L₂], (Py=pyridine and L=NCS, Cl, Br, or I) have been measured in a 10% pyridine solution in chloroform at room temperature. The experimental curves were resolved by Gaussian analysis. The various ligand field parameters are discussed in terms of their chemical utility and their relation to ligand-field strengths. The ligand field parameters were examined by the dumped nonlinear least-squares algorithm (Gauss-Newton method) and Powell solution-seeking (nongradient) algorithm. The standard deviations of the parameters have been obtained from the former. Finally, it was found that the structure of the complexes in chloroform solution are much the same as in the solid state.     

Mixed metal complexes in solution. Thermodynamic and spectrophotometric study of copper(II)-citrate heterobinuclear complexes with nickel(II), zinc(II) or cadmium(II) in aqueous solution

Summary A thermodynamic study of Cu^II–M^II-citrate (M^II=Ni^II, Zn^II or Cd^II) ternary systems has been performed by means of potentiometric measurements of hydrogen ion concentration at different temperatures (10, 25, 35 and 45°C) and at I=0.1 mol dm^–3 (KNO₃).The different binary and ternary systems involved have been further characterized by visible spectra and by calculating the spectra ( versus ) of all the Cu^II complexes.The thermodynamic data suggest strong entropic stabilization for the species under discussion. As regards the visible spectral characteristics of Cu^II(d-d transitions), the substitution of one Cu^II ion in the dimer [Cu₂(cit)₂H_–2]^4– by Ni^II or Zn^II to form heterobinuclear [CuM(cit)₂H_–2]^4– complexes, gives rise to a change in the visible spectrum.     

The far-infrared spectra of pyridine complexes of transition metal(II) isothiocyanates

The infrared spectra (500–140 cm^?1) of the complexes [M(pyridine)_n(NCS)₂] (n = 2, M = Mn, Co, Ni, Cu, or Zn; n = 4, M = Mn, Fe, Co, or Ni) are discussed. The v/M-pyridine and v/M-NCS bands are assigned by observing the band shifts induced by isotopic labelling of the coordinated pyridine and isothiocyanate, by comparing the spectra with those of the [M(pyridine)₂Cl₂] complexes and from symmetry considerations based on their known structures. The two types of metal-ligand stretching bands occur within a rather narrow frequency range and there is evidence of some vibrational coupling between these two modes. Some earlier assignments of vM-pyridine bands require revision. The spectra of the yellow [Fe(py)₄(NCS)₂] complex and its violet oxidation product suggest that the oxidation reaction involves the transformation of trans-[Fe(py)₄(NCS)₂] into cis-[Fe(py)₃(NCS)₃]     

Mixed metal complexes in solution. Part 4. Formation and stability of heterobinuclear complexes of cadmium(II)-citrate with some bivalent metal ions in aqueous solution

Summary The systems, Cd-Ni-citrate, Cd-Mn-citrate and Cd-Zn citrate have been investigated pH-metrically at 25°C and I = 0.1 mol dm^–3 (KNO₃).As previously found for analogous citrate systems (namely for Cu-Ni-, Cu-Zn- and Ni-Zn-citrate) the existence of mixed metal complexes of the type [MM(cit)₂H_–2]^4– has been shown. In addition, the species [MM(cit)₂H_–1]^3– was also found to be present for Cd-Ni- and Cd-Zn-citrate systems The significance of the formation of such species is discussed.The existence of mixed metal complexes is also discussed in connection with the transport and the absorption of metal ions in biological systems.     

Synthesis and properties of cyano-bridged nickel(II)-iron(III) complexes

Summary Four kinds of novel CN-bridged Ni^II-Fe^III complexes, [NiLn(NC)Fe(CN)₅] ^–, have been synthesized and characterized by elemental analysis, i.r. and u.v.-vis. spectral analysis, and magnetic moments. The formation of cyanide bridges is evident from the i.r. and u.v.-vis. spectra by the appearance of v(CN) shifts and changes in _max with respect to the mononuclear parent complex [Fe(CN)₆]^3–. The magnetic properties indicate the existence of magnetic spin interactions between Ni^II and Fe^III through the cyanide bridge.     

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=, , =. , , , . , . . , .

     

QTAIM study of transition metal complexes with cyclophosphazene-based multisite ligands I: Zinc(II) and nickel(II) complexes

The metal–ligand bonds in [(ZnCl₂)₂L], [NiLCl]⁺ and two isomers of [NiLCl₂] complexes with multimodal ligand L = hexakis(2-pyridyloxy)cyclotriphosphazene, cyclo-[NP(NC₅H₄O)₂]₃, are investigated at DFT level of theory using hybrid B3LYP functional. Electron density is evaluated in terms of QTAIM (quantum theory of atoms-in-molecule) topological analysis of electron density. The bonds of central transition metal atoms with phosphazene nitrogens are shorter, stronger and more polar than with the aromatic pyridine nitrogens. The atomic charges of phosphazene nitrogens are ca twice more negative than at the pyridine ones. The higher mechanical strain in the five-coordinate metal complexes than in the six-coordinate ones may be concluded.     

Mixed dimethyl sulfoxide-thiocarbamic ester complexes of platinum(II) halides

Summary The platinum(II) halidecis-[Pt(DMTC)(DMSO)X₂] andcis-[Pt(DETC)(DMSO)X₂](X=Cl or Br; DMSO=dimethyl sulfoxide; DMTC=EtOSCN-Me₂; DETC=EtOSCNEt₂) adducts and the platinum(II) and palladium(II) halide adducts,trans-[M(DETC)₂X₂] (M=Pt or Pd; X=Cl or Br), have been prepared. The complexes were characterized by i.r., and¹H and¹³Cn.m.r. spectroscopy. Both DMTC and DETC coordinate through the sulphur atoms. The 1:2 DETC complexes present the usualtrans configuration, whereas the presence of DMSO favourscis geometry in the mixed species.     

Photosensitization study of cage-like metal complexes with hexadentate ligands, tptn and tpen. Part 1. Photochemistry and spectroelectrochemistry of iron(II), cobalt(III) and nickel(II) complexes

Two hexadentate ligands, N,N,N′,N′-tetrakis(2-pyridylmethyl)-1,3-propanediamine (tptn) and N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (tpen), were used to prepare cage-like metal complexes of Fe(II), Co(III) and Ni(II). As expected, these complexes are photochemically inert. The electrochemical behaviour of these complexes was studied by spectroelectrochemical methods. The iron(II) complexes exhibit chemical irreversibility on reduction and the nickel(II) complexes show reversible reduction behaviour. The potential of cobalt(III) complexes as photosensitizers is discussed.     

Decarboxylation syntheses of transition metal organometallics. III polyfluorophenylplatinum(II) complexes with nitrogen donor ligands

Summary The platinum(II) carboxylates,trans-Pt(O₂CR)₂(py)₂ and Pt(O₂CR)₂bpy (R=C₆F₅,p-HC₆F₄,m-HC₆F₄, oro-HC₆F₄; bpy=2,2-bipyridyl), have been prepared by reactions oftrans-Pt(OH)₂(py)₂ or Pt(OH)₂bpy with the appropriate polyfluorobenzoic acids, whilst [Pt(py)₄](O₂CC₆F₅)₂ has been obtained from reaction oftrans-PtCl₂(py)₂ with thallous pentafluorobenzoate in pyridine at room temperature. In boiling pyridine, the platinum(II) polyfluorobenzoates undergo either decarboxylation givingtrans-PtR₂(py)₂ and PtR₂bpy (R= C₆F₅,p-HC₆F₄, orm-HC₆F₄) complexes or substitution, giving [Pt(py)₄](O₂CC₆F₄H-o)₂ and [Ptbpy(py)₂](O₂CC₆F₄H-o)₂. Reactions oftrans-PtX₂(py)₂ and PtX₂bpy (X=Cl or Br) with appropriate thallous polyfluorobenzoates in boiling pyridine have yielded the complexestrans-PtR₂(py)₂, PtR₂bpy, PtCl(R)bpy (R=C₆F₅,p-HC₆F₄, orm-HC₆F₄ in each case),trans-PtCl(R)(py)₂ (R = C₆F₅ orm-HC₆F₄),trans-PtBr(C₆F₅)(py)₂, and PtBr(C₆F₅)bpy. The complexestrans-PtR₂(py)₂ (R=C₆F₅ orp-HC₆F₄) have also been prepared from potassium tetrachloroplatinate(II) and the appropriate thallous polyfluorobenzoate in boiling py, andtrans-Pt(C₆F₅)₂(py)₂ has been similarly obtained fromcis-PtCl₂(py)₂ and C₆F₅CO₂Tl. Significant decarboxylation was not observed on reaction oftrans-PtCl₂(py)₂ or PtCl₂bpy with thallous 2,3,4,5-tetrafluorobenzoate.Part II, ref. 4;Preliminary communication, ref. 3;     

Admittance measurements of adsorption properties of 2,2′-bipyridine complexes: Part II. Iron(II), cobalt(II) and nickel(II) complexes inacetonitrile

Whereas trisbipyridine complexes of iron(II), cobalt(II) and nickel(II) yield successiveone-electron and reversible waves in d.c. polarographic measurements in acetonitrile, the admittance measurements indicate clearly that the charge transfer reaction is coupled with adsorption. Various tests for the detection of adsorption were used and the extent of adsorption of reactant or products in relation with charge transfer kinetics is discussed.     

Admittance measurements of adsorption properties of 2,2′-bipyridine complexes: Part I. Cobalt(II) and nickel(II) complexes in aqueous solutions

The complex [Co bipy₃]²⁺ in aqueous perchlorate solution yields on the d.c. polarogramthree adsorption type pre-waves and a main reduction wave at ?1.2 V (SCE) corresponding to the reduction to monovalent complex. From admittance measurements and other results it can be concluded that two most positive pre-waves at ?0.2 V and ?0.5 V (SCE) are of non-faradaic nature being related to the adsorption of the complex with specifically adsorbed anions of the supporting electrolyte with the formation of a compact adsorbed layer of much lower interfacial capacity. The most negative pre-wave at ?0.9 V just preceding the main wave corresponds to the reduction of the adsorbed complex. The main wave at ?1.2 V is distorted by the adsorption of reaction products. Very similar and also strong adsorption-coupled interaction was found with divalent nickel trisbipyridine complex.     

QTAIM study of transition metal complexes with cyclophosphazene-based multisite ligands II. Cobalt(II) complexes

[(CoLCl)CoCl₃], [(CoMeLCl)CoCl₃], [(CoLBr)CoBr₃], [CoLBr]⁺ and [CoMeLBr₂] complexes, L = hexakis(2-pyridyloxy)cyclotriphosphazene, MeL = hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene, in the most stable high spin states are investigated at DFT level of theory using hybrid B3LYP functional. The exchange coupling parameter evaluated using a broken symmetry treatment increases with the ligands mass. Electron density is evaluated in terms of QTAIM (Quantum Theory of Atoms-in-Molecule) topological analysis of electron density. The bonds of central Co atoms with phosphazene nitrogens are shorter, stronger and more polar than with the aromatic pyridine nitrogens and their higher ellipticities may be explained by the π contribution from the phosphazene ring. The atomic charges of phosphazene nitrogens are ca. twice more negative than at the pyridine ones.     

Mixed metal hydroxycarboxylic acid complexes. Spectrophotometric study of complexes of U(VI) with In(III), Cu(II), Zn(II) and Cd(II)

The formation of mixed metal complexes between uranium (VI), as the central metal ion, and aluminium (III), indium (III), copper (II), zinc (II) and cadmium (II), as the additional metal ions, with a hydroxycarboxylic acid chosen between citric, tartaric or malic, has been studied using spectrophotometric methods.The effect of pH has been examined, and the results show that at pH=4 stable complexes are formed for most of the systems. At this pH the method of mole ratio and Job's method of continuous variations, were employed to determine the stoichiometry of the mixed metal complexes. Al(III), In(III) and Cu(II) showed a high tendency to form mixed metal complexes with U(VI), while the formation of complexes is uncertain for Cd(II) and Zn(II). The ratio of the ligand to the total metal ion has been found to be 21 and metal:metal ratios of 11 and 12 have been observed.Represents part of the Ph.D. thesis submitted by Emanuel Manzurola to Ben Gurion University of the Negev.     

Heterogeneous reactions of solid nickel(II) complexes,III

The thermal decompositions of solid complexes of the type Ni(NCS)₂L₂ (L = pyridine,α-picoline,β-picoline, 2,6-lutidine, and quinoline) were studied by means of the derivatograph. It was found that the decompositions of complexes with pyridine,α-picoline, 2,6-lutidine, and quinoline (the pseudo-octahedral complex) are onestep processes, and those of complexes withβ-picoline and quinoline (the squareplanar complex) consist of two steps. Diffuse reflectance spectra were recorded to elucidate the structures of the decomposition intermediates. The reasons for the different stoichiometries of decomposition for complexes of the same type are discussed.     

Spectroscopic properties of (nd)10 transition metal complexes

Photoluminescence has been observed from a series of Zn(II) and Cd(II) complexes containing both N-heterocyclic and aromatic thiol ligands. The emission consists of overlapping bands, a structured phosphorescence that arises from the lowest ³ππ^* state of the heterocycle and a broad band luminescence that maximizes at still lower energies and decays on the order of 10–50 μs. This new band is assigned to an interligand charge-transfer excited configuration in which electronic charge has been transferred from the coordinated thiol ligand(s) to the N-heterocycle via the metal ion. A superexchange mechanism is proposed to account for the disposition of singlet and triplet states.     

Spin transition in iron(III) and iron(II) complexes

The main stages of the studies on the spin transitions in iron(III) and iron(II) complexes are considered. The types of the spin transitions and the factors responsible for the latter are reported. The problems arising during experiments in this field are discussed.