Transition Metal Complexes with Pyrazole-based Ligands. Part 8. Characterization and thermal decomposition of zinc(II) complexes with di- and trisubstituted pyrazoles

We report the synthesis and the characterization (elemental analysis, FT-IR spectroscopy, thermal methods and molar conductivity measurements) of the mixed complexes of zinc with acetate and 3-amino-5-methylpyrazole, HL ¹, [Zn(OAc)₂(HL¹)₂], or 3-amino-5-phenylpyrazole, HL ² [Zn(OAc)₂(HL²)₂], or 4-acetyl-3-amino-5-methylpyrazole, HL ³, [Zn(OAc)(L³)(HL³)]₂, with isothiocyanate and HL ² [Zn(SCN)₂(HL²)₂], or HL ³ [Zn(SCN)₂(HL³)₂], and with nitrate, isothiocyanate and 3,5-dimethyl-1-carboxamidinepyrazole, HL ⁴ [Zn(NO₃)(NCS)(HL⁴)₂]. The thermal decomposition of the complexes is generally continuous resulting zinc oxide as end product,except [Zn(OAc)(L³)(HL³)]₂ in which case a well-defined intermediate was observed between 570–620 K. On the basis of the IR spectra and elemental analysis data of the intermediate a decomposition scheme is proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Transition Metal Complexes with Pyrazole Based Ligands

The complex formation of cobalt(II)-, nickel(II) and copper(II) sulphate hydrates with 3,5-dimethyl-1-thiocarboxamidepyrazole (HL) was studied. The influence of the anions on the course of the reaction was also examined, using nickel(II) salts with various anions. Beside the NiSO₄·7H₂O the reaction has been carried out with Ni(OAc)₂, Ni(CF₃COO)₂ and Ni(SCN)₂. Compounds with the following composition were obtained: Co(L)₃, Ni(L)₂ and [Cu(SCN)L]₂. The structure of the ligand and the Co(L)₃ complex was determined by single crystal X-ray analysis, while that of the Ni(L)₂ was solved by analysis of powder diffraction X-ray data. The most probable structure of the copper(II) complex is proposed on the basis of the elemental analyses data, FT-IR spectrometry and magnetic measurement. The thermal decomposition of the complexes was investigated by thermogravimetry, DSC and coupled TG-MS measurements. In the case of the nickel(II) compound, a relatively stable intermediate was detected in the 550-650 K temperature range. The composition of the intermediate, Ni(SCN)(NCS), was determined by FT-IR-spectrometry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metal Complexes with Macrocyclic Ligands. Part XLI. Nickel(II) and copper(II) complexes with mono-N-functionalized dithiadiazamacrocycles

Three N₂S₂ macrocycles ( 3, 10, 12 ) carrying an amino group as a pendant arm have been synthesized and their complexation properties towards Ni²⁺ and Cu²⁺ studied. The crystal structures of the Cu²⁺ complexes with 10-methyl-1,4-dithia-7,10-diazacyclododecane-7-ethanamine ( 3 ) and 11-methyl-1,4-dithia-8,11-diazacyclotetradecane-8-ethanamine ( 10 ) show that, in both cases, the Cu²⁺ is pentacoordinated by the four donor atoms of the macrocycle and the amino group of the side chain. In aqueous solution, however, two forms of the complexes with stoichiometries [MLH] and [ML] (M = Cu²⁺ or Ni²⁺) have been observed. In [MLH], the amino group is protonated and does not bind to the metal ion, whereas in [ML] the amino group is bound, and a pentacoordinated geometry results. The pK_a values for the equilibrium [ML] + H⁺?[MLH]⁺ decrease in the order 12 > 10 > 3 , indicating that the 2-aminoethyl side chain binds better to the Cu²⁺ than the 3-aminopropyl side chain. Cyclic voltammetry for the Cu²⁺/Cu⁺ pair shows that the 2-aminoethyl pendant arm stabilizes the Cu²⁺ oxidation state, when the metal ion is in the 14-membered ring ( 10 ), whereas it stabilizes Cu⁺ for the 12-membered macrocycle ( 3 ).     

Ethers as ligands. Part VI. Transition metal(II) complexes with 18-crown-6

Summary Seven new coordination compounds are reported with the cyclicpolyether 18-crown-6 as the ligand,viz. [Mg(18-crown-6) (H₂O)₂](SbCl₆)₂, [M(18-crown-6)(MeNO₆)₂](SbCl₆)₂ with M is Ca²⁺ and Sr²⁺, [M(18-crown-6)(MeNO₂)](SbCl₆)₂ with M is Mn²⁺ and Co²⁺, and [M(18-crown-6)](SbCl₆)₂ with M is Ni²⁺ and Zn²⁺.     

Transition Metal Complexes with Pyrazole-based Ligands. Part 12. Characterisation and thermal decomposition of CuCl2 complexes with di- and trisubstituted pyrazoles

The synthesis of copper(II) chloride complexes with 3,5-dimethylpyrazole, 1-carboxamidine-3,5-dimethylpyrazole, 5-amino-4-carboxamide-1-phenylpyrazole and 4-acetyl-3-amino-5-methylpyrazole is described. The compounds are characterized by elemental analysis, FT-IR spectroscopy, thermal methods, magnetic moment and molar conductivity measurements. Thermal decomposition of the dichloro-(3,5-dimethylpyrazole)-copper(II) complex results in an unstable intermediate with a stochiometric composition. The decomposition of the other compounds is continuous. This revised version was published online in August 2006 with corrections to the Cover Date.     

Transition metal complexes with hydrazides and hydrazones

A study was made of the thermal decomposition of octahedral Co(II) complexes of the type CoL_n X ₂·mH₂O, wheren=2 and 3,m=1,2 and 5 andX=Cl, Br, I, NCS, OAc andv ₂So₄, in both air and nitrogen atmospheres. It was established that the complexes are completely decomposed below 800° and CoO is formed as final product. The most probable decomposition mechanism was proposed. The tris(ligand) complexes were characterized by elemental analysis, and spectral and magnetic measurements, and all the data suggested the presence of a point group symmetry of type O_h.

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Zusammenfassung Sowohl in Luft als auch in Stickstoffatmosphäre wurde die thermische Zersetzung von oktaedrischen Co(II)-Komplexen der allgemeinen Formel CoL_nX₂· mH₂O (n=2 und 3,m=1, 2 und 5,X=Cl, Br, I, NCS, OAc und SO₄) untersucht. Es wurde festgestellt, daß sich die Komplexe unterhalb 800°C vollkommen zu CoO als Endprodukt zersetzen. Der wahrscheinlichste Zersetzungsmechanismus wurde unterbreitet. Die tris-Ligandenkomplexe wurden mittels Elementaranalyse sowie Spektral- und magnetischen Untersuchungen charakterisiert, alle Angaben deuten auf eine Punktsymmetriegruppe vom Typ Oh hin.

     

Transition metal complexes with thiosemicarbazide-based ligands

Solvate complexes of UO ₂ ²⁺ andN(1), N(4)-bis(salicylidene)-S-methylisothiosemicarbazone, (H₂Me-L¹), of general formula [UO₂(Me-L¹)S] (S= H₂O, MeOH, EtOH, Py, DMF and DMSO) were synthesized. The methanolic UO ₂ ²⁺ ” adducts of N(1)-benzoylisopropylidene-N(4)-salicylidene-S-alkylisothiosemicarbazone, (H₂R-L²,R=Me, Prⁿ) of general formula [UO₂(R-L²)· MeOH], were also prepared. Thermal decomposition of the complexes was investigated in air and argon. The complexes decompose to α-U₃O₈ in air, while in argon the decomposition is not completed up to 1000 K. The temperature and the mechanism of decomposition of the complexes are a function of the solvent belonging to the inner coordination sphere.     

Transition metal complexes with thiosemicarbazide-based ligands

The thermal decomposition and spectroscopic (reflectance and IR spectra) characterization of the newly synthesized square-pyramidal dioxovanadium(V) complexes of the type NH₄[VO₂(L)] (L is the dianion of the terdentate ligands salicylaldehyde thiosemicarbazone (ONS), halogen-substituted salicylaldehyde and 2-hydroxy-1-naphthaldehyde S-methylisothiosemicarbazones (ONN)) are described.

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Zusammenfassung Es wird die thermische Zersetzung und spektroskopische Charakterisierung (Reflexionsvermögen und IR-Spektren) neu synthetisierter Dioxovanadium(V)-Komplexe der allgemeinen Formel NH₄[VO₂(L)] beschrieben, wobei L das Dianion des dreizahnigen Liganden Salicylaldehyd-thiosemicarbazon (ONS), halogensubstituiertes Salicylaldehyd- bzw. 2-Hydroxy-1-naphthaldehyd-S-methyl-isothiosemicarbazon (ONN) ist.

     

Transition Metal Complexes Containing Functionalized Organoimido and Phosphaneiminato Ligands

Two different types of modified imido and phosphaneiminato ligands are investigated, namely chelate ligands and redox‐functionalised ligands. The first examples of di(organoimido)chromium as well as di(phosphaneiminato)titanium and niobium chelates are described. Furthermore, the first complexes containing redox‐functionalised organoimido ligands are presented, together with the first structurally characterised redox‐functionalised phosphaneiminato complex. Compounds of the type [(RN)₂M(CH₂Ph)₂] (M = Cr, Mo) are used as catalysts for the (co‐)polymerisation of the polar olefins methyl methacrylate, acrylonitrile and vinyl acetate. A range of X‐ray crystal structure determinations provide clear evidence for the quantum‐chemical result that, similar to organoimido complexes, the potential energy well for the angle at the nitrogen atom is very shallow for phosphaneiminato complexes.     

Metal Complexes with Macrocyclic Ligands,VI. The role of substituents on the complexation rate of transition metal ions with several 1,4,7,10-tetraazacyclotridecanes

12,12-Dimethyl-1,4,7,10-tetraazacyclotridecane (I), 11,13-dimethyl-1,4,7,10-tetraazacyclotridecane (II), 11,11,13-trimethyl-1,4,7,10-tetraazacyclotridecane (III) and 1,4,7,10,12,12-hexamethyl-1,4,7,10-tetraazacyclotridecane (IV) have been synthesized and their properties are described. While the Ni²⁺ and Cu²⁺ complexes of I–III have square planar geometries, those of IV are pentacoordinate according to their absorption spectra. Similarly, while the Co²⁺ complex of I is octahedral and readily oxygenated, the analogous complex with IV is pentacoordinate and not sensitive to oxygen. The rate of complexation of these ligands with Cu²⁺ and Ni²⁺ decreases in the order I > II > III ? IV, indicating that the number as well as the position of the methyl groups are important. Finally for Cu²⁺ the formation of the thermodynamic stable end product is slown down by methyl substitution in α-position to the coordinating nitrogen atoms (ligand II and III) so that an intermediate can be observed, whereas with I Cu²⁺ directly forms the end product.     

Nickel Complexes with Non-innocent Ligands as Highly Active Electrocatalysts for Hydrogen Evolution

Rational design of a molecular catalyst for a hydrogen evolution reaction (HER)with both high rates and low overpotential remains a chal- lenge.Here we report a series of Ni-based catalysts incorporating non-innocent ligands and aimed at reduction of the overpotential by reserving electrons in the ligand,which could decouple the correlation between metal center reduction and metal hydride formation.The third-order rate constant of our catalysts can be increased by 2 orders of magnitude without increase of overpotential by altering the substituents in the imide since the electronic effect of substituents can change the kinetics of metal hydride formation dramatically.Furthermore,constructing a proton shuttle in the ligand further improves the activity.The catalyst with both of these features can catalyze HER at a turnover frequency of 2572s^-1 with low concentrations of acid and an extremely high third-order rate constant of 2.7×10^6M^-2·s^-1 at a low overpotential.     

Formation of Oligo-Nuclear Carboxylate Nickel(II) Complexes with Nitrogen-Containing Ligands. Quantum-Chemical Simulation

Using the DFT method PBE0/6-31G(d, p) and taking into account the solvent, the formation of bi- and pentahedral Ni(II) complexes with carboxylate and N-containing ligands in the gas phase was studied, and ΔG° of their formation from simple compounds was estimated. The functional role of bridging groups and hydrogen bonds in the formation of polynuclear structures was revealed. A model of self-organization of penta-nuclear coordination compounds [Ni^II₅(O₂CR)₈L_2n(μ-OH)₂]⁰ from binuclear complex [Ni^II₂(O₂CR)₄L_n(μ-H₂O)]⁰ was proposed, into the structure of which mononuclear Ni^II cations are embedding and promote proton transfer from bridging aqua ligands.

     

Hydrothermal Synthesis of Three New Transition Metal Complexes with Azido Ligands

Hydrothermal reactions of NaN₃, 1, 10‐phenanthroline or 2, 2′‐bipyridine and transition metal cations including Zn^II or Co^II in basified aqueous solutions yielded the three complexes, [Zn₂(bipy)₂(N₃)₄]_n ( 1 ), [Zn(phen)(N₃)₂]_n ( 2 ), and [Co(phen)₂(N₃)₂] ( 3 ), which were characterized by X‐ray crystallography. All three complexes crystallize in the triclinic system, space group P1¯, with a = 6.5506(2), b = 10.8441(6), c = 16.893(2)Å, α = 96.333(5), β = 95.361(7), γ = 90.548(6)° for 1 ; a = 7.0302(10), b = 10.0590(14), c = 10.4550(15)Å, α = 109.372(2), β = 103.980(2), γ = 106.137(2)° for 2 ; and a = 8.1722(2), b = 11.0332(3), c = 12.5066(2)Å, α = 82.681(8), β = 82.457(9), γ = 72.991(7)° for 3 , respectively. The photoluminescence spectra for compounds 1 and 2 have also been studied.     

Transition metal complexes with Girard reagent-based ligands

The ligand, salicylaldehyde Girard-T hydrazonium chloride, [H₂SalGT]Cl (1), and two complexes [Cu(HSalGT)X₂]·H₂O (X = Br(2); Cl(3)) were synthesized and their crystal structures were determined by single-crystal X-ray analysis. In the two isostructural complexes, the Cu(II) is located in a square-pyramidal environment, with the chelating ligand and one halogen atom in the basal plane and the second halogen in the apical position. The most apparent structural difference between the 1 and its complexes 2 and 3 is the orientation of the N(CH₃)₃ group: in 1, it is practically coplanar to the rest of the molecule, while in 2 and 3 it is oriented to the side of the axially bonded halogen, which can be explained by the C–H…X intramolecular interactions. The compounds were characterized by elemental analysis, molar conductivity, magnetic susceptibility and electronic absorption spectra.     

Metal Complexes with Macrocyclic Ligands. Part XLVI. Synthesis and structures of dinuclear metal complexes of bis-macrocycles having a pyrazole bridging unit

Three bis-macrocyclic ligands consisting of two N₃-, N₂S-, or NS₂-cyclononane rings, i.e., of two octahydro-1H-1,4,7-triazonine, octahydro-1,4,7-thiadiazonine, or hexahydro-5H-1,4-7-dithiazonine rings, connected by a 1H-pyrazolediyl unit were prepared. They form dinuclear Cu^II and Ni^II complexes which are able to bind one additional exogenous bridging molecule such as Cl^?, Br^?, N, SO, and 1H-pyrazol-1-ide. The structures determined by X-ray diffraction show that each Cu²⁺ is coordinated by the three donor atoms of the macrocyclic ring, by a pyrazolidodiyl N-atom, by an atom of the exogenous bridging ligand, and sometimes by a solvent molecule. In the majority of the Cu²⁺ cases, the metal ion exhibits square-pyramidal or trigonal-bipyramidal coordination geometry, except in the sulfato-bridged complex, in which one Cu²⁺ is hexacoordinated with the participation of a water molecule. The X-ray structure of the azide-bridged dinuclear Ni²⁺ complex was also solved and shows that both Ni²⁺ centres have octahedral coordination geometries. In all complexes, the 1H-pyrazolediyl group connecting the macrocycles is deprotonated and bridges the two metal centres, which, depending on the exogenous ligand, have distances between 3.6 and 4.5 Å. In the dinuclear Cu²⁺ complexes, antiferromagnetic coupling is present. The azido-bridged complex shows a very strong interaction with ?2J ≥ 1040 cm^?1; in contrast, the H-pyrazol-1-ide and chloride bridged species have ?2J values of 300 and 272cm^?1, respectively. Cyclic voltammetry of the Cu²⁺ complexes in MeCN reveals a strong dependence of the potentials Cu^II/Cu-^II → Cu^II/Cu^I → Cu^I/Cu^I on the nature of the donor atoms of the macrocycle as well as on the type of bridging molecule. The more S-donors are present in the macrocycle, the higher is the potential, indicating a stabilization of the Cu¹ oxidation state.     

Transition metal complexes with neutral and deprotonated malonamide

Summary New complexes of the general formulae [M(LH₂)₂Cl₂] (M = Mn, Fe, Co, Ni, Cu, Zn), [Mn(LH₂)₂X₂] (X = Br, I), [Cu(LH₂)₂Br₂], [Ni(LH₂)₂X₂] (X = Br, NCS, ONO₂), [Cu(LH₂)X₂]_n (X = Cl, Br), K₂[NiL₂]·2H₂O and K₂-[CuL₂]·H₂O, where LH₂ = malonamide, were isolated. The complexes were characterized by elemental analyses, X-ray powder patterns, magnetic susceptibilities and spectroscopic (variable-temperature ⁵⁷Fe-Mössbauer, e.s.r., u.v.-vis., i.r., far-i.r., Raman) studies. Monomeric trans pseudo-octahedral stereochemistries for the neutral 12 complexes and square planar structures of D _2h symmetry for the two ionic complexes are assigned in the solid state. Dimeric or polymeric five-coordinate structures are proposed for the 11 copper(II) compounds. LH₂ and L^2– behave as bidentate chelating ligands binding through oxygen and deprotonated nitrogen atoms, respectively. A detailed comparison of the studied complexes with the corresponding oxamide complexes is also presented.