Four-coordinate Nickel Research Articles

Thiazolidinedithiocarbamate complexes of nickel with phosphorus donor ligands in the coordination sphere

Nickel (II) thiazolidinedithiocarbamate complexes of the composition [Ni (tzdtc) 2] n , [NiX(tzdtc) (PPh 3)] (X=Cl, Br, I, SCN), [Ni (tzdtc)) (dppe)]Y· nH 2O (Y=Br, I, ClO 4, NO 3; n=0, 1), [Ni (tzdtc) (dppb)]ClO 4·H 2O and [Ni (tzdtc) (dpph)]ClO 4·H 2O (tz=C 3H 6S; dtc=S 2CN −; PPh 3=triphenylphosphine; dppe=1,2-bis (diphenylphosphino)ethane; dppb=1,4-bis (diphenylphosphino)butane; dpph=1,6-bis (diphenylphosphino)hexane) have been synthesized. The compounds have been characterized by elemental analyses, IR and electronic spectroscopies, thermal analysis, magnetochemical and conductivity measurements. A single crystal X-ray analysis of the [NiCl (tzdtc) (PPh 3)]·0.5CHCl 3 complex proved four-coordinated nickel in a distorted square-planar arrangement with the NiS 2PCl chromophore.

Nickel Complexes of N-Alkylated Derivatives of 2,6-Bis(aminomethyl)- 4-tert-butyl-thiophenol

The syntheses of N-alkylated derivatives of the arenethiol 4-tert-butyl-2,6-(diaminomethyl)- thiophenol and their coordination properties are reported. Compounds 4-tert-butyl-2,6-di(N-isopropyl- aminomethyl)thiophenol (3) and 4-tert-butyl-2-(N-isopropyl-aminomethyl)-6-hydroxymethylthiophenol (6 ) react with Ni(II) salts to give compounds of composition [Ni(3)2]·2HCl (7) and [Ni(6)2] (8). The solid- and solution-state structures of both complexes consist of mononuclear complexes with four-coordinate nickel(II) ions in approximately planar trans- N2S2 coordination environments. In contrast to the parent arenethiol 4a, the sterically more encumbered ligands do not form dinuclear complexes.

Structural studies of three isomeric forms of heterocyclic N(4)-substituted thiosemicarbazones and two nickel(II) complexes

Three structural forms have been isolated among four 2-formyl- and 2-acetylpyridine N(4)-substituted thiosemicarbazones reported. 2-Formylpyridine N(4)-methylthiosemicarbazone and 2-acetylpyridine N(4)-ethylthiosemicarbazone both exist as nonhydrogen bonding E isomers. 2-Formylpyridine 3-azabicyclo[3.2.2]nonylthiosemicarbazone crystallies as a hydrogen bondung Z isomer. The yellow 2-acetylpyridine 3-hexamethyleneiminylthiosemicarbazone crystallized with a bifurcated hydrogen bonding arrangement in which the N(3) hydrogen is formally positioned at N(2), making it tautomeric to the other two forms. Structures of four-coordinate nickel(II) complexes containing the monoanions of 2-formylpyridine 3-azabicyclo[3.2.2]nonylthiosemicarbazone and acetylpyrazine 3-hexamethyleneiminylthiosemicarbazone are included.

Synthesis and Dipole Moments of Some Novel Metal Monothio-β-diketonate Complexes Containing a Trifluoromethyl Group

Abstract This manuscript reports the synthesis of eighteen novel compounds which include four β-diketones of the type RC(OH)=CHCOCF3, three monothio-β-diketones and eleven metal complexes containing these monothio-β-diketonate ligands. The β-diketones were used to prepare the monothio-β-diketones of the type RC(SH)=CHCOCF3 where R is 4′-CF3C6H4, 3′-CF3C6H4 and 1′-naphthyl. The metal complexes synthesized include four-coordinate nickel (II), palladium (II) and platinum(II) and six-coordinate cobalt(III) compounds. The complexes have been characterized by their elemental analyses. The CF3 and R groups' influence on the effect of the dipole moment of the dipole moment of the complexes are discussed.

Racemization kinetics and spin states of four-coordinate nickel(II) complexes with bidentate NS ligands, [pyrR 2R 3(NR 1S)] 2Ni. A comparative study

Nine complexes of the type [pyrR 2R 3(NR 1S)] 2Ni (R 1iPr) were synthesized in order to investigate possible relations between the spin-spin equilibrium and racemization of four-coordinate nickel(II) complexes with bidentate NS ligands. An X-ray structure analysis of bis(1,3-dimethyl-5-thiolato-pyrazol-4-isopropylaldimino- N,S)nickel(II) shows it to be monoclinic, space group I2/ a, with 4 molecules in a cell of dimensions a=19.091(4), b=7.564(2), c=15.760(4) Å and β=101.818(14)°. The structure refined to a final R value of 0.040 for 1144 reflections. The molecule has two-fold symmetry, the coordination at Ni is close to tetrahedral with NiS=2.249(1) Å and NiN=1.989(3) Å. Every complex was almost totally high spin, but small differences in spin states were found by comparisons of isotropic shifts and extinction coefficients for a pure high spin transition. The racemization was studied for three complexes by temperature dependent 1H NMR spectroscopy. Rate constants, resulting in approximate values of Δ H # (11.1–34.6 kJ/mol) and Δ S # (−56.7 to −144 J/(K×mol)), were determined from the iPrMe shifts and linewidths. Solvent effects of the kinetics were examined for one compound: the simultaneous promotion of the low spin form and the racemization rate at low temperature in the most polar solvent indicated that the low spin form may be the racemizing species.

Ultrafast photodissociation of a metalloporphyrin in the condensed phase

The photodissociation of axial ligands from six-coordinate nickel(II) porphyrins in solution has been studied by transient absorption spectroscopy with subpicosecond resolution. Our observations indicate that the deligation process takes place during the first several picoseconds following optical excitation of the macrocycle as the initially observed 3(π,π*) state relaxes to a dissociative ligand field excited state. No evidence is found for geminate recombination of the two ejected ligands with the four-coordinate photoproduct. A small fraction of the complexes appear to loose only one ligand. The absorption bands of the initially observed excited state and of the deligated species are also found to undergo a spectral evolution within the first 10 ps similar to that uncovered recently in the photodynamics of four-coordinate nickel(II) porphyrins in noncoordinating solvents [J. Rodriguez and D. Holten, J. Chem. Phys. 91, 3525 (1989)]. Several possibilities are considered for these time-dependent spectral shifts, including vibrational dynamics.

Ultrafast vibrational dynamics of a photoexcited metalloporphyrin

The ultrafast photodynamics of four-coordinate nickel(II) porphyrins in noncoordinating solvents has been studied using femtosecond time resolved optical spectroscopy. Unambiguous evidence has been found for the formation of a metastable metal (d,d) excited state in less than 350 fs following excitation of the macrocycle. However, the transient absorption spectrum of this ligand-field electronic excited state continues to evolve and reaches the steady-state form only after about 20 ps. This spectral behavior and the attendant complex kinetics can be modeled phenomenologically in terms of a broad distribution of the (d,d) excited states evolving to a narrower distribution. The dynamics are associated with vibrational relaxation. Intramolecular and intermolecular contributions to this process are considered.

Coordination Chemistry of F430: Axial ligation equilibrium between square-planar and bis-aquo species in aqueous solution

Abstract X-ray absorption spectroscopic characterization of axial ligand coordination to factor F430, the nickel-tetrapyrrole cofactor of the S-methyl-coenzyme M (CH3SCoM) methyl reductase enzyme from methanogenic bacteria, is presented. The nickel of isolated F430 is hexacoordinate at 10 K in aqueous solution (as is the enzyme-bound cofactor), whereas the epimerized and ring-oxidized derivatives of F430 have four-coordinate nickel. Reduction of the ring-oxidized derivative, F560, with dithionite yields F430 in its native configuration, with axial ligands indistinguishable from those present when the cofactor is obtained directly from the holoenzyme. Thus, we conclude that the axial ligands to F430 in aqueous solution are water molecules. Analysis of the nickel extended x-ray absorption fine structure is consistent with this conclusion. Resonance Raman spectra obtained at room temperature contain features characteristic of both 4- and 6-coordinate forms of the cofactor. We have found that the resonance Raman, optical, and x-ray absorption spectra of aqueous solutions of F430 are temperature-dependent due to a ligand-binding equilibrium involving the square-planar and 6-coordinate bis-aquo forms of the cofactor. At low temperatures (less than 250 K) the 6-coordinate form predominates, whereas higher temperature solutions contain both 4- and 6-coordinate species in a dynamic equilibrium. Similar behavior is observed in other weakly coordinating solvents such as methanol and ethanol. The 4-coordinate form is predominant in solvents with strong electron-withdrawing substituents such as 2,2,2-trifluoroethanol and 2-mercaptoethanol. The relevance of this facile ligand exchange to the active site structure and enzymatic mechanism of the parent enzyme is discussed.

Monothio-β-Diketonate Transition Metal Complexes Having A Trifluoromethyl Substituent

Abstract The synthesis of twenty three complexes of cobalt(III), nickel(II), palladium(II), platinum(II), copper(II) and zinc(II) having three novel monothio-β-diketones, RC(SH)[dbnd]CHCOCF3, (R [dbnd] 3′-fluorophenyl, 4′-propylphenyl and 2′,4′,5′-triethoxyphenyl) and the known ligand with R as 2′-furyl is reported. Their dipole moments were determined in benzene solution at 25°C by static-polarization measurement. The dipole moment data of the four-coordinate nickel, palladium and platinum chelates clearly indicates a cis-square planar configuration. 1H and 19F NMR spectral data confirm the facial configuration of the six-coordinate cobalt(III) complexes. The four-coordinate zinc complexes have a tetrahedral structure and the copper complexes are believed to have a distorted cis-square planar structure.

Kinetics and mechanism of ligand substitution in four-coordinate nickel(II) chelate complexes: study on the reactivities of planar and tetrahedral configurational isomers and octahedral adducts

Cinetique de substitution des complexes NiA 2 (A=alkylsalicylaldimine, dialkyl amino-2 tropone imine, alkylbenzoylacetone imine) par acetylacetone et N,N'-disalicylideneethylenediamine. Constantes d'equilibre et parametres d'activation

Metal-nitroxyl interactions. 28. EPR studies of spin-labeled nickel(II) complexes in fluid solution

Three spin-labeled four-coordinate nickel(II) complexes were prepared. In these complexes the nickel(II) was diamagnetic and the EPR spectra in fluid solution were typical nitroxyl spectra. Coordination of pyridine or 2,2′-bipyridyl to the spin-labeled nickel(II) complexes produced high-spin nickel(II) and a disappearance of the nitroxyl EPR signal. Similarly when a spin-labeled bidentate ligang coordinated to a nickel xanthate with diamagnetic ligands, no EPR signal was observed for the six-coordinate complex in fluid solution. The nickel-nitroxyl distances in these complexes were 6 to 10 Å.

Synthesis and study of some new four-coordinated nickel nitro- and nitrosyl-complexes. A new Ni(NO 2)Ni(NO) redox couple

Synthesis and study of some new four-coordinated nickel nitro- and nitrosyl-complexes. A new Ni(NO 2)Ni(NO) redox couple

Optical Resolution of rac-5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane (L), Circular Dichroism Spectra of Ni(II) Complexes with the Active Ligand, and the Absolute Configuration of (−)589-[{Ni(SS-L)}2(d-tart)(H2O)](ClO4)2·2H2O as Determined by the X-Ray Analysis

Abstract The title ligand (L) has been resolved through its d-tartrato-nickel(II) complex. The X-ray analysis shows that the less-soluble (−)589-diastereomer has a dimer structure with the folded macrocycles, [{NiL}2(d-tart)(H2O)](ClO4)2·2H2O, and that the chiral carbon atoms have the absolute configuration of S. Axial methyl groups of geminal dimethyl pairs of each nickel (II) complex in the dimer provide stereoselective environment for the coordination site of the d-tartrate ion. Stereospecific hydrogen-bonds between a secondary amine group of the macrocyclic ligand or coordinated water and hydroxyl or carboxyl oxygens of the d-tartrate ion play also an important role in the optical resolution. Pairs of enantiomers of the free ligand and three isomers of the four-coordinate nickel(II) complex have been isolated. Circular dichroism spectra of various four- and six-coordinate complexes with the optically active ligand have been described.

Nickel nitrosyl complexes with the diphenylphosphinoethane ligand

Four-coordinate nickel nitrosyl complexes of the general formula Ni(NO)X(Dppe) (Dppe=Ph2PCH2CH2PPh2) have been prepared byin situ formation of Ni(NO2)X(Dppe), (X= Cl, Br, I or SCN) followed by reduction with triphenylphosphine, or carbon monoxide, and/or DMF. Oxygenation of the nitrosyl complexes gives the corresponding nitro products and as indicated by u.v.-vis spectroscopy involves formation of an intermediate. The oxygenation rate increases markedly in the presence of light or of a catalytic amount of benzoyl peroxide and a tentative explanation is offered for these observations. Ionic adducts are formed in reactions between the nitrosyl complexes and donor molecules.

One-electron-reduced nickel(II)-macrocyclic ligand complexes. Four-coordinate nickel(I) species and nickel(II)-ligand radical species which form paramagnetic, five-coordinate nickel(I) adducts

One-electron-reduced nickel(II)-macrocyclic ligand complexes. Four-coordinate nickel(I) species and nickel(II)-ligand radical species which form paramagnetic, five-coordinate nickel(I) adducts

Organometallic complex compounds, part 6(1). Property-specific ligand control of stability and reactivity of (1,3-dimethyl-?3-allyl)methylnickel-ligand complexes. Separation of electronic and steric effects

The property-specific ligand control of 28 ligands on the decomposition temperatures in solution, measured by d.t.a. of a four-coordinate nickel(II)-complex is reported. A quantitative separation of electronic and steric effects by a multilinear regression analysis (75% electronic and 25% steric influence for the chosen ligands) is presented. The controlling effect of the selectivity on the decomposition (fraction of the C-C-linked product) (25 P-ligands) leads to an electronic: steric ratio of the property-specific ligand control of 55∶45 for the chosen ligands. An increase in the relative acceptor character of the P-ligands relatively destabilizes the complexes and thereby favours formation of a C-C-bond. An increase in steric hindrance also favours C-C-bond formation. A method for revising the steric parameter of P-ligands is presented and is used to correct the Θ-value of (PhCH2)3P is corrected to 135°. SCCC-MO-calculations for testing the chemical reasoning of the separated electronic and steric ligand property control are shown.

Cobalt(II) and nickel(II) complexes with tris(2-diethylphosphinoethyl)amine. Crystal and molecular structure of the trinuclear complex [Ni 3(Etnp 3) 2Cl 4](BPH 4) 2

The new ligand tris(2-diethylphosphinoethyl)amine, N(CH 2CH 2P(C 2H 5) 2) 3, Etnp 3, has been synthesized. It forms with cobalt(II) and nickel(II) salts different types of complexes depending on the reaction conditions. The crystal and molecular structure of the [Ni 3(Etnp 3) 2Cl 4 (BPH 4) 2 complex has been determined by standard X-ray methods, and refined to R = 0.079. The crystals are monoclinic, space group P2 1/n. The unit cell dimensions are: a = 20.067(5), b = 17.555(5), c = 12.652(4) Å, β = 95.36(9)°, Z = 4. The structure of the complex cation consists of three four-coordinated nickel atoms with square planar geometry. Two Etnp 3 ligands cement together these three metal centers. Chlorine atoms also enter in the coordination sphere of each nickel atom.

Trimeric nickel(II) complexes with bridging triphosphine ligand 1,1,1-tris(diphenylphosphinoethyl)ethane (etp 3). X-ray structure of the complex [Ni 3Cl 6(etp 3) 2]·0.7CHCl 3

The tripod-like triphosphine (PPh 2CH 2CH 2) 3CCH 3, etp 3, forms with nickel(II) halides trinuclear complexes of formula [Ni 3X 6(etp 3) 2] (X = Cl, Br, I), where the etp 3 phosphine acts as trimetallic ligand, its three phosphorus atoms being linked to the three different nickel atoms. The chloroderivative has been studied by X-ray analysis, using diffractometer data. The crystal are monoclinic, space group P2 1/ a, a = 26.27(1), b = 28.84(2), c = 11.91(1), β = 99.0(2)°, d m = 1.36 g cm −3, d c = 1.354 g cm −3 for Z = 4. The structure has been solved by three-dimensional Patterson and Fourier syntheses and refined by least-squares techniques to final R and R w factors of 0.072 and 0.073 respectively. The complex molecule is trinuclear, with three four-coordinate nickel ions, bridging two etp 3 ligands.

Reactions of Ni(NO)I with pyrazolyl gallate ligands: crystal and molecular structure of [Me2Ga(N2C5H7)(OCH2CH 2NMe2)]Ni(NO)

Ni(NO)I reacts readily with pyrazolyl gallate ligands Na+L− (where L = MeGa(N2C3H3)3, MeGa(N2C5H7)3, and [Me2Ga(N2C5H7)(OCH2CH2NMe2)]) to yield four-coordinate nickel nitrosyl complexes, LNi(NO). In addition, the compound [Me2Ga(N2-C5H7)(OCH2CH2 NMe2)]Ni(N2C5H7)2Ni(NO) has been isolated from one reaction sequence. 1H nmr data show [Me2Ga(N2C5H7)(OCH2CH2NMe2)]Ni(NO) to be stereochemically non-rigid at room temperature in solution. Crystals of [dimethyl(N,N-dimethylethanol-amino)(3,5-dimethylpyrazolyl)gallato(N(2),N(3),O)] nitrosylnickel(I) are monoclinic, a = 9.119(1), b = 13.900(2), c = 14.284(2) Å, β = 107.96(1)°, Z = 4, space group P21/c. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix leastsquares procedures to R = 0.025 and Rw = 0.032 for 1828 reflections with I ≥ 3σ(I). The coordination about the nickel atom is severely distorted tetrahedral with angles at nickel ranging from 84.4(1) to 133.5(1)°. The nitrosyl group is coordinated in a non-linear fashion with Ni—N—O = 162.3(4)°, Ni—N = 1.632(4) and N—O = 1.147(4) Å. Other important bond lengths (corrected for libration) are: Ni—O, 2.045(2), Ni—N(pyrazolyl), 1.989(3), Ni—N(amino), 2.071(3), Ga—O, 1.922(2), Ga—N, 1.998(3), and Ga—C, two at 1.971(6) Å.

ChemInform Abstract: TRIDENTATE AND UNSYMMETRICAL TETRADENTATE SCHIFF BASE LIGANDS FROM SALICYLALDEHYDES AND DIAMINES‐ THEIR MONOMERIC AND DIMERIC NICKEL(II) COMPLEXES

AbstractDurch Kondensation von Salicylaldehyd mit geradkettigen oder verzweigten Diaminen wurden potentiell dreizähnige Liganden (I) erhalten, die mit Ni‐acetat zu 2: l‐Komplexen reagieren.