Coordinating Properties of Co(II) and Zn(II) Complexes with Sterically Hindered Porphyrins

Cobalt(II) and zinc(II) complexes with 5,15-di(o-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-buthylporphyrin and its capped analogues, where the MN₄ reaction site is shielded by bridging groups containing m-phenylene and dimethoxy-substitutedp-phenylene fragments, were synthesized. Equilibrium constants of additional coordination of pyridine and N-methylimidazole by these metalloporphyrins were determined at 298 K. It was found that steric distortion of the porphyrin core destabilizes extra complexes.     

Chemistry of Sterically Protected Bis(Phosphinidene)-Cyclobutenes

Abstract:

Sterically protected low-coordinated phosphorus-containing cyclobutenes were prepared and characterized as well as [4]radialenes. The reactions were studied involving E/Z isomerization, transition-metal complex formation, and coupling reactions catalyzed by some palladium complex ligated with diphosphacyclobutenes.     

Nickel(II) and Zinc(II) Complexes with Benzoylacetaldehyde Derivatives

Russian Journal of Coordination Chemistry - Ni(II) and Zn(II) complexes, [M(Ln)A] (n = 1–3, A = NH3, Py), were prepared from the products of condensation of benzoylacetaldehyde with aromatic...     

Copper(II) Complexes with β-Aminovinylimines Containing Sterically Hindered Donor Centers

Russian Journal of Coordination Chemistry -     

Palladium(II) Complexes of N-(2-Thienylmethylidene)aniline Derivatives

Coordination reactions of N-(2-thienylmethylidene)aniline derivatives, L, with PdCl₂ or [PdCl₄]^2? in ethanol yield stable complexes of the type trans-(L)₂PdCl₂ with the azomethine nitrogen atoms as σ donors. These are not readily convertible to othor-palladated complexes. An X-ray crystallographic study of the complex (L₂)₂PdCl₂ reveals a centrosymmetric geometry. The structure is in the triclinic space group $ {\rm P}\bar 1 $ with a = 8.633(2) Å, b = 12.759(3) Å, c = 8.398(2) Å, α = 96.65(5)°, β = 111.47(5)*, γ= 101.28(6)°, and Z = 1. The final R factor is 0.043 (Rw = 0.044) for 2396 observed reflections. There is no real bonding between a thiophene sulfur atom and a central palladium ion. However, a long distance interaction between S and Pd does exist.     

Phosphoryl Complexes of Some Metal(II) Trifluoromethanesulfonates

Cobalt(II), nickel(II), copper(II), and zinc(II) trifluoromethanesulfonates form complexes with the phosphoryl ligands hexamethylphosphoric triamide, nonamethyl imidodiphosphoric tetramide, trimorpholinophosphine oxide, tributylphosphine oxide, and triphenylphosphine oxide. The compounds have been prepared by a substitution reaction using trialkyl orthoformates as dehydrating agents and were investigated with the aid of infrared and ligand-field spectroscopy. In all compounds the ligands coordinate via the phosphoryl oxygen atoms. In some complexes the trifluoromethanesulfonate anions are (semi-)coordinated to the metal ions. The coordination around the metal ions was found to be tetrahedral, square pyramidal, or octahedral depending on the particular combination of metal ion and ligand. In its coordination behaviour the CF₃SO₃^? ion resembles the perrhenate ion.     

Pseudohalogeno Complexes of Sterically Hindered Tripyrrinatopalladium (TrpyPd) Fragments

Eight new pseudohalogeno complexes of sterically hindered TrpyPd fragments 4 – 11 have been prepared by salt metathesis in one step from known trifluoroacetates TrpyPdOAc^F 1 – 3 , using sodium salts of N₃, NCO, NCS, NCSe, dicyanamide (dca) and tricyanomethanide (tcm) anions. Despite the propensity of the co‐ligands to bind to two or more metal centres in a bridging coordination mode all new complexes have been shown by NMR spectroscopy to be essentially monomeric in solution. X‐ray diffraction studies performed on TrpyPdNCS( 6 ), TrpyPddca( 8 ), TrpyPddca( 9 ), and TrpyPdtcm( 10 ) revealed the presence of two different conformers in the solid state, one with a helically distorted Trpy backbone for 6 and 10 , and one with an almost planar tripyrrole but a tetrahedral distortion of the Pd^II coordination, a so‐called pseudoplanar form, for 8 and 9 . Interestingly the helical forms are also detected by unusual wavenumbers for the ν_CN stretching bands in their IR spectra. The reason for the occurrence of two different conformers in the solid state appears to be the crystal packing which depends mainly on the shape of the anionic co‐ligand and on the presense of alkyl groups on the TrpyPd fragment.     

Thermotropic Mesomorphism in Some Cu(II) and Pd(II) Metallorganic Complexes

The synthesis and liquid crystal properties of some bis(N-p-(n-alkoxy)phenyl, p-(n-alkoxy)salicylaldiminato)copper(II), of a homologous series of bis(N-p-(n-alkanoyloxy)phenyl, p-(n-alkanoyloxy)salicylaldiminato)copper(II), and of some corresponding palladium(II) complexes are reported. All of the compounds examined exhibit enantiotropic smectic mesomorphism, predominantly of the C type. Palladium(II) complexes are mesomorphic up to higher temperatures than the copper(II) homologues.     

Synthesis of Cu(II) and Mn(III) Complexes Involving Derivatives of Pyridine

Two complexes with derivatives of pyridine as ligands were synthesized and characterized. From the reaction of 2-pyridinecarboxaldehyde oxime with Cu(OAc)₂ · H₂O afforded the complex C₂₀H₃₀N₆O₁₂Cu₃ (I), and the use of 3-hydroxy-2-pyridinecarboxylic acid with anhydrous MnCl₂ · 4H₂O led to the formation of another complex C₁₂H₁₄N₂OCl₂Mn (II). They were characterized by X-ray diffraction (CIF files CCDC nos. 568718 (I) and 1568880 (II)), NMR, IR and elemental analysis. For I: terigonal, space group R\(\bar 3\)/H, a = 42.548(3), c = 10.2774(9) Å, V = 16113(2) ų, Z = 18, ρ_calcd = 1.367 Mg/m³, the final R factor was R₁ = 0.0945, 6662 for reflections were observed with I > 2σ(I), wR = 0.162 for all data. For II: triclinic, Pī, a = 5.6174(9), b = 7.7259(13), c = 9.7160(16) Å, α = 70.444(3)°, β = 88.009(3)°, γ = 89.818(3)°, V = 397.09(11) ų, Z = 1, ρ_calcd = 1.840 Mg/m³, the final R factor was R₁ = 0.0281, 4280 for reflections were observed with I > 2σ(I), wR = 0.0775 for all data.     

Bispalladium(II) Complexes of di-p-Pyrirubyrin Derivatives as Promising Near-Infrared Photoacoustic Dyes

The insertion of palladium(II) into di-p-pyrirubyrin results in mutually convertible bimetallic complexes. Post-synthetic functionalization of one of them yielded bispalladium(II) dioxo-di-p-pyrirubyrin and, after demetallation, dioxo-di-p-pyrirubyrin, introducing for the first time the α,β′-pyridin-2-one unit into the macrocyclic frame. Bispalladium(II) di-p-pyrirubyrin 6 , bispalladium(II) dioxo-di-p-pyrirubyrin 9 , and dioxo-di-p-pyrirubyrin 10 absorb and emit light around 1000 nm and are characterized by high photostability. Thus, they are promising candidates for near-infrared photoacoustic dyes, ideally targeting ( 9 ) the wavelength of Yb-based fiber lasers. The incorporation of an α,β′-pyridine moiety into expanded porphyrins opens a highly interesting area of research due to the attractive optical and coordination properties of the resulting molecules.     

Physicochemical Study of New Mono- and Binuclear Copper(II) Complexes with Sterically Hindered Acylhydrazones and Azomethines

Series of new binuclear copper(II) complexes with acylhydrazones and azomethines of substituted derivatives of salicylaldehyde containing bulky tert-butyl substituents were synthesized. The target dimerization of the monomeric fragments of the complexes caused by the steric factors was shown to predetermine the specific features of their magnetochemical behavior. The calculated exchange parameters for the complexes based on acylhydrazones range from –110 to –138 cm^–1 and those for the complexes based on azomethines lie in the interval from –400 to –500 cm^–1.     

Synthesis and Photophysical Properties of Monometallic C^C* Platinum(II) Formamidinate Complexes using Sterically Demanding Ligands

A novel class of cyclometalated platinum(II) complexes—previously considered to be inaccessible—was synthesized by an improved synthetic route utilizing ligands predicted by density functional theory calculations. Based on a concise quantum chemical screening three model ligands with varying steric demand were chosen and a series of six photoluminescent C^C* cyclometalated platinum(II) formamidinate complexes was obtained. The least sterically demanding ligand led to a bimetallic complex in two isomeric forms, which could be separated and confirmed by the corresponding solid-state structures. Sterically more hindered amidinate ligands gave the monometallic complexes supporting the theoretical predictions. The monometallic complexes show a significant hypsochromic shift of the emission wavelength, explained by the loss of the metal-metal interactions. Depending on the cyclometalating ligand quantum yields up to 87 % with short decay times were found for this new class of phosphorescent green-blue to pure blue platinum(II) emitters.     

Complexes of Co(II), Ni(II), Cu(II), and Pd(II) with Sulfametrole-Cyclodiphosph(V)azane Derivatives

Novel [1,3-di-[N ₁ -4-methoxy-1,2,5-thiadiazole-3-yl-sulfanilamide(sulfametrole)]-2″4-bis-[1,3-dithiole-2-thione-4,5-dithiolate]-2′,4′-dichl-orocyclodiphosph(V)azane] (III) , was prepared and their coordinating behavior towards the metal ions Co(II), Ni(II), Cu(II), and Pd(II) was studied. The structures of the isolated products are proposed based on elemental analyses, IR, UV, ¹ H, and ³¹ P NMR, ESR, magnetic susceptibility, molar ratio, conductometric titration and electrical conductivity measurements. The prepared complexes showed high to moderate bactericidal activity compared with the ligand.     

Thermal Studies on Some Biologically Active Organomercury(II) Complexes

Thermal behaviour of a number of organomercury(II) complexes of the type, p-XC₆H₄HgCl(L¹) (I), p-XC₆H₄HgCl₃(L²) (II), p-XC₆H₄HgL³ (III) and p-XC₆H₄HgL⁴ (IV) [L ¹=isoniazid, L ²=theobromine, L ³=phenyldithiocarbamate, L ⁴=p-nitrophenyldithiocarbamate; X=Me, MeO, NO₂] has been investigated. From TG curves, the order and activation energy of the thermal decomposition reaction have been elucidated. The variation of the activation energy has been correlated with the nature of the substituent on the phenyl ring. The heat of reaction has been elucidated from DSC or DTA studies. The fragmentation pattern has been analysed on the basis of mass spectra.This revised version was published online in November 2005 with corrections to the Cover Date.A part of this work was carried out at Intitute of Microbial Technology, Chandigarh, under the Visiting Associateship Scheme (1992–95) of the Council of Scientific and Industrial Research, New Delhi.     

Complexes of Co(II), Ni(II), and Cu(II) with 4-(3,4-dichlorophenyl)-1,2,4-triazole

Novel oligonuclear complexes of Co(II), Ni(II), and Cu(II) with 4-(3,4-dichlorophenyl)-1,2,4-triazole (L) of the composition [M₃L₁₀(H₂O)₂](NO₃)₆ (M = Co(II), Ni(II)), [Ni₃L₆(H₂O)₆]Hal₆ (Hal = Cl^?, Br^?), and [Cu₅L₁₆(H₂O)₂](NO₃)₁₀ · 2H₂O were synthesized and studied by magnetic susceptibility, electronic and IR spectroscopy, and powder X-ray diffraction methods. All the above complexes are X-ray amorphous. Antifer-romagnetic exchange interactions between the M²⁺ ions were discovered in the [Co₃L₁₀(H₂O)₂](NO₃)₆ and [Ni₃L₁₀(H₂O)₂](NO₃)₆ complexes, whereas ferromagnetic exchange interactions were observed in the complexes [Ni₃L₆(H₂O)₆]Cl₆, [Ni₃L₆(H₂O)₆]Br₆, and [Cu₅L₁₆(H₂O)₂](NO₃)₁₀ · 2H₂O.     

Kinetics of Reduction of Some Surfactant-Cobalt(III) Complexes by Iron(II)

The electron transfer kinetics of the reaction between the surfactant-cobalt(III) complex ions, cis-[Co(en)₂(C₁₂H₂₅NH₂)₂]³⁺, cis-α-[Co(trien)(C₁₂H₂₅NH₂)₂]³⁺(en:ethylenediamine, trien:triethylenetetramine, C₁₂H₂₅NH₂ : dodecylamine) by iron(II) in aqueous solution was studied at 298, 303, 308 K by spectrophotometry method under pseudo-first-order conditions using an excess of the reductant in self-micelles formed by the oxidant, cobalt(III) complex molecules, themselves. The rate constant of the electron transfer reaction depends on the initial concentration of the surfactant cobalt(III) complexes. ΔS^# also varies with initial concentration of the surfactant cobalt(III) complexes. By assuming outer-sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of the self-micelles formed by the surfactant cobalt(III) complexes in the reaction medium. The rate constant of each complex increases with initial concentration of one of the reactants surfactant-cobalt(III) complex, which shows that self micelles formed by surfactant-cobalt(III) complex itself has much influence on these reactions. The electron transfer reaction of the surfactant-cobalt(III) complexes was also carried out in a medium of various concentrations of β-cyclodextrin. β-cyclodextrin retarded the rate of the reaction.     

Complexes of Uracil (2,4-Dihydroxypyrimidine) Derivatives

Equilibrium studies have been carried out on complex formation of M²⁺ ions (M=Co, Ni, and Zn) with L = thymine, 6-chloromethyluracil, 5-hydroxymethyluracil, uracil, 6-methyluracil, and 6-umpm (dimethyl 6-uracilmethylphosphonate) in aqueous solution, at 25 ^∘;C and an ionic strength of I=0.1 mol⋅L⁻¹ (KNO₃). Potentiometric results indicate the formation of ML species (coordination via N3) for Co(II) and Ni(II) as well as a hydroxo complex MLH₋₁—with a deprotonated water of the inner coordination sphere. Titrations of Zn(II) confirmed both the existence of ML and MLH₋₁ species with 6-chloromethyluracil as well as 5-hydroxymethyluracil, whereas for uracil, thymine, and 6-methyluracil the only species accepted pH-metrically was MLH₋₁. For all the ligands under study the complexation with Zn(II) was reinvestigated by means of ion-selective electrodes (ISE). The role of substituents is discussed.