Synthesis and characterisation of cobalt(II), cobalt(III) and rhodium(III) complexes ofN,N′, N″, N‴-tetra(2-cyanoethyl) cyclam [TCEC] andN,N′, N″, N‴-tetra)3-aminopropyl) cyclam [TAPC]

Summary Complexes of cobalt(II), cobalt(III) and rhodium(III) with TCEC and TAPC have been synthesised. TCEC with cobalt(II) gave [Co(TCEC)Br]Br and [Co(TCEC)Cl]Cl, five coordinate high spin square pyramid complexes, but the corresponding cobalt(III) complex could not be characterised. Rhodium(III) gave a six coordinate [Rh(TCEC)Cl₂]Cl complex, in which the two coordinated chlorides have acis-geometry and the four pendant arms lie on one side of the N₄ plane with none of the —CN groups coordinated TAPC on the other hand gives the cobalt(III) complex, [Co(TAPC)Br]Br₂, in which one of the amino groups of the four pendant arms is coordinated to cobalt. Rhodium(III) with TAPC gave [Rh(TAPC)Cl]Cl₂ in which one axial site is occupied by the amino group of one of the pendant arms and the other by Cl^–.     

Kinetics of ammoniation of some halobis(ethylenediamine)-rhodium(III) perchlorates in liquid ammonia

Summary The ammoniation ofcis-[Rh(en)₂Cl₂] · (ClO₄) in liquid NH₃ was studied at constant ionic medium of 0.20 m perchlorate in the 0 to 35° range. The complex reacts in two distinct steps to givecis-[Rh(en)₂(NH₃)₂] · (ClO₄)₃, with the intermediate formation ofcis-[Rh(en)₂(NH₃)Cl] · (ClO₄)₂. Both steps follow a conjugate-base mechanism. Activation parameters were obtained for the acid-base preequilibrium and the rate-determining step. The entropies of activation for the rate-determining step are 0 and –42 JK^–1mol^–1 for the first and second ammoniations respectively. These values are considerably lower than those found for the cobalt(III) analogues. The entropy changes for the acid-base equilibria are –84 and –36 JK^–1mol^–1 respectively, which is less negative than those values found for the cobalt(III) analogues. Trans-[Rh(en)₂I₂] · (ClO₄) ammoniates totrans-[Rh(en)₂(NH₃)I] · (ClO₄)₂. The contribution of spontaneous ammoniation to the overall reaction oftrans-[Rh(en)₂I₂] · (ClO₄) is negligible, so the uniqueness oftrans-[Co(en)₂Cl₂] · (ClO₄) among cobalt(III) complexes in this respect is not reproduced for thetrans-dihalotetraamine structure in rhodium(III) complexes. A comparison of cobalt(III) and rhodium(III) amines with respect to activation parameters and the influence of formal charge of the metal complex on reactivity indicates a more associative type of activation for rhodium(III).     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 4. The 3-piperidinyl derivative

Summary Metal ion complexes of the thiosemicarbazone, 3-piperidinyl-3-thiocarboxylic acid-2-[1-(2-pyridyl)ethylidene]hydrazide (HLpip) have been prepared and spectrally characterized. HLpip coordinates both as the deprotonated ligand (i.e., pyridylN, azomethineN, and thione sulphur) and the neutral ligand (i.e., pyridylN and azomethineN) with the sulphur possibly weakly coordinating in [Ni(HLpip)₂](BF₄)₂. All three preparative cobalt(II) salts yielded cobalt(III) cationic complexes. The nickel(II) and copper(II) chloride salts gave [M(Lpip)Cl] solids while complexes involving the neutral ligand were prepared with the corresponding bromide salts. Significant differences in the spectral properties of the various complexes are observed when compared to other thiosemicarbazones prepared from 2-acetylpyridine.     

Cucurbit[8]uril-based inclusion compounds containing iron(II), cobalt(III), and nickel(II) complexes with cyclam and cyclen as guest molecules: Synthesis and crystal structures

New inclusion compounds containing iron(II), cobalt(III), and nickel(II) complexes with the cyclic polyamine ligands cyclam and cyclen in the macrocyclic cavitand cucurbit[8]uril (CB[8]) were obtained: {trans-[Fe(Cyclam)(CO)(OCHO)]@CB[8]}Cl · 15H₂O, {cis-[Co(Cyclen)(H₂O)Cl]@CB[8]}Cl₂ · 20H₂O, and {cis-[Ni(Cyclen)(H₂O)Cl]@CB[8]}Cl · 12H₂O. According to X-ray diffraction data, the complexes are in the cavity of each CB[8] molecule. The complexes of the above molecular formulas were isolated in the solid state as supramolecular compounds with CB[8] and structurally characterized for the first time.     

Studies on synthesis,determination of CMC values,kinetics and the mechanism of iron(II) reduction of surfactant–Co(III)–ethylenediamine complexes in aqueous acid medium

The surfactant–Co(III) complexes of the type cis-[Co(en)₂AX]²⁺ (A?=?Tetradecylamine, X?=?Cl^?,?Br^?) were synthesised from corresponding dihalogeno complexes by the ligand substitution method. The critical micelle concentration (CMC) values of these surfactant complexes in aqueous solution were obtained from conductance measurements. The kinetics and mechanism of iron(II) reduction of surfactant–Co(III) complexes, cis-[Co(en)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂ and cis-[Co(en)₂(C₁₄H₂₉NH₂)Br] (ClO₄)₂ ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co(III) using an excess of the reductant under pseudo-first-order conditions: [Fe(II)]?=?0.25?mol?dm^?3, [H⁺]?=?0.1?mol?dm^?3, [μ]?=?1.0?mol?dm^?3 ionic strength in a nitrogen atmosphere at 303, 308 and 313?K. The reaction was found to be of second order and showed acid independence in the range [H⁺]?=?0.05–0.25?mol?dm^?3. The second-order rate constant increased with surfactant–Co(III) concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe(II)], [H⁺] and [μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of [Fe(II)] with Co(III) complex proceeds by an inner-sphere mechanism.     

Preparation and photochemistry of macromolecular bound ruthenium(II) complexes in aqueous solutions

Ruthenium(II) polypyridyl complexes with macromolecular ligands poly(methylolacrylamide-co-vinylpyridine) and poly (acrylamide-co-vinylpyridine) have been synthesized. The macromolecular ruthenium (II) complexes which are soluble in water have been characterized and their absorption and emission properties have been studied in aqueous solution. Photolysis of the complex in aqueous solution leads to photoaquation reactions with release of coordinated pyridines of the polymer. In the case of monomeric complex, cis-[Ru(bpy)₂(py)₂]Cl₂, photolysis in water in presence of Cl^? ions produces only the substitution of the pyridine by water whereas in the polymeric complexes, [Ru(bpy)₂(MAAM-co-VP)₂]Cl₂ photolysis in the presence of chloride produces [Ru(bpy)₂(MAAM-co-VP)Cl]Cl and [Ru(bpy)₂(AM-co-VP)Cl]Cl, respectively. Quantum yields for the photosubstitution reactions have been determined and mechanistic details are outlined.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 3. The 3-hexamethyleneimine derivative

Summary Metal ion complexes of the thiosemicarbazone, 3-hexamethyleneimine-3-thiocarboxylic acid-2-[1-(2-pyridyl)-ethylidene]hydrazide (HLhexim) have been prepared and spectrally characterized. HLhexim coordinates primarily as the deprotonated tridentate ligand (i.e., pyridylN, azomethineN, and thione sulphur). The air oxidised cobalt(III) complex, [Co(LHexim)₂] (BF₄), was isolated from the preparation with cobalt(II) tetrafluoroborate, but other cobalt(II) salts yielded tetrahedral cobalt(II) compounds. Planar nickel(II) and copper(II) complexes were isolated from preparations with halide salts. Significant differences in the spectral properties of the various complexes are observed when compared to other thiosemicarbazones prepared from 2-acetylpyridine.     

Metallosurfactants of Chromium(III) Coordination Complexes. Synthesis, Characterization and Determination of CMC Values

A number of mixed ligand chromium(III)–surfactant coordination complexes, of the type cis-[Cr(en)₂(A)X]²⁺ and cis-α-[Cr(trien)(A)X]²⁺ (A = Dodecyl or Cetylamine; X = F⁻, Cl⁻, Br⁻) were synthesized from the corresponding dihalogeno complexes by ligand substitution. These compounds form foam in aqueous solution when shaken. The critical micelle concentration (CMC) values of these surfactant metal complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303, 308 and 313 K) served for evaluation of the temperature-dependent critical micelle concentration (cmc) and the thermodynamics of micellization (Δ G_m⁰, Δ H_m⁰ and Δ S_m⁰).     

Outer-sphere electron-transfer reactions of co(III)–polymer complexes in relation to its polymer effects

The outer-sphere electron-transfer reactions between [Co(III)(NH₃)₅L] (CIO₄)₃ [L = polyethyleneimine (PEI), L = NH₃(Amm)] or cis-[Co(III)(en)₂L′Cl]Cl₂ [L′ = poly-N-vinyl-2-methylimidazole(PVI), poly-4-vinylpyridine (PVP), N-ethylimidazole (NEI), pyridine (Py)] and various Fe(II) were studied. In the reaction with Fe(II)-(phen)₃²⁺, the reactivity of Co(III)–PEI was smaller than that of Co(III)–Amm due to the larger electrostatic repulsion. On the other hand, the reactivity of Co(III)–PEI was larger by a factor of 80 in the reaction with Fe(II)(H₂O)₆²⁺. From the results of rapid-scanning spectroscopy, the higher reactivity of Co(III)–PEI is caused by the coordination of free ethyleneimine residues in the Co(III)–PEI to Fe(II)–ion. Further more, the hydrophobic interaction between heteroaromatic polymer ligands and Fe(II)-(phen)₃²⁺ brought about the higher reactivities of Co(III)–PVI and Co(III)–PVP. Three interactions caused by the essential properties of polymers are discussed in relation to conformational changes.     

Synthesis,Structures, Ligand Substitution Reactions,and Electrochemistry of the Nitrile Complexes cis‐[Ru(dppm)2Cl(NCR)]+ PF6– (dppm = Bis(diphenylphosphino)methane,R = CH3, C2H5, tBu,Ph)

Isomerically pure nitrile complexes cis‐[Ru(dppm)₂Cl(NCR)]⁺ ( 2 a – d ) are formed upon chloride displacement from cis‐[Ru(dppm)₂Cl₂] ( 1 ) or, alternatively, by ligand substitution from the acetonitrile complex 2 a . This latter approach does also allow for the introduction of pyridine ( 3 a , b ), heptamethyldisilazane ( 4 ) or isonitrile ligands ( 5 ). All complexes are obtained as the configurationally stable cis‐isomers. Only cis‐[Ru(dppm)₂Cl(CN^tBu)]⁺ slowly isomerizes to the trans from. The solid state structures of the CH₃CN, C₂H₅CN and the trans‐^tBuNC complexes were established by X‐ray crystallography. Electrochemical investigations of the nitrile complexes 2 a – d show in addition to a chemically reversible one‐electron oxidation an irrversible reduction step. In CH₂Cl₂ solution, cis‐ and trans‐[Ru(dppm)₂Cl₂] have been identified as the final products of the electrochemically induced reaction sequence.     

Synthesis,characterization, and ascorbic acid oxidase biomimetic catalytic activity of cobalt(III) oxime complexes

A new tetradentate tetraaza ligand was prepared via Schiff-base condensation of 3,4-diaminotoluene with 2,3-butandione monoxime in aqueous solution. This ligand coordinates cobalt(III) through nitrogen donors in equatorial positions with loss of one oxime proton with concomitant formation of an intramolecular hydrogen bond. A series of cobalt(III) complexes, [CoLX₂] (X?=?Cl^?, Br^?, or I^?), [SCNCoLBr], [CNCoLBr], [BF₂CoLBr], and [YCoLBr]ClO₄ (Y?=?pyridine, thiophene, triphenylphosphine, or n-pentylamine), was synthesized. The compounds were characterized based on the elemental analysis (C, H, N), electrical conductance, magnetic moment measurements, and spectral studies (IR, ¹H NMR, and UV-Vis). Thermal stabilities of representative complexes were examined by using thermal analysis (TGA and DTG). The reported complexes are d⁶ low-spin diamagnetic and a distorted octahedral environment was proposed. All complexes undergo tetragonal distortion as evidenced by splitting of ¹T_1g and ¹T_2g levels of the pseudo-octahedral symmetry. The ligand field parameters such as Dq^E , Dq^A , and the tetragonal splitting D_t have been computed and correlated with the nature of the coordinated axial ligands. The reported cobalt(III) complexes exhibit promising catalytic activity toward aerobic oxidation of ascorbic acid to the corresponding dehydroascorbic acid. The oxidase catalytic activity is linked to both the tetragonal splitting parameter D_t and the Lewis-acidity of cobalt(III) created by the nature of the coordinated axial ligands. The probable mechanistic implications of the catalytic oxidation reactions are discussed.     

Mixed ligand complexes of palladium(II) and platinum(II) with methionine and 2,4-disubstituted pyrimidines

Summary Mixed ligand complexes ofcis-[M(MetH)Cl₂] (M=Pd²⁺ and Pt²⁺; MetH=methionine) with 2,4-disubstituted pyrimidines were prepared and characterised. Thecis-[Pd(MetH)Cl₂] complex reacted with cytosine (2-hydroxy-4-aminopyrimidine), isocytosine (2-amino-4-hydroxypyrimidine) and thiocytosine (2-thio-4-amino-pyrimidine) to form ternary complexes.cis-[Pt(MetH)Cl₂] however reacted with cytosine, uracil (2,4-pyrimidine dione or 2,4-dihydroxypyrimidine) to yield the corresponding mixed ligand complexes. The primary ligand, methionine, binds to the metal ion through sulphur and amino nitrogenvia a six membered chelate ring. The secondary ligands (substituted pyrimidines) bind to the Pd²⁺ or Pt²⁺ metal ion through the ring nitrogen (N₃), as monodentate ligand. Thiocytosine however acts as a bidentate ligand, coordinating to the metal ion through-SH and ring nitrogen (N₃). All complexes are 11 electrolytes, except the thiocytosine complex, which is a 12 electrolyte.     

Spectroscopic and Electrochemical Studies of the Interaction of Some Gold(III) Complexes with Biologically Relevant Thiones

The interaction of gold(III) complexes, [Au(cis‐DACH)Cl₂]Cl and [Au(cis‐DACH)₂]Cl₃ complexes (DACH = cis‐1,2‐diaminocyclohexane), with ¹³C, ¹⁵N‐enriched thiourea (Tu) and 1,3‐diazinane‐2‐thione ligands was investigated. The progress of these reactions was monitored by NMR (¹H, ¹³C, and ¹⁵N) and UV–vis spectroscopy as well as square wave stripping voltammetry. The kinetic studies of the substitution reactions between the above‐mentioned complexes with thiones in aqueous solutions containing 30 mM KCl, which is used to suppress the hydrolysis of the chloride complexes, were conducted. These reactions were followed under pseudo–first‐order conditions as functions of ligand concentration, pH, and temperature. The activation parameters (ΔH^#, ΔS^#) were calculated from Eyring plots, and the negative values of ΔS^≠ lend support for an associative mechanism. The kinetic data also indicated a relatively higher reactivity of [Au(cis‐DACH)Cl₂]Cl than that of [Au(cis‐DACH)₂]Cl₃ toward the thiones.     

1H and 13C NRM and infrared spectral studies on mixed ligand complexes of the type cis-[Co(en)2(Im)Cl]Cl2

A number of mixed ligand complexes of the type [Co(en)₂(Im)Cl]Cl₂ (Im = imidazole or a substituted imidazole) have been synthesized by reaction of trans-[Co(en₂Cl₂]Cl with the imidazole ligands. Electrical conductivity measurements support the ionic (1:2) formulation of the compounds, the electronic spectra is in agreement with an octahedral stereochemistry, and the IR and NMR (¹H and ¹³C) spectra strongly favour the cis configuration for the isolated complexes, [Co(en)₂(Im)Cl]Cl₂.Trans-[Co(en)₂Cl₂]Cl reacts with KNCS to form cis-[Co(en)₂(NCS)₂Cl, the crystal structure of which is briefly reported. This lends additional support in favour of the probable cis configuration of the above complexes.     

Palladium(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione

Two new palladium(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione(mpyh) were synthesized: cis-[Pd(mpyh)₂Cl₂]·H₂O and cis-[Pd(mpyh)₂Br₂]·2H₂O. The molecular formulae of the complexes were confirmed by elemental analysis, IR, ¹H NMR spectra and DTA study. The ligand is coordinated to the palladium ion with N-atom of the pyridine ring. The spectroscopic data indicate a square planar geometry with two N-pyridine atoms and two halogene anions in cis position. The final product of the thermal decomposition of cis-[Pd(mpyh)₂Cl₂]·H₂O is metallic Pd, whereas for cis-[Pd(mpyh)₂Br₂]·2H₂O the residue consists of metallic Pd and C. The cytotoxic effects of the complexes were examined in vitro on some human tumor cell lines. The cis-[Pd(mpyh)₂Cl₂]·H₂O proved to be more active as compared to the cis-[Pd(mpyh)₂Br₂]·2H₂O.     

Metalloporphyrins catalyze polyene-polymers to polyepoxides

Polyene polymers [natural rubber (cis-polyisoprene), trans-polyisoprene, and cis-polybutadiene] were transformed to the corresponding polyepoxides which are a polyalcohol and soap precursor. The catalysts used were chloro- or acetato-manganese^(III) tetraphenylporphyrin [Mn^III(TPP)Cl or Mn^III(TPP)OAc] in association with two different oxygen donors, sodium hypochloride and iodosylbenzene (Por, unspecified porphyrinato ligand; TPP, 5,10,15,20-tetraphenylporphyrinato ligand). This transformation in either biphasic system, H₂O(aqua)-CH₂Cl₂ or PhIO(solid)-CH₂Cl₂, was monitored by ¹H-NMR and IR spectroscopy. In both cases the transformation to the polyepoxide was completed within a few hours. © 1992 John Wiley & Sons, Inc.     

Potentiometric Titrations and Nickel(II) Complexes of Four Topologically Constrained Tetraazamacrocycles

Abstract

The novel high spin Ni²⁺ complexes of the topologically constrained tetraazamacrocycles (1–4) [4,11-dimethyl-1,4,8,11 - tetraazabicyclo[6.6.2]hexadecane (1); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane (2); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (3); racemic-4,5,7,7,11,12,14,14-octamethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (4)] show striking properties. Potentiometric titrations of the ligands 2 and 4 revealed them to be proton sponges, as reported earlier for 1 [1]. Ligand 3 is less basic, losing its last proton with a pK = 11.3(2). Despite high proton affinities, complexation reactions in the absence of protons successfully yielded Ni²⁺ complexes in all cases. The X-ray crystal structures of Ni(1)(acac)⁺, Ni(3)(acac)⁺ and Ni(1)(OH₂)₂ ²⁺ demonstrate that the ligands enforce a distorted octahedral geometry on Ni²⁺ with two cis sites occupied by other ligands. Magnetic measurements and electronic spectroscopy on the corresponding Ni(L)Cl₂ (L = 1–3) complexes reveal that all are high spin and six-coordinate with typical magnetic moments. In contrast, [Ni(4)Cl⁺] is five-coordinate with a slightly higher magnetic moment and its own characteristic electronic spectrum. The extra methyl groups on ligand 4 define a shallow cavity, sterically allowing only one chloride ligand to bind to the nickel(II) ion.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 1. The4N-methyl derivative

Summary A series of metal ion complexes of the thiosemicarbazone,N-methyl-2[1-(2-pyridinyl)ethylidene]-hydrazinecarbothioamide (HL4M) has been prepared and spectrally characterized. HL4M coordinates either as a neutral bidentate ligand (i.e., pyridyl N and imine N) or as deprotonated tridentate ligand (i.e., pyridyl N, imine N and thiol sulphur). The cobalt(II) salts yield hexacoordinated cobalt(III) cations, and an isoelectronic species, [Ni(L4M)₂], has been formed from Ni(C₂H₃O₂)₂. The remaining nickel(II) complexes involve the neutral ligand, as do two of the three copper(II) complexes. HL4M possesses a weaker ligand field and has less covalency in its bonding than related thiosemicarbazones that possess anN-dialkyl-function.     

Study of the Interaction of Some Potential Anticancer Gold(III) Complexes with Biologically Important Thiols Using NMR,UV–Vis,and Electrochemistry

The interaction of gold(III) complexes [Au(en)Cl₂]Cl, [Au(en)₂]Cl₃, [Au(cis‐DACH)Cl₂]Cl, and [Au(cis‐DACH)₂]Cl₃ (en = ethylenediamine, DACH = cis‐1,2‐diaminocyclohexane) with biologically important thiols, such as glutathione (GSH), dl ‐penicillamine (PSH), mercaptoacetic acid (MAA), and N‐(2‐mercaptopropionyl)glycine (MPG), has been studied using ¹H, ¹³C NMR, UV–vis spectroscopy and electrochemistry in aqueous solution. Kinetic data revealed that the reactivity of their substitution reaction followed the order: [Au(en)Cl₂]⁺ > [Au(en)₂]³⁺ > [Au(cis‐DACH)Cl₂]⁺ > [Au(cis‐DACH)₂]³⁺. The thiol reactivity increased with decreasing its size, viz. MAA ≫ MPG > PSH > GSH. Square wave stripping voltammetry displayed peaks for Au(III) and Au(I) at +0.875 V and +1.4 V respectively. The interaction of the complexes with thiols resulted in reduction of gold(III) to gold(I) and thiol ligands (RSH) were oxidized to disulfide (RSSR).     

Manipulation of Molecular and Supramolecular Structure in Cobalt(II) Complexes with Tetrachloroterephthalate through the Influence of Different Solvents

The reactions of cobalt acetates with tetrachloroterephthalic acid (H₂BDC‐Cl₄) in different solvents gave two polymeric and one mononuclear Co^II complexes. X‐ray single‐crystal structural determination revealed that the ligand BDC‐Cl₄ displays a reliable bridging tecton to construct diverse supramolecular architectures through coordinative bonds or secondary hydrogen‐bonding interactions. The complexes [Co(BDC‐Cl₄)(DMF)₂(EtOH)₂]_n ( 1 ) and {[Co(BDC‐Cl₄)(DMF)₂(MeOH)₂] · 2DMF}_n ( 2 ) demonstrate a one‐dimensional (1D) coordination motif with infinite Co^II‐tetrachloroterephthalate chains, which are tuned by different binding solvent systems of DMF/ethanol (EtOH) and DMF/methanol (MeOH). [Co(DMF)₂(H₂O)₄] · (BDC‐Cl₄) ( 3 ) represents a two‐dimensional (2D) metallosupramolecular network by hydrogen‐bonded bridging between the aqua ligand of the mononuclear complex with the uncoordinated BDC‐Cl₄ solvates. The spectroscopic, thermal, and fluorescent properties of 1 – 3 were also investigated.