Showing papers in "Transition Metal Chemistry in 1993"
TL;DR: In this article, the X-ray diffraction parameters for [CoL] and [NiL′] correspond to a tetragonal crystal lattice, while the e.r.s. spectra of the copper(II) complexes indicate a distorted dimeric structure, and the ligands chelate via two C=N groups and two deprotonated enolate groups.
Abstract: Acetylacetone bis-benzoylhydrazone (PhCONHN=CMe)2 CH2(LH2) and acetylacetone bis-isonicotinoylhydrazone (NC5H4CONHN=CMe)2CH2(L′H2) complexes of the types [ML] and [ML′] (M = CoII, NiII, CuII or ZnII) have been prepared and characterized. All the complexes are non-electrolytes and the cobalt(II) complexes are lowspin, the nickel(II) complexes are diamagnetic and the copper(II) complexes are paramagnetic. The ligands chelate via two C=N groups and two deprotonated enolate groups. The e.s.r. spectra of the copper(II) complexes indicate a tetragonally distorted dimeric structure. The X-ray diffraction parameters for [CoL] and [NiL′] correspond to a tetragonal crystal lattice.
77 citations
TL;DR: In this article, the growth inhibition of four thiosemicarbazones and their metal complexes against two human pathogenic fungi, Aspergillus niger and Paecilomyces variotii, have been evaluated.
Abstract: Nickel(II) and copper(II) complexes of acetylpyrazine 3-azabicyclo[3.2.2]-nonylthiosemicarbazone and nickel(II) complexes of acetylpyrazine 4N-methyl-, 4N-dimethyl-, and 3-hexamethyleneiminylthiosemicarbazone have been synthesized and characterized by their spectral and physical properties. Crystal structures for the nickel(II) complexes of the 4N-methyl- and 4N-dimethyl-derivatives, with a chloro ligand in the fourth coordination position, are included. The growth inhibition by the four thiosemicarbazones and their metal complexes against two human pathogenic fungi, Aspergillus niger and Paecilomyces variotii, have been evaluated.
64 citations
TL;DR: In this paper, the authors present a review of the development of palladium cluster compounds, the methods of characterization available, structural and bonding aspects, and finally their reactivities, which is limited to compounds containing Pd -Pd bonds.
Abstract: Over the past 20 years, the field of metal cluster chemistry has been one of the most rapidly developing in inorganic chemistry, and the current interest in this area can be illustrated by the recent publication of two books II'z). Clusters with up to 70 metal atoms <3) have been synthesized and characterized crystallographically, and the structures of many of these clusters have been justified theoretically in terms of molecular orbital analyses and electron counting rules <4's). Metal cluster compounds can be regarded as intermediate between coordination complexes and bulk metal surfaces. As such, the study of their chemistries can provide a model for reactions that occur on the surface of metals during heterogeneous catalytic processes the so-called 'cluster-surface analogy'% Cluster compounds themselves may prove to be of use as homogeneous catalysts, and research into the possibility of synthesizing highly selective cluster catalysts is rapidly increasing~ 7-9). Palladium, in the form of both the metal and mononuclear compounds, is one of the best catalysts for a whole host of reactions r176 so it is somewhat surprising that palladium cluster chemistry is less well developed than that of other metals, such as gold (12), ruthenium ~13) and platinum tl4). There are no obvious reasons for this lack of development, especially as palladium displays an extensive organometallic mononuclear chemistry ~ls). This review aims to collate the research that has been completed on palladium cluster compounds; the only previous reviews were limited to carbonyl phosphine clusters ~a6'7). This review will examine the syntheses of palladium cluster compounds, the methods of characterization available, structural and bonding aspects, and finally their reactivities. In cases where research has not been done with palladium examples are drawn from platinum chemistry. The review is limited to compounds containing Pd -Pd bonds, therefore, aggregates such a s [ P d 3 ( / A O A c ) 6 ] (17) and [Pd 8(/t-SPr)16] (18), in which there are no significant Pd -Pd interactions, have not been included.
46 citations
TL;DR: The results show that the ligand is coordinated to the central metal ion via amide nitrogen, imino nitrogen, phenolic oxygen and carboxyl oxygen to form a quadridentate complexes.
Abstract: Two new Schiff bases, N-4-hydroxysalicylidene-glycylglycine (K·GGRS·H2O), N-O-vanillal-glycylglycine (K· GGVS·3H2O) and their manganese(II), cobalt(II), nickel(II) and copper(II) complexes have been synthesized and characterized by elemental analysis, t.g.a., molar conductance, i.r. and u.v. spectral studies. The 13Cn.m.r. spectrum of one of the Schiff base ligands has been recorded. The results show that the ligand is coordinated to the central metal ion via amide nitrogen, imino nitrogen, phenolic oxygen and carboxyl oxygen to form a quadridentate complexes. Some of the complexes exhibit strong inhibitory action towards Candida albicans and Cryptococcus neoformans.
41 citations
TL;DR: The phototransformation of iron(III) nitrilotriacetate, Fe(NTA), was studied at 20 °C under monochromatic excitation at different pHs.
Abstract: The phototransformation of iron(III) nitrilotriacetate, Fe(NTA), was studied at 20 °C under monochromatic excitation at different pHs. The conjugation of excitation wavelength and pH gives rise to different photochemical behaviour. In acidic medium, it always results in a redox process giving rise to FeII, HCHO and CO2 but the stoichiometry of the photoproducts depends on the excitation wavelength. At long wavelength (365 nm), the FeII/HCHO ratio of unity implies a redox reaction between FeIII and the carboxylic group whereas at short wavelength (254 nm) the Fe/HCHO ratio is equal to 2 and implies a redox process between FeIII and a water ligand. In neutral solution and at 365 nm, a photosolvation is observed with NTA release; at 254 nm a subsequent redox process between OH and the hydrous ferric oxide is involved. In terms of the fate of Fe(NTA) in the environment at pH 5–6 and under sunlight, all of the above photochemical reactions can occur.
40 citations
TL;DR: In this paper, the origin of the thermochrornism is discussed in terms of changes in ligand field strength and coordination geometry, and these changes were studied by means of thermal and spectral methods.
Abstract: Nickel(II) and copper(II) complexes of Schiff bases derived from salicylaldehyde, 2-hydroxy-1-naphthaldehyde, 2,4-dihydroxybenzaldehyde, 2,3-dihydroxybenzaldehyde or 5-chlorosalicylaldehyde and 8-aminoquinoline have been prepared and characterized. Several of the complexes are thermochromic in the solid state. The origin of the thermochrornism is discussed in terms of changes in ligand field strength and coordination geometry. These changes were studied by means of thermal and spectral methods.
40 citations
34 citations
TL;DR: In this paper, 2-Thenoyltrifluoroacetone isonicotinoyl hydra/one (H2L), made by condensation of TTA with isonic acid hydrazide, and its transition metal complexes were prepared.
Abstract: 2-Thenoyltrifluoroacetone isonicotinoyl hydra/one (H2L), made by condensation of 2-thenoyltrifluoroacetone(TTA) with isonicotinic acid hydrazide, and its transition metal complexes were prepared. H2L functions as a tetradentate ligand for divalent metal ions, but as a tridentate ligand for trivalent metal ions, taking part in coordination in both mono- and divalent anions. Antioxidative tests were made to examine the elimination action for H2L and the complexes towards superoxide O
inf2
sup−.
and hydroxyl OH. radicals, which confirmed the efficient antioxidative action towards these radicals.
29 citations
TL;DR: The oxidation of selenium(IV) by permanganate has been studied kinetically in acid, neutral and alkaline media and evidence has been obtained for a one electron-transfer in the rate-determining step.
Abstract: The oxidation of selenium(IV) by permanganate has been studied kinetically in acid, neutral and alkaline media. The reaction exhibits unit-order dependence on selenium(IV) and permanganate in all the three media. Manganese(VI) retards the reaction in alkaline medium. The rate-limiting step is the same in all the three media, but the stoichiometry is different, being 2:1 in alkaline medium, 2:3 in neutral medium and 2:5 in acid medium. Evidence has been obtained for a one electron-transfer in the rate-determining step.
28 citations
TL;DR: In this article, a series of complexes with the tridentate dibasic Schiff base ligand o-vanillin isonicotinoyl hydrazone (o-VINH) were prepared and characterized by i.a.p. and electronic spectral studies, magnetic susceptibility measurements and t.m.
Abstract: A new series of complexes with the tridentate dibasic Schiff base ligand o-vanillin isonicotinoyl hydrazone (o-VINH) were prepared and characterized by i.r., 1H n.m.r. and electronic spectral studies, magnetic susceptibility measurements and t.g.a. The disappearance of low field signals due to OH, NH protons at 10.23 and 9.31 p.p.m. and downfield shift of the −CH=N proton signal at 8.17 p.p.m. in the n.m.r. spectrum confirms the involvement of these groups in coordination. Both t.g.a. and i.r. spectral data show evidence for one molecule of coordinated H2O. These results taken in conjunction with electronic spectral data allow assignation of tetrahedral geometry for manganese(II), nickel(II) and palladium(II) complexes but a square planar configuration to cobalt(II), copper(II) amd zinc(II) complexes.
28 citations
TL;DR: Nickel(II) complexes of four tridentate NNS Schiff base ligands, derived by condensing 2-acetyl-and 2-benzoylpyridine with S-methyl-and S-benzinoyldithiocarbazate, have been prepared and characterized as mentioned in this paper.
Abstract: Nickel(II) complexes of four tridentate NNS Schiff base ligands, derived by condensing 2-acetyl-and 2-benzoylpyridine with S-methyl- and S-benzoyldithiocarbazate, have been prepared and characterized. The monoligated complexes, [Ni(NNS)X] (NNS = anionic ligand; X = Cl, Br, NCS, I) are diamagnetic and square-planar, whereas the bis-ligand complexes, [Ni(NNS)2] are paramagnetic and tetragonal. The Schiff bases are fungitoxic towards A. solani, F. equisetti and M. phaseolina (approaching the toxicity of the commercial fungicide Nystatin), but the nickel(II) complexes are less fungitoxic than the free ligands.
TL;DR: In this paper, an anion (loss of 3N hydrogen) of a 2-acetylpyridine azacyclothiosemicarbazone coordinates in a planar conformation to the central Cu atom through the pyridyl N, azomethine N and thiolato S atoms.
Abstract: An anion (loss of 3N hydrogen) of a 2-acetylpyridine azacyclothiosemicarbazone coordinates in a planar conformation to the central Cu atom through the pyridyl N, azomethine N and thiolato S atoms. The interatomic distances are Cu{ie449-01}N = 2.016(6), Cu{ie449-02}N = 1.963(5) and Cu{ie449-03}S = 2.236(3) A, respectively, with the fourth co-ordination site occupied by a bromine atom, Cu{ie449-04}Br = 2.359(2) A.
TL;DR: Ruthenium complexes of some tridentate and bidentate benzimidazole, benzothiazole- and pyridine-derived ligands have been prepared as PF f6 − 1 − p− n− 1− 2− 5−1:10-phenanthroline, and their constitutions have been confirmed by elemental analysis and electrochemistry as discussed by the authors.
Abstract: Ruthenium complexes of some tridentate and bidentate benzimidazole-, benzothiazole- and pyridine-derived ligands have been prepared as their PF
f6
p−
salts, and their constitutions have been confirmed by elemental analysis, 1H-nmr spectroscopy and electrochemistry The complexes are redox-active, displaying a metal-centred RuII/ RuIII oxidation process and sequential ligand-localized reduction processes Both the 2-(2′-pyridyl)benzimidazole complex [Ru(PybimH)3]2+ and the 2,2′-dipyridylamine one, [Ru(DpyaH)3]2+ behave as weak Bronsted-Lowry acids The secondary amino nitrogen of each DpyaH in the [Ru(DpyaH)3]2+ complex can be deprotonated with hydride anion, and then acts as a strong nucleophile, allowing selective N-alkylation by alkyl halides Most of the complexes exhibit ligand-localized luminescence emission at ambient temperature The strong intrinsic fluorescences of 2-(2′-quinolyl)-N-methylbenzimidazole and 2-(2′-pyridyl)-benzimidazole are quenched when they are coordinated to RuII, and emission from the chelates entailing 5-nitro-1:10-phenanthroline occurs only from the non-nitrated ligands
TL;DR: In this paper, transition metal complexes of transition metals with acetoacetanilide thiosemicarbazone, AatH2, have been characterized for their possible antitumour activity against Ehrlich Ascites tumour cells in vitro.
Abstract: Complexes of transition metals with acetoacetanilide thiosemicarbazone, AatH2, have been prepared and characterized. The complexes were found to have the following stoichiometries: [Mn(Aat)(H2O)2]n; [Zn(Aat)(H2O)2]; [M(Aat)(H2O)], where M = CdII or HgII; [Cu(Aat)]n; [Ag(AatH)]; [M(AatH)2], where M = CoII or NiII, and [Fe(Aat)Cl(H2O)]n. The compounds have been studied for their possible antitumour activity against Ehrlich Ascites tumour cells in vitro.
TL;DR: In this article, the oridging function of dicyanamide in the six-coordinate complexes is realized either through both cyanide or through amide and cyanide nitrogens.
Abstract: Dicyanamide complexes of CuII, NiII and CoII of the type M[N(CN)2]2L2, where L = benzimidazole, 2-methyl- or 2-ethylbenzimidazole, have been prepared and studied by spectroscopy and magnetochemistry. The complexes, except for Co[N(CN)2]2 (benzimidazole)2, are six-coordinate, involving bidentate bridging dicyanamide groups. While the NiII complexes have practically octahedral structures, the CuII complexes are pseudooctahedral with similar tetragonal distortion. The ligand field strength in these complexes depends mainly on the steric effect of the benzimidazole ligands. The CoII complex of benzimidazole is monomeric tetrahedral, but that of 2-ethylbenzimidazole is tetragonal octahedral. The oridging function of dicyanamide in the six-coordinate complexes is realized either through both cyanide or through amide and cyanide nitrogens. The complex Cu[N(CN)2]2 (2-methylbenzimidazole)2 is a weak antiferromagnet (J = -0.1 cm−1), exhibiting under ca. 15 K a long-range antiferromagnetic ordering.
TL;DR: In this article, an inner sphere mechanism is proposed for pathway oxidation of both the protonated and deprotonated species of the complex, with the formation of an intermediate which slowly forms the final oxidation product, [CoIII(HEDTA)].
Abstract: The kinetics of the oxidation of [N-(2-hydroxyethyl)-ethylene-diamine-N,N′,N′-triacetato] cobalt(II), [CoII-(HEDTA)]−, by N-bromosuccinimide, NBS, have been studied in aqueous solutions and water-methanol solvent mixtures under various conditions. The reaction stoichiometry indicates that one mole of NBS reacts with one mole of [CoII(HEDTA)]−. In aqueous solutions the reaction obeys the following rate law:
$$Rate = \left\{ {k_2 + k_3 /\left[ {H^ + } \right]} \right\}\left[ {Co^{11} \left( {HEDTA} \right)^ - } \right]\left[ {NBS} \right]$$
An inner sphere mechanism is proposed for pathway oxidation of both the protonated and deprotonated species of the complex, with the formation of an intermediate which slowly forms the final oxidation product, [CoIII(HEDTA)]. In water-methanol solvent mixtures the reaction rate decreased as the methanol content was increased. An appropriate mechanism, consistent with the kinetic results, is suggested.
TL;DR: A series of metal complexes with new tridentate Schiff base derived from salicylaldehyde and furfuraldehyde with o-phenyldiamine have been prepared and characterised by physical and chemical methods as discussed by the authors.
Abstract: A series of metal complexes with new tridentate Schiff base derived from salicylaldehyde and furfuraldehyde with o-phenyldiamine have been prepared and characterised by physical and chemical methods. Electronic spectra, room temperature magnetic moment values, e.p.r. and X-ray photoelectron spectroscopy studies suggest an octahedral geometry for all the complexes, where low molar conductance values are in accord with their non-electrolytic nature. The thermal stability of the complexes is discussed and the ligand-to-metal bonding modes discussed.
TL;DR: Several cobalt(II) complexes of 5,7-dimethyl-[1,2,4]-tria-zolo]-1,5-a]-pyrimidine (DMTP) have been prepared and characterized by thermal and spectroscopic techniques.
Abstract: Several cobalt(II) complexes of 5,7-dimethyl-[1,2,4]-tria-zolo-[1,5-a]-pyrimidine (DMTP) have been prepared and characterized by thermal and spectroscopic techniques. The crystal structure of [Co(DMTP)2(H2O)4]Br2·2H2O has been determined by XRD; the metal ion is octahedrally coordinated by two DMTP ligands through the usual N(3) site and four water molecules. Metal binding to N(3) for DMTP is consistent with the electronic properties calculated with the MOPAC programme. All the complexes were screened for their activity against several types of bacteria, showing a broad-spectrum antimicrobial activity.
TL;DR: In this paper, an inner sphere mechanism was proposed for electron transfer in aquaethylenediaminetetraacetatochromium(III) [Cr(HEDTA)(H2O)] with N-bromosuccinimide (NBS) to yield chromium(VI).
Abstract: The oxidation of aquaethylenediaminetetraacetatochromium(III) [Cr(HEDTA)(H2O)] with N-bromosuccinimide (NBS) to yield chromium(VI) has been studied spectrophotometrically over the 20–40° C range. The rate is first order with respect to both reactants and increases with decreasing [H+] between pH 6.0 and 6.8. The thermodynamic activation parameters were calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [Cr(EDTA)(OH)]2- and protonated [Cr(EDTA)(H2O)]- are the reactive species. It is proposed that electron transfer proceeds via an inner sphere mechanism.
TL;DR: In this paper, the inner-sphere mechanism was proposed for electron transfer in aqueous solution of [CoII(EDTA)]2- (EDTA = ethylenediaminetetraacetate).
Abstract: The kinetics of oxidation of [CoII(EDTA)]2- (EDTA = ethylenediaminetetraacetate) by N-bromosuccinimide (NBS) in aqueous solution obey the equation: Rate = k2K3[CoII]T[NBS]/{1 + [H+]/K2 + K3[NBS]} where k2 is the rate constant for the electron-transfer process, K2 the equilibrium constant for the dissociation of [CoII(EDTAH)(H2O)]− to [CoII(EDTA)(OH)]3− and K3 the pre-equilibrium formation constant The activation parameters are reported It is proposed that electron transfer proceeds via an inner-sphere mechanism with the formation of an intermediate which slowly generates hexadentate[CoIII(EDTA)]−
TL;DR: In this paper, the electronic spectra of aqueous KVO3-H2O2-H3nta-HClO4(KOH) solutions (pH 1.45-5.62) and the thermal decomposition of K2[VO(nta)(O2)]· 2H 2O with active oxygen release at 275° C were investigated.
Abstract: M2[VO(nta)(O2)]·xH2O, where M+ is NH inf4 ♪p+ , K+ or Rb+ and nta is nitrilotriacetate, and Sr[VO(nta)(O2)]·2H2O were synthesized. The electronic spectra of aqueous KVO3-H2O2-H3nta-HClO4(KOH) solutions (pH 1.45–5.62) and the thermal decomposition of K2[VO(nta)(O2)]· 2H2O with active oxygen release at 275° C showed that the nta-monoperoxo complex is the most stable vanadium(V) peroxo complex so far investigated. The anhydrous potassium salt was prepared on heating the crystallohydrate under dynamic conditions. The i.r. spectra indicate the same anion structure in solution and in the solid state where nta is coordinated as a tetradentate ligand.
TL;DR: In this article, the analytical data show that tin(IV) forms only 1:1 metal complexes when reacted with HL1, HL3 and HL4, whereas it forms 1: 1 and 1: 2 metal complexes depending on the molar ratio.
Abstract: Tin(IV), titanium(IV) and hafnium(IV) chloride complexes of ligands such as salicylidene-4-aminoantipyrine (HL1), 5-chlorosalicylidene-4-aminoantipyrine (HL2), 2,4-dihydroxybenzylidene-4-aminoantipyrine (HL3), 2-hydroxy-1-naphthylidene-4-aminoantipyrine (HL4) and 2-hydroxyacetophenonylidene-4-aminoantipyrine (HL5) have been prepared and characterized. The analytical data show that tin(IV) forms only 1:1 metal complexes when reacted with HL1, HL3 and HL4, whereas it forms 1:1 and 1:2 metal complexes when reacted with HL2, depending on the molar ratio. HL5 produces only the binuclear complex SnHL5Cl4(H2O)SnCl4. Titanium(IV) gives only one type of complex of the general formula [Ti(HL)2Cl2]Cl2-2H2O, whilst hafnium(IV) gives HfHL3Cl4-4H2O and Hf(L5)2Cl2.
TL;DR: Rate constants for dissociation, in aqueous solution at 25° C, of [Fe(phen)3]2+, [Fe (bipy)3)2+, and [ Fe(4,4′-Me2bipY)3?]2+ in the presence of cyanide, and of the last-named complex also in the absence of hydroxide, are significantly decreased by the application of pressure.
Abstract: Rate constants for dissociation, in aqueous solution at 25° C, of [Fe(phen)3]2+, [Fe(bipy)3]2+, and [Fe(4,4′-Me2bipy)3]2+ in the presence of cyanide, and of the last-named complex also in the presence of hydroxide, are significantly decreased by the application of pressure (up to 1 kbar). Kinetic measurements were carried out using a high pressure cell of improved design to that used in our earlier investigations. Volumes of activation, ΔV*, are scarcely sensitive to ligand or to attacking nucleophile, being in the range of 10–12 cm3 mol−1. An explanation of these results resides in an associative mechanism, a scheme invoked for similar reactions reported previously.
TL;DR: In this article, transition metal (II) chloro complexes of the new Schiff base ligand 1,2-bis(2′-pyridylmethyleneimino)benzene (L), derived from 2-Pyridinecarboxaldehyde and 1, 2-phenylenediamine, were prepared.
Abstract: Transition metal(II) chloro complexes of the new Schiff base ligand 1,2-bis(2′-pyridylmethyleneimino)benzene (L), derived from 2-pyridinecarboxaldehyde and 1,2-phenylenediamine, were prepared. Compounds of [MnLCl2]-H2O, [CoLCl2]·2H2O, [NiLCl2] and [Zn3L2Cl4]Cl2 were prepared. Details are given of the formation of the complex [Cu(L·EtOH)Cl2], in which one molecule of EtOH adds across only one of the Schiff base {ie531-01} groups to give the coordinated ligand L·EtOH. The rationalization of this type of reaction by considering the steric requirements of the ligand is given. The complexes were characterized by elemental analyses, conductivity measurements, thermal techniques, mass spectra, magnetic susceptibilities and spectroscopic (i.r., ligand field, e.s.r., 1H n.m.r.) studies. The nitrogen donor atoms of the tetradentate ligands L and L·EtOH are assumed to adopt an essentially planar arrangement about manganese(II), cobalt(II), nickel(II) and copper(II), with the remaining axial coordination sites occupied by chloro ligands to yield high-spin octahedral molecules. A trinuclear structure, based on tetrahedrally coordinated metal ions, is proposed for the zinc(II) complex.
TL;DR: In this paper, a cis-[Co(phen)2-Cl2] Cl·3H2O (phen = phenanthroline) with L-proline at pH 9, isolated by chromatography using an SP-Sephadex C-25 H+ form column, and characterized by elemental analysis, spectroscopy and thermogravimetry.
Abstract: The complex was prepared by reaction of cis-[Co(phen)2-Cl2] Cl·3H2O (phen = phenanthroline) with L-proline at pH 9, isolated by chromatography using an SP-Sephadex C-25 H+ form column, and characterized by elemental analysis, spectroscopy and thermogravimetry. The X-ray crystal structure has also been determined. There are 1.5 independent complex cations, 1.5 ClOinf4sup−anions and two H2O molecules in each asymmetric unit, and two complex cations of similar structure in the crystal. There is a crystallographic C2 symmetry in the first of these. In the octahedral coordination sphere of the metal the oxygen and nitrogen chelating prolinato ligands are arranged in the trans-N,N form.
TL;DR: A series of new PtII and PdII complexes of N,N′-disubstituted thiourea derivatives of general formulae [MLCl2]2, [ML2Cl2], and [ML4]Cl2 have been prepared and characterised by physicochemical and spectroscopic methods as mentioned in this paper.
Abstract: A series of new PtII and PdII complexes of N,N′-disubstituted thiourea derivatives of general formulae [MLCl2]2, [ML2Cl2] and [ML4]Cl2 have been prepared and characterised by physicochemical and spectroscopic methods. The reaction of these ligands with [M(DMSO)2Cl2], M = Pt, cis- or Pd, trans-, in CHCl3 and EtOH at ambient temperature or under reflux, is described.
TL;DR: Aquocomplexes of copper-II and nickel-II involving (H2NCH2)2, H2CH2CO2CH3·HCl (GE), (HO)C6H4CH2-(NH2)CO2H5·Cl (CE), HSCH2CH(NH2),CO2C2H3·Cl(CysE), and [SCH2H(NH 2]2]2·2HCl 2]
Abstract: Aquocomplexes of copper(II) and nickel(II) involving (H2NCH2)2, H2NCH2CH2NHCH2CH2NH2 and H2NCH2CH2NHCH2CH2NHCH2CH2NH2 as ligands were prepared and characterised. Using a pH-stat method, the kinetics of the base hydrolysis of amino acid esters such as H2NCH2CO2CH3·HCl (GE), (HO)C6H4CH2-(NH2)CO2CH3·HCl (TE), CH3S(CH2)2CH(NH2)CO2CH3· HCl (ME), HSCH2CH(NH2)CO2C2H5·HCl (CE), \({\text{CH}}_{\text{2}} {\text{CH(NH}}_{\text{2}} ){\text{CO}}_{\text{2}} {\text{CH}}_{\text{3}} \cdot 2{\text{HCI (HE)}}\)(HE) and [—SCH2CH(NH2)CO2CH3]2·2HCl (CysE) was studied. These complexes substantially enhance the rate of hydrolysis, the values of the second-order rate constants being some 10–30 times greater than those obtained in the presence of simple metal ions.
TL;DR: In this article, the authors obtained a first crop from a 95% ethanolic solution of CuCl2 and 5,5′-6,6′-tetrahydro-2,2′-bi-4H-1, 3-thiazine-N6763,N3′)copper(II).
Abstract: The monomer in the title was obtained as a first crop and the dimer as a second crop from a 95% ethanolic solution of CuCl2 and 5,5′-6,6′-tetrahydro-2,2′-bi-4H-1,3-thiazine (2,2′-bi-2-thiazine) in the mole ratio 1∶1.1. The monomeric crystals are blue, dichloro(5,5′-6,6′-tetrahydro-2,2′-bi-4H-1, 3-thiazine- N
3,N
3′)copper(II). The crystal consists of monomeric molecules with no short contacts to neighbouring molecules. The Cu atoms occupy special positions on 2-fold axes. The bidentate 2,2′-bi-2-thiazine bonds via N as it assumes a cis configuration with a twist of 10.3° about the inter-ring C—C bond. The Cu—N distance is 2.013(5) A, and Cu—Cl is 2.231(2) A. Coordination around Cu is slightly distorted square planar with a dihedral angle of 5.8(2)° between the Cu, N, Cl plane and Cu, N′, Cl′ plane. The dimeric crystals are green, di-μ-chloro-bis[chloro(5,5′-6,6′-tetrahydro-2,2′-bi-4H-1, 3-thiazine-N
3,N
3′)copper(II)]. The structure consists of discrete centrosymmetric dimers [CuCl2(C8H12N2S2)]2. Coordination around Cu is distorted square pyramidal (τ = 0.32) with two N atoms from the bidentate 2,2′-bi-2-thiazine occupying adjacent basal sites, and two Cl atoms occupying the other two basal sites. The average Cu—N distance is 2.028(4) A, Cu—Cl(1) is 2.284(2) A, Cu—Cl(2) is 2.239(1) A. Dihedral angle between the CuN2 and CuCl2 planes is 23.7°. Cl(1)′ of the adjacent inversion-related monomer, CuCl2-(C8H12N2S2), occupies the apical position. Cu—Cl(1)′, r = 2.618(2) A. Dimensions in the chloride-bridged planar dimeric moiety, Cu2Cl2, are Cu ⋯ Cu′ 3.449(1) A; Cl(1) ⋯ Cl(1)′ 3.498(2) A; Cu—Cl(1)—Cu′, φ = 89.2(1)°, φ/r = 34.07°/A. The two saturated rings in C8H12N2S2 show a twist of 11.4° about the inter-ring C—C bond.
TL;DR: In this article, the kinetics of the solvolysis of complex ions trans-[Co(Rpy)4Cl2]+, with R = 4-t-Bu, 3-Me and 3-Et, have been investigated in mixtures formed by adding urea to water, which enhances the dielectric constant and decreases solvent structure.
Abstract: The kinetics of the solvolysis of complex ions trans-[Co(Rpy)4Cl2]+, with R = 4-t-Bu, 3-Me and 3-Et, have been investigated in mixtures formed by adding urea to water, which enhances the dielectric constant and decreases solvent structure. Differential effects of the changes in solvent structure on the initial and transition states are found to be important factors controlling changes in the rate constant with solvent composition. The variation of the enthalpy and the entropy of activation with solvent composition are contrasted with their variations found for the solvolysis of [Co(Rpy)4Cl2]+ in mixtures where solvent structure is enhanced by additions of a co-solvent to water. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the Co3+ cation in the transition state is more stable than the Co3+ cation in the initial state in the water + urea mixtures.