Coordination Sphere Of Cobalt Research Articles

Synthesis, properties and molecular structures of iron(III), cobalt(II), nickel(II), copper(II), copper(I) and zinc(II) complexes with N,N-bis(pyrazol-1-ylmethyl)benzylamine

A newly prepared ligand, N,N-bis(pyrazol-1-ylmethyl)benzylamine (L) reacted with metal ions to form [FeLCl3], [NiL(NCS)2(MeOH)], [MLX2](M = CoII, CuII or ZnII, X = Cl–, Br– or NCS–) and [(CuLI)2]. The crystallographically determined structures of [CoLCl2] and [CoL(NCS)2] reveal the co-ordination sphere of cobalt(II) to be intermediate between distorted tetrahedral and trigonal bipyramidal. In [NiL(NCS)2(MeOH)] the co-ordination sphere of nickel(II) ion is distorted octahedral while that of copper(II) in [CuLCl2] is distorted square pyramidal. The complex [(CuLI)2] displays distorted tetrahedral geometry around copper(I), and [ZnLBr2] shows distorted tetrahedral geometry around zinc(II).

{Tris[N-(salicylidene)-2-aminoethyl]amine}cobalt(III) acetonitrile hemihydrate

The slightly distorted octahedral coordination sphere of cobalt in {2,2',2″-[nitrilotris(ethylenenitrilomethylidyne-κN)] triphenolato-κ 3 O}cobalt (III) acetonitrile hemihydrate, [Co(C 27 H 27 N 4 O 3 ) . CH 3 CN . O.5H 2 O, is formed from three N and three O atoms which are in a fac arrangement. The chelate rings formed by the salicyliden-imine moieties are almost planar [maximum deviation of the Co atom from a least-squares plane calculated for the atoms of a salicylideneimine moiety is 0.101 (4) A]. Average bond lengths are 1.893 (3) A for Co−O and 1.947 (4) A dor Co−N

Cyclodimerisation and addition reactions of Bu tCP at a cobalt(I) centre

Syntheses and characterisation of [Co(η 5-C 5Me 4CH 2CH 2CHCH 2)(η 4-C 2Bu t 2P 2)] and [Co 2(η 5-C 5Me 4CH 2CH 2CHCH 2) 2(CO)(COPCBu t)] are reported. The former has been prepared by four different routes, resulting from cyclodimerisation of Bu tCP within the coordination sphere of cobalt(I) and the mechanistic pathway for its formation is discussed. The latter results from addition of Bu tCP to the CoCo double bond of [Co 2(η 5-C 5Me 4CH 2CH 2CHCH 2) 2(CO) 2]. Both complexes have been characterised by 31P{ 1H}, 13C{ 1H}, 1H NMR and mass spectroscopic studies.

Reactivity of trialkylphosphine oxide complexes of divalent cobalt, nickel, copper and zinc with sulfur dioxide. Reversible co-ordination of SO2 in ligand-bound adducts

Bis(trialkylphosphine oxide) complexes, [M(OPPrn3)2Br2](M = Co, Ni, Cu or Zn) and [M(OPEt3)2X2](M = Co, X = I; M = Zn, X = Br), have been synthesised. Magnetic susceptibility measurements have been made (M = Co, Cu or Ni), and electronic (M = Cu or Co), 31P-{1H} NMR (M = Zn), and infrared spectra (all complexes) have been recorded. Characterisation strongly supports the hypothesis that the complexes are pseudo-tetrahedral, with significant distortion in the case of copper. On exposure to SO2 all the complexes display mass increases commensurate with the absorption of 2 equivalents of SO2. During this process solid complexes become liquid, whilst oils appear visibly less viscous. The co-ordination of SO2 is easily reversed in a flow of dinitrogen or at reduced pressures and the original complexes are recovered without apparent decomposition. These properties, along with the infrared absorptions observed for co-ordinated SO2, are indicative of the formation of ligand-bound adducts, [M{O(SO2)PR3}2X2]. The equilibrium between free and co-ordinated SO2 has been examined for the complex [Zn(OPEt3)2Br2] using thermogravimetric analysis; Keqm= 3.96 atm–2(295 K), ΔH=–26.1 kJ mol–1 per binding site, whilst a Hill plot indicates no significant co-operativity between the co-ordination sites. Several complexes and their sulfur dioxide adducts were investigated by visible (M = Cu or Co), ESR (M = Cu) and 31P-{1H} NMR (M = Zn) spectroscopy. Visible spectroscopy indicates that little change occurs in the cobalt co-ordination sphere as a result of binding of SO2, but [Cu(OPPrn3)3Br2] appears to change ground state and possibly geometry on co-ordination. The ESR spectra indicate that changes do occur in the metal environment for [Cu(OPPrn3)2Br2], but fail to provide detailed information. The 31P-{1H} NMR spectra for [Zn(OPR3)2Br2](R = Et, Prn, Bun or C8H17) and their adducts, surprisingly, show small negative (upfield) shifts on co-ordination of SO2. Since the effect is opposite to that observed when SO2 binds to free OPR3 ligands, it is suggested that the net deshielding caused by zinc(II) and SO2 in the [Zn{O(SO2)PR3}2Br2] complexes is comparable to that of zinc(II) alone in the [Zn(OPR3)2Br2] precursors, and thus that significant competition occurs between the two Lewis–acid species in the [Zn{O(SO2)PR3}2Br2] complexes.

PH-dependent properties of cobalt(II) carboxypeptidase A-inhibitor complexes.

1H NMR spectroscopy of the isotropically shifted signals in cobalt carboxypeptidase, CoCPD, permits a direct and selective detection of protons belonging to the residues liganded to the metal. The chemical shift of these protons in the free enzyme and enzyme-inhibitor complexes with changing pH monitors the state of ionization of the ligands directly and of other residues in the active center indirectly. The 1H NMR spectrum of CoCPD at pH 6 shows three well-resolved isotropically shifted signals in the downfield region at 62 (a), 52 (c), and 45 (d) ppm which have been assigned to the NH proton of His-69 and to the C-4 H's of His-69 and His-196, respectively. Titration of signal a with pH is characterized by a pKa of 8.8 which is identical to that seen in prior electronic absorption and kinetic studies. The fact that the signal reflecting the NH of His-69 is still observed at pH 10 and no major shifts occur for the signals reflecting the C-4 H's indicates the alkaline pKa in carboxypeptidase A catalysis, pKEH, cannot be ascribed to ionization of the histidyl NH of either His-69 or His-196. Binding of L-Phe shifts this pKa to 7.7 while not greatly perturbing the downfield 1H NMR signals that reflect the ligation shell of the cobalt coordination sphere. These results indicate the pKa of 8.8 in CoCPD and the pKa of 7.7 in the CoCPD.L-Phe adduct reflect ionization of the same group.(ABSTRACT TRUNCATED AT 250 WORDS)

Heteronuclear NMR studies of Cobalamins. 10. Nitrogen-15 NMR studies of [15N]cyanocobalt corrins

15 N NMR chemical shifts and 13 N- 13 C coupling constants have been determined for cyanocobalamin (CNCbl) and several other monocyano and dicyanocobalt corrins enriched in 15 N or in 15 N and 13 C in the axial cyanide ligand(s). The 15 N chemical shift is found to be nearly as sensitive (ca. 75%) to changes in trans axial ligation as the 13 C chemical shift of 13 CN cyanocobalt corrins. All alterations in the cobalt coordination sphere have opposite effects on the 13 C and 15 N chemical shifts; i.e. there is a strictly inverse relationship between δ 15N and δ 13C

A spectroscopic investigation of cobalt(II) substituted alkaline phosphatase

The electronic and 1H NMR spectra are reported for the cobalt(II) alkaline phosphatase (EC 3.1.3.1.) system at pH around 6 in the range 0–2 mol of cobalt per mol protein. It is shown that under the present experimental conditions cobalt(II) selectively populates the A sites. Three isotropically shifted NH signals have been detected in the A site that indicate the presence of three histidines in the coordination sphere of cobalt(II). The electronic spectra and the nuclear relaxation properties are consistent with pentacoordination of cobalt(II) in the A site. The finding of reproducible preparation routes for the derivatives, and of appropriate experimental conditions for the observation of their 1H NMR spectra, open new possibilities for the spectroscopic investigation of alkaline phosphatase.

ChemInform Abstract: BASE HYDROLYSIS OF AMINO‐ACID ESTERS AND AMIDES IN THE COORDINATION SPHERE OF COBALT(III). PART 3. HYDROLYSIS OF METHYL AND ETHYL 4‐AMINOBUTANOATE

Chemischer InformationsdienstVolume 9, Issue 51 Organoelement Compounds ChemInform Abstract: BASE HYDROLYSIS OF AMINO-ACID ESTERS AND AMIDES IN THE COORDINATION SPHERE OF COBALT(III). PART 3. HYDROLYSIS OF METHYL AND ETHYL 4-AMINOBUTANOATE R. W. HAY, R. W. HAYSearch for more papers by this authorR. BENNETT, R. BENNETTSearch for more papers by this authorD. P. PIPLANI, D. P. PIPLANISearch for more papers by this author R. W. HAY, R. W. HAYSearch for more papers by this authorR. BENNETT, R. BENNETTSearch for more papers by this authorD. P. PIPLANI, D. P. PIPLANISearch for more papers by this author First published: December 19, 1978 https://doi.org/10.1002/chin.197851305Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume9, Issue51December 19, 1978 RelatedInformation

Base hydrolysis of amino-acid esters and amides in the co-ordination sphere of cobalt(III). Part 3. Hydrolysis of methyl and ethyl 4-amino-butanoate

The base hydrolysis of cis-[CoCl(en)2{NH2(CH2)3CO2Me}]2+(en = ethylenediamine) has been studied by pH-stat and stopped-flow spectrophotometry at 25 °C and l= 0.1 mol dm–3. Two consecutive reactions are observed in the pH-state measurements. Following loss of Cl–(kOHCl 15.2 dm3 mol–1 s–1) a slower base hydrolysis of the ester function occurs (kOH 0.72 dm3 mol–1 s–1). In the pH-stat measurements 2 mol of base are consumed per mol of complex and the final product of the reaction is the penta-amine hydroxo-complex which has been identified by visible spectra and potentiometric titration. In the stopped-flow measurements a single kinetic process is observed spectrophotometrically corresponding to chloride hydrolysis (kOHCl 15.6 dm3 mol–1 s–1). For the analogous cis-[CoBr(en)2{NH2(CH2)3CO2Me}]2+, kOHBr= 125 ± 3 dm3 mol–1 s–1 and kOHBr: kOHCl= 8 : 1. Complete base hydrolysis of the complex cis-[CoCl(en)2{NH2(CH2)3CO2}]+ containing the N-co-ordinated amino-acid requires 1 mol of base (kOHCl 10.4 dm3 mol–1 s–1 determined by pH-stat; kOHCl 9.83 dm3 mol–1 s–1 determined spectro-photometrically at l= 0.1 mol dm–1 and 25 °C). For the unprotonated ester NH2(CH2)3CO2Me, lactamisation to give 2-pyrrolidinone competes with base hydrolysis, but kOH for ester hydrolysis is ca. 0.1 dm3 mol–1 s–1 at 25 °C. Thus a small enhancement (ca. 7.2 times) occurs for hydrolysis of the N-co-ordinated ester.

Synthesis of perchloratocobaltates (II) of cesium, rubidium, and ammonium

1. The authors have investigated the reaction of cobalt(II) chloride and its complex chlorides with anhydrous perchloric acid and with solutions of ionic perchlorates in perchloric acid. The rate of replacement of chloride by perchlorate in the coordination sphere of cobalt depends on the composition of the initial chloride, the extrasphere cation, and the presence of ClO 4 − ions in the solution. 2. They have developed the synthesis conditions for three new cobalt complexes of the composition MCo(ClO4)3 (M is Cs, Rb, or NH4) with bidentate perchlorato groups, and have isolated and characterized them.

ChemInform Abstract: PREPARATION AND CRYSTAL STRUCTURE OF TRANS‐CARBONYLHYDRIDOTRIS(TRIPHENYLPHOSPHINE)COBALT(I)‐ A QUANTITATIVE ASSESSMENT OF TRIGONAL BIPYRAMIDAL GEOMETRY

AbstractDie Titelverbindung wurde mit 80% Ausbeute durch Carbonylierung von Trihydrido‐tris‐ [triphenylphosphin]‐kobalt(III) dargestellt.

Preparation and crystal structure of trans-carbonylhydridotris(triphenylphosphine)cobalt(I): a quantitative assessment of trigonal bipyramidal geometry

trans-Carbonylhydridotris(triphenylphosphine)cobalt(I) has been prepared in 80% yield via carbonylation of [CoH3(PPh3)3]. [Co(CO)H(PPh3)3] is monoclinic, space group P21/c, with four molecules per unit cell, dimensions a= 17.07(1), b= 11.41(1). c= 25.04(2)A, β= 107.41(7)°. Its crystal structure has been refined by rigid-body full-matrix isotropic-anisotropic least squares on 1 900 independent counter data to a final R′ of 0.038 and R of 0.087. The molecule is a distorted trigonal bipyramid with the hydride and carbonyl ligands in axial positions. Bond lengths in the cobalt co-ordination sphere are: Co–H = 1.41(9). Co–C = 1.70(2), Co–P(av.)= 2.188(8)A. A new quantitive measure of distortion from trigonal bipyramidal geometry is introduced : the half-open cone angle in [Co(CO)H(PPh3)3] is 81.6° and the exterior bond-cone axis angle is 1.5°.

Base hydrolysis of amino-acid esters and amides in the co-ordination sphere of cobalt(III). Part II. Hydrolysis of 2-aminoethyl acetate

Base hydrolysis of the complex cis-[Co(en)2X(NH2CH2CH2OCOMe)]2+(en = ethylenediamine; X = Cl or Br) has been studied by pH-stat and spectrophotometry at 25 °C and I= 0·1M. Two consecutive reactions occur in basic media. Following loss of halide ion (kOHCl= 1·38 × 103, kOHBr= 8·7 × 103|mol–1 min–1), slower base hydrolysis of the ester function occurs (kOHester= 1·44 × 102|mol–1 min–1). Initial base hydrolysis of halide ion is consistent with the observations that (a) rate constants for the slow hydrolysis steps in the bromo- and chloro-complexes are identical, within experimental error, and (b) a single rate process is observed spectrophotometrically with kOH= 1·42 × 102|mol–1 min–1. In the pH-stat measurements 2 mol of base are consumed per mol of complex and the final product of the reaction is the penta-aminohydroxo-complex which has been identified by visible spectra and potentiometric titration. The pKap value for ionisation (i) is 6·1 at 25 °C and I= 0·1M. [Co(en)2OH2(NH2CH2CH2OH)]3+⇌[Co(en)2OH(NH2CH2CH2OH)]2++ H+(i) Hydrolysis of the complex cis-[Co(en)2Cl(NH2CH2CH2OCOMe)]2+ in ca. 6M-hydrochloric acid gives the corresponding penta-aminechloro-complex of 2-aminoethanol. Base hydrolysis of the penta-aminechloro-complex. containing N-co-ordinated 2-aminoethanol requires 1 mol of base for complete hydrolysis (kOH= 1·23 × 103|mol–1 min–1 by pH-stat and spectrophotometry at 25 °C and I= 0·1M). It is estimated that base hydrolysis of 2-aminoethyl acetate in the dipositive cobalt(III) complex is some 18 times faster than that for the free ligand and some 2 times faster than that for the protonated ligand. Mercury(II)-catalysed aquations of the complex cis-[Co(en)2Cl(NH2CH2CH2OCOMe)]2+ and the corresponding 2-aminoethanol derivative have also been studied. The reactions follow a rate law, rate =k[HgII][Complex] in 0·57M-HClO4. There is evidence for neighbouring-group participation (NGP–5OH) in aquation of the 2-aminoethanol derivative.

Base hydrolysis of amino-acid esters and amides in the co-ordination sphere of cobalt(III). Part I. Hydrolysis of methyl 6-aminohexanoate

The base hydrolysis of cis-{Co(en)2Cl[NH2(CH2)5CO2Me]}2+ has been studied by pH-stat and stopped-flow spectrophotometric techniques at 25 °C and I= 0·1M. Two consecutive reactions occur in base. Following loss of Cl–(kOH= 12·8 l mol–1 s–1 by pH-stat, kOH= 13·6 ± 1 l mol–1 s–1 by stopped flow), a slower base hydrolysis of the ester function occurs (KOH= 0·22 l mol–1 s–1). In the pH-stat measurements 2 moles of base are consumed per mole of complex and the final product of the reaction is the hydroxypenta-ammine which has been identified by visible spectra and potentiometric titration. Base hydrolysis of the complex cis-{Co(en)2Cl[NH2(CH2)5CO2]}+ containing the N-co-ordinated amino-acid requires 1 mole of base for complete hydrolysis (kOH= 9·5 l mol–1 s–1 for loss of chloride by pH-stat, kOH= 9·2 l mol–1 s–1 determined spectrophotometrically in borax buffers at l= 0·1 M and 25 °C). For base hydrolysis of the unprotonated form of the free ester, NH2(CH2)5CO2Me + OH–→ NH2(CH2)5CO2–+ MeOH in the pH range 11·0–11·5 the value of kOH= 0·148 l mol–1 s–1. Thus a slight rate enhancement (ca. 1·5 times) occurs for hydrolysis of the N-co-ordinated ester. Such an effect is understandable owing to the length of the alkyl chain separating the cobalt(III) centre from the ester function. The present results establish a further hydrolytic pathway for N-co-ordinated amino-esters in halogenopenta-ammine complexes of cobalt(III), quite different from the reactions of glycine esters where intramolecular pathways occur.

The formation of peptide bonds in the coordination sphere of cobalt(3).

The formation of peptide bonds in the coordination sphere of cobalt(3).

Comparative absorption of vitamin B12 analogues by normal humans. II. Chloro-, sulfato-, nitro- and thiocyanato- vs. cyanocobalamin.

Summary1. Urinary excretion measurements indicate considerably lower oral absorption of sulfato-, nitro- and thiocyanato-cobalamin than is exhibited by cyanoeobalamin. In the blood stream, however, the several cobalamins are equivalent in inducing the excretion of ingested vit. B12. 2. That cobalamin urinary excretion responses truly constitute an absorption index was verified in studies comparing chlorocobalamin with cyanocobalamin, by serum level assays in humans and by fecal excretion experiments with rats. 3. Inferior absorption of orally administered nitrocobalamin was confirmed by fecal excretion observations in humans and rats. 4. The superior absorption of cyanocobalamin (vit. B12) over other cobalamins studied is attributed to either the chemical specificity of the substituent cyano group or the tightness of its binding in the cobalt coordination sphere.