M. Mylonas, A. Krężel, J. Plakatouras, N. Hadjiliadis, W. Bal
The coordination properties of Ni(II) ions towards the terminally blocked (CH3CONH- and -CONH2) hexapeptides -TESHHK-, -TASHHK-, -TEAHHK-, -TESAHK- and -TESHAK- were studied by using potentiometric and spectroscopic techniques (UV/Vis, CD, NMR). The peptides were chosen in such a way as to compare the effect of Glu, Ser and His residues on the stability, the coordination and hydrolytic abilities of the complexes formed. All peptides bind to Ni(II) ions initially through one or two imidazole nitrogens in weakly acidic and neutral solutions forming slightly distorted octahedral complexes. At higher pH values, a series of square-planar complexes are formed, where Ni(II) ions bind simultaneously through an imidazole and three amide nitrogens in an equatorial plane. This proposed conformation includes the participation of only one imidazole nitrogen, in the case of all peptides, in the coordination sphere of Ni(II) ions. In basic solutions, the peptides -TASHHK- and -TESAHK- were hydrolyzed in a Ni(II)-assisted fashion. No hydrolytic processes were noticed in peptides -TEAHHK- and -TESHAK- where the Ser or His-5 residues are replaced with the Ala residue. The Ni(II)-assisted hydrolysis of the analogues of -TESHHK- may provide an insight into the novel mechanism of genotoxicity, combining the damage to the nucleosome with the generation of further toxic Ni(II) species.
{"title":"The binding of Ni(II) ions to terminally blocked hexapeptides derived from the metal binding -ESHH- motif of histone H2A","authors":"M. Mylonas, A. Krężel, J. Plakatouras, N. Hadjiliadis, W. Bal","doi":"10.1039/B206585A","DOIUrl":"https://doi.org/10.1039/B206585A","url":null,"abstract":"The coordination properties of Ni(II) ions towards the terminally blocked (CH3CONH- and -CONH2) hexapeptides -TESHHK-, -TASHHK-, -TEAHHK-, -TESAHK- and -TESHAK- were studied by using potentiometric and spectroscopic techniques (UV/Vis, CD, NMR). The peptides were chosen in such a way as to compare the effect of Glu, Ser and His residues on the stability, the coordination and hydrolytic abilities of the complexes formed. All peptides bind to Ni(II) ions initially through one or two imidazole nitrogens in weakly acidic and neutral solutions forming slightly distorted octahedral complexes. At higher pH values, a series of square-planar complexes are formed, where Ni(II) ions bind simultaneously through an imidazole and three amide nitrogens in an equatorial plane. This proposed conformation includes the participation of only one imidazole nitrogen, in the case of all peptides, in the coordination sphere of Ni(II) ions. In basic solutions, the peptides -TASHHK- and -TESAHK- were hydrolyzed in a Ni(II)-assisted fashion. No hydrolytic processes were noticed in peptides -TEAHHK- and -TESHAK- where the Ser or His-5 residues are replaced with the Ala residue. The Ni(II)-assisted hydrolysis of the analogues of -TESHHK- may provide an insight into the novel mechanism of genotoxicity, combining the damage to the nucleosome with the generation of further toxic Ni(II) species.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"59 1","pages":"4296-4306"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78457588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The complex formation equilibria for the nickel(II)-bromide and -iodide systems in dimethyl sulfoxide and the bromide system in N,N′-dimethylpropyleneurea have been studied calorimetrically and spectrophotometrically at 298 K. An ionic strength of 0.1 mol dm−3 was kept constant using tetrabutylammonium perchlorate as supporting electrolyte. Two stable mononuclear bromo-complexes are formed in dilute N,N′-dimethylpropyleneurea solution with β1 = (2.0 ± 0.4) × 103 mol−1 dm3 and β2 = (7.2 ± 1.5) × 105 mol−2 dm6, whereas nickel(II) does not form any measurable complexes with bromide and iodide ions in dimethyl sulfoxide solution. The structures of the solids precipitating from concentrated solutions of nickel(II)-bromide and -chloride in the respective solvents have been determined by X-ray diffraction. The solid precipitating from a concentrated N,N′-dimethylpropyleneurea solution of nickel(II) bromide is a stable pseudotetrahedral bis(N,N′-dimethylpropyleneurea)dibromonickel(II) complex. Precipitation of nickel(II) chloride from a dimethyl sulfoxide solution results in hexakis(dimethyl sulfoxide)nickel(II) tetrachloronickelate(II), which is gradually transformed to hexakis(dimethyl sulfoxide)nickel(II) chloride, the most enthalpy stabilised complex. Hexakis(dimethyl sulfoxide)nickel(II) bromide precipitates from a concentrated dimethyl sulfoxide solution of nickel(II) bromide.
{"title":"Reactivity of five- and six-coordinated solvates. A complex formation and crystallographic study of the nickel(II) bromide and iodide systems in dimethyl sulfoxide and N,N′-dimethylpropyleneurea","authors":"Dorota Bobicz, O. Kristiansson, I. Persson","doi":"10.1039/B204128F","DOIUrl":"https://doi.org/10.1039/B204128F","url":null,"abstract":"The complex formation equilibria for the nickel(II)-bromide and -iodide systems in dimethyl sulfoxide and the bromide system in N,N′-dimethylpropyleneurea have been studied calorimetrically and spectrophotometrically at 298 K. An ionic strength of 0.1 mol dm−3 was kept constant using tetrabutylammonium perchlorate as supporting electrolyte. Two stable mononuclear bromo-complexes are formed in dilute N,N′-dimethylpropyleneurea solution with β1 \u0000= \u0000(2.0 ± 0.4) \u0000× 103 mol−1 dm3 and β2 \u0000= \u0000(7.2 ± 1.5) \u0000× 105 mol−2 dm6, whereas nickel(II) does not form any measurable complexes with bromide and iodide ions in dimethyl sulfoxide solution. The structures of the solids precipitating from concentrated solutions of nickel(II)-bromide and -chloride in the respective solvents have been determined by X-ray diffraction. The solid precipitating from a concentrated N,N′-dimethylpropyleneurea solution of nickel(II) bromide is a stable pseudotetrahedral bis(N,N′-dimethylpropyleneurea)dibromonickel(II) complex. Precipitation of nickel(II) chloride from a dimethyl sulfoxide solution results in hexakis(dimethyl sulfoxide)nickel(II) tetrachloronickelate(II), which is gradually transformed to hexakis(dimethyl sulfoxide)nickel(II) chloride, the most enthalpy stabilised complex. Hexakis(dimethyl sulfoxide)nickel(II) bromide precipitates from a concentrated dimethyl sulfoxide solution of nickel(II) bromide.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"458 1","pages":"4201-4205"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83029898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Susana Martín, M. Barandika, J. M. Ezpeleta, R. Cortés, J. D. Larramendi, L. Lezama, T. Rojo
The combined use of bipy (4,4′-bipyridine) and dca (dicyanamide) has led to the preparation of two polymeric compounds of formulae [Fe(dca)2bipy(H2O)]·1/2H2O (1) and [Ni(dca)2bipy] (2). Both have been synthesised and characterised through IR and UV-Vis spectroscopies, thermal analysis, X-ray difracction and measurements of the molar magnetic susceptibility. Compound 1 is 1D and exhibits weak antiferromagnetic interactions. Compound 2 consists of two interpenetrated 3D networks giving rise to weak ferromagnetic interactions. The formation of both types of structure can be related to the different Pearson acidities of FeII and NiII ions.
{"title":"Structural analysis and magnetic properties of the 1D [Fe(dca)2bipy(H2O)]·1/2H2O and the 3D [Ni(dca)2bipy] (dca = dicyanamide; bipy = 4,4′-bipyridine)","authors":"Susana Martín, M. Barandika, J. M. Ezpeleta, R. Cortés, J. D. Larramendi, L. Lezama, T. Rojo","doi":"10.1039/B206069H","DOIUrl":"https://doi.org/10.1039/B206069H","url":null,"abstract":"The combined use of bipy (4,4′-bipyridine) and dca (dicyanamide) has led to the preparation of two polymeric compounds of formulae [Fe(dca)2bipy(H2O)]·1/2H2O (1) and [Ni(dca)2bipy] \u0000(2). Both have been synthesised and characterised through IR and UV-Vis spectroscopies, thermal analysis, X-ray difracction and measurements of the molar magnetic susceptibility. Compound 1 is 1D and exhibits weak antiferromagnetic interactions. Compound 2 consists of two interpenetrated 3D networks giving rise to weak ferromagnetic interactions. The formation of both types of structure can be related to the different Pearson acidities of FeII and NiII ions.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"1 1","pages":"4275-4280"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90649753","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reaction between DADZnR2 and either B(C6F5)3 or ZnR2 and [DADH][B(C6F5)4] affords three-coordinate alkyl and amide zinc cations which are active for the ring opening polymerisation of epoxides and e-caprolactone [DAD = (MeCNC6H3Pri2-2,6)2].
{"title":"Synthesis and catalytic activity of three-coordinate zinc cations","authors":"Mark D. Hannant, M. Schormann, M. Bochmann","doi":"10.1039/B208165M","DOIUrl":"https://doi.org/10.1039/B208165M","url":null,"abstract":"Reaction between DADZnR2 and either B(C6F5)3 or ZnR2 and [DADH][B(C6F5)4] affords three-coordinate alkyl and amide zinc cations which are active for the ring opening polymerisation of epoxides and e-caprolactone [DAD = \u0000(MeCNC6H3Pri2-2,6)2].","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"1 1","pages":"4071-4073"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88621187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michael M. Bishop, L. Lindoy, D. J. Miller, Peter Turner
The syntheses of three new copper(II) complexes based on the bidentate ligand N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)ethanimidamide are reported. In the solid state these products assemble into elaborate supramolecular structures featuring hydrogen bonds within, and between, complexes as well as weak aryl–aryl and alkyl–aryl interactions between complexes; different coordination geometries and tautomeric forms are also observed. Dimethyl sulfoxide molecules show a variety of interactions within the structures, including coordination to the copper, hydrogen bonding, as well as weak alkyl–aryl interactions with the ligands.
{"title":"A comparative investigation of supramolecular structures involving copper(II) complexes of imidazolinylalkanimidamides","authors":"Michael M. Bishop, L. Lindoy, D. J. Miller, Peter Turner","doi":"10.1039/B207031F","DOIUrl":"https://doi.org/10.1039/B207031F","url":null,"abstract":"The syntheses of three new copper(II) complexes based on the bidentate ligand N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)ethanimidamide are reported. In the solid state these products assemble into elaborate supramolecular structures featuring hydrogen bonds within, and between, complexes as well as weak aryl–aryl and alkyl–aryl interactions between complexes; different coordination geometries and tautomeric forms are also observed. Dimethyl sulfoxide molecules show a variety of interactions within the structures, including coordination to the copper, hydrogen bonding, as well as weak alkyl–aryl interactions with the ligands.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"53 1","pages":"4128-4133"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73233110","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Garcia, Y. Xing, A. Paulo, A. Domingos, I. Santos
Reaction of an adequate borohydride salt with the functionalized mercaptoimidazoles timHMe,pip 1 or timHMe,CH2-pip 2 have led to Na[H2B(timMe,pip)2] 3, Na[H2B(timMe,CH2-pip)2] 4, Li[H(Ph)B(timMe)(timMe,pip)2] 6 and Li[H(Ph)B(timMe)(timMe,CH2-pip)2] 7 (timHMe = 1-methyl-2-mercaptoimidazole; timHMe,pip = 1-methyl-5-[(4-(2′-methoxyphenyl)-1-piperazinyl)carbonyl]-2-mercaptoimidazole; timHMe,CH2pip = 1-methyl-5-[(4-(2′-methoxyphenyl)-1-piperazinyl)methyl]-2-mercaptoimidazole). These symmetric and assymmetric functionalized bis(mercaptoimidazolyl)borates, carrying a piperazine fragment, react readily with (NEt)4[Re(CO)3Br3] giving [Re{κ3-H(μ-H)B(timMe,pip)2}(CO)3] 8, [Re{κ3-H(μ-H)B(timMe,CH2-pip)2}(CO)3] 9, [Re{κ3-Ph(μ-H)B(timMe)(timMe,pip)}(CO)3] 10 and [Re{κ3-Ph(μ-H)B(timMe)(timMe,CH2-pip)}(CO)3] 11. The organometallic complexes 8–11 are valuable models for the development of specific radiopharmaceuticals for imaging serotonergic CNS receptors. The new compounds (1–11) have been characterized by the usual analytical techniques (C, H, N analysis; IR and 1H NMR spectroscopies), and by X-ray diffraction analysis in the case of 8.
{"title":"Rhenium(I) tricarbonyl complexes with mercaptoimidazolylborate ligands bearing piperazine fragments","authors":"R. Garcia, Y. Xing, A. Paulo, A. Domingos, I. Santos","doi":"10.1039/B206603N","DOIUrl":"https://doi.org/10.1039/B206603N","url":null,"abstract":"Reaction of an adequate borohydride salt with the functionalized mercaptoimidazoles timHMe,pip 1 or timHMe,CH2-pip 2 have led to Na[H2B(timMe,pip)2] 3, Na[H2B(timMe,CH2-pip)2] 4, Li[H(Ph)B(timMe)(timMe,pip)2] 6 and Li[H(Ph)B(timMe)(timMe,CH2-pip)2] 7 \u0000(timHMe = 1-methyl-2-mercaptoimidazole; timHMe,pip = 1-methyl-5-[(4-(2′-methoxyphenyl)-1-piperazinyl)carbonyl]-2-mercaptoimidazole; timHMe,CH2pip = 1-methyl-5-[(4-(2′-methoxyphenyl)-1-piperazinyl)methyl]-2-mercaptoimidazole). These symmetric and assymmetric functionalized bis(mercaptoimidazolyl)borates, carrying a piperazine fragment, react readily with (NEt)4[Re(CO)3Br3] giving [Re{κ3-H(μ-H)B(timMe,pip)2}(CO)3] 8, [Re{κ3-H(μ-H)B(timMe,CH2-pip)2}(CO)3] 9, [Re{κ3-Ph(μ-H)B(timMe)(timMe,pip)}(CO)3] 10 and [Re{κ3-Ph(μ-H)B(timMe)(timMe,CH2-pip)}(CO)3] 11. The organometallic complexes 8–11 are valuable models for the development of specific radiopharmaceuticals for imaging serotonergic CNS receptors. The new compounds (1–11) have been characterized by the usual analytical techniques (C, H, N analysis; IR and 1H NMR spectroscopies), and by X-ray diffraction analysis in the case of 8.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"176 1","pages":"4236-4241"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79835116","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. M. Angus, R. J. Geue, N. B. Jensen, F. Larsen, C. Qin, A. Sargeson
The reaction of [Co(ten)]3+ {ten = 4,4′,4″-ethylidynetris(3-thiabutan-1-amine)} with methanal and base in acetonitrile or water led to the synthesis of an unusual pendant-arm macrocyclic complex, 8-(4′-ammonio-2′-thiabutyl)-8-methyl-1-oxa-6,10-dithia-3,13-diazacyclo-tetradecane(chloro)cobalt(III) triperchlorate trihydrate. The structure of the complex has been established by X-ray crystallographic analysis and such molecules can readily be tied to polymers and proteins. The synthesis, chemical reactions, spectroscopy and electrochemical properties of the macrocyclic complex are described.
{"title":"An unusual pendant-arm macrocycle formed by condensation of a cobalt(III) tripodal complex with methanal","authors":"P. M. Angus, R. J. Geue, N. B. Jensen, F. Larsen, C. Qin, A. Sargeson","doi":"10.1039/B205832D","DOIUrl":"https://doi.org/10.1039/B205832D","url":null,"abstract":"The reaction of [Co(ten)]3+ \u0000{ten = 4,4′,4″-ethylidynetris(3-thiabutan-1-amine)} with methanal and base in acetonitrile or water led to the synthesis of an unusual pendant-arm macrocyclic complex, 8-(4′-ammonio-2′-thiabutyl)-8-methyl-1-oxa-6,10-dithia-3,13-diazacyclo-tetradecane(chloro)cobalt(III) triperchlorate trihydrate. The structure of the complex has been established by X-ray crystallographic analysis and such molecules can readily be tied to polymers and proteins. The synthesis, chemical reactions, spectroscopy and electrochemical properties of the macrocyclic complex are described.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"45 1","pages":"4260-4263"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80008511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Bursten, M. Chisholm, M. Drummond, J. Gallucci, Carl B. Hollandsworth
Four equivalents of neopentanol, isopropanol, or t-butanol react with the cyclooctatetraene-bridged dimethylamide, W2(μ-η5,η5-COT)(NMe2)4, to give the corresponding tetraalkoxides, W2(μ-η5,η5-COT)(OR)4, in greater than 70% yields. The alkoxide W2(COT)(OCH2tBu)4 can be made alternatively by reacting W2(COT)(OtBu)4 with 4 equivalents of neopentanol. X-ray diffraction data for the t-butoxide compound indicate a μ-η5,η5-COT ligand spans a W–W bond of distance 2.3887(1) A. The t-butoxide is very similar in most structural parameters to the known W2(COT)(NMe2)4 precursor as well as the bis-allyl compound W2(allyl)2(NMe2)4. The COT ring is fluxional about the metal–metal fragment, undergoing rapid 1,2-shifts on the NMR timescale as determined by 1H EXSY NMR. The purple alkoxides exhibit maximum absorptions around 580 nm (e ∼ 1700 M−1 cm−1) in the visible region of the electronic absorption spectrum. This transition agrees well with DFT calculations on the model compound W2(μ-η5,η5-COT)(OH)4 that reveal the calculated HOMO–LUMO gap to be a 1.94 eV transition involving principally the metal d orbitals. The calculations also reveal the structure with an antifacial (η5,η5)-COT to be 13.7 kcal mol−1 more stable than the corresponding synfacial (η4,η4)-COT structure. In related studies, COT did not form adducts with W2(OCH2tBu)6(py)2, W2(OtBu)6, or W2(OCH2tBu)8 even upon heating to 80 °C for several hours.
{"title":"Cyclooctatetraene ditungsten alkoxides: W2(μ-η5,η5-COT)(OR)4, where R = CH2tBu, iPr, and tBu","authors":"B. Bursten, M. Chisholm, M. Drummond, J. Gallucci, Carl B. Hollandsworth","doi":"10.1039/B205130N","DOIUrl":"https://doi.org/10.1039/B205130N","url":null,"abstract":"Four equivalents of neopentanol, isopropanol, or t-butanol react with the cyclooctatetraene-bridged dimethylamide, W2(μ-η5,η5-COT)(NMe2)4, to give the corresponding tetraalkoxides, W2(μ-η5,η5-COT)(OR)4, in greater than 70% yields. The alkoxide W2(COT)(OCH2tBu)4 can be made alternatively by reacting W2(COT)(OtBu)4 with 4 equivalents of neopentanol. X-ray diffraction data for the t-butoxide compound indicate a μ-η5,η5-COT ligand spans a W–W bond of distance 2.3887(1) \u0000A. The t-butoxide is very similar in most structural parameters to the known W2(COT)(NMe2)4 precursor as well as the bis-allyl compound W2(allyl)2(NMe2)4. The COT ring is fluxional about the metal–metal fragment, undergoing rapid 1,2-shifts on the NMR timescale as determined by 1H EXSY NMR. The purple alkoxides exhibit maximum absorptions around 580 nm (e \u0000∼ 1700 M−1 cm−1) in the visible region of the electronic absorption spectrum. This transition agrees well with DFT calculations on the model compound W2(μ-η5,η5-COT)(OH)4 that reveal the calculated HOMO–LUMO gap to be a 1.94 eV transition involving principally the metal d orbitals. The calculations also reveal the structure with an antifacial (η5,η5)-COT to be 13.7 kcal mol−1 more stable than the corresponding synfacial (η4,η4)-COT structure. In related studies, COT did not form adducts with W2(OCH2tBu)6(py)2, W2(OtBu)6, or W2(OCH2tBu)8 even upon heating to 80 °C for several hours.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"1 1","pages":"4077-4083"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90173770","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sylvie L. Renard, C. Kilner, J. Fisher, M. Halcrow
Reaction of ZnCl2 with three molar equivalents of 3{5}-tert-butylpyrazole (HpztBu) yields [ZnCl(HpztBu)3]Cl (1). Treatment of 1 with an appropriate Ag(I) or Tl(I) salt gives [ZnCl(HpztBu)3]X (X− = BF4−, 4; X− = ClO4−, 5; X− = NO3−, 6; X− = CF3SO3−, 7; X− = PF6−, 8). Crystal structures of all of the complexes show a [ZnCl(HpztBu)3]+ cation, with (for 1 and 4-7) only small deviations from C3v symmetry, with the tert-butyl groups forming a bowl-shaped cavity on one face of the complex. The X− anion binds within this cavity, via hydrogen bonding to the three pyrazole N–H groups. For 8, the PF6− guest only interacts with two N–H donors, the third pyrazole ring being twisted away from the anion. We attribute this to steric repulsions between the third ligand and the PF6− anion, which is larger than the other guests used in this study. 1H, 13C and 19F NMR, ESMS and IR studies provide good circumstantial evidence for these structures being retained in solution, although the guest anions undergo rapid intermolecular exchange by NMR that cannot be frozen out above 190 K.
{"title":"Supramolecular anion binding by the [ZnCl(HpztBu)3]+ cation (HpztBu = 5-tert-butylpyrazole)","authors":"Sylvie L. Renard, C. Kilner, J. Fisher, M. Halcrow","doi":"10.1039/B207541P","DOIUrl":"https://doi.org/10.1039/B207541P","url":null,"abstract":"Reaction of ZnCl2 with three molar equivalents of 3{5}-tert-butylpyrazole (HpztBu) yields [ZnCl(HpztBu)3]Cl (1). Treatment of 1 with an appropriate Ag(I) or Tl(I) salt gives [ZnCl(HpztBu)3]X (X− \u0000= BF4−, 4; X− \u0000= ClO4−, 5; X− \u0000= NO3−, 6; X− \u0000= CF3SO3−, 7; X− \u0000= PF6−, 8). Crystal structures of all of the complexes show a [ZnCl(HpztBu)3]+ cation, with (for 1 and 4-7) only small deviations from C3v symmetry, with the tert-butyl groups forming a bowl-shaped cavity on one face of the complex. The X− anion binds within this cavity, via hydrogen bonding to the three pyrazole N–H groups. For 8, the PF6− guest only interacts with two N–H donors, the third pyrazole ring being twisted away from the anion. We attribute this to steric repulsions between the third ligand and the PF6− anion, which is larger than the other guests used in this study. 1H, 13C and 19F NMR, ESMS and IR studies provide good circumstantial evidence for these structures being retained in solution, although the guest anions undergo rapid intermolecular exchange by NMR that cannot be frozen out above 190 K.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"100 1","pages":"4206-4212"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73603556","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Complex formation in the binary and ternary uranium(VI)–glyphosate–fluoride systems was investigated with the aid of multinuclear NMR spectroscopy. The stoichiometry and the equilibrium constants of the different complexes in both systems are based on the integral values of the coordinated and free ligands in the 1H-, 19F-, 31P- and 17O-NMR spectra. These were measured at different uranium(VI) concentrations, varying the total ligand concentrations (glyphosate and/or fluoride) in the pH range of 7–10 using a NaClO4 medium at constant sodium concentration, [Na+] = 1.00 M. Tridentate and monodentate coordination has been found for the glyphosate ligand. The proposed structures are based on other spectral parameters (chemical shifts, homo- and heteronuclear couplings) and confirmed by two-dimensional homo- and heteronuclear correlation spectra. The spectra indicate the formation of several isomers for complexes 2 and 4, which differ from one another in the position of the non-chelated glyphosate. The numerical value of the stepwise stability constants for the non-chelated glyphosates in the binary complexes 4 (log K=12) and 5 (log K=11) falls between the formation constants for U(VI) with PO43− and HPO42−, that is an independent confirmation of the magnitude of the latter, but also a strong indication that complex formation with phosphate/phosphonate through a single oxygen bond is very strong. The line widths of the fluoride signals in the ternary complexes are independent of the free ligand concentrations, and from these similar external fluoride exchange rate, kobs1=10 ± 2 s−1 can be calculated as observed for other U(VI) ternary complexes. The exchange between the coordinated and the free glyphosate was studied by 1D 1H magnetization transfer experiments. From these an inter-molecular ligand exchange rate, kobs2= 0.69 ± 0.03 s−1, and a faster intra-molecular exchange rate for the methylene protons can also be calculated, kobs3 = 2.00 ± 0.21 s−1. The latter is probably a result of consecutive ring openings/chelate formation prior to the dissociation of the ligand.
{"title":"Structure, equilibrium and ligand exchange dynamics in the binary and ternary dioxouranium(VI)–glyphosate–fluoride system. A multinuclear NMR study","authors":"Z. Szabó","doi":"10.1039/B206175A","DOIUrl":"https://doi.org/10.1039/B206175A","url":null,"abstract":"Complex formation in the binary and ternary uranium(VI)–glyphosate–fluoride systems was investigated with the aid of multinuclear NMR spectroscopy. The stoichiometry and the equilibrium constants of the different complexes in both systems are based on the integral values of the coordinated and free ligands in the 1H-, 19F-, 31P- and 17O-NMR spectra. These were measured at different uranium(VI) concentrations, varying the total ligand concentrations (glyphosate and/or fluoride) in the pH range of 7–10 using a NaClO4 medium at constant sodium concentration, [Na+] \u0000= 1.00 M. Tridentate and monodentate coordination has been found for the glyphosate ligand. The proposed structures are based on other spectral parameters (chemical shifts, homo- and heteronuclear couplings) and confirmed by two-dimensional homo- and heteronuclear correlation spectra. The spectra indicate the formation of several isomers for complexes 2 and 4, which differ from one another in the position of the non-chelated glyphosate. The numerical value of the stepwise stability constants for the non-chelated glyphosates in the binary complexes 4 \u0000(log K=12) and 5 \u0000(log K=11) falls between the formation constants for U(VI) with PO43− and HPO42−, that is an independent confirmation of the magnitude of the latter, but also a strong indication that complex formation with phosphate/phosphonate through a single oxygen bond is very strong. The line widths of the fluoride signals in the ternary complexes are independent of the free ligand concentrations, and from these similar external fluoride exchange rate, kobs1=10 ± 2 s−1 can be calculated as observed for other U(VI) ternary complexes. The exchange between the coordinated and the free glyphosate was studied by 1D 1H magnetization transfer experiments. From these an inter-molecular ligand exchange rate, kobs2= 0.69 ± 0.03 s−1, and a faster intra-molecular exchange rate for the methylene protons can also be calculated, kobs3 \u0000= 2.00 ± 0.21 s−1. The latter is probably a result of consecutive ring openings/chelate formation prior to the dissociation of the ligand.","PeriodicalId":17317,"journal":{"name":"Journal of The Chemical Society-dalton Transactions","volume":"40 1","pages":"4242-4247"},"PeriodicalIF":0.0,"publicationDate":"2002-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76684680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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