N2S2 Coordination Research Articles

Zinc, Cadmium and Mercury Dithiocarboxylates: Synthesis, Characterization, Structure and Their Transformation to Metal Sulfide Nanoparticles

AbstractReactions of M(OAc)2·nH2O and M(OAc)2(tmeda) with dithiocarboxylic acids gave [M(S2CTol)2]n (1) (M = Zn or Cd; Tol = C6H4Me‐4) and [M(S2CAr)2(tmeda)] (3) (M = Zn, Cd, Hg; Ar = Ph or Tol), respectively, in high yields as deep‐colored crystalline solids. The former are soluble in pyridine to give pyridine adducts [M(S2CTol)2(py)] (2). These complexes were characterized by elemental analysis, UV/Vis and NMR (1H, 13C) spectroscopy. The absorptions in the electronic spectra have been assigned to ligand‐to‐ligand charge‐transfer transitions. The crystal and molecular structures of the monomeric species [Zn(S2CTol)2(py)] (2), [Zn(S2CPh)2(tmeda)] (3a), [Zn(S2CTol)2(tmeda)] (3b) and [Cd(S2CTol)2(tmeda)] (3d) have been established by X‐ray crystallography. In [Zn(S2CTol)2(py)], chelating dithiocarboxylate ligands and pyridine define a coordination geometry intermediate between square pyramidal and trigonal bipyramidal. In each of 3a and 3b, tetrahedral N2S2 coordination geometries are found as the dithiocarboxylate ligands are effectively monodentate; evidence for the greater coordination potential is found for –S2CTol over –S2CPh. Chelating dithiocarboxylate ligands in [Cd(S2CTol)2(tmeda)] (3d) lead to an octahedral geometry. Thermal behavior has been studied by thermogravimetric analysis. The [M(S2CAr)2(tmeda)] complexes underwent a three‐step decomposition. Pyrolysis in the temperature range 300–500 °C and solvothermal decomposition in ethylenediamine and hexadecylamine (HDA) gave metal sulfide nanoparticles. The MS (M = Zn, Cd, Hg) nanoparticles were characterized by XRD, EDAX, absorption/emission spectroscopy and electron microscopy (TEM). Solvothermal decomposition gave hexagonal phases of nanoparticles whereas heating in a furnace gave cubic ZnS and HgS, and hexagonal CdS. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Me4N](NiII(BEAAM)): A Synthetic Model for Nickel Superoxide Dismutase That Contains Ni in a Mixed Amine/Amide Coordination Environment

Nickel superoxide dismutase (NiSOD) is a metalloenzyme that converts O2*- into H2O2 and O2 by cycling between Ni(II) and Ni(III) oxidation states. Reduced NiSOD contains Ni(II) in a square-planar N2S2 coordination environment formed by two cysteinate S atoms, an amide N, and an amine N to Ni(II). [Me4N](Ni(II)(BEAAM)) represents the first NiN2S2 complex containing Ni in a mixed amine/amide environment. [Me4](Ni(II)(BEAAM)) contains Ni-S bonds at 2.177(2) and 2.137(2) A and Ni-N bonds at 1.989(7) and 1.858(6) A, which compare well with the metalloenzyme. Orange solutions of [Me(4)N](Ni(II)(BEAAM)) in MeCN are diamagnetic and stable toward O2 for weeks. A quasireversible Ni(II/III) redox couple is observed for [Ni(II)(BEAAM)](NMe4) at 0.12(1) V vs Ag/AgCl. These data suggest that NiSOD utilizes the mixed amine/amide ligands to modulate the Ni(II/III) redox couple to best match the O2*- reduction/oxidation couples while maintaining O2 stability.

Complex formation in Cu(II)-thioamide-carbonyl compound systems in ethanol solutions

The structures of metal complexes formed in systems Cu(II)-thioamide-carbonyl compounds in water-ethanol solutions were studied by spectroscopic and quantum-chemical methods. It was found that in systems containing thiocarbohydrazide, the processes of template synthesis in water-ethanol solution and in gelatin-immobilized matrices differ substantially. In the case of dithiooxamide and dithiomalonamide, no products of template synthesis were detected; these amides give with the Cu2+ ion the chelate complexes with a ratio Cu2+: ligand = 1: 2 and with the N2S2 coordination core for dithiooxamide and S4 coordination core for dithiomalonamide. The quantum-chemical calculations in terms of the density functional theory were shown to adequately describe the structures of metal complexes and relative thermodynamic characteristics of the template synthesis processes in the systems under study.

Iron nitrosyl complexes as models for biological nitric oxide transfer reagents

Owing to the indiscriminate reactivity of the free NO radical, intricate control mechanisms are required for storage, transport and transfer of NO to its various biological targets. Among the proposed storage components are protein-bound thionitrosyls (Rprotein-SNO) and protein-bound dinitrosyl iron complexes. Current knowledge suggests the latter are derived from iron-sulfur cluster degradation in the presence of excess NO. Mobilization of protein-bound NO could involve NO or Fe(NO)2 unit transfer to small serum molecules such as glutathione, free cysteine, or iron-porphyrins. The study reported is of a reaction model which addresses the key steps in NO transfer from a prototypal iron dinitrosyl complex. While the N,N'-bis(2-mercaptoethyl)-N,N'-diazacyclooctane (bme-daco) ligand typically binds in square-planar N2S2 coordination, it also serves as a bidentate dithiolate donor for tetrahedral structures in the preparation of the (H+bme-daco)Fe(NO)2 derivative (Chiang et al., J. Am. Chem. Soc. 126:10867-10874, 2004). The removal of one NO produces the mononitrosyl complex, (bme-daco)Fe(NO), and simplifies studies of NO release mechanisms. We have used heme-type model complexes, Fe or Co porphyrins as NO acceptors, yielding (porphyrin)M(NO), where M is Fe or Co, and monitored reactions by nu(NO) Fourier transform IR spectroscopy. Reaction products were verified by electrospray ionization mass spectrometry. Rudimentary mechanistic studies suggest a role for HNO in the NO release from the dinitrosyl; the mononitrosyl benefits as well from acid catalysis. Other NO uptake complexes such as [(N2S2)Fe]2 [N2S2 is bme-daco or N,N'-bis(2-mercapto-2-methylpropyl)-daco] are shown to form Fe(NO) mononitrosyls with stability and spectroscopic signatures similar to those of the porphyrins.

A Novel Methylene Dithioether as a Ligand: Synthesis and Molecular Structure of a Zinc(II) Complex with N4S2 Coordination Environment

The octadentate ligand [N(CH2CH2NH2)(CH2CH2CH2OH)(CH2CH2S)]2CH2, (NNOS-232)2CH2, was synthesized accidentally by the reaction of the unsymmetrically substituted tripod [N(CH2CH2NH2)(CH2CH2CH2OH)(CH2CH2SH)], NNOS-232, with dichloromethane in the presence of aluminum hydroxide. Ligand (NNOS-232)2CH2 was reacted with zinc bis(perchlorate) hexahydrate to yield the complex [Zn((NNOS-232)2CH2)](ClO4)2 1 exhibiting a distorted octahedrally coordinated zinc atom in an N4S2 coordination environment, as shown by an X-ray diffraction study.

Synthesis and Characterization of the First (1, 2‐Benzenedithiolato)iron(III) Complexes with Tripodal Ligands

AbstractThe reaction of iron(III) perchlorate nonahydrate with the tripodal tetradentate ligand tris[(2‐pyridyl)methyl]amine (tpa) or bis[(2‐pyridyl)methyl][(1‐methylimidazol‐2‐yl)methyl]amine (bpia) and 1, 2‐benzenedithiolate (dtc) yields the iron(III) coordination compounds [Fe(tpa)(dtc)]ClO4·0.25 MeOH (1) and [Fe(bpia)(dtc)]ClO4 (2), respectively. These are the first iron(III) complexes with tripodal ligands and dtc, resulting in a N4S2 coordination environment. The new compounds were isolated and characterized by single crystal X‐ray crystallography as well as spectroscopic methods. Compound 1 crystallizes in the monoclinic space group P21/c (No. 14) with a = 29.636(6), b = 12.502(3), c = 14.390(3)Å, β = 102.19(3)°, V = 5211(2)Å3, Z = 8. Compound 2 crystallizes in the orthorhombic space group P212121 (No. 19) with a = 8.881(2), b = 16.155(3), c = 17.895(4)Å, V = 2567.4(9)Å3, Z = 4. Furthermore the new compound [Fe(tpa)(tcc)](ClO4)·0.25 H2O (3) (where tcc = tetrachlorocatecholate dianion) is presented and compared to the dithiolato complexes. 3 crystallizes in the monoclinic space group P21/c (No. 14) with a = 8.982(1)Å, b = 34.329(6)Å, c = 8.648(1)Å, β = 94.22(1)°, V = 2659.3(6)Å3, Z = 4.

Copper(II) complexes 1-phenylpropane-1,2-dione-and benzil bis(3-piperidylthiosemicarbazone): A structural study

The crystal and molecular structure of copper(II) complexes of benzil bis(3-piperidylthiosemicarbazone), [Cu(Bnzpip)] and 1-phenylpropane-1,2-dione bis(3-piperidylthiosemicarbazone), [Cu(Pmpip)] have been determined. [Cu(Bnzpip)] is monoclinic, space group P21/n with a = 13.9375(10) A, b = 11.6621(4) A, c = 16.4710(10) A, β = 100.667(2)°, and V = 2630.9(3) A3 with Z = 4, for d calc = 1.399 g/cm3. [Cu(Pmpip)] is also monoclinic, space group P21/n with a = 11.292(6) A, b = 10.219(5) A, c = 20.292(6) A, β = 101.50(3)°, and V = 2295(2) A3 with Z = 4, for d calc = 1.525 g/cm3. Both complexes involve N2S2 coordination, are relatively planar except for the phenyl rings and have similar bond distances and angles to copper(II) complexes of other 3-piperidylthiosemicarbazones.

Synthesis and Structural Characterization of Thiolato-Bridged Tetranuclear Palladium(II) Complexes with N,N,S-Tridentate Ligands

Abstract Palladium(II) complexes with 2-[(2-aminoethyl)amino]ethanethiol (HL1), 2-[(3-aminopropyl)amino]ethanethiol (HL2), 2-[(2-pyridylmethyl)amino]ethanethiol (HL3), and 2-{[2-(2-pyridyl)ethyl]amino}ethanethiol (HL4), [Pd4(L1)4]Cl4 (1), [Pd4(L2)4]Cl4 (2), [Pd4(L3)4](ClO4)3Cl (3), [Pd4(L4)4][Pd(SCN)4]Cl2 (4), and [Pd4(L4)4](ClO4)4 (5), were synthesized and characterized by measurements of the infrared, electronic, and NMR spectra. X-ray crystal structure analyses of 1, 2, 3, and 4 show that these complexes have a thiolato-bridged tetranuclear structure, where each palladium(II) center takes a square-planar N2S2 coordination environment.

Structural and Spectral Studies of Palladium (II) Complexes of Pyridil bis{3-Piperidyl-, bis{Hexamethyleneiminyl-, bis{N(4)-Diethyl- and bis{N(4)-Dipropylthiosemicarbazone}

Pyridil bis{N(4)-substituted thiosemicarbazones}, in which the substituents replacing the NH2 group on the thiosemicarbazone moieties are piperidyl, H2Plpip; hexamethyleneiminyl, H2Plhexim; diethylamino, H2Pl4DE; and dipropylamino, H2PI4 DP, have been synthesized. Representative palladium(II) complexes of these bis (thiosemicarbazones) have been characterized by IR, electronic, mass, and 1H and 13C NMR spectroscopy. Crystal structures have been determined for H2Plhexim and two of its palladium(II) complexes. H2Plhexim is in the Z isomeric form with intramolecular hydrogen bonding from both thiosemicarbazone moieties to pyridine nitrogens. [Pd(Plhexim)] has square-planar N2S2 coordination (i.e., imine nitrogen and thiolato sulfur atoms). [Pd2 (Plhexim)Cl2 · DMSO has two PdNNSCl centers with the pyridine nitrogen, imine nitrogen or hydrazinic nitrogen and thiolato sulfur atoms coordinated

An unsymmetrical tripodal ligand with an N2OS donor set: coordination chemistry with nickel(II)ions and aerial oxidation to the sulfinate complex

The synthesis of the previously unknown tripodal ligand H4-1 is reported. The tetradentate ligand is equipped with a completely unsymmetrical N2OS donor set. It reacts with Ni(OAc)2. 4H2O or Ni(ClO4)2.6H2O to give the multinuclear nickel(II) complexes [Ni(H-1-Imin)(OAc)]2 (2) (which contains a coordinated Schiff base obtained by reation of the primary amine with the acetone solvent) and [Ni3(H3-1)(H2-1)2]-ClO4.H2O.3 MeCN (3), respectively. A solution of 3 in DMF is readily oxidized upon exposure to air or by aqueous H2O2 to yield [Ni(H2-1-sulfinate)]2. 2MeOH (4). The molecular structures of 2-4 have been determined by X-ray diffraction. Complex 2 exhibits a strongly distorted, octahedral coordination geometry around each nickel(II)ion. The primary amino group of the ligand in this case reacted with the solvent acetone to yield a Schiff base which is coordinated to the metal center. The molecular structure of the trinuclear complex cation in 3 consists of two subunits: a nickel atom with a square-planar N2S2 coordination geometry and two other nickel atoms with a trigonal-bipyramidal N2O2S coordination environment. The dinuclear complex 4 shows distorted octahedral geometry around each nickel(II) ion. The thiolato groups of the ligands are oxidized to sulfinato groups which are O,O-bound to the nickel center. This coordination mode is unusual for nickel sulfinate complexes.

Nickel(II) complexes with N2OS and N2S2 co-ordination spheres: reduction and spectroscopic study of the corresponding Ni(I) complexes

Nickel(II) complexes with Schiff-bases obtained by condensation of 1,3-propanediamine with salicylaldehyde and thiosalicylaldehyde, which present a N2OS or N2S2 co-ordination sphere, were synthesized and studied. The molecular and crystal structure of the asymmetric complex [2-({3-[(3,5-dichloro-2-hydroxyphenyl)methyleneamino]propyl}iminomethylene)benzenethiolato-O,N,N′,S]nickel(II) [Ni(t-salCl2salpd)] has been determined by X-ray crystallography and shows a tetrahedrally distorted square-planar co-ordination geometry for the nickel center. The complexes were characterized by spectroscopic and electrochemical techniques and the results were used to assess the influence of the donor-atoms on their chemical properties. The results obtained show that the compounds may be reduced, either chemically or electrochemically, to Ni(I) complexes. Reduction potentials were found to be strongly dependent on the tetrahedral distortion of the Ni(II) complexes. EPR parameters for Ni(I) complexes, although not very sensitive to ligand substituents, show a regular dependence on the co-ordination set and the tetrahedral distortion of the complexes.

Nickel Complexes of N-Alkylated Derivatives of 2,6-Bis(aminomethyl)- 4-tert-butyl-thiophenol

The syntheses of N-alkylated derivatives of the arenethiol 4-tert-butyl-2,6-(diaminomethyl)- thiophenol and their coordination properties are reported. Compounds 4-tert-butyl-2,6-di(N-isopropyl- aminomethyl)thiophenol (3) and 4-tert-butyl-2-(N-isopropyl-aminomethyl)-6-hydroxymethylthiophenol (6 ) react with Ni(II) salts to give compounds of composition [Ni(3)2]·2HCl (7) and [Ni(6)2] (8). The solid- and solution-state structures of both complexes consist of mononuclear complexes with four-coordinate nickel(II) ions in approximately planar trans- N2S2 coordination environments. In contrast to the parent arenethiol 4a, the sterically more encumbered ligands do not form dinuclear complexes.

Pyrazolate‐Based Oligonuclear Copper and Silver Complexes with N/S Coordination Spheres

AbstractA series of pyrazole‐based potential ligands bearing thioether substituents in 3‐ and 5‐positions of the heterocycle was synthesized [3,5‐bis(RSCH2)‐pyzH R=Ph (1aH), PhCH2 (1bH), iPr (1cH), tBu (1dH)]. These ligands afford oligonuclear Cu1 and Ag1 coordination compounds [LCu]x (2a–c, L = 1a ‐ c) and [LAg]x (3a‐d, L = 1a‐d), respectively. The single crystal X‐ray analysis of 3c shows the presence of trimeric planar arrays of N,N′‐bridging pyrazolates and linear coordinated silver ions, with each two of the trinuclear moieties being linked by two unsupported short intermolecular Ag…Ag contacts [3.041(1) Å]. Molecular‐weight determinations for 2a (THF) and 3c (toluene) indicate that hexanuclear entities are preserved in solution. Starting from 1bH the CuII complex [(1b)2Cu2](BF4)2 (4) was synthesized. According to an X‐ray crystal structure analysis it consists of dinuclear molecules with two bridging pyrazolates, distorted square planar N2S2 coordination spheres for Cu11 and an axially bridging tetrafluoroborate. Magnetic susceptibility data reveal an antiferromagnetic exchange (J = ‐206 cm−1) that is among the highest found for doubly pyrazolate bridged dicopper(II) complexes, which is rationalized on the basis of the rather symmetric dinuclear core of 4. The irreversibility of the electrochemical reduction and oxidation processes for the CuII and CuI compounds, respectively, is explained by the inability of the respective coordination framework to adapt to different geometric preferences.

Macrocyclic [CuI/II(bite)]+/2+ (bite = biphenyldiimino dithioether): An Example of Fully-Gated Electron Transfer and Its Biological Relevance1

Template condensation of 2,2‘-diaminobiphenyl, 1,4-bis(2-formylphenyl)-1,4-dithiabutane, and copper(II) tetrafluoroborate yields the new macrocyclic compound [CuI(bite)](BF4) (bite = biphenyldiimino dithioether). [CuI(bite)]BF4 crystallizes in the orthorhombic space group P212121 with a = 14.379(3) Å, b = 21.370(3) Å, c = 8.046(2) Å, V = 2534.7(7) Å3, Z = 4, R1 = 0.045, and R2 = 0.048. The X-ray structure of [CuI(bite)](BF4) reveals distorted tetrahedral N2S2 coordination about copper, with one unusually short Cu−S(thioether) bond of 2.194(2) Å. Oxidation of [CuI(bite)](BF4) with nitrosyl tetrafluoroborate gives [CuII(bite)](BF4)2. [CuII(bite)](BF4)2 crystallizes in the tetragonal space group I41/a with a = 11.640(2) Å, c = 39.527(3) Å, V = 5355.6(7) Å3, Z = 8, R1 = 0.061, and R2 = 0.063. X-ray crystallography of [CuII(bite)](BF4)2 reveals an approximately square planar CuN2S2 structure with two distant axial BF4- anions (Cu−F 2.546(4) Å) completing a “pseudo-octahedral” coordination sphere. Comparative EXAFS studies of solid samples and acetonitrile solutions of [CuI(bite)](BF4) and [CuII(bite)](BF4)2 demonstrate that the primary coordination environments of both species are the same in solution as in the solid. Copper(I/II) electron self-exchange kinetics measured by 1H NMR line broadening of [CuI(bite)]+ in the presence of [CuII(bite)]2+ reveal an overall first-order process with a rate constant of 21.7(1.9) s-1 at 295 K in acetone-d6. This result represents the first example of fully-gated electron transfer by small-molecule copper(I). The gating process likely involves inversion at sulfur and the tetrahedral → square planar structural change coincident with electron transfer. Variable-temperature 1H NMR coalescence temperatures for methylene ligand protons of [CuI(bite)](BF4) (287 K) demonstrate possible correlation of fast electron transfer with high ligand mobility for this and related small-molecule copper(I/II) couples. Comparison with other small-molecule copper systems also reveals that fast electron transfer is not always observed with coordination-number-invariance and conserved geometry during redox turnover, contrary to popular interpretations of the entatic state hypothesis for blue-copper protein active sites.

Zinc complexes of the N,N,S ligand (mercaptophenyl)(picolyl)amine

AbstractThe zinc complex chemistry of the tridentate thiol ligand N‐ (2‐mercaptophenyl)(2‐picolyl)amine (MPPAH) differs considerably from that of the aliphatic analogue N‐(2‐mercaptoethyl)(2‐picolyl)amine reported previously. This is due to the lower basicity and hence bridging tendency of its aromatic thiolate function. With zinc salts of oxo anions the 1:1 complexes (MPPA)ZnX (1a–c: X = ONO2, OAc, OBz) are formed which according to spectroscopic data are monomeric while the halide (MPPA)ZnBr (2) seems to be polymeric. In the absence of coordinating anions the monomeric 2:1 complex (MPPA)2Zn (3) results which according to a crystal structure determination contains tetrahedral zinc coordinated by one MPPA ligand in a tridentate fashion while the other is only monodentate and sulfur‐bound. A similar N2S2 coordination can be deduced for the 1:1:1 complex (MPPA)Zn(STrt) (4) resulting from ZnEt2, MPPAH and triphenylmethanethiol.

Controlled synthesis and reversible oxidation of a thiolate-bridged macrocyclic dinickel(II) complex

The synthesis of S-(2,6-Diformyl-4-methylphenyl) dimethylthiocarbamate, a valuable thiolate-containing ligand precursor, is reported in detail for the first time. This precursor has considerable potential in biosite modelling studies. A macrocycle L and a related acyclic ligand L′ have been prepared, as complexes, from the precursor and 1,3-diaminopropane. The macrocycle was successfully templated by both zinc(II) and nickel(II) ions yielding [Zn2L(H2O)2][O3SCF3]2·H2O 1 and the diamagnetic complex [Ni2L][ClO4]22, respectively. A single-crystal X-ray analysis of 1 showed the zinc ions to have trigonal-bipyramidal environments and the macrocycle to have a stepped conformation. In contrast, the structure determination of 2 revealed square-planar N2S2 co-ordination for NiII and a bowed macrocycle conformation which results in much shorter metal–metal and sulfur–sulfur separations than the stepped conformation adopted in the case of ZnII[average Zn ⋯ Zn 3.351(1), S ⋯ S 3.363(3) for 1vs. Ni ⋯ Ni 3.146(2), S ⋯ S 2.839(5)A for 2]. Two one-electron oxidations, the first reversible and the second quasi-reversible, were observed for the dinickel(II) complex, whereas one irreversible two-electron oxidation was observed for the dizinc(II) complex. An acetal forms in the presence of ethanol and leads to the isolation of the acyclic trinickel(II) complex [Ni2L′2Ni][ClO4]23.

Copper(II) complexes with N2S2 coordination spheres containing aliphatic thiolates

Copper(II) complexes with N2S2 coordination spheres containing aliphatic thiolates

Angle-selected nitrogen-14-ENDOR study of copper(II) complexes with distorted N2S2 and N2O2 coordination structures

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAngle-selected nitrogen-14-ENDOR study of copper(II) complexes with distorted N2S2 and N2O2 coordination structuresRyo Miyamoto, Yasunori Ohba, and Masamoto IwaizumiCite this: Inorg. Chem. 1992, 31, 14, 3138–3149Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://doi.org/10.1021/ic00040a026RIGHTS & PERMISSIONSArticle Views68Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

ChemInform Abstract: Stabilization of Nickel(III) in a Classical N2S2 Coordination Environment Containing Anionic Sulfur.

AbstractNickel acetate (III) reacts as shown with the benzamides (I) to yield the planar, diamagnetic Ni(II) complexes (IIa) and (IIb), respectively.

Stabilization of nickel(III) in a classical N2S2 coordination environment containing anionic sulfur

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStabilization of nickel(III) in a classical N2S2 coordination environment containing anionic sulfurH. J. Krueger and R. H. HolmCite this: Inorg. Chem. 1987, 26, 22, 3645–3647Publication Date (Print):November 1, 1987Publication History Published online1 May 2002Published inissue 1 November 1987https://doi.org/10.1021/ic00269a002RIGHTS & PERMISSIONSArticle Views504Altmetric-Citations72LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (376 KB) Get e-Alerts Get e-Alerts