Non-bridging Ligands Research Articles

Lanthanide(III) Complexes of Oxamic Acid

Abstract The preparation, for the first time, of the deprotonated complexes of oxamic acid with Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Dy(III), Ho(III) and Yb(III) is reported. Properties, analytical results, conductometric measurements, magnetic moments and spectral data (IR and diffuse reflectance spectra) are discussed in terms of possible structural types and the nature of the bonding. Oxamic acid acts as a bidentate non-bridging ligand.

ChemInform Abstract: A MOLECULAR ORBITAL APPROACH TO ELECTRON‐TRANSFER REACTIONS BETWEEN TRANSITION‐METAL IONS IN SOLUTION

We present a general scheme to rationalize the kinetic behavior of transition-metal redox systems in solution as a function of the detailed electronic configurations of donor and acceptor species. For the inner-sphere route, proceeding usually via atom transfer, simple molecular orbital arguments are used to predict for which electronic configurations LSM1-X-MZL5 complexes will be stable at the symmetric geometry. The results are supported by comparison with known crystal structures. For these electronic configurations then the symmetric structure corresponds to an inner-sphere intermediate, sometimes observed spectroscopically or inferred kinetically in the experimental environment. For other configurations the symmetric structure corresponds to a transition state which is never observed experimentally. The kinetic behavior of a large number of redox systems may be rationalized just on this basis. It is suggested that the normal dependence of reaction rate on bridging ligand X (I- > Br- > C1- > F) arises when the rate-determining step involves a transition state (we call this type I) and the inverse order when the rate-determining step involves intermediate decay (type 11). The dependence of reaction rate upon substituent in some carboxylate-bridged systems is also examined, and the effects of nonbridging ligands are analyzed by extending earlier ideas of Orgel. Two types of electron transfer are delineated. Smooth transfer occurs when the nature of the HOMO gradually changes as the bridge ligand is transferred and corresponds to a symmetry-allowed process. Sudden transfer occurs via an electron jump from one orbital to another, and atom transfer here is not necessary for electron transfer. Cases are observed experimentally where atom transfer does not occur. The results of the inner-sphere case are applied to outer-sphere reactions with some qualifications, and some interesting parallels are drawn. The effect of extra ions added to the solution are analyzed in molecular orbital terms, and three catalytic effects are revealed. The added species may hold together the two reacting ions as an electrostatic “glue” (if of the correct charge); it may reduce the barrier to reaction and also may ensure adiabatic behavior. It is pointed out that water itself is probably an excellent catalyst of this sort. The molecular orbital approach to inner- and outer-sphere reactions gives a ready explanation for the anomalous behavior (on the Marcus theory) of the CO~~,’I~(H~O)~ system where a spin change occurs in the reaction coordinate.

A molecular orbital approach to electron-transfer reactions between transition-metal ions in solution

We present a general scheme to rationalize the kinetic behavior of transition-metal redox systems in solution as a function of the detailed electronic configurations of donor and acceptor species. For the inner-sphere route, proceeding usually via atom transfer, simple molecular orbital arguments are used to predict for which electronic configurations LSM1-X-MZL5 complexes will be stable at the symmetric geometry. The results are supported by comparison with known crystal structures. For these electronic configurations then the symmetric structure corresponds to an inner-sphere intermediate, sometimes observed spectroscopically or inferred kinetically in the experimental environment. For other configurations the symmetric structure corresponds to a transition state which is never observed experimentally. The kinetic behavior of a large number of redox systems may be rationalized just on this basis. It is suggested that the normal dependence of reaction rate on bridging ligand X (I- > Br- > C1- > F) arises when the rate-determining step involves a transition state (we call this type I) and the inverse order when the rate-determining step involves intermediate decay (type 11). The dependence of reaction rate upon substituent in some carboxylate-bridged systems is also examined, and the effects of nonbridging ligands are analyzed by extending earlier ideas of Orgel. Two types of electron transfer are delineated. Smooth transfer occurs when the nature of the HOMO gradually changes as the bridge ligand is transferred and corresponds to a symmetry-allowed process. Sudden transfer occurs via an electron jump from one orbital to another, and atom transfer here is not necessary for electron transfer. Cases are observed experimentally where atom transfer does not occur. The results of the inner-sphere case are applied to outer-sphere reactions with some qualifications, and some interesting parallels are drawn. The effect of extra ions added to the solution are analyzed in molecular orbital terms, and three catalytic effects are revealed. The added species may hold together the two reacting ions as an electrostatic “glue” (if of the correct charge); it may reduce the barrier to reaction and also may ensure adiabatic behavior. It is pointed out that water itself is probably an excellent catalyst of this sort. The molecular orbital approach to inner- and outer-sphere reactions gives a ready explanation for the anomalous behavior (on the Marcus theory) of the CO~~,’I~(H~O)~ system where a spin change occurs in the reaction coordinate.

Magnetic exchange interactions in transition metal dimers. 10. Structural and magnetic characterization of oxalate-bridged, bis(1,1,4,7,7-pentaethyldiethylene triamine)oxalatodicopper tetraphenylborate and related dimers. Effects of nonbridging ligands and counterions on exchange interactions

Magnetic exchange interactions in transition metal dimers. 10. Structural and magnetic characterization of oxalate-bridged, bis(1,1,4,7,7-pentaethyldiethylene triamine)oxalatodicopper tetraphenylborate and related dimers. Effects of nonbridging ligands and counterions on exchange interactions

The Inner-Sphere Mechanism Interpreted by the Hydrogen Ion Effect on the Fe2+ Reduction Rate of Oxalato-, Malonato-, Glycolato-, and Chloro-Cobalt(III) Complexes in Aqueous Solution

Abstract The hydrogen ion effect on the rate of the Fe2+ reduction of oxalato-, glycolato-, and chloro-cobalt(III) complexes was investigated kinetically. It was found that the rates of the Fe2+ reduction of cobalt(III) complexes such as trans(N)-Co(ox)(β-ala)2−, trans(N)-Co(ox)(gly)2−, trans(N)-Co(ox)(gly)(en), Co(ox)33−, and trans-(O,Cl)-Co(Cl)(am)(dien)+ (am=glycinate, α-alaninate or β-alaninate ions) increase with an increase in the hydrogen ion concentration. This result can be explained by accounting for the protonation of the oxygen atom of the carbonyl group of the nonbridging ligand. The inner-sphere mechanism can be deduced for the Fe2+ reductions of these complexes due to the hydrogen-ion effect. Moreover, a kinetic study of the Fe2+ reduction reaction of Co(Hmalo)(NH3)52+ and Co(malo)(NH3)5+ was carried out. An inner-sphere mechanism for these reactions is proposed from an analysis of the kinetic data. Discussion of the structure of the precursor complex and of the rate determining step for the Fe2+ reduction reactions of cobalt(III) complexes are also made.

Crystal structure of dichlorobis(pyridine-1-oxide)copper(II)

The crystal and molecular structure of dichlorobis(pyridine-1-oxide) copper(II), C10H10N2O2Cl2Cu, has been determined from 3931 reflections measured on a Picker four-circle diffractometer, using the θ/2θ scan technique and MoKα radiation. The crystals are monoclinic, space groupP21/c,a = 6.900(4),b = 15.065(7),c = 12.065(5) A, β = 97.00(4) ° andZ = 4. The structure was solved by Fourier methods and refined by full-matrix least-squares. The final conventionalR-factor was 0.033. The compound is dimeric, and the units of the dimer are held together by oxygen bridges. The coordination polyhedron for Cu is a tetragonal pyramid, with two bridging oxygens and two chlorines in the basal plane. The apical position is occupied by oxygen in the non-bridging ligand. The Cu−Cu distance in the dimer is 3.306(1) A.

Bridging and nonbridging ligand effects in some reversible reductions of macrocyclic complexes of cobalt(III)

Bridging and nonbridging ligand effects in some reversible reductions of macrocyclic complexes of cobalt(III)

Electron-Transfer Reactions of Multidentate Ligand Cobalt(III) Complexes. I. The Reductions of Some Chloro(triethylenetetramine)cobalt(III) Complexes by Iron(II)

Abstract The kinetics of Fe2+ reductions of cis-α-Co(trien)Cl2+, cis-α-Co(trien)OH2Cl2+ and cis-β1-Co(trien)OH2Cl2+(trien=triethylenetetramine) have been studied at 25°C, [H+]=0.10 m and Σ[ClO4−]=1.0 m. The second-order rate constants obtained are 4.0×10−4 m−1 sec−1, 1.6×10−4 m−1sec−1, and 9.8×10−5 m−1 sec−1 for cis-α-Co(trien)Cl+2, cis-α-Co(trien)OH2Cl2+, and cis-β1-Co(trien)OH2Cl2+ respectively. It is demonstrated, by comparing with other rate data for the Fe2+ reductions of cis-CoN4XCln+ (N=NH3, 0.5 en and 0.25 trien, and X=H2O and Cl−) that the rate decreases with an increase in the number of chelate rings in the Co(III) complexes. The chelate effect of the nonbridging ligand on the electron-transfer reactions of Co(III) complexes is discussed on the basis of a model which involves the ligand-field strength of the trans-ligand to the bridging one, the energy needed for stretching the trans-group away from the Co(III) center, and the effect of the solvation.

Effect of thioether donor atoms as nonbridging ligands in the reduction of cobalt(III) complexes by iron(II)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of thioether donor atoms as nonbridging ligands in the reduction of cobalt(III) complexes by iron(II)Jay H. Worrell and Thomas A. JackmanCite this: J. Am. Chem. Soc. 1971, 93, 4, 1044–1046Publication Date (Print):February 1, 1971Publication History Published online1 May 2002Published inissue 1 February 1971https://doi.org/10.1021/ja00733a053RIGHTS & PERMISSIONSArticle Views52Altmetric-Citations18LEARN 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 (412 KB) Get e-Alerts Get e-Alerts

Effect of bridging and non-bridging ligands on the rates of electron-transfer reactions

The effect of bridging and non-bridging ligands on electron-transfer reactions in aqueous solution is considered in the light of results obtained for the reactions of Cr2+ with monohalogenochromium(III) complexes CrX2+† (where X is non-bridging), and the reactions of Eu2+ with CrX2+ (where X is probably a bridging ligand). The surprisingly large (ca 104) effect which non-bridging ligands have in the former reactions, I− > Br− > Cl− > F−, is comparable to the effect which bridging halide ions are known to have in the Cr2+-CrX2+ and Cr2+-Cr(NH3)5X2+ reactions. Factors which are believed to be important in determining the effectiveness of bridging and non-bridging ligands are discussed.

Effect of n-methyliminodiacetic acid as a non-bridging ligand in the chromium(II)–chromium(III) electron-transfer reaction

The rate of electron transfer between CrII and CrIII ions in solution is enhanced by the presence of the chelate ligand N-methyliminodiacetic acid (H2L). The rate law can be expressed as d[CrL+]/dt=k1[Cr3+][Cr2+][HL–]{H}2–, where k1= 0·013 min.–1 at 25·0° and ionic strength 1·0–1·2 (sodium perchlorate). The rate of the implied bimolecular process CrL + CrOH is discussed in relation to some analogous systems.

The effect of nonbridging ligands on the rate of electron-transfer reactions

The effect of nonbridging ligands on the rate of electron-transfer reactions

The chromium(II)-catalysed dissociation of monohalogenochromium(III) complexes and the effect of non-bridging ligands on electron-transfer reactions

The reactions of chromium(II) with monobromochromium(III) and monoiodochromium(III) which result in a net dissociation of the bromide and iodide have been studied in aqueous perchloric acid solutions, ionic strength µ= 2·0M, by spectrophotometric techniques. In each case the kinetics conform to a rate equation of the type Rate =k3′[Cr2+][CrX2+][H+]–1 corrections being necessary for the chromium(II)-independent aquation of CrX2+. A rate equation of the same form has previously been reported for the reaction of CrCl2+. In each case the reactants are believed to be Cr2+ and Cr(X)OH+, and the activated complex [CrOHCrX]3+. In the reaction with CrF2+ there is in addition a hydrogen-ion-independent path which is believed to correspond to the activated complex [CrOHCrHF]4+. At 25° the non-bridging anions have a large (ca. 104) effect on rates, I–(2·13 × 10–2 sec.–1) > Br–(1·74 × 10–3 sec.–1) > Cl–(3·2 × 10–4 sec.–1) > F–(ca. 1·6 × 10–6 sec.–1). This order can be accounted for by considering the relative ligand-field strengths of the halide ions and the ease with which Cr–X bonds can be stretched, but other factors may be important. The effect is of about the same order of magnitude as that of bridging halide ions in the reactions of Cr2+ with CrX2+ and of Cr2+ with Cr(NH3)5X2+. Other data for the reactions of Cr(NH3)OH2+ and Cr(H2O)OH2+ with Cr2+ are considered.

A New Class of Double-Bridged Coördination Polymers Based on Chromium (III)

Abstract : Earlier reports from this laboratory have concerned the preparation of coordination polymers of types which we write symbolically as [M(AB)X2]n and [MX2]n where AB represents a uninegative bidentate ligand and X represents a uninegative bridging group. We now wish to report a third class, [M(a)(b)X2]n, where a represents a neutral unidentate ligand and b a uninegative ligand. The preparation of this new class differs in method from that in the earlier series and appears to lead to polymers with substantially higher molecular weight than we have found for the other two types. The non-bridging ligands a and b are inorganic, so that this material is an example of a coordination polymer which in addition to its inorganic backbone has inorganic blocking groups in the repeating unit.

The Effect of Some Non-bridging Ligands on the Cr(II)-Cr(III) Oxidation1

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Effect of Some Non-bridging Ligands on the Cr(II)-Cr(III) Oxidation1John B. Hunt and Joseph E. EarleyCite this: J. Am. Chem. Soc. 1960, 82, 20, 5312–5314Publication Date (Print):October 1, 1960Publication History Published online1 May 2002Published inissue 1 October 1960https://doi.org/10.1021/ja01505a011RIGHTS & PERMISSIONSArticle Views72Altmetric-Citations11LEARN 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 (396 KB) Get e-Alerts Get e-Alerts

Anions as Bridging and Non-bridging Ligands in Reactions of Co(III) Compounds with Cr++

Anions as Bridging and Non-bridging Ligands in Reactions of Co(III) Compounds with Cr⁺⁺