Crystal and solution structure of the palladium(II) bis(1,4,7-triazacyclononane) ion: evidence for rapid fluxional behavior in a macrocyclic complex

Abstract

Con-N bond lengths. But, the Co-N stretching frequency of Com(taptacn) is 519 cm"1 (identified by an 8-cm"1 shift upon deuteriation of the primary amines) compared to 479 cm'1 for Coln(tacn)2.45 The greater force constant can then lead to a greater inner-sphere reorganization energy.It has been shown recently that the self-exchange parameters of Co3+/2+ couples may be treated in the framework of the Marcus-Sutin model for outer-sphere electron transfer.38 For complexes of the type under consideration the preequilibrium constant (A0) is 0.04 (/ = 0.1 M) and radii (/•) are 9.0 Á (with reaction thickness = 0.8 Á). From these values, a self-consistent set of parameters for the Marcus-Sutin model has been determined for the Co(taptacn)3+/2+ couple: (/ * = 13.8 kcal/mol; <7 * = 5.2 kcal/mol, and d2-d} = 0.165 A, yielding kmc = 0.04 M"1 s'1 as observed in the present study. The somewhat smaller Ad value calculated for the present complexes is in keeping with the Co(III) species being slightly distorted toward the Co(II) structure (45) Boeyens,

The Ligation Properties of some Reduced Schiff Base Selena/Telluraaza Macrocycles: Versatile Structural Trends

“…The only fluxional process that achieves this result is one in which the metal effectively hops between the six donor sites of the macrocycle, as illustrated in Scheme 2. This hopping of the Pd II center between the N4Se2 coordination sites is similar to that reported by McAuley et al, [13] where, in a square-planar palladium complex, the Pd II center hops between any four of the six donor sites. However, an N3Se coordination is ruled out, since the 77 Se NMR spectrum shows a single peak.…”

“…Though the oxidative addition of halogens and alkyl halides to the Pt II center are www.eurjic.orgcommon, [19] this is the second example of oxidative addition of C-Se bond to Pt II . 97.26 (13) The elemental analysis data confirm the formation of a 1:1 complex. Complex 12 was found to be a 1:2 electrolyte in acetonitrile (Λ M, 393 Ω -1 cm 2 mol -1 ).…”

Crystal and solution structure of a pendant-armed macrocyclic complex of palladium(II)

“…That is, the sulphur atom maintains a constant position and does not undergo any fluxional displacement. Such a fluxional process has been observed (6,21) for the platinum and palladium complexes of 1,4,7-triazacyclononane in which the apical donor is not bound to the metal center in the solid state. This results in 'H NMR spectra that may be interpreted only in terms of a "dynamic" structure in which the metal is undergoing a series of inner-sphere substitutions reactions, rotating between several equivalent configurations.…”

“…The tris(pyridylmethy1)-1,4,7-triazacyclonane (py3 [9]aneN3) complex of Pd(I1) has been shown to contain a square pyramidal PdN5 core, in which the metal-coordinated and -uncoordinated pyridine nitrogens interconvert within the NMR time scale (5). There are also several recent examples of fluxionality at Pd(I1) detected by NMR spectroscopy involving both pendant armed and simple macrocyclic ligands (6,7). In particular, several complexes with thia-macrocyclic ligands have been examined (8,9).…”

Geometrical Characteristics and Atomic Charge Variations of Pd(II) Complexes [Pd(L)Cl2] with an Axial (Pd·O) Interaction

“…[8][9][10] By the additional donor sites within the macrocyclic ligands, the square planar structure of the Pd complexes gives a kind of five coordinate complex. The distance (2.92 Å) of the axial (PdÎS) interaction between Pd(II) and the apical sulfur atom is in excess of the normal bonding range for Pd-S distance (2.30-2.50 Å).…”