15N NMR coordination shifts in Pd(II), Pt(II), Au(III), Co(III), Rh(III), Ir(III), Pd(IV), and Pt(IV) complexes with pyridine, 2,2′-bipyridine, 1,10-phenanthroline, quinoline, isoquinoline, 2,2′-biquinoline, 2,2′:6′, 2′-terpyridine and their alkyl or aryl

Abstract

The 15N NMR data for 105 complexes of Pd(II), Pt(II), Au(III), Co(III), Rh(III), Ir(III), Pd(IV), and Pt(IV) complexes with simple azines such as pyridine, 2,2'-bipyridine, 1,10-phenanthroline, quinoline, isoquinoline, 2,2'-biquinoline, 2,2':6', 2''-terpyridine and their alkyl or aryl derivatives have been reviewed. The 15N NMR coordination shifts, i.e. the differences between the 15N chemical shifts of the same nitrogen in the molecules of the complex and the ligand (Delta(15N) (coord) = delta(15N) (compl)--delta(15N) (lig)), have been related to some structural features of the reviewed coordination compounds, like the type of the central ion and the character of auxiliary ligands (mainly in trans position). These Delta(15N) (coord) parameters are negative, their absolute magnitudes (ca 30-150 ppm) generally increasing in the metal order Au(III) < Pd(II) < Pt(II) and Rh(III) < Co(III) < Pt(IV) < Ir(III), as well as with the enhanced trans influence of the other donor atoms (H, C << Cl < N).

Solvent Effects on Nitrogen Chemical Shifts

“…Due to scalar and spin-orbit relativistic effects, a larger shielding upon complex formation is seen for heavier metals [66]. As a general rule, the shielding increases to the right across the rows, periods, and downwards within the 31 Solvent Effects on Nitrogen Chemical Shifts groups of the periodic system [58].…”

“…The absolute value of Δ 15N coord may thus be applied for comparison of the interaction strength of the coordination bonds of structurally closely related complexes that encompass identical transition metal, or halogen(I), provided the same solvent is used for both the measurements of δ 15N lig and δ 15N compl . For these cases, the statement "the stronger the interaction, the larger the jΔ 15N coord j" is valid [66,78,80,81]. Herein, the general trends for δ 15N and the Δ 15N coord of transition metal complexes of aromatic nitrogenous heterocycles is reviewed, with attention given to specific studies, in which the solvent plays a key role for the complexation process.…”

“…Typical δ 15N and Δ 15N coord for the selected transition metals, taking in to account their oxidation state, the N-donor ligand(s), and the coordinating atom trans to the nitrogen donor, are shown. The magnitudes of jΔ 15N coord j of these azine-transition metal complexes vary within a considerably broad range, $30 to $150 ppm [59,60,65,66,90,91].…”

“…[59,65,83]. In complexes with one or more additional ligands coordinating to the metal, the jΔ 15N coord j is strongly affected by the nature of the ligand trans to the nitrogen donor, which phenomenon is often referred to as the trans effect [66]. Tables 4-7 show the nitrogen NMR data of selected examples of group 8-11 transition metal complex of azine ligands, indicating the solvent in which the data was acquired, the atom trans to the nitrogen donor, and the geometry of the complex.…”

“…lig for 4,4 0 -dimethyl-2,2 0 -bipyridine in DMSO-d 6 [66]. Among the metal complexes of similar structures the jΔ 15N coord j increase in the order Au(III) < Pd(II) < Pt(II) (square-planar, d 8 ), Rh(III) < Co(III) < Pt(-IV) < Ir(III) (octahedral, d 6 ), Fe(II) < Ru(II) < Os(II) (octahedral, d 6 ).…”