Syntheses, structural analyses and redox kinetics of four-coordinate [CuL₂]²⁺and five-coordinate [CuL₂(solvent)]²⁺complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)₂]²⁺in nitromethane

Abstract

[Cu(2,9-dimethyl-1,10-phenanthroline)(2)](2+) and [Cu(6,6'-dimethyl-2,2'-bipyridine)(2)](2+/+) complexes with no coordinated solvent molecule were synthesized and the crystal structures were analyzed: the coordination geometry around the Cu(i) center was in the D(2d) symmetry while a D(2) structure was observed for the four-coordinate Cu(ii) complexes. Coordination of a water or an acetonitrile molecule was found in the trigonal plane of the five-coordinate Cu(ii) complex in the Tbp(trigonal bipyramidal) structure. Spectrophotometric analyses revealed that the D(2) structure of the Cu(ii) complex was retained in nitromethane, although a five-coordinate Tbp species (green in color), was readily formed upon dissolution of the solid (reddish brown) in acetonitrile. The electron self-exchange reaction between D(2d)-Cu(I) and D(2)-Cu(II), observed by the NMR method, was very rapid with k(ex)=(1.1 +/- 0.2) x 10(5) kg mol(-1) s(-1) at 25 degrees C (DeltaH*= 15.6 +/- 1.3 kJ mol(-1) and DeltaS*=-96 +/- 4 J mol(-1) K(-1)), which was more than 10 times larger than that reported for the self-exchange reaction between D(2d)-Cu(I) and Tbp-Cu(II) in acetonitrile. The cross reduction reactions of D(2)-Cu(ii) by ferrocene and decamethylferrocene in nitromethane exhibited a completely gated behavior, while the oxidation reaction of D(2d)-Cu(i) by [Ni(1,4,7-triazacyclononane)(2)](3+) in nitromethane estimated an identically large self-exchange rate constant to that directly obtained by the NMR method. The electron self-exchange rate constant estimated from the oxidation cross reaction in 50% v/v acetonitrile-nitromethane mixture was 10 times smaller than that observed in pure nitromethane. On the basis of the Principle of the Least Motion (PLM) and the Symmetry Rules, it was concluded that gated behaviors observed for the reduction reactions of the five-coordinate Cu(ii)-polypyridine complexes are related to the high-energy C(2v)--> D(2d) conformational change around Cu(ii), and that the electron self-exchange reactions of the Cu(ii)/(i) couples are always adiabatic through the C(2v) structures for both Cu(ii) and Cu(i) since the conformational changes between D(2d), D(2) and C(2v) structures for Cu(i) as well as the conformational change between Tbp and C(2v) structures for Cu(ii) are symmetry-allowed. The completely gated behavior observed for the reduction reactions of D(2)-Cu(ii) species in nitromethane was attributed to the very slow conformational change from the ground-state D(2) to the entatic D(2d) structure that is symmetry-forbidden for d(9) metal complexes: the very slow back reaction, the forbidden conformational change from entatic D(2d) to the ground-state D(2) structure, ensures that the rate of the reduction reaction is independent of the concentration of the reducing reagent.

Semiconductive Copper(I)–Organic Frameworks for Efficient Light‐Driven Hydrogen Generation Without Additional Photosensitizers and Cocatalysts

“…[19] Thep roton likely bond to the open copper sites to afford copper hydride species for the release of hydrogen. [19] Thep roton likely bond to the open copper sites to afford copper hydride species for the release of hydrogen.…”

Two new lead(II) coordination polymer and discrete complex containing bipyridine ligands with different positioned methyl substituents: synthesis, characterization, crystal structure determination, and luminescent properties

“…In general, metal complexes of 2,2 0 -bipyridine (bpy) (and its derivatives) continue to be of great interest in many areas of chemistry, owing to their interesting structural, spectroscopic, catalytic, biomimetic, as well as photophysical and photochemical properties [13][14][15][16][17]. Pb(II) complexes with 2,2 0 -bipyridine and 4,4 0 -bipyridine ligands [18][19][20] were subject to frequent studies.…”

Flipping of the coordinated triazine moiety in Cu(i)–L2and the small electronic factor, κel, for direct outer-sphere cross reactions: syntheses, crystal structures and redox behaviour of copper(ii)/(i)–L2complexes (L = 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)

“…[5][6][7][8][9][10][11][12][13][14] On the other hand, we found that the electron transfer (cross) reactions between different copper complexes and the electron self-exchange reactions are not gated. Single crystal analyses revealed that [Cu(pdt) 2 (H 2 O) 2 ](BF 4 ) 2 was in the D 2h symmetry with two axial water molecules and two symmetrically coordinated equatorial pdt ligands, while the coordination structure of [Cu(pdt) 2 ]BF 4 was a squashed tetrahedron (dihedral angle = 54.87 o ) with an asymmetric coordination by two pdt ligands: one pdt ligand coordinated to Cu(I) through pyridine-N and triazine-N2 while another pdt through pyridine-N and triazine-N4, and a stacking interaction between the phenyl ring on one pdt and the triazine ring on another pdt caused the squashed structure and nonequivalent Cu-N bond lengths.…”

“…[5][6][7][8][9][10][11][12][13][14] On the other hand, we found that the electron transfer (cross) reactions between different copper complexes and the electron self-exchange reactions are not gated. the structural change (inner-sphere reorganization) is the essential factor that induces gated phenomena.…”