Synthesis and Characterization of Alkali-Metal Salts of 2,2′- and 2,4′-Bipyridyl Radicals and Dianions

Abstract

The reaction of ethylenediamine (en) solutions of 2,2'- and 2,4'-bipyridine (bipy) with varying stoichiometric amounts of potassium and rubidium metal resulted in the isolation of compositionally pure solids containing the respective bipyridyl radical anions (2,2'- and 2,4'-bipy(*-)) and dianions (2,2'- and 2,4'-bipy(2-)). These species were structurally characterized by single-crystal X-ray diffraction in K(2,2'-bipy)(en) (1a), K(4)(2,2'-bipy)(4)(en)(4) (1b), Rb(2)(2,2'-bipy)(en)(2) (2), K(2,4'-bipy)(en) (3), K(4)(2,4'-bipy)(2)(en)(3.5) (4), and Rb(4)(2,4'-bipy)(2)(en)(3.5) (5). The crystallographic results obtained allow for interesting relationships to be drawn between the electronic structure of the bipyridyl moieties and metric structural data. Further characterization of the solids by means of powder X-ray diffraction, elemental analysis, electron paramagnetic resonance, and IR and Raman spectroscopy is also reported. These studies provide a comprehensive overview of the structural and spectroscopic properties of these often-cited yet elusive air- and moisture-sensitive species, helping to complement the existing data in the chemical literature.

Electronic Structures of “Low‐Valent” Neutral Complexes [NiL2]0 (S = 0; L = bpy, phen, tpy) – An Experimental and DFT Computational Study

“…The latter distances are quite similar to those observed experimentally for alkali metal salts of the (bpy 2-) 2-dianion [11,23] (C py -C py = 1.399 Å; average C-N = 1.436 Å). [24] Hence, the electronic structure of this complex can be assigned as [ (Figure 9) is fully consistent with this proposal, and a gasphase BS(2,2) calculation yielded a J cald.…”

“…The average C py -C py bond lengths of 1.442(2) Å are significantly shorter than those in non-coordinated neutral (bpy 0 ) [1.490(3) Å] [10] but longer than those in alkali metal salts of the π-radical anion (bpy [11] and the diamagnetic dianion (bpy 2-) 6 -anions, is of rather low quality. [9] This is because it was determined at 295 K by using Mo-K α radiation, and only reflections with 3.0 Ͻ θ Ͻ 25°were measured.…”

Iron Dicarbonyl Complexes Featuring Bipyridine‐Based PNN Pincer Ligands with Short Interpyridine CC Bond Lengths: Innocent or Non‐Innocent Ligand?

“…Experimental CC bond lengths, determined by X‐ray diffraction, for bpy 0 , bpy . − , and bpy 2− , are approximately 1.49,32 1.43,33 and 1.40‐1.36 Å,34 respectively. This suggests that the bpy‐based ligands in 5 – 7 could be considered as radical anions, with the missing spin attributable to antiferromagnetic coupling of the unpaired electron on a low‐spin Fe I center.…”

The Electron Transfer Series [MoIII(bpy)3]n (n=3+, 2+, 1+, 0, 1−), and the Dinuclear Species [{MoIIICl(Mebpy)2}2(μ2‐O)]Cl2 and [{MoIV(tpy.)2}2(μ2‐MoO4)](PF6)2⋅4 MeCN

“…[3] In contrast to earlier work [2] in which their electronic structures were characterized as complexes containing a neutral Mo(0) (4d 6 lowspin) and three neutral bpy 0 ligands, the crystal structure of the latter clearly shows the presence of three p-radical anions ( Me bpyC) 1À rendering the central molybdenum trivalent (4d 3 ). [16] Their electronic structures are therefore best described as [Mo III (bpyC) 3 ] 0 (S = 0) and [Mo III ( Me bpyC) 3 ] 0 (S = 0). It is remarkable that the CÀC and CÀN distances of the N,N'-coordinated (bpyC) 1À ligands are within the 3s limit, identical to those reported for K(en)(bpyC) (en = ethylenediamine).…”