[M(bpy)₃] (M = Fe, Ru, Os): New Crystalline Materials from the reductive electrocrystallization of [M(bpy)₃](PF₆)₂

Abstract

Reductive electrocrystallization at a constant current density (1 1 .0-11.5 pA/cm2) of millimolar solutions of [ M (~~Y ) , ] ( P F~)~, where M = Fe, Ru, or Os, and bpy = 2,T-bipyridine in acetonitrile containing 0 . 1~ Bu4NPF, results in the formation of dark crystals on the Pt cathode. The crystals grow as long, thin, and shiny needles having a hexagonal cross section of 0.14.5 mm in diameter. 1.Introduction. -A recent article began by stating that 'tris(2,2'-bipyridine)ruthenium(II), Ru(bpy)?, has evolved from a quite esoteric complex ion of a rare platinum metal into an immensely popular, almost magic compound' [l]. We present here evidence of new crystalline materials derived from this molecule and the related species [Fe(bpy),12+ and [Os(bpy)J2+ which gives further support for this statement. Despite the multiple electrochemical [2] and photochemical [3] studies that have been performed with [Ru(bpy),]'+ for over two decades, there was no indication that these novel crystalline materials had been previously communicated.Part of the impetus behind the present work stemmed from our recent success in preparing the first crystalline CRYPTATIUM in 1991 ; a neutral, expanded-atom type species, structure 1, formed by the reductive electrocrystallization of sodium tris(2,2'-bipyridy1)cryptate [4a]. The overall interest in the electrochemical properties of similar macrobicycles, macrocycles, and even of carbon clusters was directed by the possibility of manipulating and transforming them into novel materials with unique properties [4b].The reduced complex 1 can be represented as [Na' c (bipy),], where (bipy), stands for the tris(2,2'-bipyridyl) cryptand, not for three isolated bpy groups. The X-ray structure of this CRYPTATIUM was solved and indicated that the extra unpaired electron that was added to the system upon electrocrystallization was localized in one of the three bipy units of the cryptand [4a].

Electronic Structures of the Electron Transfer Series [M(bpy)3]n, [M(tpy)2]n, and [Fe(tbpy)3]n (M = Fe, Ru; n = 3+, 2+, 1+, 0, 1–): A Mössbauer Spectroscopic and DFT Study

“…Unfortunately, we cannot define a spin ground state for [Fe(bpy) 3 ] 1from this result. It was therefore rather unexpected when in 1994 Echegoyen, Lehn et al [13] reported that crystalline solid samples of [M(bpy) 3 ] 0 (M = Fe, Ru, and Os) are EPR silent. In this case, a small Ru superhyperfine coupling of ca.…”

“…[10,12] On the other hand, "clean" electrocrystallized samples of [Ru(bpy) 3 ] 0 and [Fe(bpy) 3 ] 0 have also been reported to be EPR silent. [13] The monoanions [M(bpy) 3 ] 1and [M(tpy) 2 ] 1-(M = Fe, Ru) have been electrochemically generated in CH 3 CN solution and are all EPR active (S = 1/2 signals). Additionally, solid Na[Fe(bpy) 3 ] has been reported.…”

“…For the neutral complexes [Fe(bpy) 3 ] 0 ,10,11a,11f,12 [Fe(tpy) 2 ] 0 ,12 [Ru(bpy) 3 ] 0 ,11f,13 and [Ru(tpy) 2 ] 0 ,8d the situation is particularly unclear, with many contradictory statements and interpretations of their electronic structures in the literature. Despite the fact that all four neutral complexes possess an even number of electrons, they have been reported to be paramagnetic at 300 K, with all of them displaying EPR signals of S = 1/2 character 12.…”

“…Powdered and solution samples of [M(bpy) 3 ] 0 (M = Fe, Ru, Os) have been reported to display EPR spectra [11] with the appearance of S = 1/2 species, [11a,11j] which closely resemble those reported for the corresponding monocation and monoanions. [11a,f,j] In contrast, in 1994 Echegoyen et al [13] reported that pure microcrystals of [M(bpy) 3 ] 0 (M = Fe, Ru, Os) generated by reductive electrocrystallization from [M(bpy) 3 ]-(PF 6 ) 2 in acetonitrile solution under strictly anaerobic conditions "did not exhibit an ESR signal" and from this data the authors invoked a "lack of paramagnetism" in these compounds. In response to these observations, some authors have erroneously suggested that the two ligand radicals in [Fe II (bpy · ) 2 (bpy 0 )] 0 and [Ru II (bpy · ) 2 (bpy 0 )] 0 are electronically uncoupled, such that both coordinated (bpy · ) 1radical anions individually give rise to an S = 1/2 EPR signal.…”

Synthesis, Structure, and Properties of Al(Rbpy)3 Complexes (R = t-Bu, Me): Homoleptic Main-Group Tris-bipyridyl Compounds

“…R bpy) 3 , where R = tBu (1) or Me (2), have been synthesized from reactions between AlX precursors (X = Cl, Br) and neutral R bpy ligands through an aluminum disproportion process. The crystalline compounds have been characterized by single-crystal X-ray diffraction, electrochemical experiments, EPR, magnetic susceptibility, and density functional theory (DFT) studies.…”