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

Abstract

The five-membered electron-transfer series [M(bpy) 3 ] n and [M(tpy) 2 ] n (M = Fe, Ru; bpy = 2,2Ј-bipyridine, tpy = 2,2Ј:6Ј,2ЈЈterpyridine) and [Fe( t bpy) 3 ] n ( t bpy = 4,4Ј-di-tert-butyl-2,2Ј-bipyridine; n = 3+, 2+, 1+, 0, 1-) have been investigated and the electronic structure of the so called "low-valent" complexes (n = 1+, 0, 1-) have been established by a combination of electro-and magnetochemistry, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy, X-ray crystallography, and DFT calculations. These complexes are accessed by reduction of the d 6 S = 0 dicationic starting materials [M(bpy) 3 ] 2+ and [M(tpy) 2 ] 2+ (M = Fe, Ru) and [Fe-( t bpy) 3 ] 2+ . The monocations [M(bpy · )(bpy 0 ) 2 ] 1+ (S = 1/2) and [M(tpy · )(tpy 0 )] 1+ (S = 1/2) (M = Fe II , Ru II ) also contain a lowspin (t 2g ) 6 divalent metal center, plus a single radical monoanion (bpy · ) 1or (tpy · ) 1-, and two or one neutral (bpy 0 )[a]

Temperature Dependence of 57Fe-Mössbauer Spectra for a Trinuclear System

“…A similar effect was reported for the ferrocene diketones [5] and confi rmed by Density Functional Theory, DFT, calculations [2]. The spectrum of FeFcT comprises two partially overlapped doublets attributed to the two carboxy-ferrocenes and [Fe(tpy) 2 ] 2+ components, with parameters consistent with the literature data [6,7]. All Fe nuclei are low-spin (S=0) iron (d 6 ), but a more symmetrical pseudo-octahedral N 6 coordination results in a lower QS for [Fe(tpy) 2 ] 2+ compared to ferrocene.…”

“…The spectrum of FeFcT comprises two partially overlapped doublets attributed to the two carboxy-ferrocenes and [Fe(tpy) 2 ] 2+ components, with parameters consistent with the literature data [6,7]. All Fe nuclei are low-spin (S=0) iron (d 6 ), but a more symmetrical pseudo-octahedral N 6 coordination results in a lower QS for [Fe(tpy) 2 ] 2+ compared to ferrocene. Decrease of the QS could be expected for ferrocene in FeFcT compared to FcT as result of terpyridine-to-Fe II electron pair donation but experimentally a slightly higher (+0.04 mm/s) QS is observed.…”

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

“…[13] In the present m 2 -oxo complex 6 the MoÀOÀMo angle is 171.5(2)8, whereas in the latter this angle is 1808 by virtue of the crystallographic centrosymmetry of the tetracation. [3], this distance is quite characteristic for a (tpyC) 1À ligand, and is very close to the corresponding values found for [Fe II (tpyC) 2 ] 0 (S = 1) containing a high-spin ferrous ion [14] and [Cr III (tpyC) 2 ] 1 + (S = 1/2) and mononuclear [Mo IV Cl(tpyC) 2 ](PF 6 ) (S = 0). The geometrical details of the two N,N'-coordinated bpy ligands per Mo center in 6 are identical and typical for neutral ( Me bpy 0 ) ligands.…”

Catalyst-Inspired Charge Carriers for High Energy Density Redox Flow Batteries

“…By comparing the OCVs of complexes I and II to the previously reported non-aqueous systems, it is also evident that they are higher than those of M-acetylacetonates, e.g., Ru(acac) 3 (1.75 V) [75], V(acac) 3 (2.20 V) [34], Cr(acac) 3 (3.40 V) [37]. Since complex II has two pyridyl moieties, one should compare it to the previously reported redox potentials of the M(bpy) 3 and M(tpy) 2 complexes (M=Fe, Ru) (vs. Fc 0 /Fc + ) in the +3 → −1 charge states [76]. Within this range, the OCV value of complex II (4.74 V) is also higher than those of Fe(bpy) 3 (2.71 V [77,78] and 2.80 V [76]), Ru(bpy) 3 (2.88 V) [79,80], Fe(tpy) 2 (3.14 V) [76], and Ru(tpy) 2 (3.24 V) [81][82][83].…”