Spin-Dependent Delocalization in Three Isostructural Complexes [LFeNiFeL]^2+/3+/4+ (L = 1,4,7-(4-tert-Butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane)

Abstract

The reaction of mononuclear [LFe(III)] where L represents the trianionic ligand 1,4,7-tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane with NiCl(2).6H(2)O and subsequent oxidations with [Ni(III)(tacn)(2)](ClO(4))(3) (tacn = 1,4,7-triazacyclononane) and PbO(2)/methanesulfonic acid produced an isostructural series of complexes [LFeNiFeL](n)()(+) (n = 2 (1), n = 3 (2), n = 4 (3)), which were isolated as PF(6)(-) (1, 3) or ClO(4)(-) salts (2). The molecular structures were established by X-ray crystallography for [LFeNiFeL](ClO(4))(2).5CH(3)CN (1), C(88)H(123)Cl(2)Fe(2)N(11)NiO(8)S(6), and [LFeNiFeL](ClO(4))(3).8acetone (2), C(102)H(156)Cl(3)Fe(2)N(6)NiO(20)S(6). Both compounds crystallize in the triclinic space group P&onemacr; with a = 13.065(2) Å (13.155(2) Å), b = 13.626(3) Å (13.747(3) Å), c = 14.043(3) Å (16.237(3) Å), alpha = 114.47(3) degrees (114.20(2) degrees ), beta = 97.67(3) degrees (96.57(2) degrees ), gamma = 90.34(3) degrees (98.86(2) degrees ), Z = 1(1) (values in parentheses refer to 2). The cations in 1, 2, and 3 have been determined to be isostructural by Fe and Ni K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. All compounds contain linear trinuclear cations (face-sharing octahedral) with an N(3)Fe(&mgr;-SR)(3)Ni(&mgr;-SR)(3)FeN(3) core structure. The electronic structures of 1, 2, and 3 have been studied by Fe and Ni K-edge X-ray absorption near edge (XANES), UV-vis, EPR, and Mössbauer spectroscopy as well as by temperature-dependent magnetic susceptibility measurements. Complexes 1 and 3 possess an S(t)() = 0 whereas 2 has an S(t)() = (1)/(2) ground state. It is shown that the electronic structures cannot be described by using localized valences (oxidation states). Delocalized models invoking the double-exchange mechanism are appropriate; i.e., spin-dependent delocalization via a double-exchange mechanism yields the correct ground state in each case. 1, 2, and 3 represent the first examples where double exchange stabilizes a ground state of minimum spin multiplicity.

Molecular and Electronic Structure of Two Linear Thiophenolate-Bridged Heterotrinuclear Complexes [LFeRuFeL]2+/3+ (L = 1,4,7-Tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane)

“…Physical Measurements: UV/Vis/near-IR spectra of CH 3 CN solutions of 1 and 2 were measured on a PerkinϪElmer Lambda 19 Syntheses: The ligand H 3 L · 3 HPF 6 was prepared by following the spectrophotometer in the range 210Ϫ3200 nm at ambient temperapublished procedure for H 3 L · 3 HCl by using an HPF 6 3 OH alternating constant-acceleration spectrometer. The minimal linewidth was 0.24 mm s Ϫ1 (full width at half-height).…”

“…In contrast, both trications have an S t ϭ 1/2 ground state. In order to obtain dition of NaPF 6 , brown microcrystals of [LFeRuFeL]-(PF 6 ) 2 · 3 CH 3 OH (1) were obtained. Recrystallization of a better understanding of their electronic structure, we decided that it would be of value to investigate the isoelec-this material from acetone/acetonitrile (1:1) and addition of Na [BPh 4 ] afforded single crystals of [{LFe} 2 Ru]-tronic heterotrinuclear analogs [LFeRuFeL] 2ϩ/3ϩ .…”

“…[3,5,6] The staggered configuration of the six tertiary butyl groups (looking down the Fe···Ru···Fe axis) in the achiral stereoisomer ∆(λλλ)···Λ(δδδ) yields a stable structure which has been observed in all cases where the M1···M2 distance is >2.9 Å . Only in enantiomer Λ(δδδ)···Λ(δδδ)] diastereomer been observed.…”

“…A close inspection of the molecular structure shows a small distortion of the local iron sites in the crystal. There are 6 octahedron shows a tetragonal rays. The solid line is a simulation for a diamagnetic system (zero internal field); the parameters are given in Table 2 compression with two shorter RuϪS bonds [Ru(1)ϪS (1) and Ru(1)ϪS(1)Ј].…”

Trinuclear Early/Late‐Transition‐Metal Thiolate Complexes

“…[8] In contrast, no examples of heterometallic vanadium/cobalt or vanadium/nickel thiolato complexes were found in the literature. A series of trinuclear metal complexes of the type [LMMЈML] n+ with L = 1,4,7-tris(4-tertbutyl-2-mercaptobenzyl)-1,4,7-triazacyclononane like [LCoNiCoL] n+ (n = 2-4), [LNiCoNiL] n+ (n = 1-3), [9] [LFeNiFeL] n+ (n = 2-4), [10] [LFeMFeL] n+ (M = Cr, Co; n = 1-3) [11] and [LFeMFeL] n+ (M = Ge, Sn; n = 2,3) [12] have been synthesised and characterised with respect to their magnetic exchange properties. It was shown that in these compounds the mechanism of spin coupling cannot be described exclusively in terms of the classical superexchange mechanisms but rather spin-dependent delocalisation by means of double exchange mechanisms [9] had to be invoked.…”