A large dinuclear Fe(ii) triple helicate demonstrating a two-step spin crossover

Abstract

<p>The largest reported dinuclear Fe(<sc>ii</sc>) triple helicate system to exhibit spin crossover is presented, with exploration of the two-step spin-transition.</p>

Correlations between ligand field Δo, spin crossover T1/2 and redox potential Epa in a family of five dinuclear helicates

“…The octahedral distortion parameters (sum of deviations of the 12 cis angles from 90°) of the Fe(II) centres in 1-5 lie in a narrow range, 56.8-62.0° (Table 1 and S1 (60.3°), and falls in the range seen for all of the SCO-active helicates reported in the literature (51-70°). 11,57 The intrahelicate Fe•••Fe distances in 1-5 lie between 9.971-10.323 Å (Table 1), which falls in the range of 9-12 Å reported for seven of the literature examples SCO-active Fe(II) helicates 17, 19-21, 26, 60 (exception ~ 4Å (L7/L8), 24,25 ~15 Å (L10/L11) 23 and 19 Å (L12), 16 Figure S1, ESI).…”

“…14,15 Nevertheless, prior to this study, only 12 ligands (Figure S1.1, ESI, L1-L12), comprising either azolepyridine or azole-imine coordinating pockets (Figure 1), had been employed to form SCO-active dinuclear iron(II) helicates. 11,16 The first example of an SCO-active dinuclear helicate, [Fe 2 L1 3 ] 4+ (Figure S1.1, ESI) was reported by Williams and co-workers in 1998. 17 Since then this field has been expanded on by various authors, including Hannon, 18 Li, 16,19,20 Kruger and Clérac, [21][22][23] Sunatsuki, 24,25 and Aromi.…”

“…11,16 The first example of an SCO-active dinuclear helicate, [Fe 2 L1 3 ] 4+ (Figure S1.1, ESI) was reported by Williams and co-workers in 1998. 17 Since then this field has been expanded on by various authors, including Hannon, 18 Li, 16,19,20 Kruger and Clérac, [21][22][23] Sunatsuki, 24,25 and Aromi. 26 Despite considerable interest in redox properties, especially of iron complexes due to potential relevance to understanding the function of heme-based metalloproteins, in which spin state changes are also crucial, [27][28][29] studies of SCO and redox in families of complexes are rare: 24,[30][31][32][33][34][35] Drago, 30 Kadish 32,33 and Kuroda-Sowa 31 studied mononuclear complexes, whilst Sunatsuki and co-workers have reported the only examples involving dinuclear iron(II) helicates 24 (or tetranuclear cages 36 ).…”

“…S1.1, ESI † ) was reported by Williams and co-workers in 1998. 17 Since then this field has been expanded on by various authors, including Hannon, 18 Li, 16,19,20 Kruger and Clérac, 21–23 Sunatsuki, 24,25 and Aromí. 26 …”

Unique Spin Crossover Pathways Differentiated by Scan Rate in a New Dinuclear Fe(II) Triple Helicate: Mechanistic Deductions Enabled by Synchrotron Radiation Studies

“…These groups, along with the benzene moieties, engender key intermolecular interactions between helicate molecules that dictate the interhelical spacing and steric interactions in the resulting lattice. The packing and resulting steric interactions in helical SCO molecules have been shown previously to have a marked effect on the nature of the ST. 22,27 The three ligands used to form the helicate structure (A, B and C) were found to each be involved in a different set of intermolecular interactions (Figure 3). Ligand A forms a continuous 1D chain, stabilized by N … HC hydrogen bonds between pyridyl N atoms and imidazole CH groups, as well as ℼ-ℼ interactions between terminal pyridyl groups of adjacent helicates.…”