Slow Magnetic Relaxation in a Series of Mononuclear 8-Coordinate Fe(II) and Co(II) Complexes

Abstract

A series of homoleptic mononuclear 8-coordinate Fe and Co compounds, [Fe(L)](ClO) (2), [Fe(L)](ClO) (3), [Fe(L)](ClO) (4), [Co(L)](ClO) (5), [Co(L)](ClO) (6), [Co(L)](ClO) (7), and [Co(L)](ClO) (8) (L and L are 2,9-dialkylcarboxylate-1,10-phenanthroline ligands; L and L are 6,6'-dialkylcarboxylate-2,2'-bipyridine ligands), have been obtained, and their crystal structures have been determined by X-ray crystallography. The metal center in all of these compounds has an oversaturated coordination number of 8, which is completed by two neutral homoleptic tetradentate ligands and is unconventional in 3d-metal compounds. These compounds are further characterized by electronic spectroscopy, cyclic voltammetry (CV), and magnetic measurements. CV measurements of these complexes in MeCN solution exhibit rich redox properties. Magnetic measurements on these compounds demonstrate that the observed single-ion magnetic (SIM) behavior in the previously reported [Fe(L)](ClO) (1) is not a contingent case, since all of the 8-coordinate compounds 2-8 exhibit interesting slow magnetic relaxation under applied direct current fields.

Effect of Coordination Modes on the Tunable Luminescence of 1,10‐Phenanthroline‐Based Complexes

“…The Zn─N distances are distributed in a narrow range of 2.048(5)–2.084(5) Å. The shorter Zn─N distances result in the relatively longer Zn─O bond lengths, which are in the range of 2.614–2.703 Å …”

“…1 structurally resembles our recently reported Fe II and Co II complexes bearing the similar ligands. The Zn 2+ center is also 8‐coordinated by two symmetry‐related neutral tetradentate L via four N(diimine) and four O(carbomethoxy) atoms in a highly distorted square antiprism (D 4d ) . The degree of deviation from the standard square antiprism (D 4d ) was estimated from the continuous shape measures (CShMs) .…”

“…Herein, a new 8‐coordinate Zn 2+ complex [Zn( L ) 2 ](ClO 4 ) 2 ( 1 ) is obtained from the closed‐shell d 10 Zn 2+ ion, which is well known for its coordination flexibility. The structure of 1 has been determined by X‐ray crystallography, and is well comparable with its Fe 2+ and Co 2+ analogues . The Zn 2+ is coordinated to each of the two L via two O(carbonyl) and two N(diimine) atoms.…”

“…We also reported recently a series of novel 8‐coordinate Fe(II) and Co(II) compounds, [M II ( L ) 2 ](ClO 4 ) 2 ( L = 2,9‐bis(carbomethoxy)‐1,10‐phenanthroline, M = Fe or Co), where the ligand L was formed from the in situ esterification of 2,9‐dicarboxylphenathroline with MeOH . Two neutral tetradentate ligands coordinate to one metal center with four M─N (diimine) bonds and four relatively longer M─O bonds in a highly distorted dodecahedron . Since the two ester groups attached on the phen frame could, in principle, rotate above C(ester)–C(diimine) bonds, resulting in two different coordination modes, that is, carbonyl O versus methoxyl O ( Figure ).…”

A rare octacoordinated mononuclear iron(III) spin-crossover compound: synthesis, crystal structure and magnetic properties

“…However, compared to the universal hexacoordinated iron(II) complexes, coordination numbers for either the Fe II ion or the Fe III ion higher than six are rarely observed in discrete molecules because high coordination numbers are usually confined to the larger metal ions of the heavier f-elements rather than the comparatively lighter 3d ones. According to the Cambridge Structural Database (CSD; Groom et al, 2016), there are only about a dozen octacoordinated iron-based complexes which have been structurally characterized by single-crystal X-ray diffraction and most of them are iron(II) compounds (Long et al, 2015;Xiang et al, 2017;Jin et al, 2018;Seredyuk et al, 2015;Bu et al, 1998;Diebold & Hagen, 1998;de Martino Norante et al, 1992;Koch et al, 1996;Patra et al, 2010;Adam et al, 2016;Petzold et al, 2017;Singh et al, 1971), except for three examples based on the iron(III) ion reported over ten years ago (King et al, 1971;Koch et al, 1996;Patra et al, 2010). Recently, Jose and coworkers obtained two octacoordinated Fe II complexes using tetradentate tetrazole/triazole-based ligands, namely, [NEt 3 H]-[Fe{bipy(ttr) 2 }{Hbipy(ttr) 2 }]Á3MeOH [bipy(ttr) 2 is 6,6 0 -bis(1Htetrazol-5-yl)-2,2 0 -bipyridine] and [Fe(bptp) 2 ][BPh 4 ] 2 [bptp is bis(pyridyltriazolyl)pyridine] (Seredyuk et al, 2015;Adam et al, 2016), whose Fe II ions show a switch between a high-spin and a low-spin state within the measured temperature range.…”