Delocalization tunable by ligand substitution in [L₂Al]ⁿ⁻complexes highlights a mechanism for strong electronic coupling

Abstract

Ligand-based mixed valent (MV) complexes of Al(III) incorporating electron donating (ED) and electron withdrawing (EW) substituents on bis(imino)pyridine ligands (I2P) have been prepared. The MV states containing EW groups are...

Enabling Valence Delocalization in Iron(III) Macrocyclic Complexes through Ring Unsaturation

“…62 and 53%, respectively, of the predicted values. These fall within the range associated with recent species assigned as either valence-trapped with very strong coupling (Robin-Day class II−III) 65,67,68 or completely valence-delocalized (Robin-Day class III). 67−69 The moderate solvatochromism of 3b 2+ , 39,67,70 and the two separate ν(C�C) bands in the IR spectrum of 3c 2+ preclude a completely valence-delocalized description.…”

“…62 and 53%, respectively, of the predicted values. These fall within the range associated with recent species assigned as either valence-trapped with very strong coupling (Robin-Day class II–III) ,, or completely valence-delocalized (Robin-Day class III). − The moderate solvatochromism of 3b 2+ , ,, and the two separate ν(CC) bands in the IR spectrum of 3c 2+ preclude a completely valence-delocalized description. , Therefore, 3b / c 2+ are conservatively assigned as valence-trapped complexes exhibiting moderate ( 3c 2+ ) to strong ( 3b 2+ ) coupling (Robin-Day class II, perhaps approaching class II–III). For 3a 2+ , similar behavior to 3b 2+ is likely based both on the similar intensity of the IVCT bands (Table ) and on the apparent valence delocalization of 3a 2+ on the IR timescale.…”

“…This series demonstrates that the same metal ion can either enhance or diminish valence delocalization versus the fully organic bridge, depending on the properties of the supporting ligands. While earth-abundant metal ions have been known to function as effective bridges for mixed valency, enhancement of coupling over the analogous organic bridge has been largely limited to ruthenium species , or to cases where the metal ion results in a structural alteration instead of functioning as a simple spacer . The fact that an abundant metal ion can be used to enhance the valence delocalization of wirelike complexesin a manner similar to Ru speciesrepresents a promising result for the future development of sustainable molecular wires.…”

Redox-active ligands – a viable route to reactive main group metal compounds

“…The reactivity and electrochemistry of iminopyridine complexes of Al and Ga have been studied by Berben et al 66–69 and have been reviewed elsewhere. 70 It has been shown that a series of octahedral group 13 complexes of 2,6-bis{1-[(2-methoxyphenyl)imino]-benzyl}pyridine (I 2 P, Fig.…”

Group 13 ion coordination to pyridyl models NAD+ reduction potentials

“…This is consistent with prior work showing metalloaromatic character in Al III and Ga III complexes of I 2 P, 41,42 and work where Class III mixed-valency is supported by Al III and Ga III ions that bridge two I 2 P ligands. 35,43 Transition element analogs of these two compound classes do not have the same electronic properties.…”