The Fe^III/Fe^IIvs Fe₂^2.5Formulation in Mixed-Valent Species [(NC)₄Fe(BL)Fe(CN)₄]^3-, BL = 2,2‘-Bipyrimidine and 3,6-Bis(2-pyridyl)-1,2,4,5-tetrazine. Distance and Size Do Not Always Matter

Abstract

Two molecule-bridged bis(tetracyanoiron) complexes [(NC)(4)Fe(BL)Fe(CN)(4)](n)()(-), BL = 2,2'-bipyrimidine (bpym) and 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz), were studied by EPR, UV/vis/near-IR and IR spectroelectrochemistry (n = 2-5) in aprotic media. Following these results, the Fe(2)(2.5) formulation is the correct valence description for the metal centers in the bptz-bridged trianion (K(c) = 10(14.6) in CH(3)CN), whereas the localized Fe(III)/Fe(II) formulation is appropriate for the bpym-bridged system (K(c) = 10(5.4) in CH(3)CN and 10(6.4) in CH(2)Cl(2)). In contrast to common perception, the larger tetrazine-bridged system with the longer metal-metal distance exhibits much stronger metal-metal coupling than the bpym-bridged analogue, a consequence of the very low lying pi LUMO of tetrazines with high MO coefficients at the coordinating nitrogen centers.

Unkonventionelle gemischtvalente Komplexe des Rutheniums und Osmiums

“…Zu den auffallendsten Beispielen zählen die Komplexpaare [(μ‐BL){ML n } 2 ] k (BL=bpym gegenüber bptz; bpym=2,2′‐Bipyrimidin), für die die Metall‐Metall‐Wechselwirkung ( K c ) im Fall der 2,2′‐Bipyrimidinverbindung schwächer ist, trotz des geringeren Metall‐Metall‐Abstandes (5.5 gegenüber 7.8 Å für Komplexe des bptz) 53b. 55, 64a, 102…”

Triphenylamine/tetrazine based π-conjugated systems as molecular donors for organic solar cells

“…s-Tetrazine (Tz) is a strong electron-withdrawing molecule 1,2 which finds many fields of applications such as retro Diels-Alder cyclisation, [3][4][5][6][7][8][9] energetic compounds, [10][11][12][13][14][15][16] coordination chemistry, [17][18][19][20][21][22][23][24] electrofluorochromism. [25][26][27][28][29][30][31][32][33][34] Very recently, polymers containing s-tetrazine have been used in organic photovoltaic (OPV) cells [35][36][37][38][39] and there is one example of a transistor based on a tetrazine-naphthalene diimide system.…”

β-Cyclodextrin-Assisted Intervalence Charge Transfer in Mixed-Valent [2]Rotaxane Complexes Having Metal Centers Linked by an Interrupted π-Electron System

“…However, the absence of charge transfer between aromatic donors and acceptors, [17] separated by a saturated hydrocarbon bridge in the b-CD inclusion complex does not favor this proposition. Further, Kaim and co-workers have demonstrated [18] that a low lying p* LUMO of BLs with higher molecular orbital (MO) coefficient at the coordinating center is crucial in effecting stronger metal ± metal coupling in dinuclear complexes.…”