Recognition of fractional non-innocent feature of osmium coordinated 2,2′-biimidazole or 2,2′-bis(4,5-dimethylimidazole) and their interactions with anions

Abstract

Mononuclear complexes [Os(II)(bpy)2(H2L1)](ClO4)2 ([](ClO4)2) and [Os(II)(bpy)2(H2L2)](ClO4)2 ([](ClO4)2) incorporating two free NH protons at the back face of the coordinated H2L, and deprotonated L(2-) bridged symmetric dinuclear complexes [(bpy)2Os(II)(μ-L1(2-))Os(II)(bpy)2)](ClO4)2 ([](ClO4)2) and [(bpy)2Os(II)(μ-L2(2-))Os(II)(bpy)2)](ClO4)2 ([](ClO4)2) (bpy = 2,2'-bipyridine, H2L1 = 2,2'-biimidazole and H2L2 = 2,2'-bis(4,5-dimethylimidazole)) have been characterised. Crystal structures of [](ClO4)2 and the meso (ΔΛ) diastereomeric form of [](ClO4)2 have been determined. The crystal structure of [](ClO4)2 also reveals the hydrogen bonding interactions between its free acidic NH protons and the oxygen atoms of the perchlorate anion in the nearby asymmetric unit. Experimental and DFT/TD-DFT calculations have divulged the non-innocent feature of the doubly deprotonated L(2-) in (3+) and (3+), leading to the resonating formulation of {Os(II)(μ-L(2-))Os(III)} ↔ {Os(II)(μ-L˙(-))Os(II)}, instead of a simple mixed valent situation {Os(II)(μ-L(2-))Os(III)}. The dinuclear complexes (3+) and (3+) display one broad and moderately intense near-IR transition near 1000 nm corresponding to a mixed Os(dπ)/L(π) → Os(dπ)/L(π*) MLLMCT (metal/ligand to ligand/metal charge transfer) transition. Different experimental studies have also established the interaction of (2+) and (2+) with the selective anions.

Optical Sensing of Anions via Supramolecular Recognition with Biimidazole Complexes

“…It was further reported that for both ruthenium(II) and osmium(II) complexes a cathodic shift of the metal related M 2+ /M 3+ oxidation was observed which is in agreement with an increased electron density due to increased σ‐donation from the ligand . More recently, the groups of Wenger and Rau reported the synthesis of 2,2′‐biimidazole and 2,2′‐bibenzimidazole complexes of iridium(III) .…”

“… Osmium(II) coordinated 2,2′‐biimidazole complexes with anion recognition features reported by Lahiri et al …”

“…The osmium(II)/osmium(III) redox couple is furthermore shifted cathodically which potentially gives rise to more vivid redox chemistry. The anion sensing features of the osmium(II) biimidazole complexes 14 a and 14 b have been evaluated by Lahiri and co‐workers . Acetonitrile and aqueous solutions were used to test the anion sensing features of 14 a and 14 b with tetrabutyl ammonium salts of F − , CN − , Cl − , Br − , I − , OAc − , SCN − , NO 3 − , H 2 PO 4 − and HSO 4 − .…”

Unsymmetric (μ-oxido)/(μ-pyrazolato) and Symmetric (μ-pyrazolato)2 Bridged Diosmium Frameworks: Electronic Structure and Magnetic Properties

“…Thus, at 0.05 T, the magnetic moment strongly decreases from 3.94 μ B (300 K) to 0.35 μ B (2 K). At this magnetic field the magnetic moment at room temperature is considerably higher than that expected for a compound containing two unpaired electrons probably due to strong spin–orbit coupling (λ) involving Os III ions (λ ≈ 3000 cm –1 ) . However, at 2 K the complex is essentially diamagnetic.…”

Ru-Complex Framework toward Aerobic Oxidative Transformations of β-Diketiminate and α-Ketodiimine

“…On the other hand, MO compositions predict a reverse situation of metal dominated (59%) reduction with partial ligand contribution (26%) leading to the electronic structural form of [Ru II (acac) 2 (nacnac)] − (major) and [Ru III (acac) 2 (nacnac •– )] − (minor) for 1c – ( S = 0). This in effect implies the potential bidirectional (fractional) noninnocence of coordinated nacnac. , The instability of both 1c + and 1c – on the coulometric time scale has prevented us from checking their spectral features.…”