An Odd‐Electron Complex [Ru^k(NO^m)(Qⁿ)(terpy)]²⁺ with Two Prototypical Non‐Innocent Ligands

Abstract

Six combinations of oxidation states are conceivable for the paramagnetic title complex. Single-crystal X-ray diffraction, spectroscopic analysis (IR, EPR at conventional and high frequency), and DFT calculations establish that it is the iminosemiquinone radical structure that is formed: [Ru(k)(NO(m))(Q(n))(terpy)](2+) (k = 2+, m = 1+, n = 1-).

Electronic structures and reactivity aspects of ruthenium–nitrosyls

“…The distances between the Ru(II) ion and the pyrazolyl nitrogen atoms of tpm as well as pyridine nitrogen donor of pap match fairly well with those reported for the analogous complexes [55,56,43,77]. Similarly, Ru II -Cl, Ru II -CH 3 CN and Ru II -NO 2 bond distances in the complexes are in good agreement with those reported in the literature for the analogous systems [43][44][45][46][47][48][49][50][51][52]. The following are the striking features associated with the structures of the complexes: (i) The bite angle associated with the five-membered chelate ring involving the pap ligand, N1-Ru-N2, $76°is much shorter than that of the six-membered chelate ring involving the tpm ligand, N4-Ru-N6 or N6-Ru-N8, $84°.…”

“…The presence of strongly p-acidic pap ligand along with the weakly p-acidic tpm as ancillary ligands in the complex framework of 4 3+ has been reflected in the high m(NO) frequency which in turn signifies the nitrosonium character of the coordinated NO [42]. On the other hand the reduced nitrosyl bent geometry (138.0°, sp 2 -hybridization) in 4 2+ as observed earlier in analogous complexes [42][43][44][45][46][47][48][49][50][51][52][87][88][89][90][91]. The one-electron reduced radical species [Ru II (tpm)(pap)(NO Å )] 2+ (4 2+ ) exhibits the EPR spectrum with g = 1.989 (Fig.…”

“…{Ru II -NO Å } and {Ru II -NO Å } ? {Ru II -NO À }, respectively [42][43][44][45][46][47][48][49][50][51][52]. Accordingly, the DFT calculations predict that LUMO and LUMO+1 in 4 3+ are primarily composed of $70% NO based orbitals.…”

“…It may be noted that ruthenium-nitrosyl species involving meridionally coordinated trpy (trpy: 2,2 0 :6 0 ,2 00 -terpyridine) in combination with a wide variety of bidentate ancillary ligands have been reported in recent years [42][43][44][45][46][47][48][49][50][51][52], but the ruthenium-nitrosyl derivatives encompassing facially coordinated tpm ligand have been confined to only two molecular frameworks of [Ru II (tpm)(bpy)(NO)] n [55] and [Ru II (tpm)(Cl) 2 (NO)] n [56].…”

“…The present work originates from our interest [42][43][44][45][46][47][48][49][50][51][52] in exploring the aforesaid aspects (i-iii) of the coordinated nitrosyl function, using the specific ruthenium-nitrosyl framework of [Ru(tpm)(pap)(NO)] n+ (n = 3, {RuNO} 6 (4 3+ ) and n = 2, {RuNO} 7 (4 2+ )). Facially coordinated r-donor and weak p-donor/acceptor tridentate scorpionate ligand, tris(1-pyrazolyl)methane (tpm) [53] and strongly p-accepting bidentate 2-phenylazopyridine (pap) [54] have been selectively chosen as ancillary ligands in developing the desired Ru-NO derivatives, [Ru(tpm)(pap)(NO)] n+ .…”