Proton-Induced Tuning of Electrochemical and Photophysical Properties in Mononuclear and Dinuclear Ruthenium Complexes Containing 2,2‘-Bis(benzimidazol-2-yl)-4,4‘-bipyridine:  Synthesis, Molecular Structure, and Mixed-Valence State and Excited-State Properties

Abstract

A series of mono- and dinuclear Ru(bpy)2 complexes (bpy = 2,2‘-bipyridine) containing 2,2‘-bis(benzimidazol-2-yl)-4,4‘-bipyridine (bbbpyH2) were prepared. The mononuclear complex [Ru(bpy)2(bbbpyH2)](ClO4)2·CH3OH·4H2O was characterized by an X-ray structure determination. Crystal data are as follows: triclinic, space group P1̄, a = 14.443(4) Å, b = 15.392(4) Å, c = 11.675(2)Å, α = 101.44(2)°, β = 107.85(2)°, γ = 96.36(2)°, V = 2380(1) Å3, Z = 2. The coordination geometry of the ruthenium(II) ion is approximately octahedral. The dihedral angle between the two pyridyl rings in bbbpyH2 is 9.4(3)°, which is close to coplanar, in the complex. Mono- and dinuclear complexes exhibit broad charge-transfer absorption bands at 420−520 nm and emission at 660−720 nm in CH3CN solution with lifetimes of 200−800 ns at room temperature. Transient difference absorption spectra and resonance Raman (rR) spectra were used to assign the charge-transfer bands in the 420−520 nm region and to identify the lowest excited states. Both absorption and emission spectra are sensitive to solvent and solution pH. Deprotonation of the dinuclear complex raises the energies of the π* orbitals of the bbbpyH2 ligand, so that they become closer in energy to the π* orbitals of bpy. The intervalence band of [(bpy)2Ru(bbbpyH2)Ru(bpy)2]5+ is observed at 1200 nm ( ε = 170 M-1 cm-1) in CH3CN. The value of the electronic coupling matrix element, H AB, was determined as 120 cm-1. Upon deprotonation, the IT band was not observed. It is therefore concluded that a superexchange pathway occurs predominantly via the Ru(II) dπ−bbbpyH2 π* interaction, since deprotonation decreases the interaction. The role of the intervening fragments in the bridging ligand is discussed from the viewpoint of orbital energies and their orbital mixing with Ru dπ orbitals.

Synthesis, Electrochemical and Electrogenerated Chemiluminescence Studies of Ruthenium(II) Bis(2,2′‐bipyridyl){2‐(4‐methylpyridin‐2‐yl)benzo[d]‐X‐azole} Complexes

“…Selected distances and bond angles for 1. angles of 78.8(2)°, and the angles between the chelate rings are divided into the usual two groups of 85.9-88.5(2)°and 95.6-99.1(2)°( [15] and to bis(bipyridyl) complexes in general. [16,17] Similarly, the Ru-N bipyridyl bond lengths [2.050-2.078(4) Å] and the benzimidazole bond length [Ru-N(6) = 2.060(4) Å] are very similar to Ru-N bonds in the related complexes.…”

“…[16,17] The N(6)-C (32) and N(6)-C(26) bond lengths of 1.399(6) and 1.335(5) Å are also similar to the previously reported Ru-benzimidazole complex [1.39(1) and 1.35(1) Å] as are the other N-C bonds within the bipyridyl rings. [15] Although it is dangerous to draw conclusions about relative bond strengths from metal-ligand bond lengths alone, it would seem from these data that the benzimidazole ring has donor properties similar to those of the pyridinyl ligands and that these properties are relatively insensitive to substitution of a methyl group in the 3-position of the ring.…”

“…In addition, the closely related mononuclear and dinuclear Ru(bpy) 2 complexes of the free ligand 2,2Ј-bis(benzimidazol-2yl)-4,4Ј-bipyridine have similar oxidation and reduction potentials. [15,20] The oxidation of [Ru(bpy) 3 ] 2+ is at the somewhat more positive potential [E 1/2 (+2/+3) = +0.881 vs. Fc/Fc + ] in acetonitrile, indicating that the benzimidazole ring is a slightly better donor than bipyridyl. On the contrary, reductions of compounds 2 and 3 occur at less negative potentials.…”

Metal‐Induced Tautomerization of p‐ to o‐Quinone Compounds: Experimental Evidence from CuI and ReI Complexes of Azophenine and DFT Studies

“…[12] Furthermore, metal-induced proton migration in coordination compounds is an important feature of functional systems devised for the field of molecular electronics. [13] In this report we describe that the metal-induced tautomerization of azophenine can also occur in non-ionic systems by example of a structurally and spectroscopically characterized organorhenium(i) complex. To explore this phenomenon in a more general manner we also present DFT calculations on the model ligands p-quinonediimine and 2,5-diamino-p-quinonediimine and their ortho-quinonoid forms.…”

Synthesis and DNA Binding of cis-Dichlorobis-benzimdazolebis-(dimethylsulfoxide)ruthenium(II)- hydrate Complexes

“…Ligand's effect on anticancer property 5 is important and it is essential to design superior complexes in terms of effectiveness compared to that which are already available agent such as cis-platin. The imidazole-metal complexes are important [6][7][8][9] in medicine and coordination chemistry. The spectroscopy of these complexes in the absence and presence of plasmid DNA was examined and compared to cis-platin.…”