Crystal and molecular structures of [Ru(bpy)3](PF6)3 and [Ru(bpy)3](PF6)2 at 105 K

Abstract

Dark green-black crystals of [Ru(bpy),](PF,), (111) were obtained from [Ru(bp )3](PF6)2 (11) by oxidation with Mn02 in 7 M H2S04. The X-ray crystal structures of I11 (trigonal R k , a = 17.846 (7) 1, c = 19.915 (7) A, Z = 6) and I1 (trigonal P31c, u = 18.338 (7) A, c = 16.216 (13) A, Z = 6) were determined at 105 K. The low temperature structure of I1 shows the a-and b-axis increased by a factor of 47 relative to the room temperature structure and has three distinct Ru sites (phase transition at 190 ( 5 ) K). This explains many recent spectroscopic observations. The Ru-N distances of I1(2.053 (2) A) are virtually indistinguishable from those of I11 (2.057 (3) A). This is compatible with the high electron self-exchange rate between I1 and 111. The pattern of differences in intra-bpy bond lengths seems in contradiction to the conventional a-backbonding model. Changes of bpy distances in [M(bpy),], bpy, Hbpy', and H2bpy2+ are examined by a principal component analysis, which yields two main factors: The first factor is related to the temperature of measurement, the crystal packing pattern or the model used to interpret the diffraction data. The second factor can be characterized as electronic in nature and confirms that there are as yet unresolved contradictions in the model of a-backbonding as applied to the ligand geometry of [M(bpy),]"+ complexes.

Characterization of excited electronic and vibronic states of platinum metal compounds with chelate ligands by highly frequency-resolved and time-resolved spectra

“…It is spectrally transparent below = 17800 cm -1 and thus provides a spectral window of more than 3300 cm -~ above the lowest electronic state of [Os(bpy)3] 2+. As discussed in Section 3.6 (Table 6), [Os(bpy)3] 2+ can substitute all three crystallographic sites occurring in the low-temperature structure [184] of the [Ru(bpy)3](PF6) 2 matrix [38,92]. The dopants seem to replace the host molecules quite regularly.…”

“…Despite the fact that this matrix represents a neat material one obtains highly resolved spectra of [Ru(bpy)~] 2+ complexes (e.g., see [175][176][177][178][179][180]). An advantage is that the chromophores lie on high-symmetry C3 sites, where the molecular ~ axes lie parallel to the crystallographic ~ axis [ 184]. This is very convenient for measurements of polarized absorption spectra [145][146][147][148].…”

“…This is very convenient for measurements of polarized absorption spectra [145][146][147][148]. For emission measurements this matrix may cause some problems, if the occurrence of energy transfer processes between the three sites [184] in the unit cell (see [185]; Sect. 3.6) and/or via the lowest triplet exciton bands ~ is not taken into account.…”

“…The determination of the low-temperature structure of [Ru(bpy-hs)3](PF6)2 revealed the existence of three different crystallographic sites, where [Ru(bpy)3] 1+ sits on C3 positions [184]. This crystallographic study confirms the spectroscopic investigations of [Os(bpy)3] 2+ doped into [Ru(bpy)3] (PF6)2, where the guest molecules clearly display the occurrence of the three sites ( [38,92]; see also Sect.…”

“…According to the identification of three crystallographic sites [184], one also expects the presence of a third spectroscopic site (site C) which should lie at higher energy than site B. Moreover, when [Os(bpy)3] 2+ is doped into [Ru(bpy)3] (PF6) 2 three spectroscopic sites of the probing guest molecules can be identified.…”