DFT Optimised-Geometry Structures of Ru II Arene Complexes

A geometry optimisation of complexes 1−6 and 8−16 with the general formula [(6- arene)Ru(N,N')(L)]2+ was performed for both the ground state (S0) and the lowest- lying triplet state (T0), employing the DFT method with the B3LYP functional, as described in the Computation section in Chapter 2. The corresponding bond lengths for each geometry are shown in Tables 4.3 and 4.4.

Table 4.3. Selected calculated bond distances (Å) for RuII arene complexes 1−6 and

8−16in the ground state (S0) geometry.

Compound Ru−N(L) Ru−N,N' Ru−N,N' Ru−arene(centroid)

(1) 2.151 2.117 2.115 1.852 (2) 1.940 2.101 2.104 1.811 (3) 1.940 2.105 2.100 1.811 (4) 2.145 2.118 2.115 1.850 (5) 1.940 2.104 2.101 1.810 (6) 1.940 2.104 2.101 1.810 (8) 2.159 2.124 2.125 1.862 (9) 2.150 2.114 2.114 1.850 (10) 2.148 2.119 2.121 2.032 (11) 2.147 2.119 2.121 1.844 (12) 2.148 2.119 2.121 1.844 (13) 2.151 2.104 2.104 1.853 (14) 2.148 2.118 2.114 1.850 (15) 2.146 2.118 2.112 1.853 (16) 2.148 2.117 2.114 1.850

Table 4.4.Selected calculated bond distances (Å) for RuIIarene complexes1−6and

8−16in the lowest-lying triplet state (T0) geometry.

4.3.3.1 Ground State (S0) Geometry

All the DFT geometry-optimised RuII arene complexes have a pseudo-octahedral structure in the ground-state (S0). The calculated Ru−N,N'(bpm) distances in the bpm- containing complexes1−6, vary around the same value (~2.12 Å). The Ru−N(L) bond lengths in 1−6 are ~1.94 Å, except for complexes 1 and 4 which are slightly larger (2.15 and 2.14 Å, respectively). For complexes 2 and 6, the computed Ru−N(L) distances are slightly shorter than the ones determined by X-ray diffraction crystallography (2.11 and 2.12 Å, respectively). The experimental evidence that they are almost identical was also reproduced by the computational results. The calculated Ru−p-cym(centroid) distances for complexes 1 and 4 have similar values, which are slightly larger (~1.85 Å) when compared to those of complexes 2, 3, 5 and 6. Particularly in the case of complexes 2 and 6, the computed Ru−p-cym(centroid) distances are larger than those found in their X-ray crystal structures (1.69 and 1.70 Å, respectively). The calculated Ru−N,N'(bpm) distances in the bpm−Py containing RuII arene complexes 1 (p-cym), 8 (hmb), and 9 (ind), resulted in almost identical

Compound Ru−N(L) Ru−N,N' Ru−N,N' Ru−arene(centroid)

(1) 2.108 2.158 2.452 2.089 (2) 2.139 2.404 2.131 2.058 (3) 2.140 2.081 2.345 2.625 (4) 2.133 2.414 2.129 2.067 (5) 2.119 2.132 2.410 2.069 (6) 2.133 2.396 2.132 2.058 (8) 2.159 2.151 2.466 2.014 (9) 2.132 2.134 2.389 2.110 (10) 2.479 2.120 2.119 1.844 (11) 2.148 2.119 2.119 1.846 (12) 2.478 2.100 2.102 2.035 (13) 2.137 2.355 2.125 2.108 (14) 2.149 2.117 2.114 1.851 (15) 2.146 2.116 2.113 1.849 (16) 2.146 2.122 2.439 2.078

values, being slightly larger (~0.1 Å) in the case of complex 8 (2.13 Å). The same trend was observed for its Ru−N(Py) and Ru−hmb(centroid)bond lengths in, which are both ~0.1 Å longer. The Ru−N,N' and the Ru−N(Py) bond distances in complexes 10 and 12 (phen and bathophen, respectively) display the same value (~2.12 Å); however, complex 10 was found to have a longer Ru−p-cym(centroid) distance in comparison to complex 12. This same bond distance also differs significantly from that determined by X-ray crystallography for complex 10 (vide supra), where the value predicted isca. 0.4 Å larger. Conversely, the calculated Ru−N(Py)distances in10 were found to be in good agreement with those in the X-ray crystal structure.; its Ru−N,N'(phen) distances are barely longer. The DFT calculations show that the Ru−N,N'(bpm) distance in complex 9 is ca. 0.10 Å shorter than the analogue Ru−N,N'(bpy)distance found in complex13. TheRu−N(Py) and Ru−ind(centroid)distances in9and13are practically within the same range. When compared to the X-ray crystal structure, the calculated Ru−ind(centroid) as well as the Ru−N,N'(bpy) bond length distances of complex 13 were found to be slightly larger, whereas the corresponding Ru−N(Py) is in good agreement. Finally, for complexes 14−16, the calculations show that the Ru−N,N'(bpm), the Ru−N(L), and the Ru−p-cym(centroid)distances are identical in the three cases (~2.12, 2.15, and 1.85 Å, respectively).

4.3.3.2 Lowest-Lying Triplet State (T0) Geometry

The lowest-lying triplet states geometries were also optimised for complexes 1−6and

8−16, due to the key role that this state can play in their photochemistry. It was found that the Ru−N(Py) distances are practically within the same range for complexes 1−6 (~2.14 Å), except for complexes 1 and 4 which display slightly smaller values. All complexes have similar Ru−N(L) distances, except complexes 1 and 5 which are

slightly shorter, when compared to the ground state (S0). Within this series (1−6), one of the Ru−N,N' bond distances in the T0 state is considerably longer than the other, typically 2.18 and 2.40 Å. The Ru−p-cym(centroid) distances are in general longer compared to the ground state (~2.06 Å); complex 4having the largest value (ca. 2.26 Å). For complexes 8 and 9, the corresponding Ru−N(Py) bond lengths are slightly longer, and also remain unchanged compared to those in the ground state. Both of the calculated Ru−N,N'(bpm)distances in each case have two different values, being one of them significantly larger (~2.4 Å). Each of the computed Ru−arene(centroid) distances (hmb for 8 and ind for 9) are longer than those calculated for the ground state. Complex 11 was found to keep nearly the same geometry as in S0. In the case of complexes 10 and 12, the estimated Ru−N(Py) distance are considerably elongated (~2.5 Å) whereas the corresponding Ru−N,N' bond lengths are almost identical to the ones observed for S0 and also very similar between them (~2.11 Å). In the same way as observed in the X-ray crystal structure, the computational results show that the calculated Ru−p-cym(centroid) distance in complex 10 is shorter than that found in the ground state, whereas the opposite trend is found in the calculation results of complex

12. Complexes 9 and13 display similar Ru−N(Py) bond distances as those calculated for their S0. Furthermore, these two complexes follow the common trend of having one Ru−N,N'(bpm) bond length longer than the other, while the Ru−ind(centroid)lengths are in general larger than those in the ground state. Finally, for complexes14−16, the calculated Ru−N(L) distances are found to be larger than those computed for complex

1 (and practically for any of all the bpm−p-cym containing derivatives). The value resembles more to that obtained for the ground state. In the case of the Ru−N,N'(bpm) distances, while complex 16 follows the common trend of having one Ru−N,N'(bpm) bond length larger than the other, complexes 14and 15 do not follow it. Both of the

calculated Ru−N,N'(bpm)distances for complexes14 and15are within the same range (~2.11 Å).