rapid cis-trans isomerism in the dimeric coordination complex [(η
5 -indenyl)Ru
(CO) 2 ] 2 when this molecule is trapped in a self-assembled coordination cage [127]
and the conversion of an overcrowded chromic alkene to a metastable twisted
conformation, upon photoactivation, when incorporated into a tetrahedrally symmetric coordination cage [128]. Champness et al. have also exploited the power of
synchrotron-based X-ray crystallography to support time-resolved IR studies to probe
the fac-mer isomerism of [M(diimine)(CO) 3 X] (M ¼ Re or Mn; X ¼ Cl or Br) units
immobilised in a MOF and shown the presence of the mer-isomer in the photoactivated
crystalline solid [129]. Subsequently, they have shown that the coordination polymer
[(Cu(DMF)(H 2 O)][LRe(CO) 3 Cl].DMF] (L ¼ 2,2
0 -bipyridine-5,5
0 -dicarboxylic acid)
undergoes an irreversible photoinduced charge transfer process. Time-resolved IR
spectroscopy was used to identify the nature of this photoinduced process and how,
under suitable conditions, it is possible to initiate irreversible modification of the crystal
through induction of the charge transfer process. By using the photoinduced process,
which arises purely as a result of the structure of the coordination network, it was
possible to write on the surfaces of crystals [130].
3.3.2 Studies Using Laue Diffraction Techniques
Among the first time-resolved photocrystallographic studies using Laue diffraction
techniques, designed to probe shorter timescales and reduce crystal damage, was
carried out on a di-rhodium complex, [Rh 2 (μ-PNP) 2 (PNP) 2 ][BPh 4 ] (PNP ¼ CH 3 N(P
(OCH 3 ) 2 ) 2 ), which was studied photocrystallographically on the 100 ps timescale
[29] using Laue diffraction methods. The crystal was pumped with 35 ps pulses of a
Ti:sapphire laser tuned to a wavelength of 337 nm, at a temperature of 225 K,
followed by a single 100 ps-wide X-ray pulse after a 100 ps delay. The lifetime of the
excited state species was ca. 35 μs. In this case, the experimental results showed a
shortening of the Rh–Rh distance of 0.136(8) Å upon excitation, and the results are
quantitatively supported by quantum-mechanical calculations. The study shows
similar, but smaller, trends to those described for [Rh 2 (dimen) 4 ][PF 6 ] 2 .MeCN
above [82]. The deconvolution of the overlapping reflections was achieved during
the data reduction, and the structure was refined using the RATIO method [36].
A Cu(I) complex, [Cu(1,10-phenanthroline)(PPh 3 ) 2 ][BPh 4 ], was also studied
using Laue diffraction methods [131] and compared to the [Cu(dmp)(dppe)]
+ cation
that had been studied previously using monochromatic methods [117]. This
phenanthroline complex also crystallises with two independent cations in the asymmetric unit, with one molecule in a more sterically constrained environment.
Photoactivation in the single crystal was expected to induce a MLCT transition,
resulting in transient structural changes. The two independent molecules are again
observed to undergo different structural responses upon activation with λ ¼ 390 nm
light at 90 K. Data were collected using the single-pulse Laue method, the data was
analysed [132], and the results showed considerable distortion in the less restricted
Cu molecule, while no significant changes were observed in the cation adopting the
second, more confined arrangement (Fig. 9). Theoretical studies confirmed that the
Time-Resolved Single-Crystal X-Ray Crystallography
259
5 -indenyl)Ru
(CO) 2 ] 2 when this molecule is trapped in a self-assembled coordination cage [127]
and the conversion of an overcrowded chromic alkene to a metastable twisted
conformation, upon photoactivation, when incorporated into a tetrahedrally symmetric coordination cage [128]. Champness et al. have also exploited the power of
synchrotron-based X-ray crystallography to support time-resolved IR studies to probe
the fac-mer isomerism of [M(diimine)(CO) 3 X] (M ¼ Re or Mn; X ¼ Cl or Br) units
immobilised in a MOF and shown the presence of the mer-isomer in the photoactivated
crystalline solid [129]. Subsequently, they have shown that the coordination polymer
[(Cu(DMF)(H 2 O)][LRe(CO) 3 Cl].DMF] (L ¼ 2,2
0 -bipyridine-5,5
0 -dicarboxylic acid)
undergoes an irreversible photoinduced charge transfer process. Time-resolved IR
spectroscopy was used to identify the nature of this photoinduced process and how,
under suitable conditions, it is possible to initiate irreversible modification of the crystal
through induction of the charge transfer process. By using the photoinduced process,
which arises purely as a result of the structure of the coordination network, it was
possible to write on the surfaces of crystals [130].
3.3.2 Studies Using Laue Diffraction Techniques
Among the first time-resolved photocrystallographic studies using Laue diffraction
techniques, designed to probe shorter timescales and reduce crystal damage, was
carried out on a di-rhodium complex, [Rh 2 (μ-PNP) 2 (PNP) 2 ][BPh 4 ] (PNP ¼ CH 3 N(P
(OCH 3 ) 2 ) 2 ), which was studied photocrystallographically on the 100 ps timescale
[29] using Laue diffraction methods. The crystal was pumped with 35 ps pulses of a
Ti:sapphire laser tuned to a wavelength of 337 nm, at a temperature of 225 K,
followed by a single 100 ps-wide X-ray pulse after a 100 ps delay. The lifetime of the
excited state species was ca. 35 μs. In this case, the experimental results showed a
shortening of the Rh–Rh distance of 0.136(8) Å upon excitation, and the results are
quantitatively supported by quantum-mechanical calculations. The study shows
similar, but smaller, trends to those described for [Rh 2 (dimen) 4 ][PF 6 ] 2 .MeCN
above [82]. The deconvolution of the overlapping reflections was achieved during
the data reduction, and the structure was refined using the RATIO method [36].
A Cu(I) complex, [Cu(1,10-phenanthroline)(PPh 3 ) 2 ][BPh 4 ], was also studied
using Laue diffraction methods [131] and compared to the [Cu(dmp)(dppe)]
+ cation
that had been studied previously using monochromatic methods [117]. This
phenanthroline complex also crystallises with two independent cations in the asymmetric unit, with one molecule in a more sterically constrained environment.
Photoactivation in the single crystal was expected to induce a MLCT transition,
resulting in transient structural changes. The two independent molecules are again
observed to undergo different structural responses upon activation with λ ¼ 390 nm
light at 90 K. Data were collected using the single-pulse Laue method, the data was
analysed [132], and the results showed considerable distortion in the less restricted
Cu molecule, while no significant changes were observed in the cation adopting the
second, more confined arrangement (Fig. 9). Theoretical studies confirmed that the
Time-Resolved Single-Crystal X-Ray Crystallography
259