SO2 Phototriggered Crystalline Nanomechanical Transduction of Aromatic Rotors in Tosylates: Rationalization via Photocrystallography of [Ru(NH3)4SO2X]tosylate2 (X = pyridine, 3-Cl-pyridine, 4-Cl-pyridine)

Thermally reversible solid-state linkage SO2 photoisomers of three complexes in the [Ru(NH3)(4)SO2X]tosylate(2) family are captured in their metastable states using photocrystallography, where X = pyridine (1), 3-Cl-pyridine (2), and 4-Cl-pyridine (3). This photoisomerism exists only in the single-crystal form; accordingly, the nature of the crystalline environment surrounding the photoactive species controls its properties. In particular, the structural role of the tosylate anion needs to be understood against possible chemical influences due to varying the trans ligand, X. The photoexcited geometries, photoconversion levels, and thermal stabilities of the photoisomers that form in 1-3 are therefore studied. 1 and 2 yield two photoisomers at 100 K: the O-bound end-on eta(1)-SO2 (MS1) configuration and the side-bound eta(2)-SO2 (MS2); 3 exhibits only the more thermally stable MS2 geometry. The decay kinetics of the MS2 geometry for 1-3 demonstrate that the greater the free volume of the GS SO2 ligand for a given counterion, the greater the MS2 thermal stability. Furthermore, a rationalization is sought for the SO2 phototriggered molecular rotation of the phenyl ring in the tosylate anion; this is selectively observed in 2, manifesting as nanomechanical molecular transduction. This molecular transduction was not observed in 1, despite the presence of the MS1 geometry due to the close intermolecular interactions between the MS1 SO2 and the neighboring tosylate ion. The decay of this anionic molecular rotor in 2, however, follows a nontraditional decay pathway, as determined by time-resolved crystallographic analysis; this contrasts with the well-behaved first-order kinetic decay of its MS1 SO2 phototrigger.