Nucleation-controlled crystallization of a new, spontaneously resolved solvate of [Ru(bpy)3](PF6)2 and its desolvation reaction.
Simply by increasing the supersaturation level, racemic [Ru(bpy)(3)](PF(6))(2) no longer crystallises as the well-known true racemate (beta-modification; P$\bar 3$c1, a=10.6453(5), c=16.2987(9) A, Z=2). Rather, it spontaneously resolves and forms a conglomerate of pure Lambda- and pure Delta-crystals with a so far unknown structure type. This new modification actually is a solvate ([Ru(bpy)(3)](PF(6))(2).1.5 CH(3)COCH(3); delta-type; P32, a=13.8133(7) A, c=11.6523(7) A, Z=2). By a solution-mediated equilibration the new modification is shown to be the metastable (Ostwald) product, which is formed based on nucleation kinetics. Upon desolvation the solvate transforms into a second enantiomorphic crystal structure (gamma-type; P3(1), a=10.3809(4), c=26.2576(13) A, Z=3). The latter could previously only be obtained by chemical resolution prior to crystallisation, but could not be accessed directly from racemic solutions. However, the new delta-modification can now be utilised for optical resolution by the so-called method of "resolution by entrainment". This example emphasises the potential that both kinetically controlled crystallisation and desolvation of solvates bear with respect to crystal engineering.