Zusammenfassung
Simply by increasing the supersaturation level, racemic [Ru(bpy)(3)](PF6)(2) no longer crystallises as the well-known true racemate (beta-modification; P (3) over bar cl, a = 10.6453(5), c = 16.2987(9) Angstrom, 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 ...
Zusammenfassung
Simply by increasing the supersaturation level, racemic [Ru(bpy)(3)](PF6)(2) no longer crystallises as the well-known true racemate (beta-modification; P (3) over bar cl, a = 10.6453(5), c = 16.2987(9) Angstrom, 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)](PF6)(2).1.5CH(3)COCH(3); delta-type; P32, a = 13.8133(7) Angstrom, c 11.6523(7)Angstrom, 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) Angstrom, 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.
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