AI Article Synopsis
- Increasing the supersaturation level leads to the spontaneous resolution of racemic [Ru(bpy)(3)](PF(6))(2), forming a new structure type of pure Lambda- and Delta-crystals instead of the expected beta-modification.
- This new modification is a solvate with a unique crystal structure and is the metastable product formed through specific nucleation kinetics.
- The transformation of the solvate into a second enantiomorphic structure demonstrates the potential for novel optical resolution techniques and highlights the importance of controlling crystallization processes in crystal engineering.
Article Abstract
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.
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| http://dx.doi.org/10.1002/1521-3765(20021004)8:19<4454::AID-CHEM4454>3.0.CO;2-W | DOI Listing |
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