Polymorphism preferred conformation

A number of substituted propane-l,3-diamine (64) compounds of the type [PtL2] and [PtX2L2] (X = Cl, Br, or NH3) have been described. Several of the latter species exhibited polymorphism which was attributed to either different H-bonded linkages or different chelate ring conformations in the two forms.In solution their n.m.r. spectra are consistent with a preference for a chair-type conformation with the Cl or OH axial.Similar n.m.r. spectral studies have also been reported for some related N-methyl substituted... 

Ojala etal. (1998) reported on the crystallization of two conformational polymorphs (Bernstein 1987) (see Chapter 5) of acetone tosyUiydrazone 3-XX. A triclinic form and a monoclinic form are both obtained from anhydrous ethanol—sometimes together. If the crystallizing solution is allowed to evaporate completely, only the monoclinic form is obtained, suggesting that it is the thermodynamically preferred form at room temperature. This is consistent with Ostwald s Rule of Stages and McCrone s (1965) test for relative stability of polymorphs according to which the more stable polymorph... 

Conformational polymorphism is the existence of different conformers of the same molecule in different polymorphic modifications, as represented in Fig. 5.1(a),(b). Additionally, Corradini has specified fhaf fhe conformers are nearly isoenergefic, and also includes as an example, racemic and optically active crysfals for the case of chiral molecules. While both the general definition of polymorphism and chemists general understanding of conformation are fraught with nuances and special complicating circumstances, we prefer the general definition of conformational polymorphism here, without Corradini s additional qualifications. Specific questionable or unusual cases can be dealt with as encountered. 

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