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Guest molecular species present in organic zeolite crystalline frameworks are often disordered because of insufficient steric fit and non-stoichiometry of composition of the guest compound which may be two or multi-component. In addition to rather common order-disorder phenomena associated with local position and/or orientation of the guest, long range order-disorder effects may be observed. The present work reports on such non-local phenomena in some coordination complex type host materials of channel type crystal structure. Orientational ordering of guest molecules in a channel display interesting stepwise temperature behaviour, i.e. correlation of disorder to order transition between the channels appears in two steps. The temperature dependence of guest ordering within the range 100-350 K in a hexagonal host channel lattice has been determined by single crystal X-ray diffractometry (the crystal preserved its integrity on phase transitions). The host complex used is Ni(NCS)2(4-methylpyridine) 4; the guest species being orthoand metabromonitrobenzenes. The high temperature phase (above 282 or 320 K for ortho and meta isomers, respectively) are hexagonal with a = b = 27.5 Ǻ (approx.) which become doubled in the intermediate phase. The low temperature polymorphs are triclinic with some residual orientational disordering of the guest molecules. The phenomena seem to appear as common for this class of compounds.

Disordering patterns of guest species in organic zeolites