Chemical Reaction-Inspired Crystal Growth of a Coordination Polymer toward Morphology Design and Control

This paper reports a novel crystal growth system of a coordination framework {[Cu3(CN)3{hat-(CN)3(OEt)3}]}n (1) (hat-(CN)3(OEt)3 = 2,6,10-tricyano-3,7,11-triethoxy-1,4,5,8,9,12-hexaazatriphenylene).
The coordination polymer is crystallized through the reaction of 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (hat-(CN)6), ethanol, and copper(I) complex, involving the breaking and forming of
covalent bonds. The crystal morphologies obtained in the present system contain dumbbells, cogwheels,
and superlattices. Moreover, in the growth perpendicular to the c-axis, periodic ramification at regular interval
is observed, affording superlattice morphologies. Observation of the growth of dumbbell crystals shows
that the growth rates parallel and perpendicular to the crystallographic c-axis are quite different:  the former
shows a drastic change with the reaction duration, while the latter is almost constant. These results are
reproduced as a simple reaction−diffusion system, indicating that chemical reactions on crystal surfaces
play an important role in determining the macroscopic crystal morphologies.