Spacer-Directed Selective Assembly of Copper Square or Hexagon and Ring-Stacks or Coordination Nanotubes

The
use of simple self-assembly methods to direct or engineer porosity
or channels of desirable functionality is a major challenge in the
field of metal–organic frameworks. We herein report a series
of frameworks by modifying square ring structure of [{Cu2(5-dmpy)2(L1)2­(H2O)­(MeOH)}2{ClO4}4]·4MeOH (1·4MeOH, 5-dmpy = 5,5′-dimethyl-2,2′-bipyridine,
HL1 = 4-pyridinecarboxylic acid). Use of pyridyl carboxylates
as directional spacers in bipyridyl chelated Cu­(II) system led to
the growth of square unit into other configurations, namely, square
ring, square chain, and square tunnel. Another remarkable characteristic
is that the novel use of two isomers of pyridinyl–acrylic acid
directs selectively to two different extreme tubular formsaligned
stacking of discrete hexagonal rings and crack-free one-dimensional
continuum polymers. This provides a unique example of two extreme
forms of copper nanotubes from two isomeric spacers. All of the reactions
are performed in a one-pot self-assembly process at room temperature,
while the topological selectivity is exclusively determined by the
skeletal characteristics of the spacers.