Guest Exchange Reactions in Isostructural 3D Porous Coordination Polymers of Ni(II), Co(II), and Mn(II)

A series of isostructural compounds,
{[Ni2­(DBIBA)3]·​(BF4)·​6H2O}n (1), {[Ni2­(DBIBA)3]·​(ClO4)·​3H2O}n (2), {[Ni2­(DBIBA)3]·​(NO3)·​3H2O}n (3), {[Ni2­(DBIBA)3]·​Cl·​C2H5OH}n (4) {[Co2­(DBIBA)3]·​(ClO4)·​3H2O}n (5), {[Co2­(DBIBA)3]·​Cl·​3C2H5OH}n (7), {[Co2­(DBIBA)3]·​Cl·​3DMF}n (8), {[Co2­(DBIBA)3]·​Cl·​3CH3COCH3·​7H2O}n (9), and {[Mn2­(DBIBA)3]·​Cl·​3DMF·​3H2O}n (10), have been
afforded via anion and solvent exchanges of previously reported coordination
polymers {[Ni2­(DBIBA)3]·​Cl·​18H2O}n, {[Co2­(DBIBA)3]·​Cl·​9H2O}n, and {[Mn2­(DBIBA)3]·​Cl·​3H2O}n (DBIBA = 5-di­(1H-benzo­[d]­imidazol-1-yl)­benzoate). Anion-exchanged
compounds including {[Co2­(DBIBA)3]·​(NO3)·​3H2O}n (6) have also been synthesized under solvothermal conditions
by employing metal salts and the corresponding acid hydrolysis of
the cyanide functional group of 5-di­(1H-benzo­[d]­imidazol-1-yl) benzonitrile (DBIBN). These structures
are obtained with retaining crystallinity, and only insignificant
changes are observed in bond lengths and bond angles involving the
metal ion. However, noncovalent supramolecular interactions (anion−π,
π–π, and hydrogen bonding) are utterly affected
or changed. Interestingly, in complex 9, the chloride
ion moves from the node of the parent complex to the center of the
cavity, where it is surrounded by a hexameric water cluster revealing
strong H-bonding, which is very rare to be seen. Exchange of solvent
molecules leaves the size of the voids unaltered, but anion exchanges
are accompanied by shrinking of the voids, except in the case of NO3– exchange, where there is no change in
volume. All are isoreticular structures with a binodal 4,6-connected stp net topology. These compounds have been characterized
by single-crystal X-ray crystallography, IR spectroscopy, TGA, PXRD,
and elemental analysis.