Hydrogen-Bonded Inclusion Compounds with Reversed Polarity: Anionic Metal-Complexes and Cationic Organic Linkers

Synthesized and structurally characterized is a new series
of soft-host
frameworks assembled by charge-assisted hydrogen bonds between an
anionic metal complex (MC) and cationic organic linkers (OL), specifically
[Co­(en)­(ox)2]− and diprotonated 4,4′-bipyridinium
(H2bpy) or 1,2-bis­(4-pyridinium)­ethylene (H2bpye). While frameworks built of cationic complexes and anionic organic
linkers are already well-known, the seven new compounds described
here represent the first series of frameworks with reversed polarity,
that is, made of anionic complexes and cationic organic linkers. The
compounds have a general formula [OL]­[MC]2·n(guest), where the guest molecules 4,4′-biphenol
(bp), 4-methoxyphenol (mp), 1,4-dimethoxybenzene
(dmb), 1,6-dimethoxynaphtalene (dmn), and 4-nitroanisole (na). Structurally the compounds
can be described as pillared-layer frameworks with layers constructed
of MC anions and linked together by hydrogen-bonded cationic OL pillars.
The guest molecules occupy the galleries between the pillars while
their steric, electronic, and π–π and hydrogen-bonding
capabilities influence the overall structure of the soft frameworks.