A series of nanoporous frameworks constructed by a polycatenated isoreticular 1D ribbon of rings have been developed. The orientation of catenated ribbons can be fine tuned by varying counter anions, which allows both pore size and shape to be systematically adjusted in a pre-synthetic process. Distinct from conventional pore construction modes in which the organic linkers are alternately connected by metal nodes into a 3D periodic arrangement, the present polycatenation approach represents an alternative for constructing soft porous materials with tunable pore metrics and functions. Furthermore, these porous structures can interconvert into each other based on an anion-exchange process, accompanied by the transformation of the interpenetrating structures in different dimensional networks, which is unusual in porous frameworks. In addition, such a porous framework can be post-synthetically modified by a photoinduced [2+2] cycloaddition reaction, which not only achieves the surface modification (from conjugated to non-conjugated inner surface), but also triggers the structural transformation from low dimension to high dimension. Such a post-modification process reinforces the pore architecture through a covalent locking effect and has a great impact on the adsorption properties.

Three isoreticular hydrogen-bonded frameworks with functionalized pore structures were constructed by a modular self-assembly process in which a series of amino acids with various substituents serve as facile exchange subassemblies to decorate the pore wall. The ordered amino acid side-chain groups in the pore channels play an important role in determining the adsorption behavior of the framework materials, and ensure exclusive adsorption of methanol/water over ethanol. Gas-chromatographic separation experiments demonstrated that alcohols can be efficiently separated from ternary water/methanol/ethanol mixtures and revealed a key influence of the adsorbate–host framework interaction on the practical separation performance of mixtures.

A series of metal–organic frameworks based on a flexible, highly charged Bpybc ligand, namely 1⋅Mn⊃OH⁻, 2⋅Mn⊃SO₄²⁻, 3⋅Mn⊃bdc²⁻, 4⋅Eu⊃SO₄²⁻ (H₂BpybcCl₂=1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium dichloride, H₂bdc=1,4-benzenedicarboxylic acid) have been obtained by a self-assembly process. Single-crystal X-ray-diffraction analysis revealed that all of these compounds contained the same n-fold 2D3D Borromean-entangled topology with irregular butterfly-like pore channels that were parallel to the Borromean sheets. These structures were highly tolerant towards various metal ions (from divalent transition metals to trivalent lanthanide ions) and anion species (from small inorganic anions to bulky organic anions), which demonstrated the superstability of these Borromean linkages. This non-interpenetrated entanglement represents a new way of increasing the stability of the porous frameworks. The introduction of bipyridinium molecules into the porous frameworks led to the formation of cationic surface, which showed high affinities to methanol and water vapor. The distinct adsorption and desorption isotherms of methanol vapor in four complexes revealed that the accommodated anion species (of different size, shape, and location) provided a unique platform to tune the environment of the pore space. Measurements of the adsorption of various organic vapors onto framework 1⋅Mn⊃OH⁻ further revealed that these pores have a high adsorption selectivity towards molecules with different sizes, polarities, or π-conjugated structures.

A multifunctional pillared-layer porous coordination polymer, {[Mn₂(Bpybc)(ox)₂]⋅8 H₂O}_n, has been constructed based on a flexible viologen derivative, 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium dichloride (H₂BpybcCl₂), and an oxalate (ox) coligand. Single-crystal X-ray analysis reveals that the compound possesses multichannels with dimensions of about 6.1×6.6 Å along the [110] and [−110] directions and 4.2×7.6 Å along [100], and a void space of about 41.4 %. Hydrogen adsorption measurements at 77 K and 1 atm indicate that the compound exhibits a hydrogen uptake of 0.71 wt %. Owing to the incorporation of bipyridinium acceptor units, the compound can selectively accommodate aromatic donors into its nanosized pores based on charge-transfer interactions in an elastic way, and afford a specific color to different guests. Furthermore, the effect of perturbation exerted by the guest molecules on its magnetic properties has been investigated. The results indicate that the donor inclusion has little effect on its antiferromagnetic behavior, whereas dehydration of the compound decreases the strength of the magnetic exchange couplings and results in a change of the antiferromagnetic transition temperature from 14.7 to 9.8 K.

Self-assembly of the newly synthesized 2-methyl-4,6-bis(4′-pyridyl-1′-pyridinio)pyrimidine dichloride (MbppCl₂) with MnCl₂·4H₂O and Na₂C₂O₄ affords an unprecedented chain-like oxalate-bridged Mn^II polymer consisting of 10-membered ring units, {[Mn₃(OH)(H₂O)₂(Mbpp)(C₂O₄)_3.5]·6.5H₂O}_n (1), which exhibits spin-canted antiferromagnetism at low temperature.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)