Self-Assembly of Metal–Organic Macrocycle and Functional Metal–Organic Frameworks

Abstract

In Part I, a dodecanuclear manganese metallamacrocycle, [Mn12(dmbshz)12(EtOH)6], was prepared by the reaction of Mn(OAc)2•4H2O with 2,6-dimethoxybenzoylsalicylhydrazide (H3dmbshz). The successive manganese centers are connected by the hydrazide N–N groups of the ligands in an alternating pentadentate binding mode, hexadentate binding mode. The alternation results in two alternating chelation modes around the metal centers, a bidentate–tridentate chelation mode and a tridentate–tridentate chelation mode. The metal ions in the manganese metallamacrocycle are in a •••(AAΔBCAΛB)(AAΔBCAΛB)••• chiral sequence, the alternation of the chiralities expanding the cyclic ring system to a 36-membered dodecanuclear manganese metallamacrocyclic ring system with S6 point group symmetry. In Part II, a porous metal–organic framework (MOF), [Cu24L12(DMF)8(H2O)16]·8DMF, was designed and synthesized using a rigid and bent C2-symmetric tetra-carboxylate ligand, 1,3-bis(3,5-dicarboxylphenylethynyl)benzene (H4L). The framework, a novel twofold interpenetrating MOF based on nanometer–sized metal–organic cuboctahedra (MOCs) as supramolecular building blocks, consists of four different pores. The cavities of the various cages are interconnected to form a 3-D cavity, which comprises of 55.8% of the total unit cell volume. The framework demonstrates high thermal and hygroscopic stabilities. And the fully desolvated solid shows large surface area and high uptake capacities for various gas molecules. In Part Ш, a series of isoreticular metal–organic frameworks were prepared using two different ligands having the same functional units, an isophthalate (iph) unit and a pyridyl unit, simultaneously in each single ligand but interconnected to each other via different linking moieties of different flexibilities. These MOFs have micropores of similar (or different) ‘static aperture size’ but of different (or similar) ‘effective aperture size’. The combination of the iph unit and Cu (or Zn) ion led to 2-D layers of Kagomé (kgm) net topology, the layers being further pillared by the internal auxiliary pyridyl units to form three isoreticular 3-D microporous frameworks. These MOFs have two different types of cage-like pores, cage A and cage B, with different aperture sizes and shapes. (1) The MOFs can distinguish small adsorbates (Ar / N2 / O2 / CO / CO2) neither based on the widely used kinetic diameters (KDs) of the adsorbates nor based on the more shape-dependent minimum diameters (MIN-2s) of the adsorbates. While cage A with a sufficiently large aperture size compared with the dimensions of the adsorbates investigated does not show any size selectivity, cage B with an approximate size match between the adsorbates and the pore apertures shows selectivity for the adsorbates. While the order of the adsorbate sizes based on the KDs is CO (3.76 Å) > N2 (3.64 Å) > O2 (3.46 Å) > Ar (3.40 Å) > CO2 (3.30 Å) and the order based on the MIN-2s is Ar (3.63 Å) > CO (3.339 Å) ≈ CO2 (3.339 Å) > N2 (3.054 Å) > O2 (2.985 Å), the observed order is Ar ≥ O2 ≥ N2 ≈ CO, CO2. (2) Even though the isoreticular MOFs have similar (or different) ‘static aperture size’ of cage B, they show different (or similar) size selectivity for the adsorbates based on the ‘effective aperture size’, which reflects the different extent of the framework flexibility.