Hydrothermal crystal growth and Vernier structures of the metal benzenedicarboxylates MIL-47 and MIL-53 containing guest molecules of benzenecarboxylic acid

• Crystal growth of MIL-47, MIL-53Al, and MIL-53Ga.
• The Vernier structures have corner-sharing MO6 octrahedral chains and chains of H2BDC molecules.
• The stoichiometry is determined by the ratio of the host framework to the guest H2BDC column lengths.
• A correlation is established between the stoichiometry and the radius of the metal ion.
• All atoms in the Al and Ga compounds show sinusoidal modulations transverse to the channel axis.

The nanoporous frameworks VO(bdc), MIL-47, and M(OH)(bdc), MIL-53; bdc=1,4-benzenedicarboxylate, can absorb various guest species in their channels. As synthesized, the channels are filled with H2bdc molecules that have been reported to be disordered, except for [In(OH)bdc](H2bdc)3/4, 1, which has a inorganic-organic hybrid Vernier structure with the H2bdc molecules forming an ordered sublattice. Based on X-ray data from large single crystals grown by hydrothermal techniques, similar Vernier structures have been found for MIL-47, [VO(bdc)](H2bdc)5/7, 2, MIL-53Al, [Al(OH)(bdc)](H2bdc)11/16, 3, and MIL-53Ga, [Ga(OH)(bdc)](H2bdc)12/17, 4. The Vernier structures of 2–4 at room temperature were determined based on superstructure unit cells that index both host and guest sublattices: 2, space group P21, a=23.903(2), b=17.191(2), c=25.722(2) Å, β=105.914(8)°; 3, P21/n, a=105.224(4), b=12.2441(5), c=17.0143(6) Å, β=89.99(1)°; 4, P21, a=114.562(5), b=12.1503(5), c=17.4275(7) Å, β=89.99(1)°. The number of guest H2bdc molecules per framework metal ion is determined by the ratio of the repeat distances of the two sublattices which depends on the size of the metal ion in the octahedral chain. The octahedral chains are parallel to [201] in 2, and to [100] in 3 and 4. Remarkably, all atoms in 3 and 4 show significant sinusoidal modulations transverse to the chain axis.

The sinusoidal modulation along the channel axis direction involving all atoms in the structure of [Al(OH)(bdc)](H2bdc)11/16.Figure optionsDownload as PowerPoint slide