Hydrogen-bonded boron imidazolate frameworks

Jian Zhang, Tao Wu, Pingyun Feng, Xianhui Bu
2010 Dalton Transactions  
The research on tetrahedral imidazolate frameworks takes on a new direction into the supramolecular area through the synthesis of three hydrogen-bonded boron imidazolate (B[im] 4 -) frameworks (HBIFs) that show distinct three-and two-dimensional supramolecular architectures: (1) the ionic diamond net containing the first reported Li + complex with ethylene glycol, (2) four-connected double-layers built from a new neutral Li(tea)B(im) 4 (tea = triethanolamine) complex, and (3) three-connected
more » ... three-connected (6,3) layer of H 3 O·BH(eim) 3 . Designed synthesis of zeolitic imidazolate frameworks has attracted much attention in recent years due to their potential applications in gas storage and separation etc. 1-6 In these materials, tetrahedrally coordinated atoms (T atoms) are cross-linked by various imidazolate-type ligands to form a four-connected network. Inspired by the similarity between T-im-T angles (im = imidazolate) in metal imidazolates and T-O-T angles in zeolitic SiO 2 and AlPO 4 frameworks, two general strategies have been developed. One is based on divalent metal (M 2+ = Zn 2+ or Co 2+ ) imidazolates in which M 2+ and imreplace Si 4+ and O 2-, respectively, resulting in the general framework composition M(im) 2 (denoted ZIFs), just like SiO 2 . 2-5 Another is based on the use of pre-synthesized boron imidazolate ligands that are subsequently linked through monovalent cations (e.g., M + = Li + and Cu + ) into extended frameworks with the general framework composition MB(im) 4 (denoted BIFs), similar to AlPO 4 . 6 The use of lightweight elements (e.g., Li and B) as framework vertices has a great potential for the creation of low-density and high porosity adsorbents. Because of this, we are interested in developing strategies to create Li-B-imidazolates that extend beyond the LiB(im) 4 -type covalent frameworks to include supramolecular frameworks (denoted HBIFs) based on hydrogenbonding interactions. Such materials should be able to broaden the type of materials that can be constructed from the lightweight second-row elements. The Li-B-imidazolate system has an inherent advantage for creating hydrogen-bonded frameworks because of the unique hydrogen-bonding capability of the tetrahedrally distributed N donors in the pre-synthesized boron imidazolate ligands. With B(im) 4 as the ready hydrogen-bonding acceptor, the challenge then becomes the creation of hydrogen-bonding donors that can form suitable framework vertices. In the system with the Li + ions, one strategy to create hydrogen-bonding donors is to employ a
doi:10.1039/b924633a pmid:20449407 fatcat:asd2qmjg7zhjzpefoprer3avyi