BN-Doped Metal-Organic Frameworks: Tailoring 2D and 3D Porous Architectures through Molecular Editing of Borazines

Building on the MOF approach to prepare porous materials, herein we report the engineering of porous BN-doped materials using tricarboxylic hexaarylborazine ligands, which are laterally decorated with functional groups at the full-carbon 'inner shell'. Whilst an open porous 3D entangled structure could be obtained from the double interpenetration of two identical metal frameworks derived from the methyl substituted borazine, the chlorine-functionalised linker undergoes formation of a porous layered 2D honeycomb structure, as shown by single-crystal X-ray diffraction analysis. In this architecture, the borazine cores are rotated by 60° in alternating layers, thus generating large rhombohedral channels running perpendicular to the planes of the networks. An analogous unsubstituted full-carbon metal framework was synthesised for comparison. The resulting MOF revealed a crystalline 3D entangled porous structure, composed by three mutually interpenetrating networks, hence denser than those obtained from the borazine linkers. Their microporosity and CO2 uptake were investigated, with the porous 3D BN-MOF entangled structure exhibiting a large apparent BET specific surface area (1091 m2  g-1 ) and significant CO2 reversible adsorption (3.31 mmol g-1 ) at 1 bar and 273 K.

Zeolitic boron imidazolate frameworks

B-hive? A family of crystalline materials analogous to porous AlPO(4) but based on boron imidazolate frameworks (BIFs) can be formed by the crosslinking of various presynthesized boron imidazolates with monovalent cations (Li(+) and Cu(+), see picture). This synthetic method is capable of generating a large variety of open frameworks, ranging from the four-connected zeolitic sodalite type to the three-connected chiral (10,3)-a type.

Construction of a functional layered solid using the tetrakis(imidazolyl)borate coordinating anion

The coordination polymer Pb[B(Im)(4)](NO(3)), constructed by using tetrakis(imidazolyl)borate and lead(II) nitrate solutions, is a layered material with the metal centers facing the interlayer spacing. As in naturally occurring layered minerals, this compound can readily undergo anion exchange in the solid state with retention of crystallinity. We examined stoichiometric exchange of (15)N-nitrate for nitrate and iodide for nitrate by (15)N and (207)Pb SSNMR and confirmed retention of crystallinity by IR and powder XRD diffraction.

Crystal chemistry of tetraradial species. Part 8. Mix and match: cation geometry, ion packing, hydrogen bonding, and π–π interactions in cis-2,2′-bipyridinium(1+) and 1,10-phenanthrolinium(1+) tetraphenylborates — and what about proton sponges?

The crystal structures at −20 °C of cis-2,2′-bipyridinium(1+) (BPTB, P21/n, a = 9.249(3), b = 14.093(7), c = 20.285(3) Å, β = 92.86(2)°, Z = 4) and 1,10-phenanthrolinium(1+) (PTB, P21/c, a = 11.194(2), b = 13.837(3), c = 18.303(3) Å, β = 107.82(1)°, Z = 4) tetraphenylborates have been determined. Inasmuch as 1,10-phenanthroline is an aromatically bridged cis-2,2′-bipyridine, monoprotonation results, in both systems, in the formation of an intra-cation N—H … N′ hydrogen bond, the geometric and spectroscopic properties of which we have investigated. The cation skeleton in PTB is planar to 0.03(2) Å; in BPTB the dihedral angle between the two cation ring planes is 5.2°. In the pale yellow PTB there are significant π–π stacking interactions that persist into solution. The effect of protonation on the geometry of the 2,2′-bipyridine and 1,10-phenanthroline systems is examined in considerable detail and compared with the corresponding effects in the paraquat(2+) and similar cations. On both geometric and spectroscopic (infrared spectra between 10 and 295 K) evidence, the N—H … N′ hydrogen-bonding interaction is stronger in BPTB; in PTB this interaction is among the weakest reported in crystals, the ν(NH) stretching frequency at 10 K being as high as 3279 cm−1. A detailed comparison of the geometries of the intra-cation N—H … N′ bonds in BPTB and PTB with those in classical and modified proton-sponge cations has led to the formulation of criteria useful in predicting the occurrence of proton-sponge-like properties. Key words: bipyridinium ions, hydrogen bonding, phenanthrolinium ions, proton sponges, tetraphenylborates.