Homochiral Metal-Organic Frameworks for Enantioselective Separations in Liquid Chromatography.

Selective separation of enantiomers is a substantial challenge for the pharmaceutical industry. Chromatography on chiral stationary phases is the standard method, but at a very high cost for industrial-scale purification due to the high cost of the chiral stationary phases. Typically, these materials are poorly robust, expensive to manufacture, and often too specific for a single desired substrate, lacking desirable versatility across different chiral analytes. Here, we disclose a porous, robust homochiral metal-organic framework (MOF), TAMOF-1, built from copper(II) and an affordable linker prepared from natural l-histidine. TAMOF-1 has shown to be able to separate a variety of model racemic mixtures, including drugs, in a wide range of solvents of different polarity, outperforming several commercial chiral columns for HPLC separations. Although not exploited in the present article, it is worthy to mention that the preparation of this new material is scalable to the multikilogram scale, opening unprecedented possibilities for low-energy chiral separation at the industrial scale.

Spontaneous Magnetization in Homometallic µ6-Oxalate Coordination Polymers.

The reaction of 1,2,4-triazole and NaF with M(ox) (M = transition-metal dication; ox = oxalate dianion) under hydrothermal conditions has led to the isolation of a variety of hybrid organic-inorganic coordination polymers. Four structurally different 3D networks were obtained, depending on the transition metal, with stoichiometry [M2(H2O)(µ2-ox)][M2(µ3-trz)6] [M = Fe (1), Co (2), Ni (3)], [Zn2(H2O)(µ3-trz)2(µ2-ox)] (4), [Mn3(µ3-trz)2(µ6-ox)(µ3-F)2] (5), and [Fe3(µ3-trz)2(µ6-ox)(µ2-F)2] (6). In all cases, the magnetic behavior is dominated by antiferromagnetic exchange interactions between paramagnetic centers. Remarkably, 5 and 6 present a novel magnetic connectivity around the oxalate anion: a µ6-bridging mode. This magnetic geometry promotes multiple triangular arrangements among antiferromagnetically coupled spin carriers, resulting in a complex magnetic network because of the presence of competing interactions. These materials exhibit spontaneous magnetization below 9 and 66 K, respectively.

Controlling the self-assembly of a mixed-metal Mo/V-selenite family of polyoxometalates.

Five mixed-metal mixed-valence Mo/V polyoxoanions, templated by the pyramidal SeO(3)(2-) heteroanion have been isolated: K(10)[Mo(VI)(12)V(V)(10)O(58)(SeO(3))(8)]⋅18 H(2)O (1), K(7)[Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(SeO(3))]⋅31 H(2)O (2), (NH(4))(7)K(3)[Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(SeO(3))(Mo(V)(6)V(V)-O(22))]⋅40 H(2)O (3), (NH(4))(19)K(3)[Mo(VI)(20)V(V)(12)V(IV)(4)O(99)(SeO(3))(10)]⋅36 H(2)O (4) and [Na(3)(H(2)O)(5){Mo(18-x)V(x)O(52)(SeO(3))} {Mo(9-y)V(y)O(24)(SeO(3))(4)}] (5). All five compounds were characterised by single-crystal X-ray structure analysis, TGA, UV/Vis and FT-IR spectroscopy, redox titrations, and elemental and flame atomic absorption spectroscopy (FAAS) analysis. X-ray studies revealed two novel coordination modes for the selenite anion in compounds 1 and 4 showing η,µ and µ,µ coordination motifs. Compounds 1 and 2 were characterised in solution by using high-resolution ESI-MS. The ESI-MS spectra of these compounds revealed characteristic patterns showing distribution envelopes corresponding to 2- and 3- anionic charge states. Also, the isolation of these compounds shows that it may be possible to direct the self-assembly process of the mixed-metal systems by controlling the interplay between the cation "shrink-wrapping" effect, the non-conventional geometry of the selenite anion and fine adjustment of the experimental variables. Also a detailed IR spectroscopic analysis unveiled a simple way to identify the type of coordination mode of the selenite anions present in POM-based architectures.

Assembly of a family of mixed metal {Mo:V} polyoxometalates templated by TeO3(2-): {Mo12V12Te3}, {Mo12V12Te2} and {Mo17V8Te}.

The influence of the pyramidal heteroanion, TeO(3)(2-) in the self-assembly of mixed metal (Mo/V) systems, is demonstrated by the isolation of three novel mixed-metal, mixed-valence architectures, {Mo(12)V(12)Te(3)} (1), {Mo(12)V(12)Te(2)} (2) and {Mo(17)V(8)Te} (3) with the tellurium centres exhibiting the novel µ(8)-TeO(4) and µ(9)-TeO(3) coordination modes while compounds 1 and 2 were discovered utilizing ESI mass spectrometry.