Assembly of a Homochiral, Body-Centered Cubic Network Composed of Vertex-Shared Mg_(12) Cages: Use of Electrospray lonization Mass Spectrometry to Monitor Metal Carboxylate Nucleation

摘要

Reaction of Mg(NO_3)_2·6H_2O with (+)-camphoric acid (H_2cam) in acetonitrile results in the immediate formation of soluble, dimetallic [Mg_2(Hcam)_3]~+ cations. The formation of these stable cations in solution was determined by electrospray ionization mass spectrometry (ESI-MS). These dimers are 3-fold paddle-wheels, which associate together through the neutral acid units to build the metal-organic framework [Mg_2(Hcam)_3·3H_2O]·NO_3-MeCN, 1. The network consists of a series of fused Mg_(12) cages that have 12 water molecules at their centers, creating isolated OD cavities within the structure. Overall, the extended structure of 1 is a body-centered cubic (bcu) lattice, with the Mg_(12) cages being utilized as eight-connected nodes. The framework of 1 is chiral and adopts the very unusual space group /23. Use of 1,3-propanediol as an additive results in the formation of the simple 1D polymer [Mg(cam){HO(CH_2)_3OH}_2], 2. In 2, each carboxylate-bridged metal center is chelated by two diols. ESI-MS studies confirm the formation of new ions in these solutions. The identities of 1 and 2 were confirmed by a combination of single-crystal X-ray diffraction, elemental analyses, IR, NMR, themogravimetric analyses, and ESI-MS data. ESI-MS has proven to be a valuable technique in the identification of stable SBUs in solution prior to network formation.