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CO 2 Capture via Crystalline Hydrogen-Bonded Bicarbonate DimersA crystallization-based CO 2 -separation method involving a simple aqueous guanidine sorbent offers the prospect of energy-efficient and cost-effective carbon-capture technologies that could help mitigate climate change.

This report explores the potential of the unconventional hydrogen bonds between the hydridic hydrogens in X-BH 3 -(X ) H, CN) and traditional OH or NH proton donors (dihydrogen bonds) to serve as preorganizing interactions for the topochemical assembly of covalent materials. Evidence for such topochemical control in the reaction B-H‚‚‚H-X f B-X + H 2 was obtained in studies of the solid-state structures and reactivities of N- [2-(6-aminopyridyl)]acetamidine (NAPA) cyanoborohydride and triethanolamine (TEA) complexes of NaBH 4 and NaCNBH 3 . The X-ray crystal structures of all three new compounds studied exhibit multiple dihydrogen bonds which are significant in defining the packing of the molecules in the solid state. Moreover, this new type of interaction is a powerful tool for crystal engineering; as planned, NAPA H 3 BCN crystallized in the desired (NAPA H 3 BCN) 2 closed loop coordination. Solid-state decomposition of NaBH 4 ‚TEA is topochemical, leading to a trialkoxyborohydride, which is not achievable in solution or melt. In addition to close H-H contacts, the relative acidity/basicity of the proton-hydride pairs make a significant contribution to the solid-state reactivity of dihydrogen-bonded systems, as demonstrated by the contrasting reactivities of the NaBH 4 ‚TEA and NaCNBH 3 ‚TEA complexes.We have recently demonstrated, using X-ray and neutron diffraction, 1 IR and NMR spectroscopy, and ab initio calculations, 2 that the hydridic hydrogens, or more accurately the B-H electron pairs in the BH 4 -anion, can serve as the electron donors of a new type of hydrogen bond (dihydrogen bonding). In this new type of intermolecular interaction, the σ-bonding electron pair of a B-H bond (or other M-H where M is less electronegative than H) associates with a traditional H-bonding partner H-X (X ) N, O, halogen). The same kind of interaction was independently noted by Crabtree et al. 3 and Morris et al. 4 in organoiridium and organorhenium complexes, and by Epstein et al. in organorhenium and organotungsten compounds. 5 With H‚‚‚H distances of 1.7-2.2 Å and strengths of 4-7 kcal/mol, dihydrogen bonds are comparable with conventional hydrogen bonds.Besides the control of chemical reactivity and stereoselectivity in solution, 6 this new phenomenon has interesting implications for topochemically directed assembly of covalent materials. Such weak associations, in principle, may be used to organize and hold a structure's form while it is more firmly fastened together. A number of researchers have used H-bonding interactions to juxtapose sites that may then be photodimerized or polymerized into covalent structures. 7 A general weakness of the systems studied to date, however, is the complexity or the low dimensionality of the preorganizing/coupling subunits.Dihydrogen bonds represent an especially simple preorganizing interaction. In general, heating these systems drives off H 2 , leaving Lewis acidic and basic sites in close proximity. These subunits may combine to form strong covalent bonds, reflecting the connecti...

The development of ion-pair receptors, with the goal of achieving a higher level of control over recognition than that obtainable from simple ion binding, has intrigued researchers in supramolecular chemistry over the past decade.[1] Many reports have appeared during this period that describe the synthesis and study of very sophisticated receptor designs incorporating a range of electron-pair donor and acceptor groups. Most, if not all, of this work has been performed in the context of creating so-called ion-pair or salt hosts that will bind cation-anion pairs in homogeneous solution or enhance their extraction or transport under interfacial conditions. Whether the ditopic architecture in such systems confers real advantages over simpler combinations of single-ion receptors remains an open question. However, the utility of ion-pair

Guests -[252 refs.]. -(MOYER, B. A.; BONNESEN, P. V.; CUSTELCEAN, R.; DELMAU, L. H.; HAY, B. P.; Kem. Ind. 54 (2005) 2, 65-87; Chem. Sci. Div., Oak Ridge Natl. Lab., Oak Ridge, TN 37831, USA; Eng.) -Lindner 31-276