Structural chemistry of host – guest molecular architectures based on mercury-containing macrocycles

Metallomacrocycles that include several metal ions with the Lewis acid properties are peculiar antipodes of crown ethers (referred to as ‘anticrowns’ in the literature). Recently these architectures have been extensively investigated when searching for efficient and selective anion receptors. In this review, we analyze the data on the molecular and crystal structures of supramolecular complexes of mercury-containing macrocycles (hosts) with anions or neutral nucleophiles (guests). The emphasis is on the identification and systematization of the structure types of complexes in dependence of the guest molecule nature, as well as the macrocycle composition and structure. The factors affecting the selectivity of coordination and competitive ability of various electron donor moieties of guest molecules to binding to the macrocycle are considered. The data in the literature on the nonvalent host – guest and host – host interactions, which are responsible for the formation of molecular complexes and their supramolecular association in crystals, are analyzed. The formulated structural regularities of these coordination compounds with an unusual type of molecular architecture open ways to design directly promising molecular materials on their basis.

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Coordination of Nitroxide and Nitronyl-nitroxide Organic Radicals to Trimeric Perfluoro-o-phenylene Mercury

The interaction of trimeric perfluoro-o-phenylene mercury (1) with TEMPO (1,1,5,5-tetramethylpentamethylene nitroxide) in CH2Cl2 leads to the formation of the 1:1 adduct [1.TEMPO] (2). The same reaction carried out with NIT-Ph (2-(phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) leads to the formation of either [1.NIT-Ph.1] (3) or [1*NIT-Ph]n (4), depending on the amount of NIT-Ph present in solution. Adducts 2, 3, and 4 have been fully characterized and their crystal structures determined. The solid-state structure of 2 contains molecules of [1*TEMPO] in which the nitroxide oxygen atom is triply coordinated to the mercury centers of 1. A similar situation is encountered in the structure of 3 where each oxygen atom of the NIT-Ph molecule interacts with the mercury centers of an adjacent molecule of 1. The structure of 4 consists of extended helical polymeric chains that contain alternating molecules of 1 and NIT-Ph. As in 2 and 3, the interactions responsible for the formation of these chains involve the triple coordination of the oxygen atoms of the NIT-Ph molecule to the mercury centers of 1. DFT calculations suggest that the bonding in adducts such as 2, 3, and 4 is most likely dominated by electrostatic rather than covalent interactions. In agreement with this view, magnetic susceptibility measurements carried out on these adducts indicate that 1 does not mediate significant coupling between organic radicals coordinated on either side of the trinuclear core.

Hexacoordination of a dimethyl sulfide molecule

Interaction of the trifunctional Lewis acid [(o-C6F4Hg)3] (1) with dimethyl sulfide in dichloroethane leads to the formation of an extended supramolecule which features sandwiched dimethyl sulfide molecules. The sulfur atom of the latter interacts simultaneously with the mercury centers of two neighboring molecules of 1 and thereby achieves hexacoordination.