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.