Mercury-199 NMR Studies of Thiacrown and Related Macrocyclic Complexes:  The Crystal Structures of [Hg(18S6)](PF6)2 and [Hg(9N3)2](ClO4)2

• Published in: Inorganic chemistry Vol. 44; no. 16; pp. 5696 - 5705
• Main Authors: Helm, Monte L, Helton, Gregory P, VanDerveer, Donald G, Grant, Gregory J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08-08-2005
• DOI: 10.1021/ic050500z
• EISSN: 1520-510X
• ISSN: 0020-1669

We wish to report the first measurements of 199Hg NMR chemical shift data for a series of homoleptic Hg(II) complexes with thiacrown ligands and related aza and mixed thia/aza macrocycles. In mercury(II) complexes containing trithiacrown through hexathiacrown ligands, we observed 199Hg NMR chemical shifts in the range of −298 to −1400 ppm. Upfield chemical shifts in these NMR spectra are seen whenever (a) the number of thioether sulfur donors in the complex is decreased, (b) a thioether sulfur donor is replaced by a secondary nitrogen donor, and (c) the size of the macrocycle ring increases without a change in the nature or number of the donor atoms. Changes in noncoordinating anions, such as hexafluorophosphate and perchlorate, have little effect on the 199Hg chemical shift. For several complexes, we observed 3 J(199Hg−1H) coupling in the range of 50−100 Hz, the first example of proton−mercury coupling through a C−S thioether bond. Also, we obtained unusual upfield 13C NMR chemical shifts for methylene resonances in several of the thiacrown complexes which correspond to distortions within the five- and six-membered chelate rings bound to the mercury ion. We report the X-ray crystal structure of the complex [Hg(18S6)](PF6)2 (18S6 = 1,4,7,10,13,16-hexathiacyclooctadecane). The molecule crystallizes in the rare trigonal space group P 3̄m1 with hexakis(thioether) coordination around the Hg(II) center confirming previous X-ray photoemission spectroscopic data on the compound. The lack of an observable 199Hg NMR signal for the complex is the result of the identical length (2.689(2) Å) of all six Hg−S bonds. We additionally report the X-ray structure of the complex [Hg(9N3)2](ClO4)2 (9N3 = 1,4,7-triazacyclononane) which shows hexakis(amine) coordination of the 9N3 to form a distorted trigonal prismatic structure. Solution dissociation of the one of the 9N3 ligands from the mercury ion is confirmed by multinuclear NMR experiments. For six-coordinate macrocyclic Hg(II) complexes, N6 donor sets have a preference for trigonal prisms while S6 donor sets favor octahedral structures.