Complexation of Mercury(I) and Mercury(II) by 18-Crown-6: Hydrothermal Synthesis of the Mercuric Nitrite Complex

Abstract

A dimercury(I) 18-crown-6 complex is isolated, and its possible role in the hydrothermal preparation of the mercuric nitrite complex is discussed. The reported structures are of [Hg(2)(18-crown-6)(2)(H(2)O)(2)](ClO(4))(2) (1), monoclinic, C2/c, a = 21.0345(9), b = 12.1565(5), c = 16.8010(7) A, beta = 113.2000(10) degrees , V = 3948.7(3) A(3), Z = 16, R = 0.0230; [Hg(18-crown-6)](NO(2))(2) (2), monoclinic, P2(1)/c, a = 8.027(5), b = 14.437(9), c = 7.827(5) A, beta = 95.165(11) degrees , V = 905.6(10) A(3), Z = 2, R = 0.0175. The complex cation in compound 1 consists of a mercurous dimer exhibiting a Hg-Hg bond length of 2.524(2) A. Non-bonding interactions between adjacent crown ether macrocycles across the Hg-Hg bond result in large variations in mercury to oxygen distances within equatorial coordination sites. At low pH compound 1 is proposed to be preferentially formed under hydrothermal conditions affording compound 2 upon disproportionation. Nitrite ions ligate via a unidentate nitrito (cis to metal) coordination mode as interpreted using vibrational (infrared) spectroscopy. The conformation adopted by 18-crown-6 in compounds 1 and 2 is closely related to a D(3d) conformation as evidenced by X-ray crystallography. Band splitting readily observed in vibrational spectra of the metal free crown ether, attributed to vibrational modes of oxyethylene fragments, is absent in spectra of 1 and 2 confirming a regular D(3d) macrocyclic orientation. Short Hg-O bonds observed for axially coordinated water molecules in 1 and coordinated nitrite ligands in 2, illustrate the prevalence of relativistic effects commonly observed in mercury complexes.

Group 12 Metal Complexes of an 18-Membered N2O2S2 Macrocycle Incorporating Two Pyridines: First Examples of an Infinite Mercury(I) Complex and a Dumbbell-Shaped Heteronuclear Complex with a Macrocyclic Ligand

“…Only four Hg(I) complexes of macrocycles have been reported to date, and all of them have discrete structures (Chart 2). 9−12 Syntheses of the sandwichlike symmetric [Hg 2 (18-crown-6) 2 (H 2 O) 2 ] 2+ complex 9 (Chart 2a) and asymmetric [Hg 2 (18-crown-6)(15crown-5)(H 2 O)] 2+ complex 10 (Chart 2b) have been performed the Zhang group 20e isolated a Hg(I) complex of a pentadentate thioether ligand during an assembly reaction with a Hg(II) salt due to the reductive activity of the thioether ligand used. Therefore, the formation of the Hg(I) complex in this work also seems to be attributed to the reductive activity for the thioether ligand L.…”

Crystal structures of three mercury(II) complexes [HgCl2L] whereLis a bidentate chiral imine ligand

“…The coordination geometry for Hg II is very versatile, in particular because the available coordination numbers for this 5d 10 metal ion cover a large range, from 2 (e.g. Moreno-Alcá ntar et al, 2013) to 10 ( Williams et al, 2009). In the case of tetracoordinated Hg II complexes, the possible geometry extends from square planar, similar to d 8 transition metals, to tetrahedral, as for d 7 transition metals.…”

Macrocyclic coordination chemistry

“…The dimercury(I) cation Hg 2 2+ was isolated by coordination with 18-crown-6 and disproportionation reactions studied, revealing their importance when considering the use of crown ether ligands in mercury sensing applications. 79 A terpyridine appended 15-crown-5 was synthesised L 54 and the structure of transition metal complexes characterised by single crystal X-ray diffraction and powder diffraction techniques, see Fig. 3.…”