Mercury(II) selenolates. Crystal structures of polymeric Hg(SeMe)2 and the tetrameric pyridinates [{HgCl(py)(SeEt)}4] and [{HgCl(py)0.5(SeBut)}4]

Abstract

The crystal structures of the title compounds have been determined by single-crystal X-ray diffraction at 295 K and refined by least squares to residuals of 0.044, 0.046, 0.058 for 818, 1 678, 2 016 independent ‘observed’ reflections respectively. For all compounds, crystals are monoclinic, space group P2₁/c. For Hg(SeMe)₂, a= 8.440(4), b= 10.732(3), c= 6.681(3)Å, β= 96.14(4)°, and Z= 4. For [{HgCl(py)(SeEt)}₄](py = pyridine), a= 8.044(5), b= 17.387(14), c= 15.585(21)Å, β= 101.75(2)°, and Z= 2. For [{HgCl(py)_0.5(SeBu^t)}₄]a= 12.151(5), b= 16.738(7), c= 10.138(6)Å, β= 90.93(4)°, and Z= 2. Crystals of Hg(SeMe)₂ contain infinite one-dimensional chains along b, the pseudo-tetrahedral mercury atoms being bridged by pairs of selenium atoms; Hg–Se bond distances are in the range 2.614(2)–2.764(2)Å. The complexes [{HgCl(py)(SeEt)}₄] and [{HgCl(py)_0.5(SeBu^t)}₄] were obtained from pyridine solutions containing Hg(SeR)₂ and HgCl₂, and both contain an eight-membered ring (–Hg–SeR–)₄. The former contains two independent pseudo-tetrahedrally co-ordinated mercury atoms, ‘Hg(µ-SeEt)₂Cl(py)’; the latter contains two inversion related mercury atoms, ‘Hg(µ-SeBu^t)₂Cl(py)’, and two other inversion related mercury atoms linked by a dichloro-bridge ‘Hg(µ-SeBu^t)₂(µ-Cl)₂’. The structure of [{HgCl(py)_0.5(SeBu^t)}₄] is very similar to those of [{HgCl(L)_0.5(SBu^t)}₄](L = py or 4-methylpyridine) and is isomorphous with the 4-methylpyridine analogue. Mercury–selenium bond distances are slightly shorter than expected by comparison with covalent radii of sulphur and selenium.