A lanthanide–mercury compound: preparation and photophysical properties

A neodymium (Nd)–mercury (Hg) complex [Nd(IA)₂(H₂O)₃(NO₃)(HgCl₂)] _n ·2nH₂O·nEtOH (1; IA is isonicotinic acid anion) was synthesised and characterised. Compound 1 is of monoclinic system, space group C2/c with a = 25.4224(12), b = 8.1410(3), c = 22.2963(9) Å, β = 90.788(4)°, V = 4614.1(3) ų, C₁₄H₂₄Cl₂HgN₃NdO₁₃, Z = 8, M _r = 858.09, D _c = 2.471 g/cm³, S = 1.120, μ(Mo Kα) = 9.174 mm⁻¹, F(000) = 3256, R = 0.0530 and wR = 0.1288. The mercury (II) (Hg²⁺) ions are bound by two terminal chloride (Cl⁻) ions and two nitrogen (N) atoms, displaying a distorted tetrahedral geometry. The neodymium (III) (Nd³⁺) ion is coordinated with nine oxygen (O) atoms to form a monocapped square antiprismatic polyhedron. Every two neighbouring neodymium (III) ions are interlinked by two μ ₃-bridging IA groups to form a one-dimensional (1D) infinite –Nd–IA₂–Nd– chain. The 1D chains link to each other through HgCl₂N₂ tetrahedra and yield a two-dimensional layer. It emits cyan photoluminescence, which should be due to the ⁴ G _11/2 → ⁴ I _9/2 transition of the 4f electrons of the neodymium ions. It exhibits Commission Internationale de l’Éclairage chromaticity coordinates of (0.1274, 0.3525). A solid-state diffuse reflectance spectrum unveils that it has a 2.51 eV band gap.