A three-dimensional metal-organic polymer: poly[bis(μ₂-pyrimidine-2-thiolato-κ⁴N¹,S:S,N³)lead(II)]

Ψ-Polyhedral symbols for coordination geometries of lead(II) with a stereochemically active lone pair

Because an IUCr/IUPAC-designated set of letters/numbers identifies the configuration of the atoms linked to the Pb^II atom in its coordination compounds, a Ψ prefix before such as a polyhedral symbol provides useful information when its lone pair is stereochemically active. Such notation is especially relevant when the metal atom is connected to eight or more atoms regardless of whether the lone pair is active or inert. The polyhedral symbols for the crystal structures in some 50 articles published after 2000 are reported here as the original studies did not expressly identify coordination geometries.

One- and two-dimensional PbII compounds resulting from reaction of PbBr2 and Pb(SCN)2 with pyrimidine-2-thione

Pyrimidine-2-thione (HSpym) reacts with lead(II) thiocyanate and lead(II) bromide in N,N-dimethylformamide (DMF) to form poly[(μ-isothiocyanato-κ²N:S)(μ₄-pyrimidine-2-thiolato-κ⁶N¹,S:S:S:S,N³)lead(II)], [Pb(C₄H₃N₂S)(NCS)]_n or [Pb(Spym)(NCS)]_n, (I), and the polymeric one-dimensional (1D) compound catena-poly[[μ₄-bromido-di-μ-bromido-(μ-pyrimidine-2-thiolato-κ³N¹,S:S)(μ-pyrimidine-2-thione-κ³N¹,S:S)dilead(II)] N,N-dimethylformamide monosolvate], {[Pb₂Br₃(C₄H₃N₂S)(C₄H₄N₂S)]·C₃H₇NO}_n or {[Pb₂Br₃(Spym)(HSpym)]·DMF}_n, (IIa), respectively. Poly[μ₄-bromido-di-μ₃-bromido-(μ-pyrimidine-2-thiolato-κ³N¹,S:S)(μ-pyrimidine-2-thione-κ³N¹,S:S)dilead(II)], [Pb₂Br₃(C₄H₃N₂S)(C₄H₄N₂S)]_n or [Pb₂Br₃(Spym)(HSpym)]_n, (IIb), could be obtained as a mixture with (IIa) when using a lesser amount of solvent. In the crystal structures of the pseudohalide/halide Pb^II stable compounds, coordination of anionic and neutral HSpym has been observed. Both Spym^- (in the thiolate tautomeric form) and NCS^- ligands were responsible for the two-dimensional (2D) arrangement in (I). The Br^- ligands establish the 1D polymeric arrangement in (IIa). Eight-coordinated metal centres have been observed in both compounds, when considering the Pb...S and Pb...Br interactions. Both compounds were characterized by FT-IR and diffuse reflectance spectroscopies, as well as by powder X-ray diffraction. Compound (IIa) and its desolvated version (IIb) represent the first structurally characterized Pb^II compounds containing neutral HSpym and anionic Spym^- ligands. After a prolonged time in solution, (IIa) is converted to another compound due to complete deprotonation of HSpym. The structural characterization of (I) and (II) suggests HSpym as a good candidate for the removal of Pb^II ions from solutions containing thiocyanate or bromide ions.