ABSTRACT
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 PbII 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 PbII 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 PbII ions from solutions containing thiocyanate or bromide ions.
ABSTRACT
Semicarbazones can exist in two tautomeric forms. In the solid state, they are found in the keto form. This work presents the synthesis, structures and spectroscopic characterization (IR and NMR spectroscopy) of four such compounds, namely the neutral molecule 4-phenyl-1-[phenyl(pyridin-2-yl)methylidene]semicarbazide, C19H16N4O, (I), abbreviated as HBzPyS, and three different hydrated salts, namely the chloride dihydrate, C19H17N4O+·Cl-·2H2O, (II), the nitrate dihydrate, C19H17N4O+·NO3-·2H2O, (III), and the thiocyanate 2.5-hydrate, C19H17N4O+·SCN-·2.5H2O, (IV), of 2-[phenyl({[(phenylcarbamoyl)amino]imino})methyl]pyridinium, abbreviated as [H2BzPyS]+·X-·nH2O, with X = Cl- and n = 2 for (II), X = NO3- and n = 2 for (III), and X = SCN- and n = 2.5 for (IV), showing the influence of the anionic form in the intermolecular interactions. Water molecules and counter-ions (chloride or nitrate) are involved in the formation of a two-dimensional arrangement by the establishment of hydrogen bonds with the N-H groups of the cation, stabilizing the E isomers in the solid state. The neutral HBzPyS molecule crystallized as the E isomer due to the existence of weak π-π interactions between pairs of molecules. The calculated IR spectrum of the hydrated [H2BzPyS]+ cation is in good agreement with the experimental results.
ABSTRACT
Aroylhydrazones of ortho-hydroxy aldehydes are Schiff base ligands that typically coordinate as a chelate in an O,N,O'-manner. Dinuclear complexes are normally observed, with the phenolate O atom acting as the bridging atom. The switchable protonation state of the tridentate N'-(2-hydroxybenzylidene)benzohydrazide (H2sabhz) ligand can lead to variations in the resulting supramolecular structure. The title compound, [Pb2(C14H10N2O2)2], was prepared by the reaction of [Pb(OAc)2]·3H2O (OAc is acetate) with the benzoylhydrazone derivative of salicylaldehyde, i.e. H2sabhz, in the presence of triethylamine in methanol. In the crystal structure, each Pb(II) atom of the dimer has an NO3 coordination environment, with one sabhz ligand coordinating in an O,N,O'-manner and with the second sabhz ligand coordinating via the bridging phenolate O atom, since the dimers are located on a centre of inversion. It has been found that the dimers are connected by Pb...N interactions, resulting in a two-dimensional supramolecular network which shows the [3(2).5(2),3.5(3)] net topology. The s(2) electron pair of the Pb(II) ion clearly influences the observed intermolecular interactions.
ABSTRACT
The title compound, [Pb(C4H3N2S)2]n, was prepared by the reaction of [Pb(OAc)2]·3H2O (OAc is acetate) with pyrimidine-2-thione in the presence of triethylamine in methanol. In the crystal structure, the Pb(II) atom has an N4S4 coordination environment with four ligands coordinated by N- and S-donor atoms. This compound shows that the pyrimidine-2-thiolate anion can lead to a three-dimensional network when the coordination number of the metal ion can be higher than 6, as is the case with the Pb(II) ion. This compound presents only covalent bonds, showing that despite the possibility of the hemidirected geometries of Pb(II), the eight-coordinated ion does not allow the formation of an isolated molecular structure with pyrimidine-2-thiolate as the ligand.
