Abstract
Two new, isomeric, pyrimidine containing ligands, 4-(4-methylphenyl)-3-(2-pyrimidyl)-5-phenyl¬-1,2,4-triazole (2pympt) and 4-(4-methylphenyl)-3-(4-pyrimidyl)-5-phenyl¬-1,2,4-triazole (4pympt), were synthesised and characterised in this project. They are the first examples of pyrimidine containing analogues of the N4-substituted-3,5-di(2-pyridyl)-1,2,4-triazole (Rdpt) ligand family. The ligands were synthesised by extending a literature procedure involving the condensation of the relevant hydrazide and ethylated thioamide. Pyrimidine-4-carbohydrazide was made in four steps from cheap acyclic precursors. Pyrimidine-2-carbohydrazide was made in three steps from the commercially available 2-cyanopyrimidine. The ethylated thioamide, ethyl N-(4-methylphenyl)-benzene-carboximidothioate, was made in two steps starting with a Willgerodt-Kindler reaction.
Four mononuclear bis-npympt iron(II) thio- and seleno-cyanate complexes, [FeII(2pympt)2(NCS)2], [FeII(2pympt)2(NCSe)2] (polymorph α), [FeII(4pympt)2(NCS)2]•H2O (polymorph I) and [FeII(4pympt)2(NCSe)2]•2H2O (polymorph A), were synthesised. Variable temperature magnetic susceptibility measurements (300–4 K) showed three of them remain high spin, whereas [FeII(4pympt)2(NCSe)2]•2H2O (polymorph A) undergoes abrupt spin crossover with T1/2 = 110 K.
Single crystals of the solvent-less complexes FeII(2pympt)2(NCS)2], [FeII(2pympt)2(NCSe)2] (polymorph β), [FeII(4pympt)2(NCS)2] (polymorph II) and [FeII(4pympt)2(NCSe)2] (polymorph C), as well as the methanol solvated complex [FeII(4pympt)2(NCSe)2]•2MeOH (polymorph B) were obtained by slow evaporation or vapour diffusion. X-ray crystal structure determinations showed that in all five of them the iron(II) centres adopt the trans-NCE binding mode, and are high spin at 100 K.
Two mononuclear tris-npympt iron(II) complexes, [FeII(2pympt)3](BF4)2•2H2O and [FeII(4pympt)3](BF4)2•0.5CHCl3•2H2O (polymorph 1), were also synthesised. Single crystals of a solvatomorph, [FeII(4pympt)3](BF4)2•Et2O•0.5H2O (polymorph 2), were obtained and an X-ray crystal structure determination showed that the complex is low spin at 100 K.
The preparation and characterisation of the two new ligands and the six new complexes, including crystal structures for one ligand and six complexes, are reported herein.