| Abstract |
Several new iron(II) complexes of the types [Fe(PNP)X-2] (X = Cl, Br) containing tridentate PNP pincer-type ligands based oil 2,6-diaminopyridine and 2,6-diaminopyrimidine have been prepared. They all exhibit intermolecular Fe-X center dot center dot center dot H-N hydrogen bonds, forming supramolecular networks in the solid state. In the case of X = Cl these compounds react readily with gaseous CO both in the solid state and in solution to give selectively the octahedral complexes cis- and trans-[Fe(PNP)(CO)(Cl)(2)], respectively, whereas with X = Br mixtures of cis- and trans isomers are obtained. These transformations are accompanied by color and spin-state changes. CO binding is fully reversible in all cases, and heating solid samples of either cis- or trans-[Fe(PNP)(CO)(X)(2)] leads to complete regeneration of analytically pure [Fe(PNP)(X)(2)]. Mossbauer spectroscopy confirmed the high-spin nature of the parent five-coordinate Fe(II) complex (delta = 0.80(1) mm s(-1)) and the shift to two different low-spin octahedral species after reaction with CO in the solid (delta = 0.13(1) mm s(-1)) or in solution (delta = 0.15(1) mm s(-1)). Magnetization studies led to a magnetic moment close to 4.9 mu(B), reflecting the expected Four unpaired d-electrons in [Fe(PNP)Cl-2], which were confirmed by DFT calculations. The DFT study or the reaction pathway for CO capture led to low energy barriers (<= 3.4 kcal mol(-1)). The cis-trans isomerization reaction was found to take place with a low energy barrier (10.8 kcal mol(-1)), after initial loss of chloride, and involves also spin-state changes. |
