US EPA

4784865 

Journal Article 

Syntheses, Crystal Structures and Ligand Field Properties of Iron(II) Complexes with PNP Ligands: Origin of Large Ligand Field by a Phosphorous Donor Atom 

Mabe, T; Yamaguchi, H; Fujiki, M; Noda, K; Ishihara, K; Inamo, M; Hassan, RM; Iwatsuki, S; Suzuki, T; Takagi, HD 

2014 

Yes 

Journal of Solution Chemistry
ISSN: 0095-9782
EISSN: 1572-8927 

43 

9-10 

1574-1587 

10.1007/s10953-014-0182-3 

WOS:000344394200011 

New iron(II) complexes were synthesized with two tridentate hybrid ligands having phosphorous and nitrogen donor sites, in order to quantitatively estimate the difference of the ligand-field strengths of phosphorous and nitrogen donor sites in cationic metal complexes. Iron(II) complexes with bis(dimethylphosphinoethyl)amine (PNP) and 2,6-bis(diphenylphosphinomethyl)pyridine (PpyP) ligands crystallized as un-symmetric facial-[Fe(PNP)(2)](PF6)(2)center dot CH3NO2 and mer-[Fe(PpyP)(2)](CF3SO3)(2), respectively, as expected from the steric congestion and from the tendency to avoid the mutual trans influence between two phosphorous donor sites. Both complexes are in the low-spin electronic state up to 400 K. The pseudo-D (4h) coordination geometry of the PpyP complex made it possible to separate axial (2 x N) and equatorial (4 x P) contributions to the overall ligand-field by means of a spectrometric method: the difference in the ligand-field strengths by the equatorial Ph2P-donor sites and by the axial 2,6-disubstituted pyridine donor sites is ca. 13,200 cm(-1). A significantly reduced inter-electronic repulsion parameter (425 cm(-1) for both PNP and PpyP complexes) from the value of the free ion (1,060 cm(-1)) indicates covalent interaction between the Fe(II) and P atoms even in these cationic metal complexes. It is shown that the degree of covalency as well as the coordination bond strengths between various metal ions and phosphorous/nitrogen donor atoms is successfully explained by the relative energy levels of interacting atomic orbitals calculated on the basis of the Thomas-Fermi-Dirac potential. 

Iron(II) complexes; Bis(dimethylphosphinoethyl)amine (PNP); 2, 6-Bis(diphenylphosphinomethyl)pyridine (PpyP); Ligand field