Ligand field influence on the electronic and magnetic properties of quasi-linear two-coordinate iron( textlessspan style="font-variant:small-caps;"textgreateriitextless/spantextgreater ) complexes

Abstract

The magnetic properties and ligand-field effects for quasi-linear iron( ii ) complexes are explored with the aid of theoretical models. The 2 to 300 K magnetic susceptibilities of FeN(SiMe 2 Ph) 2 2 1 FeN(SiMePh 2 ) 2 2 2 and the diaryl complex Fe(Ar Pri4 ) 2 3 where Ar Pri4 is C 6 H 3 -2,6(C 6 H 3 -2,6-Pr i 2 ) 2 have been measured. Initial fits of these properties in the absence of an independent knowledge of their ligand field splitting have proven problematic. Ab initio calculations of the CASSCF/RASSI/SINGLE-ANISO type have indicated that the orbital energies of the complexes, as well as those of Fe(Ar Me6 ) 2 4 where Ar Me6 is C 6 H 3 -2,6(C 6 H 2 -2,4,6-Me 3 ) 2 ), are in the order d xy ≈ d x2−y2 textless d xz ≈ d yz textless d z2 and the iron( ii ) complexes in this ligand field have the (d xy d x2−y2 ) 3 (d xz d yz ) 2 (d z2 ) 1 ground electronic configuration with a substantial orbital contribution to their effective magnetic moments. An ab initio -derived ligand field and spin–orbit model is found to yield an excellent simulation of the observed magnetic properties of 1–3 . The calculated ligand field strengths of these ligands are placed in the broader context of common coordination ligands in hypothetical two-coordinate linear iron( ii ) complexes. This yields the ordering I − textless H − textless Br − ≈ PMe 3 textless CH 3 − textless Cl − ≈ C(SiMe 3 ) 3 − textless CN − ≈ SAr Pri6− textless Ar Pri4− textless Ar Me6− ≈ N 3 − textless NCS − ≈ NCSe − ≈ NCBH 3 − ≈ MeCN ≈ H 2 O ≈ NH 3 textless NO 3 − ≈ THF ≈ CO ≈ N(SiMe 2 Ph) 2 − ≈ N(SiMePh 2 ) 2 − textless F − ≈ N(H)Ar Pri6− ≈ N(SiMe 3 )Dipp − textless OAr Pri4− . The magnetic susceptibility of the bridged dimer, [FeN(SiMe 3 ) 2 2 ] 2 5 has also been measured between 2 and 300 K and a fit of χ M T with the isotropic Heisenberg Hamiltonian, Ĥ = −2 JŜ 1 · Ŝ 2 yields an antiferromagnetic exchange coupling constant, J of −131(2) cm −1 . Show more