Spectroscopic study of (two-dimensional) molecule-based magnets: M ~(II)(TCNE)(NCMe)_2SbF_6 (M = Fe, Mn, Ni)

摘要

The M-TCNE (M = 3d metal; TCNE = tetracyanoethylene) system is one of the most interesting classes of molecule-based magnets, exhibiting a plethora of compositions and structures (inorganic polymer chains, 2D layers, 3D networks, and amorphous solids) with a wide range of magnetic ordering temperatures (up to 400 K). A systematic study of vibrational (both infrared and, for the first time, Raman) properties of the family of new TCNE-based magnets of M II(TCNE) (NCMe)_2SbF_6 M = Mn, Fe, Ni composition is discussed in conjunction with their magnetic behavior and newly reso-lved crystal structures. The vibrational properties of the isolated TCNE- anion in the paramagnetic Bu_4N TCNE~- salt and recently characterized 2D layered magnet Fe~(II)(TCNE)(NCMe)_2FeCl _4 are also reported for comparison. Additionally, a linear correlation between C=C (ag) frequency of the TCNE ligand and its formal charge Z (the spin density on the orbital), Z 1571 - _(C=C) (a_g)154.5 e, is presented. It is shown that monitoring Z by Raman spectroscopy is of great use in providing information that allows understanding the peculiarity of the superexchange interaction in M-TCNE magnets and establishing the structure-magnetic properties correlations in this class of magnetic material.