Structural and Physical Properties of the Ferromagnetic\nTris-Dithiooxalato Compounds, A[M^IICr^III(C₂S₂O₂)₃], with A⁺ =\nN(<i>n</i>-C<i>_n</i>H₂<i>_n</i>₊₁)₄⁺ (<i>n</i> = 3−5) and P(C₆H₅)₄⁺ and M^II = Mn, Fe, Co, and Ni

Abstract

The structural and magnetic properties of the tris-dithiooxalato salts, A[M^IICr(C₂S₂O₂)₃], have been investigated\nwith A⁺ = PPh₄⁺, N(<i>n</i>-C<i>_n</i>H₂<i>_n</i>₊₁)₄⁺, with <i>n</i> = 3−5, where M^II is Mn, Fe, Co, and Ni. With the exception of A[MnCr(C₂S₂O₂)₃], all the salts are ferromagnets with Curie temperatures, <i>T</i>_c, between 5 and 16 K. In contrast to the\ncorresponding oxalates which are ferromagnetic, the A[MnCr(C₂S₂O₂)₃] compounds are paramagnetic above 2 K.\nPowder neutron diffraction studies of <i>d</i>₂₀-PPh₄[FeCr(C₂S₂O₂)₃] indicate that no structural phase transitions occur\nbetween 2.4 and 285 K and that the coefficient of linear expansion is four times larger for the <i>c</i>-axis than for the\n<i>a</i>-axis. The crystal structure refined from powder neutron diffraction data confirms the honeycomb layer arrangement\nobserved in the related bimetallic tris-oxalate salts. The Mössbauer spectra reveal that the iron(II) in PPh₄[FeCr(C₂S₂O₂)₃] is coordinated mainly to six oxygen atoms of the dithiooxalato ligand but with a minor component of\nsulfur coordination that increases with aging of the sample; the iron(II) is high-spin in both cases. Powder neutron\ndiffraction profiles of <i>d</i>₂₀-PPh₄[FeCr(C₂S₂O₂)₃] below <i>T</i>_c show magnetic intensity with a <i>q</i> = 0 propagation vector,\nconfirming the presence of ferromagnetic order.