Structural and Physical Properties of the Ferromagnetic Tris-dithiooxalato Compounds

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