Ferrimagnetic Mixed-Valency and Mixed-Metal Tris(oxalato)iron(III) Compounds:  Synthesis, Structure, and Magnetism

Abstract

The synthesis and structural and magnetic characterization of 16 compounds AM(II)Fe(III)(C(2)O(4))(3) (A = N(n-C(3)H(7))(4), N(n-C(4)H(9))(4), N(n-C(5)H(11))(4), P(n-C(4)H(9))(4), P(C(6)H(5))(4), N(n-C(4)H(9))(3)(C(6)H(5)CH(2)), (C(6)H(5))(3)PNP(C(6)H(5))(3), As(C(6)H(5))(4); M(II) = Mn, Fe) are reported. X-ray powder diffraction profiles are indexed in R3c or its subgroup P6(5)22 or P6/mmm to derive unit cell constants. The structures of all the compounds consist of two-dimensional honeycomb networks [M(II)Fe(III)(C(2)O(4))(3)(-)](infinity). The M(II) = Fe compounds behave as ferrimagnets with T(c) between 33 and 48 K, but five exhibit a crossover from positive to negative magnetization near 30 K when cooled in a field of 10 mT. The compounds exhibiting this unusual magnetic behavior are those that have the highest T(c). Within the set N(n-C(n)()H(2)(n)()(+1))(4)Fe(II)Fe(III)(C(2)O(4))(3) (n = 3-5), T(c) increases with interlayer separation and the low-temperature magnetization changes from positive (n = 3) to negative (n = 4, 5). In the M = Mn(II) compounds, the in-plane cell parameter a(0) is approximately 0.03 Å greater than in the corresponding M = Fe(II) ones while the interlayer separation (c(0)/6) is on average 0.08 Å smaller. All members of the M(II) = Mn series have magnetic susceptibilities showing broad maxima at 55 K characteristic of two-dimensional antiferromagnetism, but the magnetization of several of the salts increases sharply below 27 K due to the onset of spin canting, the magnitude of which varies significantly with A.

Experimental Evidence for Jahn--Teller Transition in a Fe(II)Fe(III) Bimetallic Oxalate

“…Analyt- [15]. Our results are consistent with previous report that an impurity of a few percent of Fe(C 2 O 4 )·2H 2 O is evidenced [16]. In Table, reported in Refs.…”

“…In Table, reported in Refs. [16,18], and [19]. This may result in observed multiple magnetic-pole reversals [7].…”

“…We think that the existence of a small fraction of metal vacancies because of Fe(II) becoming oxidized [16] …”

The Effect of a Random Crystal-Field on the Mixed Ising Spins (1/2, 3/2)

“…On the other hand, important advances have been made in the synthesis of two-and three-dimensional ferrimagnets, such as 2d organo-metallic ferrimagnets [10,11], and 2d networks of the mixed-metal materials [P(Phenyl) 4 ][MnCr(oxalate) 3 ] n [12]. Other interests in the mixed spin Ising models can be related to the modelling of magnetic structures suitable for describing a ferrimagnetism of certain classes of insulating materials.…”

Magnetic behavior of a mixed Ising ferrimagnetic model in an oscillating magnetic field

“…Organometallic compounds as the amorphous V (T CNE) x y(solvent) where TCNE is tetracyanoethylene are believed to have ferrimagnetic structure and ordering temperatures as high as 400 [9]. Some of these compounds have compensation temperatures near 30 K [10]. Most of these compounds have been synthesized by assembling molecular building blocks of different magnetic moments in such a way that adjacent magnetic moment are antiparallel [7].…”