A bromide analog of a one-dimensional Ising ferromagnet: trimethylammonium catena-bis(.mu.-bromo)diaquoiron(II) bromide

Abstract

The crystal structure of the title compound, FeTAB, has been determined by X-ray diffraction and has been found to be isomorphous to that of the chloride analogue, FeTAC. The structure consists of chains of bibromide-bridged Fe2+ ions extending along the b axis of the orthorhombic unit cell (space group Pnma, a = 17.287 (3) Á, b = 7.651 (2) Á, c = 8.320 (3) Á, R(Fa) = 0:0494, RW(F0) = 0.0488). The chains are linked into a 2-dimensional network in the c direction by hydrogen bonding to a third bromide ion; the resulting planes are well isolated in the a direction by the organic molecules. The low-temperature magnetic susceptibility of polycrystalline samples can be modeled by using a one-dimensional ferromagnetic Ising model with a molecular field correction.The exchange parameters are estimated to be Jjk = 4 K and z'J'/k = -0.2 K, indicating that FeTAB has an intrachain exchange constant only one-fourth of that found in the chloride analogue while the interchain interactions are more than 10-times greater. Antiferromagnetic ordering is observed in the Móssbauer spectra near 1.3 K. Analysis of the polycrystalline spectra shows that the internal magnetic field (and easy axis of magnetization) for FeTAB lies close to the ab plane, as previously found for FeTAC.

Halide-bridged polymers of divalent metals with donor ligands – structures and properties

“…This structure type is able to accommodate first-series transition metal cations of rather different size. The Cu [58], Co [59], Mn [60], Ni [61,62] and Fe [63] compounds with bridging chloride as well as the Fe derivative with bromide bridges [64] have been structurally characterized. All compounds are isomorphous in space group Pnma; the only exception is the copper chain polymer which crystallizes in the subgroup P2 1 /c with a unit cell of similar dimensions.…”

Expanding the family of tetrahalide iron complexes: Synthesis, structure and biological applications

“…The other three examples are polymeric in nature; the first example from Reiff et al is a catena-bridged ferrous bromide derivative with water molecules in the axial positions. [19] Work by Schmidt et al utilising cyanopyridine forms polymeric chains of iron bromide units where there are two possible motifs, [20,21] one where the bridging equatorial bromides are the linkers and the other where there is both the bridging bromides as well as coordination at the cyanide nitrogen. All three polymeric examples contain the iron centre with equatorial bromides with a differing axial ligand.…”