Long-range 3D magnetic order in the layered molecular network compounds M(NCO)2(pyz), M = Mn, Fe or Co
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Date
2005-02-03
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Australian Institute of Physics
Abstract
It has recently been shown that organic ligands are capable of mediating exchange interactions over convoluted pathways, giving rise to long-range magnetic order at quite high temperatures [1]. Much effort has consequently been invested in understanding the nature and origin of these interactions [2], furthering progress towards potential applications of these low-dimensional ‘molecular magnetic’ materials. The design, synthesis and study of further such coordination polymers are fundamental to this effort. We have been studying a variety of novel molecular magnetic solids comprised of pseudo-halide building blocks and first-row transition metal ions, M. The ensuing structures possess either 1-, 2- or 3D networks where divalent M cations are held together via organic anions such as dicyanamide (N(CN)−2 ) [3–5], azide (N−3 ) [6, 7], thiocyanate (NCS−) [8] or cyanate (NCO−) plus neutral organic ligands such as pyrazine (pyz) or 4,4-bipyridine (bipy). Numerous compounds have been reported that contain N(CN)−2 , N−3 , or NCS− anions but very few have been reported with NCO−. While N−3 is a well-known super-exchange mediator in molecular magnetic materials, its major drawback is that it is potentially explosive if handled in sizeable quantities. This has hampered neutron scattering studies into the magnetism of these compounds and motivated our interest in NCO−. Both NCO− and N−3 can coordinate to M ions in a different ways such as M-N-M, M-NNN-M or M-N-C-O-M, although the latter is rare in the case of NCO−. Singly-bridging M-N-M generally gives rise to ferromagnetic interactions although the strength of this coupling is dictated by the bond angle. By combining these anions with other organic bridging ligands we can build a plethora of new structures with interesting magnetic behavior.
We have now synthesised M(NCO)2(pyz) compounds where M is Mn, Fe or Co. Here, we present the results of a neutron powder diffraction (NPD) investigation into the crystal and magnetic structures of these compounds as a function of temperature. We find that the structures of all three compounds are isomorphic and related to that of Mn(N3)2(pyz) [6], and yet exhibit two distinct magnetic structures at low temperature. The relationship between these two magnetic structures, and the finely balanced interactions that lead to the adoption of one
over the other, are discussed.
Description
Keywords
Organic compounds, Ligands, Temperature range 0400-1000 K, Materials, Interactions, Cations, Pyrazines, Bipyridines
Citation
Ling, C. D. & Manson, J. L. (2005). Long-range 3D magnetic order in the layered molecular network compounds M(NCO)2(pyz), M = Mn, Fe or Co. Paper presented to the 29th Condensed Matter and Materials Meeting, "Australian Institute of Physics Sixteenth Biennial Congress", Canberra, 2005, 31 January - 4 February 2005. Retrieved from: https://www.physics.org.au/wp-content/uploads/cmm/2005/18._Ling_AIP_CMMSP_CD1(Final).pdf