Neutron diffraction study of the magnetic structures of manganese succinate $\text{Mn}\left({\text{C}}_4{\text{H}}_4{\text{O}}_4\right)$: A complex inorganic-organic framework

The antiferromagnetic structures of the Mn succinate framework, $\text{Mn}\left({\text{C}}_4{\text{H}}_4{\text{O}}_4\right)$, have been determined using neutron diffraction. The structure comprises alternating layers containing chains of edge-sharing $\text{Mn}\left(\text{II}\right){\text{O}}_6$ octahedra and sheets of corner-sharing $\text{Mn}\left(\text{II}\right){\text{O}}_6$ octahedra, respectively, with a layer separation of $\sim 7.5\text{Å}$. At 10 K the edge-sharing ${\text{MnO}}_6$ octahedral chains order antiferromagnetically into a collinear sinusoidal spin structure with a propagation vector $k_2=\left(0,-0.5225,0\right)$, in which individual edge-sharing ${\text{MnO}}_6$ chains are ferromagnetically ordered. The sheets of corner-sharing ${\text{MnO}}_6$ octahedra order magnetically at 6 K, adopting the antiferromagnetic structure expected for a square arrangement of cations with a propagation vector $k_8=\left(-1,0,1\right)$. The ordering of these sheets at a lower temperature than the chains is consistent with their longer nearest-neighbor superexchange pathway. The magnetic structure of the edge-sharing layers is unaffected by the 6 K phase transition, indicating that the orderings of the two different layers are essentially independent of each other.

Figure 1

(Color online) Ball and stick depictions of the three-dimensional structure of $\text{Mn}\left({\text{C}}_4{\text{H}}_4{\text{O}}_4\right)$. (i) Side view of the two types of ${\text{MnO}}_6$ layers present in its structure, viewed down the $c$ axis; (ii) and (iii) the two different layers depicted in the $bc$ plane (only atoms involved in intralayer bonding are included). The layer in (ii) shows the edge-sharing chains while (iii) shows a corner-sharing ${\text{MnO}}_6$ sheet. This figure is reproduced with permission from Saines et al. (Ref. 8).

Figure 2

(Color online) Heat-capacity measurements for $\text{Mn}\left({\text{C}}_4{\text{H}}_4{\text{O}}_4\right)$ and the Fisher heat capacity determined using magnetic-susceptibility data indicating the two antiferromagnetic phase transitions at approximately 6 and 10 K. This figure is reproduced with permission from Saines et al. (Ref. 8).

Figure 3

(Color online) Plot of the 4.2, 8, and 20 K neutron-diffraction patterns. The inset indicates the magnetic reflections in the two magnetic phases with the patterns offset for clarity.

Figure 4

(Color online) The Rietveld fit to the 8 K neutron pattern. The crosses, upper and lower continuous lines are the experimental, calculated, and difference plots, respectively. The upper and lower vertical lines are the Bragg reflections from the nuclear and edge-sharing layer magnetic structures, respectively. The inset plot indicates the observed reflections caused by the magnetic ordering of the edge-sharing layer.

Figure 5

(Color online) The Rietveld fit to the 4.2 K neutron pattern. The format is the same as for Fig. 4. The upper, middle, and lower vertical lines are the Bragg reflections from the nuclear, corner-sharing layer magnetic, and edge-sharing layer magnetic structures, respectively. The inset plot shows the observed magnetic reflections with the reflections caused by the magnetic ordering of the corner-sharing layer indicated by arrows.

Figure 6

(Color online) The magnetic structure of $\text{Mn}\left({\text{C}}_4{\text{D}}_4{\text{O}}_4\right)$. The complete magnetic structure is indicated by (i) displaying 12 unit cells along the $b$ axis to show approximately half a modulation wavelength of the magnetic structure of the edge-sharing chains. Pictures (ii) and (iii) are more detailed representations of the magnetic structure of the edge- and corner-sharing layers, respectively. For clarity only the ${\text{MnO}}_6$ octahedra are displayed.