Inorganic Chemistry, Vol.58, No.2, 1184-1190, 2019
Tunable Ferromagnetic Strength in Niccolite Structural Heterometallic Formate Framework Based on Orthogonal Magnetic Orbital Interactions
A series of heterometallic formate framework templated by amines were solvothermally prepared. They feature the formula of [A(I)][CrMII(HCO2)(6)] (A(I) = NH4H2OI and M = Mn for 1, A(I) = CH3NH3I and M = Fe for 2, A(I) = CH3NH2CH3I and M = Co for 3, A(I) = CH3NH3I and M = Ni for 4). The title compounds exhibit isostructural niccolite architectures with differences only in the host metal ions and guest amines. Tunable ferromagnetic (FO) strength was realized in the resulting framework under the guidance of orthogonal magnetic orbital analysis of Cr-III (t(2g)(3)e(g)) and M-II (t(2g)(3)e(g)(2) for Fe(II)e(g)(2) for Fe-II t(2g) (5)e(g) (2) for Co-II t(2g) (6)e(g) (2) for Ni-II) ions. The magnetic ordering temperatures derived from the experimental magnetic measurements for 1-4 are lower than 2, 10.3, 7.6, and 22.0 K, respectively. Notably, thanks to the weak FO coupling between Cr-III and Mn-II ions, compound 1 displays a large magnetocaloric effect bearing the maximum of magnetic entropy change (-Delta S-m(max)) up to 43.9 J kg(-1) K-1 with Delta H = 7 T and T = 3.S K, larger than most reported transition metal-based complexes and commercial gadolinium gallium garnet (Gd3Ga5O12) (-Delta S-m (max) = 38.4 J Kg(-1) K-1 with Delta H = 7 T). From 1, 2/3, to 4, an enhancement of the magnetic ordering temperature is observable due to the increasing strength of FO interactions between Cr-III and M-II ions. Our work provides a successful instance to modulate the strength of FO exchange via analyzing the orthogonal magnetic orbitals of heterometallic ions.