How to Quench Ferromagnetic Ordering in a CN-Bridged Ni(II)-Nb(IV) Molecular Magnet? A Combined High-Pressure Single-Crystal X-Ray Diffraction and Magnetic Study

Abstract

High-pressure (HP) structural and magnetic properties of a magnetic coordination polymer {[NiII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Ni2Nb) are presented, discussed and compared with its two previously reported analogs {[MnII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Mn2Nb) and {[FeII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Fe2Nb). Ni2Nb shows a significant decrease of the long-range ferromagnetic ordering under high pressure when compared to Mn2Nb, where the pressure enhances the Tc (magnetic ordering temperature), or to Fe2Nb exhibiting a pressure-induced spin crossover. The different HP magnetic responses of the three compounds were rationalized and correlated with the structural models as determined by single-crystal X-ray diffraction.

Metal–organic frameworks under pressure

“…130 Indeed, there are increasingly many reports of pressure-induced changes in magnetic behavior of coordination polymers. 81,[131][132][133][134] Perhaps, the most striking report so far is the 50 K increase in long-range magnetic ordering temperature that occurs on compression to 4.7 GPa in the ferrimagnet [Mn(en)] 3 [Cr(CN) 6 ] 2 Á 4H 2 O (en ¼ ethylenediamine). 135 Spin-state and charge localization transitions are also strongly sensitive to transition-metal d-orbital energies.…”

Guest‐Dependent Pressure‐Induced Spin Crossover in FeII4[MIV(CN)8]2 (M=Mo, W) Cluster‐Based Material Showing Persistent Solvent‐Driven Structural Transformations

“…Ad etaileda nalysis of the M(H)c urvesf or 1solv, 1 and 1H 2 O (Figure 10 d, 10e and 10f) confirms stronger pressure-induced SCO for 1solv and 1H 2 O compared to 1:t he molar magnetization at 7T decreases from 11.3 to 6.5 Nb for 1solv and from 11.9 to 7.1 Nb for 1H 2 O with increasing pressure, while for the solvent-free 1 the decreasei sm uch smaller-from1 2.7 to 11.1 Nb.M oreover,t he high pressure significantly changes the M(H)p rofile for 1 compared to 1solv and 1H 2 O.T he M(H)c urves of 1solv and 1H 2 O attain lower values with increasing pressure in the whole investigatedm agnetic field range, while 1 shows an increase of the M(H)w ith increasing pressure in the 0-3 Tr ange and its decrease in the 3-7 T range (see arrows in Figures 10 d, ea nd f). Such ab ehaviour might be explained by the appearance of the intermolecular ferromagnetic interactions [57] transmitted through p-p contacts between the clusters or weakeningo ft he intramoleculara ntiferromagnetic ones transmitted through Fe II -CN-Mo IV -CN-Fe II pathways. Another (most plausible) explanationi st he change of the magnetic anisotropy of the Fe II centres under pressure [58] for compound 1,w hich would dramatically change the M(H) profile.…”