Spin crossover in Hofmann-like coordination polymers. Effect of the axial ligand substituent and its position

Abstract

This contribution reports the preparation and thermally induced spin crossover (SCO) in the Hofmann-like Fe(3-hydroxypyridine)2[M(CN)4] series where M = Ni, Pd, Pt. These three 2D coordination polymers crystallize with a...

Thermally-induced spin-crossover (SCO) in Fe(4-ethynylpyrdine)2[Fe(CN)5NO]. Why is the SCO observed in 2D ferrous nitroprussides despite the NO–NC repulsive interaction in the interlayer region?

“…In the Fe(L) 2 [M(CN) 4 ] Hofmann-like series with SCO, the corresponding frequency shift is about + 5 cm −1 . 14,15 Such large values for the Δ ν (CN) frequency in 2D ferrous nitroprussides with SCO, up to +9 cm −1 , are in correspondence with the decrease above discussed for the values of Δ QS (Fig. 7A).…”

“…A stronger ligand-to-metal interaction results in a more symmetric coordination environment for the iron atom. 15 For the material herein considered, the unit cell volume contraction related to the spin transition is 8.97%, significantly larger than the values observed with pyridine (Py) 16 and 3F-pyridine (3FPy) 19 as pillar molecules, which remain below 1%. According to the unit cell parameters (Table 1), the observed unit cell volume reduction results from a contraction in the layer plane and not from a reduction in the distance between adjacent layers.…”

“…23 Previous studies on the SCO in Hofmann-like coordination polymers have revealed that the distortion indexes ( Σ , θ , CShM) for the iron atom coordination environment, are appropriate probes for the possibility of observing the SCO in each composition. 15,23 Such a distortion is mainly determined by the organic ligand used as pillar and the position of its substituents. 15 The refined structural information for this material was deposited in the Cambridge Crystallographic Data Centre, with the CCDC file number †…”

“…15,23 Such a distortion is mainly determined by the organic ligand used as pillar and the position of its substituents. 15 The refined structural information for this material was deposited in the Cambridge Crystallographic Data Centre, with the CCDC file number †…”

“…1 The resulting 2D metal nitroprusside is a thermodynamic product because the same solid is obtained by different preparative routes for a wide diversity of molecules. 2 The large number of studies reported for the spin crossover (SCO) in Hofmann-type Fe(L) 2 [M(CN) 4 ] solids with M = Ni, Pd, Pt, and with L being pyridine and some of its derivatives, 3–15 stimulated the evaluation of pillared 2D ferrous nitroprussides as potential SCO materials with surprising results. 16–23 Unlike [M(CN) 4 ] building block, in the formed 2D solids with the complex nitroprusside ion, the NO group and the axial CN remain as dangling ligands occupying the interlayer region.…”