Piezochromism in Nickel Salicylaldoximato Complexes: Tuning Crystal‐Field Splitting with High Pressure

Abstract

The crystal structures of bis(3-fluoro-salicylaldoximato)nickel(II) and bis(3-methoxy-salicylaldoximato)nickel(II) have been determined at room temperature between ambient pressure and approximately 6 GPa. The principal effect of pressure is to reduce intermolecular contact distances. In the fluoro system molecules are stacked, and the Ni⋅⋅⋅Ni distance decreases from 3.19 Å at ambient pressure to 2.82 Å at 5.4 GPa. These data are similar to those observed in bis(dimethylglyoximato)nickel(II) over a similar pressure range, though contrary to that system, and in spite of their structural similarity, the salicyloximato does not become conducting at high pressure. Ni-ligand distances also shorten, on average by 0.017 and 0.011 Å for the fluoro and methoxy complexes, respectively. Bond compression is small if the bond in question is directed towards an interstitial void. A band at 620 nm, which occurs in the visible spectrum of each derivative, can be assigned to a transition to an antibonding molecular orbital based on the metal 3d(x(2)-y(2)) orbital. Time-dependent density functional theory calculations show that the energy of this orbital is sensitive to pressure, increasing in energy as the Ni-ligand distances are compressed, and consequently increasing the energy of the transition. The resulting blueshift of the UV-visible band leads to piezochromism, and crystals of both complexes, which are green at ambient pressure, become red at 5 GPa.

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

“…The best fit parameters K 0 and K 0 ' are: 10.7 ± 0.9 and 8.7 ± 1.8 GPa for Mn 2 Nb, 10.4 ± 1.6 and 8.2 ± 5.6 GPa for Fe 2 Nb (from the 0-1 GPa range fit) and 11.9 ± 1.2 and 6.9 ± 2.0 GPa in the case of Ni 2 Nb. The bulk modulus K 0 value is identical for all isomorphs within the experimental error and quite similar to other molecule-based coordination compounds [6,17,18]. Noteworthy, the K 0 for the studied coordination polymers are nearly two orders of magnitude smaller than for diamond (440 GPa) and only one order larger than for rubber (1 GPa) [19].…”

Variation of M···H–C Interactions in Square-Planar Complexes of Nickel(II), Palladium(II), and Platinum(II) Probed by Luminescence Spectroscopy and X-ray Diffraction at Variable Pressure

“…[5][6][7][8] Very few studies compare systematically the luminescence proprieties of 3d, 4d and 5d metal complexes with identical ligands. Variable-pressure studies provide quantitative, continuously varied spectroscopic properties of crystalline complexes, [9][10][11] and are especially attractive to probe structure-energy relations. [12][13][14][15] Only rarely have such continuous variations been explored by any spectroscopic technique for isoelectronic complexes with different metal centers.…”

Structural chemistry of metal coordination complexes at high pressure

“…The high pressure behaviour of two Ni(II) salicylaldoximato complexes ( Figure 13) were reported in a study by Byrne et al [21]. GPa and finally takes on a strong burgundy colour at 7.60 GPa.…”