Back to Search Start Over

Activating a high-spin iron(II) complex to thermal spin-crossover with an inert non-isomorphous molecular dopant.

Authors :
Halcrow, Malcolm A.
Vasili, Hari Babu
Pask, Christopher M.
Kulak, Alexander N.
Cespedes, Oscar
Source :
Dalton Transactions: An International Journal of Inorganic Chemistry; 4/28/2024, Vol. 53 Issue 16, p6983-6992, 10p
Publication Year :
2024

Abstract

[Fe(bpp)<subscript>2</subscript>][ClO<subscript>4</subscript>]<subscript>2</subscript> (bpp = 2,6-bis{pyrazol-1-yl}pyridine; monoclinic, C2/c) is high-spin between 5–300 K, and crystallises with a highly distorted molecular geometry that lies along the octahedral–trigonal prismatic distortion pathway. In contrast, [Ni(bpp)<subscript>2</subscript>][ClO<subscript>4</subscript>]<subscript>2</subscript> (monoclinic, P2<subscript>1</subscript>) adopts a more regular, near-octahedral coordination geometry. Gas phase DFT minimisations (ω-B97X-D/6-311G**) of [M(bpp)<subscript>2</subscript>]<superscript>2+</superscript> complexes show the energy penalty associated with that coordination geometry distortion runs as M<superscript>2+</superscript> = Fe<superscript>2+</superscript> (HS) ≈ Mn<superscript>2+</superscript> (HS) < Zn<superscript>2+</superscript> ≈ Co<superscript>2+</superscript> (HS) ≲ Cu<superscript>2+</superscript> ≪ Ni<superscript>2+</superscript> ≪ Ru<superscript>2+</superscript> (LS; HS = high-spin, LS = low-spin). Slowly crystallised solid solutions [Fe<subscript>x</subscript>Ni<subscript>1−x</subscript>(bpp)<subscript>2</subscript>][ClO<subscript>4</subscript>]<subscript>2</subscript> with x = 0.53 (1a) and 0.74 (2a) adopt the P2<subscript>1</subscript> lattice, while x = 0.87 (3a) and 0.94 (4a) are mixed-phase materials with the high-spin C2/c phase as the major component. These materials exhibit thermal spin-transitions at T<subscript>½</subscript> = 250 ± 1 K which occurs gradually in 1a, and abruptly and with narrow thermal hysteresis in 2a–4a. The transition proceeds to 100% completeness in 1a and 2a; that is, the 26% Ni doping in 2a is enough to convert high-spin [Fe(bpp)<subscript>2</subscript>][ClO<subscript>4</subscript>]<subscript>2</subscript> into a cooperative, fully SCO-active material. These results were confirmed crystallographically for 1a and 2a, which revealed similarities and differences between these materials and the previously published [Fe<subscript>x</subscript>Ni<subscript>1−x</subscript>(bpp)<subscript>2</subscript>][BF<subscript>4</subscript>]<subscript>2</subscript> series. Rapidly precipitated powders with the same compositions (1b–4b) mostly resemble 1a–4a, except that 2b is a mixed-phase material; 2b–4b also contain a fraction of amorphous solid in addition to the two crystal phases. The largest iron fraction that can be accommodated by the P2<subscript>1</subscript> phase in this system is 0.7 ± 0.1. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
14779226
Volume :
53
Issue :
16
Database :
Complementary Index
Journal :
Dalton Transactions: An International Journal of Inorganic Chemistry
Publication Type :
Academic Journal
Accession number :
176784904
Full Text :
https://doi.org/10.1039/d4dt00443d