Guest Removal and External Pressure Variation Induce Spin Crossover in Halogen-Functionalized 2-D Hofmann Frameworks

Ashley T Brennan; Katrina A Zenere; Helen E A Brand; Jason R Price; Mohan M Bhadbhade; Gemma F Turner; Stephen A Moggach; Francisco J Valverde-Muñoz; Jose A Real; Jack K Clegg; Cameron J Kepert; Suzanne M Neville

doi:10.1021/acs.inorgchem.0c02092

Guest Removal and External Pressure Variation Induce Spin Crossover in Halogen-Functionalized 2-D Hofmann Frameworks

Inorg Chem. 2020 Oct 5;59(19):14296-14305. doi: 10.1021/acs.inorgchem.0c02092. Epub 2020 Sep 27.

Authors

Affiliations

¹ The School of Chemistry, UNSW Sydney, Sydney 2052, New South Wales, Australia.
² The School of Chemistry, The University of Sydney, Sydney 2006, New South Wales, Australia.
³ Australian Synchrotron, ANSTO, Clayton 3800, Victoria, Australia.
⁴ Mark Wainwright Analytical Centre, UNSW Sydney, Sydney, New South Wales 2052, Australia.
⁵ School of Molecular Sciences/Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth 6009, Western Australia, Australia.
⁶ Institut the Ciencia Molecular, Department de Quimica Inorganica, Universitat de Valéncia, 46980 Paterna, Valéncia, Spain.
⁷ School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland 4072, Australia.

PMID: 32985190
DOI: 10.1021/acs.inorgchem.0c02092

Abstract

The effect of halogen functionalization on the spin crossover (SCO) properties of a family of 2-D Hofmann framework materials, [Fe^IIPd(CN)₄(thioX)₂]·2H₂O (X = Cl and Br; thioCl = (E)-1-(5-chlorothiophen-2-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine) and thioBr = (E)-1-(5-bromothiophen-2-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine)), is reported. Inclusion of both the chloro- and bromo-functionalized ligands into the Hofmann-type frameworks (1^Cl·2H₂O and 2^Br·2H₂O) results in a blocking of spin-state transitions due to internal chemical pressure effects derived by the collective steric bulk of the halogen atoms and guest molecules. Cooperative one-step SCO transitions are revealed by either guest removal or the application of external physical pressure. Notably, removal of solvent water reveals a robust framework scaffold with only marginal variation between the solvated and desolvated structures (as investigated by powder and single crystal X-ray diffraction). Yet, one-step complete SCO transitions are revealed in 1^Cl and 2^Br with a transition temperature shift between the analogues due to various steric, structural, and electronic considerations. SCO can also be induced in the solvated species, 1^Cl·2H₂O and 2^Br·2H₂O, with the application of physical pressure, revealing a complete one-step SCO transition above 0.62 GPa (as investigated by magnetic susceptibility and single crystal X-ray diffraction measurements).