Brennan Ashley T, Zenere Katrina A, Kepert Cameron J, Clegg Jack K, Neville Suzanne M
The School of Chemistry, University of New South Wales-Sydney, Sydney 2052, New South Wales, Australia.
The School of Chemistry, The University of Sydney, Sydney 2006, New South Wales, Australia.
Inorg Chem. 2021 Mar 15;60(6):3871-3878. doi: 10.1021/acs.inorgchem.0c03651. Epub 2021 Mar 1.
We probe, here, a family of 2D Hofmann-type frameworks, [Fe(Pd(CN))(bztrzX)]·HO [·HO; X = F, Cl, Br; = 1 (X = Cl, Br) and 3 (X = F); bztrzX = ()-1-(2-Xphen-1-yl)--(4-1,2,4-triazol-4-yl)methanimine], with halogen-appended ligands. In all cases, there are two crystallographically distinct Fe sites, ({Fe1-Fe2}), driven by the presence of a range of host-host and host-guest interactions. We find that lattice modification through X variation influences the elastic coupling between the Fe sites, the emergence of ferroelastic or antiferroelastic interactions between these sites, and the relative spin-state stabilization/destabilization at each site. In ·HO, the Fe sites show strong elastic coupling, as evidenced by both Fe sites undergoing a spin transition in a single cooperative step, as driven by the volume strain over the high-spin (HS)-to-low-spin (LS) transition. The Fe sites in ·3HO are also elastically coupled; however, the change of the X atom characteristics and increased guest molecules in the pores result in an antiferroelastic interaction characteristic between Fe1 and Fe2 and a resultant two-step spin-state transition. The change of the X atom to Br in ·HO results in the Fe sites being decoupled due to halogen atom steric bulk, resulting in the independent spin-state transition of Fe1 and Fe2 sites and a two-step spin-state transition pathway. Uniquely, all three possible spin-state transition pathways of a two-site switching system are observed in this family [(1) {HS-HS} ↔ {HS-LS} ↔ {LS-LS} for ·HO, (2) {HS-HS} ↔ {LS-HS} ↔ {LS-LS} for ·3HO, and (3) {HS-HS} ↔ {LS-LS} for ·HO for {Fe1-Fe2}]. Overall, these findings broadly support recent theoretical models but highlight that additional structural and topological complexities are needed to form a holistic picture of the drivers of elastic frustration.
在此，我们探究了一族二维霍夫曼型骨架化合物[Fe(Pd(CN))(bztrzX)]·H₂O [·H₂O；X = F、Cl、Br；ν = 1（X = Cl、Br）且ν = 3（X = F）；bztrzX = (±)-1-(2-X-苯基)-1H-1,2,4-三唑-4-基甲亚胺]，其带有卤代附加配体。在所有情况下，由于存在一系列主体-主体和主体-客体相互作用，存在两个晶体学上不同的铁位点（{Fe1 - Fe2}）。我们发现，通过改变X来修饰晶格会影响铁位点之间的弹性耦合、这些位点之间铁弹性或反铁弹性相互作用的出现，以及每个位点处相对自旋态的稳定化/去稳定化。在·H₂O中，铁位点表现出强烈的弹性耦合，这由两个铁位点在单个协同步骤中经历自旋转变所证明，该转变由高自旋（HS）到低自旋（LS）转变过程中的体积应变驱动。·3H₂O中的铁位点也存在弹性耦合；然而，X原子特性的改变以及孔中客体分子数量的增加导致Fe1和Fe2之间具有反铁弹性相互作用特征以及由此产生的两步自旋态转变。在·H₂O中，X原子变为Br会由于卤原子的空间位阻使铁位点解耦，导致Fe1和Fe2位点独立的自旋态转变以及两步自旋态转变途径。独特的是，在这一族化合物中观察到了双位点切换系统的所有三种可能的自旋态转变途径[（1）对于·H₂O，{HS - HS} ↔ {HS - LS} ↔ {LS - LS}，（2）对于·3H₂O，{HS - HS} ↔ {LS - HS} ↔ {LS - LS}，以及（3）对于·H₂O中{Fe1 - Fe2}，{HS - HS} ↔ {LS - LS}]。总体而言，这些发现广泛支持了近期的理论模型，但突出表明需要额外的结构和拓扑复杂性来形成弹性失配驱动因素的整体图景。
