Giant anisotropic thermal expansion of copper-cyanido flat layers with flexible copper nodes

Flat layers are usually considered as structurally rigid motifs in two-dimensional (2D) materials. In this work, we demonstrate that a flat honeycomb-layer composed of distorted tri-coordinate copper ions bridged with cyanidos in (tetraethylammonium)Cu2(CN)3 exhibits high in-plane flexibility. This resulted in an extremely large anisotropic 2D-thermal expansion.

Negative Thermal Expansion of Undulating Coordination Layers through Interlayer Interaction

The negative thermal expansion (NTE) of solid-state materials is of significance in various fields, but a very rare phenomenon. In this study, we carried out a meta-analysis for the anisotropic thermal expansion behavior of fifteen two-dimensional coordination polymers [M(salen)]₂[M'(CN)₄(solvent)] (M = Mn, Fe; M' = MnN, ReN, Pt, Pt(I₂)_x; x = 0.18, 0.45, 0.85, 1.0; solvent = H₂O, MeOH, MeCN) with a newly synthesized [Fe(salen)]₂[MnN(CN)₄(MeCN)]. Consequently, we successfully demonstrate the unusual NTE of the undulating coordination layers by an expansion deformation of the layers via strong interlayer interaction within the layer stacking. Notably, the layer volume of [Mn(salen)]₂[ReN(CN)₄] with its powder form decreases with a large NTE coefficient, α_layer-volume = -27 × 10^-6 K^-1 (100-500 K). This is a significantly large value despite the increase in layer thickness along the layer contraction based on the anisotropic transformation of undulating layers. Conversely, the analysis demonstrates that the chemical modification of the layers to enhance intralayer interaction rather than interlayer interaction switches a direction of the layer anisotropy, yielding positive thermal expansion materials with the coefficient of the layer volume reaching +92 × 10^-6 K^-1.

Tunable magnetic anisotropy in luminescent cyanido-bridged {Dy2Pt3} molecules incorporating heteroligand PtIV linkers

The interest in the generation of photoluminescence in lanthanide(III) single-molecule magnets (SMMs) is driven by valuable magneto-optical correlations as well as perspectives toward magnetic switching of emission and opto-magnetic devices linking SMMs with optical thermometry. In the pursuit of enhanced magnetic anisotropy and optical features, the key role is played by suitable ligands attached to the 4f metal ion. In this context, cyanido complexes of d-block metal ions, serving as expanded metalloligands, are promising. We report two novel discrete coordination systems serving as emissive SMMs, {[Dy^III(H₂O)₃(tmpo)₃]₂[Pt^IVBr₂(CN)₄]₃}·2H₂O (1) and {[Dy^III(H₂O)(tmpo)₄]₂[Pt^IVBr₂(CN)₄]₃}·2CH₃CN (2) (tmpo = trimethylphosphine oxide), obtained by combining Dy^III complexes with uncommon dibromotetracyanidoplatinate(IV) ions, [Pt^IVBr₂(CN)₄]^2-. They are built of analogous Z-shaped cyanido-bridged {Dy₂Pt₃} molecules but differ in the coordination number of Dy^III (C.N. = 8 in 1, C.N. = 7 in 2) and the number of coordinated tmpo ligands (three in 1, four in 2) which is related to the applied solvents. As a result, both compounds reveal Dy^III-centred slow magnetic relaxation but only 1 shows SMM character at zero dc field, while 2 is a field-induced SMM. The relaxation dynamics in both systems is governed by the Raman relaxation mechanism. These effects were analysed using ac magnetic data and the results of the ab initio calculations with the support of magneto-optical correlations based on low-temperature high-resolution emission spectra. Our findings indicate that heteroligand halogeno-cyanido Pt^IV complexes are promising precursors for emissive SMMs with the further potential of sensitivity to external stimuli that may be related to the lability of the axially positioned halogeno ligands.

Interdigitated Pt-Br chains with π-stacking: an approach toward Robin-Day class I mixed valency in MX-chain complexes

The first interdigitated MX-type chain complex with infinite π-stacked arrays was synthesized. The synchronization between a Pt-Br⋯ chain and π-stacking periodicities led to the longest M-X-M distance (6.6978(15) Å) and nil or negligible intervalence charge transfer, which is essential to realize the Robin-Day class I mixed valence state in MX chains.