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.

Cyano-bridged polynuclear coordination compounds derived from paramagnetic [Mn(H2daptsc)]2+ and photochromic [Fe(CN)5NO]2− building blocks

Metal complexes with H₂daptsc ligand were first used as building blocks to create polynuclear multifunctional materials.

Spin Ice-like Magnetic Relaxation of a Two-dimensional Network based on Manganese(III) Salen-type Single-Molecule Magnets

Spin ice is an exotic type of magnetism displayed by bulk rare-earth pyrochlore oxides. We discovered a spin ice-like magnetic relaxation of [{Mn(saltmen)}₄ {Mn(CN)₆ }](ClO₄ )⋅13 H₂ O (saltmen^2- =N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminate)). This magnetic system can be considered as a two-dimensional network of Mn^III salen-type single-molecule magnets (SMMs) in which each SMM unit (S_T =4) has two orthogonally oriented axial anisotropies and is connected ferromagnetically through the [Mn(CN)₆ ]^3- unit (S=1). This work illustrates that a two-dimensional SMM network with competition between the ferromagnetic interaction and local noncollinear magnetic anisotropies on SMMs is a new type of magnetic system exhibiting slow relaxation of magnetization with a Davidson-Cole-type broad distribution of the relaxation time.

Investigating the effect of lanthanide radius and diamagnetic linkers on the framework of metallacrown complexes

By changing the stoichiometric ratios, the one-pot reaction of the glycinehydroxamic acid (H2glyha) ligand with copper(ii) and lanthanide(iii) salts in the presence of diamagnetic [Na2{Fe(CN)5(NO)}] led to two series of isostructural complexes, which can be designated as heterotrimetallic dimeric clusters [{LnCu5(glyha)5}{Fe(CN)5(NO)}(H2O)4]2·xNO3·yH2O (x = 2, y = 11 for La (1), x = 2, y = 11 for Pr (2), and x = 2, y = 11 for Nd (3)) and heterotetrametallic coordination polymers [Na{LnCu5(glyha)5}{Fe(CN)5(NO)}2(H2O)x·yH2O]n (x = 6, y = 4 for Sm (4), x = 6, y = 0 for Gd (5), x = 6, y = 4 for Tb (6), x = 5, y = 5 Dy (7), and x = 6, y = 4 for Ho (8)). Each molecular structure contains LnIII[15-metallacrown-5] nodes and diamagnetic [Fe(CN)5(NO)]2- linkers. The resulting products demonstrate diversified structural frameworks due to the radius effect of LnIII ions and different bridging fashions of diamagnetic [Fe(CN)5(NO)]2- linkers. An analysis of magnetic susceptibilities reveals that 7 exhibits ferromagnetic coupling between CuII and DyIII ions and field-induced SMM behavior.

The impact of counterion on the metastable state properties of nitrosyl ruthenium complexes

Complexes of the trans-[RuNO(NH₃)₄F]²⁺ cation with noble-metal anions [PtCl₆]²⁻, [PdCl₄]²⁻, and [PtCl₄]²⁻, and perchlorate ClO₄⁻ were synthesized, the photo-generated linkage isomers were studied by spectroscopic and calorimetric methods.

Pentacoordinate and Hexacoordinate Mn(III) Complexes of Tetradentate Schiff-Base Ligands Containing Tetracyanidoplatinate(II) Bridges and Revealing Uniaxial Magnetic Anisotropy

Crystal structures and magnetic properties of polymeric and trinuclear heterobimetallic Mn^III···Pt^II···Mn^III coordination compounds, prepared from the Ba[Pt(CN)₄] and [Mn(L4A/B)(Cl)] (1a/b) precursor complexes, are reported. The polymeric complex [{Mn(L4A)}₂{μ⁴-Pt(CN)₄}]_n (2a), where H₂L4A = N,N’-ethylene-bis(salicylideneiminate), comprises the {Mn(L4A)} moieties covalently connected through the [Pt(CN)₄]²⁻ bridges, thus forming a square-grid polymeric structure with the hexacoordinate Mn^III atoms. The trinuclear complex [{Mn(L4B)}₂{μ-Pt(CN)₄}] (2b), where H₂L4B = N,N’-benzene-bis(4-aminodiethylene-salicylideneiminate), consists of two [{Mn(L4B)} moieties, involving pentacoordinate Mn^III atoms, bridged through the tetracyanidoplatinate (II) bridges to which they are coordinated in a trans fashion. Both complexes possess uniaxial type of magnetic anisotropy, with D (the axial parameter of zero-field splitting) = −3.7(1) in 2a and −2.2(1) cm⁻¹ in 2b. Furthermore, the parameters of magnetic anisotropy 2a and 2b were also thoroughly studied by theoretical complete active space self-consistent field (CASSCF) methods, which revealed that the former is much more sensitive to the ligand field strength of the axial ligands.

Field-induced slow relaxation of magnetization in dinuclear and trinuclear CoIII⋯MnIII complexes

Magnetic anisotropy and field-induced slow relaxation of magnetization were studied in dinuclear and trinuclear heterobimetallic Co^III⋯Mn^III complexes.

The first photochromic bimetallic assemblies based on Mn(iii) and Mn(ii) Schiff-base (salpn, dapsc) complexes and pentacyanonitrosylferrate

The bimetallic cyano-bridged complexes demonstrating photochromism and magnetism were obtained and studied.

Synthesis, structures and magnetism of heterodinuclear Ni–Ln complexes: field-induced single-molecule magnet behavior in the dysprosium analogue

Three isomorphous Ni–Ln heterodinuclear complexes were synthesized and structurally characterized. The Dy derivative exhibits field-induced single-molecule magnet behavior with an effective energy barrier of 16.9 K under a 1000 Oe dc field.

Single-molecule magnet engineering: building-block approaches

Tailoring the specific magnetic properties of any material relies on the topological control of the constituent metal ion building blocks. Although this general approach does not seem to be easily applied to traditional inorganic bulk magnets, coordination chemistry offers a unique tool to delicately tune, for instance, the properties of molecules that behave as "magnets", the so-called single-molecule magnets (SMMs). Although many interesting SMMs have been prepared by a more or less serendipitous approach, the assembly of predesigned, isolatable molecular entities into higher nuclearity complexes constitutes an elegant and fascinating strategy. This Feature article focuses on the use of building blocks or modules (both terms being used indiscriminately) to direct the structure, and therefore also the magnetic properties, of metal ion complexes exhibiting SMM behaviour.

Towards a better understanding of magnetic exchange mediated by hydrogen bonds in Mn(iii)/Fe(iii) salen-type supramolecular dimers

Detailed investigations of the magnetic coupling and magnetic anisotropy in a series of Schiff base salen-type Fe(iii) and Mn(iii) complexes, based on SQUID experiments and DFT calculations, are reported.

Heterometallic complexes combining [MnIII(salpn)]+ and [Fe(CN)6]4− units as the products of reactions between [MnIII(salpn)(H2O)C(CN)3] and [Fe(CN)6]3−/4−

The tricyanomethanide ligand reduces Fe(iii) to Fe(ii) yielding the discrete and chain complexes.

Controlled association of single-molecule magnets (SMMs) into coordination networks: towards a new generation of magnetic materials

The field of molecular magnetism has rapidly expanded since the discovery of single-molecule magnets (SMMs) at the beginning of the 1990s. Numerous SMMs have been studied and a broad community currently works on these systems to improve their magnetic characteristics. However, it has also become an important strategy to diversify a part of our research activity toward the organization of these magnetic molecules in order to move closer to future applications. One of the possible ways is to utilize SMMs as molecular building blocks and assemble them with the help of coordination chemistry. This strategy presents a significant challenge since the intrinsic magnetic properties of the parent SMMs can be modified, which consequently also provides a unique opportunity to investigate new behaviours at the frontier between SMMs and classical bulk magnets. Furthermore, the design of systems with "enhanced" SMM properties or magnet behaviour is theoretically possible by choosing coordinating linkers that could favour an effective ferromagnetic arrangement of the SMMs. In this perspective article, we will give an overview of the known networks based on SMMs with an emphasis on the synthetic strategies, magnetic properties, and finally possible routes to a new generation of molecular magnetic materials.