Lanthanide Photoluminescence in Heterometallic Polycyanidometallate-Based Coordination Networks

Solid-state functional luminescent materials arouse an enormous scientific interest due to their diverse applications in lighting, display devices, photonics, optical communication, low energy scintillation, optical storage, light conversion, or photovoltaics. Among all types of solid luminophors, the emissive coordination polymers, especially those based on luminescent trivalent lanthanide ions, exhibit a particularly large scope of light-emitting functionalities, fruitfully investigated in the aspects of chemical sensing, display devices, and bioimaging. Here, we present the complete overview of one of the promising families of photoluminescent coordination compounds, that are heterometallic d–f cyanido-bridged networks composed of lanthanide(3+) ions connected through cyanide bridges with polycyanidometallates of d-block metal ions. We are showing that the combination of cationic lanthanide complexes of selected inorganic and organic ligands with anionic homoligand [M(CN)x]n− (x = 2, 4, 6 and 8) or heteroligand [M(L)(CN)4]2− (L = bidentate organic ligand, M = transition metal ions) anions is the efficient route towards the emissive coordination networks revealing important optical properties, including 4f-metal-centred visible and near-infrared emission sensitized through metal-to-metal and/or ligand-to-metal energy transfer processes, and multi-coloured photoluminescence switchable by external stimuli such as excitation wavelength, temperature, or pressure

4‑Bromopyridine-Induced Chirality in Magnetic M^II-[Nb^IV(CN)₈]^4– (M = Zn, Mn, Ni) Coordination Networks

The introduction of 4-bromopyridine (4-Brpy) to a self-assembled M^II-[Nb^IV(CN)₈] (M = 3d metal ion) coordination system results in the formation of three-dimensional cyanido-bridged networks, {[M^II(4-Brpy)₄]₂­[Nb^IV(CN)₈]}­·<i>n</i>H₂O (M = Zn, <i>n</i> = 1, <b>1</b>; M = Mn, <i>n</i> = 0.5, <b>2</b>; M = Ni, <i>n</i> = 2, <b>3</b>). All these compounds are coordination frameworks composed of octahedral [M^II(4-Brpy)₄­(μ-NC)₂] complexes bonded to square antiprismatic [Nb^IV(CN)₈]^4– ions bearing four bridging and four terminal cyanides. <b>1</b> and <b>2</b> crystallize in the chiral <i>I</i>4₁22 space group as the mixture of two enantiomorphic forms, named <b>1</b>(<b>+</b>)/<b>1</b>(<b>−</b>) and <b>2</b>(<b>+</b>)/<b>2</b>(<b>−</b>), respectively. The chirality is here induced by the spatial arrangement of nonchiral but sterically expanded 4-Brpy ligands positioned around M^II centers in the distorted square geometry, which gives two distinguishable types of coordination helices, A and B, along a 4-fold screw axis. The (+) forms contain left handed helices A, and right handed helices B, while the opposite helicity is presented in the (−) enantiomers. On the contrary, <b>3</b> crystallizes in the nonchiral <i>Fddd</i> space group and creates only one type of helix. Half of them are right handed, and the second half are left handed, which originates from the ideally symmetrical arrangement of 4-Brpy around Ni^II and results in the overall nonchiral character of the network. <b>1</b> is a paramagnet due to paramagnetic Nb^IV centers separated by diamagnetic Zn^II. <b>2</b> is a ferrimagnet below a critical temperature, <i>T</i>_c of 28 K, which is due to the CN^–-mediated antiferromagnetic coupling within Mn–NC–Nb linkages. <b>3</b> reveals a ferromagnetic type of Ni^II–Nb^IV interaction leading to a ferromagnetic ordering below <i>T</i>_c of 16 K, and a hysteresis loop with a coercive field of 1400 Oe at 2 K. Thus, <b>1</b> is a chiral paramagnet, <b>3</b> is a nonchiral ferromagnet, and <b>2</b> combines both of these functionalities, being a rare example of a chiral molecule-based magnet whose chirality is induced by the noninnocent 4-Brpy ligands

Green to Red Luminescence Switchable by Excitation Light in Cyanido-Bridged Tb^III–W^V Ferromagnet

Green to Red Luminescence Switchable by Excitation Light in Cyanido-Bridged Tb^III–W^V Ferromagne

Dehydration of Octacyanido-Bridged Ni^II-W^IV Framework toward Negative Thermal Expansion and Magneto-Colorimetric Switching

An inorganic three-dimensional [Ni^II­(H₂O)₂]₂­[W^IV­(CN)₈]·​4H₂O (<b>1</b>) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase Ni^II₂­[W^IV­(CN)₈] (<b>1d</b>). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While <b>1</b> reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, <b>1d</b> is the first ever reported octacyanido-based solid revealing negative thermal expansion, also exhibiting a deep red color and diamagnetism. Such drastic shift in the physical properties is explained by the removal of water molecules, leaving the exclusively cyanido-bridged bimetallic network, which is accompanied by the transformation of the octahedral paramagnetic [Ni^II­(H₂O)₂­(NC)₄]^2– to the square-planar diamagnetic [Ni^II­(NC)₄]^2– moieties

Supramolecular Chains and Coordination Nanowires Constructed of High-Spin Co^II₉W^V₆ Clusters and 4,4′-bpdo Linkers

Cyanido-bridged high-spin {Co^II[Co^II­(MeOH)₃]₈­[W^V­(CN)₈]₆} (<b>Co</b>_<b>9</b><b>W</b>_<b>6</b>) clusters revealing single-molecule magnet behavior were combined with 4,4′-bipyridine-<i>N</i>,<i>N</i>′-dioxide (4,4′-bpdo) linkers, giving unique H-bonded supramolecular {Co^II₉­(MeOH)₂₄­[W^V­(CN)₈]₆}·4,4′-bpdo·MeOH·2H₂O (<b>1</b>) chains and one-dimensional coordination {Co^II­[Co^II­(4,4′-bpdo)_1.5­(MeOH)]₈­[W^V­(CN)₈]₆}·2H₂O (<b>2</b>) nanowires. The hydrogen-bonded chains of <b>1</b> are embedded within the three-dimensional supramolecular network stabilized by the series of noncovalent interactions between <b>Co</b>_<b>9</b><b>W</b>_<b>6</b> clusters, 4,4′-bpdo, and solvent molecules. The coordination nanowires <b>2</b>, revealing an average core diameter of about 11 Å, are arranged parallel with the significant separation in the crystal structure, leading to a microporous supramolecular network with broad channels (12 × 12 Å) filled by methanol and water. Both <b>1</b> and <b>2</b> are stable only in a mother solution or an organic protectant, whereas they undergo the fast exchange of methanol ligands to water molecules during drying in the air. Synthesized materials preserve the magnetic characteristics of <b>Co</b>_<b>9</b><b>W</b>_<b>6</b> clusters with an effective ferromagnetic coupling, giving a ground-state spin of 15/2. For <b>2</b>, the additional antiferromagnetic intercluster interactions are observed. Below 3 K, the frequency-dependent χ_M″(<i>T</i>) signals of <b>1</b> and <b>2</b> indicate the onset of slow magnetic relaxation. For <b>1</b>, the relaxation time follows the Arrhenius law with an energy gap of Δ/<i>k</i>_B = 10.3(5) K and τ₀ = 4(1) × 10^–9 s, which is consistent with single-molecule magnet behavior

Cesium Cyano-Bridged Co^II–M^V (M = Mo and W) Layered Frameworks Exhibiting High Thermal Durability and Metamagnetism

Two-dimensional cesium bimetal cyano-bridged assemblies Cs^I₄Co^II[Mo^V(CN)₈]­Cl₃ (<b>CsCoMo</b>) and Cs^I₄Co^II[W^V(CN)₈]­Cl₃ (<b>CsCoW</b>) were synthesized. The negatively charged and solvent-free {Co^II[M^V(CN)₈]­Cl₃}^4– (M = Mo, W) coordination layers are separated by Cs⁺ ions. Themogravimetric measurements show that these compounds reveal high thermal durability up to 523 K (250 °C), which is due to the absence of solvent molecules in their crystal structures. The magnetic measurements show that <b>CsCoMo</b> and <b>CsCoW</b> are metamagnets showing the field-induced transition from an antiferromagnetic phase with Néel temperature of 25 K to a ferromagnetic phase, which is observed at high critical magnetic field of 24 kOe at 1.8 K. These originate from antiferromagnetic interactions between ferromagnetically coupled cyano-bridged Co^II–M^V layers, and the contribution from single-ion anisotropy of Co^II

Conjunction of Chirality and Slow Magnetic Relaxation in the Supramolecular Network Constructed of Crossed Cyano-Bridged Co^II–W^V Molecular Chains

The addition of chiral 2,2′-(2,6-pyridinediyl)­bis­(4-isopropyl-2-oxazoline) (<i>i</i>Pr-Pybox) to a self-assembled Co^II–[W^V(CN)₈] magnetic system gives two enantiomorphic cyano-bridged chains, {[Co^II((<i>S</i>,<i>S</i>)-<i>i</i>Pr-Pybox)­(MeOH)]₃[W^V(CN)₈]₂·​5.5MeOH·​0.5H₂O}_<i>n</i> (<b>1</b>-<i>SS</i>) and {[Co^II((<i>R</i>,<i>R</i>)-<i>i</i>Pr-Pybox) (MeOH)]₃[W^V(CN)₈]₂·​5.5MeOH·​0.5H₂O}_<i>n</i> (<b>1</b>-<i>RR</i>). Both compounds crystallize with a structure containing a unique crossed arrangement of one-dimensional chains that form a microporous supramolecular network with large channels (14.9 Å × 15.1 Å × 15.3 Å) filled with methanol. The investigated materials exhibited optical chirality, as confirmed by natural circular dichroism and UV–vis absorption spectra. <b>1</b>-(<i>SS</i>) and <b>1</b>-(<i>RR</i>) are paramagnets with cyano-mediated Co^II–W^V magnetic couplings that lead to a specific spin arrangement with half of the W^V ions coupled ferromagnetically with their Co^II neighbors and the other half coupled antiferromagnetically. Significant magnetic anisotropy with the easy axis along the [101] direction was confirmed by single-crystal magnetic studies and can be explained by the single-ion anisotropy of elongated octahedral Co^II sites. Below 3 K, the frequency-dependent χ_M^″(<i>T</i>) signal indicated slow magnetic relaxation characteristic of single-chain magnets