Lanthanide(III)-based
coordination complexes have been explored
as a source of bifunctional molecular materials combining Single-Molecule
Magnet (SMM) behavior with visible-to-near-infrared photoluminescence.
In pursuit of more advanced multifunctionality, the next target is
to functionalize crystalline solids based on emissive molecular nanomagnets
toward high proton conductivity and an efficient luminescent thermometric
effect. Here, a unique multifunctional molecule-based material, (H5O2)2(H)[YbIII(hmpa)4][CoIII(CN)6]2·0.2H2O (1, hmpa = hexamethylphosphoramide), composed of molecular
{YbCo2}3– anions noncovalently bonded
to acidic H5O2
+ and H+ ions, is reported. The resulting YbIII complexes present
a slow magnetic relaxation below 6 K and room temperature NIR 4f-centered
photoluminescence sensitized by [Co(CN)6]3– ions. The microporous framework, built on these emissive magnetic
molecules, exhibits a high proton conductivity of the H-hopping mechanism
reaching σ of 1.7 × 10–4 S·cm–1 at 97% relative humidity, which classifies 1 as a superionic conductor. Moreover, the emission pattern
is strongly temperature-dependent which was utilized in achieving
a highly sensitive single-center luminescent thermometer with a relative
thermal sensitivity, S
r > 1% K–1 in the 50–175 K range. This work shows an
unprecedented combination
of magnetic, optical, and electrical functionalities in a single phase
working as a proton conductive NIR-emissive thermometer based on Single-Molecule
Magnets.
Diverse functional potential of heterometallic systems based on octacyanidometallates places them at the forefront of research into modern molecule-based materials.
Microporous magnets
compose a class of multifunctional molecule-based
materials where desolvation-driven structural transformation leads
to the switching of magnetic properties. Herein, we present a special
type of microporous magnet where a dehydration–hydration process
within a bimetal coordination framework results in the switching of
emissive DyIII single-molecule magnets (SMMs). We report
a three-dimensional (3-D) cyanido-bridged coordination polymer, {[DyIII(H2O)2][CoIII(CN)6]}·2.2H2O (1), and its dehydrated form
of {DyIII[CoIII(CN)6]} (2), which was obtained through a reversible single-crystal-to-single-crystal
transformation. Both phases are composed of paramagnetic DyIII centers alternately arranged with diamagnetic hexacyanidocobaltates(III).
The hydrated phase contains eight-coordinated [DyIII(μ-NC)6(H2O)2]3– complexes
of a square antiprism geometry, while the dehydrated form contains
six-coordinated [DyIII(μ-NC)6]3– moieties of a trigonal prism geometry. This change in coordination
geometry results in the generation of DyIII single-molecule
magnets in 2, whereas slow magnetic relaxation effect
is not observed for DyIII sites in 1. The D
4d-to-D
3h symmetry
change of DyIII complexes produces also the shift of photoluminescent
color from nearly white to deep yellow thanks to the modulation of
emission bands of f–f electronic transitions. A combined approach
utilizing dc magnetic data and low-temperature emission
spectra confirmed an axial crystal field of trigonal prismatic DyIII complexes in 2, which produces an Orbach type
of slow magnetic relaxation. Therefore, we present a unique route
to the efficient switching of SMM behavior and photoluminescence of
DyIII complexes embedded in a 3-D cyanido-bridged framework.
Coordination complexes of lanthanide(3+) ions can combine Single-Molecule Magnetism (SMM) with thermally-modulated luminescence applicable in optical thermometry. We report an innovative approach towards high performance SMM-based optical thermometers which explores...
The addition of chiral 2,2'-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline) (iPr-Pybox) to a self-assembled Co(II)–[W(V)(CN)(8)] magnetic system gives two enantiomorphic cyano-bridged chains, {[Co(II)((S,S)-iPr-Pybox)(MeOH)](3)[W(V)(CN)(8)](2)·5.5MeOH·0.5H(2)O}(n) (1-SS) and {[Co(II)((R,R)-iPr-Pybox) (MeOH)](3)[W(V)(CN)(8)](2)·5.5MeOH·0.5H(2)O}(n) (1-RR). 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. 1-(SS) and 1-(RR) 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)"(T) signal indicated slow magnetic relaxation characteristic of single-chain magnets.
The design and construction of switchable materials attracts tremendous interest owing to the potential in information storing and processing or molecular sensing. [1][2][3][4] The archetypal examples involve a diversity of Fe II -, [5,6] Fe III - [7] or Co IIbased [8][9][10] spin-crossover (SCO) compounds, Co III/II -catecholate/semiquinone systems, [1,11] as well as d-d bimetallic and sd-d trimetallic cyanide-bridged systems revealing chargetransfer-induced spin transitions (CTIST). [12][13][14][15][16][17][18] Some of these compounds, for example Prussian blue analogues, are particularly promising from the point of view of photoswitching between nonmagnetic and magnetized (that is, T B , T C ) states, owing to magnetic coupling through molecular bridges in discrete species [14,15] and extended networks. [17,18] Such bistability also emerged in the magnetochemistry of octacyanidometalates, exploiting metal-to-metal electron transfer in HS Co II L[W V (CN) 8 ] 3À (L = pyrimidine, 4-methylpyridine) [19,20] or canonical SCO in Fe II L[Nb IV (CN) 8 ] 4À extended networks [21] (L = 4-pyridinealdoxime). A magnetic hysteresis loop with a coercivity of 1-3 T were observed in an optically excited low-temperature metastable phase.
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