White Light Emissive Dy(III) Single-Molecule Magnets Sensitized by Diamagnetic [Co(III) (CN)6 ](3-) Linkers

Desolvation-Induced Highly Symmetrical Terbium(III) Single-Molecule Magnet Exhibiting Luminescent Self-Monitoring of Temperature

A conjunction of Single-Molecule Magnet (SMM) behavior and luminescence thermometry is an emerging research line aiming at contactless read-out of temperature in future SMM-based devices. The shared working range between slow magnetic relaxation and the thermometric response is typically narrow or absent. We report TbIII -based emissive SMMs formed in a cyanido-bridged framework whose properties are governed by the reversible structural transformation from [TbIII (H2 O)2 ][CoIII (CN)6 ] ⋅ 2.7H2 O (1) to its dehydrated phase, TbIII [CoIII (CN)6 ] (2). The 8-coordinated complexes in 1 show the moderate SMM effect but it is enhanced for trigonal-prismatic TbIII complexes in 2, showing the SMM features up to 42 K. They are governed by the combination of QTM, Raman, and Orbach relaxation with the energy barrier of 594(18) cm-1 (854(26) K), one of the highest among the TbIII -based molecular nanomagnets. Both systems exhibit emission related to the f-f electronic transitions, with the temperature variations resulting in the optical thermometry below 100 K. The dehydration leads to a wide temperature overlap between the SMM behavior and thermometry, from 6 K to 42 K. These functionalities are further enriched after the magnetic dilution. The role of post-synthetic formation of high-symmetry TbIII complexes in achieving the SMM effect and hot-bands-based optical thermometry is discussed.

Lanthanide Hexacyanidoruthenate Frameworks for Multicolor to White-Light Emission Realized by the Combination of d-d, d-f, and f-f Electronic Transitions

We report an effective strategy toward tunable room-temperature multicolor to white-light emission realized by mixing three different lanthanide ions (Sm³⁺, Tb³⁺, and Ce³⁺) in three-dimensional (3D) coordination frameworks based on hexacyanidoruthenate(II) metalloligands. Mono-lanthanide compounds, K{Ln^III(H₂O)_n[Ru^II(CN)₆]}·mH₂O (1, Ln = La, n = 3, m = 1.2; 2, Ln = Ce, n = 3, m = 1.3; 3, Ln = Sm, n = 2, m = 2.4; 4, Ln = Tb, n = 2, m = 2.4) are 3D cyanido-bridged networks based on the Ln-NC-Ru linkages, with cavities occupied by K⁺ ions and water molecules. They crystallize differently for larger (1, 2) and smaller (3, 4) lanthanides, in the hexagonal P6₃/m or the orthorhombic Cmcm space groups, respectively. All exhibit luminescence under the UV excitation, including weak blue emission in 1 due to the d-d ³T_1g → ¹A_1g electronic transition of Ru^II, as well as much stronger blue emission in 2 related to the d-f ²D_3/2 → ²F_5/2,7/2 transitions of Ce^III, red emission in 3 due to the f-f ⁴G_5/2 → ⁶H_{5/2,7/2,9/2,11/2} transitions of Sm^III, and green emission in 4 related to the f-f ⁵D₄ → ⁷F_6,5,4,3 transitions of Tb^III. The lanthanide emissions, especially those of Sm^III, take advantage of the Ru^II-to-Ln^III energy transfer. The Ce^III and Tb^III emissions are also supported by the excitation of the d-f electronic states. Exploring emission features of the Ln^III-Ru^II networks, two series of heterobi-lanthanide systems, K{Sm_xCe_1-x(H₂O)_n[Ru(CN)₆]}·mH₂O (x = 0.47, 0.88, 0.88, 0.99, 0.998; 5-9) and K{Tb_xCe_1-x(H₂O)_n[Ru(CN)₆]}·mH₂O (x = 0.56, 0.65, 0.93, 0.99, 0.997; 10-14) were prepared. They exhibit the composition- and excitation-dependent tuning of emission from blue to red and blue to green, respectively. Finally, the heterotri-lanthanide system of the K{Sm_0.4Tb_0.599Ce_0.001(H₂O)₂[Ru(CN)₆]}·2.5H₂O (15) composition shows the rich emission spectrum consisting of the peaks related to Ce^III, Tb^III, and Sm^III centers, which gives the emission color tuning from blue to orange and white-light emission of the CIE 1931 xy parameters of 0.325, 0.333.

Luminescence thermometry and field induced slow magnetic relaxation based on a near infrared emissive heterometallic complex

The 1 : 1 : 1 reaction of YbCl₃·6H₂O, K₃[Co(CN)₆] and bpyO₂ in H₂O has provided access to a complex with formula [YbCo(CN)₆(bpyO₂)₂(H₂O)₃]·4H₂O (1) in a very good yield while its structure has been determined by single-crystal X-ray crystallography and characterised based on elemental analyses and IR spectra. Magnetic susceptibility studies showed the complex to be a field induced single molecule magnet, as confirmed by μ-SQUID measurements. CASSCF calculations confirm the existence of a m_J = 7/2 ground state, with rather large transverse components, responsible for the fast relaxation characteristic of compound 1 at zero DC field, which is reduced upon application of DC fields. Moreover, a combination of luminescence studies along with CASSCF calculation allows the identification of the band structure of the complex, which is ultimately related to its electronic properties. Compound 1 operates as a luminescent thermometer in the 125-300 K range with a maximum relative thermal sensitivity of ≈0.1% K^-1 at 180 K.

Single molecule magnet behavior and luminescence of {Ln4} and {LnZn} complexes

A serials of tetranuclear coordination clusters [Ln4L2(HL)2(μ3-OH)2(NO3)2](NO3)2 [Ln = Dy (1•3CH3CN•5H2O), Gd (2•4CH3CN•5H2O), H2L = 6,6'-dimethoxy-2,2'-[2,2-dimethylpropane-1,3-diylbis-(nitrilomethylidyne)] diphenol] and dinuclear complexes [LnZnL(NO3)3(H2O)]•2CH3CN [Ln = Dy (3), Er (4), Yb (5), Lu...

The rational construction of diamond-like dysprosium–hexacyanometallate frameworks featuring dynamic magnetic behaviour

Four novel diamond-like dysprosium–hexacyanometallate frameworks featuring slow magnetic relaxation have been rationally constructed by a feasible building block strategy using hexacyanometallate to link superparamagnetic dimeric units.

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.

Hexanuclear Co4 Dy2 , Zn4 Dy2 , and Co4 Y2 Complexes with Defect Tetracubane Cores: Syntheses, Structures, and Magnetic Properties

A hexanuclear heterometallic cluster of composition [Dy₂ Co₄ (L)₄ (NO₃ )₂ (OH)₄ (C₂ H₅ OH)₂ ] ⋅ 2 C₂ H₅ OH (1) was synthesized by employing a Schiff base 2-(((2-hydroxy-3-methoxybenzyl) imino)methyl)-4-methoxyphenol (H₂ L) as ligand and utilizing Dy(NO₃ )₃  ⋅ 6H₂ O and Co(NO₃ )₂  ⋅ 6H₂ O as metal ion sources. X-ray single-crystal diffraction analysis indicated that complex 1 contains a defect tetracubane core and possesses central symmetric structure, with two Dy^III ions being in the central body position of the molecule and four Co^II ions being arranged at the outer sites. Magnetic studies reveal that complex 1 behaves as single-molecule magnet (SMM) with energy barrier of 27.50 K. To investigate the individual contribution of Dy^III and Co^II ions to the SMM behavior, another two complexes of formulae [Dy₂ Zn₄ (L)₄ (NO₃ )₂ (OH)₄ ] ⋅ 4CH₃ OH (2) and [Y₂ Co₄ (L)₄ (NO₃ )₂ (OH)₄ (C₂ H₅ OH)₂ ] ⋅ 2 C₂ H₅ OH (3) were prepared. Complexes 1 and 3 are isomorphous. The coordination geometries of Dy^III ions in 1 and 2 are different. The Dy^III ions are eight-coordinated in 2 and nine-coordinated in 1. Complex 2 exhibits SMM behavior with energy barrier of 69.67 K, but complex 3 does not display SMM property. These results reveal that the SMM behaviors of 1 and 2 are mainly originated from Dy^III ions. It might be the higher symmetry of Dy^III ions in 2 that results in the higher energy barrier.

Influence of Fine Ligand Substitution Modification of the Isocyanidometal Bridge on Metal-to-Metal Charge Transfer Properties in Class II-III Mixed Valence Complexes

The synthesis and characterization of Class II-III mixed valence complexes have been an interesting topic due to their special intermediate behaviour between localized and delocalized mixed valence complexes. To investigate the influence of the isocyanidometal bridge on metal-to-metal charge transfer (MMCT) properties, a family of new isocyanidometal-bridged complexes and their one-electron oxidation products cis-[Cp(dppe)Fe-CN-Ru(L)₂ -NC-Fe(dppe)Cp][PF₆ ]_n (n=2, 3) (Cp=1,3-cyclopentadiene, dppe=1,2-bis(diphenylphosphino)ethane, L=2,2'-bipyridine (bpy, 1[PF₆ ]_n ), 5,5'-dimethyl-2,2'-bipyridyl (5,5'-dmbpy, 2[PF₆ ]_n ) and 4,4'-dimethyl-2,2'-bipyridyl (4,4'-dmbpy, 3[PF₆ ]_n )) have been synthesized and fully characterized. The experimental results suggest that all the one-electron oxidation products may belong to Class II-III mixed valence complexes, supported by TDDFT calculations. With the change of the substituents of the bipyridyl ligand on the Ru centre from H, 5,5'-dimethyl to 4,4'-dimethyl, the energy of MMCT for the one-electron oxidation complexes changes in the order: 1³⁺ <2³⁺ <3³⁺ , and that for the two-electron oxidation complexes decreases in the order 1⁴⁺ >3⁴⁺ >2⁴⁺ . The potential splitting (ΔE_1/2 (2)) between the two terminal Fe centres for N[PF₆ ]₂ are the largest potential splitting for the cyanido-bridged complexes reported so far. This work shows that the smaller potential difference between the bridging and the terminal metal centres would result in the more delocalized mixed valence complex.

Near-Infrared Emissive Cyanido-Bridged {YbFe2} Molecular Nanomagnets Sensitive to the Nitrile Solvents of Crystallization

One of the pathways toward luminescent single-molecule magnets (SMMs) is realized by the self-assembly of lanthanide(3+) ions with cyanido transition metal complexes. We report a novel family of emissive SMMs, {YbIII(4-pyridone)4[FeII(phen)2(CN)2]2}(CF3SO3)3·solv (solv = 2MeCN, 1·MeCN; 2AcrCN, 1·AcrCN; 2PrCN, 1·PrCN; 2MalCN·1MeOH; 1·MalCN; MeCN = acetonitrile, AcrCN = acrylonitrile, PrCN = propionitrile, MalCN = malononitrile). They are based on paramagnetic YbIII centers coordinating diamagnetic [FeII(phen)2(CN)2] metalloligands but differ in the nitrile solvents of crystallization. They exhibit a field-induced slow magnetic relaxation dominated by a Raman process, without an Orbach relaxation as indicated by AC magnetic data and the ab initio calculations. The Raman relaxation is solvent-dependent as represented by the power “n” of the BRamanTn contribution varying from 3.07(1), to 2.61(1), 2.37(1), and 1.68(4) for 1·MeCN, 1·PrCN, 1·AcrCN, and 1·MalCN, respectively, while the BRaman parameter adopts the opposite trend. This was correlated with the variation of phonon modes schemes, including the number of available vibrational modes and their energies, dependent on the increasing complexity of the applied nitrile. 1·MeCN and 1·MalCN show the additional T-independent relaxation assignable to dipole-dipole interactions as confirmed by its suppression in 1·AcrCN and 1·PrCN revealing longer Yb–Yb distances and the disappearance in the LuIII-diluted 1·MeCN@Lu. All compounds exhibit YbIII–centered near-infrared photoluminescence sensitized by organic ligands.

Incorporation of expanded organic cations in dysprosium(III) borohydrides for achieving luminescent molecular nanomagnets

Luminescent single-molecule magnets (SMMs) constitute a class of molecular materials offering optical insight into magnetic anisotropy, magnetic switching of emission, and magnetic luminescent thermometry. They are accessible using lanthanide(III) complexes with advanced organic ligands or metalloligands. We present a simple route to luminescent SMMs realized by the insertion of well-known organic cations, tetrabutylammonium and tetraphenylphosphonium, into dysprosium(III) borohydrides, the representatives of metal borohydrides investigated due to their hydrogen storage properties. We report two novel compounds, [n-Bu4N][DyIII(BH4)4] (1) and [Ph4P][DyIII(BH4)4] (2), involving DyIII centers surrounded by four pseudo-tetrahedrally arranged BH4- ions. While 2 has higher symmetry and adopts a tetragonal unit cell (I41/a), 1 crystallizes in a less symmetric monoclinic unit cell (P21/c). They exhibit yellow room-temperature photoluminescence related to the f-f electronic transitions. Moreover, they reveal DyIII-centered magnetic anisotropy generated by the distorted arrangement of four borohydride anions. It leads to field-induced slow magnetic relaxation, well-observed for the magnetically diluted samples, [n-Bu4N][YIII0.9DyIII0.1(BH4)4] (1@Y) and [Ph4P][YIII0.9DyIII0.1(BH4)4] (2@Y). 1@Y exhibits an Orbach-type relaxation with an energy barrier of 26.4(5) K while only the onset of SMM features was found in 2@Y. The more pronounced single-ion anisotropy of DyIII complexes of 1 was confirmed by the results of the ab initio calculations performed for both 1-2 and the highly symmetrical inorganic DyIII borohydrides, α/β-Dy(BH4)3, 3 and 4. The magneto-luminescent character was achieved by the implementation of large organic cations that lower the symmetry of DyIII centers inducing single-ion anisotropy and separate them in the crystal lattice enabling the emission property. These findings are supported by the comparison with 3 and 4, crystalizing in cubic unit cells, which are not emissive and do not exhibit SMM behavior.

New Cyanido-Bridged Heterometallic 3d-4f 1D Coordination Polymers: Synthesis, Crystal Structures and Magnetic Properties

Three new 1D cyanido-bridged 3d-4f coordination polymers, {[Gd(L)(H2O)2Fe(CN)6]·H2O}n (1GdFe), {[Dy(L)(H2O)2Fe(CN)6]·3H2O}n (2DyFe), and {[Dy(L)(H2O)2Co(CN)6]·H2O}n (3DyCo), were assembled following the building-block approach (L = pentadentate bis-semicarbazone ligand resulting from the condensation reaction between 2,6-diacetyl-pyridine and semicarbazide). The crystal structures consist of crenel-like LnIII-MIII alternate chains, with the LnIII ions connected by the hexacyanido metalloligands through two cis cyanido groups. The magnetic properties of the three complexes have been investigated. Field-induced slow relaxation of the magnetization was observed for compounds 2DyFe and 3DyCo. Compound 3DyCo is a new example of chain of Single Ion Magnets.

Reversible Humidity-Driven Transformation of a Bimetallic {EuCo} Molecular Material: Structural, Sorption, and Photoluminescence Studies

Functional molecule-based solids built of metal complexes can reveal a great impact of external stimuli upon their optical, magnetic, electric, and mechanical properties. We report a novel molecular material, {[EuIII(H2O)3(pyrone)4][CoIII(CN)6]}·nH2O (1, n = 2; 2, n = 1), which was obtained by the self-assembly of Eu3+ and [Co(CN)6]3- ions in the presence of a small 2-pyrrolidinone (pyrone) ligand in an aqueous medium. The as-synthesized material, 1, consists of dinuclear cyanido-bridged {EuCo} molecules accompanied by two H-bonded water molecules. By lowering the relative humidity (RH) below 30% at room temperature, 1 undergoes a single-crystal-to-single-crystal transformation related to the partial removal of crystallization water molecules which results in the new crystalline phase, 2. Both 1 and 2 solvates exhibit pronounced EuIII-centered visible photoluminescence. However, they differ in the energy splitting of the main emission band of a 5D0 → 7F2 origin, and the emission lifetime, which is longer in the partially dehydrated 2. As the 1 ↔ 2 structural transformation can be repeatedly reversed by changing the RH value, the reported material shows a room-temperature switching of detailed luminescent features including the ratio between emission components and the emission lifetime values.

Diverse physical functionalities of rare-earth hexacyanidometallate frameworks and their molecular analogues

The combination of rare-earth metal complexes and hexacyanidometallates of transition metals is a fruitful pathway for achieving functional materials exhibiting a wide scope of mechanical, magnetic, optical, and electrochemical properties.

Holmium(iii) molecular nanomagnets for optical thermometry exploring the luminescence re-absorption effect

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 tunable anisotropy and the luminescence re-absorption effect of Ho^III complexes. Our concept is shown in dinuclear cyanido-bridged molecules, {[Ho^III(4-pyridone)₄(H₂O)₂][M^III(CN)₆]}·nH₂O (M = Co, 1; Rh, 2; Ir, 3) and their magnetically diluted analogues, {[Ho^III _x Y^III _1-x (4-pyridone)₄(H₂O)₂][M^III(CN)₆]}·nH₂O (M = Co, x = 0.11, 1@Y; Rh, x = 0.12, 2@Y; Ir, x = 0.10, 3@Y). They are built of pentagonal bipyramidal Ho^III complexes revealing the zero-dc-field SMM effect. Experimental studies and the ab initio calculations indicate an Orbach magnetic relaxation with energy barriers varying from 89.8 to 86.7 and 78.7 cm^-1 K for 1, 2, and 3, respectively. 1-3 also differ in the strength of quantum tunnelling of magnetization which is suppressed by hyperfine interactions, and, further, by the magnetic dilution. The Y^III-based dilution governs the optical properties as 1-3 exhibit poor emission due to the dominant re-absorption from Ho^III while 1@Y-3@Y show room-temperature blue emission of 4-pyridone. Within ligand emission bands, the sharp re-absorption lines of the Ho^III electronic transitions were observed. Their strong thermal variation was used in achieving highly sensitive ratiometric optical thermometers whose good performance ranges, lying between 25 and 205 K, are adjustable by using hexacyanidometallates. This work shows that Ho^III complexes are great prerequisites for advanced opto-magnetic systems linking slow magnetic relaxation with unique optical thermometry exploiting a luminescence re-absorption phenomenon.

A series of lanthanide(III) metal-organic frameworks derived from a pyridyl-dicarboxylate ligand: single-molecule magnet behaviour and luminescence properties

The reactions of LnIII ions with a versatile pyridyl-decorated dicarboxylic acid ligand lead to the formation of a series of novel three-dimensional (3D) Ln-MOFs, [Ln3(pta)4(Hpta)(H2O)]·xH2O (Ln = Dy (1), Eu (2), Gd (3), Tb (4), H2pta = 2-(4-pyridyl)-terephthalic acid, x = 6 for 1, 2.5 for 2, 1.5 for 3 and 2 for 4). The Ln3+ ions act as nine-coordinated muffin spheres, linking to each other to generate trinuclear {Ln3(OOC)6N2} SBUs, which are further extended to be interesting 3D topological architectures. To the best of our knowledge, the Dy-MOF exhibits zero-field single-molecule magnet (SMM) behaviour with the largest effective energy barrier among the previously reported 3D MOF-based Dy-SMMs. The combined analyses of a diluted sample (1@Y) and ab initio calculations demonstrate that the thermally assisted slow relaxation is mainly attributed to the single-ion magnetism. Furthermore, fluorescence measurements reveal that H2pta can sensitize EuIII and TbIII characteristic luminescence.

A stable dysprosium(iii) complex with a terminal fluoride ligand showing high resolution luminescence and slow magnetic relaxation

An air-stable dysprosium(iii) complex, [C(NH₂)₃]₄[DyF(piv)₄](piv)₂ (piv = pivalate), with a terminal fluoride ligand protected by forming extensive hydrogen bonds with peripheral guanidiniums has been isolated. Though the magnetic data failed to determine the energy barrier for the magnetic reversal (U_eff) accurately, the fine emission spectrum of the ⁴F_9/2→⁶H_15/2 transition at 4.2 K and ab initio calculations reveal that the U_eff is about 376(20) K, which is among the highest for high-coordinate (coordination numbers ≥ 9) lanthanide mononuclear magnets.

Four Dinuclear and One-Dimensional-Chain Dysprosium and Terbium Complexes Based on 2-Hydroxy-3-methoxybenzoic Acid: Structures, Fluorescence, Single-Molecule-Magnet, and Ab Initio Investigation

The unique electronic configurations of lanthanide(III) ions generate abundant electronic energy levels, resulting in the fantastic magnetic and optical multifunctional properties of lanthanide complexes. Here, 2-hydroxy-3-methoxybenzoic acid (H₂MBA) was used to construct four Dy(III) and Tb(III) complexes containing two isostructural dinuclear complexes of [Ln₂(HMBA)₂(MBA)₂(DMF)₂(H₂O)₂]·6H₂O [Ln = Dy (1), Tb (2); DMF = N,N-dimethylformamide] and two other isostructural beltlike one-dimensional-chain complexes of [NH₄][Ln(HMBA)₄] [Ln = Dy (3), Tb (4)]. Fluorescence measurements reveal that H₂MBA can sensitize Dy(III) and Tb(III) characteristic luminescence. Furthermore, complex 3 can emit white light under UV-light irradiation originating from a dichromatic mixture of a blue emission of H₂MBA and a dominating yellow emission of Dy³⁺ ions. Magnetic susceptibility measurements show that two Dy(III) complexes are single-molecule magnets with anisotropy barriers of 90(2) and 31(5) cm^-1 for 1 and 3, respectively. The magnet-luminescence-structure correlations as well as relaxation pathways are investigated by ab initio calculations and fluorescent spectrometry.

Proton Conductive Luminescent Thermometer Based on Near-Infrared Emissive {YbCo2} Molecular Nanomagnets

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)[Yb^III(hmpa)₄][Co^III(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 Yb^III 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.

Europium(III) Photoluminescence Governed by d8-d10 Heterometallophilic Interactions in Trimetallic Cyanido-Bridged Coordination Frameworks

We report an efficient pathway toward sensitization of red room temperature Eu^III emission by the charge-transfer (CT) states related to d⁸-d¹⁰ heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of Pt^II/Pd^II and dicyanidometallates of Au^I/Ag^I in the construction of a trimetallic d-d-f assembly. The combination of Eu³⁺, [M^II(CN)₄]^2- (M = Pt, Pd), and [M^I(CN)₂]^- (M = Au, Ag) ions along with 4,4'-bipyridine N,N'-dioxide (4,4'-bpdo) results in four novel isostructural 2D {[Eu^III(4,4'-bpdo)(H₂O)₂][M^II(CN)₄]}·[M^I(CN)₂]·H₂O (M^II/M^I = Pt/Au, 1; Pt/Ag, 2; Pd/Au, 3; Pd/Ag, 4) coordination networks. They are built of hybrid coordination layers, based on cyanido-bridged {Eu^III[M^II(CN)₄]}_n square grids coexisting with metal-organic {Eu^III(4,4'-bpdo)}_n chains, with the further attachment of [M^I(CN)₂]^- ions through metallophilic {M^II-M^I} interactions. This results in dinuclear {M^IIM^I} units generating an orange emissive metal-to-metal-to-ligand charge-transfer (MMLCT) state, whose energy is tuned by the applied d⁸-d¹⁰ metal centers. Thanks to these CT states, 1-4 exhibit room temperature red Eu^III photoluminescence enhanced by energy transfer from {M^IIM^I} units, with the additional role of 4,4'-bpdo also transferring the energy to lanthanides. These donor CT states lying in the visible range successfully broaden the available efficient excitation range up to 500 nm. The overall emission quantum yield ranges from 8(1)% for 4 to 15(2)% for 1, with the intermediate values for 2 and 3 relatively high among the reported Eu^III-based compounds with tetracyanido- and dicyanidometallates. We found that the sensitization efficiency is equally high for all compounds because of the similar energies of the CT states, while the main differences are related to the observed emission lifetimes ranging from ca. 80 μs for 4 to 120-130 μs for 2 and 3 to ca. 180 μs for 1. This phenomenon was correlated with the energies of the vibrational states, e.g., cyanide stretching vibrations, responsible for nonradiative deactivation of Eu^III excited states, which are the highest for the Pd/Ag pair of 4 and the lowest for the Pt/Au pair in 1. Thus, the heaviest pair of Pt^II/Au^I cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature Eu^III luminescence.

Coumarin-lanthanide based compounds with SMM behavior and high quantum yield luminescence

Coumarin-based lanthanide complexes of general formula [Ln(coum)3(phen)(H2O)x]·yH2O (Ln-phen, x = 0,1, 0 ≤ y ≤ 1.5; phen = 1,10-phenanthroline; coum = 3-acetyl-4-hydroxylato-coumarin; Ln = Eu, Tb, Dy, Tm) and [Ln(coum)3(batho)]·0.7EtOH (Ln-batho, batho = 4,7-diphenyl-1,10-phenanthroline; Ln = Eu, Tb, Dy, Tm) were synthesized. The magnetic relaxation and photoluminescence behavior of these complexes was compared with that of the related compounds [Ln(coum)3(EtOH)(H2O)]·EtOH (Ln-coum), so as to investigate the effects of incorporating a second chromophore, either the phen or batho ligand, to the original coordination scaffold, provided with three coumarin (coum) ligands. Slow relaxation of the magnetization under H = 0 with moderate activation energies was observed for the Dy-phen (U/kB = 99.1 K) and Dy-batho (U/kB = 67.1 K) compounds, whereas Tb analogues presented field-induced single molecule magnet (SMM) behavior, with U/kB = 11.7 K (16.6 K@3 kOe) for Tb-phen (Tb-batho), respectively. Luminescent emission in the visible range was observed for all the Ln-coumarin based compounds upon ligand sensitization, with high quantum yields of 45 (40%) for Eu-phen (Eu-batho) compounds and 65-76-58% for Tb-coum, phen, batho analogues. Sensitization is mainly provided by the coumarin ligand having the energy difference ΔE between its triplet state T1 and the lanthanide emitting level closest to the optimum, while the second ligand can play either a synergistic or competing sensitizing role. The Tb-phen/batho compounds presented simultaneously SMM and luminescent behavior, with excellent values of the bifunctional figure of merit (ηSMM-QY ∼ 1000% K). The reported compounds represent a new class of bifunctional materials with potential interesting application in various fields.

The differential magnetic relaxation behaviours of slightly distorted triangular dodecahedral dysprosium analogues in a type of cyano-bridged 3d–4f zig-zag chain compounds

Differential magnetic properties were observed for triangular dodecahedral dysprosium analogues in a type of cyano-bridged 3d–4f zig-zag chain compound.

Understanding the near-infrared fluorescence and field-induced single-molecule-magnetic properties of dinuclear and one-dimensional-chain ytterbium complexes based on 2-hydroxy-3-methoxybenzoic acid

Two Yb(iii) complexes with a dinuclear and belt-like one-dimensional chain structure were reported. Their near-infrared luminescence and single-molecule magnetic properties were investigated in detail.

One-dimensional lanthanide coordination polymers supported by pentadentate Schiff-base and diphenyl phosphate ligands: single molecule magnet behavior and photoluminescence

Four one-dimensional lanthanide coordination polymers constructed from Ln₂ dimers showing single molecule magnet behavior and photoluminescence are reported.

The different magnetic relaxation behaviors in [Fe(CN)6]3− or [Co(CN)6]3− bridged 3d–4f heterometallic compounds

For the isomorphic tetranuclear 3d–4f compounds constructed by [M(CN)₆]³⁻ linking Ln^III-Schiff-base units, the diamagnetic Co^III ions in the system could suppress QTM effectively and obtain a field-induced SMMs behavior.

Dehydration-Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged DyIIICoIII Framework

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 Dy^III single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[Dy^III(H₂O)₂][Co^III(CN)₆]}·2.2H₂O (1), and its dehydrated form of {Dy^III[Co^III(CN)₆]} (2), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic Dy^III centers alternately arranged with diamagnetic hexacyanidocobaltates(III). The hydrated phase contains eight-coordinated [Dy^III(μ-NC)₆(H₂O)₂]^3- complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [Dy^III(μ-NC)₆]^3- moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of Dy^III single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for Dy^III sites in 1. The D_4d-to-D_3h symmetry change of Dy^III 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 Dy^III 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 Dy^III complexes embedded in a 3-D cyanido-bridged framework.

Heterometallic 3d-4d coordination polymers assembled from trans-[RuIII(L)(CN)2]- tectons and 3d cations

Five new cyanido-bridged heterometallic coordination polymers have been obtained by reacting PPh4[RuIII(salpn)(CN)2]·H2O (1) and AsPh4[RuIII(valen)(CN)2]·8.5H2O (2) (H2salpn and H2valen being Schiff-base proligands resulting from the condensation reaction of salicylaldehyde with 1,3-propanediamine and, respectively, o-vanillin with 1,2-ethanediamine) with divalent transition metal perchlorate salts: ∞1[{RuIII(salpn)(CN)2}3{MII(DMF)3}2](ClO4)·4DMF (MII = Mn, 3; Co, 4) and ∞2[{RuIII(valen)(CN)2}4{MII(DMF)3}2{MII(DMF)4}](ClO4)2·4DMF (MII = Mn, 5; Co, 6; Ni, 7), respectively. The dicyanido species, trans-[Ru(salpn)(CN)2]- and trans-[Ru(valen)(CN)2]-, act as metalloligands with the 3d metal ions. Compounds 3 and 4 are isostructural one-dimensional (1D) coordination polymers with a ladder topology. Each MII ion is hexacoordinated by three cyanido groups arising from three {Ru(salpn)(CN)2} units and by the oxygen atoms from three DMF molecules, which are coordinated at meridional positions. Compounds 5-7 are also isostructural, their structures consisting of 2D networks with a herringbone topology. The magnetic susceptibility measurements of these 1D and 2D systems reveal the presence of dominating RuIII-MII antiferromagnetic (AF) interactions in compounds 3, 4, 5 and 6, while ferromagnetic RuIII-NiII interactions are observed in 7. All these compounds stay in their paramagnetic state down to 1.8 K except compound 4 which possesses a 3D ordered AF ground state.

Photoluminescent Lanthanide(III) Single-Molecule Magnets in Three-Dimensional Polycyanidocuprate(I)-Based Frameworks

Three-dimensional bimetallic cyanido-bridged frameworks, [Ln^III (2,2'-bipyridine N,N'-dioxide)₂ (H₂ O)][Cu^I ₂ (CN)₅ ]⋅5 H₂ O (Ln=Dy, 1; Yb, 2), are reported. They exhibit the effect of slow relaxation of magnetization, leading to a magnetic hysteresis loop, and sensitized visible-to-near-infrared photoluminescence. Both physical properties are related to the eight-coordinated lanthanide(III) complexes embedded in the unprecedented coordination skeleton composed of symmetry-breaking polycyanidocuprate linkers. The three-dimensional d-f cyanido-bridged network was shown to serve as an efficient coordination scaffold to achieve emissive lanthanide single-molecule magnets.

Near-infrared emissive Er(iii) and Yb(iii) molecular nanomagnets in metal–organic chains functionalized by octacyanidometallates(iv)

Photoluminescent single-molecule magnets are formed in lanthanide(pyrazine N,N′-dioxide) chains with octacyanidometallate(iv) coordination branches playing a crucial role in sensitized NIR emission.

TbIII/3d–TbIII clusters derived from a 1,4,7-triazacyclononane-based hexadentate ligand with field-induced slow magnetic relaxation and oxygen-sensitive luminescence

A family of new Tb^III/3d–Tb^III cluster complexes based on N,N′,N′′-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane have been synthesized and they exhibit interesting magnetic and luminescent properties.

Effect of coordination anion substitutions on relaxation dynamics of defect dicubane Zn2Dy2 tetranuclear clusters

We showcase the coordination anion substitution effect on the relaxation dynamics of defect dicubane Zn₂Dy₂ tetranuclear clusters.

Multi-colour uranyl emission efficiently tuned by hexacyanidometallates within hybrid coordination frameworks

Hexacyanidometallates of transition metal ions govern the topology and the photoluminescence of bimetallic d–f hybrid coordination networks incorporating uranyl cations.

Wide-Range UV-to-Visible Excitation of Near-Infrared Emission and Slow Magnetic Relaxation in LnIII(4,4'-Azopyridine-1,1'-dioxide)[CoIII(CN)6]3- Layered Frameworks

Trivalent lanthanide ions combined with two molecular linkers, organic 4,4'-azopyridine-1,1'-dioxide (apdo), and inorganic hexacyanidocobaltate(III), gave a series of magnetoluminescent coordination polymers, [{Ln^III(apdo)(H₂O)₄}{Co^III(CN)₆}]·2H₂O (Ln = Nd, 1; Tb, 2; Dy, 3; Er, 4; Tm, 5; Yb, 6). They are hybrid organic-inorganic layered frameworks composed of cyanido-bridged {Ln₂(μ-NC)₄Co₂} squares linked by Ln-apdo-Ln bridges into a coordination network of a mixed 4- and 8-metal ring topology. Lanthanide(III) complexes, [Ln^III(μ-apdo)₂(H₂O)₄(μ-NC)₂]⁺, of a distorted dodecahedral geometry are isolated by diamagnetic [Co^III(CN)₆]^3- and apdo linkers. As a result, 1-6 reveal field-induced slow relaxation of magnetization, with typical temperature-dependent relaxation of a single-ion origin for Nd^III-containing 1, Dy^III-containing 3, and Yb^III-containing 6. The related alternate-current magnetic data were precisely analyzed, indicating the multiple magnetic relaxation pathways, including a direct process, strong quantum tunneling of magnetization, non-negligible Raman processes, and crucial two-phonon Orbach thermal relaxation. The thermal energy barriers of the Orbach process, Δ E/ k_B, are 15.1(9) K with τ₀ = 9.8(9) × 10^-6 s at H_dc = 4500 Oe, 16.1(8) K with τ₀ = 9.0(9) × 10^-5 s at H_dc = 1500 Oe, and 17.3(6) K with τ₀ = 3.2(7) × 10^-6 s at H_dc = 700 Oe, for 1, 3, and 6, respectively, proving the single-molecule magnet (SMM) behavior. Because of the presence of [Co(CN)₆]^3-, 1-6 show strong UV absorption, while the chromophoric apdo leads to the strong absorption in the visible range. As a result, the visible 4f/3d metal-centered emission is quenched, but the near-infrared luminescence from Nd^III and Yb^III is observed in 1 and 6, respectively. It is realized by Co-to-Ln metal-to-metal, and apdo-to-Ln ligand-to-metal energy transfers; thus, broad UV-to-visible excitation can be explored. Compounds 1-6 form a novel family of functional bimetallic assemblies, incorporating NIR-emissive SMMs as presented for NdCo (1) and YbCo (6) derivatives.

A Terminal Fluoride Ligand Generates Axial Magnetic Anisotropy in Dysprosium Complexes

The first dysprosium complexes with a terminal fluoride ligand are obtained as air-stable compounds. The strong, highly electrostatic dysprosium-fluoride bond generates a large axial crystal-field splitting of the J=15/2 ground state, as evidenced by high-resolution luminescence spectroscopy and correlated with the single-molecule magnet behavior through experimental magnetic susceptibility data and ab initio calculations.