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{LnIII(H2O)n[RuII(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 3T1g → 1A1g electronic transition of RuII, as well as much stronger blue emission in 2 related to the d-f 2D3/2 → 2F5/2,7/2 transitions of CeIII, red emission in 3 due to the f-f 4G5/2 → 6H5/2,7/2,9/2,11/2 transitions of SmIII, and green emission in 4 related to the f-f 5D4 → 7F6,5,4,3 transitions of TbIII. The lanthanide emissions, especially those of SmIII, take advantage of the RuII-to-LnIII energy transfer. The CeIII and TbIII emissions are also supported by the excitation of the d-f electronic states. Exploring emission features of the LnIII–RuII networks, two series of heterobi-lanthanide systems, K{SmxCe1–x(H2O)n[Ru(CN)6]}·mH2O (x = 0.47, 0.88, 0.88, 0.99, 0.998; 5–9) and K{TbxCe1–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{Sm0.4Tb0.599Ce0.001(H2O)2[Ru(CN)6]}·2.5H2O (15) composition shows the rich emission spectrum consisting of the peaks related to CeIII, TbIII, and SmIII 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

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 EuIII emission by the charge-transfer (CT) states related to d8–d10 heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of PtII/PdII and dicyanidometallates of AuI/AgI in the construction of a trimetallic d–d–f assembly. The combination of Eu3+, [MII(CN)4]2– (M = Pt, Pd), and [MI(CN)2]− (M = Au, Ag) ions along with 4,4′-bipyridine N,N′-dioxide (4,4′-bpdo) results in four novel isostructural 2D {[EuIII(4,4′-bpdo)­(H2O)2]­[MII(CN)4]}·[MI(CN)2]·H2O (MII/MI = 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 {EuIII[MII(CN)4]}n square grids coexisting with metal–organic {EuIII(4,4′-bpdo)}n chains, with the further attachment of [MI(CN)2]− ions through metallophilic {MII–MI} interactions. This results in dinuclear {MIIMI} 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 EuIII photoluminescence enhanced by energy transfer from {MIIMI} 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 EuIII-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 EuIII 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 PtII/AuI cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature EuIII luminescence

Near-Infrared Photoluminescence in Hexacyanido-Bridged Nd–Cr Layered Ferromagnet

Hexacyanidochromate­(III) anion is here explored as the building block for the construction of bimetallic 3d-4f coordination polymers that combine spin ordering and luminescence. We report the two-dimensional cyanido-bridged {[NdIII(pmmo)2­(H2O)3]­[CrIII(CN)6]} (1) layered framework obtained by the spontaneous crystallization from the aqueous solution of Nd3+, pyrimidine N-oxide (pmmo), and [CrIII(CN)6]3–. 1 crystallizes as light green plates in the orthorhombic Pbca space group and reveals a topology of a square grid built of nine-coordinated [NdIII(μ-NC)4­(H2O)3­(pmmo)2]− complexes of a nearly capped square antiprism geometry, and six-coordinated octahedral [CrIII(CN)6]3– moieties. Because of the presence of cyanide-mediated ferromagnetic coupling between paramagnetic NdIII (J = 9/2) and CrIII (S = 3/2) centers, 1 exhibits a long-range ferromagnetic ordering below Curie temperature of 2.8 K, with a tiny magnetization-field hysteresis loop detected at 1.8 K. Under the UV light irradiation, 1 shows the near-infrared fluorescence originated from the 4F3/2 → 4I9/2 (λmax = 895 nm) and 4F3/2 → 4I11/2 (λmax = 1060 nm) electronic transitions of NdIII. The near-infrared emission is realized through the energy transfer from [CrIII(CN)6]3– anions and pmmo ligands to NdIII centers which was possible due to the spectral overlap between the visible-light and near-infrared emission bands of CrIII and pmmo, and the absorption bands of NdIII. Thus, 1 can be considered as a novel type of bifunctional magneto-luminescent layered material taking advantage of the fruitful electronic and magnetic interplay between NdIII(pmmo) and [CrIII(CN)6]3– complexes

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 TbIII–WV Ferromagne

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 [NiII­(H2O)2]2­[WIV­(CN)8]·​4H2O (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase NiII2­[WIV­(CN)8] (1d). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While 1 reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, 1d 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 [NiII­(H2O)2­(NC)4]2– to the square-planar diamagnetic [NiII­(NC)4]2– moieties

Visible to Near-Infrared Emission from Ln^III(Bis-oxazoline)–[Mo^V(CN)₈] (Ln = Ce–Yb) Magnetic Coordination Polymers Showing Unusual Lanthanide-Dependent Sliding of Cyanido-Bridged Layers

Complexes of lanthanides­(III) (Ce–Yb) with 2,2′-bis­(2-oxazoline) (Box) combined with octacyanidomolybdate­(V) gave a series of magneto-luminescent coordination polymers, {[Ln^III(Box)_<i>n</i>(DMF)_<i>m</i>]­[Mo^V(CN)₈]}·<i>x</i>(solvent) (<b>1</b>–<b>12</b>). They are built of cyanido-bridged layers of a mixed 4- and 8-metal rings topology and show unique sliding of layers dependent on a 4f metal ion. For light lanthanides, dominant phase A, {[Ln^III(Box)₂(DMF)₂]­[Mo^V(CN)₈]}·1.5MeCN (Ln = Ce, <b>1</b>; Pr, <b>2</b>; Nd, <b>3</b>), consists of ideally aligned, not shifted layers, giving large channels (13.7 × 14.0 Å). Intermediate lanthanides reveal phase B, {[Ln^III(Box)₂(DMF)₂] [Mo^V(CN)₈]}·H₂O (Ln = Sm, <b>4</b>; Eu, <b>5</b>; Gd, <b>6</b>; Tb, <b>7</b>; Dy, <b>8</b>), of smaller pores (8.4 × 10.6 Å) due to layer-H₂O hydrogen bonding, which induces sliding of CN^–-bridged layers. Heavy lanthanides show phase C, {[Ln^III(Box)­(DMF)₃]­[Mo^V(CN)₈]}·MeCN (Ln = Ho, <b>9</b>; Er, <b>10</b>; Tm, <b>11</b>; Yb, <b>12</b>), with large channels (13.7 × 13.7 Å) of a similar size to light lanthanides. This effect comes from the changes in Ln^III coordination sphere affecting solvent–layer interactions. Compounds <b>1</b>–<b>12</b> reveal diverse emission depending on the interaction between Ln^III and Box luminophors. For <b>2</b>–<b>5</b>, <b>9</b>, and <b>12</b>, the ligand-to-metal energy-transfer-induced visible f-centered emission ranging from green for Ho^III-based <b>9</b>, orange from Sm^III-based <b>4</b>, to red for Pr^III- and Eu^III-containing <b>2</b> and <b>5</b>, respectively. Near-infrared emission was found for <b>2</b>–<b>4</b>, <b>9</b>, and <b>12</b>. Red phosphorescence of Box was detected for Gd^III-based <b>6</b>, whereas the selective excitation of ligand or Ln^III excited states resulting in the switchable red to green emission was found for Tb^III-based <b>7</b>. The materials revealed Ln^III–Mo^V magnetic coupling leading to ferromagnetism below 2.0 and 2.2 K for <b>4</b> and <b>7</b>, respectively. The onset of magnetic ordering at low temperatures was found for <b>6</b> and <b>8</b>. Compounds <b>1</b>–<b>12</b> form a unique family of cyanido-bridged materials of a bifunctional magneto-luminescence character combined with dynamic structural features

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

An inorganic three-dimensional [NiII­(H2O)2]2­[WIV­(CN)8]·​4H2O (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase NiII2­[WIV­(CN)8] (1d). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While 1 reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, 1d 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 [NiII­(H2O)2­(NC)4]2– to the square-planar diamagnetic [NiII­(NC)4]2– moieties