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

Chirality and Spin Crossover in Iron(II)–Octacyanidorhenate(V) Coordination Polymers Induced by the Pyridine-Based Ligand’s Positional Isomer

We present two novel coordination polymers based on octacyanidorhenate(V) metalloligands and Fe(II) complexes with two different positional isomers of a benzylpyridine ligand, namely 3-benzylpyridine (3-benzpy) that leads to a two-dimensional {[FeII(3-benzpy)4]3[ReV(CN)8]2}·2H2O (1) coordination network and 4-benzylpyridine (4-benzpy) giving a three-dimensional {[FeII(4-benzpy)4]5[ReV(CN)8]3}(ClO4)·2(4-benzpy)·6H2O·MeOH (2) coordination framework. 1 is a layered coordination polymer of a honeycomb topology, crystallizing in the centrosymmetric space group, which exhibits only residual thermal spin-crossover (SCO) effect on Fe(II) complexes at low temperatures. The lack of a significant SCO effect is probably caused by strong supramolecular interactions which do not allow the coordination framework to undergo the structural change required by the spin transition. On the other hand, 2 crystallizes as the chiral, cationic three-dimensional pillared cyanido-bridged framework, consisting of coordination layers of a deformed square grid topology, further bonded together by additional Fe(II) complexes. The structure is completed by noncoordinated 4-benzpy, water, and methanol molecules, as well as perchlorate counterions. The chiral character of the structure of 2 was confirmed by the single-crystal X-ray diffractions studies and the second-harmonic generation (SHG) effect detected at room temperature. 2 exhibits a pronounced two-step, and incomplete thermal SCO effect of embedded Fe(II) complexes. The intricate course of the spin transition in 2 is related to the presence of five crystallographically distinguishable Fe(II) centers with different supramolecular environments. The first noticeable SCO step is realized by the two Fe(II) complexes undergoing the spin transition between 250 and 150 K, while the second is related to the incomplete spin transition of one type of remaining Fe(II) complexes. Therefore, 2 is a rare example of a chiral SCO material showing also the nontrivial course of the spin transition. These properties were achieved by the subtle modification of the pyridine-based ligand indicating the advantage of iron(II)–octacyanidorhenate(V) systems in the formation of functional spin transition materials