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 (Sm 3+ , Tb 3+ , and Ce 3+ ) in three-dimensional (3D) coordination frameworks based on hexacyanidoruthenate(II) metalloligands. Mono-lanthanide compounds, K{Ln III (H 2 O) n [Ru II (CN) 6 ]}· m H 2 O ( 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 P 6 3 /m or the orthorhombic C mcm space groups, respectively. All exhibit luminescence under the UV excitation, including weak blue emission in 1 due to the d-d 3 T 1g → 1 A 1g electronic transition of Ru II , as well as much stronger blue emission in 2 related to the d-f 2 D 3/2 → 2 F 5/2,7/2 transitions of Ce III , red emission in 3 due to the f-f 4 G 5/2 → 6 H 5/2,7/2,9/2,11/2 transitions of Sm III , and green emission in 4 related to the f-f 5 D 4 → 7 F 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 x Ce 1- x (H 2 O) n [Ru(CN) 6 ]}· m H 2 O ( x = 0.47, 0.88, 0.88, 0.99, 0.998; 5 - 9 ) and K{Tb x Ce 1- x (H 2 O) n [Ru(CN) 6 ]}· m H 2 O ( 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 0.4 Tb 0.599 Ce 0.001 (H 2 O) 2 [Ru(CN) 6 ]}·2.5H 2 O ( 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.