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

Abstract

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