Structural analysis and photoluminescence properties of low dimensional lanthanide tetracyanometallates

The synthesis of a number of lanthanide tetracyanometallate (TCM) compounds have been carried out by reaction of Ln³⁺ nitrate salts and potassium tetracyanometallates in solvent systems containing dimethylsulfoxide and water. These reactions result in the isolation of three distinct structure types: (1) monoclinic [Ln(DMSO)₄(H₂O)₃M(CN)₄](M(CN)₄)_0.5·2H₂O (Ln = Eu, Tb and M = Pd, Pt), (2) orthorhombic {La(DMSO)₃(H₂O)₂(NO₃)M(CN)₄}_∞·H₂O (M = Pd, Pt), and (3) orthorhombic {Ln(DMSO)₃(H₂O)(NO₃)M(CN)₄}_∞ (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) in the form of single crystals. Single-crystal X-ray diffraction has been used to investigate their structural features. Structure type 1 is a zero dimensional ionic compound with a M/Ln ratio of 1.5:1. It contains coordinated as well as uncoordinated [M(CN)₄]²⁻ (M = Pd, Pt) anions and features relatively long platinophilic interactions. Structure types 2 and 3 differ quite drastically from structure type 1, but they are very similar to each other. Both of the latter are one-dimensional in nature due to chains containing linkage of Ln³⁺ coordination spheres with trans-bridging [M(CN)₄]²⁻ anions. These coordination polymers both have a M/Ln ratio of 1:1, a lack of platinophilic interactions, and incorporation of a bidentate NO₃⁻ for charge balance. Photoluminescence properties for select Eu³⁺ and Tb³⁺ compounds have been investigated. They show characteristic absorption and emission for the Ln³⁺ ions, but no significant influence of the tetracyanometallate anions.