Urea Route to Homoleptic Cyanates—Characterization and Luminescence Properties of [M(OCN)₂(urea)] and M(OCN)₂ with M=Sr, Eu

Abstract

A novel approach for the synthesis of urea complexes and homoleptic cyanates of alkaline earth metals and europium is described. Direct reaction of urea with elemental Sr or Eu in closed ampoules at temperatures above 120 degrees C yields [M(OCN)2(urea)] with M=Sr, Eu. According to single-crystal X-ray diffraction, the isotypic complexes exhibit a layer structure ([Eu(OCN)2(urea)]: P2(1)/c, a=7.826(2), b=7.130(1), c=12.916(3) A, beta=99.76(3) degrees , Z=4, V=710.3(2) A3). Furthermore, they were characterized by vibrational spectroscopy, thermal analysis, magnetic measurements, and photoluminescence studies. Thermal treatment of the compounds [M(OCN)2(urea)] to 160-240 degrees C affords evaporation of urea and the subsequent formation of solvent-free homoleptic cyanates of Sr and Eu. The crystal structures of Sr(OCN)2 and Eu(OCN)2 were determined from X-ray powder diffraction data and refined by the Rietveld method. Both compounds crystallize in the orthorhombic space group Fddd and adopt the Sr(N3)2 type structure (Sr(OCN)2: a=6.1510(4), b=11.268(1), c=11.848(1) A, V=821.1(2) A3; Eu(OCN)2: a=6.1514(6), b=11.2863(12), c=11.8201(12) A, V=820.63(15) A3). The cyanates are stable up to 450 degrees C. Above 500 degrees C beta-Sr(CN)2 and Eu2O2(CN)2 are formed. Excitation and emission spectra of [Eu(OCN)2(urea)], [Sr(OCN)2(urea)]:Eu2+, Eu(OCN)2, Sr(OCN)2:Eu2+ at different temperatures are reported. A strong green emission for all examined Eu-containing compounds due to a 4f(6)5d(1)-4f(7) transition is observed at low temperatures. The luminescence properties are discussed in detail and are comparable to those of thiocyanates. Compared to the latter, a blue shift of the emission bands is observed due to the higher ionicity.

Development of Metal Cyanurates: The Example of Barium Cyanurate (BCY)

“…We note here that an alternate description of reaction equivalents of BaCl 2 and 2 K(OCN) could be given to yield Ba(OCN) 2 . However, we prefer the formula Ba 3 (O 3 C 3 N 3 ) 2 to express the presence of cyanurate ions in the structure, in contrast to the yet unknown barium cyanate [Ba(OCN) 2 ] 13…”

Circularly Polarized Absorption and Luminescence of Semiconductor Eu‐OCN Nanocrystals in the Blue Region of the Electromagnetic Spectrum

“…For luminescent semiconductor nanomaterials composed of Eu(II)‐O bonds (Eu(II)‐O nanomaterials), the electronic configuration of the excited state ( 5d band) differs substantially from that of the ground state (degenerated 4 f orbitals), promoting circularly polarized absorption (circular dichroism: CD) and emission (circularly polarized luminescence: CPL) phenomena under photo‐irradiation. However, in previous studies, EuO nanocrystals have been found to be unstable under air, resulting in the formation of europium(III) oxides (Eu 2 O 3 ) on the nanocrystal surface . The development of novel air‐stable and luminescent Eu(II)‐O nanomaterials is a key point for opening a new field of optical polarized‐light‐control devices with blue light sources.…”

Novel ionic liquids and plastic crystals utilizing the cyanate anion

“…[31][32][33] These complexes show that the cyanate anion is a valuable ligand for coordination chemistry as a result of its ambidentate character. More recently, Re, Eu and Sr cyanate compounds were introduced, 34,35 and this anion has also shown interesting behaviour in combination with nonaqueous protic solvents, where it builds hydrogen bonded complexes. 36 Reluctance to use the cyanate anion in ionic liquids is possibly a result of concerns over the reactivity of the anion.…”