Pagano Sandro, Montana Giuseppe, Wickleder Claudia, Schnick Wolfgang
Ludwig-Maximilians-Universität, Department Chemie und Biochemie, Butenandtstrasse 5-13 (D), 81377 München, Germany.
Chemistry. 2009 Jun 15;15(25):6186-93. doi: 10.1002/chem.200900053.
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.
描述了一种合成碱土金属和铕的尿素配合物及纯配氰酸盐的新方法。在封闭安瓿中，尿素与单质Sr或Eu在120℃以上直接反应生成[M(OCN)₂(尿素)]，其中M = Sr、Eu。根据单晶X射线衍射，同型配合物呈现层状结构（[Eu(OCN)₂(尿素)]：P2(1)/c，a = 7.826(2)，b = 7.130(1)，c = 12.916(3) Å，β = 99.76(3)°，Z = 4，V = 710.3(2) ų）。此外，通过振动光谱、热分析、磁性测量和光致发光研究对它们进行了表征。将化合物[M(OCN)₂(尿素)]在160 - 240℃进行热处理，使尿素蒸发，随后形成Sr和Eu的无溶剂纯配氰酸盐。Sr(OCN)₂和Eu(OCN)₂的晶体结构由X射线粉末衍射数据确定，并通过Rietveld方法进行精修。两种化合物均结晶于正交空间群Fddd，并采用Sr(N₃)₂型结构（Sr(OCN)₂：a = 6.1510(4)，b = 11.268(1)，c = 11.848(1) Å，V = 821.1(2) ų；Eu(OCN)₂：a = 6.1514(6)，b = 11.2863(12)，c = 11.8201(12) Å，V = 820.63(15) ų）。氰酸盐在450℃以下稳定。500℃以上会形成β - Sr(CN)₂和Eu₂O₂(CN)₂。报道了[Eu(OCN)₂(尿素)]、[Sr(OCN)₂(尿素)]:Eu²⁺、Eu(OCN)₂、Sr(OCN)₂:Eu²⁺在不同温度下的激发光谱和发射光谱。在低温下观察到所有检测的含Eu化合物由于4f(6)5d(1)-4f(7)跃迁而产生强烈的绿色发射。详细讨论了发光性质，且其与硫氰酸盐的发光性质相当。与硫氰酸盐相比，由于离子性更高，观察到发射带发生蓝移。
