Structure, photophysics and magnetism of a europium mixed complex, Eu(HFAA)3bipy.H2O, in the solid state and solution
Introduction
In recent years interest increased in the development of efficient light conversion molecular devices (LCMD) based on lanthanide complexes [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. The design of efficient lanthanide complexes has become an important research goal and covers many different classes of ligands.
Efficient light conversion molecules may find several applications mainly in optical devices, luminescence sensors for chemical species, luminescence probes in biomedical assays, fluorescent lighting, and electroluminescent devices. In the latter area heteroleptic europium complexes of the Euβ3L type can be used [2], [4], [11], [12], [13], [14], [15], [16], [17]. Photophysical characteristics of two types of chelates based on a wide group of derivatives of both β-diketones and Lewis base (L) (1,10-phenathroline) ligands were reported by us [13], [14], [15]. In this field, important results were distinguished by many scientific groups [2], [10], [11], [12], [13], [14], [15], [19], [20], [21], [22], [23].
Based on experimental and theoretical results it was shown that the quantum yield of lanthanide complexes is controlled by the rates of several processes: ligand to metal energy transfer, multiphonon relaxation, back-transfer and cross-over to charge-transfer states [18], [19], [20], [23]. It was also shown that a number of important characteristics of the chelates (which can be applied in electroluminescence diodes) can be correlated with the donor–acceptor properties of the substituents of ligands. Furthermore, it affects the intensity of electroluminescence and remains in close relation with mobility of charge carriers and height of the potential barrier for charge carrier injection. Selection of ligands allows us to develop some promising LCMDs with high room temperature emission efficiency leading to new applications.
Undoubtedly, analysis of the total spectral data permits evaluation of the applicability of different β-diketones in electroluminescence diodes (OLEDs). The aim of the present work are X-ray, photophysical, and magnetic studies of a new mixed europium β-diketone of formulae; Euβ3L.H2OxL, where β is hexafluoroacetylacetone (HFAA) and L is the Lewis base 2,2′-bipyridine (bipy).
Section snippets
Experimental
Euβ3L.H2OxL was prepared by mixing europium (III) chloride, β-diketone, 2,2′-dipyridine and sodium hydroxide in a 1:3:1:3 ratio. The compound was recrystallized from ethanol and, after slow evaporation, crystals of the dimension (1×1×2) mm3 were growing. These crystals of the formula C35H21EuF18N4O7 were used further for X-ray analysis and single crystal spectra measurements.
Absorption spectra were recorded at 293 K using a Cary-Varian 500 spectrophotometer in the 220–700 nm range.
The emission
Results and discussion
Single crystal X-ray diffraction data show that the structure of C35H21EuF18N4O7 is triclinic with the space group . The unit cell dimensions are as follows; a=11.841(6), b=12.010(7), c=15.054(8) Å and α=82.60(1), β=88.507(9), γ=79.207(9)°.
The molecular structure of Eu(HFAA)3bipyH2O(bipy) with the numbering scheme for atoms is displayed in Fig. 1. As can be seen in this figure, the surprising result is that one water molecule is involved in metal ion coordination. In this type of lanthanide
Summary
- 1.
X-ray data show an unexpected coordination of Eu3+ in a chelate with C.N.=9 engaging water together with HFAA and 2,2′-bipyridine molecules. Additional non-coordinating 2,2′-bipyridine molecules participate in the solid state structure formation.
- 2.
Strong dependence of emission intensity and composition of the spectra in the range of the 5D0→7F1,2 transitions indicate the possible role of 2,2′-bipyridine molecules in intra- and inter-molecular energy transfer.
- 3.
Magnetic data were obtained down to
Acknowledgements
The authors acknowledge financial support from the Polish Committee for Scientific Research (grant no. 3TO9A 08610)
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