Two Cu(I) complexes constructed by different N-heterocyclic benzoxazole ligands: Syntheses, structures and fluorescent properties
Graphical abstract
Two Cu(I) complexes with different N-heterocyclic benzoxazole ligands were synthesized. The tri-coordinated copper(I) coordination polymer 1 can be described as planar trigonal configuration. The four-coordinated mononuclear copper(I) complex 2 possess a slightly distorted trigonal pyramidal geometry. The photoluminescent transition of Cu(I) complex 2 may be attributed to metal-to-ligand charge-transfer [MLCT].
Introduction
The cuprous chemistry have drawn special attention because of their unusual structural features and various applications ranging from biological sensors and interesting physical properties to catalysis, optics and luminescent materials [1]. They are being environmentally friendly, less expensive, intriguing coordination modes and exhibit rich photochemical and photophysical properties [2], especially in the promising application as emissive thermally-activated delayed fluorescence (TADF) materials in OLEDs [3]. The combination of the electron rich copper(I) center, conjugated organic ligand and high degree of inherent covalence in soft acid-soft base bonding can produce low energy electronic interactions between metal center and the ligand, and the resulting compounds possess interesting optical and electronic properties [4].
Benzoxazoles and their derivatives are part of an important class of N-heterocycles which can not only have shown strong coordination ability to the transition metal ions, but also exhibit remarkable features such as ease of preparation, electrochemical behavior, light absorption in the visible region, characteristic structural flexibility, supramolecular architecture, long-lived electronically excited states, intense luminescent and biological activity [5]. A lot of N-heterocyclic copper(I) complexes such as discrete monomers, multinuclear clusters and coordination polymers have been reported by several research groups [6]. In these complexes, the N-heterocyclic ligands play an important role in determining the overall structure of the copper(I) complexes and consequently their photophysical properties [6,7]. Therefore, the appropriate selection of N-heterocyclic ligands appeared as one key point to tune and improve the structures and properties of copper(I) species, which can be highly affected via the steric, electronic, and conformational effects [8]. Herein, two N-heterocyclic benzoxazole ligands combined with the [Cu(CH3CN)2(PPh3)2](BF4) were employed to obtain two copper(I) complexes. The structures of the two complexes have been characterized by elemental analysis, IR spectra and X-ray single crystal diffraction. In addition, their fluorescent properties have been studied.
Section snippets
Materials and general methods
The ligands BBO and PBO were prepared according to the literature procedure [9]. [Cu(CH3CN)2(PPh3)2](BF4) was synthesized on the basis of literature procedures [10]. All reactions were carried out under a nitrogen atmosphere, using anhydrous solvents or solvents treated with an appropriate drying reagent. Commercially available reagents were used without further purification unless otherwise stated. The C, H and N elemental analyses were determined using a Carlo Erba 1106 elemental analyzer.
Results and discussion
Two new copper(I) complexes were synthesized by solvent diffusion method. The synthetic routes to copper(I) complexes are shown in Scheme 1. The elemental analyses of two complexes are in good agreement with the theoretical compositions. The copper(I) complexes are remarkably soluble in polar aprotic solvents such as DMF, DMSO, dichloromethane and acetonitrile, slightly soluble in ethanol and methanol, and insoluble in water, diethyl ether, petroleum ether and hexane.
Conclusion
In this paper, two copper(I) complexes with N-heterocyclic ligands were synthesized and characterized. The structural analysis revealed that complex 1 is three-coordinated trigonal planar geometry, while mononuclear complex 2 is a four-coordinated slightly distorted triangular-pyramidal environment. In complex 1, the BBO ligand adopts the μ2-bridging mode to link two copper(I) atoms forming an one-dimensional single-stranded meso-helix chain coordination polymer. In addition, complexes 1 and 2
Supplementary data
Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Center with reference numbers CCDC 1549239 and 1848400. Copies of the data can be obtained, free of charge, on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK. Tel.:+44 01223 762 910; fax: +44 01223 336 033; e-mail: [email protected] or http://www.ccdc.cam.ac.uk.
Acknowledgments
The present research was supported Foundation of A Hundred Youth Talents Training Program of Lanzhou Jiaotong University (Grant No. 152022), Natural Science Foundation of Gansu Province (Grant No. 17JR5RA090) and National Natural Science Foundation of China (Grant No. 21367017).
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