In this paper, we report the synthesis, structure and photophysical studies of four new complexes of conformationally flexible 6-chloro-4-phenyl-2-(pyridin-2-yl)quinazoline ligand (L) with Zn(II). The coordinating ability of the ligand and geometrical preferences of the resultant complexes are tuned by varying the anion of the metal salt as confirmed by structural and DFT studies. The choice of the metal salt (especially anion) directs the stabilisation of different conformations of the ligand arising out of the twisting of pyridyl ring with respect to quinazoline ring, resulting in complexes with different nuclearities (monomer/dimer) as well as different coordination geometries (tetrahedral/trigonal bipyramidal/octahedral). Photophysical properties are also found to be tuned due to conformational change on complexation. DFT studies on the ligand establish the conformationally stable forms as observed in the reported structures.
IntroductionDesign and synthesis of transition metal complexes with structural diversities have become a fascinating area of contemporary research due to their possible applications in various fields such as heterogeneous catalysis, 1 nonlinear optical activity, 2 molecular sensors, 3 magnetic switches, 4 and micro porous materials. 5 The design of these structures is highly influenced by several key factors among others, the coordination geometry, the size of the metal ion, the structural characteristics of the ligand and the nature of the counter anion, for the creation of new functional materials with solvent inclusion or gas-adsorption characteristics and special optical, electronic, magnetic and catalytic properties. 6The d 10 configuration of zinc allows architecting flexible coordination environments and forms metal complexes with tetrahedral to octahedral geometries, which is a very important criterion for designing a wide variety of metal-organic frameworks, 7 fluorescent frameworks being one lead application. The presence of electronically saturated Zn(II) ion is advantageous for the design of fluorescent systems, because it imposes conformational rigidity to the ligand and prevents energy loss via bond vibration and electron transfer processes, whereas paramagnetic transition metals may quench fluorescence by different electron/energy transfer mechanisms. [8][9][10] Hence, zinc complexes with variable fluorescence properties have attracted much attention due to their potential applications in biological systems, 11 photophysical properties 12 and in emitting materials of organic light emitting diodes. 13 Moreover, inorganic anions can be considered as : Zn(NO 3 ) 2 ·6H 2 O (0.5949 g, 2.00 mmol) was used instead of Zn(CH 3 COO) 2 ·2H 2 O, the remaining procedure being the same as reported for complex 1. Single crystals, suitable for x-ray diffraction, were obtained after 2 days by a slow layer diffusion of methanol into a DMSO solution of the complex at room temperature (25 ºC). Yield: 0.9883 g Zn-salt directed complex formation is monitored in all the complexes 1-4. It is inte...
