Abstract
Four heteroleptic neodymium complexes, [Nd(fod)3(phen)] (Nd-1), [Nd(fod)3(bpy)] (Nd-2), [Nd(fod)3(im)2] (Nd-3) and [Nd(fod)3(μ-bpp)Nd(fod)3] (Nd-4) (fod is the anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-ocanedione (Hfod), phen is 1,10-phenanthroline, bpy is 2,2′-bipyridine, im is imidazole and bpp is 2,3-bis(2-pyridyl) pyrazine) are synthesized and thoroughly characterized by elemental analysis, TGA, DTA, 1H NMR and infra-red spectroscopy. The complexes Nd-3 and Nd-4 are new; however, the synthesis of Nd-1 and Nd-2 has been reported elsewhere and were resynthesized to investigate their photoluminescence properties. The complexes, retain their identity at higher temperatures and evaporate in the temperature range between 220 and 327-°C without decomposition. The single crystal X-ray structure has been determined for the Nd-1 complex, and ground state geometries of the other three complexes have been predicted using the Sparkle/PM7 model. The optical absorption in different solvents is studied and evaluated in terms of oscillator strength and band shape. The oscillator strength of the hypersensitive 4G5/2,2G7/2 ← 4I9/2 transition is highest in non-coordinating solvents (chloroform and dichloromethane), indicating that the ligand environment around the metal ion is adequately asymmetric. The near IR luminescence, decay curves, and intrinsic quantum yield of these complexes in chloroform are investigated and discussed. It is observed that the replacement of water molecule from the inner coordination sphere of [Nd(fod)3(H2O)] (τ = 1.37µs) by different ancillary ligands markedly enhance the decay time; Nd-2 (2.06 µs) > Nd-4 (1.98 µs) > Nd-1 (1.82 µs) > Nd-3 (1.38 µs) and intrinsic quantum yield (Nd-2 (0.82) > Nd-4 (0.79) > Nd-1 (0.73) > Nd-3 (0.55) of the complexes in chloroform. The scheme energy transfer process is presented, and it has been shown that the ancillary ligands are efficient in enhancing luminescence in the complexes. The CH vibrational quenching of the excited state of Nd3+ can effectively be reduced by using fluorinated ligands in the coordination sphere.
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