Ten-coordinate Complexes Research Articles

Synthesis and photoluminescence study of two new complexes [Sm(hfaa)3(impy)2] and [Eu(hfaa)3(impy)2] and their PMMA based hybrid films

The synthesis, characterization and photoluminescence studies of two new highly photoluminescent complexes, [Sm(hfaa)3(impy)2] and [Eu(hfaa)3(impy)2] (impy is 2-(1H-imidazol-2-yl)pyridine and hfaa is the anion of hexafluoroacetylacetone) are reported. The photoluminescence of these complexes were studied in solid, solution and PMMA thin films. These complexes were incorporated independently into polymer matrix of PMMA with varying amounts. The calculated quantum yield (φ) and experimental life time (τ) in solution for (i) Sm complex are φ = 0.013, τ = 0.036 ms and (ii) Eu complex are φ = 0.36, τ = 0.98 ms. The Judd–Ofelt intensity parameters, radiative parameters, intramolecular energy transfer rates and theoretical quantum efficiency are calculated and discussed. The intramolecular energy transfer rates, in the case of europium complex, suggest that the major energy transfer channels are T1 → 5D1 and T1 → 5D0 and these contribute 55.33% and 44.65%, respectively, to the overall energy transfer process. The emission colour changes with a change in concentration of the complexes in PMMA substrate. This feature may be employed in fabricating 'colour indicator diodes'. The thin hybrid films of these structurally ten-coordinate complexes in PMMA matrix exhibit outstanding photostability upon UV irradiation that defines their robust nature. The efficient photophysical properties of PMMA hybrids of these complexes, may possibly find their applications in optoelectronic devices.

Structural Variations in the Complete Series of Lanthanoid Complexes of a Calix[4]arene Trisamide

Lanthanoid picrate (pic) complexes of 5,11,17,23-tetra-tert-butyl-25-hydroxy-26,27,28-tris(diethylcarbamoylmethoxy)calix[4]arene (LH) have been synthesised and structurally characterised, to complete this series for all lanthanoids (other than promethium). From cerium to lutetium, three structural types are observed: Type I, [Ln(L)(O,O′-pic)](pic), Ln=Ce–Dy; Type II, [Ln(L)(O-pic)](pic), Ln=Tb, Ho; Type III, [Ln(L)(HOEt)](pic)2, Ln=Er–Lu. With lanthanum, three different ten-coordinate complexes were characterised; [Ln(L)(O,O′-pic)(HOEt)](pic), [Ln(L)(O,O′-pic)(OH2)](pic), and [Ln(L)(O,O′-pic)(HOMe)](pic). The crystallisation of Type I and II observed for terbium shows that the stability of the different structures are sensitively poised at the transition points. Nevertheless, the structures show that the vacant space in the coordination sphere left by the trisamide L tends to reduce across the series as expected. It is occupied by a bidentate picrate anion and unidentate solvent molecule with lanthanum, a bidentate picrate anion for cerium to dysprosium (Type I), a unidentate picrate anion for terbium and holmium (Type II), and finally a unidentate solvent molecule from erbium to lutetium (Type III). The coordination number thus reduces from 10 to 8 across the series.

Synthesis and visible light luminescence of mononuclear nine-coordinate lanthanide complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine

Synthesis of four nine-coordinate lanthanide (III) complexes of the type, [Ln(hfaa) 3 (tptz)], where Ln = La, Nd, Sm and Tb; hfaa = the anion of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine, by a new modified one pot in situ method is reported. The lanthanide ions are coordinated to three N-atoms of three 2-pyridyl units of tptz besides six O-atoms of three hfaa units. The formation of these volatile complexes is confirmed by molecular ion peak in ESI-MS, IR and NMR. The hypersensitive 4 G 5/2 , 2 G 7/2 ← 4 I 9/2 transition displays distinct band shape which is different from the band shape of known eight- and ten-coordinate complexes. The samarium and terbium complexes emit pink and green luminescence due to 4 G 5/2 → 6 H j (j = 5/2, 7/2, 9/2) and 5 D 4 → 7 F j (j = 3-6) transitions, respectively. Synthesis of four nine-coordinate lanthanide (III) complexes of the type, [Ln(hfaa) 3 (tptz)] by a new modified one pot in situ method is reported. The samarium and terbium complexes are highly luminescent and emit pink and green luminescence, respectively.

Solution studies of lanthanide (III) complexes based on 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and 1,10-phenanthroline Part-I: Synthesis, 1H NMR, 4 f–4 f absorption and photoluminescence

Solution studies on the complexes of the type [Ln(hfaa) 3(phen) 2] (Ln = La, Pr and Nd) and [Ln(hfaa) 3phen] (Ln = Nd, Ho, Er and Yb; hfaa stands for the anion of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and phen stands for 1,10-phenanthroline) are presented. These complexes are synthesized in high yields by an in situ method in which hfaa, ammonium hydroxide, lanthanide chlorides and phen were allowed to react in 3:3:1:1 molar ratio in ethanol. In the case of neodymium both eight- and ten-coordinate complexes are isolated. The paramagnetic shifts of the methine protons of β-diketone have their sign opposed to those of paramagnetic shifts of phen protons and the shifts are dominated by dipolar interactions. The inter- and intramolecular shift ratios have been calculated and discussed. The 4 f–4 f absorption spectra of the complexes of Pr, Nd, Ho and Er are analyzed. The eight- and ten-coordinate neodymium complexes display distinctively different band shapes of the 4G 5/2, 2G 7/2 ← 4I 9/2 hypersensitive transition. The efficient energy transfer from ligand to Pr(III) is reflected by strong red luminescence of this complex at room temperature.

A Novel Supramolecular Structure for a Lanthanum Picrate

A new complex of lanthanum picrate with N,N'-diethyl-N,N'-diphennyl-3-oxapentanediamide (L) was synthesized and its structure determined by X-ray diffraction measurements. It crystallizes as the ten-coordinate complex La(pic)3L2 in the triclinic space group P1 with a = 12.140(2), b = 14.250(2), c = 20.333(2) Å, α = 101.400(10), β = 99.390(10), γ = 102.400(10)°, U = 3289.1(8) Å3, Z = 2, Dc = 1.519 g cm-3. The complex possesses a novel ladder-like 2-D supramolecular structure directed by π-π interactions.