Synthesis, X-ray structure and luminescent properties of Sm3+ ternary complex with novel heterocyclic β-diketone and 1,10-phenanthroline (Phen)

JOURNAL OF RARE EARTHS, Vol. 29, No. 8, Aug. 2011, P. 719

Synthesis, X-ray structure and luminescent properties of Sm3+ ternary complex with novel heterocyclic ȕ-diketone and 1,10-phenanthroline (Phen) Ilya V. Taydakov1, Boris E. Zaitsev2, Sergey S. Krasnoselskiy2, Zoya A. Starikova3 (1. G. S. Petrov Institute of Plastics, JSC, Perovskiy proezd 35, Moscow 111024, Russian Federation; 2. People’s Friendship University of Russia, Miklukho-Maklaya str. 9, Moscow 117198, Russian Federation; 3. A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova str. 28, Moscow 119991, Russian Federation) Received 22 February 2011; revised 8 June 2011

Abstract: A new neutral ternary samarium complex Sm(Phen)HL3 in which Phen is 1,10-phenanthroline and HL is (1,3-bis(1,3-dimethyl1H-pyrazol-4-yl)-1,3-propanedione) was synthesized. Molecular structure of this complex was determined by X-ray diffraction. Under UV-light this complex is demonstrated bright red luminescence (Ȝmax=647 nm), which was corresponding to the electric dipole 4G5/2ĺ6H9/2 transition in Sm3+ ion. UV-absorption, excitation and emission spectra of the title compound were investigated. Keywords: samarium; pyrazole, ȕ-diketone; crystal structure; photoluminescence; rare earths

Lanthanide ȕ-diketonate complexes have been extensively studied as laser materials components[1], for light-emitting diodes (OLED)[2], fluorescent dyes[3] and non-linear materials for optical devices[4]. Ternary rare-earth ȕ-diketonates usually contains one or two additional ligands besides the ȕ-diketonate ligands due to a tendency of lanthanide ion to expand its coordination sphere and to achieve coordination number higher than six. Pyridine derivatives, ethers, phosphine oxides are the most common Lewis bases which act as co-ligands. An assistant ligand is replacing water or other small molecules in coordination sphere, which can decrease the nonradiative energy loss to obtain high luminescence[5]. This type of complexes have been well established in literatures[1,6], but the choice of ȕ-diketones was limited to a number of simplest ones. Samarium complexes are attracting considerable attention[7–9] due to their ability to produce deep-red emission (650 nm), inaccessible for the corresponding europium complexes (orange-red emission around 615 nm). Such luminescent materials having narrow deep-red emission are strongly desired for high-quality display devices[10]. Unfortunately, as a rule, the intensity of luminescence of samarium complexes is low, but could be dramatically increased by rational complex design[11]. Therefore a systematic screening of new ligands with tunable electronic and steric properties is very important. Due to our continuous interest in synthesis and application of novel pyrazole-based diketones, we reported here synthesis and solid-state structure of strong luminescent samarium complex with 1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)-1,3-

propanedione (HL) and o-phenanthroline.

1 Experimental 1.1 Materials and methods Ligand was purchased from Art-Chem GmbH (Campus Berlin Buch, Germany). All other reagents were purchased from Aldrich and used without further purification. Elemental analysis was performed on an Elementar CHNO(S) analyzer. 1H NMR spectra were recorded at a Bruker AC-300 instrument operated at 300 MHz in deuterated DMSO. UV-Vis absorption spectra were recorded on a Shimadzu UV-160 instrument. Luminescent spectra were obtained on a “Fluorat-Panorama” spectrofluorimeter (Lumex, Russia) equipped with fiber optics probe and xenon flash lamp. 1.2 Synthesis of Sm(Phen)HL3 (1) In 15 ml of hot ethanol, 0.781 g (3 mmol) of HL and 0.180 g (1 mmol) of 1,10-phenanthroline were dissolved. The hot solution was filtered and 3 ml (3 mmol) of 1 mol/L aqueous solution of NaOH was added to it with stirring. Solution of 0.327 g (1 mmol) of Sm(OAc)3·4H2O in 5 ml of hot water was added dropwise to this mixture and pH of final solution was adjusted to 7 by addition of acetic acid. The reaction mass was heated at 40 qC for 2 h, evaporated to dryness under a reduced pressure and solid residue was transferred on a small glass filter. Solid compound was partially dissolved in 40 ml of CH2Cl2, an organic phase was washed with 5 ml of water, dried over anhydrous MgSO4 and evaporated to a small volume under a reduced pressure. The crystalline solid was fil-

Corresponding author: Ilya V. Taydakov (E-mail: [email protected]; Tel.: +7(499)-1385152) DOI: 10.1016/S1002-0721(10)60529-7

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tered, washed with ether and hexane and dried in vaccuo. Yield of the colorless crystalline powder is 0.58 g (52%). Analytical sample was recrystallized from acetonitrile and dried to a constant weight under diminished pressure (1×10–2 Torr). This complex have red luminescence under UV light (356 nm) in a solid form and in the solutions. Anal. Calc. for C51H53N14O6Sm: C, 55.26%; H, 4.82%; N, 17.69%. Found: C, 55.31%; H, 4.87%; N, 17.78%. 1H NMR (300MHz, DMSO-d6, 25 ºC) į: 8.5 (broad s, 2H, CH.), 8.3 (broad s, 8H, CH), 7.8 (broad s, 5H, CH.), 7.4 (broad s, 2H, CH.), 3.8 (s, 18H, N-CH3), 1.8 (s, 18H, CH3). Additional signal at 2.0 ppm could be attributed to the residual CH3CN. Single crystals of 1 suitable for X-ray diffraction were obtained by slow evaporation of saturated solution in acetonitrile at a room temperature. Crystals are not stable in air at room temperature and easy to lose the solvent with crystal degeneration. 1.3 Single crystal X-ray diffraction analysis The colorless plate single crystal 1 C51H53N14O6Sm*0.75 MeCN (C52.50H55.25N14.75O6Sm, M=1139.21) triclinic, space group P-1, at 100 K. a=0.113033(4) nm, b=0.114149(4) nm, c=0.224607(8) nm, Į=96.625(1)º, ȕ=91.030(1)º, Ȗ=109.839(1)º, V=2.7027(17) nm3. Z=2, Dc =1.400 g/cm3, F(000)= 1167. The experimental set of 25518 reflections was obtained on a Bruker SMART APEX2 difractometer with CCD detector at 100(2) K (ȜMoKĮ, 2Tmax=52o) from a 0.43 mm×0.36 mm ×0.22 mm single crystal. The absorption correction (P=1.149 mm–1) was used by the SADABS program[12] (transmission coefficients Tmax and Tmin were 0.777 and 0.617, respectively). After averaging of equivalent reflections, 10513 unique reflections were obtained (Rint=0.0221) and used for structure solution and refinement. The structure was solved by direct method and refined by the full-matrix least-squares against F2 in anisotropic (for no-hydrogen atoms) approximation. All hydrogen atoms were placed in geometrically calculated positions and were refined in isotropic approximation in riding model with the Uiso(H) parameters equal to n Ueq(Ci), where U(Ci) are respectively the equivalent thermal parameters of the atoms to which corresponding H atoms are bonded, n=1.2 and 1.5 for CH and CH3 groups, respectively. The final uncertainty factors were as follows: R1=0.0280 (on Fhkl for 9792 reflections with I>2V(I)), wR2=0.0770 (on F2hkl for all 6956 independent reflections), GOOF=0.992, 697 refined parameters, the maximum and minimum residual elec-

tron density peaks were 1.675×103 and –0.628×103 ɟ·nm–3, respectively. All calculations were performed with the SHELXTL PLUS5 programs package[13]. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC), deposition number 782297. Selected geometric parameters for the compound 1 are listed in the Tables 1 and 2. Table 1 Selected bond lengths (10–1 nm) for 1 Bond

Length

Bond

Length

Bond

Length Bond

Length

Sm1–O1 2.398(2) O3–C31 1.283(3) N5–C22

1.458(3) N11–N12 1.360(3)

Sm1–O2 2.333(2) O4–C29 1.262(3) N6–C20

1.331(3) N11–C50 1.339(4)

Sm1–O3 2.383(2) O5–C44 1.270(2) N7–N8

1.352(4) N11–C51 1.462(4)

Sm1–O4 2.373(2) O6–C42 1.269(3) N7–C33

1.333(3) N12–C46 1.333(3)

Sm1–O5 2.359(2) N3–N4 1.360(3) N7–C36

1.459(4) N13–N14 1.357(3)

Sm1–O6 2.367(2) N3–C23 1.333(4) N8–C34

1.328(3) N13–C48 1.335(4)

Sm1–N1 2.629(2) N3–C24 1.447(4) N9–N10

1.361(3) N13–C49 1.459(4)

Sm1–N2 2.653(2) N4–C14 1.325(3) N9–C26

1.330(4) N14–C40 1.335(4)

O1–C16 1.271(3) N5–N6 1.366(3) N9–C37

1.454(4)

O2–C18 1.274(3) N5–C21 1.340(4) N10–C27 1.332(4)

Table 2 Selected angles (q) for 1 Bond

Angle

Bond

Angle

Bond

Angle

O1–Sm1–O2 71.04(6)

O3–Sm1–O5 98.96(6)

O5–Sm1–O6 73.03(6)

O1–Sm1–N1 71.47(7)

O3–Sm1–N1 79.39(7)

O5–Sm1–N1 70.05(7)

O1–Sm1–N2 76.11(6)

O3–Sm1–N2 138.17(7) O5–Sm1–N2 83.47(6)

O2–Sm1–O3 99.26(7)

O4–Sm1–O5 79.19(6)

O6–Sm1–N1 122.48(7)

O2–Sm1–O4 79.89(7)

O4–Sm1–O6 78.15(6)

O6–Sm1–N2 71.34(6)

O2–Sm1–N2 101.21(7) O4–Sm1–N1 133.18(7) N1–Sm1–N2 62.10(7) O3–Sm1–O4 71.38(6)

O4–Sm1–N1 133.18(7)

2 Results and discussion 2.1 Synthesis To the best of our knowledge, the only one example of complex based on pyrazolic diketone ligand (bis(3-(3,5-dimethylpyrazole-4-yl)pentane2,4-dionate)beryllium) was described in Ref. [14]. Unfortunately, synthetic approach, developed for the synthesis of this compounds does not work well with lantanoids. We have modified known Melby’s synthetic strategy[15] to obtain desired complexes in good yields and high purity (Scheme 1).

Scheme 1 Preparation of 1

Ilya V. Taydakov et al., Synthesis, X-ray structure and luminescent properties of Sm3+ ternary complex with novel heterocyclic … 721

Due to relatively low solubility in ether, compound 1 was separated from unreacted ligands and inorganic by-products were removed by filtration and washing with water. Complex 1 has a tendency to form solvates while being crystallized from a donor solvents such as acetonitrile. These solvates were very sensitive to solvent loss and required storage under mother liquor. Nevertheless, solvent could not be removed completely even by drying under vacuum as it was indicated by the data of elemental analyses.

One can see that the absorption spectrum of 1 looks like a superposition of the spectra of Phen and HL, where shortlength band can be attributed to the absorption of Phen fragment, and long-length band, to the absorption of diketone. This combination provides effective energy transfer (“antenna effect”)[17] from ligands to Sm3+ core in relatively wide spectral range (200–400 nm).

2.2 Crystal structure The eightfold coordination of the Sm atom is in the form of a distorted square antiprism. The ligands span on the opposite edges of the two square faces of the coordination antiprism. In contrast with the known compound Sm(acac)3 (Phen) (2)[16], crystals of which are monoclinic (space group P21/n), crystals of the complex 1 are triclinic (space group P-1). The Sm–O bond distances are in the range 0.2398(2) – 0.2333(2) nm (practically the same range of Sm–O bond distances was measured for the compound 2). The Sm–N bonds (0.2629(2) and 0.2653(2) nm) in the compound 1 are longer than in the complex 2 (0.2589(5) and 0.2641(5) nm). The angles between O–Sm–O and N1–Sm–N2 atoms in the complexes 1 and 2 are very similar (around 71q and 62q respectively). No hydrogen bonds were detected in the structure of 1. The molecular and crystal structures of the compounds 1 are shown in Figs. 1 and 2.

Fig. 2 View along the b-axis on the crystal structure of 1 (Atoms appear by color: Sm (green), N (blue), O (red), C (grey). Hydrogen atoms have been omitted for clarity)

2.3 Optical spectroscopy The UV-Vis absorption spectra of Phen, HL and complex 1 in acetonitrile (solutions with equal concentrations of 1.35×10–5 mol/L were used) are shown in Fig. 3. The excitation spectrum (1) of Sm(Phen)HL3 crystal (Ȝem=647 nm) and emission spectra of 1 in crystals (2) and in the solution (3) are shown in Fig. 4. Three peaks at about 225, 275 and 350 nm (shifted to 375 nm at excitation spectrum) can be assigned to ʌĺʌ* transitions of the ligands. Fig. 3 UV-Vis absorption spectra of HL (1), Phen (2) and complex 1 (3) in acetonitrile

Fig. 1 Molecular structure of 1 (Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms have been omitted for clarity)

Fig. 4 Excitation spectrum of Sm(Phen)L3 crystal (Ȝem=647 nm) (1) and normalized emission spectra of 1 in crystals (2) and in the solution (3) (Intensity is magnified in 10 times)

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The luminescence spectra (Ȝex=365 nm) of the complex 1 (Fig. 4) are typical for the samarium complexes[18,19]: four peaks are generally attributed to the transitions from the ground state 4G5/2 to 6H5/2 (around 564 nm), 6H7/2 (around 605 nm), 6H9/2 (around 647 nm) and to 6H11/2 (around 703 nm) respectively. The highest emission intensity in the spectra is corresponding to the electric dipole 4G5/2ĺ6H9/2 transition. The fine structure of bands can not be resolved at room temperature. Emission spectra (Ȝex=365 nm) for saturation (Approx. 1×10–3 mol/L) solution in EtOH-DMSO (2:1) mixture was obtained. Emission spectra of the compound 1 in the solution and in the solid form are identical, but in the solution luminescence is much weaker. Nevertheless, red luminescence can be easily detected under UV-lamp (312 nm) by naked eye in both cases.

3 Conclusions The first example of neutral Sm3+ complex 1 with novel ligand (1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)-1,3-propanedione) and 1,10-phenanthroline was prepared. Composition of complex was proved by elemental analysis and 1H NMR spectroscopy. Molecular structure of 1 (as an adduct with acetonitrile) was determined by X-ray diffraction. Photophysical properties of the compound 1 in crystals and in the solution were investigated. Complex 1 was demonstrating bright red luminescence in crystals and in polymer films. According to the photoluminescence data complex 1 will be a promising material for the active layer of red-emmiting OLEDs and the potential fluorescent marker. Acknowledgements: We are grateful to the Art-Chem GmbH (Campus Berlin-Buch, Germany) for the donation of sample of ligand. Besides we are very much appreciative of the assistance from Mr. Alexander M. Shirimov and Mr. Alexander A. Sukhodoev in the recording of luminescent spectra and helpful discussion.

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