Characterization, crystal structure and luminescence properties of a new europium(III) complex with macrocyclic ligand derived from 2,6-diformyl-4-methylphenol and diethylenetriamine

JOURNAL OF RARE EARTHS, Vol. 26, No. 6, Dec. 2008, p. 795

Characterization, crystal structure and luminescence properties of a new europium(III) complex with macrocyclic ligand derived from 2,6-diformyl-4-methylphenol and diethylenetriamine HU Xuelei ()1,2, CHEN Zhong ( )1, QIU Li ( )1, ZHAO Yuandi ( )2, PAN Zhiquan ( )1 (1. Key Laboratory of Green Chemical Process of Ministry of Education-Hubei Key Laboratory of Novel Chemical Reactor and Green Chemical Technology, Wuhan Institute of Technology, Wuhan 430073; 2. The Key Laboratory of Biomedical Photonics of Ministry of Education, Huazhong University of Science and Technology, Wuhan 430074, China) Received 27 September 2007; revised 18 February 2008

Abstract The title compound (13,27-dimethyl-3,6,9,17,20,23-hexaazatricyclo-[23.3.1.111,15]-triaconta-1(29),2,9,11,13,15(30),16,23,25,27decaene-29,30-diol-N3, N6, N9, O29, O30)-bis (nitrato-O,O')-europium (III) nitrate hydrate ([EuL(NO3)2](NO3)·H2O, L denotes the macrocyclic ligand) was prepared and characterized by elemental analysis, infrared spectra, and electrospray mass spectra. Its crystal and molecular structure was determined by X-ray diffraction. The crystal crystallized in the monoclinic system, space group C2/c with a=2.3757 (4) nm, b=1.4302(3) nm, c=1.9584(3) nm, β=91.654(5)°, M=818.60, V=6.651(2) nm3, Z=8, D=1.635 g/cm, F(000)=3312, R=0.0542, wR=0.1045. The central ion Eu3+ was nine-coordinated in the coordinaton geometry of a distorted tricapped trigonal prism. The macrocycle was coordinated through two oxygen and three nitrogen atoms. Two nitrate are chelate in the opposite positions of the macrocycle, the third nitrate being ionic. At room temperature, excitation of the title complex gave rise to the characteristic emissions of the Eu3+ ion. Keywords: crystal structure; lanthanide; macrocycle; luminescence; rare earths

Lanthanide complexes have attracted extensive attention due to their unique properties and many valuable applications[1,2] such as fluorescent probes in biological systems[3], contrast agents in clinical NMR image[4], selective extraction agents of lanthanide ions[5] and new materials[6]. Many lanthanide complexes are able to exhibit luminescence in solid state, but their luminescence efficiency in solution is substantially lowered due to the coordination of solvent molecules to the central ions. Macrocyclic ligands possess spherical cavities and polydented recognition sites towards metal ions, and they are able to shield effectively the metal ions from interaction with solvent molecules when preparing lanthanide complexes with strong fluorescence in solution[7]. Generally the syntheses of macrocyclic complexes are carried out in the presence of a suitable metal ion which acts as a template for the macrocycle formation[8–10]. Trivalent lanthanides can act as template agents in the formations of 18and 20-membered pyridine-based and 24-menbered phenol-based polyazamacrocyclic complexes where the lanthanides ion is encapsulated in the macrocycle[11,12], but few reports on fluorescent properties about these complexes have been reported. Herein we synthesized a new Eu(III)

macrocyclic complex by 2+2 template condensation of diethylenetriamine with 2,6-diformyl-4-methylphenol in the presence of Eu3+(Scheme 1). At room temperature, excitation of the title complex in methanol solution gave rise to the characteristic emissions of the Eu3+ ion.

Scheme 1 Chemical formula of the complex [EuL(NO3)2]( NO3)·H2O

Foundation item: Project supported by the National Natural Science Foundation of China (20671075), the Natural Science Foundation of Hubei Province (2005ABA021) and China Postdoctoral Science Foundation (20060390858) Corresponding author: HU Xuelei (E-mail: [email protected]; Tel.: +86-27-62136030)

3') SGI)DFWRU\3UR ZZZILQHSULQWFQ

796

1 Experimental 1.1 Physical measurements Elemental analysis of C, H and N were performed on a Perkin-Elmer 240c analytical instrument. The molar electrical conductivities in aqueous solution containing 10–4 mol/dm3 complex were measured at (25±0.1) °C using a BSD-A conductometer (Jangsu, China). Electronic spectra were recorded on a UV-3100 spectrophotometer. IR spectra were measured using KBr discs with a Vector 22 FI-IR spectrophotometer. Electrospray mass spectrum (ES-MS) was determined on a Finnigan LCQ ES-MS mass spectrograph using methanol as mobile phrase with sample concentration about 1.0 mmol/dm3. The diluted solution was electro sprayed at a flow rate of 5×10–6 dm3/min–1 with needle voltage of +4.5 kV. The temperature of the heated capillary in the interface was 200 °C and a fuse silica sprayer was used. Luminescence spectra were measured on a PE LS55 spectrofluorometer. In measurements of emission and excitation spectra the band pass was 5.0 nm. 1.2 Preparation of title compound To a methanol solution (20 ml) of 2,6-diformyl-4-methylphenol(164 mg, 1 mmol) and Eu(NO3)3.6H2O (230 mg, 0.51 mmol),1,5-diamino-3-azapentane (127 mg, 1 mmol) was added dropwise. After refluxing 3 h, the solvent was removed. Yellow solid was recrystallized in acetonitrile and then yellow block crystals suitable for X-ray analysis were obtained. Yield 48%. Anal. Calc. for C26H36N9O12Eu: C, 38.15; H, 4.43; N, 15.40%. Found: C, 37.79; H, 4.65; N, 14.98%. IR (KBr, cm–1): 1654(s, C=N); 1384(vs, ionic NO3–); 1632(s, C=C); 1471, 1288, 1030, 818(s, coordinated NO3–). UV-Vis (λmax/nm (ε/dm3/mol/cm), CH3OH): 221(28000), 239(17900), 362(4050), 402(4227). ΛM(H2O, 293K): 121 S/cm2/mol. 1.3 X-ray structure determination Intensity data were collected on a SAMRT CCD diffractometer with monochromated Mo Kα (λ=0.071073 nm) radiation. Data reduction and cell refinement were performed by SMART and SAINT Program[13]. The structure was solved by direct method (Bruker Shelxtl) and refined on F2 by full-matrix least squares (Bruker Shelxtl) using all unique data[13]. The non-H atoms in the structure were anisotropic. Hydrogen atoms bounded to C or N atoms were located geometrically (C-H 0.93 to 0.097 nm) and refined in riding mode with Uiso (H)=1.2 times Ueq of the parent atom. The water molecule was disordered, the occupation factors were restrained to 0.4 and 0.6. The H atoms of the water molecule were located in a difference Fourier map, the O-H distances

JOURNAL OF RARE EARTHS, Vol. 26, No. 6, Dec. 2008

were normalized to 0.085 nm, and they were then allowed to ride with Uiso(H)=1.2Ueq(O). A summary of crystallographic data and additional data collection parameters was given in Table 1.

2 Results and discussion 2.1 Characterization Based on the conductivity of the complex, it behaves as 1:1 electrolytes, which is consistent with the chemical formula predicated by elemental analysis and crystal structural analysis. The intense absorptions in the electronic spectra of the complex at 220–240 nm and 360–400 nm are designed to the π–π* transitions of the phenols and of C=N groups, respectively. The IR spectra show the characteristics of the C=N bond (1654 cm–1). Absorptions centered at 1471, 1288, 1030 and 818 cm–1 are attributable to bidentate nitrate groups[11,12], while the strong absorption at 1384 cm–1 shows the characteristic of free nitrate. This is agreement with the study of X-ray crystal structural analysis. The positive-ion ES mass spectra of the title complex in methanol are shown in Fig.1. The base peak at m/z=338.8 Table 1 Crystal data structure refinement for complex [EuL(NO3)2](NO3)·H2O Empirical formula

C26H36N9O12Eu

Formula weight

818.60

Temperature/K

291(2)

Crystal shape/color

Block / yellow

Crystal size/mm

0.30×0.26×0.24

Crystal system

Monoclinic

Space group

C2/c

a, b, c/nm

2.3757(4), 1.4302(3),1.9584(3)

α, β, γ/ ( o)

90, 91.654(5), 90

V/nm 3

6.651(2)

Z

8

D(calc)/(mg/cm3)

1.635

Absorption coefficient/mm–1

1.959

F(000)

3312

θ range for data collection/( o)

2.6, 19.9

Radiation/nm

Mo Kα 0.071073

Index ranges (h, k, l)

–2h29, –17k17, –24l23

Reflections collection

15512

Independent reflections

6523 ]Rint=0.0505]

Data/restrains/parameters

6523/0/440

Final R indices [I>2.0 sigma(I)]

R1=0.0542, wR2=0.1045

R indices (all data)

R1=0.0909, wR2=0.1088 2

Goodness of fit on F

1.037

Largest difference peak and

0.523, –1.767

hole/nm

3') SGI)DFWRU\3UR ZZZILQHSULQWFQ

HU X L et al., Characterization, crystal structure and luminescence properties of a new europium(III) complex with the…

Fig.1 Positive-ion ES mass spectrum of the complex [EuL(NO3)2]( NO3)·H2O in methanol

and at m/z=738.8 are assigned to [EuL(NO3–)]2+ and [EuL(NO3–)2]+. The peak at m/z=676.1 can be assigned to [Eu(L-H+)(NO3–)]+. The isotopic distribution of the peak at m/z=676.1 is shown in Fig.2(a). From the numbers and isotopic abundances of the atoms in [Eu(L-H+)(NO3–)]+, a revised program is used to calculated the pattern (Fig.2(b)) which is in agreement with the experimental one well. No protonated free macrocyclic ligand is observed, which shows the lanthanide ion in the macrocycle is very stable. 2.2 Crystal structure The structure of the title complex [EuL(NO3)2](NO3)·H2O is show in Fig.3(a). Selected bond lengths and angles are given in Table 2. In the title complex, Eu1 is placed asymmetrically at one end of macrocycle which provided five donor atoms (the two oxygens O1, O2 from the phenol group, an amine nitrogen atom N2, two imine nitrogen at-

797

oms N1, N3). The nine-fold coordination around Eu1 is completed by two bidentate nitrates. The third nitrate is ionic. Very roughly, O1, O2, N1, N2, N3 from the macrocycle form a pentagon around the central metal ion while the two coordinate nitrates are located on the opposite sides of the two phenol groups. The coordination polyhedron can be described as a distorted tricapped trigonal prism, N3, O3 and O7 are the caps while N1, N2, O6 and O1, O2 , O4 form the upper and basal planes of prism, respectively (Fig.3(b)). At the free end of the macrocycle, a five-membered ring is further formed by contraction, which makes the ligand more compact hence allowing a more appropriate spatial arrangement of the donor atoms of the macrocyclic ligand around the lanthanide ions. This ring contraction is also observed for the free pyridine-based macrocycle[14] and the Tb analogue based on 2,6-diformyl-4-chlorophenol[11,12]. 2.3 Luminescence properties Excitation of the title complex in methanol with light of 365 nm gives rise to the characteristic emissions of the Eu3+ ion (Fig.4). All emissions arise from the 5D0 level corresponding to the 5D0→7Fj (=0,1-4) transition. The weak bands at 580 nm (5D0→ 7F1) and the intense bands around 613 nm (5D0→7F2) are magnetic dipole-allowed and electric dipole-allowed transitions, respectively. The intensities for the (5D0→7F2) transition are much higher than those for 5 D0→7Fj, showing that the complex has no inversion center. This is conformed by crystal structure study. The bands around 700nm are produced from the transitions 5D0→7F3 and 5D0→7F4. The intensity around 655 nm (5D0→7F3) is so weak that it can almost not be observed.

Fig.2 Isotopic distribution of the peak at m/z=676.1 (a) Experimental; (b) Calculated

3') SGI)DFWRU\3UR ZZZILQHSULQWFQ

798

JOURNAL OF RARE EARTHS, Vol. 26, No. 6, Dec. 2008

Fig.3 A perspective view of structure of the complex [EuL(NO3)2](NO3)·H2O (a); structure of coordination polyhedron (b) Table 2 Selected bond distances(nm) and angles(o) of

References:

[EuL(NO3)2]( NO3)·H2O Bond distances/nm Eu1-O1

0.2257(4)

Eu1-O2

0.2282(4)

Eu1-N1

0.2566(5)

Eu1-N2

0.2550(5)

Eu1-N3

0.2556(6)

Eu1-O3

0.2466(4)

Eu1-O4

0.2521(5)

Eu1-O6

0.2478(5)

Eu1-O7

0.2543(5)

o

Bond angles/( ) O2- Eu1-O1 95.90(15)

O2- Eu1-O3

74.65(16)

O1- Eu1-O3 126.28(16)

O2- Eu1-O6 122.45(16) O1- Eu1-O6

82.31(16)

O3- Eu1-O6 147.35(16)

O2- Eu1-N3 145.82(15) O1- Eu1-N3

72.35(16)

O3- Eu1-N3 86.57(16)

O6- Eu1-N3 88.47(17)

O2- Eu1-N2

133.64(16) O1- Eu1-N2 130.45(17)

O3- Eu1-N2 76.04(18)

O6- Eu1-N2

72.62(17)

N3- Eu1-N2 65.10(19)

O2- Eu1-O4 69.38(15)

O1- Eu1-O4

75.97(16)

O3- Eu1-O4 50.91(16)

O6- Eu1-O4 156.50(17) N3- Eu1-O4

76.58(16)

N2- Eu1-O4 115.50(19)

O2- Eu1-N1 72.55(16)

O1- Eu1-N1

148.44(16) O3- Eu1-N1 79.90(17)

O6- Eu1-N1 79.91(18)

N3- Eu1-N1

132.56(17) N2- Eu1-N1 67.53(18)

O4- Eu1-N1 123.53(18) O2- Eu1-O7

73.45(17)

O1- Eu1-O7 71.33(16)

O3- Eu1-O7 145.01(18) O6- Eu1-O7

51.37(17)

N3- Eu1-O7 128.31(18)

N2- Eu1-O7 117.8(2)

126.71(17) N1-Eu1-O7

O4- Eu1-O7

77.20(16)

Fig.4 Emission spectrum of complex [EuL(NO3)2]( NO3)·H2O in MeOH solution containing complex (1.8×10–5 mol/L) (298 K)

[1] Bünzli J C G, Comby S, Chauvin A S, Vandevyver C D B. New opportunities for lanthanide luminescence. J. Rare Earths, 2007, 25: 257. [2] Hu X L, Qiu L, Chen Z, Huang Q M, Pan Z Q. Syntheses of alkaline earth and lanthanide cryptates with pyridine-based group. J. Rare Earths, 2007, 25: 674. [3] Chen Q Y, Luo Q H, Hu X L, Shen M C, Chen J T. Heterodinuclear cryptates [Eu ML (dmf)](ClO4)(2) (M=Ca, Cd, Ni, Zn): Tuning the luminescence of europium(III) through the selection of the second metal ion. Chem. Eur. J., 2002, 8: 3984. [4] Alexander V. Design and synthesis of macrocyclic ligands and their complexes of lanthanides and actinides. Chem. Rev., 1995, 95: 273. [5] Izatt R M, Bradshaw J S, Nielsen S A, Lamb J D, Christensen J J. Thermodynamic and kinetic data for cation macrocycle interaction. Chem. Rev., 1985, 85: 271. [6] Mao J G. Structures and luminescent properties of lanthanide phosphonates. Coord. Chem. Rev., 2007, 251: 1493. [7] Hu X L, Li Y Z, Luo Q H. Characterization and crystal structure of lanthanide cryptates of a ligand derived from 2,6-diformyl-pyridine. Polyhedron, 2004, 23: 49. [8] Feng C J, Luo Q H, Duan C Y, Shen M C, Liu Y J. Synthesis and crystal structural characterization of an unsymmetric neodymium (III) cryptate. J. Chem. Soc. Dalton Trans., 1998, 1377. [9] Hu X L, Liu H, Hu D, Yuan J, Chen Z, Huang Q M, Pan Z Q. The synthesis of lanthanide cryptates by transmetalation reaction. J. Rare Earths, 2005, 23(s1): 543. [10] Vigato P A, Tamburini S, Bertolo L. The development of compartmental macrocyclic Schiff bases and related polyamine derivates. Coord. Chem. Rev., 2007, 251: 1311.

3') SGI)DFWRU\3UR ZZZILQHSULQWFQ

HU X L et al., Characterization, crystal structure and luminescence properties of a new europium(III) complex with the… [11] Bünzli J C G, Moret E. Preparation, X-ray and spectroscopic investigations of europium(III) trinitrato complexes with the macrocycle derived from 2,6-diformyl-4-chlorophenol and diethylenetriamine. Inorg. Chim. Acta, 1988, 150: 133. [12] Guerriero P, Casellato U, Tamburini S, Vigato P A. Lanthanide complexes with compartmental Schiff base. Inorg. Chim. Acta, 1987, 129: 127.

799

[13] Bruker. SMART, SAINT, SADABS and SHELXTL (version 6.10). Bruker AXS Inc., Madison, Wisconsin, USA, 2000. [14] Zhou H, Pan Z Q, Luo Q H, Mei G Q, Long D L, Chen J T. Study on the crystal structure of a macrocycle and tyrosinase activity of its dinuclear copper complexes. Chin. J. Chem., 2005, 23: 835.

3') SGI)DFWRU\3UR ZZZILQHSULQWFQ