Dinuclear lanthanide(III) complexes containing β-diketonate terminal ligands bridged by 2,2′-bipyrimidine

Dinuclear lanthanide(III) complexes containing β-diketonate terminal ligands bridged by 2,2′-bipyrimidine

Inorganic Chemistry Communications 9 (2006) 979–981 www.elsevier.com/locate/inoche Dinuclear lanthanide(III) complexes containing b-diketonate termin...

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Inorganic Chemistry Communications 9 (2006) 979–981 www.elsevier.com/locate/inoche

Dinuclear lanthanide(III) complexes containing b-diketonate terminal ligands bridged by 2,2 0-bipyrimidine Deepika D’Cunha, Daniel Collins, Gregory Richards, Gilford S. Vincent, Shawn Swavey

*

Department of Chemistry, University of Dayton, 300 College Park, Dayton, OH 45469-2357, United States Received 1 May 2006; accepted 11 June 2006 Available online 20 June 2006

Abstract Reactions of lanthanide(III) (LnIII) salts with the polyazine bridging ligand 2,2 0 -bipyrimidine (bpm) and b-diketonate terminal ligands yield 16 new monometallic and bimetallic complexes of the form Ln(tl)3bpm and [Ln(tl)3]2bpm respectively, where tl = terminal ligand. Formation of the dinuclear complex is governed by the size of the lanthanide metal and the type of terminal ligand. The smallest LnIII metals form dinuclear complexes when the terminal ligand consists of an aromatic and a fluoro group. The largest LnIII metals (Pr and Nd) form only mononuclear complexes with the bpm bridging ligands regardless of the terminal ligand. The electronic spectra of the complexes is dominated by the pp* transitions associated with the terminal ligand and the emission spectra are due to 4f–4f lanthanide transitions. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Bridging; Lanthanide; Bipyrimidine; Homodinuclear

1. Introduction Coordination of organic ‘‘antenna’’ ligands to lanthanide(III) ions for the purpose of stimulating the metals forbidden 4f–4f transition is well established [1]. b-Diketones which typically absorb in the ultra-violet region of the spectrum have been shown to be exceptional ‘‘antenna’’ ligands [2]. This has lead to the synthesis of numerous monometallic lanthanide complexes whose spectroscopic features include long-lived emissions in the visible or near-infrared region of the spectrum. These spectroscopic properties have been utilized in the fabrication of materials for diode lasers and optical fibers [3]. Other applications include biomedical assays [4], immunoassays [5], early detection of cancer [6] and in time resolved luminescence measurements [7]. The emission wavelength associated with the monometallic lanthanide complex is related to the energy gap of the 4f orbitals. This allows the emission wavelength to be tuned by choice of the lanthanide metal. *

Corresponding author. E-mail address: [email protected] (S. Swavey).

1387-7003/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2006.06.006

Recently work in the area of bridged bimetallic f-block/ d-block complexes has resulted in a number of structurally and spectroscopically interesting complexes [8]. The design goal for the d-block/f-block mixed metal complexes is to use the lower energy metal to ligand charge transfer (MLCT) transitions associated with the d-block metal to induce the lanthanide 4f–4f emission. To ensure electronic communication between the metal centers polyazine bridging ligands such as 2,2 0 -bipyrimidine (bpm) have been used [9]. Despite the variety of uses for monometallic lanthanide complexes and the synthesis and characterization of very interesting bridged f-block/d-block complexes there are very few reports of homodinuclear lanthanide bridged complexes and even fewer complexes bridged by the polyazine ligand bpm [10]. We report herein the synthesis of homodinuclear lanthanide and mononuclear lanthanide complexes bridged by bpm and capped with terminal ligands (tl) thenoyltrifluoroacetone (tta), furyltrifluoroacetone (tfa) and hexafluoroacetone (hfa) in the form [Ln(tl)3]2bpm or Ln(tl)3bpm as illustrated in Scheme 1. The synthetic route to the bimetallic complexes is adapted from a previous report [10b,11] in which an

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D. D’Cunha et al. / Inorganic Chemistry Communications 9 (2006) 979–981

R1

R1 N

R1 N

O

N

N

O

6

+

+ N

O

Ln

2 LnCl3 O

N

3

N

O

F 3C

F 3C

R1

abbr.

CF3

hfa

S

O 3

N

N

S

O

R1 = Ln = PrIII or NdIII

Ln = EuIII, GdIII, TbIII, ErIII, YbIII or LuIII

tta

N

F 3C

O

R1 =

N Ln

3 CF3

S

Ln = PrIII, NdIII, EuIII, GdIII, TbIII, ErIII, YbIII or LuIII

O

or

Ln N

R1

O

and R1 = CF3 Ln = PrIII, NdIII, EuIII, GdIII or TbIII

O

tfa

Scheme 1. Synthetic scheme of the bimetallic and monometallic lanthanide complexes.

aqueous solution of the lanthanide salt is added to a basic ethanolic solution containing the appropriate equivalents of the terminal and bridging ligands. The resulting precipitate is filtered, air dried and recrystallized from an ethyl acetate/hexanes mixture. Once the recrystallized product is filtered and dried under vacuum samples are sent for elemental analysis. The results of the analysis and the percent yield of each complex are listed in Table 1. When 2,4-pentandione (acac) is used as the terminal ligand under the synthetic conditions described in Scheme 1 neither the monometallic nor the bimetallic complexes could be isolated, regardless of the lanthanide metal used. Elemental analysis of the product of these reactions indicate that bpm does not coordinate in the case of Pr(III),

Nd(III), Eu(III), Gd(III) and Er(III). The carbon and hydrogen results suggest that these metals form Ln(acac)3 complexes. Mixed product formations are produced when Tb(III), Yb(III) or Lu(III) are used. Looking at Table 1 some interesting trends can be pointed out with regard to the affect of the terminal ligand and the metal ion on product formation. When the least bulky and least basic of the three terminal ligands, hfa, is used only monometallic complexes are obtained. These complexes, Pr(hfa)3bpm, Nd(hfa)3bpm, Eu(hfa)3bpm, Gd(hfa)3bpm and Tb(hfa)3bpm represent the largest of the metal ions in this study. With the smallest lanthanide ions ErIII, YbIII, LuIII a precipitate is not observed when the metal and ligand solutions are combined after several hours of stirring.

Table 1 Elemental analysis results and % yield of the complexes in this report Complex

C (%) found (calc.)

H (%) found (calc.)

N (%) found (calc.)

Yield (%)

Pr(hfa)3bpm Nd(hfa)3bpm Eu(hfa)3bpm Gd(hfa)3bpm Tb(hfa)3bpm Pr(tfa)3bpm Nd(tfa)3bpm [Eu(tfa)3]2bpm [Gd(tfa)3]2bpm [Tb(tfa)3]2bpm [Er(tfa)3]2bpm [Yb(tfa)3]2bpm [Lu(tfa)3]2bpm Pr(tta)3bpma Nd(tta)3bpm a [Eu(tta)3]2bpma [Gd(tta)3]2bpm [Tb(tta)3]2bpma [Er(tta)3]2bpma [Yb(tta)3]2bpm [Lu(tta)3]2bpm

29.67 29.52 29.62 29.61 28.36 41.71 41.48 39.94 39.49 39.25 38.51 38.25 38.43 40.50 40.70 37.68 37.40 37.10 37.03 36.72 36.29

0.97 0.99 1.03 0.94 0.85 1.89 1.82 1.71 1.77 1.73 1.66 1.71 1.75 2.13 2.14 1.73 1.65 1.84 1.90 1.57 1.57

6.17 5.87 6.10 6.04 5.61 6.12 6.14 3.44 3.51 3.32 3.16 3.41 3.31 5.70 5.57 3.23 3.24 3.15 3.06 3.11 3.10

53 53 45 43 53 53 50 76 61 91 48 77 70 45 34 73 58 63 70 73 65

a

From Ref. [10b].

(30.02) (29.91) (29.66) (29.50) (29.44) (42.03) (41.88) (39.74) (39.48) (39.41) (39.03) (38.77) (38.68) (39.93) (39.79) (37.59) (37.37) (37.30) (36.96) (36.73) (36.65)

(0.99) (0.98) (0.97) (0.97) (0.97) (1.98) (1.98) (1.79) (1.78) (1.77) (1.75) (1.74) (1.74) (1.98) (1.88) (1.69) (1.68) (1.68) (1.66) (1.65) (1.65)

(6.09) (6.07) (6.02) (5.98) (5.97) (6.13) (6.10) (3.31) (3.29) (3.28) (3.25) (3.23) (3.22) (5.82) (5.80) (3.13) (3.11) (3.11) (3.08) (3.06) (3.05)

D. D’Cunha et al. / Inorganic Chemistry Communications 9 (2006) 979–981

When comparing complexes made with the bulkier, tfa and tta, ligands similar trends are observed. Only monometallic complexes are formed with the larger metal ions PrIII and NdIII while the homodinuclear complexes are formed with the smaller metal ions EuIII, GdIII, TbIII, ErIII, YbIII and LuIII. Steric strain created in the bpm bridging ligand upon coordination of the larger PrIII and NdIII ions prevents formations of the bridged complex. Recently we reported the crystal structure of [Tb(tta)3]2bpm [10d] one of only a couple structural reports of a homodinuclear lanthanide complex bridged by bpm. The structure exhibits an unusual torsion angle in the typically planar bpm ligand due to the TbIII ions suggesting that larger ions like PrIII and NdIII would place such a strain on the bridging ligand as to prevent formation of the bimetallic complex. Electronic spectra of the complexes are dominated by intense terminal ligand centered transitions in the ultra-violet region of the spectra with molar absorptivities in the hundreds of thousands. Weak emissions are observed in the visible region of the spectrum for the TbIII and GdIII complexes. Emissions for the ErIII complexes are most likely in the near-infrared region of the spectrum beyond 1100 nm which is the limit of our instrument. The EuIII complexes, Eu(hfa)3bpm and [Eu(tfa)3]2bpm, emit very strongly in the visible region of the spectrum in the range 580–620 nm corresponding to transitions from the 5Do excited state to the 7FJ (J = 0–3) level [12]. Studies are currently underway to elucidate the structural and spectroscopic characteristics of these complexes. This report offers a straightforward one-pot synthetic route to high purity lanthanide complexes with the possibility for many more new bimetallic lanthanide complexes. Acknowledgements The authors thank the following people for their support of this work, Dr. Howard Knachel, Dr. Kim Trick,

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Carl Boeshart, Michelle Cunningham, Kyle Davia, Katrina Duckett, Michael Elliott, Eric Fehrman, Jessica Henry, Katie Kubala, Emily Larder, Leah Makley, Gregory Richards, Rebecca Sweet, Wendy Vent and Zachary Wolf. References [1] F.S. Richardson, Chem. Rev. 82 (1982) 541. [2] L.R. Melby, L.J. Rose, E. Abramson, J.C. Caris, J. Am. Chem. Soc. 86 (1964) 5117. [3] H.V. Martinus, J.W. Verhoeven, J.W. Hofstraat, Appl. Phys. Lett. 74 (1999) 3576. [4] H.V. Martinus, R.H. Woudenberg, P.G. Emmerink, R. van Gassel, J.H. Hofstraat, J.W. Verhoeven, Angew. Chem. Int. Ed. 39 (2000) 4542. [5] D. Imbert, M. Cantuel, J.-C.G. Bunzil, G. Bernardinelli, C. Piguet, J. Am. Chem. Soc. 125 (2003) 15698. [6] S. Liu, Chem. Soc. Rev. 33 (2004) 445. [7] B. Isabelle, Handbook on the Physics and Chemistry of Rare Earths, vol. 33, 2003, p. 465. [8] V. Balzani, S. Campagna, G. Denti, A. Juris, S. Seroni, Chem. Rev. 96 (1996) 759; D.P. Rillema, K.B. Mack, Inorg. Chem. 21 (1982) 3849; R.A. Pavinato, J.A. Walk, M.E. McGuire, Inorg. Chem. 32 (1993) 4982. [9] N.M. Shavaleev, G. Accors, D. Virgili, Z.R. Bell, T. Lazarides, G. Calogero, N. Armaroli, M.D. Ward, Inog. Chem. 44 (2005) 61. [10] (a) J.A. Fernandes, R.A. Sa Ferreira, M. Pillinger, P. Ribeiro-Claro, I.S. Goncalves, J. Lum. 113 (2005) 50; (b) R. Sultan, K. Gadamsetti, S. Swavey, Inorg. Chim. Acta 359 (2006) 1233; (c) H. Jang, C.-H. Shin, B.-J. Jung, D. Kim, H.-K. Shim, Y. Do, Eu. J. Inorg. Chem. (2006) 718; (d) K. Kirschbaum, A. Fratini, S. Swavey, Acta Cryst. C 62 (2006) m186. [11] To a solution of 6.0 mL of absolute ethanol containing 2.1;mmoles of b-diketone, 0.35 mmoles of 2,2-bipyrimidine and 2.1 mmoles of NaOH (which had stirred for 30 min at ambient temperature) is added 5.0 mL of an aqueous solution containing 0.70 mmoles of LnCl3. The resulting precipitate is filtered and recrystallized from an ethyl acetate/hexanes mixture. [12] A. Bellusci, G. Barberio, A. Crispini, M. Ghedini, M.L. Deda, D. Pussi, Inorg. Chem. 44 (2005) 1818.