New Complexes of Lanthanides with Unusual Main Group Ligands

Chapter 16

New Complexes of Lanthanides with Unusual Main Group Ligands 1,

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Richard A. Jones *, Xiaoping Yang , Abdul Waheed , Michael Wiester , and Lilu Zhang Downloaded by PEPPERDINE UNIV on August 24, 2017 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch016

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The University of Texas at Austin, Department of Chemistry and Biochemistry, 1 University Station A5300, Austin, TX 78712 University of Pennsylvania, Department of Chemistry, Philadelphia, PA 19104 2

We describe the synthesis and structures of new multinuclear lanthanide complexes which are formed from conventional "salen" style Schiff base ligands, derivatives of these ligands, or from vanallin based ligands.

As part of a study aimed at generating new large supramolecular complexes of both main group and transition metals, we recently began the investigation of modified Schiff-base ligands such as 1 shown in Figure 1. The reaction of 1 with Zn(OAc) -2H 0 in THF followed by Co (CO) gave the unusual Zn Co complex 2 (Figure 2) (1). 2

2

2

8

3

8

Figure J. Coventional "salen" style Schiff-base ligand I modified with -C=C

© 2006 American Chemical Society

Lattman and Kemp; Modern Aspects of Main Group Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

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Downloaded by PEPPERDINE UNIV on August 24, 2017 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch016

Hz

Figure 2. The unusual Zn Co complex 2. {Chemical Communications, 2004, 2986.) Reproduced by permission of the Royal Society of Chemistry. 3

8

In addition to the unusual linear Zn core, the four outer —C=C—SiMe groups of 2 each added Co (CO) units. One may view the central core of 2 as consisting of Zn(OAc) units sandwiched between two "ZnL" groups (L = Schiff base 1). We also noted that Nabeshima and coworkers recently reported the conversion of a Zn complex into a mixed metal "(3d-4f)" compound with a Zn Eu core (2). Since 3d-4f complexes (3) are of interest for their magnetic (4) and luminescent properties (5) we explored the idea of using a Schiff-base complex of Zn(II) as an unusual "main group" ligand system for the coordination of lanthanide ions. 3

2

3

6

2

3

2


223


Rather than relying on the fortuitous presence of acetate ligands in order to facilitate the coordination of the central metal as in 2, we initially focused on modified Schiff-base ligands such as 3 shown in Figure 3.

3

4

Figure 3. Schiff-base ligands for the stabilization of 3d-4f complexes. Pioneering work by Costes and coworkers has shown that coordination of lanthanide ions is achieved via the extra OMe groups of 4 (Figure 3) (6). In our hands the reaction of 3 with Ζη(Ν0 ) ·6Η 0 in MeOH in a 2:3 molar ratio afforded the trinuclear Zn complex S as shown in Figure 4 (7). This compound reacts with YbCl -6H 0 (1:2 molar ratio) in acetonitrile in the presence of Et N to give the tetrameric Zn Yb complex 6 (Figure 4). 3

2

2

3

3

2

3

2

2

Figure 4. Synthesis of the Zn complex S and conversion to the Zn Yb dimer 6, (Chloride and nitrate ligands omittedfor clarity). 3


2

2


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Figure 5. Views of the X-ray crystal structures of 5 and 6.


225 The X-ray structures of 5 and 6 are shown in Figure 5. In 5 the molecule displays an interesting intramolecular π-π stacking interaction between two aryl rings (dihedral angle 4.8°) with the distance between the centers of each ring of 3.577 Â. The formation of 6 is accomplished by the replacement of the central zinc atom of 5 by two Y b ions, which are bridged by two hydroxides. These OH units give the molecule an overall slipped sandwich configuration. The photophysical properties of the lanthanides are of considerable interest for their applications in biology, medicine and materials science (8). Recently, because of the potential applications in bioassays and laser systems, attention has focused on the near-infrared (NIR) emissive properties of complexes of Yb(III), Nd(III) and Er(III) (9). In the case of 6 we were able to observe the NIR luminescence at 977 nm assigned to the ¥ -* Fm transition upon excitation of the ligand centered absorption band either at 275 or 350 nm. The relevant absorption and NIR luminescence spectra are shown in Figure 6. 3+

2

2


5/2

3

800

1000

1200

1400

1600

A/ n m

Figure 6a. Absorption spectra of3 (thin), 5 (dotted) and 6 (solid). Figure 6b. The NIR luminescence of 6 in MeCN(l(T M) at room tempera 5


226 Here we are no doubt using the main group ligand system as the chromophore to act as the antenna or sensitizer to facilitate the fluorescence of Yb(III) ions. The composition of the final product in these 3d-4f complexes seems to depend to some extent on the nature of the counter anions of both metals. Thus with Zn(OAc) H 0 as the 3d starting material, with Yb(N0 ) -6H 0, complexes which display a simple 1:1 (3d:4f) metal ratio are obtained. Figures 7a and 7b show the X-ray structures of two representative examples 7 and 8 formed from Schiff base ligands with C and C backbones respectively. 2

3

3

2

2


4

3

Zn(OAc) -2H 0 Yb(N0 ) -6H 0 2

2

3 3

2

• C11

010 2

7 [ZnYbL (N0 ) (OAc)]C H OH 3

2

2

5

Figure 7a. 3d-4f Complex 7 with 1:1 metal ratio.


227

OMe

MeO Ζη(ΟΑο) ·2Η 0 Yb(N0 ) -6H 0 2


3

3

2

2

053

3

8 [ZnLnL (N0 ) ] (Ln = Nd, Eu, Tb and Yb) 3

3

Figure 7b. Complex 8 with 1:1 metal ratio.

In order to explore the results obtained by further variations of the backbones of these Schiff base ligands, we investigated the reaction of the vanallin derivative 5-bromo-3-methoxysalicylaldehyde with 1,2diaminobenzene. At room temperature in ethanol the conventional Schiff base ligand is formed, however at 78 °C a rearrangement occurs to give the benzimidazole derivative as shown in Figure 8. This kind of rearrangement is well known (10). Reaction of the salen type Schiff-base with TbCl -6H 0 (4:3 ratio) in MeCN/MeOH leads to the unusual "tetra-decker" complex [Tb L (H 0)2]Cl (9) shown in Figure 9 along with its excitation and emission spectra. Interestingly the benzimidazole derivative (Figure 8) is also capable of forming a variety of different complexes with metal ions via the imizadole N , OH and OMe groups (Type I, Figure 8.) or the two-OH and two OMe groups (Type II, Figure 8). Examples of such complexes (10, 11) involving the coordination of Zn and ZnEu groups are shown in Figure 10. Mixed metal (3d3

3

4

2

2

2

2



Type Ιί

Figure 8. Ligands derivedfrom 1,2-diaminobenzene

Type I



229

[Τ^(^) (Η 0),1·α·90Η ΟΗ·4Η,0 4

2

3

Em(1) ι 1

*·

f

\

(

'• '· ; 200

•

\

; ii ' _ i ±

• ,.,„„ΐΤ,»400.p., ,,ψ 500 ,„600 ., , , 700 , M,„.t

300 ΓΙ

Wavolengtb(nm)

Figure 9, The tetra decker [Tb3L4]+complex 9 and itsfluorescencespectrum.



230

Figure I0a. Complex 10: Example ofcoordination mode for the benzimidaz ligand.



231



232

4

12 [CuYb(L ) Cl ]-3(C H OH) 2

13

3

2

5

4

[CuLn(L ) (N0 ) ] (Ln = Yb, Eu, Tb and Er) 2

3

3

Figure 11. Mixed metal 3d-4fcomplexes found with the benzimidazole


233 4f complexes can also be prepared with this ligand. The X-ray structures of two dinuclear examples (Cu(II)-Yb) (12) and Cu(II)-(Yb, Eu, Tb and Er) (13) are shown in Figure 11. We were also interested in the possibility of forming mixed metal (3d-4f) complexes with the vanillin based starting materials themselves. However, the reaction of 5-bromo-3-methoxysalicylaldehyde with TbCl -6H 0 and Zn(OAc)-2H 0 in methanol gave the unusual Tb complex (14) shown in Figure 12, and which contained in no Zinc (11). Complex 14 has several interesting features. The overall Tbi core is stabilized by eight μ -ΟΗ groups and has a 3

2

0


2

10

3

B r — O C H

Zn(OAc) *2H 0 2

2

3

TbCl -6H 0/CH OH 3

2

3

BrlA

BHCj

|Br1G

Br1E

14[Tb

9

1 0

(L\(L ^

Figure 12. Structure of the TbJO complex (Dalton Trans., 2004, 1787.) Reproduced by permission of the Royal Society of Chemistry.



234

Figure 13. Detail of the coordinated methyl hemiacetal unit in 14 (Dalton Trans., 2004, 1787.) Reproduced by permission of the Royal Society of Chemistry.


235 slipped sandwich configuration formed by the partial overlap of two nearly planar Tb units. The compound also features an unusual example of a coordinated methyl hemiacetal group as illustrated in Figure 13. Although the mechanism of formation of 14 is not known at present, the use of Zn(OAc) *2H 0 is important in its formation. Under similar conditions in the absence of zinc acetate similar reactions with LnCl -6H 0 (Ln = Tb, Er) gave the isostructural trinuclear complexes 15 and 16. A view of the X-ray structure of 15 and 16 is shown in Figure 14. The central cores of the complexes are similar to that of the trinuclear Gd complex [L'Gd (OH) (N0 ) (H 0) ] (L = deprotonated 3-methoxysalicylaldehyde) recently reported by Costes and coworkers (12). 5

2

2

3

2

2+

3

3

3

2

2

4


3

[ L n ^ L O ^ O H ^ C I ^ C H j O H ^ H j O J - a - a C H j O H (Ln - Tb and Er)

Figure 14. Trinuclear complexes ofTb (15) andEr (16).

(Dalton Trans., 2004, 1787.) Reproduced by permission of the Royal Society of Chemistry. Lattman and Kemp; Modern Aspects of Main Group Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

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236 Acknowledgements We are grateful to the Robert A. Welch Foundation for financial support (Grant F-816).

References 1. 2.


3.

4. 5.

6. 7. 8.

9.

10. 11. 12.

Zhang, L; Jones, R. Α.; Lynch, V. M . ; Chem. Comm., 2002, 2986. Akine, S,; Taniguchi, T.; Nabeshima, T., Angew. Chem. Int. Ed, 2002, 41, 4671 (a) Sakamoto, M ; Manseki, K.; Okawa, H, Coord. Chem. Rev., 2001, 219, 379. (b) Costes, J.-P.; Dahan, F; Dupuis, Α., Inorg. Chem., 2000, 39, 165. Winpermy, R. E., Chem. Soc. Rev., 1998, 27, 447. Wong, W.-K.; Liang, H.; Wong, W.-Y.; Cai, Z.; L i , K.-F.; Cheah, K.W., New J. Chem., 2002, 26, 275. See also Yang, X.-P., Su, C.-Y.; Kang B.-S.; Fong, X.-L.; Xiao, W.-L.; Liu, H.-Q., J. Chem. Soc., Dalton Trans., 2000, 3253. Yang, X.-P.; Kang, B.-S., Wong, W.-K., Su, C.-Y.; Liu, H.-Q., Inorg. Chem., 2003, 42, 169. Costes J.-P.; Laussac, J.-P.; Nicodème, F., J. Chem. Soc., Dalton Trans., 2002, 2731. Yang, X.-P.; Jones, R. Α.; Lynch, V. M.; Oye, M . M.; Holmes, A. L., Dalton Trans., 2005, X X X X . (a) McGehee, M . D.; Bergstedt, T.; Zhang, C.; Saab, A. P., O'Regan, M . B.; Bazan, G. C.; Strdanov, V. I.; Heeger, Α., J. Adv. Mater., 1999, 11, 1349; (b) Piguet, C.; Edder, C.; Rigault, S.; Bernardinelli, G.; Bünzli, J.-C. G.; Hopfgartner, G., J. Chem Soc., Dalton Trans., 2000, 3999, (c) Sabbatini, N.; Guardigli, M . ; Lehn, J. M., Coord. Chem. Rev., 1993, 123, 201. (a) Werts, M . Η. V., Hofstraat, J. W.; Geurts, F. A. J.; Verhoeven, J. W., Chem. Phys. Lett., 1997, 276, 196; (b) Hasegawa, Y., Ohktbo, T.; Sogabe, K.; Kawamura, Y.; Wada, Y.; Nakashima, H.; Yanagida, S., Angew. Chem., 2000, 112, 365 and Angew. Chem. Int. Ed., 2000, 39, 357. Kitazume, T.; Ishikawa, N., Bull. Chem. Soc. Jap., 1974, 47, 785. Yang, X.-P.; Jones, R. A.; Wiester, M . J., Dalton Trans, 2004, 1787. Costes, J.-P.; Dahan, F.; Nicodème, F., Inorg. Chem., 2001, 40, 5285.


New Complexes of Lanthanides with Unusual Main Group Ligands

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