IX. Chapter IV – Effect of amino acid and Cs + coordination on the assembly
5.4 Results and discussion
5.4.6. EPR spectral study
The solution EPR spectroscopic data for complex 1 at 77K is consistent with the tetragonally distorted octahedral Cu(II) structures of the complexes (Figure 5.8A, B Table 5.7).8 The solution glass spectra of three Cu(II) containing assembly indicates monomeric
structures as expected (Figure 5.8C).9 Solid state EPR spectral studies indicates the tetragonally distorted octahedral Cu(II) present in the mixed metal assembly with three resolved hyperfine spectrum (g║=2.256and A║=181G). While, in the three Cu(II) containing assembly, the hyperfine lines became weak and broadened and thus may be merged within the broad central line, which might be due to all the three Cu(II)’s are spin coupled, with g
~2.107 in the solid state at 77K (Figure 5.8D, Table 5.7).10,11
Table 5.7 EPR data of complexesa at 77K
Complexesa g║ g A║/G
(A) [KNi2Cu(HLL-leu)6]ClO4 2.247 2.023 179 (B) [KNi2Cu(HLL-leu)6]ClO4 2.256 2.061 181 (C) [K{Cu(HLL-leu)2}3]NO3 2.246 2.019 179 (D) [K{Cu(HLL-leu)2}3]NO3 2.107
a(A) In MeOH solution, (B) in solid, (C) in MeOH Solution, (D) in solid state at 77K. Complex [K{Cu(HLL-leu)2}3]NO3 from chapter 2 (section 2.2.7)
Figure 5.8.(A) EPR spectra of [KNi2Cu(HLL-leu)6]ClO4 in MeOH (B) in solid state and (C)EPR spectra of [K{Cu(HLL-leu)2}3]NO3 in MeOH (D) in solid state at 77K.
Conclusions
In this chapter, we have synthesized and well characterized a hetero-metallic, chiral self assembly with Ni(II) and Cu(II) in the 2:1 ratio. Interestingly, assembly is quite selective towards Ni(II) to Cu(II) 2:1 ratio. The assembly is present in solution which is supported by ESI-Mass spectroscopy. Most importantly the results presented in this chapter showed that the assembly is quite accommodative in terms of bivalent metal ion.
References
1. Nakamoto, K. Infrared and Raman Spectra of Inorganic Compounds, 5th ed.; Wiley- Interscience: New York, 1997; Part B.
2. Earnshaw, A. Introduction to Magnetochemistry; Academic Press: London, 1968. (b) Figgis, B. N.; Lewis, J. P. Inorg. Chem. 1964, 6, 37.
3. Johnson, C. K. ORTEP, Report ORNL-3794; Oak Ridge National Laboratory: Oak Ridge, TN, 1976.
4. O··O range (2.5 to 3.0) Å: (a) Miyake, R.; Tashiro, S.; Shiro, M.; Tanaka, K.;
Shionoya, M. J. Am. Chem. Soc. 2008, 130, 5646. (b) Desiraju, G. R. Perspective in Supramolecular Chemistry, Wiley, Vol 7. (c) Yang, C. T.; Moubaraki, B.; Murray, K.
S.; Vittal, J. J. Dalton Trans. 2003, 880.
5. (b) Ghattas, W.; Giorgi, M.; Gaudin, C.; Rockenbauer, A.; eglier, M. R.; Simaan, A. J.
Bioinorganic Chemistry and Applications 2007. (c) Sun, Y.; Wang, Z.; Zhang, H.;
Cao, Y.; Zhang, S.; Chen, Y.; Huang, C.; Yu, X. Inorg. Chim. Acta, 2007, 360, 2565.
6. (a) Rajendiran, V.; Palaniandavar, M.; Swaminathan, P.; Uma, L. Inorg. Chem. 2007, 46, 10446. (b) Zurowska, B.; Erxleben, A.; Glinka, L.; Łe˛czycka, M.; Zyner, E.;
Ochocki, J.; Inorg. Chim. Acta. 2009, 362, 739.
7. Lever, A. B. P. Inorganic Electronic Spectroscopy, 2nd ed.; Elsevier: 1984; p 507.
8. Yokoi, H.; Addision, A. W. Inorg. Chem. 1997, 16, 1341.
9. Dubey, M.; Koner, R.R.; Ray, M. Inorg. Chem. 2009, 48, 9294.
10. Klingele, J.; Prikhod’ko, A. I.; Leibeling, Guido; Demeshko, S.; Dechert S.; Meyer F.
Dalton Trans., 2007, 2003.
11. Spin coupled systems (a) Addison, A.W.; Burke, P. J.; Henrick, K. Inorg. Chem.
1982, 21, 60. (b) Yang, Fuh-An; Guo, Chih-Wei; Chen, Yao-Jung; Chen, Jyh-Horung;
Wang, Shin-Shin; Tung, Jo-Yu; Hwang, Lian-Pin; Elango, S. Inorg Chem. 2007, 46, 578. (c) Jung, M.; Sharma, A.; Hinderberger, D.; Braun, S.; Schatzschneider, U.;
Rentschler, E. Inorg. Chem. 2009, 48, 7244. (d) Das S.; Muthukumaragopal, G. P.;
Pal, S.; Pal S. New J. Chem. 2003, 27, 1102.
In the previous chapters, we have synthesized and characterized a set of multinuclear self assemblies and monomers by using salicylaldehydeamino acid derived ligand as well as observed the effect of cation, anion, and amino acids on assembly formation.
In this chapter, we have redesigned the ligand. Compared to the ligands in the earlier chapters, we have replaced the phenolic part of the ligand by pyrene. This would render the ligand a simple bidentate ligand similar to ferrocene derivatives reported earlier from our group. The absence of phenol would prevent the formation of phenol carboxylate Hbond which played an important role in stabilizing the trinuclear assemblies. On the other hand, whatever the type of assembly it forms (if it does) it would be due to the amino acid. This way the assembly formation observed (if any) might have some relevance to natural system.
Pyrene unit here acts as hydrophobic backbone as well as fluorescence probe. One could argue that we could have done such studies directly with amino acids. But results presented earlier from our group1 showed that a hydrophobic/aromatic substitution at the amine end does produces interesting Hbonded network formation which are simply not possible with unsubstituted amino acids as ligand.
In this chapter, we are presenting results showing that attachment of an aromatic pyrene unit to the amino acid, specifically to leucine, made an easy to synthesize, efficient fluorescent gelator which forms hydrogel exclusively in presence of LiOH. Further, use of other base, different amino acid, variation of chirality showed that gelation is sensitive to amino acid arm, LiOH, solvent and chirality of the amino acids.
Gels find number of important applications in diverse areas.2 Recently number of reports appeared on gel formation using low molecular weight molecules.3-5 Majority of such gelators are long chain amphiphiles with amide head groups constituted from amino acids3 or sugar4 and few have pyrene5a-c or bile acid5d-f derivative as gelator. Most of the gelators form hydrogel or organogel alone or along with neutral organic molecule5b but fewer2d in presence of ionic salt. We have not come across any report where hydrogel formation was observed in presence of LiOH. LiOH, widely used as electrolyte in batteries, used as organogel with polymer gelators.6
Scheme 6.1. Synthesis of the gelator as well as 1H NMR labelling scheme.
Scheme 6.2. Gelators used in this chapter as well as 1H NMR labelling scheme.
6.1 Experimental section