Sains Malaysiana 41(5)(2012): 597–601

Sifat Foto-Kimia Kompleks Molibdenum Ditiolena

(Photo-Chemical Properties of Molybdenum Dithiolene)

Mark Lee Wun Fui, Lorna Jeffery Minggu & Mohammad B. Kassim*

Pusat Pengajian Sains Kimia dan Teknologi Makanan, Fakulti Sains dan Teknologi

Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor D.E. Malaysia

Received: 29 June 2011 / Accepted: 2 November 2011

ABSTRAK

Faktor yang perlu diberi perhatian bagi bahan pemeka foto yang baik adalah keamatan serapan dan kedudukan serapan spektrum elektronik dalam julat cahaya nampak, keupayaan redoks dan kestabilan-fotonya. Kompleks molibdenum ditiolena dengan formula am [MoTp*(NO)(L)] dengan Tp* = tris(3,5-dimetilpirazolil)hidroborat dan L = toluena-3,4-ditiolat (L1); 1,2-benzenaditiolat (L2); 3,6-dikloro-1,2-benzenaditiolat (L3) didapati mempunyai sifat-sifat kimia dan fizik yang diperlukan untuk dijadikan sebagai anod pemeka-foto-elektron untuk sel foto-elektrokimia penguraian molekul air kepada hidrogen dan oksigen. Kompleks Mo-ditiolena yang disintesis daripada prekursor [MoTp*(NO)(I)2] dan sebatian ditiol dengan kehadiran Et3N sebagai agen penurunan dan penyahprotonan telah diciri dengan menggunakan kaedah analisis mikro unsur CHNS, spektroskopi IR, ultra-lembahyung dan cahaya nampak (UV-Vis), dan elektrokimia. Puncak penyerapan UV-Vis (λmax/ nm) dikesan pada 321-331, 369-372, 576-589 dan 736-741nm. Sifat keaktifan foto-kimia dan foto-fizik turut dikaji bagi menentukan kesesuaiannya sebagai bahan pemeka foto bagi sel foto-elektrokimia. Ujian kestabilan-foto menunjukkan tiada berlaku penguraian terhadap ketiga-tiga kompleks tersebut selepas sinaran cahaya selama 24 jam.

Kata kunci: Bahan pemeka foto; kestabilan-foto; molibdenum ditiolena

ABSTRACT

The important factors for a good photosensitizer are intensity and position of the spectral absorption in visible region, redox potentials and photo-stability. Molybdenum dithiolene complexes with a general formula [MoTp*(NO)(L)] where Tp* = tris(3,5-dimethylpyrazolyl)hidroborate and L = toluene-3,4-dithiolate (L1); 1,2-benzenedithiolate (L3); 3,6-dichloro-1,2-benzenedithiolate (L3) were found to exhibit the required chemical and physical properties as an anode for photo-electron-sensitizer to generation hydrogen and oxygen via water splitting in photo-electrochemical cell. Mo-dithiolene complexes were synthesized from the precursor [MoTp*(NO)(I)2] and dithiol compound in the presence of Et3N as reducing and deprotonating agents. These complexes were characterised by micro-elemental analysis for CHNS, infrared and UV-Vis spectroscopy, and electrochemical analysis. UV-Vis absorption peaks were detected at 321-331, 369-372, 576-589, 736-741 nm (λmax/ nm). The photo-chemical and photo-physical reactivities were studied to determine the suitability of these complexes as photosensitizers in photo-electrochemical cells. The photo-stability test showed no significant degradation of the complexes after 24 h of light illumination.

Keywords: molybdenum dithiolene; photosensitizer; photo-stability

REFERENCES

Alobaidi, N., Chaudhury, M., Clague, D., Jones, C.J. & Pearson, J.C., McCleverty, J.A. & Salam S.S. 1987. Monometallic, homo- and hetero-bimetallic complexes based on redox active tris(3,5-dimethylpyrazolyl)borato-molybdenum and -tungsten nitrosyls. Part 4. The effects of ligating atom type on the reduction potentials of monometallic complexes. Journal of the Chemical Society, Dalton Transactions (7): 1733-1736.

Alobaidi, N., Jones, C.J. & McCleverty, J.A. 1989. Chelate complexes containing the {Mo(NO)HB(3,5-Me2C3N2H)3} moiety and an example of a pyrazole substitution reaction involving the HB(3,5-Me2C3N2H)3 ligand. Polyhedron 8: 1033-1037.

Falaras, P., Mitsopoulou, C.A., Argyropoulos, D., Lyris, E., Psaroudakis, N., Vrachnou, E. & Katakis, D. 1995. Synthesis, cyclic voltammetric and electrospray mass spectrometric studies of a series of tris-substituted 1,2-dithiolene complexes of tungsten and molybdenum. Inorganic Chemistry 34: 4536-4542.

Fujishma, A. & Honda, K. 1972. Electrochemical photolysis of water at a semiconductor electrode. Nature 238 : 37-38.

Greenwood, N.N. & Earnshaw, A. 1984. The Chemistry of the Elements Oxford, UK: Pergamon Press.

Joshi, H.K., Inscore, F.E., Schirlin, J.T., Dhawan, I.K., Carducci, M.D., Bill, T.G. & Enemark, J.H. 2002. Six-coordinate molybdenum nitrosyls with a single ene-1,2 –dithiolate ligand. Inorganica Chimica Acta 337: 275-/286.

Katakis, D., Mitsopoulou, C. & Konstantatos, J. 1992. Photocatalytic splitting of water. Journal of Photochemistry and Photobiology A: Chemistry 68: 375-388.

Lyris, E., Argyropoulos, D., Mitsopoulou, C.A., Katakis, D. & Vrachnou, E. 1997. New catalyst in the photo-oxidation of water. Journal of Photochemistry and Photobiology A: Chemistry 108: 51-54.

McCleverty, J.A., Seddon, D., Bailey, N.A. & Walker, N.W. 1976. The chemistry of cyclopentadienyl and related nitrosyl complexes of molybdenum. Part V. Dihalogenonitrosyl[tris(pyrazolyl)borato]molybdenum complexes, their alcoholysis, and the crystal structure of chloronitrosylisopropoxo[tris(4-chloro-3,5-dimethylpyrazolyl)borato]molybdenum. Journal of the Chemical Society, Dalton Transactions (10): 898-908.

McCleverty, J.A. & Ward, M.D. 1998. The role of bridgind ligands in controlling electronic and magnetic properties in polynuclear complexes. Accounts of Chemical Research 31: 842-851.

Mueller-Westerhoff U.T., Vance, B. & Yoon, D.L. 1991. The synthesis of dithiolenes dye with strong near-IR absorption. Tetrahedron 47(6): 909-932.

Wlodarczyk, A., Maher, J.P., Coles, S., Hibbs, D.E., Hursthouse, M.H.B., Abdul Malik & K.M. 1997. Oxo-bridged binuclear molybdenum nitrosyl halides: structural and redox studies, mixed-valence behavior, and characterisation of mononuclear hydroxo precursors. Journal of Chemical Society, Dalton Transaction (15): 2597-2606.

*Corresponding author; email: mbkassim@ukm.my