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This study involved the syntheses of fluorescent transition metal complexes that bear luminophores. Syntheses, Structures and Photophysical Properties of Metal Carbonyl Clusters with Dansyl and Acridone Luminophores Wai-Yeung Wong, Ka-Ho Choi, and Zhenyang Lin • • • • • • An overview of what will be discussed: • The syntheses: • A new series of fluorescent dinuclear and trinuclear metal complexes bearing dansyl and acridone entities were produced. • Used groups 8 and 9 transition metal elements with acetylenes • Properties of the new compounds: • Spectroscopic • Structural • photophysical Luminophore: atomic grouping in a molecular entity that increases its ability to emit light (ie. when its electronic excitation is associated with a given emission band that is approx. localized. Origin: L. Lumen, light, + G. Phoros, bearing In this study, dansyl and acridone luminophores were used Importance: wide applications in environmental and biological sciences, and molecular electronics In fact, fluorescent methylmercury acetylides (containing acridone and dansyl) have been synthesized which could provide methods for detecting methylmercury in environmental and biological samples. Methylmercury: health risk to humans and wildlife that consume large quantities of mercury contaminated fish. How they synthesized the fluorescent complexes : • Fluorescent-labeled alkyne ligands were reacted with metal carbonyl compounds • Dansyl (R1) and Acridone (R2) are the fluorescent labels. • Dansyl: 5-(dimethylamino)napthalene-1-sulfonyl • Acridone: structure on next page • These were incorporated into the following derivitized molecules (alkyne ligands). • 5-(dimethylamino)-N-(2-propynyl)-1naphthalenesulfonamide (I) • 10-(2-propynyl)-9-acridone (II) 1 5-(dimethylamino)-N-(2-propynyl)-1-naphthalenesulfonamide (I) Structures I and II are alkyne ligands: 10-(2-propynyl)-9-acridone (II) • Reaction of alkynes (RC=CR) in organometallic complexes: – – – – Has 2 occupied π-MO’s Can potentially donate 2- or 4- electrons The C=C bond length usually lengthens upon complexation Bond length in complexes: ~124-137pm (indicates a weaker bond, with loss of triple bond character) – The C=C bond length of a free alkyne~120pm – There are many known mono- and polynuclear organometallic complexes involving alkyne ligands – This study involves polynuclear complexes. The alkyne ligands bearing the luminophores were reacted with the following metal carbonyl compounds: • • • • [Co2(CO)8] [Et3NH][Fe2(CO)6(µ-CO)(µ-StBu) [Ru3(CO)10(NCMe)2] [Os3(CO)10(NCMe)2] • Structures I and II provide a way of attaching a fluorescent label to a metal core via an acetylide linkage. 8 new cluster complexes were obtained: [Co2(CO)8( µ-η2-RCH2CCH) R=R1,R2 (1,2) [Fe2(CO)6(µ-StBu)(µ-η2-RCH2C=CH2)] (3,4) [Os3(CO)9(µ-CO)(µ3- η2-RCH2CCH)] (5,6) [Ru3(CO)9(µ-CO)(µ3- η2-RCH2CCH)] (7,8) 4 x 2(using R1 and R2) complexes were produced. Total=8 Recall: R1 represents dansyl, R2 Acridone (the luminophores) 2 The syntheses: • The fluorescent dinuclear colbalt complexes (1,2) were prepared using one equivalent of I and II, respectively [Co2(CO)8] + RCH2C=CH Reaction performed at 0 degress celsius [Co2(CO)8( µ-η2-RCH2CCH) The iron carbonyl salt, [Et3NH][Fe2(CO)6(µ-CO)(µ-StBu)] was thermally treated with I and II: • • • σ,π-vinyl complexes (3,4) were obtained Vinyl: from organic chemistry, a vinyl group is CH2=CHσ,π refers to bonding that occurs (more later) [Fe2(CO)6(µ-StBu)(µ-η2-RCH2C=CH2)] The reaction of the alkynes (I and II) with [Ru3(CO)10(NCMe)2]& [Os3(CO)10(NCMe)2]: • Displacement of MeCN by the terminal alkynes occurred at room temperature • And the following Ru and the Os complexes were produced : [M3(CO)9(µ-CO)(µ3- η2-RCH2CCH)] where M = (Ru, Os) 3 These new complexes have been fully characterized by: The New Compounds: • Purified by preparative TLC on silica • Isolated as: – orange to red solids (1-4) – yellow solids (5-8) • (1-8)- high solubility in dichloromethane • • • • FTIR H NMR spectroscopy UV/Vis spectroscopy FABMS (fast atom bombardment mass spec) Also, single x-ray structural analyses and molecular orbital calculations were performed on selected complexes (1,2,4 and 8 from previous slide) The results of IR, HNMR, Mass spectrometry & Absorption/Emission Spectra: • A little bit about IR: - organic molecules (ie. the alkyne ligands) are constantly vibrating. - Each stretching/bending vibration occurs at a specific frequency depending on what kind of bond(s) are involved. - The molecule will absorb the energy of the IR radiation if it matches the frequency of one of its vibrations (molecule will stretch and bend more) - In this way, different kinds of bonds can be identified by the specific wavenumber (1/cm) of light that is absorbed. The IR spectrum of the new series of fluorescent complexes indicated the following: • The disappearance of the ν(C=C) and ν(=C-H) bands showed that the acetylenic unit (-CH2C=CH) must be coordinated to the metal carbonyl fragments. This was observed for all of the new complexes (1-8) • The Ru (5,6) and Os (7,8) complexes displayed a broad peaks at 1880 1/cm and 1848 1/cm. These peaks indicate the presence of a bridging carbonyl group in each case. 4 HNMR spectra: • NMR spectroscopy- absorption of radiation to determine structural feature of organic compounds. HNMR specifically determines C-H framework. • Resonances stemming from the coordinated dansyl and acridone group show: – Signals for the –C=CH protons in I and II were absent – Presence of singlet peak was resolved for –CCH protons (except in 3 & 4) – 3&4 have vinyl protons- were shown as doublets Mass spectroscopic data: • A 1:1 metal/ligand stoichiometry was established from the parent ion peaks (for each of the new compounds) Electronic Absorption and Luminescence Spectra: • • • • • • Luminescence: is the emission of light by a substance caused by physical or chemical means. In this case, the free alkynes absorb light in the near-UV region which are a result of π- π* transitions in the ligand framework. (remember: the ligand framework contains the luminophores ;acridone and dansyl) The absorption of light promotes an electron into a higher energy state/level Since the excited electronic states are unstable, the electron eventually falls back to a lower energy state and loses its excess energy. These molecules are capable of emitting some of this energy as light (fluorescence). . -Complexes 1-8 were excited in CH2Cl2 which resulted in blue to greenish-blue luminescence (emission) bands. -The peaks of these bands were in the range of 506-509 nm for the dansyl derivatives while the adridone derivatives had peaks in the 425431 nm range. -The complexed fluorophores were found to have very similar emission wavelengths to the uncomplexed ligands (I and II). -However, an important finding was that the fluorescence quantum yields of the metal complexes were less than I and II by one to two orders of magnitude. - Quantum yield: # of species removed/number of photons absorbed. -this decrease in luminescence intensity is known as quenching and may be due to the heavy-atom effect, energy transfers or electrontransfer mechanism. -The excitation and photoluminescence spectra of 1 and 2 are represented on the following slide 5 506-509 nm (dansyl luminophore) 425-431 nm (acridone luminophore) Now, an overview of what was determined via crystal structure analyses and molecular orbital calculations: X-ray crystallography: -a standard technique used for solving crystal structures -good quality crystals of the compounds are required for x-ray diffraction studies -By using this technique, the experimental geometries of 1,2,4,and 8 were determined. -For 1 and 2 (dinuclear cobalt complexes), the structural features are similar This is structure 1. Here it can be seen that the Co(1) and Co(2) axis forms a pseudo-tetrahedron with the C=C bond of the alkyl ligand. -The C=C vector lies ppd to the Co-Co vector -Co-Co separation: 2.492 A -C(7)-C(8) bond length: 1.341 A -suggests loss of triple bond character of alkyne ligand upon complexation - actual triple bond length ~1.20A -Structure 1 is shown on next slide. 6 This is the structure of 4 (the dinuclear iron complex). -the Fe-Fe edge is bridged by both the thiolate and the µ-σ-vinyl group -Fe(2)-S(1) length shorter then Fe(1)-S(1) -this asymmetric bridge is typical for diiron compounds -However, the C(7)-S(1) bond is slightly longer than typical C-S bonds indicating delocalization of electron density (from thiolate bridge to metal core). -The C(11)-C(12) bond is bound to Fe(2) by π-interaction -bound to Fe(1) via σ –interaction -the C(11)-C(12) bond length 1.37A characteristic of vinylic coordination This is the structure of 8 (the trinuclear osmium complex): -the three Os atoms are coordinated to the alkyne ligand by 2 σ bonds through Os(1) and Os(3) and a π bond to Os(2). -the C(11) –C(12) bridges the Os(1)-Os(3) bond -a 4 membered ring is formed, making a 58.1 degree dihedral angle with Os3 triangle The x-ray data provided the experimental geometries of the compounds. Molecular orbital calculations were then performed based on these geometries. • Common features for the 4 complexes (1,2,4,&8): • • • The molecular orbitals in the frontier region show very similar characteristics HOMO-LUMO gaps (for the 4 clusters) are close to each other HOMO corresponds to pi-bonding in the aromatic unit (from dansyl/acridone) in alkyne ligand LUMO corresponds to metal-metal antibonding • 7 • In comparison to the uncomplexed alkyne ligand (I): • • • • • • • HOMO-a contribution from the p-pi orbital of NMe2 along with the pibonding within the aromatic unit. LUMO-the π* orbital of the aromatic moiety (fragment). The energy gap: 33,792 1/cm HOMO-LUMO energy gap of complex 1 was calculated to be 23, 356 1/cm This energy gap is less than I. Thus, the bridging of the alkyne ligand significantly affects the orbital structure in the HOMO-LUMO region. From the fact that the LUMO’s for the new complexes involve metalmetal antibonding (possibility of fragmentation), the life-time of the excited state of these complexes is shortened compared to the luminophore itself. From the earlier discussion of the absorption/emission spectra, we know that there was a strong quenching of the fluorescence intensity upon comlexation of the alkynes. – LUMO’s for I (alkyne): corresponds to the π* orbital of the aromatic moiety (fragment). Longer-lived excited state – LUMO’s for complex: metal- metal antibonding. Shorter-lived excited state. Wong, Choi and Lin suggest that poor fluorescence intensity is a result of the shortened lifetime of the excited states in the new complexes. In Conclusion: • • • • • A new series of fluorescent-labeled metal clusters was successfully synthesized. The metal complexes (groups8, 9) containing dansyl and acridone luminophores were obtained in moderate yield. They were characterized spectroscopically (IR, Mass Spec, Absorption/ emission spec. etc.) and with x-ray crystallography, and molecular orbital calculations The new complexes emit blue to blue-green light (in solution at room temp.) The luminescence bands were typical of the fluorophores (although they had been quenched considerably) • They demonstrated how luminescence properties of fluorophores can be altered in presence of metal cluster cores. • The understanding of the quenching processes will be important in the development of new molecular luminescent sensing systems. 8