Examination of the Silver Colloid Binding Behavior of Disulfide-Tethered Bipyridine Ligands and Theirfac-Tricarbonylrhenium(I) Complexes

Abstract

The syntheses of 2,2'-bipyridin-5-ylmethyl-5-(1,2-dithiolan-3-yl)pentanoate (L1) and N-(2,2'-bipyridin-5-ylmethyl)-5-(1,2-dithiolan-3-yl)pentanamide (L2) and their neutral fac carbonylrhenium(I) complexes [Re(L1)(CO)(3)Br] and [Re(L2)(CO)(3)Br] are reported. The electronic absorption and emission spectra of the complexes are similar to the spectrum of the reference compound [Re(bipy)(CO)(3)Br] and correlate well with the density functional theory calculations undertaken. The surface-enhanced Raman spectroscopy (SERS) spectra (excited at both 532 and 785 nm) of the ligands and complexes were examined and compared to the spectrum of ethyl 5-(1,2-dithiolan-3-yl)pentanoate (L3), revealing that there is very little contribution to the spectra of these species from the dithiolated alkyl chains. The spectra are dominated by the characteristic peaks of a metalated 2,2'-bipyridyl group, arising from the silver colloid/ion complexation, and the rhenium center. The rhenium complexes show weak SERS bands related to the CO stretches and a broad band at 510 cm(-1) assigned to Re-CO stretching. Concentration-dependent studies, measured by the relative intensity of several assigned peaks, indicate that, as the surface coverage increases, the bipyridine moiety lifts off the surface. In the case of L1 and L2, this gives rise to complexes with silver at low concentration, enhancing the signals observed, while for the tricarbonylbromorhenium complexes of these ligands, the presence of the disulfide tether allows an enhancement in the limits of detection of these surface-borne species of 20 times in the case of [ReL2(CO)(3)Br] over [Re(bipy)(CO)(3)Br].

SERS Detection of Hg2+ using Rhenium Carbonyl Labelled Nanoparticle Films

“…Previously, studies had focused on ligand L1, with the appended functionalization at the 5 position. [11] But it had been noticed that the relative orientation of the bipyridyl group with respect to the surface, varied with concentration. It was hoped that this could be limited by moving the thiolated group to the 4 position.…”

“…The prominent bands appearing at 616, 997, and 1024 cm À 1 correspond to aliphatic CÀ S stretching, aromatic ring breathing and ring-ring stretch respectively, which are in good agreement with the previously reported bulk aggregation of L1 with AgNPs. [11,22] 2,2'-Bipyridine has well documented coordination to most metal cations. Metal perchlorate salts of Hg 2 + , Pb 2 + , Zn 2 + , Fe 2 + and Co 2 + were added to freshly prepared AgNP@L2 MeLLFs without appearing to impact the stability of the film.…”

“…[11] [Re(L2)(CO) 3 Br] was synthesized in a similar fashion by refluxing L2 with [Re(CO) 5 Br] in toluene (Figure S2). [11] Subsequent addition of a dilute acetone solution containing the resulting complex to citrate-stabilized silver nanoparticles results in a colour change from green/yellow to brown (Figure S3). MeLLF formation is achieved by shaking the aqueous suspension with DCM until a mirror-like appearance is observed at the interface between the two immiscible solvents.…”

“…Yet they have seen limited investigation as possible SERS labels despite the potential to drive sensitivity to even greater levels through surface-enhanced resonance Raman spectroscopy (SERRS). Previously, we have reported the synthesis of a fac-[Re(L1)(CO) 3 Br] complex (Scheme 1) that demonstrated a remarkably sensitive SERRS response on aggregated Ag nanoparticles, [11] although we are yet to illustrated this system as a selective detection platform. These Re(I) complexes present metal carbonyl vibrational modes (ReÀ CO stretch at 510 cm À 1 and ReC=O stretches around 1910 and 2025 cm À 1 ) outside the conventional organic Raman window, as also shown by Pérez-Mirabet et al by the coordination of {Re(CO) 3 } to 3-mercaptopropionic acid stabilized gold and silver nanoparticles.…”

Manganese, technetium and rhenium

“…86 Fac-tricarbonylrhenium(I) complexes containing disulfide-tethered bipyridine ligands have been synthesised and their silver colloid binding behaviour investigated. 87 The same Re(I) tricarbonyl unit has been combined with bidentate pyrazolyl-pyridyl-based ligands to produce bright yellow-green luminescent complexes for use as potential oxygen sensors. 88 Elsewhere, a complete family of mono-, bi-and tri-nuclear rhenium(I) tricarbonyl complexes of the bridging polypyridyl ligand 2,3,8,9,14,15-hexamethyl-5,6,11,12,17,18-hexaazatrinaphthalene has been prepared and characterised, 89 while the same fac-Re(CO) 3 core has been used to prepare luminescent complexes containing either 6-amino-5-nitroso-2-thiouracil or violuric acid derivatives as ligands.…”