Divalent Tetra- and Penta-phenylcyclopentadienyl Europium and Samarium Sandwich and Half-Sandwich Complexes: Synthesis, Characterization, and Remarkable Luminescence Properties

Abstract

The synthesis of the bulky divalent (polyphenylcyclopentadienyl)lanthanoid sandwich complexes [Ln(C 5 Ph 5 ) 2 ] (Ln = Sm, Eu) and [Ln(C 5 Ph 4 H) 2 (solv)] (Ln = Sm, solv = thf; Ln = Eu, solv = dme)], from redoxtransmetalation/protolysis (RTP) reactions, has been achieved. An analogous reaction with Yb afforded the solvent-separated ion pair [Yb(dme) 4 ][C 5 Ph 4 H] 2 . In addition, rare divalent samarium halide complexes [Sm(C 5 Ph 5 )(μ-Br)(thf) 2 ] 2 and [Sm(C 5 Ph 4 H)I(thf) 3 ], were also prepared, either by RTP or ligand rearrangement. X-ray studies showed that the [Ln(C 5 Ph 5 ) 2 ] complexes adopt highly symmetrical sandwich structures, whereas the [Ln(C 5 Ph 4 H) 2 (solv)] complexes have open sandwich structures. The unexpected, but limited, solubility of the [Ln(C 5 Ph 5 ) 2 ] complexes allowed for variabletemperature NMR spectra of [Sm(C 5 Ph 5 ) 2 ] to be obtained. Detailed 1D and 2D NMR studies were conducted on [Sm(C 5 Ph 4 H) 2 (thf)] to ascertain its structure in donor and nondonor solvents. During the course of these studies, the mixed tetraarylcyclopentadienyl sandwich complex [Sm{C 5 (2,5-Ph) 2 (3,4-p-tol 2 )H} 2 (thf)] was also prepared in order to fully assign the spectrum of [Sm(C 5 Ph 4 H) 2 (thf)]. The europium sandwich complexes [Eu(C 5 Ph 5 ) 2 ] and [Eu(C 5 Ph 4 H) 2 (dme)] exhibit remarkable luminescence properties with high quantum yields (45% and 41%, respectively) coupled w i th long emission lifetimes (approximately 800 and 1300 ns, respectively) in toluene.

Lanthanide Luminescence in Visible-Light-Promoted Photochemical Reactions

“…The tunabilty of the luminescence of divalent europium has been studied by altering the coordination environment of Eu II with a variety of ligands and organometallic moieties, ranging from crown ethers [ 47 ] to sandwich complexes [ 48 , 49 , 50 , 51 , 52 ] to other divalent complexes [ 30 , 31 , 32 , 53 , 54 ]. However, the majority of these complexes do not absorb visible light.…”

Synthesis of Samarium-Based Metal Organic Compound Nanoparticles with Polychromatic-Photoluminescence for Bio-Tissue Fluorescence Imaging

“…Samarium-based compounds are interesting lanthanide emitters. They typically show orange/red fluorescence [6,7,8,9,10,11,12,13,14,15,16], which is just at the edge of the visible light and the beginning of the NIR light. Reports of Sm–based compounds showing luminescence other than orange/red are fairly rare in the literature [17,18,19].…”

“…The spectroscopic chemistry behind the luminescence of the compounds may be related to ligand-to-metal charge transfer [6,7,8,9,10,11,12,13,14,15,16,17,18,19]. In order to tailor the luminescence of the Sm compound, a special design can be made in the ligands, where the electron can transfer between Sm atoms and the ligands.…”

Synthesis, Characterization, and Handling of EuII-Containing Complexes for Molecular Imaging Applications

“…Divalent europium is a paramagnetic ion with photophysical and electrochemical properties that can be modulated with coordination chemistry (Gansow et al, 1977 ; Yee et al, 1980 , 1983 ; Sabbatini et al, 1982 , 1984 ; Antonio and Soderholm, 1996 ; Jiang et al, 1998 ; Shipley et al, 1999 ; Burai et al, 2000 ; Soderholm et al, 2002 ; Botta et al, 2003 ; Christoffers and Starynowicz, 2008 ; Gamage et al, 2010 ; Pan et al, 2011 ; Garcia and Allen, 2012a , b ; Gál et al, 2013 ; Kelly et al, 2015 ; Kuda-Wedagedara et al, 2015 ; Regueiro-Figueroa et al, 2015 ; Allen, 2016 ; Ekanger et al, 2016a , 2017 ; Jin et al, 2016 ; Vanek et al, 2016 ; Basal et al, 2017a , b ; Burnett et al, 2017 ; Kawasaki et al, 2017 ; Corbin et al, 2018 ; Jenks et al, 2018 ). Because of these tunable properties, divalent europium complexes have potential use as molecular-imaging probes that sense O 2 , which is important because O 2 imbalances are often correlated with disease (Shweiki et al, 1992 ; Barnham et al, 2004 ; Mattson, 2004 ; Lin and Beal, 2006 ; Park et al, 2008 ; Facciabene et al, 2011 ).…”