Phase Transitions in Self‐Assembled Monolayers Detected by Electrochemistry

Abstract

COMMUNICATIONSN M R evidence for a persistent phosphirenyl cation in a compound formulated as (PhiBuC,P)+[B(OSO,CF,)J .f2 '] In 4, the slightly shorter C -C bond length (1.33(3)A) and the elongated P-C bonds (1.78(2)A and 1.82(2)A) would suggest incomplete delocalization when compared with the theoretical models of the free ligand. although the effect of a bound transition metal fragment on the latter is not clear. The Ni-PI bond (2.207(5)A) in 4 lies close to the average Ni-P bond length found by H,tBu2)]. It is noteworthy that in 4 the P 1 atom in the three-membered ring lies closest to P 3 in the five-membered ring, suggesting that the large 'JPp coupling constant between these nuclei may have a through space component similar to that previously observed for [Fe(ti'-P,C,rBu,),] .["I Expcrimentd Procedure 3: Electron beam (400 W) vaporired nickel (0.99 g) \\as cocondensed with an excess of rBiiCP (20 g) at 77 K over a period of 2.5 h. The residue was washed froin the belljar with petroleum ether (40-60 ) and filtered through a celite pad to remove colloidal metal. Removal of solvent i n vacuo afforded a dark oil. Extraction of the oil into petroleum ether (40-60 )followed by chromatographic workup on alumina (4% in:m HzO) with petroleum ether (40 60 ) as eluent afforded 3 as an oil (ca 0.2 g. 3 % ) and 5 (0.2 g. 3 % ) analqtically pure, after recrystalliration from pentane. For spectroscopic data see Tablc 1 . 4 . To [W(C'O),(thf)] generated in situ from [W(CO),] (0.10 g) in THF (25 mL) was added 3 (ca. 0.05 g) and the mixture stirred for 4 h . The solvent was removed in u c u o to yield a dnrk oil. Extraction of the oil into petroleum ether (40-60 ) followed by chromatographic workup on Kieselgel 60 GFL4 with petroleum ether (40-60 ) as eluent allbrded 4 as a microcrystalline powder on removal of mlvent. Recrystallization from pentane (223K) afforded analytically pure 4 (0.05 s. 58%). [23] a) Crystal data for 4 : C2sH,,,N~0,P,W, M =?83.0. triclinic. space group PI (no. 2). (I = 9.415(4), h =12.021(9). c =13.964(4)A. 1 -7X.31(4). /j = 81.66(3).;. = 86.51(5). V = 1 5 3 0 ( I ) A Z , Z = 2 .~)~. ,~~~ =1.70gcm~'.(MoKC) = 46.9 cm-', CAD4: 4241 measured reflections, 3448 observed ( I > 20(1)). K = 0.072. R, = 0.089 (M = l;nz(FJ) for 175 parameters, b) Further details of the crystal structure investigation are available on request from the Director of the Cambridge Crystalloeraphic Data Centre. 12 Union Road, GB-Cambridge CB2 1EW (UK). on quoting thc full journal citation.Self-assembled monolayers (SAMs) of rz-alkanethiols (RSH) on metals have been used both as models for organic surfaces and as modulators of metal surface properties.[" These SAMs are prepared under readily accessible laboratory conditions, and the strong interaction between the metal substrate (Au, Pt. Ag. Cu, Hg. etc.) and the sulfur atom provides a monolayer film that is sufficiently stable to desorption to allow spectroscopic. diffraction, and electrochemical experiments to be performed with a minimum of precautions.['] Crazing-angle FT-IR stud...

Relationship Between Structure and Solubility of Thiol-Protected Silver Nanoparticles and Assemblies

“…The chain melting of n-C n H 2n + 1 thiol-coated gold nanoparticles occurs at the following temperatures for the indicated chain length: 3°C (n = 12), 22°C (n = 14), 41°C (n = 16), 51°C (n = 18), and 64°C (n = 20) [25]. These 'melting' transition temperatures are quite comparable to those found for gold SAMs, for which the temperatures are found to be: 39°C (n = 16), 53°C (n = 18), and 63°C (n = 20), measured electrochemically [26]. Gold nanoparticles coated with alkylthiol chains having 12, 10, and 8 carbons display broad melt transitions at temperatures less than 0°C, indicating they are melted at room temperature, as evidenced by the viscous nature of these materials.…”

Copper Electrodeposition on Alkanethiolate Covered Gold Electrodes*

“…We found the same behaviour as for the double layer current mentioned above: the redox waves' current rose at high temperatures and for short chain lengths. Note that the temperature behaviour can be more complex [68]. Experiments with Ru(NH3)6/2+ normally showed a much higher current; however, the same dependence on the thiolate chain length is found (Fig.…”

Current understanding of the structure, phase transitions and dynamics of self-assembled monolayers on two- and three-dimensional surfaces

“…Using in situ vibrational spectroscopy they confirmed that this behaviour is due to phase transitions of the monolayer. The electrochemical studies carried out by Badia et al confirm the order-disorder transitions in SAMs [142]. They too found a chain length dependence of melting temperature; the values vary between 313 and 338 K.…”