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Already known molecules which exhibit good electrochemiluminescence (ECL) efficiencies and high photoluminescence quantum yields (PLQY) have been structurally modified in order to increase their performance. The followed strategy is to stiffen the structures to limit the rotational and vibrational freedom degrees and favour radiative decay processes once excited. Molecules under investigation consist of donor-acceptor systems in which the acceptor fraction is a benzonitrile with an imidazole in para position, while the donor fraction consists of four diphenylamine (NPh 2 ) or 3,6-di(tert-butyl)-9H-carbazole ( t-Bu Cz) groups in the remaining positions on the central benzene ring. Therefore, in order to stiffen these systems and restrict the intramolecular rotations (RIR), the imidazole in the para position has been replaced with more extended π-systems, i. e., benzimidazole and phenanthro[9,10-d]imidazole. The restriction of the intramolecular rotation can be clearly observed by 1 H NMR analysis. We expected to observe an increase in ECL efficiency and PLQY with the rigidity. Surprisingly, we observed a generally opposite trend: molecules with the smallest imidazole fraction showed the best performance in ECL and higher PLQY. Notably, NPh 2 derivatives with benzimidazole and phenanthro[9,10-d]imidazole showed an hypsochromic shift of the emission spectra with concomitant increase of the PLQY as the solvent polarity increases., (© 2024 The Authors. Chemistry - An Asian Journal published by Wiley-VCH GmbH.)

Copper nanowires (CuNWs), featuring anisotropic highly conductive crystalline facets, represent an ideal nanostructure to fabricate on-demand materials as transparent electrodes and efficient electrocatalysts. The development of reliable and robust CuNWs requires achieving a full control over their synthesis and morphology growth, a challenge that continues to puzzle materials scientists. In this study, we systematically investigated the correlation between the critical synthetic parameters and the structural properties of nanowires using a design of experiments (DOE) approach. Multiparametric variation of experimental reaction conditions combined with orthogonal technical analysis allowed us to develop a sound predictive model that provides guidelines for designing CuNWs with controlled morphology and reaction yield. Beyond these synthetic achievements, voltammetric and electrocatalytic experiments were used to correlate the CuNWs morphology and structure to their catalytic activity and selectivity toward CO 2 electroreduction, thus opening new avenues for further intersectoral actions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Copper and silver nanowires have been extensively investigated as the next generation of transparent conductive electrodes (TCEs) due to their ability to form percolating networks. Recently, they have been exploited as electrocatalysts for CO 2 reduction. In this review, we present the most recent advances in this field summarizing different strategies used for the synthesis and functionalization/activation of copper and silver nanowires, as well as, the state of the art of their electrochemical performance with particular emphasis on the effect of the nanowire morphology. Novel perspectives for the development of highly efficient, selective, and stable electrocatalysts for CO 2 reduction arise from the translation of NW-based TCEs in this challenging field.

We report the identification and quantitative isolation of Au 145 (SR) 60 X (R = n -butyl, n -pentyl; X = halide) along with elucidation of key properties as compared to the corresponding ubiquitous chiral-icosahedral Au 144 (SR) 60 cluster known to have a central vacancy. The stoichiometries were assessed by electrospray mass spectrometry (ESI-MS) at isotopic resolution, and induced dissociation patterns indicate the 'extra' (Au,Br) atoms are strongly bound components of these structures. Voltammetric and spectroscopic characterization reveals Au 145 (SR) 60 X behaviors that are qualitatively similar to yet fascinatingly distinct from those of Au 144 (SR) 60 . ( 1 H, 13 C)-NMR spectra clearly show how both Au 145 (SR) 60 X and Au 144 (SR) 60 are capped by 12 distinct ligand types of 5-fold equivalence, as was recently established for Au 144 (SR) 60 capped by shorter ligands, demonstrating that this novel cluster shares the same chiral-icosahedral motif. Intriguingly, Au 145 (SR) 60 X is strongly near-IR luminescent, whereas under comparable conditions Au 144 (SR) 60 barely emits. The photoluminescence pattern of Au 145 (SR) 60 X is very similar to that observed for Au 25 (SR) 18 , which contains the Au 13 core. The combined results are interpreted as consistent with neutral Au 145 (SR) 60 X as a diamagnetic species, electronically and structurally similar to the corresponding Au 144 (SR) 60 compounds.

Atomically precise ligand-protected nanoclusters (NCs) constitute an important class of compounds that exhibit well-defined structures and, when sufficiently small, evident molecular properties. NCs provide versatile building blocks to fabricate hierarchical superstructures. The assembly of NCs indeed offers opportunities to devise new materials with given structures and able to carry out specific functions. In this Concept article, we highlight the possibilities offered by NCs in which the physicochemical properties are controlled by the introduction of foreign metal atoms and/or modification of the composition of the capping monolayer with functional ligands. Different approaches to assemble NCs into dimers and higher hierarchy structures and the corresponding changes in physicochemical properties are also described., (© 2020 Wiley-VCH GmbH.)

Singlet oxygen, 1 O 2 , can be generated by molecules that upon photoexcitation enable the 3 O 2 → 1 O 2 transition. We used a series of atomically precise Au 24 M(SR) 18 clusters, with different R groups and doping metal atoms M. Upon nanosecond photoexcitation of the cluster, 1 O 2 was efficiently generated. Detection was carried out by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The resulting TREPR transient yielded the 1 O 2 lifetime as a function of the nature of the cluster. We found that: these clusters indeed generate 1 O 2 by forming a triplet state; a more positive oxidation potential of the molecular cluster corresponds to a longer 1 O 2 lifetime; proper design of the cluster yields results analogous to those of a well-known reference photosensitizer, although more effectively. Comprehensive kinetic analysis provided important insights into the mechanism and driving-force dependence of the quenching of 1 O 2 by gold nanoclusters. Understanding on a molecular basis why these molecules may perform so well in 1 O 2 photosensitization is instrumental to controlling their performance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The study of the structures and properties of atomically precise gold nanoclusters is the object of active research worldwide. Recently, research has been also focusing on the doping of metal nanoclusters through introduction of noble metals, such as platinum, and less noble metals, such as cadmium and mercury. Previous studies, which relied extensively on the use of mass spectrometry and single-crystal X-ray crystallography, led to the assignment of the location of each of these foreign-metal atoms. Our study provides new insights into this topic and, particularly, compelling evidence about the actual position of the selected metal atoms M = Pt, Pd, Hg, and Cd in the structure of Au 24 M(SR) 18 0 . To make sure that the results were not dependent on the thiolate, for SR we used both butanethiolate and phenylethanethiolate. The clusters were prepared according to different literature procedures that were supposed to lead to different doping positions. Use of NMR spectroscopy and isotope effects, with the support of mass spectrometry, electrochemistry, and single-crystal X-ray crystallography, led us to confirm that noble metals indeed dope the cluster at its central position, whereas no matter how the doping reaction is conducted and the nature of the ligand, the position of both Cd and Hg is always on the icosahedron shell, rather than at the central or staple position, as often reported. Our results not only provide a reassessment of previous conclusions, but also highlight the importance of NMR spectroscopy studies and cast doubts on drawing conclusions mostly based on single-crystal X-ray crystallography.

For two decades, Au 144 (SR) 60 has been one of the most studied and used thiolate (SR) protected gold nanoclusters. In many ways, however, it proved to be a challenging and elusive case, also because of the difficulties in solving its structure by single-crystal X-ray crystallography. We used very short thiols and could prepare Au 144 (SC 2 H 5 ) 60 and Au 144 (SC 3 H 7 ) 60 in a very pure form, which was confirmed by UV-vis absorption spectroscopy and very regular electrochemistry patterns. Inductively coupled plasma and electrospray ionization mass spectrometries gave definite proof of the Au 144 (SR) 60 stoichiometry. High-resolution 1D and 2D NMR spectroscopy in the solution phase provided the result of assessing the presence of 12 ligand types in exactly the same amount (5-fold equivalence). Equally important, we found that the two protons belonging to each methylene group along the thiolate chain are diastereotopic. For the α-CH 2 protons, the diastereotopic effect can be indeed gigantic, as it reaches chemical-shift differences of 2.9 ppm. DFT calculations provided insights into the relationship between structure and NMR results. In particular, the 12 ligand types and corresponding diastereotopic effects may be explained by considering the presence of C-H···S hydrogen bonds. These results thus provide fundamental insights into the structure of the thiolate layer capping this long-studied gold nanocluster.

The study of the molecular cluster Au 25 (SR) 18 has provided a wealth of fundamental insights into the properties of clusters protected by thiolated ligands (SR). This is also because this cluster has been particularly stable under a number of experimental conditions. Very unexpectedly, we found that paramagnetic Au 25 (SR) 18 0 undergoes a spontaneous bimolecular fusion to form another benchmark gold nanocluster, Au 38 (SR) 24 . We tested this reaction with a series of Au 25 clusters. The fusion was confirmed and characterized by UV-vis absorption spectroscopy, ESI mass spectrometry, 1 H and 13 C NMR spectroscopy, and electrochemistry. NMR evidences the presence of four types of ligand and, for the same proton type, double signals caused by the diastereotopicity arising from the chirality of the capping shell. This effect propagates up to the third carbon atom along the ligand chain. Electrochemistry provides a particularly convenient way to study the evolution process and determine the fusion rate constant, which decreases as the ligand length increases. No reaction is observed for the anionic clusters, whereas the radical nature of Au 25 (SR) 18 0 appears to play an important role. This transformation of a stable cluster into a larger stable cluster without addition of any co-reagent also features the bottom-up assembly of the Au 13 building block in solution. This very unexpected result could modify our view of the relative stability of molecular gold nanoclusters.

Several research groups have observed magnetism in monolayer-protected gold cluster samples, but the results were often contradictory, and thus, a clear understanding of this phenomenon is still missing. We used Au 25 (SCH 2 CH 2 Ph) 18 0 , which is a paramagnetic cluster that can be prepared with atomic precision and whose structure is known precisely. Previous magnetometry studies only detected paramagnetism. We used samples representing a range of crystallographic orders and studied their magnetic behaviors using electron paramagnetic resonance (EPR). As a film, Au 25 (SCH 2 CH 2 Ph) 18 0 exhibits a paramagnetic behavior, but at low temperature, ferromagnetic interactions are detectable. One or few single crystals undergo physical reorientation with the applied field and exhibit ferromagnetism, as detected through hysteresis experiments. A large collection of microcrystals is magnetic even at room temperature and shows distinct paramagnetic, superparamagnetic, and ferromagnetic behaviors. Simulation of the EPR spectra shows that both spin-orbit (SO) coupling and crystal distortion are important to determine the observed magnetic behaviors. Density functional theory calculations carried out on single cluster and periodic models predict the values of SO coupling and crystal-splitting effects in agreement with the EPR-derived quantities. Magnetism in gold nanoclusters is thus demonstrated to be the outcome of a very delicate balance of factors. To obtain reproducible results, the samples must be (i) controlled for composition and thus be monodisperse with atomic precision, (ii) of known charge state, and (iii) well-defined in terms of crystallinity and experimental conditions., Competing Interests: The authors declare no competing financial interest.

Thiolate-protected metal clusters are materials of ever-growing importance in fundamental and applied research. Knowledge of their single-crystal X-ray structures has been instrumental to enable advanced molecular understanding of their intriguing properties. So far, however, a general, reliable, chemically clean approach to prepare single crystals suitable for accurate crystallographic analysis was missing. Here we show that single crystals of thiolate-protected clusters can be grown in large quantity and very high quality by electrocrystallization. This method relies on the fact that charged clusters display a higher solubility in polar solvents than their neutral counterparts. Nucleation of the electrogenerated insoluble clusters directly onto the electrode surface eventually leads to the formation of a dense forest of millimeter-long single crystals. Electrocrystallization of three known Au 25 (SR) 18 0 (S-nC 25 (S-nC 5 H 11 ) 18 , was also prepared and found to crystallize by forming bundles of millimeter-long Au 25 polymers.

We describe the synthesis, computational analysis, photophysics, electrochemistry and electrochemiluminescence (ECL) of a series of compounds formed of two triphenylamines linked by a fluorene or spirobifluorene bridge. The phenylamine moieties were modified at the para-position of the two external rings by electron-withdrawing or electron-donating substituents. These modifications allowed for fine-tuning of the photoluminescence (PL) and ECL emission from blue to green, with an overall wavelength span of 73 (PL) and 67 (ECL) nm, respectively. For all compounds, we observed a very high PL quantum yield (79-89%) and formation of stable radical ions. The ECL properties were investigated by direct annihilation of the electrogenerated radical anion and radical cation. The radical-ion annihilation process is very efficient and causes an intense greenish-blue ECL emission, easily observable even by naked eye, with quantum yield higher than the standard 9,10-diphenylanthracene. The ECL spectra show one single band that almost matches the PL band. Because the energy of the annihilation reaction is higher than that required to form the singlet excited state, the S-route is considered the favored pathway followed by the ECL process in these molecules. All these features point to this type of molecular system as promising for ECL applications.

The field of molecular metal clusters protected by organothiolates is experiencing a very rapid growth. So far, however, a clear understanding of the fine interactions between the cluster core and the capping monolayer has remained elusive, despite the importance of the latter in interfacing the former to the surrounding medium. Here, we describe a very sensitive methodology that enables comprehensive assessment of these interactions. Pulse electron nuclear double resonance (ENDOR) was employed to study the interaction of the unpaired electron with the protons of the alkanethiolate ligands in four structurally related paramagnetic Au 25 (SR)018 clusters (R = ethyl, propyl, butyl, 2-methylpropyl). Whereas some of these structures were known, we present the first structural description of the highly symmetric Au 25 (SPr)018 cluster. Through knowledge of the structural data, the ENDOR signals could be successfully related to the types of ligand and the distance of the relevant protons from the central gold core. We found that orbital distribution affects atoms that can be as far as 6 Å from the icosahedral core. Simulations of the spectra provided the values of the hyperfine coupling constants. The resulting information was compared with that provided by 1 H NMR spectroscopy, and molecular dynamics calculations provided useful hints to understanding differences between the ENDOR and NMR results. It is shown that the unpaired electron can be used as a very precise probe of the main structural features of the interface between the metal core and the capping ligands.

Au25(SR)18 has provided fundamental insights into the properties of clusters protected by monolayers of thiolated ligands (SR). Because of its ultrasmall core, 1 nm, Au25(SR)18 displays molecular behavior. We prepared a Au25 cluster capped by n-butanethiolates (SBu), obtained its structure by single-crystal X-ray crystallography, and studied its properties both experimentally and theoretically. Whereas in solution Au25(SBu)18(0) is a paramagnetic molecule, in the crystal it becomes a linear polymer of Au25 clusters connected via single Au-Au bonds and stabilized by proper orientation of clusters and interdigitation of ligands. At low temperature, [Au25(SBu)18(0)]n has a nonmagnetic ground state and can be described as a one-dimensional antiferromagnetic system. These findings provide a breakthrough into the properties and possible solid-state applications of molecular gold nanowires.

X-ray crystallography has been fundamental in discovering fine structural features of ultrasmall gold clusters capped by thiolated ligands. For still unknown structures, however, new tools capable of providing relevant structural information are sought. We prepared a 25-gold atom nanocluster protected by the smallest ligand ever used, ethanethiol. This cluster displays the electrochemistry, mass spectrometry, and UV-vis absorption spectroscopy features of similar Au25 clusters protected by 18 thiolated ligands. The anionic and the neutral form of Au25(SEt)18 were fully characterized by (1)H and (13)C NMR spectroscopy, which confirmed the monolayer's properties and the paramagnetism of neutral Au25(SEt)18(0). X-ray crystallography analysis of the latter provided the first known structure of a gold cluster protected by a simple, linear alkanethiolate. Here, we also report the direct observation by electron nuclear double resonance (ENDOR) of hyperfine interactions between a surface-delocalized unpaired electron and the gold atoms of a nanocluster. The advantages of knowing the exact molecular structure and having used such a small ligand allowed us to compare the experimental values of hyperfine couplings with DFT calculations unaffected by structure's approximations or omissions.

The monolayer protecting small gold nanoparticles (monolayer-protected clusters, MPCs) is generally represented as the 3D equivalent of 2D self-assembled monolayers (SAMs) on extended gold surfaces. However, despite the growing relevance of MPCs in important applied areas, such as catalysis and nanomedicine, our knowledge of the structure of 3D SAMs in solution is still extremely limited. We prepared a large series of monodisperse Au25(SCnH2n+1)18 clusters (n=2, 4, 6, 8, 10, 12, 14, 16, 18) and studied how electrons tunnel through these monolayers. Electron transfer results, nicely supported by 1H NMR spectroscopy, IR absorption spectroscopy, and molecular dynamics results, show that there is a critical ligand length marking the transition between short ligands, which form a quite fluid monolayer structure, and longer alkyl chains, which self-organize into bundles. At variance with the truly protecting 2D SAMs, efficient electronic communication of the Au25 core with the outer environment is thus possible even for long alkyl chains. These conclusions provide a different picture of how an ultrasmall gold core talks with the environment through/with its protecting but not-so-shielding monolayer.

We synthesized two molecular systems, in which an endofullerene C60 , incarcerating one hydrogen molecule (H2 @C60 ) and a nitroxide radical are connected by a folded 310 -helical peptide. The difference between the two molecules is the direction of the peptide orientation. The nuclear spin relaxation rates and the para → ortho conversion rate of the incarcerated hydrogen molecule were determined by (1) H NMR spectroscopy. The experimental results were analyzed using DFT-optimized molecular models. The relaxation rates and the conversion rates of the two peptides fall in the expected distance range. One of the two peptides is particularly rigid and thus ideal to keep the H2 @C60 /nitroxide separation, r, as large and controlled as possible, which results in particularly low relaxation and conversion rates. Despite the very similar optimized distance, however, the rates measured with the other peptide are considerably higher and thus are compatible with a shorter effective distance. The results strengthen the outcome of previous investigations that while the para → ortho conversion rates satisfactorily obey the Wigner's theory, the nuclear spin relaxation rates are in excellent agreement with the Solomon-Bloembergen equation predicting a 1/r(6) dependence., (© 2013 The American Society of Photobiology.)

Au25(SR)18 (R = -CH2-CH2-Ph) is a molecule-like nanocluster displaying distinct electrochemical and optical features. Although it is often taken as an example of a particularly well-understood cluster, very recent literature has provided a quite unclear or even a controversial description of its properties. We prepared monodisperse Au25(SR)18(0) and studied by cyclic voltammetry, under particularly controlled conditions, the kinetics of its reduction or oxidation to a series of charge states, -2, -1, +1, +2, and +3. For each electrode process, we determined the standard heterogeneous electron-transfer (ET) rate constants and the reorganization energies. The latter points to a relatively large inner reorganization. Reduction to form Au25(SR)18(2-) and oxidation to form Au25(SR)18(2+) and Au25(SR)18(3+) are chemically irreversible. The corresponding decay rate constants and lifetimes are incompatible with interpretations of very recent literature reports. The problem of how ET affects the Au25 magnetism was addressed by comparing the continuous-wave electron paramagnetic resonance (cw-EPR) behaviors of radical Au25(SR)18(0) and its oxidation product, Au25(SR)18(+). As opposed to recent experimental and computational results, our study provides compelling evidence that the latter is a diamagnetic species. The DFT-computed optical absorption spectra and density of states of the -1, 0, and +1 charge states nicely reproduced the experimentally estimated dependence of the HOMO-LUMO energy gap on the actual charge carried by the cluster. The conclusions about the magnetism of the 0 and +1 charge states were also reproduced, stressing that the three HOMOs are not virtually degenerate as routinely assumed: In particular, the splitting of the HOMO manifold in the cation species is severe, suggesting that the usefulness of the superatom interpretation is limited. The electrochemical, EPR, and computational results thus provide a self-consistent picture of the properties of Au25(SR)18 as a function of its charge state and may furnish a methodology blueprint for understanding the redox and magnetic behaviors of similar molecule-like gold nanoclusters.

In this study, we employed thiolated peptides of the conformationally constrained, strongly helicogenic α-aminoisobutyric acid (Aib) residue to prepare self-assembled monolayers (SAMs) on gold surfaces. Electrochemistry and infrared reflection absorption spectroscopy support the formation of very well packed Aib-peptide SAMs. The immobilized peptides retain their helical structure, and the resulting SAMs are stabilized by a network of intermolecular H bonds involving the NH groups adjacent to the Au surface. Binary SAMs containing a synthetically defined glycosylated mannose-functionalized Aib-peptide as the second component display similar features, thereby providing reproducible substrates suitable for the controlled display of bioactive carbohydrate ligands. The efficiency of such Aib-based SAMs as a biomolecular recognition platform was evidenced by examining the mannose-concanavalin A interaction via surface plasmon resonance biosensing.

Au₂₅L₁₈ (L = S(CH₂)₂Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au₂₅L₁₈⁺ quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au₂₅L₁₈⁺ was used in homogeneous redox catalysis experiments with a series of sym-substituted benzoyl peroxides, including the above peroxide, bis(para-cyanobenzoyl) peroxide, dibenzoyl peroxide, and bis(para-methoxybenzoyl) peroxide. Peroxide dissociative ET was catalyzed using both the Au₂₅L₁₈/Au₂₅L₁₈⁻ and the Au₂₅L₁₈⁺/Au₂₅L₁₈ redox couples as redox mediators. Simulation of the CV curves led to determination of the ET rate constant (k(ET)) values for concerted dissociative ET to the peroxides. The ET free energy ΔG° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log k(ET)vs.ΔG°) relationship. Comparison with the k(ET) obtained using a ferrocene-type donor with a formal potential similar to that of Au₂₅L₁₈/Au₂₅L₁₈⁻ showed that the presence of the capping monolayer affects the ET rate rather significantly, which is attributed to the intrinsic nonadiabaticity of peroxide acceptors.

We synthesized two series of compounds in which a nitroxide radical and a fullerene C(60) moiety were kept separated by a 3(10)-helical peptide bridge containing two intramolecular C═O···H-N hydrogen bonds. The direction of the resulting molecular dipole moment could be reversed by switching the position of fullerene and nitroxide with respect to the peptide nitrogen and carbon termini. The resulting fullerene-peptide-radical systems were compared to the behaviors of otherwise identical peptides but lacking either C(60) or the free radical moiety. Electrochemical analysis and chemical nitroxide reduction experiments show that the dipole moment of the helix significantly affects the redox properties of both electroactive groups. Besides providing evidence of a folded helical conformation for the peptide bridge, IR and NMR results highlight a strong effect of peptide orientation on the spectral patterns, pointing to a specific interaction of one of the helical orientations with the C(60) moiety. Time-resolved EPR spectra show not only that for both systems triplet quenching by nitroxide induces spin polarization of the radical spin sublevels, but also that the coupling interaction can be either weak or strong depending on the orientation of the peptide dipole. As opposed to the concept of dyads, the molecules investigated are thus better described as fullerene-peptide-radical systems to stress the active role of the bridge as an important ingredient capable of tuning the system's physicochemical properties.

Monodisperse Au(25)L(18)(0) (L = S(CH(2))(2)Ph) and [n-Oct(4)N(+)][Au(25)L(18)(-)] clusters were synthesized in tetrahydrofuran. An original strategy was then devised to oxidize them: in the presence of bis(pentafluorobenzoyl) peroxide, the neutral or the negatively charged clusters react as efficient electron donors in a dissociative electron-transfer (ET) process, in the former case yielding [Au(25)L(18)(+)][C(6)F(5)CO(2)(-)]. As opposed to other reported redox methods, this dissociative ET approach is irreversible, easily controllable, and clean, particularly for NMR purposes, as no hydrogen atoms are introduced. By using this approach, the -1, 0, and +1 charge states of Au(25)L(18) could be fully characterized by (1)H and (13)C NMR spectroscopy, using one- and two-dimensional techniques, in various solvents, and as a function of temperature. For all charge states, the NMR results and analysis nicely match recent structural findings about the presence of two different ligand populations in the capping monolayer, each resonance of the two ligand families displaying distinct NMR patterns. The radical nature of Au(25)L(18)(0) is particularly evident in the (1)H and (13)C NMR patterns of the inner ligands. The NMR behavior of radical Au(25)L(18)(0) was also simulated by DFT calculations, and the interplay between theory and experiments revealed a fundamental paramagnetic contribution coming from Fermi contact shifts. Interestingly, the NMR patterns of Au(25)L(18)(-) and Au(25)L(18)(+) were found to be quite similar, pointing to the latter cluster form as a diamagnetic species.

We investigated the reducing properties of a series of 1,2-diaryl-1,2-disodiumethanes by means of equilibration reactions. The electron-donor power of these vic-diorganometals is strongly affected by the nature of substituents present either on the aromatic ring(s) or on the carbanionic centers, and it can be correlated with their ability to delocalize the arylmethyl carbanions. These findings are supported by electrochemical analysis of the reduction behavior of the parent 1,2-diarylalkene. Applications of these results to the reduction of selected substrates are described.