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The thermal reactions of [NEt4][Fe(CO)4(AuNHC)] [NHC = IMes ([NEt4][1]) or IPr ([NEt4][2]); IMes = C3N2H2(C6H2Me3)2; IPr = C3N2H2(C6H3iPr2)2], Fe(CO)4(AuNHC)2 [NHC = IMes (3) or IPr (4)], Fe(CO)4(AuIMes)(AuIPr) (5), and Fe(CO)4(AuNHC)(AuPPh3) [NHC = IMes (6) or IPr (7)] were investigated in different solvents [CH2Cl2, CH3CN, dimethylformamide, and dimethyl sulfoxide (dmso)] and at different temperatures (50–160 °C) in an attempt to obtain higher-nuclearity clusters. 1 and 2 completely decomposed in refluxing CH2Cl2, resulting in [Fe2(CO)8(AuNHC)]− [NHC = IMes (10) or IPr (11)]. Traces of [Fe3(CO)10(CCH3)]− (12) were obtained as a side product. Conversely, 6 decomposed in refluxing CH3CN, affording the new cluster [Au3{Fe(CO)4}2(PPh3)2]− (15). The relative stability of the two isomers found in the solid state structure of 15 was computationally investigated. 4 was very stable, and only after prolonged heating above 150 °C in dmso was limited decomposition observed, affording small amounts of [Fe3S(CO)9]2– (9), [HFe(CO)4]− (16), and [Au16S{Fe(CO)4}4(IPr)4]n+ (17). A dicationic nature for 17 was proposed on the basis of density functional theory calculations. All of the other reactions examined led to species that were previously reported. The molecular structures of the new clusters 11, 12, 15, and 17 were determined by single-crystal X-ray diffraction as their [NEt4][11]·1.5toluene, [Au(IMes)2][15]·0.67CH2Cl2, [NEt4][12], and [17][BF4]n·solvent salts, respectively., The nuclearity of Au−Fe molecular clusters has been increased by thermal methods, resulting in heterometallic species stabilized by CO, NHC, and phosphine ligands.

The direct reactions of homometallic [Ni6(CO)12]2– and [Pt6(CO)12]2– Chini carbonyl clusters result in heterometallic Ni–Pt Chini-type clusters of the general formula [Pt6–xNix(CO)12]2– (x = 0–6). Their molecular structures have been determined by single-crystal X-ray diffraction (SC-XRD), showing a common octahedral (staggered, D3d) structure analogous to that of [Ni6(CO)12]2–, whereas [Pt6(CO)12]2– displays a trigonal-prismatic (eclipsed, D3h) structure. This structural change after replacing one single Pt with Ni may be classified as an alloying effect, and it has been theoretically investigated by DFT methods. Spectroscopic (IR and 195Pt and 13C NMR) and ESI-MS studies indicate that mixtures of [Pt6–xNix(CO)12]2– (x = 0–6) clusters are actually present in solution, whose compositions may be varied in an almost continuous way. Thus, they may be viewed as random alloy clusters whose overall compositions depend on the stoichiometry of the reagents., Molecular Pt−Ni random alloy clusters adopting a Chini-type structure have been obtained upon mixing related homometallic clusters and investigated by structural, spectroscopic, and theoretical methods.

The reaction of [Co(CO)4]− (1) with M(I) compounds (M = Cu, Ag, Au) was reinvestigated unraveling an unprecedented case of polymerization isomerism. Thus, as previously reported, the trinuclear clusters [M{Co(CO)4}2]− (M = Cu, 2, Ag, 3, Au, 4) were obtained by reacting 1 with M(I) in a 2:1 molar ratio. Their molecular structures were corroborated by single-crystal X-ray diffraction (SC-XRD) on isomorphous [NEt4][M{Co(CO)4}2] salts. [NEt4](3)represented the first structural characterization of 3. More interestingly, changing the crystallization conditions of solutions of 3, the hexanuclear cluster [Ag2{Co(CO)4}4]2− (5) was obtained in the solid state instead of 3. Its molecular structure was determined by SC-XRD as Na2(5)·C4H6O2, [PPN]2(5)·C5H12 (PPN = N(PPh3)2]+), [NBu4]2(5) and [NMe4]2(5) salts. 5 may be viewed as a dimer of 3 and, thus, it represents a rare case of polymerization isomerism (that is, two compounds having the same elemental composition but different molecular weights) in cluster chemistry. The phenomenon was further studied in solution by IR and ESI-MS measurements and theoretically investigated by computational methods. Both experimental evidence and density functional theory (DFT) calculations clearly pointed out that the dimerization process occurs in the solid state only in the case of Ag, whereas Cu and Au related species exist only as monomers.

The molecular nanocluster [Ni36–xPd5+x(CO)46]6– (x = 0.41) (16–) was obtained from the reaction of [NMe3(CH2Ph)]2[Ni6(CO)12] with 0.8 molar equivalent of [Pd(CH3CN)4][BF4]2 in tetrahydrofuran (thf). In contrast, [Ni37–xPd7+x(CO)48]6– (x = 0.69) (26–) and [HNi37–xPd7+x(CO)48]5– (x = 0.53) (35–) were obtained from the reactions of [NBu4]2[Ni6(CO)12] with 0.9–1.0 molar equivalent of [Pd(CH3CN)4][BF4]2 in thf. After workup, 35– was extracted in acetone, whereas 26– was soluble in CH3CN. The total structures of 16–, 26–, and 35– were determined with atomic precision by single-crystal X-ray diffraction. Their metal cores adopted cubic close packed structures and displayed both substitutional and compositional disorder, in light of the fact that some positions could be occupied by either Ni or Pd. The redox behavior of these new Ni–Pd molecular alloy nanoclusters was investigated by cyclic voltammetry and in situ infrared spectroelectrochemistry. All three compounds 16–, 26–, and 35– displayed several reversible redox processes and behaved as electron sinks and molecular nanocapacitors. Moreover, to gain insight into the factors that affect the current–potential profiles, cyclic voltammograms were recorded at both Pt and glassy carbon working electrodes and electrochemical impedance spectroscopy experiments performed for the first time on molecular carbonyl nanoclusters., The synthesis, molecular structure, electrochemical, and infrared spectroelectrochemical behavior of three new atomically precise Ni−Pd alloy carbonyl nanoclusters are reported, together with the first electrochemical impedance spectroscopy investigation of redox active carbonyl nanoclusters.

Reductive carbonylation of RuCl3·3H2O at CO-atmospheric pressure results in the [H3Ru4(CO)12]− (1) polyhydride carbonyl cluster. The one-pot synthesis involves the following steps: heating RuCl3·3H2O at 80 °C in 2-ethoxyethanol for 2 h, addition of three equivalents of KOH, heating at 135 °C for 2 h, addition of a fourth equivalent of KOH and heating at 135 °C for 1 h. The resulting K[1] salt is transformed into [NEt4][1] upon metathesis with [NEt4]Br in H2O. The IR, 1H and 13C{1H} NMR spectroscopic data are in agreement with those reported in the literature. [Ru8(CO)16(X)4(CO3)4]4− (X = Cl, Br, I; 2-X) is formed as a by-product during the synthesis of 1, and the two compounds are separated on the basis of their different solubilities in organic solvents. The nature of the halide of 2-X depends on the [NEt4]X salt used for metathesis. 2-Br is transformed into [Ru10(CO)20(Br)4(CO3)4]2− (3) upon reaction with an excess of HBF4·Et2O. 1 is readily deprotonated by strong bases affording the previously known [H2Ru4(CO)12]2− (4). The reaction of 1 with [Cu(MeCN)4][BF4] affords [H3Ru4(CO)12(CuMeCN)] (7), whereas [H2Ru4(CO)12(CuBr)2]2− (8) is obtained from the reaction of 4 with [Cu(MeCN)4][BF4]/[NEt4]Br. All the compounds have been spectroscopically characterized, their molecular structures determined by single crystal X-ray diffraction (SC-XRD) and investigated using DFT methods in selected cases in order to confirm the hydride positions and to study the relative stability of possible isomers.

The reaction of [HFe4(CO)12(IrCOD)]2− (1) with CO at ambient conditions afforded [HFe4Ir(CO)14]2− (2), that, in turn, reacted with HBF4·Et2O affording [Fe4Ir(CO)15]− (3). 1 reacted with a slight excess of PPh3 resulting in a mixture of [HFe2Ir2(CO)10(PPh3)2]− (ca. 37%) (5) and [H2Fe3Ir(CO)10(PPh3)2]− (ca. 63%) (6). 5 and 6 co-crystallized as their [NEt4][H1+xFe2+xIr2-x(CO)10(PPh3)2]·CH2Cl2 (x = 0.63) salt. The reaction of 1 with Au(PPh3)Cl afforded [Fe3Ir(CO)12(AuPPh3)]2− (7). The related hydride [HFe3Ir(CO)12]2− (9) was prepared from the reaction of [HFe4(CO)12]3− (8) with [Ir(COE)2Cl]2 (COE = cyclo-octene). For sake of comparison, [HFe3Co(CO)12]2− (10) was obtained from 8 and Co2(CO)8. All the new clusters have been fully characterized via IR, 1H,13C{1H} and 31P{1H} NMR spectroscopies and their structures determined by means of single crystal X-ray crystallography. Possible isomers have been investigated by DFT calculations.

Chemical research in synthesizing metal nanoparticles has been a major topic in the last two decades, as nanoparticles can be of great interest in many fields such as biology, catalysis, and nanotechnology. However, as their chemical and physical properties are size-dependent, the reliable preparation of nanoparticles at a molecular level is highly desirable. Despite the remarkable advances in recent years in the preparation of thiolate- or p-MBA or PA-protected gold and silver nanoclusters (p-MBA = p-mercaptobenzoic acid; PA = phenylalkynyl), as well as the large palladium clusters protected by carbonyl and phosphine ligands that initially dominated the field, the synthesis of monodispersed and atomically precise nanoparticles still represents a great challenge for chemists.Carbonyl cluster compounds of high nuclearity have become more and more part of a niche chemistry, probably owing to their handling issues and expensive synthesis. However, even in large size, they are known at a molecular level and therefore can play a relevant role in understanding the structures of nanoparticles in general. For instance the icosahedral pattern, proper of large gold nanoparticles, is also found in some Au-Fe carbonyl cluster compounds.Rh clusters in general can also be employed as precursors in homo- and heterogeneous catalysis, and the possibility of doping them with other elements at the molecular level is an important additional feature. The fact that they can be obtained as large crystalline species, with dimensions of about 2 nm, allows one to place them not only in the nanometric regime, but also in the ultrafine-metal-nanoparticle category, which lately has been attracting growing attention. In fact, such small nanoparticles possess an even higher density of active catalytic sites than their larger (up to 100 nm) equivalents, hence enhancing atom efficiency and reducing the cost of precious-metal catalysts. Finally, the clusters' well-defined morphology could, in principle, contribute to expand the studies on the shape effects of nanocatalysts.In this Account, we want to provide the scientific community with some insights on the preparation of rhodium-containing carbonyl compounds of increasing nuclearity. Among them, we present the synthesis and molecular structures of two new heterometallic nanoclusters, namely, [Rh23Ge3(CO)(41)](5-) and [Rh16Au6(CO)(36)](6-), which have been obtained by reacting a rhodium-cluster precursor with Ge(II) and Au(III) salts. The growth of such clusters is induced by redox mechanisms, which allow going from mononuclear complexes up to clusters with over 20 metal atoms, thus entering the nanosized regime.

The reactions of [Pt6(CO)12]2- with CH(PPh2)2 (dppm), CH2═C(PPh2)2 (P^P), and Fe(C5H4PPh2)2 (dppf) proceed via nonredox substitution and result in the heteroleptic Chini-type clusters [Pt6(CO)10(dppm)]2-, [Pt6(CO)10(P^P)]2-, and [Pt6(CO)10(dppf)]2-, respectively. Conversely, the reactions of [Pt6(CO)12]2- with Ph2P(CH2)4PPh2 (dppb) and Ph2PC≡CPPh2 (dppa) can be described as redox fragmentation that afford the neutral complexes Pt(dppb)2, Pt2(CO)2(dppa)3, and Pt8(CO)6(PPh2)2(C≡CPPh2)2(dppa)2. The oxidation of [Pt6(CO)10(dppm)]2- results in its oligomerization to yield the larger heteroleptic Chini-type clusters [Pt12(CO)20(dppm)2]2-, [Pt18(CO)30(dppm)3]2-, and [Pt24(CO)40(dppm)4]2- (for the latter there is only IR spectroscopic evidence). All the clusters were characterized by means of IR and 31P NMR spectroscopies and electrospray ionization mass spectrometry. Moreover, the crystal structures of [NEt4]2[Pt6(CO)10(dppm)]·CH3CN, [NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·2dmf, [NEt4]2[Pt12(CO)20(dppm)2]·4dmf, [NEt4]2[Pt6(CO)10(dppf)]·2CH3CN, Pt2(CO)2(dppa)3·0.5CH3CN, Pt8(CO)6(PPh2)2(C≡CPPh2)2(dppa)2·2thf, and Pt(dppb)2 were determined by single-crystal diffraction (dmf = dimethylformamide; thf = tetrahydrofuran).

The reaction of Collman's reagent Na2[Fe(CO)4]·2thf with one equivalent of Au(NHC)Cl (NHC = IMes, IPr; IMes = C3N2H2(C6H2Me3)2; IPr = C3N2H2(C6H3iPr2)2) in dmso resulted in the [Fe(CO)4(AuNHC)]– (NHC = IMes, 1; IPr, 2) mono-anions. 1–2 further reacted with Au(NHC)Cl or Au(PPh3)Cl affording the neutral complexes Fe(CO)4(AuNHC)2 (NHC = IMes, 3; IPr, 4), Fe(CO)4(AuIMes)(AuIPr) (5) and Fe(CO)4(AuNHC)(AuPPh3) (NHC = IMes, 6; IPr, 7). 1–7 have been spectroscopically characterized by IR, 1H, 13C1H and 31P1H NMR techniques. Moreover, the molecular structures of 1, 2, 4, 6 and 7 have been determined through single-crystal X-ray diffraction as their [NMe4][Fe(CO)4(AuIMes)], [NEt4][Fe(CO)4(AuIMes)], [NEt4][Fe(CO)4(AuIPr)], Fe(CO)4(AuIPr)2·1.5toluene, Fe(CO)4(AuIPr)(AuPPh3), Fe(CO)4(AuIMes)(AuPPh3)·0.5CH2Cl2 salts and solvates. The nature of the bonds in 1 and 2 was elucidated on the basis of atoms-in molecules (AIM) analyses on the DFT-optimized structures and compared with the corresponding compounds 3 and 4. 1–7 contained strong Fe-CO, Fe-Au, Au-P and Au–NHC bonds as well as weak Au···Au interactions. The different stability and reactivity of IMes-derivatives vs. IPr-ones was rationalized on the basis of steric effects.

The reactions of [Pt6(CO)6(SnX2)2(SnX3)4]4– (X = Cl, 1; Br, 2) with an excess of HBF4·Et2O afforded the new [Pt12(CO)10(SnCl)2(SnCl2)4{Cl2Sn(μ-OH)SnCl2}2]2– (3) and [Pt7(CO)6(SnBr2)4{Br2Sn(μ-OH)SnBr2}{Br2Sn(μ-Br)SnBr2}]2– (4) heterometallic clusters. The molecular structures of 3 and 4 were determined by means of single crystal X-ray diffraction. The bonding within these bimetallic Pt–Sn clusters were investigated computationally by means of DFT methods and Atoms-In-Molecules analyses. 3 and 4 displayed a low valent Pt core stabilised by the interaction with CO and Sn(II) based ligands. The solid state structures of these clusters revealed the presence on H-bonds involving the OH-groups of the {X2Sn(μ-OH)SnX2}– ligands.

The reaction of [NEt4]2[Ni6(CO)12] in thf with 0.5 equiv of PCl3 affords the monophosphide [Ni11P(CO)18]3- that in turn further reacts with PCl3 resulting in the tetra-phosphide carbonyl cluster [HNi31P4(CO)39]5-. Alternatively, the latter can be obtained from the reaction of [NEt4]2[Ni6(CO)12] in thf with 0.8-0.9 equiv of PCl3. The [HNi31P4(CO)39]5- penta-anion is reversibly protonated by strong acids leading to the [H2Ni31P4(CO)39]4- tetra-anion, whereas deprotonation affords the [Ni31P4(CO)39]6- hexa-anion. The latter is reduced with Na/naphthalene yielding the [Ni31P4(CO)39]7- hepta-anion. In order to shed light on the polyhydride nature and redox behavior of these clusters, electrochemical and spectroelectrochemical studies were carried out on [Ni11P(CO)18]3-, [HNi31P4(CO)39]5-, and [H2Ni31P4(CO)39]4-. The reversible formation of the stable [Ni11P(CO)18]4- tetra-anion is demonstrated through the spectroelectrochemical investigation of [Ni11P(CO)18]3-. The redox changes of [HNi31P4(CO)39]5- show features of chemical reversibility and the vibrational spectra in the νCO region of the nine redox states of the cluster [HNi31P4(CO)39]n- (n = 3-11) are reported. The spectroelectrochemical investigation of [H2Ni31P4(CO)39]4- revealed the presence of three chemically reversible reduction processes, and the IR spectra of [H2Ni31P4(CO)39]n- (n = 4-7) have been recorded. The different spectroelectrochemical behavior of [HNi31P4(CO)39]5- and [H2Ni31P4(CO)39]4- support their formulations as polyhydrides. Unfortunately, all the attempts to directly confirm their poly hydrido nature by 1H NMR spectroscopy failed, as previously found for related large metal carbonyl clusters. Thus, the presence and number of hydride ligands have been based on the observed protonation/deprotonation reactions and the spectroelectrochemical experiments. The molecular structures of the new clusters have been determined by single-crystal X-ray analysis. These represent the first examples of structurally characterized molecular nickel carbonyl nanoclusters containing interstitial phosphide atoms.

The reaction of the [Rh7(CO)16]3− cluster anion with Ge2+ salts, in different stoichiometric ratios and under different atmospheres, leads to the formation of new heterometallic Rh–Ge clusters, representing the first known examples of Rh carbonyl compounds containing interstitial germanium atoms. More specifically, under N2 the reaction progressively affords the new [Rh13Ge(CO)25]3− and [Rh14Ge2(CO)30]2− clusters in good yields, with the Ge atoms located in cubic and square-anti-prismatic cavities, respectively. However, under a CO atmosphere, the [Rh13Ge(CO)25]3− derivative undergoes a significant structural and chemical rearrangement giving the new compound, [Rh12Ge(CO)27]4−, where Ge is hosted in an icosahedral metal cage. All species have been characterized by IR spectroscopy and ESI mass spectrometry, and their structures have been elucidated by single-crystal X-ray diffraction. Additionally, preliminary biological tests on the [Rh13Ge(CO)25]3− and [Rh14Ge2(CO)30]2− clusters show that they are cytotoxic to various cell lines.

The photodimerization of anthracene derivatives constitutes a model system for intermolecular [4 + 4] cycloadditions. In this paper we deal with the elusive 9-anthracene–carboxylic case and study the crystal state of the head-to-tail dimer, obtained by the reaction of the monomer in various solvents both in its unary and solvated forms, by X-ray diffraction and confocal Raman microscopy in the lattice phonon region. A number of solvates have been identified, and their structures have been solved and here presented. The 9-anthracene–carboxylic acid dimer appears to be an exemplary case of a molecular crystal easily prone to host solvent molecules in the interstices of the framework generated by homomolecular hydrogen bonds. Alternatively, the hydrogen bonds between solvent molecules and the carboxylic group may establish supramolecular structures of closely packed architectures. Raman microscopy has also allowed us to investigate the short-lived dimer, which is produced in the crystal-to-crystal photoreaction triggered by the irradiation of the monomer single crystal.

The reaction of [Rh7(CO)16]3– with BiCl3 under N2 and at room temperature results in the formation of the new heterometallic [Bi@Rh12(CO)27]3– cluster in high yields. Further controlled addition of BiCl3 leads first to the formation of the dimeric [(Bi@Rh12(CO)26)2Bi]5– and the closo-[Bi@Rh14(CO)27Bi2]3– species in low yields, and finally, to the [Bi@Rh17(CO)33Bi2]4– cluster. All clusters were spectroscopically characterized by IR and electrospray ionization mass spectrometry, and their molecular structures were fully determined by X-ray diffraction studies. Notably, they represent the first examples of Bi atoms interstitially lodged in metallic cages that, in this specific case, are all based on an icosahedral geometry. Moreover, [Bi@Rh14(CO)27Bi2]3– forms an exceptional network of infinite zigzag chains in the solid state, thanks to intermolecular Bi–Bi distances.

Invited for the cover of this issue is the group of Stefano Zacchini from Bologna University, Italy. The cover image shows the effect of aurophilic interactions on the assembly of a hexanuclear iron carbide tetraanionic cluster with two cationic gold–phosphine fragments.

The reactivity of [Rh7(CO)16]3- with SbCl3 has been deeply investigated with the aim of finding a new approach to prepare atomically precise metalloid clusters. In particular, by varying the stoichiometric ratios, the reaction atmosphere (carbon monoxide or nitrogen), the solvent, and by working at room temperature and low pressure, we were able to prepare two large carbonyl clusters of nanometer size, namely, [Rh20Sb3(CO)36]3- and [Rh21Sb2(CO)38]5-. A third large species composed of 28 metal atoms was isolated, but its exact formulation in terms of metal stoichiometry could not be incontrovertibly confirmed. We also adopted an alternative approach to synthesize nanoclusters, by decomposing the already known [Rh12Sb(CO)27]3- species with PPh3, willing to generate unsaturated fragments that could condense to larger species. This strategy resulted in the formation of the lower-nuclearity [Rh10Sb(CO)21PPh3]3- heteroleptic cluster instead. All three new compounds were characterized by IR spectroscopy, and their molecular structures were fully established by single-crystal X-ray diffraction studies. These showed a distinct propensity for such clusters to adopt an icosahedral-based geometry. Their characterization was completed by ESI-MS and NMR studies. The electronic properties of the high-yield [Rh21Sb2(CO)38]5- cluster were studied through cyclic voltammetry and in situ infrared spectroelectrochemistry, and the obtained results indicate a multivalent nature.

Miscellaneous 2-D molecular alloy clusters of the type [MxM′5-xFe4(CO)16]3- (M, M′ = Cu, Ag, Au; M ≠ M′) have been prepared through the reactions of [Cu3Fe3(CO)12]3-, [Ag4Fe4(CO)16]4- or [M5Fe4(CO)16]3- (M = Cu, Ag) with M′(I) salts (M′ = Cu, Ag, Au). Their formation involves a combination of oxidation, condensation, and substitution reactions. The total structures of several [MxM′5-xFe4(CO)16]3- clusters with different compositions have been determined by means of single crystal X-ray diffraction (SC-XRD) and their nature in solution elucidated by electron spray ionization mass spectrometry (ESI-MS) and IR and UV-visible spectroscopy. Substitutional and compositional disorder is present in the solid state structures, and ESI-MS analyses point out that mixtures of isostructural clusters differing by a few M/M′ coinage metals are present. SC-XRD studies indicate some site preferences of the coinage metals within the metal cores of these clusters, with Au preferentially in corner sites and Cu in the central site. DFT studies give theoretical support to the experimental structural evidence. The site preference is mainly dictated by the strength of the Fe-M bonds that decreases in the order Fe-Au > Fe-Ag > Fe-Cu, and the preferred structure is the one that maximizes the number of stronger Fe-M interactions. Overall, the molecular nature of these clusters allows their structures to be fully revealed with atomic precision, resulting in the elucidation of the bonding parameters that determine the distribution of the different metals within their metal cores.

The [Fe(CO)4{M(NHC)}]– (M = Cu, NHC = IMes, 1; M = Cu, NHC = IPr, 2; M = Ag, NHC = IMes, 3; M = Ag, NHC = IPr, 4; IMes = C3N2H2(C6H2Me3)2; IPr = C3N2H2(C6H3iPr2)2) mono-anions were obtained from the reaction of Na2[Fe(CO)4]·2thf with one equivalent of M(NHC)Cl (M = Cu, Ag; NHC = IMes, IPr) in dmso. Furthermore, the reaction of Na2[Fe(CO)4]·2thf with two equivalents of M(NHC)Cl in thf afforded the neutral compounds Fe(CO)4{M(NHC)}2 (M = Cu, NHC = IMes, 11; M = Cu, NHC = IPr, 12; M = Ag, NHC = IMes, 13; M = Ag, NHC = IPr, 14). 2 and 4 further reacted with one equivalent of M(IPr)Cl (M = Cu, Ag, Au) resulting in the trimetallic clusters Fe(CO)4{Cu(IPr)}{Ag(IPr)} (18), Fe(CO)4{Cu(IPr)}{Au(IPr)} (19), and Fe(CO)4{Ag(IPr)}{Au(IPr)} (20). 1-4, 11-14 and 18-20 have been spectroscopically characterized by IR, 1H and13C{1H} NMR techniques. The molecular structures of 2, 12, 18, 19 and 20 have been determined through single crystal X-ray diffraction. The structure, bonding and stability of the copper and silver IMes derivatives were compared to the related Fe-Au clusters previously reported on the basis of theoretical calculations. Stability of the Fe-M bonds decreases in the order Au > Cu > Ag, and the same trend was found for what concerns the M-IMes interactions. The decomposition products of 1-4, 11-14 and 18-20 have been studied allowing, among the others, the structural characterization of the new species [Fe2(CO)8{Ag(IPr)}]– (10) and Fe(CO)4(CH2IMes) (21).

The reaction of [Ni6(CO)12]2– as a [NBu4]+ salt in CH2Cl2 with 0.8 equiv of PCl3 afforded [Ni14P2(CO)22]2–. In contrast, the reactions of [Ni6(CO)12]2– as a [NEt4]+ salt with 0.4–0.5 equiv of POCl3 afforded [Ni22–xP2(CO)29–x]4– (x = 0.84) or [Ni39P3(CO)44]6– by using CH3CN and thf as a solvent, respectively. Moreover, by using 0.7–0.9 mol of POCl3 per mole of [NEt4]2[Ni6(CO)12] both in CH3CN and thf, [Ni23–xP2(CO)30–x]4– (x = 0.82) was obtained together with [Ni22P6(CO)30]2– as a side product. [Ni23–xP2(CO)30–x]4– (x = 0.82) and [Ni22P6(CO)30]2– were separated owing to their different solubility in organic solvents. All the new molecular nickel phosphide carbonyl nanoclusters were structurally characterized through single crystal X-ray diffraction (SC-XRD) as [NBu4]2[Ni14P2(CO)22] (two different polymorphs, P21/n and C2/c), [NEt4]4[Ni23–xP2(CO)30–x]·CH3COCH3·solv (x = 0.82), [NEt4]2[Ni22P6(CO)30]·2thf, [NEt4]4[Ni22–xP2(CO)29–x]·2CH3COCH3( x = 0.84) and [NEt4]6[Ni39P3(CO)44]·C6H14·solv. The metal cores’ sizes of these clusters range from 0.59 to 1.10 nm, and their overall dimensions including the CO ligands are 1.16–1.63 nm. In this respect, they are comparable to ultrasmall metal nanoparticles, molecular nanoclusters, or atomically precise metal nanoparticles. The environment of the P atoms within these molecular Ni–P–CO nanoclusters displays a rich diversity, that is, Ni5P pentagonal pyramid, Ni7P monocapped trigonal prism, Ni8P bicapped trigonal prism, Ni9P monocapped square antiprism, Ni10P sphenocorona, Ni10P bicapped square antiprism, and Ni12P icosahedron., Five new molecular nickel phosphide carbonyl clusters have been obtained displaying overall sizes in the range 1.16−1.63 nm and very diverse environments for the phosphide atoms.

The oxidation of [Ph3P(CH2)12PPh3][Pt15(CO)30] with CF3COOH in THF afforded [Ph3P(CH2)12PPh3][Pt18(CO)36] as a precipitate which was re-crystallized from dmf/iso-propanol. This salt self-assembles in the solid state adopting an unprecedented morphology which consists of infinite chains of [Pt9(CO)18]– units. The solid state structure of [Ph3P(CH2)12PPh3][Pt18(CO)36] may be viewed as a snapshot in which [Pt9(CO)18]– units are approaching and ready to exchange outer Pt3(CO)6 fragments. The reactions of Chini clusters with isonitriles proceed via redox-fragmentation, at difference with those involving phosphines that may occur both via non-redox substitution and redox fragmentation, depending on the experimental conditions. Thus, the reaction of [Pt6(CO)12]2– with CNXyl afforded Pt5(CNXyl)10, whereas Pt9(CNXyl)13(CO) was obtained from the reaction of [Pt15(CO)30]2– with CNXyl. These two new neutral clusters have been structurally characterized as their Pt5(CNXyl)10·2toluene and Pt9(CNXyl)13(CO)·solv solvates. DFT studies on the CO exchange of [Pt6(CO)12]2– suggest an associative interchange mechanism, which may be extended also to larger Chini clusters and the initial steps of their reactions with other soft nucleophiles.

The Co6C(CO)(12)(AuPPh3)(4) carbide carbonyl cluster was obtained from the reaction of [Co6C(CO)(15)](2-) with Au(PPh3)Cl. This new species was investigated by variable-temperature P-31 NMR spectroscopy, X-ray crystallography, and density functional theory methods. Three different solvates were characterized in the solid state, namely, Co6C(CO)(12)(AuPPh3)(4) (I), Co6C(CO)(12)(AuPPh3)(4).THF (II), and Co6C(CO)(12)(AuPPh3)(4).4THF (III), where THF = tetrahydrofuran. These are not merely different solvates of the same neutral cluster, but they contain three different isomers of Co6C(CO)(12)(AuPPh3)(4). The three isomers IIII possess the same octahedral [Co6C(CO)(1)2(]4) carbidocarbonyl core differently decorated by four [AuPPh3]+ fragments and showing a different Au(I)...Au(I) connectivity. Theoretical investigations suggest that the formation in the solid state of the three isomers during crystallization is governed by packing and van der Waals forces, as well as aurophilic and weak pi-pi and pi-H interactions. In addition, the closely related cluster Co6C(CO)(12)(PPh3)(AuPPh3)(2) was obtained from the reaction of [Co8C(CO)(18)](2) with Au(PPh3)Cl, and two of its solvates were crystallographically characterized, namely, Co6C(CO)(12)(PPh3)(AuPPh3)(2).toluene (IV) and Co6C(CO)(12)(PPh3)(AuPPh3)(2).0.stoluene (V). A significant, even if minor, effect of the cocrystallized solvent molecules on the structure of the cluster was observed also in this case.

The reaction of the Collman’s reagent Na2Fe(CO)4 with two equivalents of Au(NHC)Cl (NHC = IMes, IPr, IBu) in thf results in the bimetallic Fe(CO)4(AuNHC)2 (NHC = IMes, 2; IPr, 3; IBu, 4; IMes = C3N2H2(C6H2Me3)2; IPr = C3N2H2(C6H 3 i Pr2)2; IBu = C3N2H2(CMe3)2) clusters in good yields. Heating 2 in dmf at 100 °C results in the higher nuclearity cluster [Au3Fe2(CO)8(IMes)2]− (5). 2–5 have been fully characterized via IR, 1H and 13C NMR spectroscopies and their structures determined by means of single crystal X-ray crystallography. Gas-phase DFT calculations were carried out on 2–5 and the model compound cis-Fe(CO)4(AuIDM)2 (6) (IDM = C3N2H2Me2), in order to better understand the metal–metal and metal–ligand interactions in these compounds without the influence of packing forces.

The reaction of [Pt6(CO)6(SnCl2)2(SnCl3)4]4– (1) with CO under atmospheric pressure resulted in the new [Pt6(CO)8(SnCl2)(SnCl3)4]4– (2) cluster by the addition of two CO ligands and the elimination of a stannylene SnCl2 group. In turn, 2 reacted with 2 equivalents of PPh3 under a CO atmosphere to afford [Pt6(CO)8(SnCl2)(SnCl3)2(PPh3)2]2– (3) by elimination of two stannyl [SnCl3]– ligands. Conversely, the reaction of 2 with 2 equivalents of PPh3 under a N2 atmosphere resulted in a species tentatively formulated as [Pt6(CO)5(SnCl2)2(SnCl3)2(PPh3)2]2– (4–5CO) on the basis of 13C NMR, 31P NMR spectroscopy and ESI-MS studies. Compounds 2–4 were spectroscopically characterized by IR spectroscopy and multinuclear (13C and 31P) variable-temperature NMR spectroscopy. The crystal structures of 2 and 3 were determined by means of single-crystal X-ray diffraction, and their bonding was computationally investigated by DFT calculations. The possible structure of 4–5CO was predicted by means of DFT methods.

The reaction of [Ni 10 (C 2 ) (CO) 16 ] 2– with CuCl in thf affords [Ni 45 C 10 (CO) 46 ] 6– as the major product. This represents the first deca-carbide carbonyl cluster and this is the highest number of C-atoms found in a molecular cluster. Besides, the new octa-carbide [HNi 42 C 8 (CO) 44 (CuCl)] 7– and the previously reported tetra-carbide [Ni 34+x C 4 (CO) 38+x ] 6– (x = 0,1) have been obtained as side-products. Whilst studying the reactions of miscellaneous Ni carbide clusters with Cu(I) salts in the search for a better synthesis of [HNi 42 C 8 (CO) 44 (CuCl)] 7– , the homoleptic [Ni 32+x C 6 (CO) 36+x ] 6– (x = 0–2) and the heteroleptic [Ni 38 C 6 (CO) 36 (MeCN) 6 (CuMeCN) 2x ] 2– clusters have been isolated in low yields. By analysing the Ni carbide clusters herein reported as well as those previously described in the literature, it results that they are built-up starting from four fundamental building blocks: octahedral Oh-Ni 6 C, trigonal prismatic TP-Ni 6 C, capped trigonal prismatic cTP-Ni 7 C and square anti-prismatic SA-Ni 8 C. These may be joined into larger Ni x C y metal-carbide frameworks by sharing vertices, edges or faces. Even though infinite combinations are possible, some Ni x C y motives are common to two or more clusters, envisioning a possible rationale behind their building-up.

Self-supporting membranes built entirely of carbon nanotubes have been prepared by wet methods and characterized by Raman spectroscopy. The membranes are used as supports for the electrodeposition of Pt nanoparticles without the use of additional additives and/or stabilizers. The Pt precursor is an ad hoc synthesized ammonium-ethylimidazolium chloroplatinate(IV) salt, [NH3(CH2)2MIM)][PtCl6]. The Pt complex was characterized using NMR spectroscopy, XRD, ESI-MS, and FTIR spectroscopy. The interaction between the Pt-carbon nanotubes nanocomposites and hydrogen is analyzed using electrochemical and quartz microbalance measurements under near-ambient conditions. The contribution of the Pt phase to the hydrogen adsorption on nanotube is found and explained by a kinetic model that takes into account a spillover event. Such a phenomenon may be exploited conveniently for catalysis and electrocatalysis applications in which the hybrid systems could act as a hydrogen transfer agent in specific hydrogenation reactions. Adsorption advantage: Self-supporting membranes of carbon nanotubes are prepared and used as supports for the electrodeposition of Pt nanoparticles by using an ad hoc synthetized ammonium-ethylimidazolium chloroplatinate(IV) salt as Pt precursor. The hydrogen adsorption on Pt-carbon nanotubes nanocomposites is studied experimentally by electrochemical and quartz microbalance measurements and explained by a kinetic model that takes into account a spillover event.

Syngas and Hydrogen productions from methane are industrially carried out at high temperatures (900 &deg, C). Nevertheless, low-temperature steam reforming can be an alternative for small-scale plants. In these conditions, the process can also be coupled with systems that increase the overall efficiency such as hydrogen purification with membranes, microreactors or enhanced reforming with CO2 capture. However, at low temperature, in order to get conversion values close to the equilibrium ones, very active catalysts are needed. For this purpose, the Rh4(CO)12 cluster was synthetized and deposited over Ce0.5Zr0.5O2 and ZrO2 supports, prepared by microemulsion, and tested in low-temperature steam methane reforming reactions under different conditions. The catalysts were active at 750 &deg, C at low Rh loadings (0.05%) and outperformed an analogous Rh-impregnated catalyst. At higher Rh concentrations (0.6%), the Rh cluster deposited on Ce0.5Zr0.5 oxide reached conversions close to the equilibrium values and good stability over long reaction time, demonstrating that active phases derived from Rh carbonyl clusters can be used to catalyze steam reforming reactions. Conversely, the same catalyst suffered from a fast deactivation at 500 &deg, C, likely related to the oxidation of the Rh phase due to the oxygen-mobility properties of Ce. Indeed, at 500 &deg, C the Rh-based ZrO2-supported catalyst was able to provide stable results with higher conversions. The effects of different pretreatments were also investigated: at 500 &deg, C, the catalysts subjected to thermal treatment, both under N2 and H2, proved to be more active than those without the H2 treatment. In general, this work highlights the possibility of using Rh carbonyl-cluster-derived supported catalysts in methane reforming reactions and, at low temperature, it showed deactivation phenomena related to the presence of reducible supports.

The new bimetallic [HCo15Pd9C3(CO)(38)](2-) tri-carbide carbonyl cluster has been obtained from the reaction of [H2Co20Pd16C4(CO)(48)](4-) with an excess of acid in CH2Cl2 solution. The mono-hydride di-anion can be reversibly protonated and deprotonated by means of acid-base reactions leading to closely related [H3-nCo15Pd9C3(CO)(38)](n-) (n = 0-3) clusters. The crystal structures of the three anionic and the neutral clusters have been determined as their H3Co15Pd9C3(CO)(38)center dot 2thf, [NEt4][H2Co15Pd9C3(CO)(38)]center dot 0.5C(6)H(14), [NMe3(CH2Ph)](2)[HCo15Pd9C3(CO)(38)]center dot C6H14 and [NEt4](3)[Co15Pd9C3(CO)(38)]center dot thf salts. They are composed of a Pd-9(mu(3)-CO)(2) core stabilised by three Co5C(CO)(12) organometallic fragments. The poly-hydride nature of these clusters has been indirectly inferred via chemical, electrochemical and magnetic measurements. Besides, cyclic voltammetry shows that the [H3-nCo15Pd9C3(CO)(38)](n-) (n = 1-3) anions are multivalent, since they undergo two or three reversible oxidations. SQUID measurements of [HCo15Pd9C3(CO)(38)](2-) indicate that this even electron cluster is paramagnetic with two unpaired electrons, giving further support to its hydride nature. Finally, structural studies show that the Pd-9 core of [H3-nCo15Pd9C3(CO)(38)](n-) (n = 0,1) is a tri-capped octahedron, which becomes a tri-capped trigonal prism in the more charged [H3-nCo15Pd9C3(CO)(38)](n-) (n = 2,3) anions. Such a significant structural rearrangement of the metal core of a large carbonyl cluster upon protonation-deprotonation reactions is unprecedented in cluster chemistry, and suggests that interstitial hydrides may have relevant stereochemical effects even in large carbonyl clusters.

The reaction of [Pt15(CO)30](2-) with increasing amounts of SnCl2 affords [Pt8(CO)10(SnCl2)4](2-) (2), [Pt10(CO)14{Cl2Sn(OH)SnCl2}2](2-) (5), [Pt6(CO)6(SnCl2)2(SnCl3)4](4-) (3), [Pt9(CO)8(SnCl2)3(SnCl3)2(Cl2SnOCOSnCl2)](4-) (4) and [Pt5(CO)5{Cl2Sn(OR)SnCl2}3](3-) (R = H, Me, Et, and (i)Pr) (1-R). 1-R and 2 have been previously described, whereas 3-5 are herein reported for the first time. The species 1-3 are the main products of the reaction under different experimental conditions, whereas 4 and 5 are by-products of the synthesis of 3 and 2, respectively. From a structural point of view, the clusters 1-5 all show a perfect segregation of the two metals, which are composed of a low valent Pt core decorated on the surface by Sn(II) fragments such as SnCl2, [SnCl3](-), [Cl2Sn(OH)SnCl2](-) and [Cl2SnOCOSnCl2](2-). These fragments behave as two electron donor ligands via each Sn-atom (and also the C-atom in the case of [Cl2SnOCOSnCl2](2-)). The [Cl2SnOCOSnCl2](2-) ligand is rather unique and may be viewed as a bis-stannyl-carboxylate, a carbon dioxide μ3:k(3)-C,O,O'-CO2 or a carbonite ion [CO2](2-) stabilized by coordination to metal atoms. Compounds 1-5 have been fully characterised via IR spectroscopy, X-ray crystallography and DFT calculations.

The state of art of the chemical, spectroscopic and structural characterization of platinum carbonyl clusters is reviewed. We begin by enlightening the fundamental contribution given to this chemistry of two great scientists: Paolo Chini and Larry Dahl, two without equal maestros of science and life. We then focus the main body of this review on the challenge represented by studying molecular ions already belonging to the nano regime by size almost 50 years ago, and the challenges their chemistry continues to present also nowadays. In detail, the possible reasons which enable the [Pt-3n (CO)(6n) ](2-) oligomers to grow up to n = 10, and why the oligomers with n > 5 may self-assemble in infinite molecular conductor wires are suggested. The interplay between the CO/Pt-surface ratios and electronic effects in driving the platinum cluster from pseudo one- to tri-dimensional globular structures, often representing chunks of the fcc metal lattice or interpenetrated pentagonal prisms and icosahedra, is examined by means of two significant examples. The nanocapacitor behavior of most high-nuclearity carbonyl clusters is briefly recalled and is confirmed by most recent results. The size-induced transition of their metal kernels from insulator to semiconductor and the expected consequences of their eventual transition to a metallic state are also discussed. Finally, we conclude by commenting the present lack of Pt cluster interstitially lodging a main group element and not yet quantitatively-assessed aggregation phenomena in solution, perhaps peculiar of ionic salts of carbonyl clusters, which could make undetectable the NMR signal of any spin-active nuclei beyond a cluster nuclearity of ca. 20-25.

The reaction of [Fe4C(CO)(12){Cu(MeCN)}(2)] (1) with 3 equivalents of L-L (phen or Me(2)phen) affords [Cu(L-L)(2)][Fe4C(CO)(12){Cu(L-L)}] (L-L = phen, 2; Me(2)phen, 3) in good yields. These are protonated by strong acids resulting in [HFe4C(CO)(12){Cu(L-L)}] (L-L = phen, 4; Me(2)phen, 5). The reaction may be reversed with bases, resulting in the quaternary ammonium salts [NR4][Fe4C(CO)(12){Cu(phen)}] (6). 4 and 5 react with a slight excess of L-L resulting in the elimination of copper in the form of [Cu(L-L)(2)](+) and formation of the previously reported [HFe4C(CO)(12)](-) homometallic cluster. Conversely, the reaction of 1 with a monodentate N-ligand such as quinoline, even if used in large excess, results in the substitution product [Fe4C(CO)(12){Cu(quinoline)}(2)] (8), which is then transformed into [Cu(Me(2)phen)(2)] [Fe4C(CO)(12){Cu(quinoline)}] (9) after reaction with Me(2)phen. By using the anionic cluster [Fe5C(CO)(14){Cu(MeCN)}](-) instead of the neutral 1, only substitution has been observed by using both phen and quinoline, resulting in [Fe5C(CO)(14){Cu(phen)}](-) (10) and [Fe5C(CO)(14){Cu(quinoline)}](-) (11), respectively. Finally, the reaction of 1 with [Ru(tpy)(bpy)(N4C-C6H4-CN)]Cl affords crystals of [Fe4C(CO)(12)Cu2Cl{Ru(tpy)(bpy)(N4C-C6H4-CN)}] (12). All compounds 2-12 have been characterized by a combination of spectroscopic (IR, NMR) and crystallographic methods. All these clusters may be viewed as composed by a butterfly [Fe4C(CO)(12)](2-) core bonded to Cu(I) fragments and/or H+ ions.

The thermal decomposition of [Pt3n(CO)6n]2− (n = 2–10) Chini clusters results in the formation of globular molecular platinum carbonyl clusters, whose nature depends of the nuclearity of the parent cluster as well as the counter-ion and solvent employed. Among these, the new [Pt14+x(CO)18+x]4− (x = 0,1) and [Pt44(CO)45]n−, as well as the previously reported [Pt15(CO)19]4−, [Pt19(CO)22]4−, [Pt24(CO)30]2−, [Pt26(CO)32]2−, [Pt33(CO)38]2− and [Pt38(CO)44]2− have been identified. Oxidation of [Pt14+x(CO)18+x]4− (x = 0,1) with HBF4·Et2O affords [Pt26(CO)32]2−, which is further oxidized to the related [Pt26(CO)32]− mono-anion. Oxidation of [Pt19(CO)22]4−, under similar conditions, affords the unstable [Pt19(CO)22]2− di-anion, that rearranges during crystallization into the new [Pt36(CO)44]2−. Conversely, the reduction of [Pt19(CO)22]4− with Na/naphthalene results in the [Pt19(CO)22]5− penta-anion which, after work-up, is transformed into the new [Pt23(CO)27]2−. The new clusters [Pt14+x(CO)18+x]4− (x = 0,1) and [Pt26(CO)32]− have been fully characterized by means of single crystal X-ray diffractometry as their [NEt4]4[Pt14+x(CO)18+x]·MeCN (x = 0.18) and [NEt4][Pt26(CO)32]·2.12thf·0.38C6H14 salts. Conversely, in the case of the new [Pt23(CO)27]2−, [Pt36(CO)44]2− and [Pt44(CO)45]n−, due to the poor quality of their crystals, only a partial structural determination has been possible. [Pt14+x(CO)18+x]4− (x = 0,1) displays a distorted bcc structure, [Pt26(CO)32]− and [Pt23(CO)27]2− adopt hcp structures, [Pt36(CO)44]2− presents a distorted ccp metal core, whereas [Pt44(CO)45]n− possesses a twinned hcp/ccp ABCBA structure. The structures of the metal cores of these clusters is compared to previously reported globular platinum carbonyl nanoclusters (“platinum browns”).

In this review, the authors describe the role of gold in the chemistry of transition metal carbonyl clusters, a field that has been very active over the past fifty years. Both homo- and heteroleptic Au-containing species of metal carbonyl clusters, fully characterized by X-ray analysis, are discussed across three categories: those which are surface decorated by Au(I) fragments, cluster units connected by naked Au(I) atoms, and Au core–shell species with metallic gold structures embedded in the cluster frameworks.

In this microreview, the authors summarize the reactions of [Pt3n(CO)6n]2-(n = 1-10) Chini clusters aimed at their functionalization, modification and transformation. The results are organized on the basis of the fact that the final products do or do not retain the structure of the parent Chini clusters. The first category comprises the redox reactions of homoleptic Chini clusters, CO/phosphine substitution affording heteroleptic Chini-type clusters and the formation of Lewis acid-base adducts by capping the external Pt3-triangular faces with Lewis acids. The second category consists of globular molecular platinum nanoclusters (platinum browns) obtained by thermal decomposition of Chini clusters, as well as surface decorated platinum carbonyl clusters, composed of a low valent Pt-CO core decorated by cationic metal fragments. The relevance of such species to molecular cluster chemistry and metal nanoclusters is outlined.

The reaction of [HFe4(CO)(12)](3) (1) with [Ir(COD)Cl](2) results in the formation of the bimetallic FeIr monohydride carbonyl cluster [HFe4(CO)(12)(IrCOD)](2) (2). This is quantitatively protonated by strong acids to the dihydride [H(2)Fe4(CO)(12)(IrCOD)]- (3). Further addition of acids to 3 results in the tetranuclear dihydride [H2Fe3(CO)(10)(IrCOD)]- (4) via formal oxidative elimination of a Fe(CO)(2) fragment. Compounds 24 have been fully characterized by means of H-1 VT NMR spectroscopy, X-ray crystallography, and DFT calculations. In 2 and 3 the Fe4Ir cluster core adopts a trigonal bipyramidal geometry, while the Fe3Ir core in 4 is tetrahedral. In addition, H-1 VT NMR studies indicate that 2 and 3 are fluxional in solution, whereas 4 is not.

Within the reinvestigation of Ni–Sb carbonyl cluster chemistry, we report here the synthesis and characterization of the new [Ni19Sb4(CO)26]4– cluster and the synthesis, structure, magnetic characterization and electrical resistivity of the viologen salts of the previously known [Ni13Sb2(CO)24]n– (n = 2, 3) anionic species. The crystal structures of [NEt4]4[Ni19Sb4(CO)26], [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 and [EtV]3[Ni13Sb2(CO)24]·1.5THF (EtV = 1,1′-diethyl-4,4′-bipyridilium cation, DMF = N,N-dimethylformamide, THF = tetrahydrofuran) are described. Notably, the unit cell of [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 involves a mixture of two [Ni13Sb2(CO)24]3– trianions and one [Ni13Sb2(CO)24]2– dianion, as it also contains eight [EtV]+· radical monocations, which are assembled in infinite stacks. In contrast, the unit cell of the [EtV]3[Ni13Sb2(CO)24]·1.5THF salt contains four [Ni13Sb2(CO)24]3– trianions along with twelve [EtV]+· radical monocations, four of which are arranged into two pairs of isolated dimers, whereas the other two sets of four form two infinite stacks that extend over the whole crystal. The charges of the miscellaneous ions have been assigned on the basis of electroneutrality and spectroscopic evidence. More specifically, the infrared spectra of [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14, both in the solid state and in solution, clearly indicate the presence of a 2:1 mixture of [Ni13Sb2(CO)24]3– and [Ni13Sb2(CO)24]2– anions. Resistivity measurements performed on pellets of powdered samples indicate that the [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 salt substantially behaves as an insulator. A study of the magnetic behaviour of [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 evidences pairing among the electrons of the EtV+· molecules, in agreement with DFT calculations, and the odd-electron clusters behave as paramagnetic centres of spin S = 1.

We studied the anisotropic charge transport properties of solution-grown organic single crystals based on a dipolar molecule 4HCB (4-hydroxy-cyanobenzene) by electrical transport measurements, current-voltage and space charge limited current (SCLC), and by X-ray diffraction analyses.Optical excitation differently affects the flow of charge carriers along the two main planar crystal axis, altering the charge transport anisotropy induced by the molecular π-orbitals stacking. We attribute this behaviour to the presence of an intrinsic molecular dipole and to its different orientation within the crystal lattice. The anisotropy of transport along the three crystallographic directions has been assessed by electrical characterization and correlated to the crystal molecular packing as determined by X-ray analyses.

The reaction of the [Ni6(CO)12]2− dianion with [Rh(COD)Cl]2 (COD = cyclooctadiene) in acetone affords a mixture of bimetallic Ni–Rh clusters, mainly consisting of the new [Ni7Rh3(CO)18]3− and [Ni8Rh(CO)18]3− trianions. A study of the reactivity of [Ni7Rh3(CO)18]3− led to isolation of the new [Ni3Rh3(CO)13]3− and [NiRh8(CO)19]2− anions. All these new bimetallic Ni–Rh carbonyl clusters have been isolated in the solid state as tetrasubstituted ammonium salts and have been characterised by elemental analysis, X-ray diffraction studies, ESI-MS and electrochemistry. The unit cell of the [NEt4]3[Ni7Rh3(CO)18] salt contains two orientationally-disordered ν2-tetrahedral [Ni7Rh3(CO)18]3− trianions with occupancy factors of 0.75 and 0.25. Besides, their inner Ni3Rh3 octahedral moieties show two cis sites purely occupied by Rh atoms, two trans sites purely occupied by Ni atoms and the remaining two cis sites are disordered Ni and Rh sites with respective occupancy fraction of 0.5. At difference from the parent [Ni7Rh3(CO)18]3−, the octahedral [Ni3Rh3(CO)13]3− displays an ordered distribution of Ni and Rh atoms in two staggered triangles. The [NiRh8(CO)19]2− dianion adopts an isomeric metal frame with respect to that of the [PtRh8(CO)19]2− congener. As a fallout of this work, new high-yield synthesis of the known [Ni6Rh3(CO)17]3− and [Ni6Rh5(CO)21]3−, as well as other currently-investigated bimetallic Ni–Rh clusters have been obtained.

The reaction of [Pt12(CO)24]2– with CH2═C(PPh2)2 (P∧P) results in the neutral tetrahedral cluster Pt4(CO)4(P∧P)2. This reacts with strong acids such as HBF4 to afford, first, the [HPt4(CO)4(P∧P)2]+ monohydride monocation and, then, the [H2Pt4(CO)4(P∧P)2]2+ dihydride dication. The three clusters have been fully characterized in solution by means of IR and 1H and 31P NMR spectroscopy. Both Pt4(CO)4(P∧P)2 and [H2Pt4(CO)4(P∧P)2]2+ are static in solution, whereas [HPt4(CO)4(P∧P)2]+ displays a fluxional behavior of the unique hydride ligand. In addition, the molecular structures of all these clusters have been fully determined in the solid state via single-crystal X-ray diffraction, showing that all of them possess the same 56-electron tetrahedral Pt4(CO)4(P∧P)2 core to which the hydride ligands are added stepwise.

This paper reports a detailed study of the oxidation and reduction reactions of simple nickel mono-carbide and mono-acetlyde carbonyl clusters. The reduction of [Ni 9 C(CO) 17 ] 2– with Na/naphtalene affords the new [Ni 12 C(CO) 18 ] 4– mono-carbide cluster. Under the same experimental conditions, [Ni 10 (C 2 )(CO) 16 ] 2– reacts with Na/naphtalene yielding a mixture of the previously reported [Ni 11 (C 2 )(CO) 15 ] 4– and [Ni 12 (C 2 )(CO) 16 ] 4– mono-acetylide tetra-anions. The oxidation reactions of both [Ni 9 C(CO) 17 ] 2– and [Ni 10 (C 2 )(CO) 16 ] 2– , carried out with miscellaneous reagents, e.g. , [C 7 H 7 ][BF 4 ], [Cp 2 Fe][PF 6 ], AgNO 3 , are more complicated and less selective, leading to mixtures of products, among which the previously reported [Ni 8 C(CO) 16 ] 2– , [Ni 16 (C 2 ) 2 (CO) 23 ] 4– , [Ni 38 C 6 (CO) 42 ] 6– and [Ni 32 C 6 (CO) 36 ] 6– species have been identified. Interestingly, oxidation of [Ni 10 (C 2 )(CO) 16 ] 2– with Pd(Et 2 S) 2 Cl 2 affords the new tetra-acetylide [Ni 22 (C 2 ) 4 (CO) 28 (Et 2 S)] 2– , even if in low yields. The new species [Ni 12 C(CO) 18 ] 4– and [Ni 22 (C 2 ) 4 (CO) 28 (Et 2 S)] 2– have been structurally characterized by means of single crystal X-ray diffraction. Electrochemical and spectroelectrochemical studies have been performed on [Ni 12 C(CO) 18 ] 4– . This compound can be electrochemically oxidized and reduced reversibly affording [Ni 12 C(CO) 18 ] 3– and [Ni 12 C(CO) 18 ] 5– , respectively. The same species can be obtained by chemical methods but, due to their limited stability during work-up, it has not been possible to isolate them.

none 6 no The reactions of [Pt3n(CO)6n]2- (n = 2-4) homoleptic Chini-type clusters with stoichiometric amounts of Ph2PCH2CH2PPh2 (dppe) result in the heteroleptic Chini-type clusters [Pt6(CO)10(dppe)]2-, [Pt9(CO)16(dppe)]2-, and [Pt12(CO)20(dppe)2]2-. Their formation is accompanied by slight amounts of neutral species such as Pt4(CO)4(dppe)2, Pt6(CO)6(dppe)3, and Pt(dppe)2. A similar behavior was observed with the chiral ligand R-Ph2PCH(Me)CH2PPh2 (R-dppp), and two isomers of [Pt9(CO)16(R-dppp)]2- were identified. All the new species were spectroscopically characterized by means of IR and 31P NMR, and their structures were determined by single-crystal X-ray diffraction. The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh3, as well as more rigid bidentate ligands, that is, CH2C(PPh2)2 (P^P), CH2(PPh2)2 (dppm), and o-C6H4(PPh2)2 (dppb). From a structural point of view, functionalization of anionic platinum Chini clusters preserves their triangular Pt3 units, whereas the overall trigonal prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such transformations may be just local deformations, as found in [Pt9(CO)16(dppe)]2-, [Pt9(CO)16(R-dppp)]2-, [Pt12(CO)22(PPh3)2]2-, and [Pt9(CO)16(PPh3)2]2-; an inversion of the cage from trigonal prismatic to octahedral, as observed in [Pt6(CO)10(dppe)]2- and [Pt6(CO)10(PPh3)2]2-; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt-Pt contact as found in [Pt12(CO)20(dppe)2]2-. Cesari, Cristiana; Ciabatti, Iacopo; Femoni, Cristina; Iapalucci, Maria Carmela; Mancini, Federica; Zacchini, Stefano Cesari, Cristiana; Ciabatti, Iacopo; Femoni, Cristina; Iapalucci, Maria Carmela; Mancini, Federica; Zacchini, Stefano

The reactions of anionic platinum carbonyl Chini clusters [Pt3n(CO)6n](2-) [n = 2 (1), 3 (2), 4 (3)] with Ag(IPr)Cl [IPr = C3N2H2(C6H3(i)Pr2)2] afford the neutral acid-base Lewis adducts [Pt9(CO)18(AgIPr)2] (4) and [Pt6(CO)12(AgIPr)2] (5). These are thermally transformed into the homometallic heteroleptic neutral cluster [Pt3(CO)4(IPr)2] (6). Alternatively, 6 can be obtained from the reactions of 1-3 with an excess of the free IPr carbene ligand. The formation of 6 is sometimes accompanied by trace amounts of [Pt4(CO)4(IPr)3] (7). The reaction of 6 with free IPr affords the closely related [Pt3(CO)3(IPr)3] (8) heteroleptic cluster by substitution of the unique terminal CO ligand with a third IPr ligand. The reactions of 1-3 with Ag(IMes)Cl [IMes = C3N2H2(C6H2Me3)2] proceed differently from those involving Ag(IPr)Cl. Indeed, the only product isolated after workup is the bimetallic tetranuclear cluster [Pt3(CO)3(IMes)3(AgCl)] (9). 9 slowly reacts under a CO atmosphere, resulting in the pentanuclear [Pt5(CO)7(IMes)3] (10) complex. All of the new clusters 4-10 have been spectroscopically characterized and their molecular structures determined by X-ray crystallography. 4 and 5 retain the original trigonal-prismatic structures of the parent anionic Chini clusters, which are capped by two [Ag(IPr)](+) moieties. Conversely, 6-9 are based on a Pt3 triangular core decorated by CO and N-heterocyclic carbene ligands as well as Pt(CO) (in the case of 7) and AgCl (9) moieties. 10 displays an edge-bridged tetrahedral geometry.

The previously ill-characterized [HxRh22(CO)35]4−/5− carbonyl cluster has been obtained as a byproduct of the synthesis of [H3Rh13(CO)24]2− and effectively separated by metathesis of their sodium salts with [NEt4]Cl. Although the yields are modest and never exceed 10−15% (based on Rh), this procedure affords spectroscopically pure [H3Rh22(CO)35]5− anion. Formation of the latter in mixture with other Rh clusters was also observed by electrospray ionization-mass spectrometry (ESI-MS) in the oxidation of [H2Rh13(CO)24]3− with Cu2+ salts. The recovery of further amounts of [H3Rh22(CO)35]5− was hampered by too similar solubility of the salts composing the mixture. Conversely, the reaction in CH3CN of [H2Rh13(CO)24]3− with [Cu(MeCN)4]+[BF4]− leads to the [H2Rh13(CO)24{Cu(MeCN)}2]− bimetallic cluster. The X-ray crystal structures of [H4Rh22(CO)35]4−, [H3Rh22(CO)35]5−, and [H2Rh13(CO)24{Cu(MeCN)}2]− are reported. From a formal point of view, the metal frame of the former two species can be derived by interpenetra...

The new [Pt13(CO)12{Cd5(μ-Br)5Br2(dmf)3}2]2− and [Pt19(CO)17{Cd5(μ-Br)5Br3(Me2CO)2}{Cd5(μ-Br)5Br(Me2CO)4}]2− clusters have been obtained in good yields by reaction of [Pt12(CO)24]2− with CdBr2·H2O in dmf at 90 °C and structurally characterized by X-ray diffraction. Their structures consist of a Pt-centered Pt13(CO)12 icosahedron and a Pt19(CO)17 interpenetrated double icosahedron, respectively, decorated by two Cd5(μ-Br)5Br5−x(solvent)x rings. Their surface decoration may be related to that of Au−Fe−CO clusters as well as to the staple motifs stabilizing gold−thiolates nanoclusters. An oversimplified and unifying approach to interpret their electron count is suggested.

The reaction of [Ni 10 C 2 (CO) 15 ] 2- in thf with a large excess of CdCl 2 ·2.5H 2 O (8-15 equiv.) resulted in the formation of the new carbonyl octacarbide clusters [H 5-n Ni 36 C 8 (CO) 36 -(Cd 2 Cl 3 )] n- (n = 3-5), which undergo partial CO replacement to give [Ni 36-y C 8 (CO) 34-y (MeCN) 3 (Cd 2 Cl 3 )] 3- (y = 0-2) after a prolonged time in MeCN. Treatment of the former with an excess of NaOH afforded the larger [H 7-n Ni 42+y C 8 (CO) 44+y -(CdCl)] n- (n = 6, 7 ; y = 0, 1) octacarbides. Their structures (as well as those of the analogous Br-containing clusters) have been fully elucidated by single-crystal X-ray analysis of their [Me 4 N] 5 [Ni 36 C 8 (CO) 36 (Cd 2 Cl 3 )]·(7-2y)MeCN·yC 6 H 14 (y = 0.40), [Me 4 N] 3 [Ni 36-y C 8 (CO) 34-y (MeCN) 3 (Cd 2 Cl 3 )]·5MeCN (y = 0.61), [Me 4 N] 7 [Ni 42+y C 8 (CO) 44+y (CdCl)]·(5-y)MeCN (y = 0.19) and [Me 4 N] 6 [HNi 42+y C 8 (CO) 44+y (CdBr)]·(6-y)MeCN (y = 0.19) salts, which feature highly distorted metal cages (due to the inclusion of several carbide atoms), and the presence of partially vacant capping Ni(CO) fragments. This aspect, together with the fact that all these species undergo several protonation-deprotonation equilibria in solution as well as reversible redox processes under electrochemical control, indicates that a detailed description of molecular species containing a few dozen metal atoms might be sometimes rather troublesome and non-trivial. A complete elucidation of these systems can be achieved only by combining structural, chemical, spectroscopic, electrochemical and spectroelectrochemical studies.

The reaction of [Ni 5 (CO) 12 ] 2- or [Ni 6 (CO) 12 ] 2- with GaCl 3 in dichloromethane under a nitrogen atmosphere affords a mixture of [Ni 12+x (μ 12 -Ga)(CO) 22+x ] 3- (x = 0-3) clusters. Short exposure of the above mixture to a carbon monoxide atmosphere leads to the green icosahedral [Ni 12 (μ 12 -Ga)(CO) 22 ] 3- trianion, which was isolated and characterized as its [NnBu 4 ] + salt. In contrast, crystallization of the above mixture in the presence of Ni(CO) 4 enabled isolation of a cocrystallized mixture of [Ni 14 (μ 12 -Ga)(CO) 24 ] 3- (70%) and [Ni 15 (μ 12 -Ga)(CO) 25 ] 3- (30 %). As inferable from its structure, the additional three Ni(CO) moieties condense onto interlayer faces of the icosahedron. Protonation of [Ni 12 (μ 12 -Ga)-(CO) 22 ] 3- affords the corresponding [HNi 12 (μ 12 -Ga)(CO) 22 ] 2- hydride derivative, which was isolated in a pure state and fully characterized. All of the above compounds conform to the cluster-borane analogy, by the inclusion principle, and none exhibits relevant redox behaviour.

The reaction of [Ni9C(CO)17]2– (1) with [Rh(cod)Cl]2 (2) results in the formation of the new hetero-bimetallic [Ni10Rh2C(CO)20]2– (3) and [Ni9Rh3C(CO)20]3– (4) clusters, which have been separated by differential solubility. Degradation of 3 under a carbon monoxide atmosphere leads to the formation of the first bis-acetylide Ni-Rh cluster, i.e. [Ni6Rh8(C2)2(CO)24]4– (5). These new compounds have been characterised by X-ray crystallography, elemental analysis, ESI-MS, IR and 13C NMR spectroscopy (on 13C-carbido-enriched samples). The 13C NMR spectra indicate that 3 exists as a mixture of two isomers in a 4:1 ratio, as also inferable from partial Ni/Rh disorder in the solid-state structure. More interestingly, coordination of Rh atoms to the interstitial carbide atom seems to be very effective in shortening its longitudinal relaxation time (T1) by ca. two orders of magnitude compared to homometallic Ni carbido clusters. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The new [{Co5C(CO)(12)}Au{Co(CO)(4)}](-), [1](-), cluster has been obtained from the reaction of [Co6C(CO)(15)](2)(-) with two equivalents of [AuCl4](-). [1](-) reacts with an excess of HBF4 resulting in the formation of [{Co5C(CO)(12)}(2)Au](-), [2](-). The new derivatives [Co5C(CO)(12)(AuPPh3)], 3, and [Co5C(CO)(11)(AuPPh3)(3)], 4, have been obtained by reacting [2](-) with two and four equivalents of [Au(PPh3)Cl], respectively. All the new species have been structurally characterised by means of X-ray crystallography as their [NEt4][1], [NEt4][2], [NMe3(CH2Ph)][2], 3 and 4 center dot thf center dot 0.5C(6)H(14) salts and solvates. [2](-) may be viewed as a homoleptic Au(I) complex containing two [Co5C(CO)(12)](-) clusters as ligands. Similarly, [1](-) and 3 are heteroleptic Au(I) complexes containing one [Co5C(CO)(12)](-) cluster ligand as well as [Co(CO)(4)](-) or PPh3. Conversely, 4 contains the [Co5C(CO)(11)](3)(-) cluster stabilized by three [AuPPh3](+) fragments. [1](-) and [2](-) have been investigated in solution by means of electrochemical and spectroelectrochemical methods, revealing a very rich redox propensity to form the closely related [1](n-) (n = 1-3) and [2](n-) (n = 0-3) species.