Peraurated ruthenium hydride carbonyl clusters: aurophilicity, isolobal analogy, structural isomerism, and fluxionality.

The stepwise addition of increasing amounts of Au(PPh3)Cl to [HRu4(CO)12]3- (1) results in the sequential formation of [HRu4(CO)12(AuPPh3)]2- (2), [HRu4(CO)12(AuPPh3)2]- (3), and HRu4(CO)12(AuPPh3)3 (4). Alternatively, 4 can be obtained upon addition of HBF4·Et2O (two mole equivalents) to 3. Further addition of acid to 3 (three mole equivalents) results in the formation of the tetra-aurated cluster Ru4(CO)12(AuPPh3)4 (5). Compounds 2-5 have been characterized by IR, 1H and 31P{1H} NMR spectroscopies. Moreover, the molecular structures of 3-5 have been determined by single crystal X-ray diffraction as [NEt4][3]·2CH2Cl2, 4-b·2CH2Cl2, 4-a, 5·0.5CH2Cl2·solv, and 5·solv crystalline solids. Two different isomers of 4, that is 4-a and 4-b, have been crystallographically characterized and their rapid interconversion in solution was studied by variable temperature 1H and 31P{1H} NMR spectroscopies. Weak aurophilic Au⋯Au contacts have been detected in the solid state structures of 3-5. Computational studies have been performed in order to elucidate bonding and isomerism, as well as to predict the possible structure of the elusive species 2.

Highly Reduced Ruthenium Carbide Carbonyl Clusters: Synthesis, Molecular Structure, Reactivity, Electrochemistry, and Computational Investigation of [Ru6C(CO)15]4.

The reaction of [Ru6C(CO)16]2- (1) with NaOH in DMSO resulted in the formation of a highly reduced [Ru6C(CO)15]4- (2), which was readily protonated by acids, such as HBF4·Et2O, to [HRu6C(CO)15]3- (3). Oxidation of 2 with [Cp2Fe][PF6] or [C7H7][BF4] in CH3CN resulted in [Ru6C(CO)15(CH3CN)]2- (5), which was quantitatively converted into 1 after exposure to CO atmosphere. The reaction of 2 with a mild methylating agent such as CH3,I afforded the purported [Ru6C(CO)14(COCH3)]3- (6). By employing a stronger reagent, that is, CF3SO3CH3, a mixture of [HRu6C(CO)16]- (4), [H3Ru6C(CO)15]- (7), and [Ru6C(CO)15(CH3CNCH3)]- (8) was obtained. The molecular structures of 2-5, 7, and 8 were determined by single-crystal X-ray diffraction as their [NEt4]4[2]·CH3CN, [NEt4]3[3], [NEt4][4], [NEt4]2[5], [NEt4][7], and [NEt4][8]·solv salts. The carbyne-carbide cluster 6 was partially characterized by IR spectroscopy and ESI-MS, and its structure was computationally predicted using DFT methods. The redox behavior of 2 and 3 was investigated by electrochemical and IR spectroelectrochemical methods. Computational studies were performed in order to unravel structural and thermodynamic aspects of these octahedral Ru-carbide carbonyl clusters displaying miscellaneous ligands and charges in comparison with related iron derivatives.

From M6 to M12, M19 and M38 molecular alloy Pt-Ni carbonyl nanoclusters: selective growth of atomically precise heterometallic nanoclusters.

Heterometallic Chini-type clusters [Pt6-xNix(CO)12]2- (x = 0-6) were obtained by reactions of [Pt6(CO)12]2- with Ni-clusters such as [Ni6(CO)12]2-, [Ni9(CO)18]2- and [H2Ni12(CO)21]2-, or from [Pt9(CO)18]2- and [Ni6(CO)12]2-. The Pt/Ni composition of [Pt6-xNix(CO)12]2- (x = 0-6) depended on the nature of the reagents employed and their stoichiometry. Reactions of [Pt9(CO)18]2- with [Ni9(CO)18]2- and [H2Ni12(CO)21]2-, as well as reactions of [Pt12(CO)24]2- with [Ni6(CO)12]2-, [Ni9(CO)18]2- and [H2Ni12(CO)21]2-, afforded [Pt9-xNix(CO)18]2- (x = 0-9) species. [Pt6-xNix(CO)12]2- (x = 1-5) were converted into [Pt12-xNix(CO)21]4- (x = 2-10) upon heating in CH3CN at 80 °C, with almost complete retention of the Pt/Ni composition. Reaction of [Pt12-xNix(CO)21]4- (x ≈ 8) with HBF4·Et2O afforded the [HPt14+xNi24-x(CO)44]5- (x ≈ 0.7) nanocluster. Finally, [Pt19-xNix(CO)22]4- (x = 2-6) could be obtained by heating [Pt9-xNix(CO)18]2- (x = 1-3) in CH3CN at 80 °C, or [Pt6-xNix(CO)12]2- (2-4) in DMSO at 130 °C. The molecular structures of these new alloy nanoclusters have been determined by single crystal X-ray diffraction. The site preference of Pt and Ni within their metal cages has been computationally investigated. The electrochemical and IR spectroelectrochemical behavior of [Pt19-xNix(CO)22]4- (x = 3.11) has been studied and compared to the isostructural homometallic nanocluster [Pt19(CO)22]4-.

2-D Molecular Alloy Ru-M (M = Cu, Ag, and Au) Carbonyl Clusters: Synthesis, Molecular Structure, Catalysis, and Computational Studies.

The reactions of [HRu3(CO)11]- (1) with M(I) (M = Cu, Ag, and Au) compounds such as [Cu(CH3CN)4][BF4], AgNO3, and Au(Et2S)Cl afford the 2-D molecular alloy clusters [CuRu6(CO)22]- (2), [AgRu6(CO)22]- (3), and [AuRu5(CO)19]- (4), respectively. The reactions of 2-4 with PPh3 result in mixtures of products, among which [Cu2Ru8(CO)26]2- (5), Ru4(CO)12(CuPPh3)4 (6), Ru4(CO)12(AgPPh3)4 (7), Ru(CO)3(PPh3)2 (8), and HRu3(OH)(CO)7(PPh3)3 (9) have been isolated and characterized. The molecular structures of 2-6 and 9 have been determined by single-crystal X-ray diffraction. The metal-metal bonding within 2-5 has been computationally investigated by density functional theory methods. In addition, the [NEt4]+ salts of 2-4 have been tested as catalyst precursors for transfer hydrogenation on the model substrate 4-fluoroacetophenone using iPrOH as a solvent and a hydrogen source.

Atomically Precise Platinum Carbonyl Nanoclusters: Synthesis, Total Structure, and Electrochemical Investigation of [Pt27(CO)31]4- Displaying a Defective Structure.

The molecular Pt nanocluster [Pt27(CO)31]4- (14-) was obtained by thermal decomposition of [Pt15(CO)30]2- in tetrahydrofuran under a H2 atmosphere. The reaction of 14- with increasing amounts of HBF4·Et2O afforded the previously reported [Pt26(CO)32]2- (32-) and [Pt26(CO)32]- (3-). The new nanocluster 14- was characterized by IR and UV-visible spectroscopy, single-crystal X-ray diffraction, direct-current superconducting quantum interference device magnetometry, cyclic voltammetry, IR spectroelectrochemistry (IR SEC), and electrochemical impedance spectroscopy. The cluster displays a cubic-close-packed Pt27 framework generated by the overlapping of four ABCA layers, composed of 3, 7, 11, and 6 atoms, respectively, that encapsulates a fully interstitial Pt4 tetrahedron. One Pt atom is missing within layer 3, and this defect (vacancy) generates local deformations within layers 2 and 3. These local deformations tend to repair the defect (missing atom) and increase the number of Pt-Pt bonding contacts, minimizing the total energy. The cluster 14- is perfectly diamagnetic and displays a rich electrochemical behavior. Indeed, six different oxidation states have been characterized by IR SEC, unraveling the series of 1n- (n = 3-8) isostructural nanoclusters. Computational studies have been carried out to further support the interpretation of the experimental data.

Inverted Ligand Field in a Pentanuclear Bow Tie Au/Fe Carbonyl Cluster.

Gold chemistry has experienced in the last decades exponential attention for a wide spectrum of chemical applications, but the +3 oxidation state, traditionally assigned to gold, remains somewhat questionable. Herein, we present a detailed analysis of the electronic structure of the pentanuclear bow tie Au/Fe carbonyl cluster [Au{η2-Fe2(CO)8}2]- together with its two one-electron reversible reductions. A new interpretation of the bonding pattern is provided with the help of inverted ligand field theory. The classical view of a central gold(III) interacting with two [Fe2(CO)8]2- units is replaced by Au(I), with a d10 gold configuration, with two interacting [Fe2(CO)8]- fragments. A d10 configuration for the gold center in the compound [Au{η2-Fe2(CO)8}2]- is confirmed by the LUMO orbital composition, which is mainly localized on the iron carbonyl fragments rather than on a d gold orbital, as expected for a d8 configuration. Upon one-electron stepwise reduction, the spectroelectrochemical measurements show a progressive red shift in the carbonyl stretching, in agreement with the increased population of the LUMO centered on the iron units. Such a trend is also confirmed by the X-ray structure of the direduced compound [Au{η1-Fe2(CO)8}{η2-Fe2(CO)6(µ-CO)2}]3-, featuring the cleavage of one Au-Fe bond.

Synthesis, molecular structure and fluxional behavior of the elusive [HRu4(CO)12]3- carbonyl anion.

The elusive mono-hydride tri-anion [HRu4(CO)12]3- (4) has been isolated and fully characterized for the first time. Cluster 4 can be obtained by the deprotonation of [H3Ru4(CO)12]- (2) with NaOH in DMSO. A more convenient synthesis is represented by the reaction of [HRu3(CO)11]- (6) with an excess of NaOH in DMSO. The molecular structure of 4 has been determined by single-crystal X-ray diffraction (SC-XRD) as the [NEt4]3[4] salt. It displays a tetrahedral structure of pseudo C3v symmetry with the unique hydride ligand capping a triangular Ru3 face. Variable temperature (VT) 1H and 13C{1H} NMR experiments indicate that 4 is fluxional in solution and reveal an equilibrium between the C3v isomer found in the solid state and a second isomer with Cs symmetry. Protonation-deprotonation reactions inter-converting H4Ru4(CO)12 (1), [H3Ru4(CO)12]- (2), [H2Ru4(CO)12]2- (3), [HRu4(CO)12]3- (4) and the purported [Ru4(CO)12]4- (5) have been monitored by IR and 1H NMR spectroscopy. Whilst attempting the optimization of the synthesis of 4, crystals of [NEt4]2[Ru3(CO)9(CO3)] ([NEt4]2[7]) were obtained. Anion 7 contains an unprecedented CO32- ion bonded to a zero-valent Ru3(CO)9 fragment. Finally, the reaction of 6 as the [N(PPh3)2]+ ([PPN]+) salt with NaOH in DMSO affords [Ru3(CO)9(NPPh3)]- (9) instead of 4. Computational DFT studies have been carried out in order to support experimental evidence and the location of the hydride ligands as well as to shed light on possible isomers.

Atomically Precise Ni-Pd Alloy Carbonyl Nanoclusters: Synthesis, Total Structure, Electrochemistry, Spectroelectrochemistry, and Electrochemical Impedance Spectroscopy.

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.

Heterometallic rhodium clusters as electron reservoirs: Chemical, electrochemical, and theoretical studies of the centered-icosahedral [Rh12E(CO)27]n- atomically precise carbonyl compounds.

In this paper, we present a comparative study of the redox properties of the icosahedral [Rh12E(CO)27]n- (n = 4 when E = Ge or Sn and n = 3 when E = Sb or Bi) family of clusters through in situ infrared spectroelectrochemistry experiments and density functional theory computational studies. These clusters show shared characteristics in terms of molecular structure, being all E-centered icosahedral species, and electron counting, possessing 170 valence electrons as predicted by the electron-counting rules, based on the cluster-borane analogy, for compounds with such metal geometry. However, in some cases, clusters of similar nuclearity, and beyond, may show multivalence behavior and may be stable with a different electron counting, at least on the time scale of the electrochemical analyses. The experimental results, confirmed by theoretical calculations, showed a remarkable electron-sponge behavior for [Rh12Ge(CO)27]4- (1), [Rh12Sb(CO)27]3- (3), and [Rh12Bi(CO)27]3- (4), with a cluster charge going from -2 to -6 for 1 and 3 and from -2 to -7 for cluster 4, making them examples of molecular electron reservoirs. The [Rh12Sn(CO)27]4- (2) derivative, conversely, presents a limited ability to exist in separable reduced cluster species, at least within the experimental conditions, while in the gas phase it appears to be stable both as a penta- and hexa-anion, therefore showing a similar redox activity as its congeners. As a fallout of those studies, during the preparation of [Rh12Sb(CO)27]3-, we were able to isolate a new species, namely, [Rh11Sb(CO)26]2-, which presents a Sb-centered nido-icosahedral metal structure possessing 158 cluster valence electrons, in perfect agreement with the polyhedral skeletal electron pair theory.

Metal carbonyl clusters of groups 8-10: synthesis and catalysis.

In this review article, we discuss advances in the chemistry of metal carbonyl clusters (MCCs) spanning the last three decades, with an emphasis on the more recent reports and those involving groups 8-10 elements. Synthetic methods have advanced and been refined, leading to higher-nuclearity clusters and a wider array of structures and nuclearities. Our understanding of the electronic structure in MCCs has advanced to a point where molecular chemistry tools and other advanced tools can probe their properties at a level of detail that surpasses that possible with other nanomaterials and solid-state materials. MCCs therefore advance our understanding of structure-property-reactivity correlations in other higher-nuclearity materials. With respect to catalysis, this article focuses only on homogeneous applications, but it includes both thermally and electrochemically driven catalysis. Applications in thermally driven catalysis have found success where the reaction conditions stabilise the compounds toward loss of CO. In more recent years, MCCs, which exhibit delocalised bonding and possess many electron-withdrawing CO ligands, have emerged as very stable and effective for reductive electrocatalysis reactions since reduction often strengthens M-C(O) bonds and since room-temperature reaction conditions are sufficient for driving the electrocatalysis.

Heterometallic Ni-Pt Chini-Type Carbonyl Clusters: An Example of Molecular Random Alloy Clusters.

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.

One-pot atmospheric pressure synthesis of [H3Ru4(CO)12].

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.

Polymerization Isomerism in Co-M (M = Cu, Ag, Au) Carbonyl Clusters: Synthesis, Structures and Computational Investigation.

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.

Synthesis, Structural Characterization, and DFT Investigations of [MxM'5-xFe4(CO)16]3- (M, M' = Cu, Ag, Au; M ≠ M') 2-D Molecular Alloy Clusters.

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.

Structural Diversity in Molecular Nickel Phosphide Carbonyl Nanoclusters.

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.

Redox active Ni-Pd carbonyl alloy nanoclusters: syntheses, molecular structures and electrochemistry of [Ni22-xPd20+x(CO)48]6- (x = 0.62), [Ni29-xPd6+x(CO)42]6- (x = 0.09) and [Ni29+xPd6-x(CO)42]6- (x = 0.27).

A redox active Ni-Pd alloy nanocluster [Ni22-xPd20+x(CO)48]6- (x = 0.62) ([1]6-) was obtained from the redox condensation of [NBu4]2[Ni6(CO)12] with 0.7-0.8 equivalents of Pd(Et2S)2Cl2 in CH2Cl2. Conversely, [Ni29-xPd6+x(CO)42]6- (x = 0.09) ([2]6-) and [Ni29+xPd6-x(CO)42]6- (x = 0.27) ([3]6-) were obtained by employing [NEt4]2[Ni6(CO)12] and 0.6-0.7 equivalents of Pd(Et2S)2Cl2 in CH3CN. The molecular structures of these high nuclearity Ni-Pd carbonyl clusters were determined by single-crystal X-ray diffraction (SC-XRD). [1]6- adopted an M40ccp structure comprising five close-packed ABCAB layers capped by two additional Ni atoms. Conversely, [2]6- and [3]6- displayed an hcp M35 metal core composed of three compact ABA layers. [1]6-, [2]6- and [3]6- showed nanometric sizes, with the maximum lengths of their metal cores being 1.3 nm ([1]6-) and 1.0 nm ([2]6- and [3]6-), which increased up to 1.9 and 1.5 nm, after including also the CO ligands. Ni-Pd distribution within their metal cores was achieved by avoiding terminal Pd-CO bonding and minimizing Pd-CO coordination. As a consequence, site preference and partial metal segregation were observed, as well as some substitutional and compositional disorders. Electrochemical and spectroelectrochemical studies revealed that [1]6- and [2]6- were redox active and displayed four and three stable oxidation states, respectively. Even though several redox active high nuclearity metal carbonyl clusters have been previously reported, the nanoclusters described herein represent the first examples of redox active Ni-Pd carbonyl alloy nanoclusters.

Thermal Growth of Au-Fe Heterometallic Carbonyl Clusters Containing N-Heterocyclic Carbene and Phosphine Ligands.

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.

Polymerization Isomerism in [{MFe(CO)4} n] n- (M = Cu, Ag, Au; n = 3, 4) Molecular Clusters Supported by Metallophilic Interactions.

Triangular clusters [{MFe(CO)4}3]3- (M = Cu, 4; Ag, 5; Au, 6) were selectively obtained by heating Fe(CO)4(MIMes)2 (M = Cu, 1; Ag, 2; Au, 3; IMes = C3N2H2(C6H2Me3)2). 1-3 were synthesized by reacting Na2[Fe(CO)4]·2thf with 2 equiv of M(IMes)Cl. As previously described, the direct reactions of Na2[Fe(CO)4]·2thf with one equivalent of M(I) salts resulted in the triangular cluster [{CuFe(CO)4}3]3- for Cu, whereas the square clusters [{MFe(CO)4}4]4- were formed for Ag and Au. Thus, depending on the synthetic protocol adopted, both the triangular [{MFe(CO)4}3]3- and square [{MFe(CO)4}4]4- polymerization isomers can be selectively obtained, at least for Ag and Au. Polymerization isomerism, that is two compounds having the same elemental compositions but different molecular weights, was investigated in [{MFe(CO)4} n] n- ( n = 3, 4; M = Cu, Ag, Au) by means of structural and theoretical methods and the role of metallophilic interactions was computationally studied by means of the atoms-in-molecules (AIM) approach.

Synthesis of [Pt12(CO)20(dppm)2]2- and [Pt18(CO)30(dppm)3]2- Heteroleptic Chini-type Platinum Clusters by the Oxidative Oligomerization of [Pt6(CO)12(dppm)]2.

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).

Water soluble derivatives of platinum carbonyl Chini clusters: synthesis, molecular structures and cytotoxicity of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- .

The reactions of [Pt3n(CO)6n]2- (n = 2-5) homoleptic Chini-type clusters with increasing amounts of 1,3,5-triaza-7-phosphaadamantane (PTA) result in the stepwise substitution of one terminal CO ligand per Pt3 triangular unit up to the formation of [Pt3n(CO)5n(PTA)n]2- (n = 2-5). Competition between the nonredox substitution with retention of the nuclearity and the redox fragmentation to afford lower nuclearity heteroleptic Chini-type clusters is observed as a function of the amount of PTA and the nuclearity of the starting cluster. Because of this, [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- are more conveniently obtained via the oxidation of [Pt9(CO)15(PTA)3]2-. All the new species were spectroscopically characterized, and the structures of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- were determined by single-crystal X-ray diffraction. These clusters may be viewed as heteroleptic Chini-type clusters composed of stacks of four and five Pt3(µ-CO)3(CO)2(PTA) units, respectively. The solubility in water of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- has been determined and their cytotoxicity towards human ovarian (A2780) cancer cells and their cisplatin-resistant strain (A2780cisR) has been evaluated.