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.

Molecular Nickel Phosphide Carbonyl Nanoclusters: Synthesis, Structure, and Electrochemistry of [Ni11P(CO)18]3- and [H6-nNi31P4(CO)39]n- (n = 4 and 5).

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.

Cluster Core Isomerism Induced by Crystal Packing Effects in the [HCo15Pd9C3(CO)38]2- Molecular Nanocluster.

This article describes a rare case of cluster core isomerism in a large molecular organometallic nanocluster. In particular, two isomers of the [HCo15Pd9C3(CO)38]2- nanocluster, referred as TP-Pd9 and Oh-Pd9, have been structurally characterized by single-crystal X-ray crystallography as their [NMe3(CH2Ph)]2[HCo15Pd9C3(CO)38]·CH2Cl2 (ca. 1:1 TP-Pd9 and Oh-Pd9 mixture), [NMe3(CH2Ph)]2[HCo15Pd9C3(CO)38]·2CH2Cl2 (mainly TP-Pd9), [NEt3(CH2Ph)]2[HCo15Pd9C3(CO)38]·CH2Cl2 (mainly TP-Pd9), [MePPh3]2[HCo15Pd9C3(CO)38]·2.5CH2Cl2 (mainly TP-Pd9), and [MePPh3]2[HCo15Pd9C3(CO)38] (Oh-Pd9) salts. The cluster core of TP-Pd9 is a tricapped trigonal prism, whereas this is a tricapped octahedron in Oh-Pd9. The presence in the solid state of the Oh-Pd9 or TP-Pd9 isomers depends on the cation employed and/or the number and type of co-crystallized solvent molecules. Often, mixtures of the two isomers, within the same single crystal or as mixtures of different crystals within the same crystallization batch, are obtained. Structural isomerism in organometallic nanoclusters is discussed and compared to that in Au-thiolate nanoclusters.

Reactions of Platinum Carbonyl Chini Clusters with Ag(NHC)Cl Complexes: Formation of Acid-Base Lewis Adducts and Heteroleptic Clusters.

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(C6H3iPr2)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.

Interstitial Bismuth Atoms in Icosahedral Rhodium Cages: Syntheses, Characterizations, and Molecular Structures of the [Bi@Rh12(CO)27]3-, [(Bi@Rh12(CO)26)2Bi]5-, [Bi@Rh14(CO)27Bi2]3-, and [Bi@Rh17(CO)33Bi2]4- Carbonyl Clusters.

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.

Heteroleptic Chini-Type Platinum Clusters: Synthesis and Characterization of Bis-Phospine Derivatives of [Pt3n(CO)6n]2- (n = 2-4).

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-.

Syntheses, Structures, and Electrochemistry of the Defective ccp [Pt33(CO)38](2-) and the bcc [Pt40(CO)40](6-) Molecular Nanoclusters.

The molecular [Pt33(CO)38](2-) nanocluster was obtained from the thermal decomposition of Na2[Pt15(CO)30] in methanol. The reaction of [Pt19(CO)22](4-) with acids (1-2 equiv) affords the unstable [Pt19(CO)22](3-) trianion, which evolves with time leading eventually to the [Pt40(CO)40](6-) hexa-anion. The total structures of both nanoclusters were determined via single-crystal X-ray diffraction. [Pt33(CO)38](2-) displays a defective ccp Pt33 core and shows that localized deformations occur in correspondence of atomic defects to "repair" them. In contrast, [Pt40(CO)40](6-) shows a bcc Pt40 core and represents the largest Pt cluster with a body-centered structure. The rich electrochemistry of the two high-nuclearity platinum carbonyl clusters was studied by cyclic voltammetry and electrochemical in situ Fourier transform infrared spectroscopy. The redox changes of [Pt33(CO)38](2-) show features of chemical reversibility and electrochemical quasi-reversibility, and the vibrational spectra in the CO stretching region of the nine redox forms of the cluster [Pt33(CO)38](n) (n = 0 to -4, -6 to -9) are reported. Almost all the redox processes exhibited by [Pt40(CO)40](6-) are chemically and electrochemically reversible, and the eight oxidation states of [Pt40(CO)40] from -4 to -11 were spectroscopically characterized. The effect of the more regular bcc Pt-carbonyl cluster structure of [Pt40(CO)40](6-) with respect to that of the defective ccp Pt33 core on the redox behavior is discussed.

Platinum carbonyl clusters stabilized by Sn(II)-based fragments: syntheses and structures of [Pt6(CO)6(SnCl2)2(SnCl3)4](4-), [Pt9(CO)8(SnCl2)3(SnCl3)2(Cl2SnOCOSnCl2)](4-) and [Pt10(CO)14{Cl2Sn(OH)SnCl2}2](2.).

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.

Peraurated nickel carbide carbonyl clusters: the cationic [Ni6(C)(CO)8(AuPPh3)8]2+ monocarbide and the [Ni12(C)(C2)(CO)17(AuPPh3)3]- anion containing one carbide and one acetylide unit.

Two new peraurated Ni-carbide carbonyl clusters have been prepared and structurally characterized, i.e. [Ni6(C)(CO)8(AuPPh3)8](2+) and [Ni12(C)(C2)(CO)17(AuPPh3)3](-). The latter is the first molecular cluster containing one carbide atom and one tightly bonded C2-unit. These display sub-van der Waals contacts suggesting the incipient formation of more extended C-C bonding.

Octahedral co-carbide carbonyl clusters decorated by [AuPPh3]⁺ fragments: synthesis, structural isomerism, and aurophilic interactions of Co6C(CO)12(AuPPh3)4.

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 (31)P 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 I-III possess the same octahedral [Co6C(CO)12](4-) carbido-carbonyl 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 π-π and π-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)2·0.5toluene (V). A significant, even if minor, effect of the cocrystallized solvent molecules on the structure of the cluster was observed also in this case.

Hydride migration from a triangular face to a tetrahedral cavity in tetranuclear iron carbonyl clusters upon coordination of [AuPPh(3)](+) fragments.

Metal hydrides are of fundamental importance in chemistry, both as solid-state materials and molecular compounds. The first low-valent molecular metal cluster containing an interstitial four-coordinate hydride in a tetrahedral site is decribed, which undergoes hydride migration from the surface to the tetrahedral cavity of the cluster upon coordination of a [AuPPh3 ](+) fragment. The [HFe4 (CO)12 (AuPPh3 )2 ](-) mono-anion, which contains a surface µ3 -H, was obtained from the reaction of [HFe4 (CO)12 ](3-) with two equivalents of [Au(PPh3 )Cl]. This is, in turn, transformed into the neutral [HFe4 (CO)12 (AuPPh3 )3 ] upon addition of a third [AuPPh3 ](+) fragment, with concomitant migration of the unique hydride from the surface of the cluster to its tetrahedral cavity. All of these species have been fully characterized in solution by means of IR and multinuclear NMR spectroscopy, and in the solid state by single-crystal X-ray diffractometry.

Homoleptic and heteroleptic Au(I) complexes containing the new [Co5C(CO)12](-) cluster as ligand.

The new [{Co5C(CO)12}Au{Co(CO)4}](-), , cluster has been obtained from the reaction of [Co6C(CO)15](2-) with two equivalents of [AuCl4](-). reacts with an excess of HBF4 resulting in the formation of [{Co5C(CO)12}2Au](-), . The new derivatives [Co5C(CO)12(AuPPh3)], , and [Co5C(CO)11(AuPPh3)3], , have been obtained by reacting 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][], [NEt4][], [NMe3(CH2Ph)][], and thf·0.5C6H14 salts and solvates. may be viewed as a homoleptic Au(i) complex containing two [Co5C(CO)12](-) clusters as ligands. Similarly, and are heteroleptic Au(i) complexes containing one [Co5C(CO)12](-) cluster ligand as well as [Co(CO)4](-) or PPh3. Conversely, contains the [Co5C(CO)11](3-) cluster stabilized by three [AuPPh3](+) fragments. and have been investigated in solution by means of electrochemical and spectroelectrochemical methods, revealing a very rich redox propensity to form the closely related (n = 1-3) and (n = 0-3) species.

The redox chemistry of [Co6C(CO)15](2-): a synthetic route to new co-carbide carbonyl clusters.

The oxidation and reduction reactions of [Co6C(CO)15](2-) have been studied in detail, leading to the isolation of several new Co-carbide carbonyl clusters. Thus, [Co6C(CO)15](2-) reacts in tetrahydrofuran (THF) with oxidants such as HBF4·Et2O and [Cp2Fe][PF6], resulting first in the formation of the previously reported [Co6C(CO)14](-); then, in CH2Cl2, the new dicarbide [Co11C2(CO)23](2-) is formed. The latter may be further oxidized, yielding the isostructural monoanion [Co11C2(CO)23](-), whereas its reduction with (cyclopentadienyl)2Co affords the unstable trianion [Co11C2(CO)23](3-), which decomposes during workup. Oxidation of [Co6C(CO)15](2-) in CH3CN with [C7H7][BF4] affords the same major products, and besides, the new monoacetylide [Co10(C2)(CO)21](2-) was obtained as side-product. Conversely, the reduction of [Co6C(CO)15](2-) in THF with increasing amounts of Na/naphthalene results in the following species: [Co6C(CO)13](2-), [Co11(C2)(CO)22](3-), [Co7C(CO)15](3-), [Co8C(CO)17](4-), [Co6C(CO)12](3-), and [Co(CO)4](-). The new [Co11C2(CO)23](-), [Co11C2(CO)23](2-), [Co10(C2)(CO)21](2-), [Co8C(CO)17](4-), [Co6C(CO)12](3-), and [Co7C(CO)15](3-) clusters were structurally characterized. Moreover, the paramagnetic species [Co11C2(CO)23](2-) and [Co6C(CO)12](3-) were investigated by means of electron paramagnetic resonance spectroscopy. Finally, electrochemical studies were performed on [Co11C2(CO)23](n-) (n = 1-3).

Structural rearrangements induced by acid-base reactions in metal carbonyl clusters: the case of [H(3-n)Co15Pd9C3(CO)38]n- (n = 0-3).

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 [H(3-n)Co15Pd9C3(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)38·2thf, [NEt4][H2Co15Pd9C3(CO)38]·0.5C6H14, [NMe3(CH2Ph)]2[HCo15Pd9C3(CO)38]·C6H14 and [NEt4]3[Co15Pd9C3(CO)38]·thf salts. They are composed of a Pd9(µ3-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 [H(3-n)Co15Pd9C3(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 Pd9 core of [H(3-n)Co15Pd9C3(CO)38](n-) (n = 0,1) is a tri-capped octahedron, which becomes a tri-capped trigonal prism in the more charged [H(3-n)Co15Pd9C3(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.

Intramolecular d10-d10 interactions in a Ni6C(CO)9(AuPPh3)4 bimetallic nickel-gold carbide carbonyl cluster.

The Ni6C(CO)9(AuPPh3)4 bimetallic carbide carbonyl cluster was obtained from the reaction of [Ni9C(CO)17](2-) with Au(PPh3)Cl. It contains a rare carbon-centered (distorted) Ni6C octahedral core decorated by four Au(PPh3) fragments. These are µ3-bonded to four contiguous Ni3-triangular faces and display weak intramolecular Au···Au d(10)-d(10) interactions. The cluster has been characterized in the solid state on two different solvato crystals, i.e., Ni6C(CO)9(AuPPh3)4·THF and Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14. The two solvates show some interesting differences concerning the weak Au···Au contacts. Density functional theory calculations have demonstrated that the presence of the two isomers is related to solid-state packing effects and not to the existence of two double minima in the potential energy surface. This, in turn, confirms that Au···Au d(10)-d(10) interactions are rather soft and thus influenced also by weak van der Waals forces because of the interaction of the cluster with the cocrystallized solvent molecules.

Selective synthesis of the [Ni36Co8C8(CO)48]6- octa-carbide carbonyl cluster by thermal decomposition of the [H2Ni22Co6C6(CO)36]4- hexa-carbide.

The thermal decomposition in thf solution of [H2Ni22Co6C6(CO)36](4-) results in the new [HNi36Co8C8(CO)48](5-) bimetallic Ni-Co octa-carbide, which can be converted into the closely related [H6-nNi36Co8C8(CO)48](n-) (n = 3-6) polyhydrides by means of acid-base reactions. The structure of the [Ni36Co8C8(CO)48](6-) hexa-anion has been established via X-ray crystallography, showing that the eight interstitial carbide atoms are lodged within different metal cages. Thus, two C-atoms are enclosed within regular square anti-prismatic Ni8C cages, four within irregular Ni8C square anti-prismatic cages, and the last two within mono-capped trigonal prismatic Ni5Co2C cages. The structure of [Ni36Co8C8(CO)48](6-) is non-compact and closely related to [Ni32C6(CO)38](6-) and [HNi38C6(CO)44](5-). [Ni36Co8C8(CO)48](6-) approaches the nanosize regime and the whole molecular ion has a diameter (measured from the outer oxygen atoms) of ca. 1.61 nm.

PPh3-derivatives of [Pt3n(CO)6n]2- (n = 2-6) Chini's clusters: syntheses, structures, and 31P NMR studies.

The reaction of the [Pt3n(CO)6n](2-) (n = 2-6) Chini's clusters with increasing amounts of PPh3 has been investigated in detail by combined FT-IR, (31)P{(1)H} NMR, and electrospray ionization-mass spectrometry (ESI-MS) studies, showing that up to three CO ligands are gradually substituted by PPh3, resulting in isonuclear phosphine-substituted anionic clusters of general formula [Pt3n(CO)(6n-x)(PPh3)(x)](2-) (n = 2-6; x = 1-3). Further addition of PPh3 results in the elimination of the neutral Pt3(CO)3(PPh3)3 species and formation of lower nuclearity anionic clusters. [Pt12(CO)22(PPh3)2](2-) and [Pt9(CO)16(PPh3)2](2-) have been structurally characterized, and they maintain the trigonal prismatic structures of the parent homoleptic clusters, with the two PPh3 ligands bonded to different external Pt3-triangles in relative cis-position. Conversely, the crystal structure of [Pt6(CO)10(PPh3)2](2-) shows that its metal cage is transformed from trigonal prismatic to trigonal antiprismatic after CO/PPh3 exchange.

Ni-Cu tetracarbide carbonyls with vacant Ni(CO) fragments as borderline compounds between molecular and quasi-molecular clusters.

The reaction of [Ni(9)C(CO)(17)](2-) with [Cu(CH(3)CN)(4)][BF(4)] (1.1-1.5 equiv.) afforded the first Ni-Cu carbide carbonyl cluster, i.e., [H(2)Ni(30)C(4)(CO)(34){Cu(CH(3)CN)}(2)](4-) ([H(2)1](4-)). This has been crystallised in a pure form with miscellaneous [NR(4)](+) (R = Me, Et) cations, as well as co-crystallised with [H(2)Ni(29)C(4)(CO)(33){Cu(CH(3)CN)}(2)](4-) ([H(2)2](4-)) which differs from [H(2)1](4-) by a missing Ni(CO) fragment. By increasing the [Cu(CH(3)CN)(4)](+)/[Ni(9)C(CO)(17)](2-) ratio to 1.7-1.8, the closely related [H(2)Ni(30)C(4)(CO)(35){Cu(CH(3)CN)}(2)](2-) ([H(2)3](2-)), [H(2)Ni(29)C(4)(CO)(34){Cu(CH(3)CN)}(2)](2-) ([H(2)4](2-)), and [H(2)Ni(29)C(4)(CO)(32)(CH(3)CN)(2){Cu(CH(3)CN)}(2)](2-) ([H(2)5](2-)) dianions have been obtained. Replacement of Cu-bonded CH(3)CN with p-NCC(6)H(4)CN afforded, after protonation of the tetra-anion, mixtures of [H(3)Ni(30)C(4)(CO)(34){Cu(NCC(6)H(4)CN)}(2)](3-) ([H(3)6](3-)) and [H(3)Ni(29)C(4)(CO)(33){Cu(NCC(6)H(4)CN)}(2)](3-) ([H(3)7](3-)). The species 1-7 display a common Ni(28)C(4)Cu(2) core and differ for the charge, the presence of additional Ni atoms, the number and nature of the ligands, even though they are obtained under similar experimental conditions and often in mixtures. Their nature in solution has been investigated via FT-IR, chemical and electrochemical methods. Electrochemical studies, besides confirming the poly-hydride nature of these clusters, show that they undergo different redox processes with features of chemical reversibility, and this might be taken as proof of the incipient metallisation of their metal cores.

Metal Segregation in Bimetallic CoPd Carbide Carbonyl Clusters: Synthesis, Structure, Reactivity and Electrochemistry of [H6-n Co20 Pd16 C4 (CO)48 ]n- (n=3-6).

Nanometric CoPd bimetallic [H6-n Co20 Pd16 C4 (CO)48 ]n- (n=3-6) tetracarbide carbonyl clusters have been prepared by redox condensation of [Co6 C(CO)15 ]2- with [PdCl2 (Et2 S)2 ]. The crystal structures of both the dihydride tetra-anion and monohydride penta-anion have been determined as their [NEt4 ]4 [H2 Co20 Pd16 C4 (CO)48 ]⋅4 CH3 COCH3 and [NMe3 (CH2 Ph)][NMe4 ]4 [HCo20 Pd16 C4 (CO)48 ]⋅5 CH3 COCH3 salts, respectively. The two species are isostructural and their structures display a perfect segregation of the two metals. They are composed of a cubic close-packed (ccp) Pd16 core stabilised on its surface by four {Co5 C(CO)12 } organometallic fragments. Their polyhydride nature has been corroborated by the study of their reactions with acids and bases, and confirmed by electrochemical studies. In addition, the reactions of [H2 Co20 Pd16 C4 (CO)48 ]4- with Na/naphthalene and PPh3 /CO allowed the isolation of other lower nuclearity homoleptic and heteroleptic clusters, that is, [H6-n Co16 Pd2 C3 (CO)28 ]n- (n=5, 6), [Co4 Pd2 C(CO)11 (PPh3 )2 ], [Co2 Pd5 C(CO)8 (PPh3 )5 ], and [Co4 Pd4 C2 (PPh3 )4 (CO)10 Cl]- . [H6-n Co16 Pd2 C3 (CO)28 ]n- (n=5, 6) represent the first homoleptic metal-carbonyl clusters containing three interstitial carbide atoms.