Redox Behavior of [H6-nNi38Pt6(CO)48]n- (n = 4−6) Anions:  A Series of Metal Carbonyl Clusters Displaying Electron-Sink Features

Angewandte Chemie Intl Edit

et al. 2000

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Recent collision-induced dissociation studies on the gasphase [Pd 3 (CO) 6 ] À cluster [1] supplement other experimental observations, [2±7] which seem to suggest the feasibility of homoleptic carbonylpalladium derivatives. Thus, although the measured average PdÀCO bond dissociation energy (ca. 134 kJ mol À1) is weaker than that measured for the [Pt 3 (CO) 6 ] À congener (ca. 173 kJ mol À1 ), its value does not seem, however, sufficient to rule out the possible existence of binary palladium carbonyl compound in solution, unless their formation is hindered by some competing reaction.[1] The belief that the preassembly of a Pd kernel of critical size could ultimately favor the synthesis of a binary palladium carbonyl compound in solution led us to tackle the synthesis of Ni ± Pd homoleptic carbonyl bimetallic clusters (HCBCs) 6 [2] were obtained in low yields (5 ± 10 %) from the filtered THF reaction solution upon layering with n-hexane. The structure of 1 [11] is shown in Figure 1; its metal skeleton is represented in Figure 2 (left) as deriving from condensation of two Ni 8 Pd 8 vertex-truncated n 3 -tetrahedra through their Ni 2 Pd 5 hexagonal faces, giving rise to a six-layer close-packed metal framework. Two Pd atoms are encapsulated in two Ni 2 Pd 10 twinned cubooctahedral moieties and the cluster surface solely comprises triangular faces with all possible combinations of the two metals. The forty carbonyl groups display most possible CO coordination modes. They comprise linear, and symmetrical edge-and face-bridging ligands, as well as unsymmetrical and semibridging carbonyl groups with sub-van-der-Waals PdÀC contacts of 2.3 ± 2.5 . Only nickel atoms bind terminal carbonyl groups. Both homo-and heterometallic edges are spanned by bridging CO groups. Notably, only the Pd 3 triangles of the miscellaneous Ni 3Àx Pd x

mentioning

confidence: 93%

Homoleptic Carbonyl Ni–Pd Clusters: Synthesis of [Ni ₁₆ Pd ₁₆ (CO) ₄₀ ] ⁴⁻ and [Ni ₂₆ Pd ₂₀ (CO) ₅₄ ] ⁶⁻ and Structural Characterization of [N n Bu ₄ ] <

Femoni¹,

Iapalucci²,

Angewandte Chemie Intl Edit

et al. 2000

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“…The present work originates from the recognition that high-nuclearity metal carbonyl clusters often behave as nanosized molecular capacitors, [6,17] as well as the observation that their electronic and chemical behaviour are modu- [ 25 ] nÀ (x = 0, 1, 2, 5). [18] As part of our efforts to develop more efficient molecular capacitors, we wished to test the effect of substituting the internal Pt atoms of [Ni 38 Pt 6 (CO) 48 ] 6À with Pd atoms, as well as the partial exchange of surface Ni with congener Pd or Pt atoms.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterisation of ν₃‐Octahedral [Ni₃₆Pd₈(CO)₄₈]⁶⁻ and [Ni₃₅Pt₉(CO)₄₈]⁶⁻ Clusters Displaying Unexpected Surface Segregation of Pt Atoms and Molecular and/or Crystal Substitutional Ni/Pd and Ni/Pt Disorder

Femoni¹,

Iapalucci²,

et al. 2004

Chemistry A European J

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The synthesis and structure, as well as the chemical and electrochemical characterisation of two new nu(3)-octahedral bimetallic clusters with the general [Ni(44-x)M(x)(CO)(48)](6-) (M = Pd, x = 8; M = Pt, x = 9) formula is reported. The [Ni(35)Pt(9)(CO)(48)](6-) cluster was obtained in reasonable yields (56 % based on Pt) by reaction of [Ni(6)(CO)(12)](2-) with 1.1 equivalents of Pt(II) complexes, in ethyl acetate or THF as the solvent. The [Ni(36)Pd(8)(CO)(48)](6-) cluster was obtained from the related reaction with Pd(II) salts in THF, and was isolated only in low yields (5-10 % based on Pd), mainly because of insufficient differential solubility of its salts. The unit cell of the [NBu(4)](6)[Ni(35)Pt(9)(CO)(48)] salt contains a substitutionally Ni-Pt disordered [Ni(24)(Ni(14-x)Pt(x))Pt(6)(CO)(48)](6-) (x = 3) hexaanion. A combination of crystal and molecular disorder is necessary to explain the disordering observed for the Ni/Pt sites. The unit cell of the corresponding [Ni(36)Pd(8)(CO)(48)](6-) salt contains two independent [Ni(30)(Ni(8-x)Pd(x))Pd(6)(CO)(48)](6-) (x = 2) hexaanions. The two display similar substitutional Ni-Pd disorder, which probably arises only from crystal disorder. The structure of [Ni(36)Pd(8)(CO)(48)](6-) establishes the first similarity between the chemistry of Ni-Pd and Ni-Pt carbonyl clusters. A comparison of the chemical and electrochemical properties of [Ni(35)Pt(9)(CO)(48)](6-) with those of the related [Ni(38)Pt(6)(CO)(48)](6-) cluster shows that surface colouring of the latter with Pt atoms decreases redox as well as protonation propensity of the cluster. In contrast, substitution of all internal Pt and two surface Ni with Pd atoms preserves the protonation behaviour and is only detrimental with respect to its redox aptitude. A qualitative rationalisation of the different surface-site selectivity of Pt and Pd, based on distinctive interplays of M--M and M--CO bond energies, is suggested.

“…Die Ni-umkleideten Palladium-Clusterkerne von 1 und 2 (Abbildung 3) haben in ihrer Struktur wenig ¾hnlichkeit mit den bis jetzt bekannten Ni-Pt-HCBCs [H 4Àn Ni 9 Pt 3 (CO) 21 ] nÀ (n 2 ± 4), [Ni 36 Pt 4 (CO) 45 ] 6À und [H 6Àn Ni 38 Pt 6 (CO) 48 ] nÀ (n 4 ± 6). [18] Die einzige ¾hnlichkeit besteht in den Metallatomen der äuûeren Ni 6 Pd 3 -Einheiten, die wie die entsprechenden Einheiten von [H 4Àn Ni 9 Pt 3 (CO) 21 ] nÀ angeordnet sind.…”

unclassified

“…[18] Die einzige ¾hnlichkeit besteht in den Metallatomen der äuûeren Ni 6 Pd 3 -Einheiten, die wie die entsprechenden Einheiten von [H 4Àn Ni 9 Pt 3 (CO) 21 ] nÀ angeordnet sind. Extended-Hückel(EH)-MO-Rechnungen an 1 und 2 mit dem Programm CACAO [19] ergeben klare Energielücken nach dem 360. bzw.…”

unclassified

See 1 more Smart Citation

Homoleptische Ni-Pd-Carbonylcluster: Synthese von [Ni16Pd16(CO)40]4− und [Ni26Pd20(CO)54]6− und strukturelle Charakterisierung von [NnBu4]4[Ni16Pd16(CO)40]

Femoni¹,

Iapalucci²,

et al. 2000

Angewandte Chemie

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Neuere Untersuchungen zur stoûinduzierten Fragmentierung des Clusters [Pd 3 (CO) 6 ] À in der Gasphase [1] weisen gemeinsam mit weiteren experimentellen Befunden [2±7] darauf hin, dass homoleptische Carbonylpalladium-Derivate zugänglich sein könnten. So ist die gemessene mittlere Pd-CO-Bindungsspaltungsenergie (ca. 134 kJ mol À1 ) zwar niedriger als die von [Pt 3 (CO) 6 ] À (ca. 173 kJ mol À1 ), doch scheint ihr Wert nicht groû genug, um die Existenz binärer Palladiumcarbonyle in Lösung auszuschlieûen, falls deren Bildung nicht durch eine Konkurrenzreaktion verhindert wird. [1] Da wir davon überzeugt waren, dass die Voraggregation eines Pd-Clusterkerns mit kritischer Gröûe die Synthese einer binären Palladiumcarbonylverbindung in Lösung erleichtern würde, nahmen wir die Synthese von Ni-Pd-haltigen homoleptischen Dimetallcarbonylclustern (homoleptic carbonyl bimetallic clusters, HCBCs) als potentielle Vorstufen in Angriff. Bis jetzt sind nur das verwandte phosphansubstituierte Derivat [Ni 9 Pd 33 (CO) 41 (PPh 3 ) 6 ] 4À [8] und das Trimetallderivat [Au 6 Ni 6 -(Pd 6Àx Ni x )Ni 20 (CO) 44 ] 6À [9] beschrieben worden. Unseres Wissens ist der einzige bislang in der Literatur erwähnte Ni-Pd-HCBC die unvollständig charakterisierte Spezies [Ni 30Àx Pd x -(CO) y ] 4À (x % 16, y % 36 ), die als Vorstufe für die Synthese des Riesenkomplexes [Pd 59 (CO) 32 (PMe 3 ) 21 ] eingesetzt wurde. [10] Wie sich bei der Untersuchung der Reaktion von [Ni 6 (CO) 12 ] 2À mit Pd II -Verbindungen in unterschiedlichen Molverhältnissen und Lösungsmitteln herausstellte, existiert ein breites Spektrum von Ni-Pd-HCBCs. Unsere hier beschriebenen ersten Ergebnisse umfassen zum einen die Synthese, die chemischen Eigenschaften und die vollständige Röntgenbeugungscharakterisierung des Tetraanions [Ni 16 Pd 16 -(CO) 40 ] 4À 1 und zum anderen vorläufige Ergebnisse zum damit eng verwandten Hexaanion [Ni 26 Pd 20 (CO) 54 ] 6À 2. Das Tetrabutylammoniumsalz von 1 schied sich direkt bei der Reaktion von [NnBu 4 ] 2 [Ni 6 (CO) 12 ] mit [Pd(SEt 2 ) 2 Cl 2 ] in THF in ca. 50 % Ausbeute (bezogen auf Pd) als mikrokristalliner, dunkler Niederschlag ab und wurde durch Extraktion mit Aceton und Ausfällung mit n-Hexan umkristallisiert. Kristalle von [NnBu 4 ] 6 [2] wurden in niedriger Ausbeute (5 ± 10 %) aus der filtrierten THF-Reaktionslösung