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

Abstract

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.

Redox Control of Light‐Induced Platinum‐Cluster‐to‐Iron Charge Transfer in a Bis(ferrocenylethynyl)‐Substituted Hexanuclear Platinum Derivative

“…Electron transfer from, to, or across the cluster‐containing spacer, triggered by external stimuli, would make these units promising candidates for the preparation of connector elements in nanoscale switchable molecular devices 11. Indeed, the utilization of carbonyl clusters as single‐electron tunneling transistors has been reported,12a and their employment as molecular capacitors12b is also under scrutiny. However, well‐documented examples of electron transfer in molecular frameworks containing cluster subunits are exceedingly rare; in all the above‐mentioned compounds the metal‐cluster spacers do not allow significant electronic communication between the ferrocene units.…”

Syntheses, structures and properties of primarily nanosized homo/heterometallic palladium CO/PR 3 -ligated clusters

“…Although such Pd 38 and Pd 44 clusters are (as yet) unknown as distinct structural entities, analogous metal-core clusters of the congeneric Ni/Pt elements have been prepared and structurally analysed; these include the vertex-truncated Pt 38 core in [Pt 38 (Femoni et al 2004b). The common vertex-truncated Pd 38 kernel of O h symmetry in the Pd 52 and Pd 66 clusters encapsulates six octahedrally arranged Pd atoms and possesses six {100} square Pd 4 faces and eight {111} centred hexagonal Pd 7 faces (figure 7b).…”

Ein oktaedrischer Rhodium‐Cluster mit sechs Phosphan‐ und zwölf Hydridliganden, dem zehn Elektronen fehlen

“…Aber auch ohne die hochgesteckten Erwartungen von damals bleibt sie ein fruchtbares Gebiet, und einige hervorragende Arbeiten sind seither ausgeführt worden. Vielkernige Cluster wie [Os 20 (CO) 40 ] 2− ,16 [Ni 35 Pt 9 (CO) 48 ] 6− ,17 [Pd 145 (CO) x (PEt 3 ) 30 ]18 und [Cu 146 Se 73 (PPh 3 ) 30 ]19 wurden hergestellt und kristallographisch charakterisiert – einige davon übertreffen die Größe vieler Kolloide. Es wurde über eine faszinierende Reihe von Ruthenium‐Palladium‐ und Ruthenium‐Platin‐Clustern berichtet, die durch Kondensation vorgefertigter Ruthenium‐Cluster mit der {M(P t Bu 3 ) 2 }‐Einheit (ebenfalls eine aktive Katalysator‐Vorstufe, allerdings für C‐C‐Kupplungen) zugänglich sind 20.…”