Abstract
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.
Highlights
Redox condensation has been widely exploited in the field of molecular metal carbonyl clusters.[13−18] direct metal reduction and metal exchange have been mainly applied to Au nanoclusters
Thiolate protected alloy nanoclusters and, generally speaking, Au-based alloy nanoclusters have been largely investigated in recent years, as part of the great interest for atomically precise and ultrasmall Au nanoparticles.[19−27] Within this framework, we reported some years ago a few examples of molecular Au nanoclusters protected by Fe-carbonyl frag
The synthesis of several 2-D molecular alloy clusters of general formula [MxM′5−xFe4(CO)16]3− (M, M′ = Cu, Ag, Au; M ≠ M′; x = 0−5) has been reported. These have been fully characterized by means of electron spray ionization mass spectrometry (ESI-MS), IR, and UV−visible spectroscopies and their total structures determined through single crystal X-ray diffraction (SC-XRD)
Summary
In the recent years, alloying has attracted considerable interest in the field of molecular metal clusters and nanoclusters from both a fundamental and applicative point of view.[1−6] mixing different metals with atomic control may lead to nanomaterials with new physical or chemical properties.[7−10] Different methods may be used for the synthesis of alloy clusters, including direct reduction, redox condensation, and metal exchange.[11,12] Redox condensation has been widely exploited in the field of molecular metal carbonyl clusters.[13−18] direct metal reduction and metal exchange have been mainly applied to Au nanoclusters. Ag4Au4Fe4(CO)16(dppe)[36] and Cu2Au6Fe4(CO)16(dppe) (dppe = Ph2PCH2CH2PPh2)[37] represent examples of 2-D molecular alloy heteroleptic organomentallic clusters, which have been obtained by condensation of preformed anionic clusters with metal salts. Within this context, 2-D molecular clusters are molecular planar clusters, that is, molecular clusters whose metal atoms lie on the same plane (Figure 1 and Scheme 1). We report a systematic study on [MxM′5−xFe4(CO)16]3− (M, M′ = Cu, Ag, Au; M ≠ M′; x = 0−5) 2-D alloy molecular clusters obtained by a combination of oxidation, condensation, and substitution reactions Their total structures have been determined by means of single crystal X-ray diffraction (SC-XRD) methods. The relative stability of different isomers was rationalized on the basis of DFT calculations
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