No abstract

Reaction of [NBu4]2[Pt9(CO)18] with the soft Lewis acid CdCl2 gives the [Pt9(CO)18(micro3-CdCl2)2]2- adduct, which self-assembles upon crystallization into a 1-D [[Pt9(CO)18(micro3-CdCl2)2]2-]infinity polymer via the formation of chloride bridges.

The so-called "platinum carbonyl", which probably consists of [Pt 3n (CO) 6n ] 2À oligomers with an average n value of approximately 10, was reported several years ago. [1,2] To date only discrete [Pt 3n (CO) 6n ] 2À oligomers with n = 1-5 have been selectively synthesized and characterized. [2][3][4][5][6][7] 1D molecular metal wires, [8,9] and 1D and 2D superclusters [10,11] are interesting in themselves as low-dimensional molecular materials with possible applications in molecular electronics and nanolithography. [12][13][14] The recent improvement of the synthesis of "platinum carbonyl" [7] prompted a reinvestigation of the chemistry of the [Pt 3n (CO) (CO) 48 ] reveals a distribution of oligomers centered at n = 5, with peaks of lesser intensity at n = 4 and n = 6. The observed distribution is narrower than the bellshaped distribution of n = 3-10 oligomers, centered at n = 6 or 7, exhibited by "platinum carbonyl".[7] The absence of the expected molecular peak for the [Pt 24 (CO) 48 ] 2À ion and the observed distribution of oligomers with n = 4-6 is clearly due to fragmentation processes occurring during the ESI-MS analysis, because the IR spectrum of the injected solution does not show the characteristic carbonyl absorptions of oligomers with n = 4-6.[2]The nature of the [NBu 4 2À oligomer consists of a sequence of eight {Pt 3 (CO) 6 } units stacked with a clock-or anticlockwise twist of 3-268 between consecutive units. The twist probably allows the minimization of repulsive intra-and intermolecular nonbonding interactions between the carbonyl groups of consecutive units and of adjacent oligomers. This twist is also responsible for the Pt À Pt contacts between neighboring {Pt 3 (CO) 6 } units being longer than the distance between the Pt 3 planes of these units. The PtÀPt bond distances within the individual {Pt 3 (CO) 6 } units fall in the narrow range of 2.666(2)-2.679(2) . In contrast, the PtÀPt contacts between neighboring {Pt 3 (CO) 6 } units are spread over a wider range of 3.024(2)-3.307(2) . The shortest interplane distances occur between the inner {Pt 3 (CO) 6 } units. The interplane distances become longer towards the top and bottom of the stack, like in an accordion (Figure 1). The longest PtÀPt contacts between neighboring {Pt 3 (CO) 6 } units (3.292(2)-3.307(2) ) are those involving the top {Pt 3 (CO) 6 } unit, and these are deliberately not shown as bonds in Figure 1. The PtÀPt contacts and the interplane distances (3.21 ) between this unit and the {Pt 21 (CO) 42 } stacks above and below it are the same. Thus, the pseudo-1D [Pt 24 (CO) 48 ] 2À molecular ions are arranged in infinite chains composed of alternating

Carbonylation of Na2PtCl6.6H2O, as well as K2PtCl6, in water under a CO pressure of 900 mm Hg selectively and quantitatively affords [Pt3n(CO)6n]2- (n > 6) salts; conversely, their corresponding carbonylation at reduced CO pressure of 760-800 mm Hg leads to a convenient one-step synthesis of [Pt38(CO)44]2-.

A reinvestigation of the redox chemistry of [Rh7(CO)16]3- resulted in the finding of new alternative syntheses for a series of previously reported Rh-centered carbonyl clusters, i.e., [H4-nRh14(CO)25]n- (n = 3 and 4) and [Rh17(CO)30]3-, as well as new species such as a different isomer of [Rh15(CO)27]3-, the carbonyl-substituted [Rh15(CO)25(MeCN)2]3-, and the conjuncto [Rh17(CO)37]3- clusters. All of the above clusters are suggested to derive from oxidation of [Rh7(CO)16]3- with H+, arising from dissociation either of [M(H2O)n]2+ aquo complexes or nonoxidizing acids. The nature of the previously reported species has been confirmed by IR, electrospray ionization mass spectrometry, and complete X-ray diffraction studies. Only the molecular structures of the new clusters are reported in some details. The ready conversion of [Rh7(CO)16]3- in [HRh14(CO)25]3- upon oxidation has been confirmed by electrochemical techniques. In addition, electrochemical studies point out that the close-packed [H3Rh13(CO)24]2- dianion undergoes a reversible monoelectronic reduction followed by an irreversible reduction. The irreversibility of the second reduction is probably a consequence of H2 elimination from a purported [H3Rh13(CO)24]4- species. Conversely, the body-centered-cubic [HRh14(CO)25]3- and [Rh15(CO)27]3- trianions display several well-defined redox changes with features of electrochemical reversibility, even at low scan rate. The major conclusion of this work is that mild experimental conditions and a tailored oxidizing reagent may enable more selective conversion of [Rh7(CO)16]3- into a higher-nuclearity rhodium carbonyl cluster. It is also shown that isonuclear Rh clusters may display isomeric metal frameworks [i.e., [Rh15(CO)27]3-], as well as almost identical metal frames stabilized by a different number of carbonyl groups [i.e., [Rh15(CO)27]3- and [Rh15(CO)30]3-]. Other isonuclear Rh clusters stabilized by a different number of CO ligands more expectedly exhibit completely different metal geometries [i.e., [Rh17(CO)30]3- and [Rh17(CO)37]3-]. The first pair of isonuclear and isoskeletal clusters is particularly astonishing in that [Rh15(CO)30]3- features six valence electrons more than [Rh15(CO)27]3-. Finally, the electrochemical studies seem to suggest that interstitial Rh atoms are less effective than Ni and Pt interstitial atoms in promoting redox properties and inducing molecular capacitor behavior in carbonyl clusters.