Structures of two isomers of hexairidium hexadecacarbonyl

Abstract

a chair ~n f o r m a t i o n .~~ The results show that the HOMO orbital is primarily a *-type orbital centered on sulfur b and delocalized somewhat on sulfur a (Figure 3). The LUMO orbital is a mixture of the d+3 and d2 orbitals. The lowest energy transition (HOMO -L U M O ) is thus described as a S(a) -Ti charge-transfer transition. The photochemistry of the Cp2TiSS complex is essentially wavelength independent. To explain this observation, we must either propose that fast internal conversion to the lowest energy excited state occurs or the absorption bands in the 300-700-nm region are all of the same type (Le., S -Ti charge transfer). We favor the latter explanation because the Xa calculation predicts that several S -Ti CT bands will occur to lower (33) The techniques used in the SCF-Xa-SW calculation have been previously de~cribed.~) energy than the first Cp -Ti bands. Accordingly, we qualitatively assign all three absorption bands in the region 300-700 n m a s S -T i bands.Acknowledgment is made to the Procter and Gamble Co. for a University Exploratory Research G r a n t . A.E.B. thanks A merican Cyanamid for a fellowship. Ian Gould is thanked for his assistance with the flash photolysis experiments. Anthony Sclafani is acknowledged for experimental assistance.Abstract: Ir6(CO),, has been isolated in two different isomeric forms, both of which have been crystallographically characterized.The red isomer is isostructural with Rh,(CO)l,, with four face-bridging carbonyl groups. The black isomer, in contrast, has four edge-bridging carbonyl groups, each of them being asymmetrically bonded. For both isomers, a crystallographic 2-fold rotation axis passes through two of the iridium atoms. Crystallogra hic details: Red isomer of Ir6(co)]6, space group C2/c (monoclinic); a = 16.656 (2) A, b = 9.761 (1) A, c = 16.776 (2) 1, B = 118.09 ( I ) O , V = 2406 A', Z = 4; R = 3.4% for 1508 reflections. Black isomer of h6(co)]6, space group P2/c (monoclinic); a = 13.622 ( 5 ) A, b = 12.807 (4) A, c = 18.589 ( 5 ) A, 0 = 132.65 (2)O, V = 2385 A3, Z = 4; R = 5.1% for 1973 reflections.

An Unusual Carbonyl Chemical Shift in a Carbonylhexairidium Cluster: A Combined Solid‐State NMR and DFT Approach

“…[5] However, in solution they show very different behaviors. Indeed, Rh 6 (CO) 16 possesses an O h symmetry and its spectrum, reported by Heaton et al, [6] is characterized by two resonances, in a 3:1 ratio, at δ = 180.1 and at 231.5 ppm attributed to the terminal and bridging (µ 3 ) carbonyl ligands, respectively.…”

“…[Ir 6 (CO) 15 ] 2-shows 12 terminal and three edge-bridging CO ligands, [4] while Ir 6 (CO) 16 has been isolated in two different isomeric forms: a red and a black isomer, the latter being quite unstable. [5] Our aim is to elucidate and compare the particular spectroscopic properties of the [Ir 6 (CO) 15 ] 2-and Ir 6 (CO) 16 complexes, using a combined experimental-theoretical approach, employing solid-state NMR and DFT calculations of 13 C NMR chemical shifts. Within this paper the discussion of only the red isomer of Ir 6 (CO) 16 has been taken into account.…”

Supported Iridium Cluster Catalysts for Propene Hydrogenation: Identification by X-Ray Absorption Spectra Measured During Catalysis

“…16 ] (2.77 ); the former value was determined both by X-ray diffraction [10] and by EXAFS spectroscopy, [1] as was the latter. [19,20] The implication of the comparison is that the clusters in the presence of H 2 , propene, and mixtures of H 2 propene had a substantial number of coordinated ligands. However, theoretical calculations by density functional methods have shown that Ir 4 clusters supported on zeolite NaY have essentially this same distance when only a single carbon or hydrogen ligand is present in addition to the support.…”

The Decomposition of Hydrazine in the Gas Phase and over an Iridium Catalyst

“…Clusters from Ir 18 to Ir 39 on Ir(111) have been studied [50], finding a preference for planar hexagonal shapes. The Gates group has performed extensive experiments using carbonyl precursors such as Ir 4 (CO) 12 [51] and Ir 6 (CO) 16 [52], with review articles available [53,54]. Flow treatment by H 2 removes all carbonyls, leaving a bare Ir 4 or Ir 6 cluster on γ -alumina.…”