| Abstract
| - A general method for deconstructing cluster frameworks via heterometal substitution is demonstrated withapplication to the two-dimensional phase Re6Se8Cl2. Solid-state reactions intended to replace two of the ReIIIcenters in the parent compound with OsIVCl units indeed yield Re4Os2Se8Cl4. The crystal structure of this newphase reveals a less tightly connected two-dimensional framework, wherein face-capped octahedral [Re4Os2Se8]4+ cluster cores are linked through μ2-chloride bridges in one dimension and unsupported metal−seleniumbonds in the other. Use of CsCl as a standard dimensional reduction agent in conjunction with heterometalsubstitution affords Cs3Re5OsSe8Cl6 and Cs2Re4Os2Se8Cl6, soluble salts containing discrete molecular clusters.Reactions employing KCl and targeting a triosmium cluster further produce the soluble mixed-cluster salt K2[Re3Os3Se8Cl6][Re4Os2Se7Cl7]. FT-ICR mass spectra confirm the presence of [Re6-nOsnSe8Cl6](4-n)- (n = 1−3) clustersin solutions of these solids. Metathesis reactions supply (Bu4N)3[Re5OsSe8Cl6] and (Bu4N)2[Re4Os2Se8Cl6], whichthen react with PEt3 under forcing conditions to give [Re5OsSe8(PEt3)6]3+ and [Re4Os2Se8(PEt3)6]4+ in high yield.Analysis of the latter diosmium species by 31P NMR spectroscopy indicates a mixture of isomers, in which 55%of the clusters have the osmium atoms disposed trans to each other, while the remainder adopt the alternative cisconfiguration. Cyclic voltammetry measurements reveal a reversible one-electron reduction for [Re5OsSe8Cl6]3-and multiple one-electron reductions for the mono- and diosmium hexaphosphine clusters; in the latter case, thetrans isomer is observed to be more easily reduced than the cis isomer. Electronic structure calculations utilizingdensity functional theory show the trans isomer of [Re4Os2Se8Cl6]2- to be 4.5 kcal/mol more stable than the cisisomer, in approximate agreement with the observed ratio of reaction products. Moreover, the calculations exposesignificant differences in the contributions of rhenium and osmium to the frontier orbitals of the clusters, suggestingthe possibility of observing metal-selective reactivity. An initial example of such behavior is provided with thesynthesis of trans,trans-[Re4Os2Se8(PEt3)2Cl4], wherein PEt3 ligands preferentially bind the osmium centers.
- The substitution of OsIVCl units for ReIII centers is demonstrated as an effective means of dismantling the two-dimensional cluster framework of Re6Se8Cl2. Simultaneous incorporation of CsCl or KCl in the solid-state reactions generates a series of soluble phases containing [Re5OsSe8Cl6]3-, [Re4Os2Se8Cl6]2-, and [Re3Os3Se8Cl6]- clusters. The solution chemistry of these species is briefly explored, and metal-selective reactivity is established with isolation of the trans,trans-[Re4Os2Se8(PEt3)2Cl4] cluster depicted here.
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