Structural chemistry of "defect" cyanometalate boxes: {Cs⊂[CpCo(CN)3]4[Cp*Ru]3} and {M⊂[Cp*Rh(CN)3]4[Cp*Ru]3} (M = NH4, Cs)

Matthew L. Kuhlman, Thomas B. Rauchfuss

Research output: Contribution to journalArticle

Abstract

A series of heptametallic cyanide cages are described; they represent soluble analogues of defect-containing cyanometalate solid-state polymers. Reaction of 0.75 equiv of [Cp*Ru(NCMe)3]PF6, Et 4N-[Cp*Rh(CN)3], and 0.25 equiv of CsOTf in MeCN solution produced {Cs⊂[Cp*Rh(CN)3] 4[Cp*Ru]3} (Cs⊂Rh4Ru3). 1H and 133Cs NMR measurements show that Cs⊂Rh 4Ru3 exists as a single Cs isomer. In contrast, {Cs⊂[CpCo(CN)3]4[Cp*Ru]3} (Cs⊂Co4Ru3), previously lacking crystallographic characterization, adopts both Cs isomers in solution. In situ ESI-MS studies on the synthesis of Cs⊂Rh4Ru3 revealed two Cs-containing intermediates, Cs⊂Rh2Ru2+ (1239 m/z) and Cs⊂Rh3Ru3+ (1791 m/z), which underscore the participation of Cs+ in the mechanism of cage formation. 133Cs NMR shifts for the cages correlated with the number of CN groups bound to Cs+: Cs⊂Co4Ru4+ (δ 1 vs δ 34 for CsOTf), Cs⊂Rh4Ru3 where Cs+ is surrounded by ten CN ligands (δ 91), Cs⊂Co 4Ru3, which consists of isomers with 11 and 10 π-bonded CNs (δ 42 and δ 89, respectively). Although {K⊂[Cp*Rh(CN)3]4[Cp*Ru]3} could not be prepared, {NH4⊂-[Cp*Rh(CN)3] 4[Cp*Ru]3} (NH4⊂Rh4Ru 3) forms readily by NH4+-template cage assembly. IR and NMR measurements indicate that NH4+ binding is weak and that the site symmetry is low. CsOTf quantitatively and rapidly converts NH4⊂Rh4Ru3 into Cs⊂Rh4Ru3, demonstrating the kinetic advantages of the M7 cages as ion receptors. Crystallographic characterization of CsCo4Ru3 revealed that it crystallizes in the C s-(exo)1(endo)2 isomer. In addition to the nine μ-CN ligands, two CNt ligands are π-bonded to C s+. M⊂Rh4Ru3 (M = NH 4, Cs) crystallizes as the second Cs isomer, that is, (exo)2(endo)1, wherein only one CNt ligand interacts with the included cation. The distorted framework of NH 4⊂Rh4Ru3 reflects the smaller ionic radius of NH4+. The protons of NH4+ were located crystallographically, allowing precise determination of the novel NH4⋯CN interaction. A competition experiment between calix[4]arene-bis(benzocrown-6) and NH4⊂Rh4Ru 3 reveals NH4⊂Rh4Ru3 has a higher affinity for cesium.

Original languageEnglish (US)
Pages (from-to)10084-10092
Number of pages9
JournalJournal of the American Chemical Society
Volume125
Issue number33
DOIs
StatePublished - Aug 20 2003

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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