title: Sodium congener of the classical lithium methylchromate dimer: synthetic, X-ray crystallographic, and magnetic studies of Me8Cr2[Na(OEt2)]4.
abstract: One of the milestone structures in the development of transition-metal complexes with metal-metal bonds of multiple bond order was the lithium methylchromate dimer Me(8)Cr(2)[Li(donor)](4) (donor = THF or Et(2)O). Using a simple salt metathesis reaction mixing this compound with sodium tert-butoxide, the sodium congener Me(8)Cr(2)[Na(OEt(2))](4) has been synthesized as a green crystalline compound and isolated in 51% yield. Its solid-state structure was determined by single-crystal X-ray diffraction. Exhibiting exact crystallographic C(4h) symmetry, this heavier alkali-metal chromate structure is also dimeric, formally comprising a (Me(8)Cr(4))(4-) tetranionic core with four peripheral Na(+) cations carrying supporting ether ligands. Its salient feature is the long Cr···Cr distance of 3.263(2) Å, which is remarkably elongated compared to that in the lithium THF-solvated congener [1.968(2) Å]. With respect to the methyl C atoms, the Cr coordination is distorted-square-planar. Each Na(+) interacts with four methyl C atoms, and there are also some short Na···H(C) contacts. Unlike for lithium chromate, no NMR spectroscopic data could be obtained for sodium chromate. The paramagnetic character of sodium chromate was confirmed by variable-temperature magnetization measurements, which indicated antiferromagnetic behavior.
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK.
authors.forename: Ross
authors.initials: R
authors.lastname: Campbell
authors.forename: Luca M
authors.initials: LM
authors.lastname: Carrella
authors.forename: William
authors.initials: W
authors.lastname: Clegg
authors.forename: Robert E
authors.initials: RE
authors.lastname: Mulvey
authors.forename: Eva
authors.initials: E
authors.lastname: Rentschler
authors.forename: Stuart D
authors.initials: SD
authors.lastname: Robertson
authors.forename: Luca
authors.initials: L
authors.lastname: Russo