characterisation of selenoether macrocyclic complexes of Corn, Rhm and p: crystal structures of trans-[ CoBr,( [ 161 an&,)] BPh, and trms-[IrBr,( [ 16]aneSe4)]BPh, ([ 16]aneSe4 = 1,5,9,13-tetraselenac yclohexadecane)

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Treatment of NCSe(CH 2 ) 3 SeCN with o-C 6 H 4 (CH 2 Br) 2 in Na-NH 3 -tetrahydrofuran yielded L 2 (3H-1,4,5,7tetrahydro-2,6-benzodiselenonine) in greater than 80% yield. This cyclic diselenoether has been fully characterised spectroscopically and structurally. Reaction of [Cu(MeCN) 4 ]Y (Y = BF 4 or PF 6 ) or AgBF 4 with 2 molar equivalents of L 1 (1,5-diselenacyclooctane) or L 2 afforded the mononuclear species [M(L) 2 ]Y (M = Cu, Y = BF 4 or PF 6 ; M = Ag, Y = BF 4 ). These compounds have been characterised by IR and 1 H NMR spectroscopy, mass spectrometry and microanalysis. Crystal structure determinations on [Cu(L 2 ) 2 ]BF 4 , [Ag(L 1 ) 2 ]BF 4 and [Ag(L 2 ) 2 ]BF 4 confirmed the discrete molecular nature of these products, giving distorted tetrahedral cations in each case. These structures are compared to the structures of related species involving acyclic bidentate thio-, seleno-and telluroethers. The preparation of the tetraselenoether macrocyclic complex [Ag([16]aneSe 4 )]BF 4 ([16]aneSe 4 = 1,5,9,13tetraselenacyclohexadecane) has also been determined. Compounds L 1 and L 2 reacted with 2 molar equivalents of [AuCl(tht)] (tht = tetrahydrothiophene) to yield [(AuCl) 2 L 1 ] or [(AuCl) 2 L 2 ] respectively as white solids. These neutral compounds are thought to involve linear Se᎐Au᎐Cl fragments. Compound L 2 reacted with 1 molar equivalent of MCl 2 (M = Pd or Pt) in refluxing MeCN to give cis-[MCl 2 (L 2 )]. Unusual low-frequency coordination shifts [δ(free ligand) Ϫ δ(complex)] were revealed by 77 Se-{ 1 H} NMR spectroscopy in each case. This is in contrast to cis-[MCl 2 (L 1 )] which display high-frequency co-ordination shifts. The 195 Pt NMR spectroscopic data on cis-[PtCl 2 (L 2 )] are consistent with an Se 2 Cl 2 donor set at Pt II . The crystal structure of cis-[PdCl 2 (L 2 )] shows a distorted square-planar arrangement, with d(Pd᎐Se) slightly longer than in cis-[PdCl 2 (L 1 )].

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