Syntheses, structures and vibrational spectroscopy of some unusual silver(I) (pseudo-) halide/unidentate nitrogen base polymers

Abstract

The meagre (structurally defined) array of 1:2 silver(I) (pseudo-)halide:unidentate nitrogen base adducts is augmented by the single-crystal X-ray structural characterization of the 1:2 silver(I) thiocyanate:piperidine (‘pip’) adduct. It is of the one-dimensional ‘castellated polymer’ type previously recorded for the chloride: ⋯Ag(pip) 2(μ- SCN)Ag(pip) 2⋯ a single bridging atom ( S) linking successive silver atoms. By contrast, in its copper(I) counterpart, also a one-dimensional polymer, the thiocyanate bridges as end-bound SN-ambidentate: ⋯Cu SC NCu SC N⋯ A study of the 1:1 silver(I) bromide:quinoline (‘quin’) adduct is recorded, as the 0.25 quin solvate, isomorphous with its previous reported ‘saddle polymer’ chloride counterpart. Recrystallization of 1:1 silver(I) iodide:tris(2,4,6-trimethoxyphenyl)phosphine (‘tmpp’) mixtures from py and quinoline (‘quin’)/acetonitrile solutions has yielded crystalline materials which have also been characterized by X-ray studies. In both cases the products are salts, the cation in each being the linearly coordinated silver(I) species [Ag(tmpp) 2] +, while the anions are, respectively, the discrete [Ag 5I 7(py) 2] 2− species, based on the already known but unsolvated [Cu 5I 7] 2− discrete, and the [ Ag 5 I 7 ] ( ∞ | ∞ ) 2 - polymeric, arrays, and polymeric [ Ag 5 I 6 ( quin ) ] ( ∞ | ∞ ) - . The detailed stereochemistry of the [Ag(tmpp) 2] + cation is a remarkably constant feature of all structures, as is its tendency to close-pack in sheets normal to their P–Ag–P axes. The far-IR spectra of the above species and of several related complexes have been recorded and assigned. The vibrational modes of the single stranded polymeric AgX chains in [XAg(pip) 2] (∞|∞) (X = Cl, SCN) are discussed, and the assignments ν(AgX) = 155, 190 cm −1 (X = Cl) and 208 cm −1 (X = SCN) are made. The ν(AgX) and ν(AgN) modes in the cubane tetramers [XAg(pip)] 4 (X = Br, I) are assigned and discussed in relation to the assignments for the polymeric AgX:pip (1:2) complexes, and those for the polymeric [XAg(quin)] (∞|∞) (X = Cl, Br) compounds. The far-IR spectra of [Ag(tmpp) 2] 2[Ag 5I 7(py) 2] and its corresponding 2-methylpyridine complex show a single strong band at about 420 cm −1 which is assigned to the coordinated tmpp ligand in [Ag(tmpp) 2] +, and a partially resolved triplet at about 90, 110 and 140 cm −1 which is assigned to the ν(AgI) modes of the [Ag 5I 7L 2] 2− anion. An analysis of this pattern is given using a model which has been used previously to account for unexpectedly simple ν(CuI) spectra for oligomeric iodocuprate(I) species.