Lewis-Base Adducts of Group 11 Metal(I) Compounds. Synthesis and Structural Characterization of Some Halopyridin/triphenylphosphinesilver(I) Complexes: Some Space Group Revisions for Parts LII-LIV

Abstract

Redetermination of the room-temperature crystal structures of mononuclear chloro- and bromo-pyridinebis ( triphenylphosphine )silver(I) (previously described in space group P2₁/m) and di-μ-iodo-bis [(pyridine)( triphenylphosphine )silver(I)](previously described in space group C2/m), consequent upon the availability of crystals of improved quality, has permitted the reassignment of space groups as P2₁/a (with doubled a axis) and C2/c respectively, by virtue of the facilitated detection of weak superlattice reflections. Crystals of [ Cl,BrAg ( py )(PPh₃)₂] are monoclinic, P2₁/a, a ≈ 19.6, b ≈ 20.0, c ≈ 9.1Ǻ, β ≈ 97.5°, Z = 4; the structures were refined to residuals of 0.034 and 0.040 for 2965 and 2315 'observed' reflections respectively. [(PPh₃)( py )AgI₂Ag( py )(PPh₃)] is monoclinic, C2/c, a 27.145(6), b 14.548(3), c 11.316(4)Ǻ, β 94.83(2)°, Z 4, refining to R 0.035 for 1892 'observed' reflections, and isomorphous with the [(PPh₃)( py )CuX₂Cu( py )(PPh₃)] family. In spite of this reassignment, the previous descriptions of the AgX /N/P cores of the species are essentially unchanged, the previous residuals of the misassigned space group determinations being comparable with the present; the only non- trivial change lies in the fact that the disordered phenyl rings of the earlier work are now fully ordered. It now seems certain that the 'second polymorph' of [(PPh₃)( py )CuBr₂Cu( py )(PPh₃)], recorded as being isomorphous with its C2/m silver iodide counterpart, is spurious and a consequence of the use of an inferior specimen.