Synthesis and Structural Systematics of Nitrogen Base Adducts of Group 2 Salts. I. Some Adducts of Group 2 Halides With Acetonitrile

Abstract

Recrystallization of anhydrous Group 2 halides from anhydrous acetonitrile has yielded, in a number of cases, adducts MX2.nMeCN suitable for characterization by room-temperature single-crystal X-ray studies, which revealed novel stereochemical types. Magnesium(II) bromide yields a trisolvate, ionic with disproportionated ligand arrays, as [Mg(NCMe)6][MgBr4] (1), an unusual combination of homoleptic cationic and anionic species. Crystals are triclinic, Pī , a 19.129(1), b l6.870(8), c 8.737(7) Ǻ,α 83.96(3), β 87.93(4), γ 65.24(2)°, Z=4 f.u .; R was 0.068 for N o 3181 'observed' (I > 3σ(I)) reflections. Mg-N are 2.12(2)-2.18(2) Ǻ, and Mg-Br are 2.452(7)-2.481(6) Ǻ. Calcium(II) bromide, by contrast, yields a disolvate , an infinite polymer, with the two MeCN ligands trans in a quasi-octahedral coordination sphere, and the polymer comprising a ... Ca(μ-Br)2Ca(μ-Br)2... linear array. Crystals of 1:2 CaBr2/MeCN (2) are orthorhombic, Pbam , a l4.252(3), b 8.539(2), c 4.2088(6) Ǻ, Z=2 f.u .; R 0.043 for N o 352. Ca-N is 2.46(1) Ǻ, and Ca-Br 2.8765(9) Ǻ. CaI2 and SrI2 yield pentasolvates as neutral, molecular species [( MeCN )5MX2] (3) and (4), with the halides trans in a pentagonal bipyramidal coordination sphere. They are isomorphous . orthorhombic, Pcab , a ≈ 18.4, b ≈ 14.6, c ≈ 14.3 Ǻ, Z = 8 f.u .; R were 0.042 and 0.059 for N o 2297 and 1489 respectively. Ca-I are 3.132(2), 3.116(2) Ǻ and Sr -I are 3.265(3), 3.238(3) Ǻ, while Ca-N are (range) 2.518(8)-2.566(8) Ǻ and Sr -N 2.68(2)-2.73(2) Ǻ.