Synthesis and Structural Systematics of Nitrogen Base Adducts of Group 2 Salts. II. Some Adducts of Group 2 Salts With Pyridine

Abstract

Recrystallization of Group 2 halides from pyridine ( py ) solution has yielded, in a number of cases, crystalline adducts MX₂.npy which have been the subject of room-temperature single-crystal X-ray structural characterization. MgBr₂.6py (1) is orthorhombic, Ccca, a 11.575(2), b 14.999(4), c 17.292(2) Ǻ, Z = 4; conventional R on [F] for N_o = 752 'observed' (I > 3σ(I)) reflections was 0.043. The compound is formulated as [( py )₄MgBr₂].2py, the metal atom on a site of 222 symmetry having a trans-X₂MN₄ coordination environment. With CaCl₂, a 1:2 adduct (2) is formed, orthorhombic, Fdd2, a 33.83(1), b 18.143(2), c 3.981(7) Ǻ, Z = 8 f.u ., R 0.040 for N_o 451; the complex is an infinite polymer along c, [( py )2CaCl2](∞ ׀ ∞), the…CaCl₂CaCl₂Ca…spine having six-coordinate, octahedral calcium environments in which the pyridine nitrogen atoms are bound trans to either side, with the calcium site symmetry being 2. With SrBr₂, a 1:5 adduct (3) is found, mononuclear, [( py )5SrBr2], with the metal atom in a pentagonal bipyramidal coordination environment (orthorhombic, Pcab , a 18.611(5), b 17.768(7), c 17.411(7) Ǻ, Z = 8; R 0.060 for N_o 949). With BaI2, a 1:6 adduct (4) is obtained, [( py )6BaI₂], the eight-coordinate barium atom lying on a crystallographic 2 axis in a monoclinic C2/c cell, Z = 4, a 18.311(2), b 9.960(3), c l8.856(8) Ǻ, β 99.28(3)° (R 0.031 for N_o 2279), with the iodide atoms occupying a pair of B sites in one of the trapezoidal planes of a quasi-dodecahedral array. [(2-mpy)₂MgBr₂] (5), 2-mpy=2-methylpyridine, is of interest, offering a four-coordinate N₂MgBr₂ array (triclinic, Pī, a 8.046(3), b 8.873(3), c 11.475(1) Ǻ, α 86.25(2), β 78.82(5), γ 67.88(5)°, Z = 2; R 0.069 for N_o 2091), while [( py )6/(4-mpy)₆Ba(O₂ClO₂)₂] (6) and (7), perhaps surprisingly, are isomorphous with (4), with O,O'-bidentate perchlorates replacing iodide in the coordination sphere (R 0.031 and 0.052 for N_o 2401 and 2204 respectively). With 3,5-dmpy (3,5-dimethylpyridine), strontium iodide yields a trans-six- rather than seven-coordinate adduct, [(3,5-dmpy)4SrI2] (8), the molecule conforming to crystallographic 4/m symmetry in the tetragonal space group I4/m, a 9.808(4), c 17.196(8) Ǻ, Z = 2; R 0.066 for N_o 608.