Structural systematics of 2/4-nitrophenoxide complexes of closed-shell metal ions. VII - Acid salts of the 4-nitrophenoxides of Group 2

Room-temperature single-crystal X-ray structure determinations are recorded for a number of Group 2 4-nitrophenoxide acid salts, variously hydrated M(4-np)(2).x(4-npH).yH(2)O. Ca(4-np)(2).2(4-npH).8H(2)O is monoclinic, P2(1)/n, a 30.52(1), b 10.027(1), c 23.65(2) Angstrom, beta 116.33(5)degrees, Z = 8, conventional R on \F\ being 0.058 for N-o 5092 independent 'observed' (I > 3 sigma(I)) reflections. Sr(4-np)(2).2(4-npH).8H(2)O, based on a subcell of the former, is monoclinic, P2(1)/c, a 15.576(5), b 10.081(6), c 24.20(2) Angstrom, beta 117.99(5)degrees, Z = 4, R 0.054 for N-o 2908. Ba(4-np)(2).2(4-npH).4H(2)O is orthorhombic, Fdd2, a 28.01(1), b 19.90(1), c 10.692(7) Angstrom, Z = 8, R 0.028 for N-o 1967. The strontium array (and that of the calcium salt developed from it) may be represented as [(H2O)(6)Sr(4-npH.4-np)] (4-npH.4-np), a neutral ligand being unsymmetrically chelated to the strontium through the nitro group, with a quasi-parallel counter ion hydrogen-bonded to it by phenoxide confrontation. The other two 4-np residues make up a similar phenoxide-confronting pair (4-npH.4-np), the hydrogen being more intimately associated with one moiety. The barium salt is also an interesting array: the 10-coordinate barium lies on a crystallographic 2 axis, in an environment of two pairs of symmetry-related nitro-chelating ligand anions, and a pair of nitro-O coordinating neutral 4-npH ligands; the whole [(H2O)(4)Ba(4-np)(2)(4-npH)(2)] array may be envisaged as a single neutral (super)molecule. Hydrogen bonds between confronting phenoxides of the neutral 4-npH components of the parent and the 4-np(-) components of neighbouring molecules link the whole into a three-dimensional array.