Structural Systematics of 2/4-Nitrophenoxide Complexes of Closed-Shell Metal Ions. VII Acid Salts of the 4-Nitrophenoxides of Group 2

Abstract

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).yH₂O. Ca(4-np)₂.2(4-npH).8H₂O is monoclinic, P 2₁/n, a 30·52(1), b 10·027(1), c 23·65(2) Å, β 116·3(5)°, Z = 8, conventional R on |F| being 0·058 for N_o 5092 independent ‘observed’ (I > 3s(I)) reflections. Sr(4-np)₂.2(4-npH).8H₂O, based on a subcell of the former, is monoclinic, P 2₁/c, a 15·576(5), b10·081(6), c 24·20(2) Å, β 117·99(5)° , Z = 4, R 0·054 for N_o 2908. Ba(4-np)₂.2(4-npH).4H₂O is orthorhombic, Fdd2, a 28·01(1), b 19·90(1), c 10·692(7)Å, 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)₆Sr(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)₄Ba(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.