Abstract

Room-temperature single-crystal X-ray studies are recorded for a number of ‘acid salts’ formed between Group 1 salts of 4-nitrophenol, M(4-np), and the parent ligand 4-npH, variously hydrated. The 1 : 1 salts M(4-np)(4-npH).x H₂O are found for all of M = Li, Na, K, Rb and Cs. The lithium adduct (tetrahydrate) is monoclinic, C2/c, a 19·438(4), b 11·207(2), c 7·421(2) Å, β 91·38(2)°, Z = 4, conventional R on |F| being 0·043 for 1369 independent ‘observed’ (I > 3σ(I)) diffractometer reflections. The sodium adduct (dihydrate) is monoclinic, C2, a 2·174(3), b 3·674(2), c 10·358(1) Å, β 117·21(1)°, Z = 2, R 0·035 for N_o 1092; the potassium adduct (monohydrate) is monoclinic, C 2/c, a 22·10(1), b 3·798(3), c 21·270(6) Å, β 120·97(4)°, Z = 4, R 0·050 for N_o 1065. The isomorphous rubidium and caesium monohydrates are triclinic, P^-1, a ≈ 11·9, b ≈ 10·2,c ≈ 6·3 Å, α ≈ 90, β ≈ 92, γ ≈ 112°, Z = 2, R 0·042, 0·028 for N_o 2340, 3053 respectively. For M = Rb, a 1 : 3 adduct Rb(4-np).3(4-npH) is also obtained (with an isomorphous thallium counterpart recorded elsewhere): a 12·143(5), b 11·50(1), c 11·36(1) Å, α 114·38(9), β 110·54(6), γ 96·73(6)°, Z = 2, R 0·034 for N_o 3945. The lithium salt may be represented as [Li(OH₂)₄]⁺ (4-npH.4-np)½^-. The cation lies disposed about a crystallographic 2 axis; the anion, close to an axis, confronts its rotational image, with the associated hydrogen atom modelled as disordered between them, rather than located on the 2 axis. The sodium salt is a sheet structure, the six-coordinate sodium atoms being disposed on a crystallographic 2 axis and linked up that axis ... Na(µ-O)₂Na(µ-O)₂Na ... by bridging water molecule oxygen atoms, while symmetry-related trans O-nitrophenoxide moieties are bridged by confronting phenoxide oxygen atoms about an associated hydrogen atom provisionally disposed on a 2 axis also. The potassium salt structure is developed from this array, modelled with disordered potassium atoms, now lying off the 2 axis, 0·922(2) Å apart. In the rubidium/caesium structure, columns of oxygen-bridged metal ions are disposed about c, crosslinked by O-nitro-bonded phenoxide moieties, with confronting phenoxide oxygen atoms about a shared associated hydrogen.