Room-temperature single-crystal X-ray structure determinations are recorded for 4-nitrophenolate (4-np(-)) salts of Group 2 metal ions, variously hydrated, M(4-np)(2).xH(2)O, M = Mg, Ca, Sr, Ba. Mg(4-np)(2).8H(2)O is monoclinic, P2(1)/c, a 12.402(3), b 6.673(7), c 11.833(6) Angstrom, beta 93.70(3)degrees, Z = 2; conventional R on \F\ was 0.041 for N-o 1995 independent 'observed' (I > 3 sigma(I)) reflections. Ca(4-np)(2).4H(2)O is monoclinic, P2(1)/c, a 13.109(8), b 3.644(1), c 21.181(8) Angstrom, beta 125.55(3)degrees, Z = 2, R 0.050 for N-o 1371. Sr(4-np)(2).8H(2)O is monoclinic, P2(1)/n, a 7.934(1), b 10.658(1), c 23.602(2) Angstrom, beta 91.36(1)degrees, Z = 4, R 0.038 for N-o 2050. Ba(4-np)(2).8H(2)O is monoclinic P2(1)/c, a 15.990(8), b 6.337(3), c 25.634(8) Angstrom, beta 126.91(3)degrees, Z = 4, R 0.021 for N-o 3115. The magnesium salt is ionic with [Mg(OH2)(6)](2+) cations and interleaved anion stacks up b. The calcium salt is a one-dimensional polymer with ...Ca(mu-O)(2)Ca(mu-O)(2)Ca... spine, the bridges being phenolic oxygen atoms. trans-Coordinated water molecules make up six-coordination about the calcium, the anion planes stacking at the b spacing. The strontium adduct is also a one-dimensional polymer with a similar spine, but with water molecule oxygen atoms bridging, the nine-coordinate strontium environment being made up by a chelating nitro group and three unidentate water molecules. Coordinated anions stacked up a are interleaved by free anions. The barium salt is simply [Ba(4-np)(OH2)(8)](+) (4-np(-)), the ligand anion (semi)chelated through the nitro pair of oxygen atoms, again with interleaving anion/ligand stacking.
