Structural studies of the alkali metal picrates

J.M. Harrowfield, Brian Skelton, Allan White

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A comparative series of room-temperature, single-crystal X-ray studies of the alkali metal (and ammonium) picrate structures is presented, all being in some sense revisitations of earlier work of various vintages, except for that of the sodium salt. Lithium picrate monohydrate is triclinic, P ($) over bar 1, a 10.710(6), b 7.186(1), c 7.112(1) Angstrom, alpha 65.89(1), beta 71.90(3), gamma 84.45(2)degrees, Z = 2 f.u.; conventional R on /F/ was 0.053 for N-o = 1792 'observed' (I > 3 sigma(I)) reflections. Sodium picrate monohydrate is monoclinic, G2/m, a 13.074(6), b 20.080(6), c 3.690(3) Angstrom, beta 90.67(3)degrees, 2 = 4 f.u.; R was 0.056 for N-o 519. Potassium picrate (anhydrous) is orthorhombic, Ibca, a 13.316(3), b 19.107(5), c 7.138(2) Angstrom, 2 = 8 f.u., R 0.036 for N-o 1308; the ammonium salt is isomorphous, a 13.474(4), b 19.790(7), c 7.131(4) Angstrom, R 0.040 for N-o 981. Rubidium picrate (anhydrous) is monoclinic, P2(1)/c, a 10.604(1), b 4.556(3), c 19.183(2) Angstrom, beta 101.41(1)degrees, Z = 4 f.u., R 0.039 for N-o 1878; the caesium salt is isomorphous, a 10.810(1), b 4.700(1), c 19.400(3) Angstrom, beta 101.43(1)degrees, R 0.027 for N-o 2177. The lithium salt is binuclear, the phenolic oxygen atoms bridging the five-coordinate lithium atoms, while the sodium salt is a two-dimensional polymer parallel to the ab plane, the picrates cross-linking one-dimensional arrays of sodium atoms of two types, one eight-coordinate and linked by bridging phenolic oxygen atoms, and the other six-coordinate and linked by water molecules. The potassium and ammonium salts are also two-dimensional polymers parallel to the ab planes, linked in the second dimension by pairs of picrates opposed in polarity and linking the eight-coordinate potassium atoms by phenolic oxygen atoms on the one hand, and the 4-nitro group oxygen atoms on the other. The rubidium and caesium salts are two-dimensional polymers in the ac plane, eight-coordinate metal atoms being linked by a complex web of picrate groups; unlike the other compounds, they do not contain bridging phenolic oxygen atoms.
Original languageEnglish
Pages (from-to)1311-1331
JournalAustralian Journal of Chemistry: an international journal for chemical science
Publication statusPublished - 1995


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