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Comparison of crystal structures of the tetramethylammonium and sodium salts of 3-nitrophenolate.

Article Excerpt
ABSTRACT

The addition of either sodium hydroxide or tetramethylammonium hydroxide to 3-nitrophenol led to orange-red crystals of sodium 3-nitrophenolate dihydrate or a complex of 3-nitrophenol and tetramethylammonium 3-nitrophenolate. For the sodium salt, 11707 Mo-Ka reflections were measured at 150 K via Bruker SMART 1-K CCD diffractometer. For the tetramethylammonium salt, 12664 Mo-Ka reflections were measured at 173 K via Bruker SMART 2-K CCD diffractometer. The unit cell of the sodium salt has: a = 6.814(1) [Angstrom], b = 6.5437(8) [Angstrom], c = 18.206(4) [Angstrom], [beta] = 94.46(3)[degrees], V = 809.4(3) [[Angstrom].sup.3], space group = P[2.sub.1]/n. The unit cell of the tetramethylammonium salt has: a = 23.543(4) [Angstrom], b = 5.636(1) [Angstrom], c = 16.387(3) [Angstrom], [beta] = 128.513(3) [degrees], V = 1701.4(9) [[Angstrom].sup.-3], space group = C2/c. The bond lengths of the 3-nitrophenolate moiety were statistically the same in the two crystal structures, showing that it is not affected by the cation.

INTRODUCTION

A crystallographic study of phenolates is underway in an attempt to determine whether or not the alpha effect is an electrostatic phenomenon. In the determination of the alpha effect of N-methylbenzohydroxamates, phenolates are often chosen as the non-alpha-nucleophiles (1). In order to study the alpha effect, a high-precision data set must be collected along with specific conditions including the reduction of the crystal temperature and the correction of the data for absorption of the X-rays by heavy atoms. Then one's data may be used to reliably determine the distribution of electron density of the compound (2, 3). However, first the compound must be successfully synthesized, and then the crystal structure must be solved in order to confirm that the crystal is in fact what it was intended to be without any impurities or disorder.

In 2000, the strong base sodium hydroxide was combined with 3-nitro-phenol and crystals were formed. The solved crystal structure of the synthesized compound sodium 3-nitrophenolate dihydrate resulted in a phenolate of reasonable geometry. The results were shared at the annual meeting of the Georgia Academy of Science, but due to a large R-factor the results were never published.

The crystal structure of sodium 3-nitrophenolate dihydrate had already been solved by Krygowski et al (4). However, that study was conducted at 298 K. In order to perform a charge density analysis, the X-ray data set must be collected at reduced temperature. The unit cell parameters of sodium 3-nitrophenolate dihydrate at 150 K agree very well with those measured at 298 K [compare: a = 6.814(1) [Angstrom], b = 6.5437(8) [Angstrom], c = 18.206(4) [Angstrom], [beta] = 94.46(3)[degrees] at 150 K; a = 18.192(3) [Angstrom]. b = 6.579(1) [Angstrom], c = 6.842(2) [Angstrom], and [beta] = 94.11(2) [degrees] at 298 K]. The differences can be attributed to a unit cell transformation in which the a...

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