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The crystal structure of isophthalic acid has been determined by direct methods. The crystals are monoclinic, space group P21]e, a= 3.76/~, b= 16.42 &, e= 11-72/~, fl=90°_+ 30 '. There are 4 molecules per unit cell. Measurement was made of 809 reflexions by the multiple-film equi-inclination method using Cu Ke radiation. An E-map was calculated, based on 160 phases developed by statistical methods. All the carbon and two of the oxygen atoms were located from this E-map. A three-dimensional Fourier synthesis, computed with the phase signs given by these atoms, revealed the locations of all the nonhydrogen atoms. The hydrogen atoms were located from a difference map. Refinement proceeded anisotropically for the heavier atoms and isotropically for the hydrogen atoms to a final discrepancy index R= 0-05. The molecules of isophthalic acid are strongly hydrogen-bonded between the carboxyl groups forming dimers related by screw axes.

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Zinc diborate crystallizes in the orth0rhombic system, space group Pbca, with eight formula units in a cell of dimensions a= 13"714_+0"005, b=8"091 _+0.005 and c=8.631 _+0.005 A. The calculated density is 3"07 g.cm-3, and all atoms are in general positions. The structure of ZnB407 has been solved by three-dimensional Fourier syntheses. The positional and isotropic thermal parameters were refined by the least-squares method based on 530 observed reflexions. The final conventional R index is 0.067. The structure consists of BO3 triangles and BO4 tetrahedra sharing a common vertex. Each zinc atom is surrounded by four close oxygen atoms, arranged in an irregular tetrahedron.

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