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Analysis of {hkl) X-ray data for 0 < (sin )/ < 0.95 from monoclinic crystals of Mn3(HY)2 • 10H2O yields definitive struc" ture determination. The unit cell contains two 3( )2• 10H2O; all atoms, save two Mn at inversion centers, occupy fourfold general positions of C62h-P2i/n (Table I). The atomic arrangement can be put together as follows: Sexadentate seven-coordinate Mn(OH2)Y~2 ions (Fig. 1) are distributed in general positions (Fig. 2) and are converted into quasiinfinite chains [Mn(OH2)YH]m-™ parallel to b (Fig. 2) by the addition of protons (the acid hydrogens) to hydrogen bond contiguous pairs of 06 and atoms (Fig. 1) along the sequence. This bonding is very tight, 03--O7 = 2.469 ± 0.010 A., and is at least quasi-symmetric. Manganese occupying inversion centers displays octahedral coordination; the coordination group comprises two carboxylate oxygens of Os type (Fig. 1), two water molecules which are hydrogen bonded at 2.708 ± 0.019 A. to carboxylate Oe atoms, and two water molecules which are hydrogen bonded at 2.698 ± 0.010 Á. to carboxylate 02 atoms.All water molecules, including two sets not complexed to manganese, are involved in hydrogen bonding (Table IV). C-N and C-C bond lengths average 1.471 ± 0.007 and 1.519 ± 0.008 A. and are otherwise notable for the internal consistency displayed by the individual data (Table II). C-O bond lengths seem to reflect quantitative variations in the strength of the bidentate complexing displayed by carboxylate. Ring, bond angles conform rather well to the quasi-symmetry C2-2 for the sexadentate seven-coordinate Mn(OH2)Y group (Table V). Departure from this ideal symmetry is manifest in the loosely packed inner coordination group (Table VI) and in the weak Mn-0 and Mn-N complexing bonds (Table III). Table VII and Fig. 1 and 3 describe the coordination group of the idealized Mn(OH2)Y~2 ion which is regarded as the most probable species in solutions of appropriate pH.(1) Supported by the National Science Foundation, the U. S. Army Research Office (Durham), and the Advanced Research Projects Agency. We thank also the Staff of the Cornell Computing Center, Mr. Richard C. Lesser, Director.(2) Publication as numbered contributions under a common generic title begins with this paper {cf. ref. 4, 7, 8, 18, and 19 for earlier work published elsewhere).(3) The abbreviations EDTA and short formula H4Y are used throughout for ethylenediaminetetraacetic acid. No quasi-structural formula simple enough to be written in linear form is accurately descriptive of the partially three-dimensional complexing in the "acid salt," Mm(HY)2' IOH2O. (4)

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