COMPARISON OF CRYSTAL-STRUCTURES IN THE SERIES M(NH3)5NO2!XY AND M(NH3)5ONO!XY - CRYSTAL-STRUCTURE OF CO(NH3)5NO2!I2

Two modifications of Co(NH3)5NO2!I2, orthorhombic (1) and tetragonal (II), are synthesized and characterized by IR spectroscopy, x-ray phas e analysis, and x-ray structure analysis. Octahedral crystals of I are prepared by recrystallization from a concentrated aqueous solution of a mixture of I and II; needlelike crystals of II, from a dilute solut ion of this same mixture. A full x-ray structure study was completed f or I: automated diffractometer, a = 14.534(3), b = 7.592(l), c = 10.97 8(2) angstrom, V(C) = 1211.2(4) angstrom3, space group Pnam, Z = 4, d( calc) = 2.434 g/cm3, Cu K(alpha)-radiation, RF = 0.0492 for 274 I(hkl) > 3 sigma(I). A good quality crystal could not be found for II. The u nit-cell constants were determined on an automated diffractometer a = 17.745(9), c = 7.584(2) angstrom, V(C) = 2388(2) angstrom, Z = 8, d(c alc) = 2.469 g/cm3!. The coordinates of the heavy atoms Co and I were found by direct methods for space group I4/m R(F) = 0.315 for 335 I(h kl) > 3sigma(I)!. The crystal-chemical structural features of I and II are compared to each other and to similar structures in the series M (MH3)5NO2!XY in terms of the closest packing of the cations approximat ed as spheres with an effective radius.