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Dichlorotris-(2-methylimidazole)manganese(II), MnCl2(2-meim)a, is monoclinic with a= 8.189 (1), b= 14.763 (1), c= 14"419 A, fl= 108.69 (1) °, space group P21/c and Z=4. The structure has been determined from diffractometer data, and least-squares refinement with 2397 independent reflexions has reached R = 0.046. A monomeric pentacoordinate structure is found, in which the coordination, though severely distorted towards square pyramidal, is essentially trigonal bipyramidal. A C1 atom and a 2-meim ligand occupy the axial positions with Mn-C1 and Mn-N distances of 2-525 and 2"249 A respectively. For the equatorial groups the respective bonds are somewhat shorter -a C1 at 2.392 A and two 2-meim ligands with a mean Mn-N of 2.195 /~. The molecule has approximate m (C~) symmetry.

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The crystal structure of tetraphenylarsonium nitridotetrachloroosmate(VI), (Ph4As)[OsNC14], has been determined from three-dimensional X-ray diffractometer data. The crystals are tetragonal with unit-cell dimensions a=12.667(3), c=7.820(2) A, space group P4/n and Z=2. Full-matrix least-squares refinement, using 1189 independent reflections, has reached R = 0.037.Two discrete ionic species are present in the structure. The [OsNC14]-anion has 4ram (C4v) point symmetry, and the osmium atom has a square-pyramidal coordination with Os-N and Os-C1 bond lengths of 1.604 and 2.310 A respectively. Because of the strongly ~-donating nature of the terminal nitrido ligand the basal plane is depressed to 0.58 A below the osmium atom, such that the N Os-C1 angles are 104.5 ~ The tetrahedral tetraphenylarsonium cation has 4($4) crystallographic symmetry with As-C distances of 1.912 A and two independent C-As-C angles of 105.1 and 111.7 ~ .

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