Pergamon Pdyhedmn Vol. 13, No. I, p. 165, 1994

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ADDENDUM

THE PHENOMENON OF CONGLOMERATE CRYSTALLIZATION-XxX11. THE CRYSTALLIZATION BEHAVIOUR OF [CIS-CO(EN),(N02),]I (1) COUNTER ION

EFFECTS ON CRYSTALLIZATION PATHWAY OF RACEMATE SOLUTIONS-III. AN ADDENDUM

IYAN BERNAL,” JOZEF MYRCZEKt$ and JIWEN CA17

Chemistry Department, University of Houston, Houston, TX 77204-5641, U.S.A.

(Received 1 July 1993 ; accepted 4 August 1993)

In a recent paper,’ we reported the structure of the title compound, [cis-Co(en),(NO&]I (l), which we assigned to the tetragonal space group P4, since the reflections (1 ,O,O) and (3,0,0) were observed, the former having substantial intensity, the latter being above background, even if weak. Consequently the systematic (h,O,O with h # 2n) absences required by the higher symmetry space group, P4,2,2, seemed to be violated by those reflections.

More recently, we obtained a new set of PC cry- stallographic programs2 which we tested with data sets from crystals belonging to different space groups and known to be of good quality. One of them was the data set for (l), which was processed in both, P4,, and P412,2, space groups. In case of the latter, we eliminated the two (h,O,O) reflections, which we now know are observed due to multiple scattering of the very strong (2,0,0) reflection. Inter- estingly, we found that the higher symmetry space group, which requires the cation and anion to lie at two-fold axes, gave better RQ and R,(fl residuals

* Author to whom correspondence should be addressed. TFellow of the Robert A. Welch Foundation. $On leave from the Technical University of Wroclaw,

1-5, Wroclaw, Poland.

1.

2.

despite the fact that there are half as many inde- pendent atoms (and therefore variables) in space group P4,2,2. In P4, the residuals are, respectively, 0.048 and 0.056, whereas in P4,2,2 they are 0.042 and 0.046 which is, obviously, a superior refine- ment.

Nothing said in the previous manuscript con- cerning conglomerate crystallization, molecular geometry, etc.... needs to be modified. Moreover, refinement in the higher space group is consistent with the previous observation’ that the two en rings have the same helical chirality, as required by the presence of a two-fold axis through the cation. The correct coordinates in the new space group are obtained by shifting those in P4, to (-x, y- l/2, -0.0780) which positions the iodide and Co ions at (0.35783,0.35783,0.00000) and (0.92713,0.92713 and 0.00000).

A complete set of tables describing the new refinement has been deposited with the Editor of Polyhedron. We regret the need for this correction.

REFERENCES

I. Bernal, J. Myrczek and J. Cai, Polyhedron 1993,12, 1157. We thank Dr Peter White (University of North Caro- lina) for the PC version of the NRCVAX programs.

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