Abstract
The crystal and molecular structures are reported for the two mixed diamine complexes [Cr(en) 2(tn)]Br 3·H 2O ( I ) and [Cr(en)(tn) 2]I 3·H 2O ( II ) (en = ethylenediamine, tn = 1,3-propanediamine). Single crystal X-ray diffraction data were collected by automated counter techniques using θ-2θ scans. The intensity data were corrected for absorption and both structures refined by full-matrix least-squares methods. The number of independent reflection (and final weighted agreement factor) were 1847 (5.l%) and 2292 (5.05%) for I and II , respectively. Both salts crystallize in space group Pbca (D 15 2h) with similar structures. Unit cell constants are a = 11.571(3), 11.823(6); b = 13.152(3), 14.183(71); and c = 22.994(5), 24.023(9) Å for I and II , respectively. Both the cations of I and II have only C 1 point symmetry, although the coordination environment defines a pseudo-threefold axis. The [Cr(en) 2(tn)] 3+ cation in I exists in the Λ∂λa conformation (and its mirror image). In this conformation one of the five-membered Cren rings has its CC bond parallel to the pseudo-threefold axis (∂) and the other ring is oblique to that axis (λ). The six-membered Crtn ring is in a chair conformation The inner coordination geometry CrN bond lengths are equal within experimental error and average 2.073(4) Å. The Cren interior NCrN bond angles average 82.9(2)° while the corresponding Crtn bond angle of 90.8(3)° is near that of an octahedron. The [Cr(en)(tn) 2] 3+ cation in II exist in the Λaa∂ conformation (and its mirror image). In this conformation the five-membered Cren ring has its CC bond parallel to the coordination pseudo-threefold axis (∂) and the six-membered Crtn rings are both in chair conformations. The inner coordination geometry has CrN bond lengths which are equal within experimental error and average 2.060(6) Å. The Cren interior NCrN angle is 84.2(4)° while the corresponding Crtn angles average 88.6(9)°.
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