The structures and conformations of the mixed ethylenediamine 1,3-propanediamine complexes [Cr(en) 2(tn)] Br 3·H 2O and [Cr(en)(tn) 2]I 3·H 2O

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 Cren rings has its CC bond parallel to the pseudo-threefold axis (∂) and the other ring is oblique to that axis (λ). The six-membered Crtn ring is in a chair conformation The inner coordination geometry CrN bond lengths are equal within experimental error and average 2.073(4) Å. The Cren interior NCrN bond angles average 82.9(2)° while the corresponding Crtn 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 Cren ring has its CC bond parallel to the coordination pseudo-threefold axis (∂) and the six-membered Crtn rings are both in chair conformations. The inner coordination geometry has CrN bond lengths which are equal within experimental error and average 2.060(6) Å. The Cren interior NCrN angle is 84.2(4)° while the corresponding Crtn angles average 88.6(9)°.