Abstract
The chromium(II) complexes Cr(mepy) 4X 2 and Cr(mepy) 2(H 2O) 2I 2, where mepy is 3- or 4-methylpyridine and X is Cl, Br, or I, are high-spin with essentially temperature-independent magnetic moments of approximately 4.8 BM. Reflectance spectra indicate six-coordination, with trans-structures for the complexes Cr(mepy) 4X 2, the tetragonal distortion increasing in the order Cl < Br < I. The complexes Cr(mepy) 2X 2, where X is Cl or Br, have been assigned halide-bridged structures because their magnetic moments decreased considerably as the temperature was lowered, and their reflectance spectra show that the metal ion is six-coordinate. From the far infrared spectra of Cr(mepy) 2Cl 2 and Cr(mepy) 2Br 2 it appears that stretching vibrations of short CrCl bonds occur well above 300 cm −1, and CrN and short CrBr stretching vibrations overlap in the region of 280 cm −1. The spectra of Cr(mepy) 4X 2 contain strong bands near 290 cm −1 which are assigned to metal-nitrogen stretching vibrations. There are no halogen-dependent bands above 200 cm −1. It is therefore believed that only long CrX bonds are present.
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