Crystal spectrum of copper biguanides

In a previous communication it was shown that the absorption spectrum of a microscopic crystal of copper-ethylene- diamine-bis(acetylacetone) consists of three bands as predicted by the ligand field theory. Copper biguanides form transparent reddish crystals, very convenient for measurement in our experimental arrangement. In Fig. 1 are given the spectrophotometric optical density (O.D.) vs. wave-length (λ) curves for a thin crystal of copper bis-biguanide dibromide dihydrate with light polarized along the long axis of the crystal and at right angles to it, respectively. It is evident that the first curve consists of three bands, but the sharpness and fine structure are not as well defined as was the case with copper-ethylene-diamine-bis(acetylacetone). The decomposition of the curve into its component bands shows three peaks at 485 mμ, 540-550 mμ and 600 mμ. When the light was polarized at right angles to the long axis of the crystal, the absorption spectrum was found to consist of two bands, with peaks at 485 mμ and 550 mμ, the peak at 600 mμ being missing. If we associate the band of longest wave-length with the transition dz2 → dxy, then the result may mean that the z-axis of the molecular field coincides with the long axis of the crystal