Synthesis and characterization of the dimeric chromium(III) complex di-μ- hydroxobis[{N,N′-bis(2-pyridylmethyl)-1,3-propanediamine}-chromium(III)] perchlorate, [(bispictn)Cr(OH)] 2(ClO 4) 4·3H 2O

Abstract

The synthesis and spetroscopic properties of two isomers of the complex [(bispictn)Cr(OH)] 2 4+ where bispictn = N,N′-bis(2-pyridylmethyl)-1,3-propanediamine, C 15H 20N 4, are described. The crystal structure of the perchlorate salt trihydrate of the violet isomer has been determined from 3-dimensional counter X-ray data. The complex crystallizes in the monoclinic space group C2/c with eight dinuclear formula units in a cell of dimensions α = 38.323(11), b = 14.458(7), c = 17.027(7) Å, β = 106.24(3)°. The structure has been refined to a final R-factor of 0.065 based on 3710 independent intensities. The crystals contain a racemic mixture, but in any given molecule the configurations at both chromium centers are the same (ΔΔ or ΛΛ). Both ligands bind in the cis-β form, the configurations at all four secondary nitrogen atoms being the same, so the complex is best described as a racemic mixture of the {Λ(β)(RR′)Λ(β)(RR′)} and {Δ(β)(SS′)} isomers. The six-membered chelate rings from a chair conformation at one metal and a skew-boat at the other. The magnetic susceptibility of the complex indicates antiferromagnetic coupling between the chromium centers, the triplet state lying approximately 32.5 cm −1 higher in energy than the ground state singlet.