THE PHENOMENON OF CONGLOMERATE CRYSTALLIZATION VI. HYDRATION POLYMORPHISM. I. THE SYNTHESES, CRYSTAL AND MOLECULAR STRUCTURES OF [cis-α-Co(trien)Cl₂]Cl.nH₂O With n = 3,2

Abstract

Abstract Two hydration polymorphs [cis-α-Co(trien)Cl2]Cl.nH2O (n = 3, dark blue, IV; n = 2, red-purple. V) were studied by single crystal. X-ray diffraction methods. IV belongs to the triclinic system, crystallizing in the space group P 1 with cell constants of a = 7.216(4), b = 8.474(5), c = 12.348(6) Å, α = 98.96(5). β = 97.18(5) and γ = 94.02(5)° V = 736.95 Å, d(calc; z = 2) = 1.647 gm-cm−3. V is monoclinic, crystallizing in the space group P21/n with cell constants of a = 7.323(8), b = 8.330(2), c = 22.648(9) Å. β = 95.94(6)° V = 1376.30 Å3, d(calc; z = 4) = 1.677 gm-cm−3. The structural analysis of IV refined to final R and Rw values of 0.0604 and 0.0689, respectively, using 2108 observed data. That of V refined to 0.0323 and 0.0413 with 2070 data. Despite the difference in the number of waters of hydration and space groups, the two cations are essentially identical and have the cis-α geometry. The difference in colour is a solid-state artifact caused by differences in orientation of the cation's axes to the crystallographically developed faces. The average value of the Co-Cl distances in IV and V are, respectively. 2.265(1) and 2.269(2) Å and the C11-Co-C12 angles are both 90.9(1)°. In both compounds the cis < C1-Co-N angles are close to 90° while the cis < N-Co-N angles range from 85 to 95°. For both compounds, the distances Co-N; (secondary) are somewhat shorter than those between Co and the terminal –NH2 nitrogens. Since the lattices are centrosymmetric, enantiomeric pairs having energy-minima Δ(ΔλΔ) and Δ(λΔλ) configurations are present. Key Words: Isomerismhydratescomplexescobalttrien