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Pentaammine complexes of chromium(III) and cobalt(III) with tbutylamine and some other alkylamines (NH2nProp,NH2Me) have been prepared from the pentaammine triflate complexes and the neat alkylamines. The products were characterized by C, H, N analysis, IR, UV-Vis and if possible by 1H NMR spectroscopy. The structure of the pentaammine(tbutylamine)chromium(III) complex has been determined by single-crystal X-ray diffraction. Crystals containing two different anions were studied. Crystallographic data: [Cr(NH3)5-(NH2tBu)]ZnCl4Cl·H2O, monoclinic, P2 1 c , a = 10.429(2), b = 9.818(3), c = 18.650(4) A , β = 93.03(2)°, Z = 4 ; [Cr(NH3)5-(NH2tBu)](ClO4)3·2H2O, monoclinic, P2 1 m , a = 10.088(3), b = 8.116(1), c = 13.278(4) A , β = 97.44(3)°, Z = 2 . The compounds are stable in acid aqueous solution but solvolyse in alkaline solution. The binding of tbutylamine to the pentaammine moiety is exceptional as the metal nitrogen distance is very large indicating weak bonds. The stability in solution is explained by shielding effects. The hydrophobic tbutyl group protects the complex against attacking solvent molecules. |
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