The tetrachlorozincate(II) salt of AA(&-(Iaminopropane-2-ol-N)chlorobis(l,2-diaminoethane)cobalt(III) has been resolved by asymmetric association with sodium arsenyl tartrate. The chiroptical properties suggest the A-configuration for the arrangement of the chelate rings and this has been confirmed by a single crystal X-ray structure analysis of the resolved complex. The structure also confirms that the I-aminopropane-2-01 (pnol) is N-bonded and reveals that the potentially asymmetric carbon atom in pnol has the S-configuration and the 1,2-diaminoethane (en) rings adopt the 6h conformation. Crystals of 6 A-(-Is a.&(S)-cis-[CoCl(en)z(pnol-N) ] ZnC& are orthorhombic P212121 with a = 12.330(I), b = 13.905(2), c = 10.916(l) A and Z = 4. The structure has been refined to an R value of 0.047 on the basis of 767 observed reflections collected by diffractometry. Mercury(II) assisted chloride release in acidic solution (p = I.0 M) is relatively rapid (I O2 kHg (298.2) = 2.92 K' s-') to give A(S)-Co(en)2(pnol-N)(OH2)3' and this is followed by a slower cyclisation reaction (possibly complicated by racemisation) to give AA(S)(? )-plus A(S)-Co(en)2(pnol-NO)3' (1$$,01 (298.2) = 2.0 ;-', E4= IO7 f 3 kJ mar', = +14 + 6 J K-mar ). In the absence of Hg2+, the final product is again the cyclised complex, but the intermediate aqua ion is not detected as chloride release is about 20 times slower than cyclisation. (IO6 ,_kH (298.2) = I.0 s-l, E, = 103 f 3 W mar', asfg8= -24 f 6 JK-' mar').