In the preparation of [Co(adao)(NO
2)
2] (adao: -00CCH
2NH(C H
2)
2NH(CH
2)
2NH
2) by using the modified Collman's method, it was found that an nitrocobalt(III) complex other than [Co(adao) (NO
2)
2] could be obtained as reddish orange crystals, The elemental analysis indicated that the complex contained a quinquedentate ligand, 3, 6, 9-triazaundecanedioate (
-COOCCH
2NH(CH
2)
2NH(CH
2)
2NHCH
2COO
-: taud), and had the composition of [Co(taud)(NO2)]. From these facts, it has been found that the aqueous solution of adao pro duced by the modified collman's method contains the above taud as a by-product. It has also been clarified that taud can be easily separated from the solution containing various components by the complex formation of [Co(taud)(NO
2)]. On the basis of the aqueous absorption spectrum of [Co(taud)(NO
2)], its structure has been determined to be trans(O), and the coordination mode of taud is necessarily trans(O). The complex of [Co(taud)(H
2O)]CIO
4 too could be isolated as pinkish red crystals from the reaction product of [Co(taud)(NO
2)] with HCIO
4, , Taking into consideration of the 1H-NMR spectrum and the preparative route for the complex, it has been inferred that the coordinated taud is a linear-chain quinquedentate ligand and has the trans(O) coordination mode.
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