Treatment of the two Co-III-hexaamine complexes [Co(taci)(2)](3+) and [Co(tmca)(2)](3+) (taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, tmca = all-cis-2,4,6-trimethoxycyclohexane-1,3,5-triamine) in CH3CN with NEt3 and excess paraformaldehyde gave the corresponding hexamethylideneimino (hmi) derivatives [Co(taci)(2)-hmi](3+) and [Co(tmca)(2)-hmi](3+) in excellent yield. Both hexaimines were stable in acidic aqueous solution and were isolated as solid compounds. They were characterized by elemental analyses, C-13 NMR, H-1 NMR, IR, and visible spectroscopy, mass spectrometry, and single-crystal X-ray analyses. [Co(taci)(2)-hmi]Cl-3. 6H(2)O crystallizes in the monoclinic space group C2/m, C18Cl3CoH42N6O12, Z = 2, a = 13.046(2) Angstrom, b = 9.802(2) Angstrom, c = 12.332(2) Angstrom, beta = 118.42(1)degrees. [Co(tmca)(2)-hmi](HSO4)(3) crystallizes in the monoclinic space group C2/c, C24CoH45N6O18S3, Z = 4, a = 14.087(3) Angstrom, b = 15.890(3) Angstrom, c = 15.502(3) Angstrom, beta = 95.27(3)degrees. Subsequent treatment of [Co(taci)(2)-kmi](3+) with nitromethane and base resulted in the formation of [Co(hebdoc)](+) (hebdoc = 8,10,18,20,21,22-hexahydroxy-9,19-bis(methylamino)-4,14-dinitro-2,6,12,16-tetraazatricyclo[15.3.1.1(7,11)]docosa-2,12-diene-4,14-diate), where the two taci fragments were fused by two anionic N=CH-C(=NO2-)-CH2-NH bridges. Two major diastereoisomers were formed from fifteen possibilities. They had different configurations at coordinated methylamino groups and were incorporated in a disordered manner in the crystal structure of [Co(hebdoc)](2)Cl-2. 3.5H(2)O : C40Cl2CO2H75N16O23.50, orthorhombic, space group Pna2(1), Z = 4, a = 33.835(2) Angstrom, b = 15.356(2) Angstrom. c = 9.967(2) Angstrom. In the base-catalyzed reaction of [Co(tmca)(2)](3+) with an appropriate mixture of formaldehyde and acetaldehyde, the condensation process was followed by a coupling reaction. After reduction with NaBH4 and air oxidation, a Co-III complex with the novel hexadentate ligand N-(9'-amino-8',10',11'-trimethoxy-2',6'-diaza-bicyclo [5.3.1]undec-4'-yl-methyl)-2,4,6-trimethoxycyclohexane- 1,3,5-triamine was formed as the major product. Direct treatment of [Co(taci)(2)-hmi](3+) and [Co(tmca)(2)-hmi](3+) with NaBH4 resulted in the liberation of the new triamines 1,3,5-trideoxy-1,3,5-tris(methylamino)-cis-inositol and all-cis-2,4,6-trimethoxytris(N-methyl)cylohexane-1,3,5-triamine.