The interaction of Mn II , Fe II , and Co II with the ligand taci ()1,3,5-triamino-1,3,5-trideoxy-cis-inositol) was studied in the solid state and in aqueous solution. Magnetic susceptibility measurements revealed a high-spin electron configuration for the Mn and the Fe complexes. Crystal data: [Mn(taci) 2 ](NO 3 ) 2 ‚2H 2 O (1), C 12 H 34 MnN 8 O 14 , monoclinic, space group P2 1 /c, a ) 7.107(5) Å, b ) 8.742(2) Å, c ) 18.527(6) Å, ) 100.20(4)°, Z ) 2; [Fe(taci) 2 ]Cl 2 ‚6H 2 O (2), C 12 Cl 2 FeH 42 N 6 O 12 , monoclinic, space group C2/m, a ) 11.420(2) Å, b ) 9.300 (2) (2) Å, ) 99.49(1)°, Z ) 2. All three structures exhibited distorted octahedral MN 6 coordination. The stability constants for the complexes [M(taci)] 2+ (M ) Mn, Fe, Co) and [M(taci) 2 ] 2+ (M ) Fe, Co) in aqueous media have been evaluated by potentiometric titration. Comparison with other divalent cations showed that the order of stability increases Mn II < Cd II ≈ Fe II < Zn II < Co II < Cu II < Ni II . In alkaline aqueous media, the complexes 1-3 are readily oxidized by dioxygen. The redox properties were analyzed by a series of polarographic and cyclic voltammetric measurements. A new isomeric form of a bis-taci Co III complex was formed, where one of the taci ligands coordinates the metal cation by one nitrogen and two oxygen atoms. The complex was isolated in crystalline form as [Co(taci)(Htaci)](NO 3 ) 4 ‚0.5H 2 O (4), C 12 -CoH 32 N 10 O 18.5 , monoclinic, space group C2/c, a ) 30.541(3) Å, b ) 9.015(1) Å, c ) 17.852(2) Å, ) 95.63-(1)°, Z ) 8. [Co(tach)(H 2 O) x (NO 3 ) 3-x ] x+ (tach ) all-cis-1,3,5-triaminocyclohexane, 0 e x e 3) was used as a model to demonstrate that, for Co III , the substitution of the three monodentate coligands by a taci molecule resulted generally in an asymmetric binding. An N,O,O and an N,N,O coordination mode were observed for [Co(taci)-(tach)](NO 3 ) 3 ‚3H 2 O (5), and [Co(H -1 taci)(tach)](NO 3 ) 2 ‚(3 -x)H 2 O‚xMeOH, 0.2 e x e 0.5 (6), respectively. Crystal data: 5 (C 12 CoH 36 N 9 O 15 ), monoclinic, P2 1 /n, a ) 8.942(5) Å, b ) 30.07(3) Å, c ) 9.354(5) Å, ) 109.25(4)°, Z ) 4; 6 (x ≈ 0.2, C 12.2 CoH 35.4 N 8 O 12 ), monoclinic, P2 1 /n, a ) 7.337(2) Å, b ) 19.847(4) Å, c ) 15.226(3) Å, ) 93.59(3)°, Z ) 4.

The addition of [N(CH(3))(4)]OH to a methanolic solution of FeCl(3) and thme (thme = 1,1,1-tris(hydroxymethyl)ethane) yielded [N(CH(3))(4)](2)[OFe(6)(H(-)(3)thme)(3)(OCH(3))(3)Cl(6)].2H(2)O (1). Crystal data: C(26)H(64)Cl(6)Fe(6)N(2)O(15), trigonal space group P31c, a = 12.459(2) Å, c = 18.077(4) Å, Z = 2. The complex anion exhibits the well-known &mgr;(6)-O-Fe(6)-(&mgr;(2)-OR)(12) structure with three &mgr;(2)-methoxo bridges, three triply deprotonated H(-)(3)thme ligands, where each alkoxo group bridges two Fe(III) centers, and six terminally coordinating Cl(-) ligands. In contrast to two previously described ferric complexes with an analogous structure of the complex core, compound 1 is stable in air. Variable-temperature magnetic susceptibility measurements established antiferromagnetic exchange coupling interactions with J(trans)(Fe-&mgr;(6)-O-Fe) = 24.5 cm(-)(1), J(cis)(Fe-&mgr;(2)-O(thme)-Fe) = 11.5 cm(-)(1), and J(cis)'(Fe-&mgr;(2)-OCH(3)-Fe) = 19.5 cm(-)(1). The unexpectedly high value for J(trans) is explained by means of a superexchange pathway and is discussed for a simplified model by using MO calculations at the extended Hückel level.

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