Structure, Stability, and Redox Properties of Mn^II, Fe^II, Co^II, and Co^III Complexes with 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol¹

Abstract

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 Coordination Chemistry of 1,4‐Diazepan‐6‐amine

“…As noted previously for cis-dapi, [14] the formation constants measured for the bis complex [Cd(daza) 2 ] 2+ are sigwww.eurjic.org [31] Only complexes with a defined coordination environment containing a set of sp 3 2+ does not interact directly with Cl -to a significant extent, which lends strong support for a coordination number of six within the hexaamine complex.…”

“…The constants of the daza complexes are from this work (Table 4), the formation constants of the other ligands are from refs. [3,14,20,21,36] more pronounced for the addition of a second ligand moiety (Figure 8b), where a distinct maximum is now observed at Ni II for all the ligands. The preferred binding of Ni II is obviously due to the exclusive facial coordination mode of these ligands, which results in the above-mentioned weak binding of the third amine donor to the Cu II center.…”

“…Triamines with a cyclic backbone and a restriction to facial coordination such as all-cis-1,3,5-cyclohexanetriamine (cis-tach), [1] 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci), [2][3][4] or 1,4,7-triazacyclononane (tacn) [5,6] have received considerable attention in coordination chemistry. In particular, these ligands have been used to model the active site of metalloenzymes and to stabilize catalytically active metal centers.…”

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N1,N2‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

“…The weak tendency of L e to bind to Mn II coincides with the low stability of the corresponding taci complexes (log b 110 = 4.0, log b 120 < 7). [38] In aqueous solutions containing an equimolar ratio of Zn 2 + x is formed. The CdÀL esystem behaves similarly (log b 110 = 10.4).…”

“…[7,41] (1)À(4) discussed in the text (taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, tmca = all-cis-2,4,6-trimethoxycyclohexane-1,3,5-triamine). The formation constants of the taci and tmca complexes are from references [13], [24], [38], and [40].…”