| Abstract
| - The interaction of MnII, FeII,and CoII with the ligand taci(=1,3,5-triamino-1,3,5-trideoxy-cis-inositol) wasstudiedin the solid state and in aqueous solution. Magneticsusceptibility measurements revealed a high-spin electronconfiguration for the Mn and the Fe complexes. Crystal data: [Mn(taci)2](NO3)2·2H2O(1),C12H34MnN8O14,monoclinic, space group P21/c,a = 7.107(5) Å, b = 8.742(2) Å,c = 18.527(6) Å, β = 100.20(4)°,Z = 2;[Fe(taci)2]Cl2·6H2O(2),C12Cl2FeH42N6O12,monoclinic, space group C2/m, a =11.420(2) Å, b = 9.300(2) Å,c= 13.330(3) Å, β = 111.97(3)°, Z = 2;[Co(taci)2](NO3)2·1.5H2O(3),C12CoH33N8O13.5,monoclinic, space groupP21/c, a = 7.081(1)Å, b = 8.743(1) Å, c = 18.181(2)Å, β = 99.49(1)°, Z = 2. All threestructures exhibiteddistorted octahedral MN6 coordination. The stabilityconstants for the complexes [M(taci)]2+ (M = Mn, Fe,Co)and [M(taci)2]2+ (M = Fe, Co) in aqueousmedia have been evaluated by potentiometric titration.Comparisonwith other divalent cations showed that the order of stabilityincreases MnII< CdII ≈ FeII<ZnII< CoII< CuII< NiII. In alkaline aqueous media, the complexes1−3 are readily oxidized by dioxygen. Theredox propertieswere analyzed by a series of polarographic and cyclic voltammetricmeasurements. A new isomeric form of abis-taci CoIII complex was formed, where one of the taciligands coordinates the metal cation by one nitrogen andtwo oxygen atoms. The complex was isolated in crystalline form as[Co(taci)(Htaci)](NO3)4·0.5H2O(4), C12CoH32N10O18.5, monoclinic, spacegroup C2/c, a = 30.541(3) Å,b = 9.015(1) Å, c = 17.852(2) Å,β = 95.63(1)°, Z = 8.[Co(tach)(H2O)x(NO3)3-x]x+(tach = all-cis-1,3,5-triaminocyclohexane, 0 ≤x ≤ 3) was used as amodel to demonstrate that, for CoIII, the substitution ofthe three monodentate coligands by a taci moleculeresultedgenerally in an asymmetric binding. An N,O,O and an N,N,Ocoordination mode were observed for [Co(taci)(tach)](NO3)3·3H2O(5), and[Co(H-1taci)(tach)](NO3)2·(3− x)H2O·xMeOH, 0.2 ≤x ≤ 0.5 (6), respectively.Crystal data: 5(C12CoH36N9O15),monoclinic, P21/n, a =8.942(5) Å, b = 30.07(3) Å, c =9.354(5) Å, β =109.25(4)°, Z = 4; 6 (x ≈0.2,C12.2CoH35.4N8O12),monoclinic, P21/n, a =7.337(2) Å, b = 19.847(4) Å, c=15.226(3) Å, β = 93.59(3)°, Z =4.
- The bis complexes[M(taci)2]2+ (M = MnII,FeII, CoII; taci =1,3,5-triamino-1,3,5-trideoxy-cis-inositol) all have aMN6 coordination, while different coordination modes areobserved in the trivalent stage, giving rise to complex redoxreactions.
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