Reactions of MCl(2).nH(2)O with N,N'-bis(D-glucopyranosyl)-1,4,7-triazacyclononane ((D-Glc)(2)-tacn), which was formed from D-glucose and 1,4,7-triazacyclononane (tacn) in situ, afforded a series of mononuclear divalent metal complexes with two beta-D-glucopyranosyl moieties, [M((D-Glc)(2)-tacn)Cl]Cl (M = Zn (11), Cu (12), Ni (13), Co (14)). Complexes 11-14 were characterized by analytical and spectroscopic measurements and X-ray crystallography and were found to have a distorted octahedral M(II) center ligated by the pentacoordinate N-glycoside ligand, (beta-D-glucopyranosyl)(2)-tacn, and a chloride anion. Each D-glucose moiety is tethered to the metal center through the beta-N-glycosidic bond with tacn and additionally coordinated via the C-2 hydroxyl group, resulting in a lambda-gauche five-membered chelate ring. When L-rhamnose (6-deoxy-L-mannose) was used instead of D-glucose, the nickel(II) complex with two beta-L-rhamnopyranosyl moieties, [Ni((D-Man)(2)-tacn)(MeOH)]Cl(2) (15), was obtained and characterized by an X-ray analysis. Reactions of 11 (M = Zn) with [Zn(XDK)(H(2)O)] (21) or [Cu(XDK)(py)(2)] (22) (H(2)XDK = m-xylylenediamine bis(Kemp's triacid imide)) yielded homo and heterotrimetallic complexes formulated as [Zn(2)M'((D-Glc)(2)-tacn)(2)(XDK)]Cl(2) (M' = Zn (31), Cu (32)). The similar reactions of 12 (M = Cu) with complex 21 or 22 afforded [Cu(2)M'((D-Glc)(2)-tacn)(2)(XDK)]Cl(2) (M' = Cu (33), Zn (34)). An X-ray crystallographic study revealed that complexes 31 and 34 have either Zn(II)(3) or Cu(II)Zn(II)Cu(II) trimetallic centers bridged by two carboxylate groups of XDK and two D-glucopyranosyl residues. The M...M' separations are 3.418(3)-3.462(3) A (31) and 3.414(1)-3.460(1) A (34), and the M...M'...M angles are 155.18(8) degrees (31) and 161.56(6) degrees (34). The terminal metal ions are octahedrally coordinated by the (D-Glc)(2)-tacn ligand through three nitrogen atoms of tacn, two oxygen atoms of the C-2 hydroxyl groups of the carbohydrates, and a carboxylate oxygen atom of XDK ligand. The central metal ions sit in a distorted octahedral environment ligated by four oxygen atoms of the carbohydrate residues in the (D-Glc)(2)-tacn ligands and two carboxylate oxygen atoms of XDK. The deprotonated beta-D-glucopyranosyl unit at the C-2 hydroxyl group bridges the terminal and central ions with the C-2 mu-alkoxo group, with the C-1 N-glycosidic amino and the C-3 hydroxyl groups coordinating to each metal center. Complexes 31-34 are the first examples of metal complexes in which D-glucose units act as bridging ligands. These structures could be very useful substrate binding models of xylose or glucose isomerases, which promote D-glucose D-fructose isomerization by using divalent dimetallic centers bridged by a glutamate residue.
Peroxo-bridged dinuclear cobalt(III) complexes, [{Co((D-Glc) 2 -tren)} 2 (µ-O 2 )]X 3 ‚5H 2 O (X ) Cl (2‚5H 2 O), Br (3‚5H 2 O)) and [{Co((Mal) , were prepared from CoX 2 ‚6H 2 O, tris(2-aminoethyl)-amine, and D-glucose (D-Glc) or maltose (R-D-glucopyranosyl-(1f4)-D-glucose; Mal), and were characterized by elemental analysis, UV-vis absorption, circular dichroism, 1 H and 13 C NMR spectroscopic techniques, and X-ray absorption and crystallographic analyses, where (aldose) 2 -tren is bis(N-aldosyl-2-aminoethyl)(2-aminoethyl)amine (aldose ) D-Glc, Mal). The structure of 2 and 4 were determined by X-ray crystallography to consist of two Co(III) ions bridged by a peroxo unit: 2‚4H 2 O‚CH 3 OH, orthorhombic, P2 1 2 1 2 1 (No. 19), a ) 19.384 (8) Å, b ) 23.468(5) Å, c ) 13.195(5) Å, V ) 6002(2) Å 3 , Z ) 4, D calcd ) 1.440 g cm -3 , T ) -99°C, R ) 0.078, R w ) 0.085 for 4961 reflections with I > 3σ(I); 4‚2.25H 2 O‚3.75CH 3 OH, monoclinic, P2 1 (No. 4), a ) 12.819(7) Å, b ) 49.168(18) Å, c ) 14.973(6) Å, ) 104.59(4)°, V ) 9130(7) Å 3 , Z ) 4, D calcd ) 1.459 gcm -3 , T ) -136°C, R ) 0.101 for 6837 reflections with I > 2σ(I). The hydrogen bondings between the sugar moieties deviates the Co-O-O-Co torsional angle from planarity to 100.4(6)°(2) and av 102(1)°(4). The electronic structures of the twisted Co 2 (µ-O) 2 core were discussed on the basis of extended Hückel MO calculations. The present discrete complexes have a tetravalent sugar domain around the dinuclear center and clearly demonstrated distinct sugarsugar interactions which could be a minimal model for so-called sugar clusters of glycoproteins on cell surfaces.
Novel seven-coordinated cage-type cobalt(II) complexes containing N-glycosides from mannose-type aldoses and tris(2-aminoethyl)amine (tren), [Co((aldose)3tren)]X2·nH2O (1a·5H2O, aldose = d-mannose (d-Man), X = Cl-; 1b·5H2O, aldose = 6-deoxy-l-mannose (l-Rha), X = Cl-; 2a·4H2O, aldose = d-Man, X = Br-; 2b·H2O, aldose = l-Rha, X = Br-) and [Co((aldose)3tren)]SO4·nH2O (3a·4H2O, aldose = d-Man; 3b·3H2O, aldose = l-Rha), where (aldose)3tren is tris(2-(aldosylamino)ethyl)amine, were prepared and characterized by elemental analysis, electronic absorption and circular dichroism spectroscopies, and X-ray crystallography. Crystal data are as follows. 2b·2CH3OH: C26H56N4O14Br2Co, monoclinic, space group P2 1, a = 11.045(2) Å, b = 17.283(6) Å, c = 10.996(3) Å, β = 117.371(6)°, V = 1864(1) Å3, Z = 2, R = 0.072 for 2787 independent reflections. 3b·3H2O·CH3OH: C25H58N4O20SCo, orthorhombic, space group P212121, a = 14.836(2) Å, b = 22.489(2) Å, c = 12.181(3) Å, V = 4064(1) Å3, Z = 4, R = 0.077 for 2010 independent reflections. The complex cation of 2b consists of a cobalt atom coordinated by a heptadentate (l-Rha)3tren ligand to produce a mono-face-capped octahedron having pseudo-C 3 symmetry with a Λ (λ3-ob form) configuration around the metal. The complex cation of 3b has a mono-face-capped octahedron coordinated by a heptadentate (l-Rha)3tren ligand having pseudo-C 3 symmetry with a Δ (λ3-lel form) configuration. The other facial site of the complex cation is capped by the SO4 2- anion through hydrogen bonding with the hydroxy groups of l-rhamnose residues. The C 3 helical-configurational inversion around the cobalt(II) center, Δ ↔ Λ, induced by an interaction between the sugars and the SO4 2- anion, was monitored by circular dichroism spectroscopy, for which the sign of the Cotton effect of 1 and 2, having halide counteranions, is opposite to that of 3, having sulfate counteranions, and was found to proceed reversibly upon addition and removal of sulfate anions. The intensities of circular dichroism spectra for [Co((l-Rha)3tren)]2+ and [Co((d-Man)3tren)]2+ were appreciably changed upon addition of sulfate ions. The spectral changes were interpreted in terms of ion-pair formation. On the basis of electrostatic theories of ion association, the closest distance between the sulfate ion and the [Co((d-Man or l-Rha)3tren)]2+ cation was estimated as ∼5 Å, which is consistent with the Co−S distance of 4.697(6) Å observed in the crystal structure of 3b. The sulfate ion was suggested to fit into the cavity composed of the sugar hydroxyl groups through hydrogen bonds even in the solution state.
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