Peroxo-bridged dinuclear cobalt(III) complexes, [{Co((D-Glc)(2)-tren)}(2)(mu-O-2)]X-3. 5H(2)O (X = Cl (2 . 5H(2)O), Br (3 . 5H(2)O)) and [{Co((Mal)(2)-tren)}(2)(mu-O-2)]Cl-3. 6H(2)O (4 . 6H(2)O), were prepared from CoX2. 6H(2)O, tris(2-aminoethyl)amine, and D-glucose (D-Glc) or maltose (alpha-D-glucopyranosyl-(1-->4)-D-glucose; Mal), and were characterized by elemental analysis, UV-vis absorption, circular dichroism, H-1 and C-13 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 . CH3OH, orthorhombic, P2(1)2(1)2(1) (No. 19), a = 19.384(8) Angstrom, b = 23.468(5) Angstrom, c = 13.195(5) Angstrom, V = 6002(2) Angstrom(3), Z = 4, D-calcd = 1.440 g cm(-3), T = -99 degrees C, R = 0.078, R-w = 0.085 for 4961 reflections with I > 3 sigma(I); 4 . 2.25H(2)O . 3.75CH(3)OH, monoclinic, P2(1) (No. 4), a = 12.819(7) Angstrom, b = 49.168(18) Angstrom, c = 14.973(6) Angstrom, beta = 104.59(4)degrees, V = 9130(7) Angstrom(3), Z = 4, D-calcd = 1.459 g cm(-3), T = -136 degrees C, R = 0.101 for 6837 reflections with I > 2 sigma(I). The hydrogen bondings between the sugar moieties deviates the Co-O-O-Co torsional angle from planarity to 100.4(6)degrees (2) and av 102(1)degrees (4). The electronic structures of the twisted Co-2(mu-O)(2) core were discussed on the basis of extended Huckel MO calculations. The present discrete complexes have a tetravalent sugar domain around the dinuclear center and clearly demonstrated distinct sugar-sugar interactions which could be a minimal model for so-called sugar clusters of glycoproteins on cell surfaces.