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The structural and spectroscopic properties of a novel dinuclear chromium-oxo and a trinuclear chromium-hydroxo complex are reported. The dinuclear assembly, [Cr(2)(&mgr;-O)(2)(&mgr;-O(2)CMe)(bpy)(2)(H(2)O)(2)]ClO(4).bpy.[bpyH]ClO(4) (1), crystallizes in the monoclinic space group Cc with a = 16.8259(8) Å, b = 21.9622(11) Å, c = 14.6056(8) Å, beta = 122.1830(10) degrees, V = 4568.0(4) Å(3), and Z = 4. The structure was refined with 4378 observed reflections having F > 2.0sigma(F), giving final R factors of 0.0721 and 0.1305 for R and R(w2), respectively. The [Cr(2)(&mgr;-O)(2)(&mgr;-O(2)CMe)](+) core is structurally akin to those of recently reported isoelectronic [Mn(2)(&mgr;-O)(2)(&mgr;-O(2)CMe)](3+) complexes. The trinuclear assembly, [Cr(3)(&mgr;-OH)(2)(&mgr;-O(2)CMe)(4)(O(2)CMe)(2)(bpy)(2)]ClO(4) (2).5CHCl(3) crystallizes in the triclinic space group P&onemacr; with a = 16.104(5) Å, b = 17.623(5) Å, c = 12.236(3) Å, alpha = 93.33(1) degrees, beta = 92.81(1) degrees, gamma = 64.84(1) degrees, V = 3136.68 Å(3), and Z = 2. The structure was refined with 6732 observed reflections having F > 2.33sigma(F), giving final R factors of 0.0602 and 0.0616 for R and R(w), respectively. Results of electronic, (1)H and (2)H NMR, and EPR spectroscopy, fast atom bombardment mass spectrometry, and variable-temperature magnetic susceptibility studies of these materials and the use of Cr-oxo assemblies as isoelectronic models of the photosynthetic manganese assembly in high-S states are discussed.