Intense effort is currently directed toward elucidating the structure and mode of action of the Mn4 aggregate responsible for photosynthetic water oxidation in green plants and cyanobacteria.' The arrangement of the metal ions at any of the oxidation levels (S, states; n = -1 to 4) of this water oxidation center (WOC) is currently unclear. A number of structural proposals for SI have been put forward.2 Which of these is correct

Cyclic voltammetric examination of [Co 4 O 4 (O 2 CR) 2 -(bpy) 4 ](ClO 4 ) 2 cubane complexes 1 (R = various; bpy = 2,2A-bipyridine) in MeCN reveals a one-electron reversible oxidation in the range 0.68-0.86 V vs. ferrocene; the oneelectron oxidized clusters can be obtained in analytical purity by either controlled potential electrolysis to give [Co 4 O 4 (O 2 CR) 2 (bpy) 4 ](ClO 4 ) 3 2 or oxidation with (NH 4 ) 2 Ce(NO 3 ) 6 to give [Co 4 O 4 (O 2 CR) 2 (bpy) 4 ][Ce(NO 3 ) 6 ] 3.

Synthetic procedures are described that allow access to an octanuclear, mixed-valence ~C O~~,~C O~~' molecular aggregate. Oxidation of Co(O2CPh)2 in DMF with aqueous H202 leads to a dark emerald-green solution from which can be isolated [CO~O~(O~CP~)~~(DMF)~(H~O)] (la) in -60% yield. The same reaction in MeCN leads to [Co804(02CPh)12(MeCN)3(H20)] (lb). Complex lb*2MeCN crystallizes in triclinic space group Pi with the following unit cell dimensions at -153 "C: a = 15.056(4) A, b = 23.548(6) A, c = 14.697(4) A, a = 90.74(1)", p = 114.75(1)", y = 75.12(1)", V = 4546.5 A3, Z = 2. A total of 10 207 unique data with F > 3a(F) were used to solve the structure, which refined to R and R, values of 4.01 and 4.24%, respectively. The structure consists of a central [C0"'404]~+ cubane unit, with each p3-0'-ion becoming p4 by attachment to a CO" center to give a [coSo4]'2+ core; the [Co404l4+ cubane is thus bridging the four Co" ions. Twelve PhC02-groups bridge the Co". Co"' pairs, and terminal MeCN/H20 groups complete the peripheral ligation at the five-coordinate, highspin CoI1 centers. The Co"' centers are low-spin. Excluding differences in terminal ligation (MeCN or H20), the molecule has idealized T d symmetry. Variable-temperature, solid-state magnetic susceptibility studies on la have been carried out in the range 4.00-320 K. The effective magnetic moment decreases from 8.35 p~ICo8 (4.18 per Co") at 320 K to 5.29 pB/cO8 (2.65 ~B/COII) at 4.00 K. The data were fit to the theoretical expression for an axial symmetry Co" ion undergoing zero-field splitting. The fitting parameters were I D 1 = 23.5(2.0) cm-l, 0 = -1.76(8) K, and g = 2.05(2), with TIP set at 700 x cm3 mol-'. Low-temperature (e20 K) deviation between experimental and calculated peff values is taken as evidence of weak, antiferromagnetic intra-and intermolecular interactions being present, the latter mediated by hydrogen-bonding contacts between two Cog units. 'H NMR spectra recorded in (CD3)zCO, CD2C12, or CD30D show only one set of paramagneticallyshifted benzoate resonances suggesting effective T d solution symmetry and retention of the [COS041 core on dissolution; this conclusion is supported by electronic spectral studies. Cyclic and differential pulse voltammetric studies show a quasi-reversible oxidation at 1.54 V vs SCE for IC; however, for la, the oxidation appears irreversible.

The cover picture shows the structure transformation from a well-known gold nanocluster Au 25 (SCH 2 CH 2 Ph) 18 (Au 25 for short) to a novel cadmium doped gold nanocluster [Au 13 Cd 2-(PPh 3) 6 (SC 2 H 4 Ph) 6 (NO 3) 2 ] 2 Cd(NO 3) 4 (Au 26 Cd 5 for short) by a combined peeling and doping process. Although the mother nanocluster Au 25 is inactive, the as-prepared Au 26 Cd 5 exhibits high catalytic activity, as well as good recyclability and sub-strate tolerance at room temperature. The high catalytic activity is attributed to the cooperation between the exerted cadmium atoms and the neighbor gold atoms in the Au 13 icosahedron based on some experimental results. More details are discussed in the article by Wu et al. on page 567-571. REVIEWS 531 This review summarizes the transition metal complex catalyst with high thermal stability. The structures of complex include the backbone of bis(imino)pyridine, α-diimine ligands and other types of ligands. The plausible mechanism on the thermostable catalysts was proposed which gives guidance to design this class of catalyst. Recent Progress on Transition Metal (Fe, Co, Ni, Ti and V) Complex Catalysts in Olefin Polymerization with High Thermal Stability

I b is formed on oxidation of cobalt(ii) benzoate in MeCN or dmf with aqueous H202, and contains a [Co40414+ cubane unit with each oxide attached to an additional Co atom; studies stimulated by this result show that preformed [C0~04(02CR)~( bipy),]Z+ (bipy = 2,T-bipyridine) can be mono-and dou bly-protonated to [Co403(0H )(02CR)2( bi ~y ) ~1 3 + and [Co4O2(OH),( 02CR),( bi ~y ) ~] 4 + , respectively.