Di-, tetra- and hexanuclear iron(III), manganese(II/III) and copper(II) complexes of Schiff-base ligands derived from 6-substituted-2-formylphenols.

Acyclic Schiff base ligands, derived from the condensation of 2,3-disubstituted benzaldehydes and 1,3-diaminopropan-2-ol, react with iron(II/III), manganese(II/III) and copper(II) salts to give di-, tetra- and hexanuclear complexes [Fe(III)(2)(L5)(2)].2MeOH (), [Fe(III)(4)(mu(3)-OMe)(2)(HL4)(2)Cl(2)] (), [Mn(II)(2)Mn(III)(2)(micro-OMe)(2)(HL4)(2)(DMF)(2)].2DMF () and [Cu(II)(6)(L5)(2)(micro(5)-SO(4))(2)(micro-SO(4))(MeOH)(2)].H(2)O.15.5(MeOH).15.5(MeCN) (). All compounds have been characterised by X-ray crystallography. Variable-temperature solid-state dc magnetisation studies have been performed in the temperature range 1.8-300 K. Antiferromagnetic interactions are present in all the compounds. The dinuclear compound has a zero total spin ground state with J = -9.66(1) cm(-1) and g = 2.07(1). The magnetic data for the tetranuclear compounds and have been interpreted using a tetranuclear butterfly model (b = body, w = wingtip) with the parameters: J(wb) = -9.35(4) cm(-1), J(bb) = -6.02(7) cm(-1), zJ' = -0.21(4) cm(-1) and g = 2.03(1) for ; and J(wb) = -3.40(3) cm(-1), J(bb) = -8.11(7) cm(-1), zJ' = -0.042(2) cm(-1) and g = 2.0 (fixed) for . The hexanuclear compound contains two {Cu(3)(L5)(MeOH)} units linked by three sulfate ligands: antiferromagnetic interactions are present in each trinuclear unit leading to two S = 1/2 motifs which do not or only very weakly interact across the sulfate bridges.

A series of new structural models for the OEC in photosystem II.

A new series of MMn(II-III)(4) clusters (M = Na, Ca) has been structurally characterised and their relevance to understanding the oxygen evolving centre of photosystem II is discussed.

Iron(III) activation hits a [4 + 4] macrocycle.

The tetranuclear complex [Fe(III)2(L')(OH)(CH3O)]2, 1, has been synthesised from the reaction of either ferrous [in excess as 4:1 or stoichiometric 2:1 iron(II) : H4L] or ferric ions [4:1 iron(III) : H4L] with the large macrocycle, H4L, using aerobic conditions in methanol in the presence of triethylamine. The structure of 1 was determined by single-crystal X-ray diffraction. These reaction conditions lead to the modification of the original macrocycle through the incorporation of a methylene group between two amine groups to give an imidazolidine ring in (L')4-. The controlled addition of formaldehyde into the reaction system results in a significantly improved yield of 1, suggesting that it is involved in the reaction mechanism. The (L')4- macrocycle binds to two, well-separated, iron(III) centres [Fe(1)...Fe(1a) > 8 A]. Each iron(III) centre is further linked via hydroxy and methoxy bridges to equivalent iron(iii) centres contained in a second macrocycle. Overall this gives a structure containing two {Fe(OH)(CH(3)O)Fe} dimers [Fe(1)...Fe(2)ca. 3.2 A] sandwiched by two (L')4- macrocycles. The complex was further characterised by SQUID magnetic measurements and can be interpreted in terms of two isolated antiferromagnetically coupled Fe(III) dimers (J=-23.75 K).