A series of model complexes for the diamagnetic type III site in multicopper oxidases has been developed based on tridentate ligands formed from the Schiff base condensation of bifunctional primary amines with the monoximes ofβ-diketones. The complexes resulting when copper salts, CuX₂, react with the resulting ligands, HL, have the general formula Cu₂L₂X₂ and have a central core made up of the two copper atoms bridged by two oxime groups resulting in a six-membered Cu(ON)₂Cu moiety. This grouping is strictly planar and has significant shortening of the N-O bond length along with lengthening of the C=N bond indicating a delocalization of theπ-electrons in the ring. The result is a copper(II) dimer which is diamagnetic at all measurable temperatures (< 400 K). Spectroscopic, magnetic and electrochemical properties of the series of compounds will be compared with those of the parent enzyme containing the type III dicopper site. A second series of model complexes for both the type III site and the newly reported structure of the joint type II and type III site in ascorbate oxidase (crystal structure reported at the 3rd International Conference on Bioinorganic Chemistry, Boston, Mass, July 24–28, 1989) is also discussed. These compounds are obtained when ligands, H₃L, resulting from the condensation of derivatives of salicylaldehyde with 1,3-diamino-2-propanol, are reacted with copper carboxylates resulting in compounds of formula Cu₂L (carb). The carboxylate bridging group can be displaced by other better donors, L’, such as pyrazole, or indoles to give compounds (Cu₂LL’)⁺ which have bridging L’ groups. The properties of this series of compounds will be compared with those of the type III site. If the L’ ligand is suitably derivatized, i.e. 6-aminoindole, then by a Schiff base condensation with copper salicylaldehyde, compounds of formula (Cu₂LL’)₂Cu(sal)₂ can be obtained, which are models for multicopper oxidases having both the type II and type III sites in the same molecule, as has been found in the recent crystal structure of ascorbate oxidase. Comparisons between these models and multicopper oxidases will be drawn.

Ten new binuclear singly oxo-bridged molybdenum complexes (complexes 1-10) were prepared using five pyrimidine derived Schiff base ligands and two Mo(V) precursors (NH₄)₂MoOCl₅ and (NH₄)₂MoOBr₅. The ligands are prepared by the condensation of 4,6-dimethyl 2-hydrazino pyrimidine with salicylaldehyde (for HL₁), 𝑜-hydroxy acetophenone (for HL₂) and substituted salicylaldehydes (for HL₃, HL₄ and HL₅) respectively. These ligands are already reported as good donors for Mo(VI) state. The 𝜇-oxo Mo(V) complexes reported here bears a distorted octahedral geometry around each Mo atom with either N₂O₂Cl or N₂O₂Br chromophores. Fine variations in the spectroscopic behaviour of the complexes are observed in accordance with the varying electron donating properties of the ligands. All the complexes are unstable in solution and X-ray quality crystal of complex 1 could be isolated. All the complexes are characterized by IR and UV-Vis spectra.

We report here the synthesis and characterization of a few phenolate-based ligands bearing tertamino substituent and their Zn(II) and Cu(II) metal complexes. Three mono/binuclear Zn(II) and Cu(II) complexes [Zn(L1)(H₂O)].CH₃OH.H₂O (1) (H₂ L1 = 6,6′-(((2-dimethylamino)ethylazanediyl)bis(methylene))bis(2, 4-dimethylphenol), [Zn₂(L₂)₂] (2) (H₂L2 = 2,2′-(((2-dimethylamino)ethyl)azanediyl)bis(methylene)bis(4-methylphenol) and [Cu₂(L3)₂.CH₂ Cl₂] (3) (H₂L3 = (6,6′-(((2-(diethylamino)ethyl)azanediyl)bis(methylene)) bis(methylene))bis(2,4-dimethylphenol) were synthesized by using three symmetrical tetradendate ligands containing N₂O₂ donor sites. These complexes are characterized by a variety of techniques including; elemental analysis, mass spectrometry, ¹H, ¹³C NMR spectroscopic and single crystal X-ray analysis. The new complexes have been tested for the phosphotriesterase (PTE) activity with the help of ³¹P NMR spectroscopy. The ³¹P NMR studies show that mononuclear complex [Zn(L1)(H₂O)].CH₃OH.H₂O (1) can hydrolyse the phosphotriester i.e., p-nitrophenyl diphenylphosphate (PNPDPP), more efficiently than the binuclear complexes [Zn₂(L2)₂] (2) and [Cu₂(L3)₂.CH₂Cl₂] (3). The mononuclear Zn(II) complex (1) having one coordinated water molecule exhibits significant PTE activity which may be due to the generation of a Zn(II)-bound hydroxide ion during the hydrolysis reactions in CHES buffer at pH 9.0.

The synthesis and characterization of low-valent organoselenium and tellurium derivatives of hexabromododecahydrotriphenylene has been attempted. The reaction of hexabromododecahydrotriphenylene with in situ generated disodium dichalcogenides (Na₂E₂; E = Se, Te) afforded insoluble chalcododecahydrotriphenylene derivatives, 20, 21 respectively. Attempted aromatization of 20 and 21 using DDQ (2, 3-dichloro-5, 6-dicyano-1,4-benzoquinone) as an oxidizing agent afforded the co-crystals. The hexaselenophenyl derivative, 22 and the hexaselenocyanate derivative 23 were synthesized by the reaction of in situ generated sodium arylselenolate/potassium selenocyanate with hexabromododecahydrotriphenylene, respectively. The compounds were characterized by common spectroscopic tools and a few by single crystal x-ray crystallographic studies.