FROM TETRANUCLEAR MU(4)-OXO TO MU(4)-PEROXOCOPPER(II) COMPLEXES

The mu(4)-peroxotetracopper(II) complexes [Cu-4(L-1)(2)(O-2)(OMe)(2)(C lO4)]-ClO4 . MeOH (I), [Cu-4(L-2)(2)(O-2)-(OMe)(2)(ClO4)]ClO4 . MeOH ( 2), [Cu-4-(L-3)(2)(O-2) (OMe)(2)(ClO4)]ClO4 . MeOH (3) and the mu(4)-o xotetracopper(II) complex [Cu-4(L-1)(2)(O)(OH)(2)(MeOH)(2)-(ClO4)(2)] (4) were synthesized (HL1= 2,6-bis(pyrrolidinomethyl)-4-methylphenol, HL2=2,6-bis(piperidinomethyl)4-methylphenol, HL3=2,6-bis(morpholinomet hyl)-4-methylphenol). The molecular structures of 1 and 4 were establi shed by single-crystal X-ray crystallography. I crystallizes in the mo noclinic space group P2/n, with a=14.797(8), b=11.007(7), c= 15.434(10 ) Angstrom, beta=118.29 degrees, V=2214 Angstrom(3) (150 K) and Z=2. C omplex 4 crystallizes in the monoclinic space group P2(1)/n, with a=11 .498(2), b=13.311(3), c= 14.794(3) Angstrom, beta = 93.56(3)degrees, V = 2259.9 Angstrom(3) (213 K) and Z=2. Electrospray ionization mass sp ectra of 1 and 4 in dichloromethane solution confirm that the tetranuc lear structure is maintained in this solvent. The UV/Vis spectra of 1- 3 in dichloromethane are dominated by a very strong absorption at abou t 390 nm with a shoulder around 420-440nm interpreted as a superpositi on of a peroxo-->Cu-II and a phenolate-->Cu-II charge-transfer transit ion. A band at about 580 nm may be a superposition of d-d transitions and a second, less intense peroxo-->Cu-II charge transfer. The frequen cies of the O-O stretching vibrations of 1-3 were determined by FT Ram an and resonance Raman experiments and found to be 878, 898 and 888 cm (-1), respectively. A frequency shift to 841 cm(-1) is observed upon O -18 substitution in 1. The tetranuclear copper(Ir) complexes 1 and 4 a re strongly antiferromagnetically coupled. They possess S=0 ground sta tes separated from a triplet state by 510 and 720 cm-l, respectively. Good fits result from a regular spin Hamiltonian as well as from the B leaney-Bowers equation, which shows that only the two lowest-lying sta tes are notably thermally populated. Magnetostructural correlations es tablished for dimeric complexes are not easily transferable to these k inds of tetrameric complexes. Investigations in methanolic solution pr ovide evidence that a tetranuclear mu(4)-oxocopper(II) complex analogo us to 4 can be converted into a tetranuclear mu(4)-peroxocopper-(II) c omplex analogous to 1.