OCTANUCLEARITY IN COPPER(II) CHEMISTRY - PREPARATION, CHARACTERIZATION, AND MAGNETOCHEMISTRY OF R-DOT-OH)(8)(O2CCH3)(4)](CLO4)(4)CENTER-DOT-9H(2)O (DPK-CENTER-DOT-H2O EQUALS THE HYDRATED, GEM-DIOL FORM OF DI-2-PYRIDYI KETONE)

The complexes [Cu-8(dpk . OH)(8)(O2CMe)(4)](ClO4)(4) . 9H(2)O (1) and [Cu(dpk . H2O)(2)](O2CMe)(ClO4). 2H(2)O (2), where dpk . H2O is the hy drated, gem-diol form of di-2-pyridyl ketone, have been prepared. Comp lex I crystallizes in triclinic space group P (1) over bar with the fo llowing unit cell dimensions at 25 degrees C: a = 18.396(1) Angstrom, b = 16.720(1) Angstrom, c = 19.171(1) Angstrom, alpha = 96.10(1)degree s, beta = 87.68(1)degrees, gamma = 99.14(1)degrees, Z = 2. Crystal str ucture data for 2 al room temperature are as follows: monoclinic, P2(1 )/c, a = 13.000(2) Angstrom, b = 8.008(1) Angstrom, c = 27.095(3) Angs trom, beta = 93.19(1)degrees, Z = 4. The two centrosymmetrically relat ed cubanes in the tetracation of 1 are doubly-bridged with two syn, an ti acetate groups bridging two Cu-II atoms. The monoanion dpk . OH- fu nctions as a eta(1):eta(3):eta(1):mu(3) ligand, Three Cu-II atoms have distorted octahedral coordination geometries with CuO3N3 and CuNO5 ch romophores, while the fourth Cu-II center displays a distorted square pyramidal geometry; a terminal monodentate acetate is Ligated to this latter Cu-II atom. In the mononuclear [Cu(dpk . H2O)(2)](2+) cation of 2, the four pyridyl nitrogens can be viewed as strongly coordinating to the metal (Cu-N = 2.013(4)-2.022(4) Angstrom), while one of the hyd roxyl oxygens on each ligand forms a weak bond to Cu-II (Cu-O=2.417(4) , 2.352(3) Angstrom). Variable-temperature magnetic susceptibility stu dies on 1 are in line with both an overall antiferromagnetic interacti on between Cu-II atoms and the magnetic behavior of a simple cubane. E xchange parameters, J, derived by using a four-J magnetic model, are f ound to be J(1) = 6 cm(-1), J(2) = -144 cm(-1), J(3) = -14 cm(-1), J(4 ) = 3 cm(-1) and g 2.29 (adjustable parameter) by least-squares fittin g to the spin Hamiltonian H = -2 Sigma(i<j)J(ij)S(i) . S-j. The thus d erived energy level spectrum shows a S = 1 ground state further suppor ted by the solid-stare and solution EPR spectra of 1. insight concerni ng the effect of structural parameters on the magnitude of the magneti c exchange interactions was gained through EHMO calculations performed on a model Cu(OR)(2)Cu moiety. Accordingly, estimates of the J parame ters, experimentally derived, were in close agreement both with known magneto-structural correlations established for planar Cu(OR)(2)Cu moi eties and a criterion established by us, holding for the magneto-struc tural correlations in symmetrical roof-shaped, alkoxo-bridged Cu(OR)(2 )Cu moieties.