Rational design of homo and hetero hexanuclear coordination compounds: Syntheses and magnetic properties of [(Cu2M4II)-M-II] (M = Cu, Ni) species andthe crystal structure of {[Cu(tmen)(H2O)](2)[Cu(tmen)](2)[Cu2L] (H2O)}(ClO4)(4)center dot 2 H2O

New homo- and heterometallic hexanuclear complexes of formula {[Cu(tmen)(H2 O)](2)[Cu(tmen)](2)[Cu2L](H2O)} 2 H2O [Cu-6-tmen] {[Cu(pmdien)](4)[Cu2L]}(C lO4)(4) . 4 H2O [Cu-6-pmdien] and {[Ni(cyclam)](4)[Cu2L]}(ClO4)(4) . 4 H2O [Cu2Ni4-cyclam] [H8L = tetrakis(aminomethylene)methane-tetrakis(oxamic acid ), tmen = N,N,N',N' -tetramethylethylenediamine, pmdien = N,N,N',N',N"-pent amethyldiethylenetriamine, and cyclam = 1,4,8,11-tetraazacyclotetradecane] have been synthesized. The crystal structure of [Cu-6-tmen] has been determ ined by single-crystal X-ray diffraction. The structure consists of cationi c {[Cu(tmen) (H2O)](2)[Cu(tmen)](2)[Cu2L](H2O)}(4+) hexanuclear units. The hexanuclear cation is made up of two symmetry-related oxamato-bridged trinu clear units connected through the central carbon atom C(6) of the L8- ligan d. Variable-temperature magnetic susceptibility measurements (1.8-300 K) ha ve been performed for these series of complexes including the dinuclear pre cursors of formula Na-4[Cu2L] . 10.5 H2O [Cu-2-Na], (NMe4)(4)[Cu2L] . 4 H2O [Cu-2-NMe4] and (PPh4)(4)[Cu2L] . 6 H2O [Cu-2-PPh4]. The magnetic data hav e been interpreted. Evidence of a weak intramolecular ferromagnetic interac tion between the two Cu-II ions in [Cu2L](4-) has been observed. For the he xanuclear species, the interaction through the oxamato bridge was found to be equal to -6790, -2650, and -1643 yJ (-342, -133, and -82 cm(-1)) for [Cu -6-tmen], [Cu-6-pmdien], and [Cu2Ni4-cyclam], respectively. In these comple xes, the weak intramolecular ferromagnetic coupling between the two Cu-II i ons within the dinuclear synthon was masked by intermolecular interactions or local anisotropy.