Bulky Pyrazolate-Based Compartmental Ligand Scaffolds: Encapsulation of an Edge-Sharing Cu6O2 Bitetrahedral Core

Upon reaction with Cu(OAc)(2)center dot H2O, pyrazole-based ligands with two appended imine chelate arms in the 3- and 5-positions of the pyrazole and bulky substituents at the imine-N yield Cu-6 complexes [L2Cu6(mu-OAc)(6)(mu(4)-O)(2)] (1a,b). They feature an unusual {Cu-6(mu(4)-O)(2)}-bitetrahedral core, only the second example of this structural motif. ESI mass spectrometric and UV/Vis data confirm that the Cu-6 complexes stay intact in solution, and magnetic and high-field EPR measurements reveal an S = 0 ground state with the first excited triplet at Delta E approximate to 95 cm(-1). Although the new hexanuclear systems are too complex for deriving all individual exchange constants from powder susceptibility data, a rough idea of the complete energy level spectrum could be obtained. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)