An "S"-shaped pentanuclear CuII cluster derived from the metal-assisted hydrolysis of pyCOpyCOpy:: structural, magnetic and spectroscopic studies

Reaction of [Cu-2(O2CMe)(4)(H2O)(2)] with 2,6-di-(2-pyridylcarbonyl)-pyridine (pyCOpyCOpy or dpcp) in MeCN-H2O 10 : 1, led to the pentanuclear copper(II) complex [Cu-5(O2CMe)(6){pyC(O)(OH)- pyC(O)(OH)py}(2)] (1) which crystallizes in the triclinic P (1) over bar space group. The copper(II) atoms are arranged in an "S"-shaped configuration, and are bridged by the doubly deprotonated bis(gem-diol) form of the ligand, pyC(O)(OH) pyC(O)(OH)py(2-). Magnetic susceptibility data indicate the interplay of both ferro- and antiferromagnetic intramolecular interactions stabilizing an S = 3/2 ground state. Fitting of the data according to a next-nearest-neighbour model {H =-[J(1)((S) over cap (1)(S) over cap (2) + (S) over cap (1')(S) over cap (2')) + J(2)((S) over cap (2)(S) over cap (3) + (S) over cap (3')(S) over cap (2')) + J(3)((S) over cap (1)(S) over cap (3) + (S) over cap (3')(S) over cap (1')) + J(4)((S) over cap (2)(S) over cap (2'))]} yields exchange coupling constants J(1) = + 39.7 cm(-1), J(2) = -15.9 cm(-1), J(3) =-8.3 cm(-1) and J(4) = + 4.3 cm(-1), leading to an S = 3/2 ground state. X-Band EPR spectroscopy indicates a zero-field splitting of the ground state with |D-3/2| = 0.38 cm(-1).