Molecular enneanuclear Cu II phosphates containing planar hexanuclear and trinuclear sub-units: syntheses, structures, and magnetism.

Highly symmetric enneanuclear copper(ii) phosphates [Cu-9(Pz)(6)(mu-OH)(3)(mu(3)-OH)(ArOPO3)(4)(DMF)(3)] (PzH = pyrazole, Ar = 2,6-(CHPh2)(2)-4-R-C6H2; R = Me, 2(MeAr); Et, 2(EtAr); iPr, 2(iPrAr); and Ar = 2,6-iPr(2)C(6)H(3), 2(Dip)) comprising nine copper(ii) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving the arylphosphate monoester, 1, copper(i)chloride, pyrazole, and triethylamine in a 4:9:6:14 ratio. All four complexes were characterized by single crystal structural analysis. The complexes contain two distinct structural motifs within the multinuclear copper scaffold: a hexanuclear unit and a trinuclear unit. In the latter, the three Cu(ii) centres are bridged by a mu(3)-OH. Each pair of Cu(ii) centers in the trinuclear unit are bridged by a pyrazole ligand. The hexanuclear unit is made up of three dinuclear Cu(ii) motifs where the two Cu(ii) centres are bridged by an -OH and a pyrazole ligand. The three dinuclear units are connected to each other by phosphate ligands. The latter also aid the fusion of the trinuclear and the hexanuclear motifs. Magnetic studies reveal a strong antiferromagnetic exchange between the Cu(ii) centres of the dinuclear units in the hexanuclear part and a strong spin frustration in the trinuclear part leading to a degenerate ground state.