Molecular Enneanuclear CuII Phosphates Containing Planar Hexanuclear and Trinuclear Sub-Units: Syntheses, Structures, and Magnetism

Highly symmetric enneanuclear copper(II) phosphates [Cu9(Pz)6(μ-OH)3(μ3-OH)(ArOPO3)4(DMF)3] (PzH = pyrazole, Ar = 2,6-(CHPh2)2-4-R-C6H2; R = Me, 2MeAr; Et, 2EtAr; iPr, 2iPrAr; and Ar = 2,6-iPr2C6H3, 2Dip) comprising nine copper(II) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving arylphosphate monoester, copper(I)chloride, pyrazole, and triethylamine in a 4:9:6:14 ratio. All four complexes were characterized by single crystal structural analysis and reveals the presence of two distinct structural motifs within the multinuclear copper scaffold: hexanuclear and trinuclear. In the latter, the three Cu(II) centres are bridged by a µ3-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 a –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 and their analysis reveals 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 with interesting implications for quantum computing.