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

Abstract

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, 2^MeAr; Et, 2^EtAr; iPr, 2^iPrAr; and Ar = 2,6-iPr₂C₆H₃, 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 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 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.