Loops, Chains, Sheets, and Networks from Variable Coordination of Cu(hfac)₂ with a Flexibly Hinged Aminoxyl Radical Ligand

One pair of reactants, Cu(hfac)₂ = M and the hinge-flexible radical ligand 5-(3-N-tert-butyl-N-aminoxylphenyl)pyrimidine (3PPN = L), yields a diverse set of five coordination complexes: a cyclic loop M₂L₂ dimer; a 1:1 cocrystal between an M₂L₂ loop and an ML₂ fragment; a 1D chain of M₂L₂ loops linked by M; two 2D M₃L₂ networks of (M–L)_n chains cross-linked by M with different repeat length pitches; a 3D M₃L₂ network of M₂L₂ loops cross-linking (M–L)_n-type chains with connectivity different from those in the 2D networks. Most of the higher dimensional complexes exhibit reversible, temperature-dependent spin-state conversion of high-temperature paramagnetic states to lower magnetic moment states having antiferromagnetic exchange within Cu–ON bonds upon cooling, with accompanying bond contraction. The 3D complex also exhibited antiferromagnetic exchange between Cu^II ions linked in chains through pyrimidine rings.