Ferromagnetic Cu 8 pinwheel clusters as building blocks for larger magnetic networks: Long-range structural and magnetic ordering

Abstract

The structural and magnetic properties of a series of Cu 8 pinwheel clusters with the tritopic ligands 2POMP, 2POPP, Cl2POMP and SEt2POMP are described. Two different ligand binding modes lead to two different arrangements of Cu–Cu bridge connections within the pinwheel. In one case, all the Cu(II) centers are bridged by hydrazone oxygen atoms, and the Cu–Cu distances are all similar (∼4 Å). In the other case, the central Cu(II) centers are bridged by hydrazone oxygen atoms, while the peripheral Cu 2+ cations are bridged to the core by diazine (N–N) groups. In both cases, the bridges are orbitally strictly orthogonal and so ferromagnetic exchange dominates. In the complex [(2POMP-2H) 4Cu 8Br 6](CuBr 4)(H 2O) 11 ( 1) bromide ions bridge the peripheral Cu(II) centers of adjacent Cu 8 pinwheel cluster molecules forming a 2D network with additional CuBr 4 2 - ions occupying cavities in the lattice. In [(Cl2POMP-2H) 4Cu 8(N(CN) 2) 8](H 2O) 9(CH 3CN) ( 3), nitrogen atoms of the coordinated dicyanamide (dca) ions bound to the peripheral Cu(II) centers interact with ligand bound chlorine atoms of adjacent molecules to form stacks of pinwheels. In [(Set2POMP-2H) 4Cu 8(H 2O) 8](PF 6) 8(CH 3OH) 6(CH 3CN) 1.5 ( 4) relatively short S⋯S contacts exist between pinwheels and cause stacking in the extended structure. Surprisingly, there is evidence for long-range magnetic interactions in 3 via the intermolecular contacts, but not in 1, which has direct bonding between pinwheel subunits. Exchange integrals within the pinwheel clusters fall in the range J = 4–7 cm −1.