Long-range magnetic order displayed by a bimetallic pentanuclear cluster complex [(Ni(2,2′-bipy)2)3(Fe(CN)6)2]·13H2O and by a Cu(II) analog

Abstract A bimetallic pentanuclear cluster complex contains three bis(2,2′-bipyridine)nickel(II) moieties bridged, through two vacant cis -positions around each nickel, to two separate hexacyanoferrate(III) groups via NiNCFe linkages. Freshly prepared crystals of this compound contain 17 water and two dimethylformamide molecules of solvation per cluster. Loss of some solvent molecules is rapid in air, the resulting ‘partly desolvated’ material showing intracluster ferromagnetic coupling and a S =4 ground state, but without long-range magnetic order. In contrast, a rapidly precipitated powder sample, containing 13 waters of hydration [(Ni(2,2′-bipy) 2 ) 3 (Fe(CN) 6 ) 2 ]·13H 2 O, displays long-range order at a T C of 11 K. Inter-cluster interactions occur via the H-bonded water pathways which join neighbouring Fe(CN) 6 3− groups in separate clusters. Thus, a new example of inter-cluster magnetic ordering has been achieved. A copper(II)-bipy analog also shows long-range order, with T C of 13 K. In the absence of a crystal structure, the magnetic and spectral properties of this Cu derivative point to a different structural topology being present.