Hexacyanometalate molecular chemistry: Heptanuclear heterobimetallic complexes; Control of the ground spin state

Following a bottom-up approach to nanomaterials, we present a rational synthetic route from hexacyanometalates [M(CN)(6)](3-) (M = Cr-III, C-III) cores to well-defined heptanuclear complexes: By changing the nature of the metallic cations and using a localised orbital model it is possible to control and to tune the ground state spin value. Thus, with M = Cr-III, d(3), S = 3/2, three heptanuclear species were built and characterised by mass spectrometry in solution, by single-crystal X-ray diffraction and by powder magnetic susceptibility measurements, [Cr-III(CN-M'L-n)(6)](9+) (M' = Cu-II, Ni-II, Mn-II, L-n = polydentate ligand), showing spin ground states S-G = 9/2 [Cu-II], with ferromagnetic interactions J(Cr,Cu) = +45 cm(-1), S-G =15/2 [Ni-II] and J(Cr,Ni) = + 17.3 cm(-1), S-G = 27/2 [Mn-II], with an antiferromagnetic interaction J(Cr,Mn) = - 9 cm(-1), (interaction Hamiltonian H = - J(Cr,Mn) [S(Cr)Sigma(i)S(M)(i)], i = 1-6). With M = Co-III, d(6), S = 0, the heptanuclear analogues [Co-III(CN - M'L-n)(6)](9+) (M' = Cu-II, Ni-II, Mn-II) were similarly synthesised and studied. They present a singlet ground state and allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.