Transition metal azolates from metallocenes. Part 3: Polymeric manganese(II) and nickel(II) pyrazolates; synthesis, characterization, and magnetochemistry

Direct reactions of nickelocene and manganocene with molten pyrazoles in an inert atmosphere or under vacuum have led to the isolation of the following metal pyrazolate compounds: [Ni(4-Xpz)(2)](x) (where X = EI, CI and pz = pyrazolate); [M(4-Xdmpz)(2)](x) (where X = H, CH3, Cl, Br and M = Ni, Mn and dmpz = 3,5-dimethylpyazolate); and [Mn(4-Xpz)(2)(4-XpzH)](x) (where X = Cl, Br and pzH = pyrazole). On the basis of indirect evidence all compounds are considered to have extended chain structures with metal ions linked in chains by double bridging pyrazolates. The two [Ni(4-Xpz)2], compounds are diamagnetic while all others are paramagnetic. Variable temperature magnetic susceptibility studies on the paramagnetic compounds reveal antiferromagnetic coupling between neighbouring metal ions. Analysis of the magnetic data (Hamiltonian of the form II = -2J Sigma S-i S-j) yields values of the exchange coupling constant J of -14 to -17 cm(-1) for the [Ni(4-Xdmpz)(2)](x) compounds, -1.2 to -2.1 cm(-1) for the [Mn(4-Xdmpz)(2)](x) compounds, and -0.41 cm(-1) for the [Mn(4-Xpz)(2)(4-XpzH)](x) compounds.