One-Dimensional Polymers Containing Strictly Collinear Metal Ions:  Synthesis and XRPD Characterization of Homoleptic Binary Metal Pyrazolates

The synthesis of a number of 3d transition metal binary pyrazolates in microcrystalline form, thus suitable for a full XRPD characterization, has been pursued. The crystal and molecular structures of the Fe(pz)₃, Co(pz)₂, Co(pz)₃, and Ni(pz)₂ polymers, together with the few congeners reported in the recent literature, show that these species tend to afford highly crystalline materials where strictly collinear chains of metal atoms are present. Depending on the synthetic strategy used, Ni(pz)₂ has been found to crystallize as two different α (orthorhombic) and β (monoclinic) phases, possessing nearly identical intramolecular features. Data for each compound follow. Fe(pz)₃:  C₉H₉FeN₆, hexagonal, P6₃/m, a = 9.1745(3) Å, c = 7.2191(4) Å, Z = 2. Co(pz)₂: C₆H₆CoN₄, orthorhombic, Ibam, a = 7.5239(5) Å, b = 14.3461(9) Å, c = 7.4331(5) Å, Z = 4. Co(pz)₃:  C₉H₉CoN₆, hexagonal, P6₃/m, a = 9.1966(3) Å, c = 7.1051(3) Å, Z = 2. α-Ni(pz)₂:  C₆H₆N₄Ni, orthorhombic, Cmcm, a = 16.6758(11) Å, b = 6.4872(4) Å, c = 6.9423(6) Å, Z = 4. β-Ni(pz)₂:  C₆H₆N₄Ni, monoclinic, P2₁/m, a = 9.967(2) Å, b = 6.975(1) Å, c = 6.016(1), Å, β = 98.50(1)°, Z = 2. The thermal stability and the detailed structural properties of these model compounds have been evaluated, in the light of the technologically relevant crystal phases (the well-known metal-diazolates showing reversible spin-crossover or spin-transition behavior) obtainable upon doping, magnetic dilution, and ring substitution (in the 4-position).