Directed synthesis of μ-1,3,5 bridged dicyanamides by thermal decomposition of μ-1,5 bridged precursor compounds.

Reaction of transition-metal dicyanamides with pyridazine leads to the formation of the ligand-rich 1 : 2 (1 : 2 = ratio between metal salt and organic co-ligand) compounds M(dca)(2)(pydz)(2) (dca = dicyanamide, pydz = pyridazine) with M = Mn (1-Mn), Fe (1-Fe), Co (1-Co), Ni (1-Ni). In their crystal structures linear polymeric M-(dca)(2)-M chains are found, in which the M(ii) cations are μ-1,5 bridged by the dca anions. The pydz ligands are terminally N-bonded to the cations, which are octahedrally coordinated by two pydz ligands and four dca anions. On heating these precursor compounds, 1-Mn, 1-Fe and 1-Co transform quantitatively into new ligand-deficient 1 : 1 intermediate compounds of composition M(dca)(2)(pydz) with M = Mn (2-Mn), Fe (2-Fe) and Co (2-Co). Investigations by IR spectroscopy, and single crystal X-ray structure analysis, show that the intermediates form a more condensed layered structure in which half of the pristine μ-1,5 bridged dca anions become μ-1,3,5 bridging. This structural transformation is accompanied by a pronounced change of their magnetic properties: whereas the ligand-rich 1 : 2 compounds show only Curie-Weiss paramagnetism, the ligand-deficient 1 : 1 intermediates show either antiferro- or ferromagnetic ordering at lower temperatures mediated by the three-atom pathway of the μ-1,3,5 bridging dca anions.