New Route to Polynuclear Ni(II) and Cu(II) Complexes with Bridging Oxime Groups That Are Inaccessible by Conventional Preparations

A series of new polynuclear complexes of divalent Ni and Cu with 2-cyano-2-oximino-acetic acid (later AACO(2)-) were obtained as the result of the ligand modification reaction in the process of complexation, using 2-cyano-2-oximino-acetates such as methyl- (later as MeCO), and ethyl- (as ECO later on). Synthesized compounds were characterized by spectroscopic methods, thermal analysis, magnetochemistry, and X-ray crystallography. Crystal data revealed the formation of the dimeric [Ni(AACO) (H2O)(3)](2)center dot H2O (1), trimeric K-2[Ni-3(AACO)(4)(H2O)(4)]center dot 4H(2)O (2), and K-2[Cu-3(AACO)(4)(H2O)(4)]center dot 4H(2)O (3) complexes, with bridging NO-groups cyanoxime dianions. In the latter two compounds, the AACO(2-) anions adopt cis-arrangements around metal centers. One mononuclear complex of K-2[Cu(AACO)(2)(H2O)]center dot 2H(2)O (4) composition was isolated and characterized as well, where the cyanoxime forms the trans-complex 4. There is moderate-to-strong antiferromagnetic coupling between metal centers in polynuclear complexes. Data of thermal analysis studies revealed high-energy properties for dehydrated complexes 3 and 4, which violently decompose at similar to 200 degrees C. These compounds may be viewed as room temperature completely safe, but heat-triggered actuators, because of their pronounced mechanical action upon leaving the system (crucible). Final products of thermal decomposition are Ni and NiO for 1, and the mixture of NiO and K2O for 2, with metallic copper for 3 and 4.