Structural variation from heterometallic heptanuclear or heptanuclear to cubane clusters based on 2-hydroxy-3-ethoxy-benzaldehyde: effects of pH and temperature

Five new Hheb complexes, HN(C2H5)(3)center dot[M4Na3(heb)(6)(mu(3)-N-3)(6)], (M = Ni (1), and Co (2), [Co-4(heb)(4)(mu(3)-OCH3)(4)(mu(1)-HOCH3) (4)]center dot(H2O)(2) (3), [M-7(heb)(6)(mu(3)-OCH3)(6)]center dot(ClO4)(2) (M = Ni (4), and Co (5), Hheb = 2-hydroxy- 3-ethoxy-benzaldehyde), were synthesized by reaction of hexahydrate perchlorate salt, Hheb, and NaN3 under different temperature and pH conditions. Careful investigation of the effect of the reaction temperature and pH resulted in a series of compounds with different compositions and nuclearities. The diverse compounds obtained illustrate the marked sensitivity of the structural chemistry of Co- or Ni-Hheb ligand-like systems to synthesis conditions. Complexes 1 and 2, which are heterometallic heptanuclear anion [M4Na3(heb)(6)(N-3)(6)](-) clusters, are formed at a pH of 5.5 and at room temperature. At a pH of 7.5 and at room temperature, a neutral molecular cubane cluster, namely 3, is formed with a lower nuclearity. Further increase of the reaction temperature to 140 degrees C at the same pH resulted in formation of two heptanuclear cation [M-7(heb)(6)(mu(3)-OCH3)(6)](2+) clusters, 4 and 5. The results show that the pH and reaction temperatures play a key role in the structural control of the self-assembly process. Interestingly, heterometallic heptanuclear anion [M4Na3(heb)(6)(N-3)(6)](-) clusters have never been reported for the family of mu(3)-N-3(-) or mu(3)-O-bridged heptanuclear clusters. The magnetic properties of 1-5 were investigated and are discussed in detail.