Effect of Ancillary Ligands in Hydrolysis of 1,8-Naphthalic Anhydride for Synthesis of Metallacycles of Co2+, Ni2+, and Zn2+

Di-, tetra- and hexanuclear metallacycles of Zn2+, Co2+, and Ni2+ prepared by ring-opening reactions of 1,8-naphthalic anhydride with corresponding metal acetate in the presence of 2,2'-bipyridine or 1,10-phenanthroline, namely [Co-4(bpy)(4)(naphDA)(4)(H2O)(4)]center dot 12H(2)O (I), [Co-6(phn)(6)(naphDA)(6)(H2O)(12)]center dot 20H(2)O (II), [Ni-6(phn)(6)(naphDA)(6)(H2O)(12)]center dot 20H(2)O (III), [Zn-4(bpy)(4)(naphDA)(4)(H2O)(4)]center dot 2H(2)O (IV), and [Zn-2(phn)(2)(naphDA)(2)(H2O)(2)]center dot H2O (V) (H(2)naphDA = 1,8-naphthalene dicarboxylic acid, bpy = 2,2'-bipyridine, phn = 1,10-phenanthroline) were structurally characterized. In the case of the reaction of nickel(II) acetate with 1,8-naphthalic anhydride in the presence of bpy a mononuclear complex [Ni(bpy)(naphDA)(H2O)(3)]center dot H2O (VI) was observed. Both the Co2+-metallacycles on heating to 420 degrees C resulted in the formation of CoO. The magnetic properties of the metallacycles containing Co2+ and Ni2+ ions were investigated. Dominant antiferromagnetic interactions in the tetra- and hexanuclear Co2+-metallacycles were observed. The hexanuclear Ni2+-metallacycle III with a spin state S = 3 showed intramolecular ferromagnetic interactions. For the metallacycle III, the magnetic susceptibility data above 50 K could be reproduced with the parameters of g = 2.26 and J(Ni-Ni) = +1.2 cm(-1) using single J-model based on Hamiltonian H = -2J (S-1.S-2 + S-2.S-3 + S-3.S-4 + S-4.S-5 + S-5.S-6 + S-6.S-1).