Nuclearity Control in Molecular Copper Phosphates Derived from a Bulky Arylphosphate: Synthesis, Structural and Magnetic Studies

Starting from sterically encumbered 2,6-di-tert-butylphenyl phosphate (dtbppH(2)) and co-ligand 3,5-dimethyl pyrazole (dmpz), it is possible to isolate either mono-, di- or tetranuclear copper phosphates by varying the copper source and making attendant changes in the reaction conditions. For example, reaction of copper nitrate with dtbppH(2) and dmpz at 60 degrees C leads to the isolation of the mononuclear copper phosphate [Cu(dtbppH)(2)(dmpz)(MeOH)(2)] (1) as the only product. However, the use of copper acetate in place of copper nitrate and conducting the reaction at the room temperature leads to the formation of both dinuclear [Cu(dtbpp)(dmpz)(2)](2) (2) and tetranuclear [Cu-2(dtbpp)(dmpz)(2)(OAc)(MeO)](2) (3) from the same reaction mixture. Compounds 2 and 3 could be isolated in pure form through fractional crystallization. Copper phosphates 1-3 have been characterized by both analytical and spectroscopic methods including EPR and magnetic measurements. The molecular structures of all three compounds were established through single crystal diffraction studies. Dc magnetic measurements indicate antiferromagnetic interactions between the metal centres in all the compounds.