Structural diversity and properties of a series of dinuclear and mononuclear copper(ii) and copper(i) carboxylato complexes

Abstract

The syntheses, crystal structures, magnetic and photoluminescence properties of a series of dinuclear and mononuclear copper(II) and copper(I) N-carbazolylacetate [N-carbazolylacetic acid = Hcabo] with different carboxylato coordination modes are reported. Although the carboxylato group has different coordination modes, the same carboxylate ligand binding to copper ion via four coordinating modes is rare. The crystal structure of complex [Cu₂(Cabo)₄(dmf)₂]·2dmf (1) consists of a symmetrical dimeric Cu(II) carboxylato paddle-wheel core and oxygen atoms from dmf at the apical positions. The dinuclear complex [Cu₂(Cabo)₃(phen)₂]ClO₄·H₂O·C₂H₅OH (2) (phen = 1,10-phenanthroline) consists of an unusual dimeric core with two copper atoms bridged by three carboxylates one of which is in the η∶η∶μ₂ bridging mode and the other two are in the rarer monoatomic bridging mode. To our knowledge, the present bridging mode has not been reported hitherto. Magnetic susceptibilities were measured in the temperature range 2–300 K. It is found that paddle-wheel copper(II) ions in 1 are strongly coupled antiferromagnetically with 2J = −356.4(6) cm⁻¹, whereas complex 2 shows weak antiferromagnetic interaction with a 2J value of −12.8(4) cm⁻¹. Copper(I) N-carbazolylacetate with strong fluorescence in the solid state as well as high thermal stability was obtained by reduction of the copper(II) N-carbazolylacetate using PPh₃ (triphenylphosphine) in dmf solution.