A series of new hetero-decanucleus sandwich Cd-Ln clusters constructed from open-chain ether Schiff base and niacin ligands: Synthesis, structure, luminescence and antioxidant activity

Three heteronuclear Cd-Ln clusters based on open-chain ether Schiff (bis(5-bromine-3-methoxysalicylidene)-3-oxapentane-1,5-diamine (H2L) and niacin (NA), with composition [Cd(6)Ln(4)L(5) (OAc)(5)(NA)(5)(CH3OH)(5)](NO3)(4).x (CH3OH).y(CH2Cl2) (1 Ln = Sm, x = 1, y = 1; 2 Ln = Eu, x = 0, y = 1; 3 Ln = Tb, x = 2, y = 1), have been synthesized and structural characterizated. The structure analysis reveals that 1-3 contain the similar sandwich-type polycationic unit [Cd(6)Ln(4)L(5)(OAc)(5)(NA)(5)(CH3OH)(5)](4+). Solid-state luminescence studies show that the emission peaks of the H2L ligand located in the range of 340 similar to 373 nm in 1-3. The characteristic emission peaks of Sm3+ ion appear in cluster 1, but there is no Eu3+ or Tb3+ ion emission peak in clusters 2 and 3. The fluorescence spectra of 1-3 in N,N-dimethylformamide (DMF) solution only appear emission peaks of pi*->pi transition of [CdL] coordination units, but characteristic emission peaks of Ln(3+) ions didn't emerge. It is possible that the DMF molecules impeded the energy transfer from [CdL] coordination units to the lanthanum(III) ions. Moreover, antioxidation properties indicate that H2L and 1-3 have outstanding biological activity in scavenging oxygen free radicals.

Automated summary

Three heteronuclear Cd-Ln clusters based on open-chain ether Schiff and niacin have been synthesized and structurally characterized, containing sandwich-type polycationic units. Solid-state luminescence studies revealed emission peaks of the H2L ligand, while in solution only emission peaks of [CdL] coordination units were observed.