Search for: All records

A family of Zn 16 Ln(HA) 16 metallacrowns (MCs; Ln = Yb III , Er III , and Nd III ; HA = picoline- (picHA 2− ), pyrazine- (pyzHA 2− ), and quinaldine- (quinHA 2− ) hydroximates) with an ‘encapsulated sandwich’ structure possesses outstanding luminescence properties in the near-infrared (NIR) and suitability for cell imaging. Here, to decipher which parameters affect their functional and photophysical properties and how the nature of the hydroximate ligands can allow their fine tuning, we have completed this Zn 16 Ln(HA) 16 family by synthesizing MCs with two new ligands, naphthyridine- (napHA 2− ) and quinoxaline- (quinoHA 2− ) hydroximates. Zn 16 Ln(napHA) 16 and Zn 16 Ln(quinoHA) 16 exhibit absorption bands extended into the visible range and efficiently sensitize the NIR emissions of Yb III , Er III , and Nd III upon excitation up to 630 nm. The energies of the lowest singlet (S 1 ), triplet (T 1 ) and intra-ligand charge transfer (ILCT) states have been determined. Ln III -centered total ( Q LLn) and intrinsic ( Q LnLn) quantum yields, sensitization efficiencies ( η sens ), observed ( τ obs ) and radiative ( τ rad ) luminescence lifetimes have been recorded and analyzed in the solid state and in CH 3 OH and CD 3 OD solutions for all Zn 16 Ln(HA) 16 . We found that, within the Zn 16 Ln(HA) 16 family, τ rad values are not constant for a particular Ln III . The close in energy positions of T 1 and ILCT states in Zn 16 Ln(picHA) 16 and Zn 16 Ln(quinHA) 16 are preferred for the sensitization of Ln III NIR emission and η sens values reach 100% for Nd III . Finally, the highest values of Q LLn are observed for Zn 16 Ln(quinHA) 16 in the solid state or in CD 3 OD solutions. With these data at hand, we are now capable of creating MCs with desired properties suitable for NIR optical imaging. 

Two Gd III Fe III 4 metallacrown complexes are presented and analyzed for their magnetic properties. One of these species is newly identified and exhibits a bent ring geometry as opposed to the more conventional flatter conformation of the other. Both complexes are quite similar magnetically, exhibiting antiferromagnetic exchange coupling values ca . J (Fe III –N–O–Fe III ) = −7 cm −1 and J (Gd III –O–Fe III ) = −0.7 cm −1 . When analyzed for the molecular magnetocaloric effect, maximum −Δ S m values of 7.3 J K −1 kg −1 at 3 K and at 6.1 J K −1 kg −1 at 4 K were exhibited. A detailed structural-magnetic correlation is established and an assessment of several similar magnetic metallacrowns with diverse metal combinations is given with regards to their potential magnetocaloric properties. Strategies for improving the magnetocaloric properties within the Metaln + FeIII4 family of metallacrowns are proposed regarding the ratio between coupling parameters J (Fe III –N–O–Fe III )/ J (Metal n+ –O–Fe III ).