Multifunctionality in Bimetallic Ln~(III)[W~V(CN)_8]~(3-) (Ln=Gd, Nd) Coordination Helices: Optical Activity, Luminescence, and Magnetic Coupling

摘要

Two chiral luminescent derivatives of pyridine bis- (oxazoline) (Pybox), (SS/RR)-iPr-Pybox (2,6-bis[4-isopropyl-2- oxazolin-2-yl]pyridine) and (SRSR/RSRS)-Ind-Pybox (2,6- bis[8H-indeno[1,2-d]oxazolin-2-yl]pyridine), have been combined with lanthanide ions (Gd~(3+), Nd~(3+)) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN~--bridged coordination chains: {[Ln~(III)(SS/RR-iPr- Pybox)(dmf)_4]_3[W~V(CN)_8]_3}_n·dmf·4H_2O (Ln=Gd, 1-SS and 1-RR; Ln=Nd, 2-SS and 2-RR) and {[Ln~(III)(SRSR/RSRS-Ind-Pybox)- (dmf)_4][W~V(CN)_8]}_n·5MeCN·4MeOH (Ln=Gd, 3-SRSR and 3- RSRS; Ln=Nd, 4-SRSR and 4-RSRS). These materials display enantiopure structural helicity, which results in strong optical activity in the range 200–450 nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/ Vis absorption spectra. Under irradiation with UV light, the Gd~(III)-W~V chains show dominant ligand-based red phosphorescence, with λ_(max)≈660 nm for 1-(SS/RR) and 680 nm for 3- (SRSR/RSRS). The Nd~(III)-W~V chains, 2-(SS/RR) and 4-(SRSR/RSRS), exhibit near-infrared luminescence with sharp lines at 986, 1066, and 1340 nm derived from intra-f ~4F_(3/2)→~4I_(9/2,11/2,13/2) transitions of the Nd~(III) centers. This emission is realized through efficient ligand-to-metal energy transfer from the Pybox derivative to the lanthanide ion. Due to the presence of paramagnetic lanthanide(III) and [W~V(CN)_8]~(3-) moieties connected by cyanide bridges, 1-(SS/RR) and 3-(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between Gd~(III) (S_(Gd)=7/2) and W~V (S_W=1/2) centers with J_(1-(SS))=-0.96(1) cm~(-1), J_(1-(SS))=-0.95(1) cm~(-1), J_(3-(SRSR))= -0.91(1) cm~(-1), and J_(3-(RSRS))=-0.94(1) cm~(-1). 2-(SS/RR) and 4- (SRSR/RSRS) display ferromagnetic coupling within their Nd~(III)NC-W~V linkages.