Multifunctionality in Bimetallic LnIII[WV(CN)8]3- (Ln = Gd, Nd) Coordination Helices: Optical Activity, Luminescence, and Magnetic Coupling

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 (Gd3+, Nd3+) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN--bridged coordination chains: {[LnIII(SS/RR-iPr-Pybox)(dmf)4]3[WV(CN)8]3}ndmf4H2O (Ln=Gd, 1-SS and 1-RR; Ln=Nd, 2-SS and 2-RR) and {[LnIII(SRSR/RSRS-Ind-Pybox)(dmf)4][WV(CN)8]}n5MeCN4MeOH (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 200-450nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/Vis absorption spectra. Under irradiation with UV light, the GdIII-WV chains show dominant ligand-based red phosphorescence, with max approximate to 660nm for 1-(SS/RR) and 680nm for 3-(SRSR/RSRS). The NdIII-WV chains, 2-(SS/RR) and 4-(SRSR/RSRS), exhibit near-infrared luminescence with sharp lines at 986, 1066, and 1340nm derived from intra-f 4F3/24I9/2,11/2,13/2 transitions of the NdIII 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 [WV(CN)8]3- moieties connected by cyanide bridges, 1-(SS/RR) and 3-(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between GdIII (SGd=7/2) and WV (SW=1/2) centers with J1-(SS)=-0.96(1)cm-1, J1-(RR)=-0.95(1)cm-1, J3-(SRSR)=-0.91(1)cm-1, and J3-(RSRS)=-0.94(1)cm-1. 2-(SS/RR) and 4-(SRSR/RSRS) display ferromagnetic coupling within their NdIII-NC-WV linkages.