Multifunctionality in Bimetallic Ln^III[W^V(CN)₈]³⁻ (Ln=Gd, Nd) Coordination Helices: Optical Activity, Luminescence, and Magnetic Coupling

Abstract

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⋅4 H2O (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⋅5 MeCN⋅4 MeOH (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 λmax ≈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 (4)F3/2 → (4)I9/2,11/2,13/2 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) (SGd = 7/2) and W(V) (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 Nd(III)-NC-W(V) linkages.

Structural Transformation from Dimerization to Tetramerization of Serine‐Decorated Rare‐Earth‐Incorporated Arsenotungstates Induced by the Usage of Rare‐Earth Salts

“…In the case of 3‐Sm , the intensity ratio of I ( 4 G 5/2 → 6 H 9/2 )/ I ( 4 G 5/2 → 6 H 5/2 ) is approximately 5.7:1, which is strong evidence that the Sm 3+ ions exist in low‐symmetric coordination environments. The excitation spectrum of 3‐Sm exhibits several peaks at λ =346, 362, 375, 391, 402, 416, 441, 465, 478, 489, and 501 nm, which could be refer to the transitions from the ground state 6 H 5/2 to the excited states ( 4 K 17/2 + 4 L 17/2 , 4 L 15/2 , 6 P 7/2 , 4 K 11/2 , 4 F 7/2 , 6 P 5/2 , 4 G 9/2 , 4 I 13/2 , 4 I 11/2 , 4 I 9/2 , and 4 G 7/2 ; see Figure S23 b in the Supporting Information) . The decay–time profile of 3‐Sm measured by monitoring the emission at λ =642 nm is in agreement with a second‐order exponential function, thus providing τ 1 =5.70 μs (22.62 %), τ 2 =9.68 μs (79.38 %), and τ *=8.86 μs (Figure d), which gives a slightly longer lifetime relative to the Sm 3+ compound [H 2 N(CH 3 ) 2 ] 6 Na 24 H 16 {[Sm 10 W 16 (H 2 O) 30 O 50 ](B‐α‐AsW 9 O 33 ) 8 }⋅97 H 2 O (i.e., τ =8.31 μs) .…”

Lanthanide Photoluminescence in Heterometallic Polycyanidometallate-Based Coordination Networks

“…It enables the observation of visible and NIR photoluminescence of accompanying emissive chromophores [32]. In effect, a considerable number of photoluminescent d–f coordination networks based on octacyanidometallates were reported (Figure 7 and Figure 8, Table 4) [101,102,103,104,105,106,107,108,109,110]. In the aqueous solution, trivalent lanthanide(3+) and [M V (CN) 8 ] 3− ions produce the cyanido-bridged [Ln III (H 2 O) 5 ][M V (CN) 8 ] (Ln = Sm, Eu, Gd, Tb; M = Mo, W) layered frameworks of a square grid topology [101,102,103].…”

“…The implementation of the enantiopure derivatives of 2,2’-(2,6-pyridinediyl)bis(2-oxazoline) (pybox) molecule into the Ln III –[W V (CN) 8 ] 3− systems resulted in the formation of chiral cyanido-bridged [Ln III ( i Pr-pybox)(dmf) 4 ][W V (CN) 8 ]·dmf·4H 2 O (Ln = Nd, Eu, Gd; i Pr-pybox = ( SS )- or ( RR )-2,2’-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline); Figure 7a) and [Ln III (ind-pybox)(dmf) 4 ] [W V (CN) 8 ]·5MeCN·4MeOH (Ln = Nd, Gd; ind-pybox = ( SRSR )- or ( RSRS )-2,6-bis[8H-indeno[1,2-d]oxazolin-2-yl]pyridine) helices [107,108]. Taking advantage of both luminescent Ln 3+ and pybox ligand, the Eu( i Pr-pybox)W chains reveal the thermal switching between red Eu 3+ emission predominant at low temperature due to the effective ligand-to-metal energy transfer, and blue i Pr-pybox-centred photoluminescence prevailing at room temperature, as the energy back transfer to ligand is operating at higher temperatures (Figure 7b) [107].…”

“…The GdW helices with i Pr-pybox, and the more expanded ind-pybox ligands, exhibit exclusively the ligand-based red phosphorescence. The NdW chains show the 4f-metal-centred NIR emission enhanced by the pybox-to-Nd 3+ energy transfer process [108]. …”

Synthesis, Structures and Properties of Cobalt Thiocyanate Coordination Compounds with 4-(hydroxymethyl)pyridine as Co-ligand

“…For this purpose, structure-property relationships are investigated systematically and strategies for a rational construction of their crystal structures are required. Compounds that consist of paramagnetic metal cations are of particular interest because they can show different magnetic properties and thus it is not surprising that an increasing number of new compounds were recently reported [5][6][7][8][9][10][11][12][13][14]. One group of these compounds are transition metal thiocyanato coordination polymers, which show a variety of different coordination modes including the terminal and the bridging coordination, with the latter being of special importance because cooperative magnetic properties can be expected [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34].…”