Near-infrared (NIR) luminescent homoleptic lanthanide Salen complexes Ln4(Salen)4 (Ln = Nd, Yb or Er)

Synthesis, characterization and oscillator-vibrated near-infrared (NIR) luminescence of two pseudo-polymorphic [Yb4((OH)2-Salophen)4] complexes

“…Moreover, PXRD analysis (Fig. 5S) on another series of complexes 4-6 shows that they are also iso-structural, where the measured patterns from complexes 4-6 are well consistent with the simulated pattern of 4 ] host structure in both 2ÁDMF and 5ÁDMFÁ2MeOHÁ9H 2 O is distinctively different from binuclear triple-decker Ln 2 (Salen) 3 [22] or trinuclear triple-decker Ln 3 (Salen) 3 complexes [23] from the typical quadridentate Salentype Schiff-base ligands, and also incomparable to trinuclear triple-decker Ln 3 (Salen) 3 [24], cyclic tetranuclear Ln 4 (Salen) 4 [25] or Ln 4 (Salen) 2 [26] and pentanuclear tetra-decker Ln 5 (Salen) 4 [27] frameworks from the hexadentate Salen-type Schiff-base ligands with two AOMe groups, where the charge balance inevitably depends on the counter-anions.…”

Near-infrared (NIR) luminescent homoleptic linear tetranuclear [Ln 4 ((OH) 2 -Salophen) 4 ] (Ln = Nd or Yb) complexes self-assembled from the dihydroxylated Salophen ligand

“…Moreover, the excited state of the Nd 3+ ions in 2 with the smaller energy gap is more sensitive to luminescent quenching especially with the nearby O-H oscillators of partially deprotonated (H 2 L) 2− and coordinated EtOH around the Nd 3+ ions. It is worth noting that the NIR intrinsic quantum yields of both complexes 2-3 are relatively smaller than those of Ln 4 (Salen) 4 [20] or Ln 4 (Salen) 2 [21] complexes based on the typical Salen-type Schiff-base ligands, which should be primarily due to the use of the rigid linker for complexes 2-3 while not flexible linkage with the NIR sensitization from both 3 LC and 1 LC excited states of the ligand.…”

“…The solvate DMF molecule of 3·DMF, contributes to the stability of the structure, while exhibits no observed hydrogen-bonding interactions with the framework. It is worth noting the linear tetranuclear [Yb 4 ((OH) 2 -Salophen) 4 ] host structure in 3·DMF is distinctively different from binuclear triple-decker Ln 2 (Salen) 3 [17] and trinuclear triple-decker Ln 3 (Salen) 3 complexes [18] from the typical quadridentate Salen-type Schiff-base ligands, and also incomparable to trinuclear triple-decker Ln 3 (Salen) 3 [19], cyclic tetranuclear Ln 4 (Salen) 4 [20] or Ln 4 (Salen) 2 [21] and pentanuclear tetra-decker Ln 5 (Salen) 4 [22] frameworks from the hexadentate Salen-type Schiff-base ligands with the two -OMe groups, where the charge balance just depends on the counter-anions while not the mixed (L) 4− and (H 2 L) 2− coordination modes of four (OH) 2 -Salophen ligands in 3·DMF. As to the bulk purity of the four polycrystalline samples of complexes 2-5, it is convincingly established by PXRD measurements.…”

“…Moreover, the excited state of the Nd 3+ ions in 2 with the smaller energy gap is more sensitive to luminescent quenching especially with the nearby O-H oscillators of partially deprotonated (H 2 L) 2− and coordinated EtOH around the Nd 3+ ions. It is worth noting that the NIR intrinsic quantum yields of both complexes 2-3 are relatively smaller than those of Ln 4 (Salen) 4 [20] or Ln 4 (Salen) 2 [21] complexes based on the typical Salen-type Schiff-base ligands, which should be primarily due to the use of the rigid linker for complexes 2-3 while not flexible linkage with the NIR sensitization from both 3 LC and 1 LC excited states of the ligand.In conclusion, on the basis of self-assembly of the dicarboxylmodified (OH) 2 -Salophen ligand H 4 L with LnCl 3 ·6H 2 O, the mixed (L) 4− and (H 2 L) 2− coordination modes induce the formation of anionindependent linear tetranuclear [Ln 4 ((OH) 2 -Salophen)] 4 -arrayed complexes [Ln 4 (H 2 L) 2 (L) 2 (EtOH) 2 ] (1-5). Moreover, the result of their photophysical studies shows that the (OH) 2 -Salophen ligand may work as antennae for the sensitization of the characteristic NIR luminescence of Nd 3+ and Yb 3+ ions despite the luminescent quenching with the OH-oscillators around the Ln 3+ ions.…”

Mixed anion-induced Salen-based Zn2Ln3 (Ln=Nd, Yb or Er) complexes with near-infrared (NIR) luminescent properties

“…In both heterometallic systems, the relatively "soft" Lewis acid 3d Zn 2+ ion usually lies in the cis-N 2 O 2 core of the ligand and the "hard" Lewis acid 4f Ln 3+ ion necessarily occupies the outer O 2 O 2 moiety, and the Zn 2+ Schiff-base complexes, as the suitable chromophores, could effectively sensitize of the NIR luminescence of the Ln 3+ ions. As a matter of fact, it is well known that the coordination of Ln 3+ ion in the inner cis-N 2 O 2 core is common as shown in polynuclear [21,22] or polymeric Ln 3+ Salen complexes [23]. To some extent, it should make self-assembly of 3d and 4f mixed metal complexes from the Salen-type Schiff-base ligands with the outer O 2 O 2 moieties more complicated, which stimulates us to further explore new bimetallic polynuclear complexes with coordination modes of Ln 3+ ions in both the cis-N 2 O 2 cores and the outer O 2 O 2 cavities.…”