Anion-Induced Self-Assembly of Luminescent and Magnetic Homoleptic Cyclic Tetranuclear Ln₄(Salen)₄ and Ln₄(Salen)₂ Complexes (Ln = Nd, Yb, Er, or Gd)

Abstract

Unique homoleptic cyclic tetranuclear Ln(4)(Salen)(4) complexes [Ln(4)(L)(2)(HL)(2)(μ(3)-OH)(2)Cl(2)]·2Cl (Ln = Nd, 1; Ln = Yb, 2; Ln = Er, 3; Ln = Gd, 4) or Ln(4)(Salen)(2) complexes [Ln(4)(L)(2)(μ(3)-OH)(2)(OAc)(6)] (Ln = Nd, 5; Ln = Yb, 6; Ln = Er, 7; Ln = Gd, 8) have been self-assembled from the reaction of the hexadentate Salen-type Schiff-base ligand H(2)L with LnCl(3)·6H(2)O or Ln(OAc)(6)·6H(2)O (Ln = Nd, Yb, Er, or Gd), respectively (H(2)L: N,N'-bis(salicylidene)cyclohexane-1,2-diamine). The result of their photophysical properties shows that the strong and characteristic NIR luminescence for complexes 1-2 and 5-6 with emissive lifetimes in microsecond ranges are observed, and the sensitization arises from the excited state (both (1)LC and (3)LC) of the hexadentate Salen-type Schiff-base ligand with the flexible linker. Temperature dependence (1.8-300 K) magnetic susceptibility studies of the eight complexes suggest the presence of an antiferromagnetic interaction between the Ln(3+) ions.

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.…”

Structures and luminescent sensors of mixed‐counterions based salen‐type lanthanide coordination polymers

“…Salen‐type lanthanide complexes/coordination polymers have been reported in terms of various structural designs and function . It is well known that structures of salen‐type lanthanide complexes/coordination polymers are dominated by various reaction factors, such as the radii of lanthanide ions, the ligand structure, and even lanthanide counterions . Chiefly, lanthanide counterions play essential parts on the structures of salen‐type lanthanide complexes.…”