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)

Unique homoleptic cyclic tetranuclear Ln4(Salen)4 complexes [Ln4(L)2(HL)2(μ3-OH)2Cl2]·2Cl (Ln = Nd, 1; Ln = Yb, 2; Ln = Er, 3; Ln = Gd, 4) or Ln4(Salen)2 complexes [Ln4(L)2(μ3-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 H2L with LnCl3·6H2O or Ln­(OAc)6·6H2O (Ln = Nd, Yb, Er, or Gd), respectively (H2L: 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 1LC and 3LC) 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 Ln3+ ions.