Synthesis and NIR luminescence of a series of salen type erbium complexes

A series of five rigid hexadentate salen-type (H2L) erbium complexes, namely, [Er2L(OAc)4(CH3OH)2]·2CH3OH (1), [Er2L3(CH3OH)]·2CH3OH (2), [Er3L3(OAc)3]·3CH3OH·H2O (3), [Er2L(acac)4]·2CH2Cl2 (4) and [Er2LL′L″(CH3OH)(H2O)2](ClO4)2·CH3OH·H2O (5) (H2L = N,N′-bis(2-oxy-3-methoxybenzylidene)-1,2-phenylenediamine, HL′=2-(2′-hydroxy-3′-methyloxy-phenyl)-benzimidazole and HL″=3-methoxysalicylaldehyde) have been isolated by reactions of H2L with various Er(III) salts. X-ray crystallographic analyses demonstrate that complexes 1, 2, 4 and 5 possess the unique Er2 core with a ratio of H2L/Er=1:2, 3:2, 1:2 and 1:1, respectively. Complex 3 is trinuclear with sandwich-type structure. All complexes 1-5 exhibit near-IR luminescence of Er(III) ions around 1530 nm with lifetime (2.45 μs), which can be rationalized on the basis of the disparate structural effects.