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

•Dihydroxylated Salen-type ligand (OH)2-Salophen.•Pseudo-polymorphic complexes [Ln4((OH)2-Salophen)4].•Oscillator-vibrated NIR luminescence.

Through the self-assembly of the (OH)2-Salophen H4L (H4L = N,N′-bis(3-hydroxylsalicylidene)benzene-1,2-diamine) with LnCl3·6H2O or Ln(NO3)3·6H2O (Ln = La, Yb or Gd) in different solvent systems MeCN–EtOH and MeCN–DMF, the mixed (L)4− and (H2L)2− coordination modes induce the formation of anion-independent while pseudo-polymorphic homoleptic linear tetranuclear complexes [Ln4(H2L)2(L)2(EtOH)2] (Ln = La, 1; Ln = Yb, 2 or Ln = Gd, 3) and [Ln4(H2L)2(L)2(DMF)2] (Ln = La, 4; Ln = Yb, 5 or Ln = Gd, 6), respectively. The result of their photophysical properties shows the characteristic NIR luminescence for both Yb3+-based complexes 2 and 5 with emissive lifetimes in microsecond ranges, while the difference of nearby and/or distant oscillator-based (OH and/or CH) vibrations from two coordinated EtOH or DMF molecules within the inner coordination spheres of Yb3+ ions in the two complexes has a decisive effect on their NIR luminescent properties.

Graphical abstractTwo series of anion-independent while pseudo-polymorphic homiletic linear tetranuclear [Ln4(H2L)2(L)2(EtOH)2] (Ln = La, 1; Ln = Yb, 2 or Ln = Gd, 3) and [Ln4(H2L)2(L)2(DMF)2] (Ln = La, 4; Ln = Yb, 5 or Ln = Gd, 6) are obtained from the self-assembly of the (OH)2-Salophen H4L (H4L = N,N′-bis(3-hydroxyl salicylidene)benzene-1,2-diamine) with LnCl3·6H2O or Ln(NO3)3·6H2O (Ln = La, Yb or Gd) in different solvent systems MeCN–EtOH and MeCN–DMF, respectively. The different NIR luminescence between Yb3+-based complexes 2 and 5 should be resulted from the difference of nearby and/or distant oscillator-based (OH and/or CH) vibrations from two coordinated EtOH or DMF molecules within the inner coordination spheres of Yb3+ ions.Figure optionsDownload full-size imageDownload as PowerPoint slide