Regulation of the Metal Center and Coordinating Anion of Mononuclear Ln(III) Complexes to Promote an Efficient Luminescence Response to Various Organic Solvents

A series of mononuclear lanthanide
complexes [Ln­(L1)­(NO3)3], (Ln =
Dy­(III), 1; Tb­(III), 3; and Eu­(III), 4; L1 = (N1E,N2E)-N1,N2-bis­((1-methyl-1H-benzo­[d]­imidazol-2-yl)­methylene)­cyclohexane-1,2-diamine)
is obtained by reacting N-methylbenzimidazole-2-carbaldehyde
(L2) and 1,2-cyclohexanediamine (L3) with
Ln­(NO3)3·6H2O under solvothermal
conditions. L1 ligand is produced via an in situ Schiff
base reaction of two molecules of L2 and one molecule
of L3. The metal center Ln­(III) is in a N4O6 environment formed by L1 and NO3–. NaSCN is added on the basis of 1 synthesis. One SCN– replaces one of the three
coordinated NO3– anions in the 1 structure, and the complex [Dy­(L1)­(NO3)2(SCN)]·CH3CN (2) is synthesized.
The complex 1 shows excellent luminescence response to
petroleum ether (PET), an organic solvent. To the best of our knowledge,
this study is the first to use a complex for sensing responses to
PET. When the metal center is changed, the obtained mononuclear complexes 3 and 4 show an excellent luminescence response
to tetrahydrofuran (THF). Lastly, 2 obtained by changing
the coordinating anion shows an excellent luminescence response to
dichloromethane. Herein, for the first time, we regulate the metal
center and coordinating anion of lanthanide complexes to adjust the
recognition and response of these complexes to different organic solvents.