Relations between structure and physicooptical properties of Eu3+ and Tb3+ tetraphosphonates

• QUADRAMET®.
• Luminescence properties of Eu3+ and Tb3+ tetraphosphonate crystals.
• Untypical luminescence quenching of Eu and Tb by OH oscillators.

The crystal structure of the Tb3+ complex with ethylenediaminetetra(methylenephosphonic acid) (H8EDTMP) was determined and it was found that the compound is isostructural with the previously studied [C(NH2)3]7[Eu(EDTMP)(CO3)]⋅10H2O crystal. The Eu3+ and Tb3+ complexes with trans-cyclohexane-1,2-diamine-N,N,N′,N′-tetrakis(methylenephosphonic acid) (H8CDTMP) of known crystal structures were also obtained. As it results from the X-ray analyses both tetraphosphonate ligands (EDTMP and CDTMP) bind the Ln3+ ion with 2 nitrogen atoms and 4 oxygen atoms in such a way that only one oxygen atom from each phosphonate group is linked with the central ion. The coordination sphere is completed by two oxygen atoms of the bidendate carbonate anion in the case of Ln3+–EDTMP complexes, whereas two monomeric Ln3+–CDTMP complex anions are connected by two hydroxyl ions and one water molecule. The spectroscopic (FTIR and emission) studies of crystals are presented and discussed with respect to their structures. It was shown that OH oscillators present in the inner-sphere of Eu3+ and Tb3+ complexes with CDTMP do not quench lanthanide emission. The reasons of that are three very short hydrogen bonds (∼2 Å) formed between two hydroxyl groups and a water molecule. The luminescence lifetimes and quantum yields of lanthanide tetraphosphonates were compared with those obtained for Ln3+ tetracarboxylates.