Synthesis and Spectral Investigation of Anionic Tetrakis-Complexes of Rare Earth Elements With Dimethyl-N-Trihloracetylamidophosphate and Tetraphenylphosphonium Cation

Abstract

As a continuation of studies of carbacylamidophosphate based coordination compounds a series of the lanthanide and yttrium complexes of general formula PPh4[LnL4], where Ln=La, Nd, Tb and Y; L– = [CCl3(CO)N(PO)(OCH3)2]– has been synthesized. The resulting compounds were characterized by means of thermal gravimetric analysis, IR, 1H NMR, UV-Vis absorption and luminescent spectroscopy. It was found, that each lanthanide ion of the [Ln(L)4]– complex anion is bonded to two oxygen atoms belonging to the phosphoryl and carboxyl groups of four bidentate chelated ligands, completing coordination number of lanthanide ion to eight. Analysis of signals integral intensity in the investigated NMR spectra of coordination compounds PPh4[LnL4] (Ln = La, Y) indicates the molar ratio of dimethyl-N-trichloroacetylamidophosphate ligand and tetraphenylphosphonium cation as 4:1, which corresponds to the proposed structure of the complexes. According to the absorption spectroscopy investigations data there is one type of lanthanide sites in the complexes. Low symmetry of lanthanide ion coordination environment was concluded from bands ratio in the europium complex luminescence spectrum. From the TGA analysis the stability of the coordination compounds till 160°C can be concluded. It was shown that tetraphenylphosphonium cation sensitizes europium ion emission and photo-excitation of PPh4[EuL4] complex by UV light results in red Eu3+ centered luminescence with dominating band of 5D0–7F2 transition in the spectrum and decay time equal one and a half millisecond.

Crystal structure of tetraphenyl phosphate tetrakis[dimethyl (2,2,2-trichloroacetyl)phosphoramidato]lutetium(III), PPh4[LuL 4]

“…The complexes of composition PPh 4 [LnL 4 ] with metals La, Nd, Eu, Tb and Y have been synthesized and described previously. The previously used method (Olyshevets et al, 2017) was adopted for the preparation of the title compound.…”

The influence of different cations on the structure and spectral properties of Ln3+ tetrakis-complexes with the CAPh-type ligand dimethyl-N-trichloroacetylamidophosphate

“…5 and 6. An Eu 3+ complex with tetraphenylphosphonium cation was investigated at 77 K. Its luminescence properties at room temperature were published previously 15 and are being here used for comparison.…”

“…The 7 F 0 -5 L 6 transition prevails in the excitation spectra of Q[EuL 4 ], a characteristic feature of CAPh-based tetrakiscomplexes, 15,18,25,32,33 as well as many other Eu 3+ compounds. Conversely, the 7 F 0 -5 D 2 band may dominate the excitation spectrum if the 5 L 6 level is depopulated by LMCT states.…”

“…These compounds have been successfully applied as ''antennas'' providing efficient intramolecular energy transfer to the lanthanide ion, highly intensifying its luminescence. [12][13][14][15][16][17][18] The PO group in the chelating core of the CAPh and SAPh molecule is known to have high affinity towards lots of metal ions, [19][20][21] particularly lanthanides, 2,[22][23][24] hence the stability of the complexes increases.…”