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

The crystal structure of the anionic lutetium(III) tetrakis-CAPh complex (CAPh = carbacylamidophosphate) with tetraphenyl phosphate as the cation, PPh4[LuL 4], is presented and discussed.


Chemical context
Luminescent coordination compounds of lanthanides have attracted significant attention due to their diverse potential applications in lighting technology, including fluorescent lamps, LEDs, displays, telecommunications, lasers, sensors, luminescent probes for biological applications, for solar energy conversion and photocatalysis (Binnemans, 2009).Some of the extensively investigated ligands used for binding lanthanide(III) ions include �-diketones and compounds structurally akin to them (Nehra et al., 2022;Duan et al., 2022;Magennis et al., 1999).Within this category, a noteworthy subset comprises ligands known as carbacylamidophosphates (CAPhs), which incorporate a functional unit C(O)NHP(O), and enable bidentate chelation upon coordination.The inclusion of the phosphoryl group in CAPhs imparts a strong affinity for lanthanides (Amirkhanov et al., 2014).In this work, we intended to design a new lutetium(III) CAPh-based tetrakis complex with a bulk cation in order to obtain it in a crystalline form and investigate a quite rare example of a lutetium complex structure.From this idea, the compound PPh 4 [LuL 4 ] was synthesized in high yield via reaction between lutetium nitrate, tetraphenylphosphonium bromide and the sodium salt of the ligand NaL.

Structural commentary
The title compound (C 24 H 20 P)[Lu(C 4 H 6 Cl 3 NO 4 P) 4 ] crystallizes in the monoclinic system in space group P2 1 /c with four molecules in the unit cell.All four ligands are coordinated in a bidentate chelate manner through the oxygen atoms of the carbonyl and phosphoryl groups.The complex comprises the [LuL 4 ] À anion and the PPh 4 + counter-ion, which are interconnected by hydrogen bonds (Table 1) and weak intermolecular interactions.The molecular structure of the complex is shown in Fig. 1 and the coordination polyhedron in Fig. 2. The coordination polyhedron of the Lu 3+ ion was determined to be a nearly perfect triangular dodecahedron formed by the eight O atoms of the bidentate CAPh ligands.The calculation was carried out using SHAPE 2.1 (Llunell et al., 2013).
The average Lu-O bond length in PPh 4 [LuL 4 ] is 2.3116 A ˚, which is longer than in {Lu 2 L 6 •�-(�, � 0 -dipy)} (2.2403A ˚; Trush et al., 2001).The Lu-O(C) bond lengths [2.348 (3)-2.411(2) A ˚] are all longer than the Lu-O(P) bonds [2.236 (3)-2.267(3) A ˚], which is explained by higher affinity of the phosphoryl group towards the metal ion.Deprotonation of the ligands leads to an increase of the �-conjugation in the chelating fragments and results in changes in the bond lengths.The C-O and P-O bond lengths are shorter than in the binuclear Lu III complex and are in the ranges 1.233 (4)-1.245(5) A ˚and 1.483 (3)-1.489(3) A ˚, respectively, with corresponding average values of 1.2399 and 1.486A ˚.In contrast, in {Lu 2 L 6 •�-(�, � 0 -dipy)} (Trush et al., 2001) the C-O bond lengths lie within 1.237-1.258A ˚(average 1.247A ˚) and the P-O bond lengths lie between 1.492 and 1.509A (average 1.501A ˚).The corresponding bond lengths in the neutral ligand HL are 1.202 (2) and 1.459 (2) A ˚ (Amirkhanov et al., 1995).The C-O and P-O bonds in the complex are longer than those in the neutral ligand (HL), indicating greater C-O and P-O double-bond character in HL than in the complex.The C-N and P-N bonds in PPh 4 [LuL 4 ], with lengths in the ranges 1.295 (6)-1.315(5) and 1.613 (3)-1.624(4) A ˚, respectively, are shorter compared to those in the free ligand, in which the reported C-N bond length is 1.347 (2) A ˚and P-N is 1.676 (1) A ˚.The C-N bond lengths in the binuclear lutetium complex are proportional to those in the tetrakis-and lie between 1.297 and 1.314A ˚while the P-N distances are shorter (1.602-1.621A ˚).

Supramolecular features
The crystal packing of the title compound viewed down the caxis is shown in Fig. 3.The Lu III polyhedra are isolated and do not share edges or vertices.
To visualize the intermolecular contacts in PPh 4 [LuL 4 ], the Hirshfeld surfaces (HS) mapped over d norm and the two-

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.Alkyl groups of the ligand and hydrogen atoms are omitted for clarity.

Figure 2
Coordination environment of the lutetium(III) ion.
dimensional fingerprint plots were generated using Crystal-Explorer 21.5 (Spackman et al., 2021).Fig. 4 illustrates the Hirshfeld surfaces for the PPh 4 + cation and the [LuL 4 ] À anion.The anion contains oxygen, chlorine, and nitrogen atoms that act as proton acceptors, forming hydrogen bonds (Table 1) and making a significant contribution to the intermolecular interactions, in addition to electrostatic attraction between the cations and anions.In contrast, the phenyl groups of the PPh 4 + cation only act as proton donors for hydrogen-bond formation.Weak hydrogen bonds, such as O� � �HC(Ph), Cl� � �HC(Ph) and N� � �HC(Ph), are formed between the cations and anions (Table 1, Fig. 4).The regions on the Hirshfeld surface of the cation colored in red correspond to hydrogen bonds of the C-H� � �O, C-H� � �Cl and C-H� � �N (light red) types (Fig. 4).On the Hirshfeld surface of the complex anion, the red regions represent close contacts between cations and anions, with the most significant interactions being intermolecular hydrogen bonds and C-H� � �O, C-H� � �Cl, C-H� � �N and Cl� � �Cl interactions.The figure also shows the atomic contributions (as percentages of the total surface) to the interactions between anions and cations.�-� stacking is not observed in the compound.There are six interacting anions around the cation and six interacting cations around the anion.
Hydrogen bonds are shown as dashed cyano lines.

Figure 4
The Hirshfeld surface mapped over d norm and two-dimensional fingerprint plots for intermolecular contacts for the anion and the cation in PPh 4 [LuL 4 ].

Materials and methods
Commercially available lutetium nitrate, Lu(NO 3 ) 3 •7H 2 O, and tetraphenylphosphonium bromide, PPh 4 Br, of reagent grade were used in the synthesis.The acetone used was dried and distilled.The 1 H NMR spectrum of a solution of the title compound in DMSO-d 6 was recorded on a Varian 400 NMR spectrometer at room temperature.The infrared (FT-IR) spectrum was recorded on a Perkin-Elmer BX-II spectrometer using a KBr pellet.
The dimethyl (2,2,2-trichloroacetyl)phosphoramidate ligand and its sodium salt were obtained according to a known procedure (Kirsanov et al., 1956).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.

Preparation of PPh 4 [LuL 4 ]
Lu(NO 3 ) 3 •7H 2 O (0.0487 g, 0.1 mmol) in the presence of HC(OC 2 H 5 ) 3 (0.14 ml, 0.7 mmol) as dehydrating agent was dissolved in acetone under heating.In a separate flask, NaL (0.1122 g, 0.4 mmol) was dissolved in acetone and PPh 4 Br (0.0419 g, 0.1 mmol) was added under stirring and heating.The two mixtures were combined and boiled for few minutes, then cooled to room temperature.A white precipitate of NaNO 3 and NaBr was filtered off and the filtrate was left in a flask in a desiccator over CaCl 2 .After two days, colorless crystals suitable for X-ray diffraction studies were obtained.The crystals were filtered off, washed with 2-propanol and dried in air.
IR (KBr pellet, cm A comparison of the IR spectra of the obtained compound with the spectra of the ligand and of its sodium salt was carried out.In the IR spectrum of PPh 4 [LuL 4 ], characteristic absorption bands of the carbonyl and phosphoryl groups are observed at 1622 and 1164 cm À 1 , respectively.There is a noticeable shift of the absorption bands of the carbonyl and phosphoryl groups in the spectrum of the complex towards lower wavenumbers compared to the spectra of the free ligand (110 and 104 cm À 1 , respectively) and the sodium salt (2 and 36 cm À 1 , respectively).This is consistent with the observed lengthening of the P O and C O bond lengths in the structure when compared to the ligand and sodium salt structures.The absorption band �(N-H), which is observed in the IR spectrum of HL at 3080 cm À 1 , is absent in the IR spectrum of the PPh 4 [LuL 4 ] complex, indicating ligand coordination in the deprotonated form.The presence of the

Refinement
Crystal data, data collection and structure refinement details are summarized in

Special details
Experimental.X-ray analyses of PPh 4 [LuL 4 ] were performed on an XtaLAB Synergy R, Dual Wavelength system, using Cu Kα radiation (λ = 1.5418Å) and a Hybrid Pixel Array HyPix-Arc 150 detector at 100 K. Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.

Table 2
Experimental details. �� min (e A ˚À 3 ) 1.32, À 1.07 tetraphenylphosphonium cation in the complex can be confirmed by the IR spectrum, showing bands at 1439, 1108, and 528 cm À 1 , which are absent in the IR spectrum of NaL.

Table 2 .
The hydrogen-atom positions were positioned geometrically (C-H = 0.95-0.98A ˚) refined using a riding model, with fixed U iso values of 1.2U iso of the attached C atom for aromatic H atoms and 1.5 for CH 3 groups.The methyl group was refined as a rotating group.One of the phosphoryl ligands is disordered.The chlorine atoms of the CCl 3 group and the CH 3 group of the methoxy substituents refined to occupancy ratios of 0.868 (3):0.132(3) and 0.62 (5):0.38 (5).The major component of the disordered CCl 3 group was refined in an anisotropic approximation, while the minor component was refined isotropically.Additionally, some C-Cl distances were restrained to 1.750 A ˚with a sigma value of 0.001.