Hexafluoroacetylacetonate Anion Research Articles

Syntheses, crystal structures, and magnetic properties of three cyclic dimeric M2L2 complexes constructed from a nitronyl nitroxide ligand and M(hfac)2 (M = Ni2+, Co2+, and Cu2+)

Three complexes derived from a new functional nitronyl nitroxide ligand, [Ni(hfac)2(NIT-3-OMe-4PhPy)]2 (1), [Co(hfac)2(NIT-3-OMe-4PhPy)]2 (2), and [Cu(hfac)2(NIT-3-OMe-4PhPy)]2 (3) were synthesized and characterized structurally and magnetically, where NIT-3-OMe-4PhPy stands for 2-[3-methoxy-4-(4-pyridinylmethoxy)phenyl]-4,4,5,5-tetramethyl-imidazolyl-1-oxyl-3-oxide and hfac is hexafluoroacetylacetonate anion (hfac). Complexes 1–3 are isomorphous in which the NIT-3-OMe-4PhPy molecule acts as a bridging ligand linking two M(II) ions (M = Ni2+, Co2+, and Cu2+) through the nitrogen of pyridine and the oxygen of the nitroxide unit to form a rectangle-like centrosymmetric dimer. The magnetic behaviors of 1–3 were investigated. For 1, the nitronyl nitroxides and Ni(II) ions are strongly antiferromagnetically (AFM) coupled, yielding the intradimer magnetic exchange constant of J = −87.3 cm−1. The temperature dependence of the magnetic susceptibility for 2 in the T > 30 K region was simulated with a two-spin model with S1 = 3/2 and S2 = 1/2 because of depopulation of the higher energy Kramers doublets of the Co(II) centers and the interaction of Co(II)…O coordination bonding, leading to J = −18.6 cm−1, g = 2.16, and zj′ = −2.94 cm−1 for the magnetic interactions between Co(II) ions and nitronyl nitroxides through pyridine rings. The ferromagnetic interaction between Cu(II) ions and nitronyl nitroxide radicals was observed in 3 with J = 68.9 cm−1 and θ = 0.51 k.

Highly Efficient and Thermally Durable Luminescence of 1D Eu3+ Coordination Polymers with Arsenic Bridging Ligands.

In this work, bisarsine oxides were evaluated as novel bridging ligands, aiming to develop practical and efficient luminescent lanthanide coordination polymers. We have synthesized one-dimensional (1D) Eu3+ coordination polymers that incorporate bisarsine oxide bridging ligands and hexafluoroacetylacetonate anions. These polymers exhibited a denser packing of chains compared to analogous polymers bridged with bisphosphine oxides. The coordination polymers demonstrated exceptional thermal stability and substantial emission quantum yields. Additionally, the bisarsine oxides induced a pronounced polarization effect, facilitating a sensitive electric dipole transition that yields considerably narrow band red emission. Remarkably, the Eu3+ coordination polymers with bisarsine oxides maintained intense emission even at 550 K. A distinctive feature of these polymers is their heating-induced emission enhancement observed when the temperature was increased from 300 K to 400 K.

Ferrocenyl-substituted nitronyl nitroxide in the design of one-dimensional magnets.

By the reaction of M(hfac)2 (M = Mn(II), Co(II), Cu(II), and Zn(II); hfac is the hexafluoroacetylacetonate anion) and ferrocenyl-substituted nitronyl nitroxide (L), we succeeded in the synthesis of stable heterospin complexes: mononuclear [Zn(hfac)2L], trinuclear {[Cu(hfac)2]3L2} and chain polymer [Mn(hfac)2L]n and [Co(hfac)2L]n. The specific steric bulkiness of the ferrocenyl substituent leads to the formation of trans-type coordination polyhedra in the [Mn(hfac)2L]n and [Co(hfac)2L]n chains. The introduction of the ferrocene substituent leads to an effective weakening of intermolecular or interchain magnetic exchange coupling. Ferrimagnetic ordering was observed for one-dimensional complexes [M(hfac)2L]n (M = Mn(II), Co(II)). [Co(hfac)2L]n exhibits features of single-chain magnet behaviour: slow relaxation of magnetization below 13 K is associated with a high coercive field (54 kOe at 2 K).

Symmetry and Rigidity for Boosting Erbium‐Based Molecular Light‐Upconversion in Solution

AbstractPreviously limited to highly symmetrical homoleptic triple‐helical complexes [Er(Lk)3]3+, where Lk are polyaromatic tridentate ligands, single‐center molecular‐based upconversion using linear optics and exploiting the excited‐state absorption mechanism (ESA) greatly benefits from the design of stable and low‐symmetrical [LkEr(hfa)3] heteroleptic adducts (hfa−=hexafluoroacetylacetonate anion). Depending on (i) the extended π‐electron delocalization, (ii) the flexibility and (iii) the heavy atom effect brought by the bound ligand Lk, the near‐infrared (801 nm) to visible green (542 nm) upconversion quantum yield measured for [LkEr(hfa)3] in solution at room temperature can be boosted by up to three orders of magnitude.

Symmetry and Rigidity for Boosting Erbium-Based Molecular Light-Upconversion in Solution.

Previously limited to highly symmetrical homoleptic triple-helical complexes [Er(Lk)3 ]3+ , where Lk are polyaromatic tridentate ligands, single-center molecular-based upconversion using linear optics and exploiting the excited-state absorption mechanism (ESA) greatly benefits from the design of stable and low-symmetrical [LkEr(hfa)3 ] heteroleptic adducts (hfa- =hexafluoroacetylacetonate anion). Depending on (i) the extended π-electron delocalization, (ii) the flexibility and (iii) the heavy atom effect brought by the bound ligand Lk, the near-infrared (801 nm) to visible green (542 nm) upconversion quantum yield measured for [LkEr(hfa)3 ] in solution at room temperature can be boosted by up to three orders of magnitude.

Synthesis, Crystal Structure, and Optical Properties of Mononuclear Eu(III) and Tb(III) Complexes Containing a Chalcone Ligand

Chalcones are α,β-unsaturated ketones with great structural diversity and various applications. A chalcone produced by condensation of 2-acetylpyridine with 2-naphthaldehyde (L) was employed for synthesis of two mononuclear complexes: [Eu(L)(hfac)3(H2O)]·0.5CHCl3 and [Tb(L)(hfac)3], where hfac is the hexafluoroacetylacetonate anion. The chalcone and complexes were structurally characterized by single-crystal X-ray diffraction. The chalcone acts as a chelating bidentate ligand. Luminescent properties of the ligand L and the complexes were investigated in the solid state. For these heteroleptic mononuclear complexes, the emission of the Eu(III) and Tb(III) ions was influenced by the excitation wavelength.

Luminescent La3+, Eu3+ and Tb3+ mononuclear complexes with a Schiff base tripodal ligand derived from 9-anthracenecarboxaldehyde

Tripodal ligands represent a category of molecules able to offer a good containment to the metal ions. The N-donor tripodal ligand derived from tris(2-aminoethyl)amine and 9-anthracenecarboxaldehyde (L) was employed for synthesis of three mononuclear complexes: [La(L)(hfac)3], [Eu(L)(hfac)3] and [Tb(L)(hfac)3] where hfac is the hexafluoroacetylacetonate anion. The complexes were structurally characterized by single-crystal X-ray diffraction. The Schiff base tripodal ligand behaves as tridentate ligand coordinating through the amino and two (out of the three) imino nitrogen atoms. Luminescent properties of the ligand L and the complexes were investigated in solid-state.

Formation and desorption of nickel hexafluoroacetylacetonate Ni(hfac)2 on a nickel oxide surface in atomic layer etching processes

Thermal atomic layer etching (ALE) of nickel (Ni) may be performed with a step of thin-layer oxidation of its surface and another step of its removal by gas-phase hexafluoroacetylacetone (hfacH) as an etchant. In this study, adsorption of hfacH and possible formation of volatile nickel hexafluoroacetylacetonate Ni(hfac)2 on a NiO surface were investigated based on the density functional theory (DFT) with more realistic surface material models than those used in the previous study [A. H. Basher et al., J. Vac. Sci. Technol. A 38, 022610 (2020)]. It has been confirmed that an hfacH molecule approaching a NiO surface deprotonates without a potential barrier and adsorbs on the surface exothermically. In addition, stable adsorption of two deprotonated hfacH molecules on a NiO (100) surface was found to occur not on a single Ni atom but over a few Ni atoms instead, which makes the formation of a Ni(hfac)2 complex on the flat surface very unlikely even at elevated temperature. However, if the surface is rough and a Ni atom protrudes from the surrounding atoms, two hexafluoroacetylacetonate anions (hfac−) can bond to the Ni atom stably, which suggests a possibility of desorption of a Ni(hfac)2 complex from the surface at elevated temperature. Given the experimentally observed fact that desorption of Ni(hfac)2 complexes typically takes place on a NiO surface at a temperature of ∼300–400 °C, our DFT calculations indicate that the surface roughness of an oxidized Ni surface facilitates the formation and desorption of organometallic complexes Ni(hfac)2, and therefore, the resulting Ni surface after ALE can be smoother than the initial surface.

Stability of hexafluoroacetylacetone molecules on metallic and oxidized nickel surfaces in atomic-layer-etching processes

Adsorption of enol hexafluoroacetylacetone (hfacH) on nickel oxide (NiO) fcc (100) and metallic Ni fcc (100) surfaces and the stability of the adsorbate was examined using first-principles quantum mechanical simulations. It was shown that an hfacH molecule can be unstable and dissociate on an Ni metal surface. On an NiO surface; however, an hfacH molecule can be deprotonated and form a hexafluoroacetylacetonate anion (hfac−) bonded stably with positively charged Ni atoms of the surface. The results are consistent with observations of the interaction of hfacH with NiO and Ni surfaces in earlier experiments. The results also explain the mechanisms of the adsorption steps in the thermal atomic layer etching of Ni based on the cyclic processes of surface oxidation and formation of volatile organo-nickel complexes.

Synthesis and photoluminescence study of two new complexes [Sm(hfaa)3(impy)2] and [Eu(hfaa)3(impy)2] and their PMMA based hybrid films

The synthesis, characterization and photoluminescence studies of two new highly photoluminescent complexes, [Sm(hfaa)3(impy)2] and [Eu(hfaa)3(impy)2] (impy is 2-(1H-imidazol-2-yl)pyridine and hfaa is the anion of hexafluoroacetylacetone) are reported. The photoluminescence of these complexes were studied in solid, solution and PMMA thin films. These complexes were incorporated independently into polymer matrix of PMMA with varying amounts. The calculated quantum yield (φ) and experimental life time (τ) in solution for (i) Sm complex are φ = 0.013, τ = 0.036 ms and (ii) Eu complex are φ = 0.36, τ = 0.98 ms. The Judd–Ofelt intensity parameters, radiative parameters, intramolecular energy transfer rates and theoretical quantum efficiency are calculated and discussed. The intramolecular energy transfer rates, in the case of europium complex, suggest that the major energy transfer channels are T1 → 5D1 and T1 → 5D0 and these contribute 55.33% and 44.65%, respectively, to the overall energy transfer process. The emission colour changes with a change in concentration of the complexes in PMMA substrate. This feature may be employed in fabricating 'colour indicator diodes'. The thin hybrid films of these structurally ten-coordinate complexes in PMMA matrix exhibit outstanding photostability upon UV irradiation that defines their robust nature. The efficient photophysical properties of PMMA hybrids of these complexes, may possibly find their applications in optoelectronic devices.

Influence of the interaction of polymeric chains on thermal transitions of Jahn—Teller exchange clusters in compounds of "breathing" crystal family

Based on the method of random field distribution functions in Ising magnets, for the first time a theoretical description of thermal transitions in Jahn—Teller exchange clusters is suggested, which takes into account the interactions of polymeric chains in "breathing" crystal compounds. It was shown that the inclusion of this interaction can lead to both an intensification of spin-crossover type cooperative transitions in exchange clusters and their deceleration. The approach in question is generalized to include non-Jahn—Teller metal impurities in "breathing" crystals, which suppress cooperative effects in thermal transitions of Jahn—Teller exchange clusters. The obtained results qualitatively reproduce the temperature dependencies of magnetic properties of solid solutions Cu1—x Ni x (hfac)2LR (hfac is hexafluoroacetylacetonate anion, ligand LR is nitronyl nitroxide radical with pyrazole substituent at the second position of the imidazoline ring) when R = Et.

Crystal structures of two one-dimensional coordination polymers constructed from Mn2+ ions, chelating hexafluoro-acetylacetonate anions, and flexible bipyridyl bridging ligands

The syntheses and crystal structures of two one-dimensional coordination polymers, [Mn(C5HO2F6)2(C16H20N2)] n (1) and [Mn(C5HO2F6)2(C20H20N2)] n (2), are described, where C5HO2F6 − is the hexafluoro acetylacetonate anion, C16H20N2 is 1,6-bis(4-pyridyl)-hexane, and C20H20N2 is 1,4-bis[2-(3-pyridyl)ethyl]-benzene. In both phases, the metal ion lies on a crystallographic twofold axis and is coordinated by two chelating C5HO2F6 − anions and two bridging bipyridyl ligands to generate a cis-MnN2O4 octahedron. The bridging ligands, which are completed by crystallographic inversion symmetry in both compounds, connect the metal nodes into zigzag [20 1 ] chains in 1 and contorted [001] chains in 2. Intrachain C–H•••O interactions occur in 1 but not in 2, which may be correlated with the relative orientations of the ligands. Crystal data: 1, C26H22F12MnN2O4, M r = 709.40, monoclinic, C2/c (No. 15), a = 9.3475(2) A, b = 16.6547(3) A, c = 18.3649(4) A, β = 91.1135(8)°, V = 2858.50(10) A3, Z = 4, R(F) = 0.030, w R(F 2) = 0.075. 2, C30H22F12MnN2O4, M r = 757.44, monoclinic, C2/c (No. 15), a = 19.9198(2) A, b = 10.6459(2) A, c = 16.8185(3) A, β = 119.8344(8)°, V = 3093.91(9) A3, Z = 4, R(F) = 0.032, w R(F 2) = 0.078.

Crystal structures of two one-dimensional coordination polymers constructed from Mn2+ ions, chelating hexafluoro-acetylacetonate anions, and flexible bipyridyl bridging ligands

Crystal structures of two one-dimensional coordination polymers constructed from Mn2+ ions, chelating hexafluoro-acetylacetonate anions, and flexible bipyridyl bridging ligands

Theoretical study of the structures of [M(18C6)](HFA)2 complexes (M = Ba, Sr, Pb, Cd, Mn; 18C6 = 18-crown-6; HFA = hexafluoroacetylacetonate anion)

The structures of the [M(18C6)]2+ cations (M = Ba, Sr, Pb, Cd, Mn) and their salts [M(18C6)](HFA)2 and [M(18C6)](NO3)2 have been calculated by the density functional theory method (in the B3LYP/6-311++G** + LanL2Dz approximation). Upon geometry optimization, the gas-phase structures of compounds of different composition have been calculated; for them, the strength of binding of the central cation to the crown ether (18C6) and the degree of structural similarity have been evaluated. The structure of the [NH4(18C6)]+ cation identified in a practical synthesis has also been considered. For metal cations acting as a central atom, NH4+ and [M(18C6)]2+ complex cations, as well as for intermediate and ultimate products [M(18C6)](NO3)2 and [M(18C6)](HFA)2 (M = Ba, Sr, Pb, Cd, Mn), the electronic chemical potential and Pearson hardness, which enables the consideration of the propensity of various reagents to interact with each other in terms of the empirical HSAB principle (hard with hard and soft with soft), have been evaluated. Comparison of the estimates with the properties of the synthesized compounds with M = Ba, Sr, and Pb makes it possible to preliminarily verify the applicability of this principle to the systems under consideration and predict some properties of isostructural analogues important in the search for methods of synthesis of [M(18C6)](HFA)2, where M = Cd and Mn. The possibility of establishing a correlation between the electron density of the system, stability, and hydrolytic activity of complexes has been shown.

Complexes of CuII with nitroxides and their magnetochemical behavior

The synthesis, structures, and magnetochemical data for the heterospin chain polymer complexes Cu(hfac)2LAll and Cu(hfac)2LBu·0.5Solv, where hfac is the hexafluoroacetylacetonate anion, LAll and LBu are 2-(1-allyl-1H-pyrazol-4-yl)- and 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls, respectively, Solv is isopropylbenzene or tert-butylbenzene, were described. These polycrystalline solids were found to exhibit similar magnetic anomalies. Thus, the effective magnetic moment first decreases and then increases with temperature, resulting in the specific minimum in the curve μeff(T). The study of the magneto-structural correlations showed that the appearance of the minimum is attributed to different factors. For Cu(hfac)2LAll, this is the phase transition accompanied by the structural rearrangement of the exchange cluster >N—·O—CuII—O·—N<, which leads to a change in the energy of the exchange interaction between the unpaired electrons of the paramagnetic centers. By contrast, for Cu(hfac)2LBu·0.5PriPh and Cu(hfac)2LBu·0.5ButPh, the appearance of the minimum is a consequence of the coexistence of exchange interaction energies with opposite signs, while the structure of the solid phase remains unchanged.

Sensitization of Visible and NIR Emitting Lanthanide(III) Ions in Noncentrosymmetric Complexes of Hexafluoroacetylacetone and Unsubstituted Monodentate Pyrazole

A series of highly volatile eight-coordinate air and moisture stable lanthanide complexes of the type [Ln(hfaa)3(L)2] (Ln = Pr (1), Nd (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Tm (9), and Yb (10); hfaa = anion of hexafluoroacetylacetone and L = pyrazole) have been synthesized and characterized by elemental analysis, IR, ESI-MS(+), and NMR studies. Single-crystal X-ray structures have been determined for the Eu(III) and Dy(III) complexes. These complexes crystallize in the monoclinic space group P2(1)/c. The lanthanide ion in each of these complexes is eight-coordinate with six oxygen atoms from three hfaa and two N-atoms from two pyrazole units, forming a coordination polyhedron best describable as a distorted square antiprism. The NMR spectra reveal that both the pyrazole units remain attached to the metal in solution and the β-diketonate and pyrazole protons are shifted in opposite directions in the case of paramagnetic complexes. The lanthanide-induced chemical shifts are dipolar in nature. The hypersensitive transitions of Nd(III), Ho(III), and Er(III) are sensitive to the environment (solvent), which is reflected by the oscillator strength and band shape of these transitions. The band shape due to the hypersensitive transition of Nd(III) in noncoordinating chloroform and dichloromethane is similar to those of the typical eight-coordinate Nd(III) β-diketonate complexes. The quantum yield and lifetime of Pr(III), Eu(III), Tb(III), Dy(III), and Tm(III) in visible and Pr(III), Nd(III), Dy(III), Ho(III), Er(III) Tm(III), and Yb(III) in the NIR region are sizable. The environment around these metal ions is asymmetric, which leads to increased radiative rates and luminescence efficiencies. The quantum yield of the complexes reveal that ligand-to-metal energy transfer follows the order Eu(III) > Tb(III) ≫ Pr(III) > Dy(III) > Tm(III). Both ligands (hfaa and pyrazole) are good sensitizers for all the visible and NIR emitters effectively, except for Tb(III), Dy(III), and Tm(III), where pyrazole gave a negative effect (e.g., energy back-transfer) that is due to poor intramolecular energy transfer match. The good luminescent properties make these NIR-luminescent complexes to have potential application in optical communication, telecommunications, and fluoroimmunoassays.

Exchange interactions in a dinuclear manganese (II) complex with cyanopyridine-N-oxide bridging ligands

The magnetic properties of dinuclear manganese(II) complex [Mn(hfa)2cpo]2 (where hfa is hexafluoroacetylacetonate anion and cpo is 4-cyanopyridine-N-oxide) are presented. The non-monotonous dependence of magnetic susceptibility is explained in terms of the hierarchy of exchange parameters by using exact diagonalization. The thermodynamic behavior of pure cpo and [Mn(hfa)2(cpo)]2 is simulated numerically by an extrapolation to spin S=5/2. The Mn–Mn exchange integral is evaluated.

Crystals of the CuII complex with nitronyl nitroxide and imino nitroxide exhibiting mechanical activity

As part of continuing studies of multispin compounds capable of exhibiting chemomechanical activity, a series of heterospin solids of the composition [Cu(hfac)2LxL′2−x], [Cu(hfac)2L′], [Cu2(Piv)4L′2]·0.5C6H14, and [Cu2(hfac)2(Piv)2L′2], where hfac is the hexafluoroacetylacetonate anion, L is 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, L′ is the imino nitroxide analog of L, viz., 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-1-oxyl, and Piv is the 2,2-dimethylpropionate anion, were synthesized and characterized. The packing of the synthesized crystals of the solid solutions [Cu(hfac)2LxL′2-x], where L predominates, is similar to that for [Cu(hfac)2L2], and these crystals are able to undergo chemomechanical motion. On the contrary, the crystals of [Cu(hfac)2LxL′2−x], where L′ predominates, have structural parameters similar to those of [Cu(hfac)2L′2] and do not exhibit thermally activated or photoactivated chemomechanical activity.

Synthesis and luminescence study of a highly volatile Sm(III) complex

A highly volatile air and moisture stable eight-coordinate samarium complex, [Sm(hfaa)3(pz)2] (hfaa=anion of hexafluoroacetylacetone and pz=pyrazole), has been synthesized and structurally characterized by single crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P21/c and the coordination polyhedron around the samarium ion is best describable as a distorted square antiprism. The NMR spectrum reveals that both the pz units remain coordinated to the samarium in solution. The quantum yield of the complex is determined to be 0.012 in solution. The lifetime of the complex is found to be 0.039ms (χ2=1.071). The experimental intensity parameter (ηSm) is calculated for the complex.

N‐Heterocyclic Tridentate Aromatic Ligands Bound to [Ln(hexafluoroacetylacetonate)3] Units: Thermodynamic, Structural, and Luminescent Properties

Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac(-)) and neutral, semi-rigid, tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands (Lk) to trivalent lanthanide atoms (Ln(III)). The solid-state structures of [Ln(Lk)(hfac)(3)] (Ln=La, Eu, Lu) showed that [Ln(hfac)(3)] behaved as a neutral six-coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron-withdrawing trifluoromethyl substituents limited charge-neutralization and favored cascade complexation with Lk; 3) nine-coordination was preserved for [Ln(Lk)(hfac)(3)] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of [Eu(Lk)(hfac)(3)], the ternary system Ln(III)/hfac(-)/Lk is a promising candidate for the planned metal-loading of preformed multi-tridentate polymers.