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Lanthanides such as europium with more accessible divalent states are useful for studying redox stability afforded by macrocyclic organic ligands. Substituted cryptands, such as 2.2.2B cryptand, that increase the oxidative stability of divalent europium also provide coordination environments that support synthetic alterations of Eu(II) cryptate complexes. Two single crystal structures were obtained containing nine-coordinate Eu(II) 2.2.2B cryptate complexes that differ by a single coordination site, the occupation of which is dictated by changes in reaction conditions. A crystal structure containing a [Eu(2.2.2B)Cl]+ complex is obtained from a methanol-THF solvent mixture, while a methanol-acetonitrile solvent mixture affords a [Eu(2.2.2B)(CH3OH)]2+ complex. While both crystals exhibit the typical blue emission observed in most Eu(II) containing compounds as a result of 4f65d1 to 4f7 transitions, computational results show that the substitution of a Cl- anion in the place of a methanol molecule causes mixing of the 5d excited states in the Eu(II) 2.2.2B cryptate complex. Additionally, magnetism studies reveal the identity of the capping ligand in the Eu(II) 2.2.2B cryptate complex may also lead to exchange between Eu(II) metal centers facilitated by π-stacking interactions within the structure, slightly altering the anticipated magnetic moment. The synthetic control present in these systems makes them interesting candidates for studying less stable divalent lanthanides and the effects of precise modifications of the electronic structures of low valent lanthanide elements.

The activation of U-N multiple bonds in an imido analogue of the uranyl ion is accomplished by using a system that is very electron-rich with sterically encumbering ligands. Treating the uranium(VI) trans-bis(imido) UI2(NDIPP)2(THF)3 (DIPP = 2,6-diisopropylphenyl and THF = tetrahydrofuran) with tert-butyl(dimethylsilyl)amide (NTSA) results in a reduction and rearrangement to form the uranium(IV) cis-bis(imido) [U(NDIPP)2(NTSA)2]K2 (1). Compound 1 features long U-N bonds, pointing toward substantial activation of the N═U═N unit, as determined by X-ray crystallography and 1H NMR, IR, and electronic absorption spectroscopies. Computational analyses show that uranium(IV)-imido bonds in 1 are significantly weakened multiple bonds due to polarization toward antibonding and nonbonding orbitals. Such geometric control has important effects on the electronic structures of these species, which could be useful in the recycling of spent nuclear fuels.

The interplay of bond strength and covalency are examined in AnO2Cl2(OPcy3)2(An = Pu, U) complexes. The synthesis oftrans-PuO2Cl2(OPcy3)2,1-Pu, has been carried out and confirmed by single crystal X-ray diffraction along with UV-vis-NIR, and31P NMR spectroscopies. Theoretical analysis finds that despite a higher calculated covalency for the Pu-Cl interaction, the Pu-OPcy3interaction is stronger due to the accumulation of electron density in the interatomic region. The coordination of equatorial ligands slightly decreases the strength of the Pu Oylinteractions relative to the free gas phase (PuO2)2+ion.

Three samarium(II) crown ether complexes, [Sm(15-crown-5)2]I2 (1), [Sm(15-crown-5)2]I2·CH3CN (2), and [Sm(benzo-15-crown-5)2]I2 (3), have been prepared via the reaction of SmI2 with the corresponding crown ether in either THF or acetonitrile in good to moderate yields. The compounds have been characterized by single crystal X-ray diffraction and a variety of spectroscopic techniques. In all cases, the Sm(II) centers are sandwiched between two crown ether molecules and are bound by the five etheric oxygen atoms from each crown ether to yield 10-coordinate environments. Despite the higher symmetry crystal class of 1 (R3c), the samarium center resides on a general position, whereas in 2 and 3 (both in P21/c) the metal centers lie upon inversion centers. Moreover, the complexes in 2 and 3 are approximated well by D5d symmetry. The molecule in 1, however, is distorted from idealized D5d symmetry, and the crown ethers are more puckered than observed in 2 and 3. All three complexes luminesce in the NIR at low temperatures. However, the nature of the luminescence differs between the three compounds. 1 exhibits broadband photoluminescence at 20 °C but at low temperatures transitions to narrow peaks. 2 only exhibits nonradiative decay at 20 °C and at low temperatures retains a mixture of broadband and fine transitions. Finally, 3 displays broadband luminescence regardless of temperature. Spin-orbit (SO) CASSCF calculations reveal that the outer-sphere iodide anions influence whether broadband luminescence from 5d → 4f or fine 4f → 4f transitions occur through the alteration of symmetry around the metal centers and the nature of the excited states as a function of temperature.

A fragmentation scheme combined with a series of theoretical approximations like TD-DFT, and multiconfigurational CASSCF/NEVPT2 methods, has been used to describe the photophysical phenomena associated with the antenna effect and lanthanide ion emission. The theoretical protocol was used in (Cp2Ph)3Tb and (Cp2Ph)TbCl2(THF)3, where Cp2Ph = diphenylcyclopentadienyl and THF = tetrahydrofuran, organometallic complexes recently reported by Roitershtein et al. (Inorg. Chem., 2018, 57, 10199) The excited-state dynamic of the antenna ligand shows an important vibronic coupling associated with the radiative and non-radiative process with rate constants in the order normally reported for organic molecules. The methodology proposed herein allows a justification of the back-energy transfer observed experimentally in the (Cp2Ph)3Tb complex and the efficient energy transfer mechanism in (Cp2Ph)TbCl2(THF)3, thus proving to be a robust tool in the determination of the sensitization pathways in organometallic lanthanide complexes.

The design of organometallic complexes used as selective intercalators to bind and react at DNA mismatch sites has concentrated efforts in the last few years. In this context, lanthanides have received attention to be employed as active optical centers due to their spectroscopic properties. Despite the fact that there are several experimental data about synthesis and DNA binding of these compounds, theoretical analyses describing their interaction with DNA are scarce. To understand the binding to regular and mismatched DNA sequences as well as to determine the effect of the intercalation on the spectroscopic properties of the complexes, a complete theoretical study going from classical to relativistic quantum mechanics calculations has been performed on some lanthanide complexes with phenanthroline derivatives synthesized and characterized herein, viz. [Nd(NO3)3(H2O)(dppz-R)] with R = H, NO2-, CN- and their [Nd(NO3)3(H2O)(dpq)] analogue, which was computationally modeled. The results were in correct agreement with the available experimental data showing that dppz complexes have higher binding affinities to DNA than dpq one and supporting the idea that these complexes are not selective to mismatch sites in the sampled time scale. Finally, the spectroscopic analysis evidence an intercalative binding mode and made possible the elucidation of the emission mechanism of these systems. This approach is proposed as a benchmark study to extend this methodology on similar systems and constitutes the first theoretical insight in the interaction between DNA and lanthanide complexes.

The activation of U-N multiple bonds in an imido analogue of the uranyl ion is accomplished by using a system that is very electron-rich with sterically encumbering ligands. Treating the uranium(VI)

A pair of neptunium Schiff base coordination complexes, NpVIO2L(MeOH) and NpIVL2 {H2L = N,N′-bis[(4,4′-diethylamino)salicylidene]-1,2-phenylenediamine}, have been synthesized and analyzed by severa...

In this work, we synthesized and structurally characterized a series of six coordinatively saturated EuIII and TbIII complexes: [Ln(R-TPY)(TTA)3] (1–6), having three β-diketonate ligands i.e.TTA = 1,1,1-trifluoro-3-(2-theonyl)acetone, and one judiciously substituted terpyridine derivative (R-TPY), viz. [Eu(FTPY)(TTA)3] (1), [Tb(FTPY)(TTA)3] (2), [Eu(TTPY)(TTA)3] (3), [Tb(TTPY)(TTA)3] (4), [Eu(PTPY)(TTA)3] (5) and [Tb(PTPY)(TTA)3] (6), where FTPY = 4′-(2-furyl)-2,2′:6′,2′′-terpyridine, TTPY = 4′-(2-thienyl)-2,2′:6′,2′′-terpyridine, and PTPY = 4′-(2-pyrolyl)-2,2′:6′,2′′-terpyridine. The complexes were synthesized and structurally characterized by X-ray crystallography and various other physicochemical and spectroscopic methods to realize their optical properties and energy transfer pathways from dual antennae. The structural characterization of the complexes shows discrete nine-coordinated {LnN3O6} geometry originating from six oxygen donors of three monoanioninc β-diketonate ligands and three nitrogens from a tridentate terpyridine derivative (R-TPY). We elucidate the energy transfer (ET) pathways from two coordinating antennae moieties (i.e.R-TPY and TTA) in these complexes using relativistic multiconfigurational methods. For this purpose, a theoretical analysis was performed through a method that consists of a fragmentation scheme, wherein all the constituent fragments (TTA, R-TPY and LnIII) were treated at the same level of theory. These calculations were based on scalar relativistic time-dependent density functional theory (SR-TDDFT) and the multireference complete active space self-consistent field (CASSCF/PT2) technique to construct the respective energy level diagrams and determine the most probable ET pathways. Possible pathways were elucidated from the optimum energy difference between the ligand-centered triplet (3T) states and the emissive excited states of the LnIII fragments. These calculations and energy transfer pathways were in good agreement with the experimental photophysical data and explain the involvement of several parallel energy transfer pathways to varying extent in these luminescent LnIII complexes.

The suitability of aryloxide ligands for stabilizing +2 oxidation states of Sc and Y has been examined and EPR evidence indicating the first O-donor complexes of ScII and YII has been obtained, as well as an X-ray crystal structure of a ScII aryloxide complex. The trivalent rare-earth metal aryloxide precursors, Ln(OAr')3 , 1-Ln (Ln=Sc, Y, Gd, Dy, Ho, Er; OAr'=OC6 H2 tBu2 -2,6-Me-4), were synthesized from the corresponding rare-earth metal trichlorides and LiOAr'⋅OEt2 . Reduction of THF solutions of 1-Ln with potassium graphite in the presence of 2.2.2-cryptand (crypt) yielded dark-colored solutions, 2-Ln, whose EPR spectra at 77 K are characteristic of the LnII ions: a two-line spectrum (g∥ =1.99, g□ =1.97, Aave =154 G) for 2-Y and an eight-line spectrum (gave =2.01 and Aave =291 G) for 2-Sc. Solutions of 2-Y decompose within one minute at room temperature, wheras 2-Sc persists up to 40 min at room temperature. 2-Sc was identified by X-ray crystallography as [K(crypt)][Sc(OAr')3 ], which has a trigonal-planar arrangement of oxygen-donor atoms around ScII . Analogous reductions of 1-Ln for Ln=Gd, Dy, Ho, and Er also gave dark solutions of limited stability. Theoretical analysis using time-dependent density functional theory (TD-DFT) along with complete active space self-consistent field (CASSCF) methods, and structural analysis with the Guzei ligand solid angle G-parameter method are presented.

Three new types of transition metal carboranylamidinate complexes are reported. The tetranuclear Mn(ii) complex Mn4Cl6[(o-C2B10H10)C(NiPr)(NHiPr)]2(THF)4·THF (2) was prepared by treatment of anhydrous MnCl2 with Li[(o-C2B10H10)C(NiPr)(NHiPr)] ([double bond, length as m-dash]Li[HLiPr]) in THF, while the analogous reaction with FeCl2 afforded ionic [Li(DME)3][FeCl2{(o-C2B10H10)C(NiPr)(NHiPr)}] (3). The dinuclear Mo(ii) complex Mo2[(o-C2B10H10)C(NiPr)(NHiPr)]2(OAc)2·2THF (4), obtained from Mo2(OAc)4 and 2 equiv. of Li[HLiPr], represents the first example of a M-M multiple bond stabilized by carboranylamidinate ligands. All title compounds were structurally characterized by single-crystal X-ray diffraction. The M-M bonding in compound 4 has been further elucidated through Complete Active Space Self Consistent Field (CASSCF) calculations.

Research on heavy actinides has experienced an increased interest in the last few years due to new synthetic techniques and recent technological advances that have allowed for obtaining important information even from very small samples. This area presents challenges not only from the experimental point of view but also from the theoretical perspective. This work deals with a multiconfigurational CASSCF and NEVPT2 benchmark study based on a two-step methodology that considers first correlation effects and then the spin-orbit coupling applied to berkelium (Bk), californium (Cf), einsteinium (Es) and fermium (Fm) hexahalides. Optical properties, such as f → d transitions and crystal-field parameters, have been calculated and rationalized. The results for these trivalent actinides indicate that the electronic structure of the low-lying states is reproduced accurately with small basis sets. The ground-state multiplets are isolated, in the same manner as their isoelectronic lanthanide counterparts. In the case of tetravalent berkelium, the picture is different regarding the electronic structure where crystal-field theory fails due to considerable ligand-to-metal charge transfer contributions to the ground state.

A theoretical protocol to study the sensitization and emission mechanism in lanthanide compounds on the basis of multireference CASSCF/PT2 calculations is proposed and applied to [Eu(NO3)3(dppz-CN)] and [Eu(NO3)3(dppz-NO2)] compounds synthesized and characterized herein. The method consists of a fragmentation scheme where both the ligand and the lanthanide fragments were calculated separately but at the same level of theory, using ab initio wave-function-based methods which are adequate for the treatment of quasi-degenerate states. This is based on the fact that the absorption is ligand-localized and the emission is europium-centered. This characteristic allowed us to describe the most probable energy transfer pathways that take place in the complexes, which involved an ISC between the S1 to T1 ligand states, energy transfer to 5D2 in the lanthanide fragment, and further 5D0 → 7FJ emission. For both compounds, the triplet and 5D2 states were determined at the CASPT2 level to be around ∼26000 and ∼22400 cm...

The design of organometallic complexes used as selective intercalators to bind and react at DNA mismatch sites has concentrated efforts in the last few years. In this context, lanthanides have received attention to be employed as active optical centers due to their spectroscopic properties. Despite the fact that there are several experimental data about synthesis and DNA binding of these compounds, theoretical analyses describing their interaction with DNA are scarce. To understand the binding to regular and mismatched DNA sequences as well as to determine the effect of the intercalation on the spectroscopic properties of the complexes, a complete theoretical study going from classical to relativistic quantum mechanics calculations has been performed on some lanthanide complexes with phenanthroline derivatives synthesized and characterized herein, viz. [Nd(NO

This work presents a theoretical protocol to analyze the symmetry effect on the allowed character of the transitions and to estimate the probability of energy transfer in lanthanide(III) complexes. For this purpose, a complete study was performed based on the multireference CASSCF/PT2 technique along with TDDFT, to build the energy level diagrams and determine the spectral overlap integrals, respectively. This approach was applied on a series of LnIII complexes, viz. [LnCl3(DMF)2(Dpq)]/[Ln(NO3)3(DMF)2(Dpq)], where Ln = SmIII, TbIII, ErIII/EuIII, NdIII and dpq = dipyridoquinoxaline, synthesized and characterized by Patra et al. ( Dalton Trans. 2015, 44 (46), 19844−19855; CrystEngComm 2016, 18 (23), 4313–4322; Inorg. Chim. Acta 2016, 451, 73–81). A fragmentation scheme was applied where both the ligand and the lanthanide fragments were treated separately but at the same level of theory. The symmetry analysis only partially reproduced the expected results, and a more detailed analysis of the crystal field be...