Synthesis, Characterization, and Reactivity of Bispidine-Iron(IV)-Tosylimido Species.

Reported are the synthesis and detailed studies of the iron(IV)-tosylimido complexes of two isomeric pentadentate bispidine ligands (bispidines are 3,7-diazabicyclo[3.3.1]nonane derivatives). This completes a series of five tosylimido complexes with comparable pentadentate amine/pyridine ligands, where the corresponding [(L)FeIV═O]2+ oxidants have been studied in detail. The characterization of the two new complexes in solution (UV-vis-NIR, Mössbauer, HR-ESI-MS) shows that these oxidants have an intermediate spin (S = 1) electronic ground state. The reactivities have been studied as oxidants in C-H activation at 1,3-cyclohexadiene and nitrogen atom transfer to thioanisole. For the latter substrate, the entire set of data for the five ligands and for both nitrogen and oxygen atom transfer is now available and the interesting observation is that oxygen atom transfer is, as expected, generally faster than nitrogen atom transfer, with the exception of the two ligands that have four and three pyridine groups oriented parallel to the Fe-O and Fe-N axes. A thorough DFT analysis indicates that this is due to steric effects in the case of the [(L)FeIV═O]2+ species, which are less important in the [(L)FeIV═NTs]2+ compounds due to partial electron transfer from the thioanisole substrate to the iron(IV)-tosylimido oxidant.

Hourglass-Shaped Homo- and Heteronuclear Nonanuclear Lanthanide Clusters: Structures, Magnetism, Photoluminescence, and Theoretical Analysis.

Synthesis of nonameric cationic clusters [Dy9(acac)16(µ3-OH)8(µ4-OH)2]OH·6H2O (1), [Dy8Tb (acac)16(µ3-OH)8(µ4-OH)2]OH·2H2O (2), and [Gd9(acac)16(µ3-OH)8(µ4-OH)2]OH·6H2O (3) (acac = acetylacetonate) is reported. The emission spectrum of 1 shows Dy(III) ion characteristic bands assignable to the 4F9/2 → 6HJ (J = 15/2 to 9/2) transitions. Emission due to both Dy(III) and Tb(III) ions is observed for 2 in the visible range, with Tb(III) specific bands appearing due to the 5D4 → 7FJ (J = 6, 4, and 3) transitions. Cluster 3 exhibits a significant magnetocaloric effect (MCE), with -ΔSm values increasing with decrease in temperature and increase in field, reaching -ΔSmmax = 20.98 J kg-1 K-1 at 2 K and 9 T. Isotropic magnetic coupling constants (Js) in 3 derived from density functional theory (DFT) calculations reveal that the exchange interactions are antiferromagnetic and weak. Compound 3 possesses S = 7/2 ground state arising from the central Gd(III) ion along with several nested excited states due to competing antiferromagnetic interactions that yield reasonably large MCE values. Utilizing computed exchange coupling interactions, we have performed ab initio CASSCF/RASSI-SO/POL_ANISO calculations on antiferromagnetic 1 and 2 to estimate the exchange interactions using the Lines model. For 2, Dy(III)···Tb(III) exchange interactions were extracted for the first time and were found to be weakly antiferromagnetically coupled.

Unravelling the Mechanism of CO2 Activation: Insights Into Metal-Metal Cooperativity and Spin-Orbit Coupling with {3d-4f} Catalysts.

Converting CO2 into useful chemicals using metal catalysts is a significant challenge in chemistry. Among the various catalysts reported, transition metal lanthanide hybrid {3d-4f} complexes stand out for their superior efficiency and site selectivity. However, unlike transition metal catalysts, understanding the origin of this efficiency in lanthanides poses a challenge due to their orbital degeneracy, rendering the application of DFT methods ineffective. In this study, we employed a combination of density functional theory (DFT) and ab initio CASSCF/RASSI-SO calculations to explore the mechanism of CO2 conversion to cyclic carbonate using a 3d-4f heterometallic catalyst for the first time. This work unveils the importance of 3d and 4f metal cooperativity and the role of individual spin-orbit states in dictating the overall efficiency of the catalyst.

ATI stabilized germylene cation as a cyanosilylation catalyst for aldehydes and ketones.

The aminotroponiminate (ATI) ligand stabilized germylene cation [(i-Bu)2ATIGe][B(C6F5)4] (2) is found to be an efficient low-valent main-group catalyst for the cyanosilylation of aldehydes and ketones (ATI = aminotroponiminate). It was synthesized by reacting [(i-Bu)2ATIGeCl] (1) with Na[B(C6F5)4]. The catalytic cyanosilylation of diverse aliphatic and aromatic carbonyl compounds (aldehydes and ketones) using 0.075-0.75 mol% of compound 2 was completed within 5-45 min. The catalytic efficiency seen with aliphatic aldehydes was around 15,800 h-1, making compound 2 a capable low-valent main-group catalyst for the aldehyde and ketone cyanosilylation reactions.

Unravelling the role of spin-vibrational coupling in designing high-performance pentagonal bipyramidal Dy(iii) single ion magnets.

At the cutting edge of high-performance single-molecule magnets (SMMs) lie lanthanide-based complexes, renowned for their potent magnetic anisotropy. SMMs containing one metal centre are defined as single-ion magnets (SIMs). The performance of SMMs is measured generally via the barrier height for magnetisation reversal (Ueff) and blocking temperature (TB), below which the magnetisation is fully frozen. To enhance the Ueff and TB values in lanthanide-based SMMs, the static crystal field splitting of mJ levels has been effectively adjusted through ligand design, leveraging the oblate/prolate ground state 4f electron density shape. However, the maximum fine-tuning achievable through ligand design, known as the axial limit, has already been reached in this class of compounds. This necessitates new design principles to enhance SMM characteristics to better suit end-user applications. Among other avenues that can be explored to improve SMM characteristics, a deeper understanding of spin-phonon coupling is critical to advancing TB values. However, there are only a handful of examples where this has been deciphered. In this work, using a combination of DFT and ab initio CASSCF calculations, we have performed spin-phonon calculations on five classes of pentagonal bipyramidal Dy(iii) SIMs exhibiting TB values in the range of 4.5 K to 36 K ([Dy(bbpen)Br] (1, H2bbpen = N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl)ethylenediamine), [Dy(OCMe3)Br(THF)5][BPh4] (2) [Dy(OSiMe3)Br(THF)5] [BPh4] (3), [Dy(LN5)(Ph3SiO)2](BPh4)·CH2Cl2 (4) and [L2Dy(H2O)5][I]3·L2·H2O (5, L = tBuPO(NHiPr)2)). Unlike the method employed elsewhere for the calculation of spin-phonon coupling, in this work, we have employed a set of criteria and intuitively selected vibrational modes to perform the spin-phonon coupling analysis. The approach provided here not only reduces the computational cost significantly but also suggests chemical intuition to improve the performance of this class of compounds. Our calculations reveal that low-energy vibrational modes govern the magnetisation relaxation in these SIMs. A flexible first coordination sphere found on some of the complexes was found to be responsible for low-energy vibrations that flip the magnetisation, reducing the TB values drastically (complexes 2 and 3). On the other hand, a rigid first coordination sphere and a stiff ligand framework move the spin-vibrational coupling that causes the relaxation to lie beyond the secondary coordination sphere, resulting in an increase in TB values. Our calculations also reveal that not only the atoms in the first coordination sphere but also those in the secondary coordination sphere affect the performance of the SMMs. Learning from this exercise, we have undertaken several in silico models based on these vibrations to improve the TB values. Some of these predictions were correlated with literature precedents, offering confidence in the methodology employed. To this end, our comprehensive investigation, involving twenty-three molecules/models and five sets of geometries for pentagonal bipyramidal Dy(iii) single-ion magnets (SIMs), unveils a treasure trove of chemically sound design clues, poised to enhance the TB values in this fascinating molecular realm.

Origin of Unprecedented Formation and Reactivity of FeIV═O Species via Oxygen Activation: Role of Noncovalent Interactions and Magnetic Coupling.

Emulating the capabilities of the soluble methane monooxygenase (sMMO) enzymes, which effortlessly activate oxygen at diiron(II) centers to form a reactive diiron(IV) intermediate Q, which then performs the challenging oxidation of methane to methanol, poses a significant challenge. Very recently, one of us reported the mononuclear complex [(cyclam)FeII(CH3CN)2]2+ (1), which performed a rare bimolecular activation of the molecule of O2 to generate two molecules of FeIV═O without the requirement of external proton or electron sources, similar to sMMO. In the present study, we employed the density functional theory (DFT) calculations to investigate this unique mechanism of O2 activation. We show that secondary hydrogen-bonding interactions between ligand N-H groups and O2 play a vital role in reducing the energy barrier associated with the initial O2 binding at 1 and O-O bond cleavage to form the FeIV═O complex. Further, the unique reactivity of FeIV═O species toward simultaneous C-H and O-H bond activation process has been demonstrated. Our study unveils that the nature of the magnetic coupling between the diiron centers is also crucial. Given that the influence of magnetic coupling and noncovalent interactions in catalysis remains largely unexplored, this unexplored realm presents numerous avenues for experimental chemists to develop novel structural and functional analogues of sMMO.

Magnetic anisotropy in octahedral Dy(III) and Yb(III) complexes.

New organophosphate complexes [Ln(dippH)3(dippH2)3]·(H2O)6, (Ln = Dy, Yb and Y; dippH2 = 2,6-diisopropylphenyl phosphate), displaying octahedral coordination geometry around the metal ion, exhibit unusual slow relaxation of magnetisation, which is investigated through experimental studies and ab initio CASSCF calculations.

Unusual Stabilisation of Remarkably Bent Tetra-Cationic Tetra-radical Intermolecular Fe(III) µ-Oxo Tetranuclear Complexes.

A hitherto unknown series of air stable, π-conjugated, remarkably bent tetra-cation tetra-radical intermolecular Fe(III) µ-oxo tetranuclear complex, isolated from the dication diradical diiron(III) porphyrin dimers, has been synthesised and spectroscopically characterised along with single crystal X-ray structure determination of two such molecules. These species facilitate long-range charge/radical delocalisation through the bridge across the entire tetranuclear unit manifesting an unusually intense NIR band. Assorted spin states of Fe(III) centres are stabilised within these unique tetranuclear frameworks: terminal six-coordinate iron centres stabilise the admixed intermediate spin states while the central five-coordinate iron centres stabilise the high-spin states. Variable temperature magnetic susceptibility measurements indicated strong antiferromagnetic coupling for the Fe(III)-O-Fe(III) unit while the exchange interactions between the Fe centres and the porphyrin π-cation radicals are weaker as supported both by magnetic data and DFT calculations. The nature of orbital overlap between the SOMOs of Fe(III) and π* orbital of the porphyrin was found to rationalise the observed exchange coupling, establishing such a complex magnetic exchange in this tetranuclear model with a significant bioinorganic relevance.

Rebound or Cage Escape? The Role of the Rebound Barrier for the Reactivity of Non-Heme High-Valent FeIV =O Species.

Owing to their high reactivity and selectivity, variations in the spin ground state and a range of possible pathways, high-valent FeIV =O species are popular models with potential bioinspired applications. An interesting example of a structure-reactivity pattern is the detailed study with five nonheme amine-pyridine pentadentate ligand FeIV =O species, including N4py: [(L1 )FeIV =O]2+ (1), bntpen: [(L2 )FeIV =O]2+ (2), py2 tacn: [(L3 )FeIV =O]2+ (3), and two isomeric bispidine derivatives: [(L4 )FeIV =O]2+ (4) and [(L5 )FeIV =O]2+ (5). In this set, the order of increasing reactivity in the hydroxylation of cyclohexane differs from that with cyclohexadiene as substrate. A comprehensive DFT, ab initio CASSCF/NEVPT2 and DLPNO-CCSD(T) study is presented to untangle the observed patterns. These are well reproduced when both activation barriers for the C-H abstraction and the OH rebound are taken into account. An MO, NBO and deformation energy analysis reveals the importance of π(pyr) → π*xz (FeIII -OH) electron donation for weakening the FeIII -OH bond and thus reducing the rebound barrier. This requires that pyridine rings are oriented perpendicularly to the FeIII -OH bond and this is a subtle but crucial point in ligand design for non-heme iron alkane hydroxylation.

Enhancing Spin-Transport Characteristics, Spin-Filtering Efficiency, and Negative Differential Resistance in Exchange-Coupled Dinuclear Co(II) Complexes for Molecular Spintronics Applications.

Single-molecule spintronics, where electron transport occurs via a paramagnetic molecule, has gained wide attention due to its potential applications in the area of memory devices to switches. While numerous organic and some inorganic complexes have been employed over the years, there are only a few attempts to employ exchange coupled dinuclear complexes at the interface, and the advantage of fabricating such a molecular spintronics device in the observation of switchable Kondo resonance was demonstrated recently in the dinuclear [Co2(L)(hfac)4] (1) complex (Wagner et al., Nat. Nanotechnol. 2013, 8, 575-579). In this work, employing an array of theoretical tools such as density functional theory (DFT), the ab initio CASSCF/NEVPT2 method, and DFT combined with nonequilibrium Green Function (NEGF) formalism, we studied in detail the role of magnetic coupling, ligand field, and magnetic anisotropy in the transport characteristics of complex 1. Particularly, our calculations not only reproduce the current-voltage (I-V) characteristics observed in experiments but also unequivocally establish that these arise from an exchange-coupled singlet state that arises due to antiferromagnetic coupling between two high-spin Co(II) centers. Further, the estimated spin Hamiltonian parameters such as J, g values, and D and E/D values are only marginally altered for the molecule at the interface. Further, the exchange-coupled state was found to have very similar transport responses, despite possessing significantly different geometries. Our transport calculations unveil a new feature of the negative differential resistance (NDR) effect on 1 at the bias voltage of 0.9 V, which agrees with the experimental I-V characteristics reported. The spin-filtering efficiency (SFE) computed for the spin-coupled states was found to be only marginal (∼25%); however, if the ligand field is fine-tuned to obtain a low-spin Co(II) center, a substantial SFE of 44% was noted. This spin-coupled state also yields a very strong NDR with a peak-to-valley ratio (PVR) of ∼56 - a record number that has not been witnessed so far in this class of compounds. Additionally, we have established further magnetostructural-transport correlations, providing valuable insights into how microscopic spin Hamiltonian parameters can be associated with SFE. Several design clues to improve the spin-transport characteristics, SFE and NDR in this class of molecule, are offered.

Tuning Magnetic Anisotropy in Co(II) Tetrahedral Carbazole-Modified Phosphine Oxide Single-Ion Magnets: Importance of Structural Distortion versus Heavy-Ion Effect.

Three mononuclear cobalt(II) tetrahedral complexes [Co(CzPh2PO)2X2] (CzPh2PO = (9H-carbazol-9-yl)diphenylphosphine oxide and X = Cl (1), Br (2), I (3)) have been synthesized using a simple synthetic approach to examine their single-ion magnetic (SIM) behavior. A detailed study of the variation in the dynamic magnetic properties of the Co(II) ion in a tetrahedral ligand field has been carried out by the change of the halide ligand. The axial zero-field splitting parameter D was found to vary from -16.4 cm-1 in 1 to -13.8 cm-1 in 2 and +14.6 cm-1 in 3. All the new complexes exhibit field-induced SIM behavior. The results obtained from ab initio CASSF calculations match well with the experimental data, revealing how halide ions induce a change in the D value as we move from Cl- to I-. The ab initio calculations further reveal that the change in the sign of D is due to the multideterminant characteristics of the ground state wave function of 1 and 2, while single-determinant characteristics are instead observed for 3. To gain a better understanding of the relationship between the structural distortion and the sign and magnitude of D values, magnetostructural D correlations were developed using angular relationships, revealing the importance of structural distortions over the heavy halide effect in controlling the sign of D values. This study broadens the scope of employing electronically and sterically modified phosphine oxide ligands in building new types of air-stable Co(II) SIMs.

Unravelling the Effect of Acid-Driven Electron Transfer in High-Valent FeIV =O/MnIV =O Species and Its Implications for Reactivity.

The electron transfer (ET) step is one of the crucial processes in biochemical redox reactions that occur in nature and has been established as a key step in dictating the reactivity of high-valent metal-oxo species. Although metalloenzymes possessing metal-oxo units at their active site are typically associated with outer-sphere electron transfer (OSET) processes, biomimetic models, in contrast, have been found to manifest either an inner-sphere electron transfer (ISET) or OSET mechanism. This distinction is clearly illustrated through the behaviour of [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) complexes, where complex 1 showcases an OSET mechanism, while complex 2 exhibits an ISET mechanism, especially evident in their reactions involving C-H bond activation and oxygen atom transfer reactions in the presence of a Lewis/Bronsted acid. However, the precise reason for this puzzling difference remains elusive. This work unveils the origin of the perplexing inner-sphere vs outer-sphere electron transfer process (ISET vs OSET) in [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) species in the presence of Bronsted acid. The calculations indicate that when the substrate (toluene) approaches both 1 and 2 that is hydrogen bonded with two HOTf molecules (denoted as 1-HOTf and 2-HOTf, respectively), proton transfer from one of the HOTf molecules to the metal-oxo unit is triggered and a simultaneous electron transfer occurs from toluene to the metal centre. Interestingly, the preference for OSET by 1-HOTf is found to originate from the choice of MnIV =O centre to abstract spin-down (ß) electron from toluene to its δ(dxy ) orbital. On the other hand, in 2-HOTf, a spin state inversion from triplet to quintet state takes place during the proton (from HOTf) coupled electron transfer (from toluene) preferring a spin-up (α) electron abstraction to its σ* (dz 2 ) orbital mediated by HOTf giving rise to ISET. In addition, 2-HOTf was calculated to possess a larger reorganisation energy, which facilitates the ISET process via the acid. The absence of spin-inversion and smaller reorganisation energy switch the mechanism to OSET for 1-HOTf. Therefore, for the first time, the significance of spin-state and spin-inversion in the electron transfer process has been identified and demonstrated within the realm of high-valent metal-oxo chemistry. This discovery holds implications for the potential involvement of high-valent Mn-oxo species in performing similar transformative processes within Photosystem II.

Bis-Olefin Based Crystalline Schlenk Hydrocarbon Diradicals with a Triplet Ground State.

A modular approach for the synthesis of isolable crystalline Schlenk hydrocarbon diradicals from m-phenylene bridged electron-rich bis-triazaalkenes as synthons is reported. EPR spectroscopy confirms their diradical nature and triplet electronic structure by revealing a half-field signal. A computational analysis confirms the triplet state to be the ground state. As a proof-of-principle for the modular methodology, the 4,6-dimethyl-m-phenylene was further utilized as a coupling unit between two alkene motifs. The steric conjunction of the 4,6-dimethyl groups substantially twists the substituents at the nonbonding electron bearing centers relative to the central coupling m-phenylene motif. As a result, the spin delocalization is decreased and the exchange coupling between the two unpaired spins, hence, significantly reduced. Notably, 108 years after Schlenk's m-phenylene-bis(diphenylmethyl) synthesis as a diradical, for the first time we were able to isolate its derivative with the same spacer, i.e. m-phenylene, between two radical centers in a crystalline form.

Unraveling the origin of the cooperative adsorption of carbon monoxide in an Fe(II) metal-organic framework.

Using periodic DFT calculations, we have established the mechanism of the unusual cooperative adsorption of CO gas in an Fe-bistriazolate MOF observed previously. The binding of one CO molecule to FeII triggers structural alteration of the neighbouring Fe centres, reducing the steric energy penalty and aiding cooperative adsorption. This is similar to the entatic state concept proposed for metalloenzymes, and offers novel strategies for selective gas adsorption.

Probing the Origins of Puzzling Reactivity in Fe/Mn-Oxo/Hydroxo Species toward C-H Bonds: A DFT and Ab Initio Perspective.

Activation of C-H bonds using an earth-abundant metal catalyst is one of the top challenges of chemistry, where high-valent Mn/Fe-oxo(hydroxo) biomimic species play an important role. There are several open questions related to the comparative oxidative abilities of these species, and a unifying concept that could accommodate various factors influencing reactivity is lacking. To shed light on these open questions, here, we have used a combination of density functional theory (DFT) (B3LYP-D3/def2-TZVP) and ab initio (CASSCF/NEVPT2) calculations to study a series of high-valent metal-oxo species [Mn+H3buea(O/OH)] (M = Mn and Fe, n = II to V; H3buea = tris[(N'-tert-butylureaylato)-N-ethylene)]aminato towards the activation of dihydroanthracene (DHA). The H-bonding network in the ligand architecture influences the ground state-excited state gap and brings several excited states of the same spin multiplicity closer in energy, which triggers reactivity via one of those excited states, reducing the kinetic barriers for the C-H bond activation and rationalizing several puzzling reactivity trends observed in various high-valent Mn/Fe-oxo(hydroxo) species.

The role of agostic interaction in the mechanism of ethylene polymerisation using Cr(III) half-sandwich complexes: What dictates the reactivity?

Chromium-based catalysts play a significant role in the production of ultra-high molecular weight polyethylene, and half-sandwich functionalised-metallocene complexes were proven to be one of the most suitable candidates as catalysts for generating such large polymeric-length olefins. Earlier experimental studies on olefin polymerisation using a series of catalysts such as [L1-2CrCl2] (where L1 = 1-((pyridin-2-yl)methyl)indenyl (1) and L2 = 2-methyl-1-{[4-(yridinene-1-yl)yridine-2-yl]methyl}-1H-indenyl (2)) reveal significant variation where peripheral substitution on the ligand was found to influence the reactivity significantly. However, the specific ligand position that affects the reactivity has not been established. As these reactions are fast and robust, it is challenging to establish reactive intermediates via experiments, and therefore, mechanistic clues for such reactions are elusive. Here we have undertaken a detailed computational study by employing an array of DFT (uB3LYP-D3/def2-TZVP, CASSCF/NEVPT2, and DLPNO-CCSD(T) methods to explore the substituted and non-substituted pyridine-cyclo-pentadienyl chromium complexes and their influence on the catalytic activity in ethylene polymerisation. Our study not only unravels the catalytic pathway for olefin polymerisation for such Cr(III)-half-sandwich complexes but also reveals that the energetics of the formation of pseudo-three-coordinate alkyl intermediates is key to the variation in the reactivity observed. A detailed examination using MO and NBO analysis unveils the presence of a C-H⋯Cr agostic interaction that is found to significantly stabilise this intermediate when the pyridine ligand has strong electron-donating groups at its para position. The other substitutions, such as on the cyclopentadienyl ligand, neither yield the desired stability nor the desired interaction. Further studies on models support this proposal. In order to improve the efficiency and selectivity of catalytic systems in olefin polymerisation, we strongly advocate for the integration of agostic interactions as a crucial criterion in the design of future catalysts. Considering the prevalence of electron-deficient metal centres in successful olefin polymerisation catalysts, this research prompts a broader mechanistic inquiry to propose a unified approach for this industrially crucial reaction.

Accessing Bioactive Hydrazones by the Hydrohydrazination of Terminal Alkynes Catalyzed by Gold(I) Acyclic Aminooxy Carbene Complexes and Their Gold(I) Arylthiolato and Gold(III) Tribromo Derivatives: A Combined Experimental and Computational Study.

Hydrohydrazination of terminal alkynes with hydrazides yielding hydrazones 5-14 were successfully catalyzed by a series of gold(I) acyclic aminooxy carbene complexes of the type [{(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)}methylidene]AuCl, where R2 = H, R1 = Me (1b); R2 = H, R1 = Cy (2b); R2 = t-Bu, R1 = Me (3b); R2 = t-Bu, R1 = Cy (4b). The mass spectrometric evidence corroborated the existence of the catalytically active solvent-coordinated [(AAOC)Au(CH3CN)]SbF6 (1-4)A species and the acetylene-bound [(AAOC)Au(HC≡CPhMe)]SbF6 (3B) species of the proposed catalysis cycle. The hydrohydrazination reaction was successfully employed in synthesizing several bioactive hydrazone compounds (15-18) with anticonvulsant properties using a representative precatalyst (2b). The DFT studies favored the 4-ethynyltoluene (HC≡CPhMe) coordination pathway over the p-toluenesulfonyl hydrazide (NH2NHSO2C6H4CH3) coordination pathway, and that proceeded by a crucial intermolecular hydrazide-assisted proton transfer step. The gold(I) complexes (1-4)b were synthesized from the {[(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)]CH}+OTf- (1-4)a by treatment with (Me2S)AuCl in the presence of NaH as a base. The reactivity studies of (1-4)b yielded the gold(III) [{(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)}methylidene]AuBr3 (1-4)c complexes upon reaction with molecular bromine and the gold(I) perfluorophenylthiolato derivatives, [{(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)}methylidene]AuSC6F5 (1-4)d, upon treatment with C6F5SH.

Fluxionality Modulating the Magnetic Anisotropy in Lanthanoarene [(ηCnRn)2Ln(II/III)] (n = 4-8) Single-Ion Magnets.

Lanthanoarenes have emerged as the best bet for the futuristic application of single-ion magnets in information storage devices. While dysprosocenium molecules with various substituents at the arene ring exhibit a very large blocking temperature, the corresponding Er(III) analogues do not, and this is reversed if the size of the arene ring is eight. Using a combination of ab initio CASSCF and DFT-based molecular dynamics (MD) study, we have explored 25 Dy(III)/Er(III)/Ho(II)/Tb(II)/Dy(II) arene complexes with the ring size varying from 4 to 8 to understand the differences observed and decipher the correlation of structure to the spin dynamics behavior. Among the oxidation state of +2 complexes studied, Tb(II) exhibits the highest barrier, with the Cp-Tb-Cp angle being linear. Further, one of the four-membered arene model studied exhibits a very large barrier of 1442 cm-1, suggesting a potential high-blocking SIM. While bulky substituents at the arene ring help increase the axiality and the CR-Ln-CR angle, this also fetches several agostic C-H···Ln interactions, which injects transverse anisotropy. Furthermore, MD coupled with the CASSCF study reveals that the fluxional behavior of the arene ring generates several rotational conformers that are even accessible at lower temperatures offering a shortcut to the magnetization relaxation process. The importance of structural fluctuations in controlling the magnetic anisotropy by choosing apt metal-ion/ring partners and the corresponding substituents has been highlighted to offer clues to the futuristic SIM design.

Field-induced SIM behaviour in early lanthanide(III) organophosphates containing 18-crown-6.

Single-ion magnets (SIMs) have attracted wide attention in recent years. Despite tremendous progress in late lanthanide SIMs, reports on early lanthanides exhibiting SIM characteristics are scarce. A series of five novel 18-crown-6 encapsulated mononuclear early lanthanide(III) organophosphates, [{(18-crown-6)Ln(dippH)3}{(18-crown-6)Ln(dippH)2(dippH2)}]·[I3] [Ln = Ce (1), Pr (2), Nd (3)] and [{Ln(18-crown-6)(dippH)2(H2O)}·{I3}] [Ln = Sm (4) and Eu (5)], have been synthesised in the present study. 18-crown-6 coordinates to Ln(III) ions in an equatorial position while the axial positions are occupied by either three phosphate moieties as in 1-3 or two phosphate moieties and one water molecule as in 4 and 5, resulting in a muffin-shaped coordination geometry around the Ln(III) centres. Magnetic susceptibility measurements reveal that Ce and Nd complexes are field-induced single-ion magnets with significant barrier heights. Furthermore, the ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations on complexes 1 and 3 reveal significant QTM in the ground state rationalising the field-induced single-ion magnetism behaviour of these complexes.

Role of molecular modelling in the development of metal-organic framework for gas adsorption applications.

More than 47,000 articles have been published in the area of Metal-Organic Framework since its seminal discovery in 1995, exemplifying the intense research carried out in this short span of time. Among other applications, gas adsorption and storage are perceived as central to the MOFs research, and more than 10,000 MOFs structures are reported to date to utilize them for various gas storage/separation applications. Molecular modeling, particularly based on density functional theory, played a key role in (i) understanding the nature of interactions between the gas and the MOFs geometry (ii) establishing various binding pockets and relative binding energies, and (iii) offering design clues to improve the gas uptake capacity of existing MOF architectures. In this review, we have looked at various MOFs that are studied thoroughly using DFT/periodic DFT (pDFT) methods for CO2, H2, O2, and CH4 gases to provide a birds-eye-view on how various exchange-correlation functionals perform in estimating the binding energy for various gases and how factors such as nature of the (i) metal ion, (ii) linkers, (iii) ligand, (iv) spin state and (v) spin-couplings play a role in this process with selected examples. While there is still room for improvement, the rewards offered by the molecular modelling of MOFs were already substantial that we advocate experimental and theoretical studies to go hand-in-hand to undercut the trial-and-error approach that is often perceived in the selection of MOFs and gas partners in this area. Graphical abstract: The importance of density functional theory-based molecular modeling studies in offering design clues to improve the gas adsorption and storage capacity of existing MOF architectures is discussed here. The use of DFT-based investigation in conjunction with experimental synthesis is an imperative tool in designing new-generation MOFs with enhanced uptake capacity.