Spin State Structure Research Articles

Binuclear methylphosphinidine complexes of cyclopentadienylruthenium carbonyls: effects of the higher ligand field strength of ruthenium derivatives relative to iron derivatives.

The structures and energetics of the binuclear methylphosphinidene complexes of cyclopentadienylruthenium carbonyls of the type [MePRu2(CO)nCp2] (n = 4, 3, 2, 1) have been investigated for comparison with their previously studied iron analogues. For the tetracarbonyls and tricarbonyls [MePM2(CO)nCp2] (n = 4, 3) substituting ruthenium for iron has relatively little effect on the energetically preferred structures. Thus such structures have two-electron donor bridging MeP groups with no metal-metal bond for the tetracarbonyls and a metal-metal single bond for the tricarbonyls. This leads to favored 18-electron configurations for both ruthenium atoms in all cases. However, the higher ligand field strengths of ruthenium complexes relative to analogous iron complexes have major effects on the energetically preferred structures for the dicarbonyls and monocarbonyls [MePM2(CO)nCp2] (M = Fe, Ru; n = 2, 1). Thus the 11 lowest energy structures for the dicarbonyl [MePFe2(CO)2Cp2] are triplet or quintet spin state structures whereas the 6 lowest energy structures for the ruthenium analogue [MePRu2(CO)2Cp2] are all singlet structures. These low-energy singlet [MePRu2(CO)2Cp2] structures include species in which both ruthenium atoms attain the favored 18-electron configurations in different ways: either by a Ru-Ru single bond and an agostic C-H-Ru interaction from the methyl group, a Ru-Ru single bond and a four-electron donor bridging MeP ligand with PRu double bonds, or a formal RuRu double bond with a two-electron donor bridging MeP ligand. The 8 lowest energy structures for the diiron monocarbonyl [MePFe2(CO)Cp2] are all triplet or quintet spin structures whereas the lowest energy structure for the diruthenium monocarbonyl [MePRu2(CO)Cp2] by more than 20 kcal mol-1 is a singlet structure with a formal RuRu double bond and bridging CO and four-electron donor MeP groups. Thermochemical information predicts such monocarbonyl derivatives to be the dominant binuclear decarbonylation products of the tricarbonyls [RPRu2(CO)3Cp2] by thermal or photochemical methods.

Low-energy high-spin binuclear hexamethylbenzene manganese carbonyl structures with partially bonded benzene rings

The geometries and energetics of binuclear hexamethylbenzene manganese carbonyls (Me6C6)2Mn2(CO)n (n = 4, 3, 2, 1), including the experimentally known tetracarbonyl, have been examined using density functional theory. Relatively low- energy structures include trans- and cis-(η6-Me6C6)2Mn2(CO)2(µ-CO)2 doubly bridged tetracarbonyl structures and a triplet (η6-Me6C6)2Mn2(µ-CO)3 triply bridged structure analogous to experimentally known isoelectronic binuclear cyclopentadienyliron carbonyls. However, in addition, a series of low-energy quintet spin state structures (η10–2n-Me6C6)Mn(CO)n–Mn(η6-C6Me6) (n = 4, 3, 2) is found. The tetracarbonyls and tricarbonyl of this series have partially bonded hexamethylbenzene rings suggesting a certain fragility of the hexamethylbenzene-manganese linkage not found in the isoelectronic cyclopentadienyliron compounds. For the dicarbonyl and monocarbonyl (Me6C6)2Mn2(CO)n (n = 2, 1) systems, singlet structures having the triple or quadruple manganese-manganese bonds necessary to give each manganese atom the favored 18-electron configuration are very high-energy structures relative to isomeric triplet and quintet spin state structures.

Spin state and deep interior structure of Mars from InSight radio tracking.

Knowledge of the interior structure and atmosphere of Mars is essential to understanding how the planet has formed and evolved. A major obstacle to investigations of planetary interiors, however, is that they are not directly accessible. Most of the geophysical data provide global information that cannot beseparated into contributions from the core, the mantle and the crust. The NASA InSight mission changed this situation by providing high-quality seismic and lander radio science data1,2. Here we use the InSight's radio science data to determine fundamental properties of the core, mantle and atmosphere of Mars. By precisely measuring the rotation of the planet, we detected a resonance with a normal mode that allowed us to characterize the core and mantle separately. For an entirely solid mantle, we found that the liquid core has a radius of 1,835 ± 55 km and a mean density of 5,955-6,290 kg m-3, and that the increase in density at the core-mantle boundary is 1,690-2,110 kg m-3. Our analysis of InSight's radio tracking data argues against the existence of a solid inner core and reveals the shape of the core, indicating that there are internal mass anomalies deep within the mantle. We also find evidence of a slow acceleration in the Martian rotation rate, which could be the resultof a long-term trend either inthe internal dynamics of Mars or in its atmosphere and ice caps.

Electro-Elastic Modeling of Multi-Step Transitions in Two Elastically Coupled and Sterically Frustrated 1D Spin Crossover Chains

One-dimensional spin crossover (SCO) solids that convert between the low spin (LS) and the high spin (HS) states are widely studied in the literature due to their diverse thermal and optical characteristics which allow obtaining many original behaviors, such as large thermal hysteresis, incomplete spin transitions, as multi-step spin transitions with self-organized states. In the present work, we investigate the thermal behaviors of a system of two elastically coupled 1D mononuclear chains, using the electro-elastic model, by including an elastic frustration in the nearest neighbors (nn) bond length distances of each chain. The chains are made of SCO sites that are coupled elastically through springs with their nn and next-nearest neighbors. The elastic interchain coupling includes diagonal springs, while the nn inter-chain distance is fixed to that of the high spin state. The model is solved using MC simulations, performed on the spin states and the lattice distortions. When we only frustrate the first chain, we found a strong effect on the thermal dependence of the HS fraction of the second chain, which displays an incomplete spin transition with a significantly lowered transition temperature. In the second step, we frustrate both chains by imposing different frustration rates. Here, we demonstrate that for high frustration values, the thermal dependence of the total HS fraction exhibits multi-step spin transitions. The careful examination of the spin state structures in the plateau regions showed the coexistence of special dimerized ferro–antiferro patterns of type LL-HH-LL-HH along the first chain and HH-LL-HH-LL (H=HS and L=LS) along the second one, revealing that the two chains are antiferro-elastically coupled. This type of spatial modulation of the spin state and bond length distances is very attractive because it anticipates the possible existence of periodic structures in 2D lattices, made of alternate 1D SCO strings with HLHLHL structures, coupled in the ferro-like fashion along the interchain direction.

General approach for atomically dispersed precious metal catalysts toward hydrogen reaction

AbstractAs a carbon‐free energy carrier, hydrogen has become the pivot for future clean energy, while efficient hydrogen production and combustion still require precious metal‐based catalysts. Single‐atom catalysts (SACs) with high atomic utilization open up a desirable perspective for the scale applications of precious metals, but the general and facile preparation of various precious metal‐based SACs remains challenging. Herein, a general movable printing method has been developed to synthesize various precious metal‐based SACs, such as Pd, Pt, Rh, Ir, and Ru, and the features of highly dispersed single atoms with nitrogen coordination have been identified by comprehensive characterizations. More importantly, the synthesized Pt‐ and Ru‐based SACs exhibit much higher activities than their corresponding nanoparticle counterparts for hydrogen oxidation reaction and hydrogen evolution reaction (HER). In addition, the Pd‐based SAC delivers an excellent activity for photocatalytic hydrogen evolution. Especially for the superior mass activity of Ru‐based SACs toward HER, density functional theory calculations confirmed that the adsorption of the hydrogen atom has a significant effect on the spin state and electronic structure of the catalysts.

Addressing the Origin of Single-Atom-Activated Supports Monitored by Electrochemiluminescence.

Currently, much attention has been paid to the efforts to stabilize and regulate single atoms through supports to obtain decent electrocatalytic behaviors. However, little concern was given to the effect of single atoms on modulating the electronic structure of supports, despite the catalytic activities and large quantities of supports in the catalytic reactions. Herein, we have localized Ru single atoms onto two-dimensional layered double hydroxide (NiFe-LDH) and studied the role of Ru single atoms in adjusting the electronic structure of the NiFe-LDH support. Spin polarization of 3d electrons for Fe and electron redistribution in NiFe-LDH were effectively modulated through the interaction between Ru single atoms and NiFe-LDH. As a result, the luminol redox reaction and reactive oxygen revolution were simultaneously promoted by Ru single-atom-modulated NiFe-LDH, manifested as boosted electrochemiluminescence (ECL). Therefore, we have provided valid information to reveal the regulation effect of single atoms on the spin state and electronic structure of the supports. It is anticipated that our strategy may arouse wide interest in manipulating single-atom-modulated supports.

Triplet Spin-State Capped Deltahedral Structures Rather than Singlet Spin-State Oblatocloso Structures as Energetically Favored Dimanganaborane Structures

Density functional studies show that the singlet spin-state flattened oblatocloso deltahedral structures found experimentally in the dimetallaboranes Cp*2Re2Bn-2Hn-2 (Cp* = Me5C5; n = 8-12) of the third row group 7 element rhenium are not favored for analogous dimetallaboranes Cp2Mn2Bn-2Hn-2 (n = 8-14) of its first row congener manganese. Instead, the energetically preferred structures for the dimanganaboranes are higher spin-state triplet and quintet spin-state structures. This appears to be related to the lower ligand field splittings in complexes of the first row transition-metal manganese relative to analogous complexes of the third row transition-metal rhenium. The lowest-energy Cp2Mn2Bn-2Hn-2 (n = 8-13) structures typically have a central MnBn-2 closo deltahedron with one face capped by the second CpMn unit. However, for the 14-vertex Cp2Mn2B12H12 system the lowest-energy structures consist of B12 icosahedra with faces capped by both CpMn units. The thermochemistry of cluster buildup reactions of the type Cp2Mn2Bn-2Hn-2 + BH → Cp2Mn2Bn-1Hn-1 suggests that the 11- and 13-vertex structures are likely to be favored products in reactions of cyclopentadienylmanganese derivatives with borane sources. The paramagnetism of the predicted triplet and quintet spin states for the lowest-energy dimanganaboranes Cp2Mn2Bn-2Hn-2 (n = 8-14) suggests possible applications in novel magnetic materials.

Trinuclear cyanido-bridged MII-WV complexes (M = Mn, Co): Crystal structures and magnetic properties

Two new trinuclear heterometallic complexes, [{MnII(L)(CH3OH)}2{WV(CN)8}](NO3)·CH3OH·H2O (2) and [{CoII(L)(CH3OH)}2{WV(CN)8}](NO3)·CH3OH·H2O (3), have been assembled from mononuclear cationic modules, [M(L)(H2O)2]2+, and [W(CN)8]3– as a metalloligand (M = MnII; CoII, L is the pentadentate ligand resulting from the condensation reaction between 2,6-diacetylpyridine and semicarbazide). The crystal structure of the manganese(II) precursor, [MnII(L)(H2O)2](NO3)2·H2O 1, and of the trinuclear compounds 2 and 3 have been solved. Within the three compounds the 3d metal ions show a pentagonal bipyramidal coordination geometry. The magnetic properties of compounds 2 and 3 have been investigated. Compound 2 shows an irregular spin state structure with S = 9/2 arising from MnII-WV antiferromagnetic interactions (J = −8.00 cm−1, H = -2JS1S2). In compound 3, the CoII-WV exchange interaction was found ferromagnetic (J = +12.3 cm−1).

Combining a weak-field rigid chelating bidentate dicarbene ligand with a strong-field carbonyl ligand in binuclear cyclopentadienyliron carbonyl derivatives

Binuclear cyclopentadienyliron carbonyl derivatives of the weak-field rigid chelating bidentate dicarbene vegiMe ligand with a tricyclic backbone are shown by theoretical studies on the Cp2Fe2(vegiMe)(CO)n (n = 3, 2, 1) systems to have higher spin triplet and quintet structures of comparable energies to isomeric singlet structures satisfying the 18-electron rule. Thus triplet structures of the tricarbonyl Cp2Fe2(vegiMe)(CO)3 with the vegiMe ligand as a bidentate chelate to a single iron atom are of comparable energies to singlet isomers with no iron-iron bond and the vegiMe ligand bridging the two iron atoms. Similarly, triplet and quintet structures for the dicarbonyl Cp2Fe2(vegiMe)(CO)2 are of comparable energies to singlet structures with Fe–Fe single bonds that are substitution products of the well-known Cp2Fe2(CO)2(µ-CO)2. The only low-energy singlet structure for the monocarbonyl Cp2Fe2(vegiMe)(CO) has an unusual six-electron donor bridging vegiMe ligand forming not only the usual two C(carbene)→Fe dative bonds but also a N→Fe dative bond. The other low-energy Cp2Fe2(vegiMe)(CO) structures are various types of triplet and quintet spin state structures.

Regulating the Local Spin State and Band Structure in Ni3S2 Nanosheet for Improved Oxygen Evolution Activity

AbstractThe separate modulation of the adsorption of *O and *OOH is challenging in oxygen evolution reaction (OER), which results in a large overpotential and slow kinetics. To balance the adsorption of the two active species, here, a way to regulate the local spin state and band structure simultaneously in Ni3S2 nanosheets is reported. The adequate doping of W heteroatoms causes the electron depletion from the Ni active site, which modulates the spin state of eg electrons, weakening the adsorption of *O. Additionally, the introduction of S vacancies contributes to the upshift of the d band center, which strengthens the adsorption of *OOH. In this manner, the adsorption of Ni3S2 for the active intermediates is optimized, resulting in a considerably improved overpotential of 246 mV at 100 mA cm−2 and a Tafel slope of 66 mV dec−1. This work provides insights into the exploration of OER catalysts through synergistic modulation of the spin state and the band structure.

Theoretical DFT Study on the Mechanisms of CO/CO2 Conversion in Chemical Looping Catalyzed by Calcium Ferrite.

The CO/CO2 conversion mechanism on the calcium ferrite (CFO) surface in chemical looping was explored by a computational study using the density functional theory approach. The CFO catalytic reaction pathway of 2CO + O2 → 2CO2 conversion has been elucidated. Our results show that the Fe center in CFO plays the key role as a catalyst in the CO/CO2 conversion. Two energetically stable spin states of CFO, quintet and septet, serve as the effective catalysts. The presence of the triplet O2 molecule caused the conversion of these two spin-state structures into each other along the catalytic reaction pathway. A double release of CO2 was predicted following this reaction mechanism. The rate-determining step is the formation of the 2CO2-CFO complex (P4) in the quintet state (19.0 kcal/mol). The predicted energy barriers for all the steps suggest that the proposed pathway is plausible.

CaMn3IV O4 Cubane Models of the Oxygen-Evolving Complex: Spin Ground States S

We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn3IV O4 and YMn3IV O4 complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen-evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin-state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn3IV O4 complexes and variants with protonated oxo moieties need not be S=9/2. Desymmetrization of the pseudo-C3 -symmetric Ca(Y)Mn3IV O4 core leads to a lower S=5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and an S=3/2 spin ground state is observed in CaMn3IV O3 (OH). Our studies complement the observation that the interconversion between the low-spin and high-spin forms of the S2 state is pH-dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin-state changes.

Binuclear 1,3-diphosphacyclobutadiene vanadium carbonyls: Bending of the P2C2 ring in an unsaturated system with a vanadium-vanadium multiple bond

The structures and energetics of the binuclear 1,3-diphosphacyclobutadiene vanadium carbonyls of the type (Me2C2P2)2V2(CO)n have been investigated by density functional theory. The lowest energy (Me2C2P2)2V2(CO)n (n = 8, 7, 6, 5) structures are singlet spin state structures with various combinations of single and double vanadium-vanadium bonds and six-electron donor bridging η1,η4-Me2C2P2 ligands to give each vanadium atom the favored 18-electron configuration. Higher energy singlet (Me2C2P2)2V2(CO)6 structures have terminal η4-Me2C2P2 ligands and formal VV triple bonds similar to that found in the experimentally known binuclear cyclopentadienylvanadium carbonyl derivative (η5-C5H5)2V2(CO)5. The lowest energy structure of the highly unsaturated (Me2C2P2)2V2(CO)4 by a significant margin has an unprecedented type of eight-electron donor bent tetrahedrane-like Me2C2P2 ligand not found in the low energy structures of the later first row transition metals. The lowest energy structure of the even more highly unsaturated (Me2C2P2)2V2(CO)3 has a vanadium (η4-Me2C2P2)2V sandwich functioning as a bidentate chelating ligand to a V(CO)3 unit supplemented by a VV triple bond.

Iron carbonyl complexes of a rigid chelating dicarbene: A density functional theory study

The series of vegiR dicarbenes with a phenanthroline-like backbone synthesized by Kunz and co-workers provide rigid chelating bidentate ligands with carbon donor atoms. Such ligands can, in principle, replace two carbonyl groups in a metal carbonyl derivative leading to analogues of metal carbonyls but with weaker-field carbon-based ligands. Density functional theory has been used to investigate the structures and energetics of the iron carbonyl complexes (vegiMe)Fe(CO)n (n = 3, 2) and (vegiMe)Fe2(CO)n (n = 7, 6, 5) of the simplest such ligands with methyl substituents. Replacement of two carbonyl groups in Fe(CO)5 with one vegiMe ligand is predicted to give trigonal bipyramidal and tetragonal pyramidal isomers of the tricarbonyl (vegiMe)Fe(CO)3 having similar energies within ~2 kcal/mol suggesting a fluxional system. Removal of a carbonyl group from (vegiMe)Fe(CO)3 is predicted to give singlet and triplet (vegiMe)Fe(CO)2 dicarbonyl structures with similar energies having a hole in the coordination sphere for the “missing” carbonyl group. A quintet (vegiMe)Fe(CO)2 structure with tetrahedral FeC4 coordination is a higher energy isomer by ~10 kcal/mol. The three lowest energy (vegiMe)Fe2(CO)7 structures, obtained by replacing two carbonyl groups in Fe2(CO)9 with one vegiMe ligand, have the vegiMe ligand bridging a Fe–Fe single bond to form a six-membered Fe2CN2C ring. Isomeric (vegiMe)Fe2(CO)7 structures with the vegiMe ligand chelated to a single iron atom forming a five-membered FeC2N2 ring lie at least 10 kcal/mol above the lowest energy isomer. The lowest energy isomers of the unsaturated (vegiMe)Fe2(CO)n (n = 6, 5) are triplet and quintet spin state structures reflecting the lower field strength of the vegiR ligands relative to carbonyl groups.

Bridging cyclobutadiene ligands with agostic hydrogen atoms in binuclear chromium carbonyl derivatives

The binuclear cyclobutadiene chromium carbonyls (C4H4)2Cr2(CO)n (n = 7, 6, 5, 4, 3), potentially accessible from the experimentally known (η4-C4H4)Cr(CO)4, have been examined by density functional theory. The low-energy structures for the heptacarbonyl (C4H4)2Cr2(CO)7 have terminal (η4-C4H4)2Cr2(CO)7 rings with a central Cr–Cr single bond bridged by one or three CO groups and the remaining CO groups as terminal ligands evenly distributed among the chromium atoms. The lowest energy structure for the hexacarbonyl (C4H4)2Cr2(CO)6 has a (η4-C4H4)2Cr(CO)2 complex functioning as a bidentate chelating ligand to a Cr(CO)4 fragment through the formation of two three-center C–H–Cr bonds with agostic hydrogen atoms exhibiting short Cr–H distances of ∼1.85 Å. The pentacarbonyl (η4-C4H4)2Cr2(CO)5 resembles the analogous experimentally known (η5-C5H5)2V2(CO)5 by having terminal η4-C4H4 rings, two bridging CO groups, and a central CrCr triple bond. The three lowest energy structures for the tetracarbonyl (η4-C4H4)2Cr2(CO)4 are singlet structures with two four-electron donor bridging η2-μ-CO groups, a terminal CO group on each chromium atom, and a central CrCr double bond. The lowest energy structure for the more highly unsaturated tricarbonyl (η4-C4H4)2Cr2(CO)3 by a margin of more than 12 kcal/mol is a triplet spin state structure with a terminal η4-C4H4 ring, a bridging η4,η1-C4H4 ring through an agostic C–H–Cr interaction, and a central CrCr triple bond. Thermochemistry suggests that the lowest energy structures for all of the (C4H4)2Cr2(CO)n (n = 7, 6, 5, 4) systems, especially the pentacarbonyl, are viable towards carbonyl dissociation.

Toward the Prediction of Multi-Spin State Charges of a Heme Model by Random Forest Regression.

The random forest regression (RFR) model was introduced to predict the multiple spin state charges of a heme model, which is important for the molecular dynamic simulation of the spin crossover phenomenon. In this work, a multiple spin state structure data set with 39,368 structures of the simplified heme–oxygen binding model was built from the non-adiabatic dynamic simulation trajectories. The ESP charges of each atom were calculated and used as the real-valued response. The conformational adapted charge model (CAC) of three spin states was constructed by an RFR model using symmetry functions. The results show that our RFR model can effectively predict the on the fly atomic charges with the varying conformations as well as the atomic charge of different spin states in the same conformation, thus achieving the balance of accuracy and efficiency. The average mean absolute error of the predicted charges of each spin state is <0.02 e. The comparison studies on descriptors showed a maximum 0.06 e improvement in prediction of the charge of Fe2+ by using 11 manually selected structural parameters. We hope that this model can not only provide variable parameters for developing the force field of the multi-spin state but also facilitate automation, thus enabling large-scale simulations of atomistic systems.

Investigating the spin state and electronic structure of the Fe3O cluster from MOF MIL-100(Fe)

In this paper, we investigate the spin state of the Fe3O cluster from MIL-100(Fe), each Fe site of which possesses either one unpaired electron, three unpaired electrons, or five unpaired electrons. Total energies with respect to different spin states were optimized with the PBE, B3LYP, HF, and MP2 methods in combination with various basis sets (6-31G, 6-31G*, 6-311G(d,p)) for non-metal ions and pseudopotentials for Fe (SDD and LanL2DZ). The results of B3LYP, MP2, and HF methods predicted that each Fe site had five unpaired electrons in the most stable spin state. However, the results of PBE show two opposite cases. In one case, PBE predicted each Fe had one unpaired electron, while in the remaining PBE cases, each Fe site was predicted to exhibit five unpaired electrons. We finally conclude the Fe3O cluster with 15 unpaired electrons is the most stable structure.

Binuclear pentalene titanium carbonyls involved in the deoxygenation of carbon dioxide

The complete series of binuclear pentalene titanium carbonyls Pn2Ti2(CO)n and Pn†2Ti2(CO)n (Pn = pentalene; Pn† = 1,4-(iPr3Si)2C8H4; n = 0, 1, 2, 3, 4), including Pn†2Ti2(CO)2 obtained experimentally from Pn†2Ti2 and carbon dioxide, have been investigated by density functional theory. For the carbonyl-free Pn2Ti2 system the singlet structure is found to lie 22.5 and 18.5 kcal/mol in energy below the isomeric triplet and quintet structures, respectively. However, for the experimentally known Pn†2Ti2 system (Pn† = 1,3-(iPr3Si)2C8H4) the singlet, triplet, and quintet spin state structures have essentially equal energies within 0.3 kcal/mol suggesting the possibility of complicated magnetic behavior. The Ti–Ti distance of 2.399 Å found in crystalline Pn†2Ti2 by X-ray crystallography is closest to the 2.415 Å Ti-Ti distance predicted for the triplet spin state structure. Carbonylation of Pn2Ti2 results in successive lengthening of the Ti-Ti distance as CO groups are added. Three CO groups are the maximum number that can be introduced into a viable Pn2Ti2(CO)n derivative as indicated by the predicted exothermic CO dissociation energy of the tetracarbonyl Pn2Ti2(CO)4. The lowest energy structure for the monocarbonyl Pn2†Ti2(CO) has a four-electron donor bridging η2-μ-CO group in accord with the experimental structure. The lowest energy structure for the dicarbonyl Pn†2Ti2(CO)2 has exclusively terminal CO groups in a cis configuration, again in accord with the experimental Pn†2Ti2(CO)2 structure. Two terminal CO groups are accompanied by a third highly unsymmetrical semibridging CO group in the lowest energy structures for the tricarbonyls Pn2Ti2(CO)3 and Pn†2Ti2(CO)3. However, the lowest energy structures for the tetracarbonyls Pn2Ti2(CO)4 and Pn†2Ti2(CO)4 have exclusively terminal CO groups.

Cyano bridged heterometallic Mn(II)-Fe(III) aggregates: Synthesis, structure and magnetic properties

Syntheses, structures and magnetic properties of two new cyano bridged heterometallic complexes, [{Mn(L)(H2O)}2{Mn(L)}{Fe(CN)6}2]·9H2O (1) and [Mn(L)(H2O)2]2[{Mn(L)(H2O)}2{Fe(CN)6}][{Mn(L)}2{Fe(CN)6}3]·13H2O (2) [L=2,6-diacetylpyridine bis(phenylhydrazone)] are reported. Although the pentanuclear cyano bridged structural morphology observed in 1 is prevalent, complex 2 represents a hitherto unknown cyano bridged decanuclear species where pentanuclear {Mn2Fe3}, trinuclear {Mn2Fe} and mononuclear complex ions are present. Investigation of magnetic properties reveal that both the complexes 1 &2 have irregular spin state structures and antiferromagnetic interactions are operative between the adjacent spin carriers.

Multilevel model for magnetic deflagration in nanomagnet crystals

We extend the existing theoretical model for determining the characteristic features of magnetic deflagration in nanomagnet crystals. For the first time, all energy levels are accounted for calculation of the the Zeeman energy, the deflagration velocity, and other parameters. It reduces the final temperature and significantly changes the propagation velocity of the spin-flipping front. We also consider the effect of a strong transverse magnetic field, and show that the latter significantly modifies the spin-state structure, leading to an uncertainty concerning the activation energy of the spin flipping. Our front velocity prediction for a crystal of Mn$_{12}$-acetate in a longitudinal magnetic field is in much better agreement with experimental data than the previous reduced-model results.