Ground State Spin Values Research Articles

A [Mn8] Defective Supertetrahedron T3 and Its Dimeric [Mn16] Analogue.

The initial use of 2-(pyridin-2-yl)propane-1,3-diol (pypdH2) in Mn cluster chemistry has afforded two new mixed-valence polynuclear Mn clusters, namely, [Mn8Ο5(pypd)(hmp)3(O2CCMe3)8] (1) and [Mn16Ο10(N3)2(pypd)2{(py)2CO2}4(O2CEt)12] (2) (hmp- = deprotonated 2-hydroxymethylpyridine; (py)2CO2 2- = deprotonated gem-diol form of di-2-pyridyl ketone). Compound 1 features a novel [MnIII 7MnII(μ4-O)2(μ3-O)3(μ-OR)5]8+ structural core resembling a supertetrahedron T3, lacking two apexes, while complex 2 has a [MnIII 14MnII 2(μ4-O)4(μ3-O)6(μ-N3)2(μ3-OR)2(μ-OR)8]14+ core consisting of two [Mn8] subunits related to 1 and thus is a dimeric analogue of 1. Direct current (dc) magnetic susceptibility studies revealed the presence of dominant antiferromagentic exchange interactions between the Mn ions in complexes 1 and 2 and small ground state spin values for both compounds. Overall, this work highlights the capability of polyol-like chelates like pypdH2 to stabilize high nuclearity 3d metal clusters based on polynuclear building blocks.

Alpha-decay half-lives and alpha-capture cross-sections

The same alpha-nucleus interaction describes the alpha-decay and alpha-capture reactions in the Unified Model for Alpha-Decay and Alpha-Capture (UMADAC). The data for the ground-state-to-ground-state alpha-transition half-lives in 420 nuclei, the half-lives for alpha-transition from the ground state to the first excited 2+ state in 74 even–even nuclei, and the alpha-capture cross sections of 20 spherical and deformed nuclei are used for defining the parameters of the UMADAC. The pointed data are well described in the framework of the UMADAC utilizing the obtained parameters. The ground-state-to-ground-state alpha-transition half-lives in 3802 nuclei with the proton Z and nucleon A numbers in the ranges 50 ≤Z≤ 126 and 97 ≤A≤ 340 are calculated in the UMADAC and presented in the Table 1. The quadrupole and hexadecapole deformations of the daughter nucleus are considered in the UMADAC. The minimal values of the orbital momenta of the alpha-transition between the ground states are found using available experimental and theoretical data for the ground state spin and parity values of nuclei. The half-lives for 223 alpha-transitions from the ground-state of the parent even–even nuclei to the lowest 2+ state of the daughter nuclei with the proton Z and nucleon A numbers in the ranges 52 ≤Z≤ 102 and 108 ≤A≤ 254 are obtained in the UMADAC and given in the Table 2.

Spin state and magnetic coupling in polynuclear Ni(II) complexes from density functional theory: is there an optimal amount of Fock exchange?

Reliable prediction of the ground-state spin and magnetic coupling constants in transition-metal complexes is a well-known challenge for density functional theory (DFT). One popular strategy for addressing this long-standing issue involves the modification of the fraction of Fock exchange in a hybrid functional. Here we explore the viability of this approach using three polynuclear metal-organic complexes based on a Ni4O4 cubane motif, having different ground state spin values (S = 0, 2, 4) owing to the use of different ligands. We systematically search for an optimum fraction of Fock exchange, across various global, range-separated, and double hybrid functionals. We find that for all functionals tested, at best there only exists a very narrow range of Fock exchange fractions which results in a correct prediction of the ground-state spin for all three complexes. The useful range is functional dependent, but general trends can be identified. Typically, at least two similar systems must be used in order to determine both an upper and lower limit of the optimal range. This is likely owing to conflicting demands of minimizing delocalization errors, which typically requires a higher percentage of Fock exchange, and addressing static correlation, which typically requires a lower one. Furthermore, we find that within the optimal range of Fock exchange, the signand relative magnitude of Ni-Ni magnetic coupling constants are reasonably well reproduced, but there is still room for quantitative improvement in the prediction. Thus, the prediction of spin state and magnetic coupling in polynuclear complexes remains an ongoing challenge for DFT.

Prediction of ground-state spin in odd-<i>A</i> nuclei within decision tree

Ground-state spin, as a fundamental parameter of nucleus, has consistently been a hot topic in research on nuclear data and structure. In this paper, we extensively investigate the odd-mass nuclei (odd-<i>A</i> nuclei) on the nuclide chart by using decision trees, including odd-proton nuclei (odd-<i>Z</i> nuclei) and odd-neutron nuclei (odd-<i>N</i> nuclei), and train ground-state spin prediction models of odd-<i>Z</i> nuclei and odd-<i>N</i> nuclei. In the case of randomly dividing the training set and validation set in a ratio of 75% to 25%, the accuracy rate of the training set and validation set for odd-<i>Z</i> nuclei reach 98.9% and 79.3%, respectively. The accuracy rate of the training set and validation set for the odd-<i>N</i> nuclei reach 98.6% and 71.6%, respectively. At the same time, by 1000 random selections of training set and validation set, after being validated repetitively, the standard error of the accuracy rate obtained can be less than 5%, further verifying the reliability and generalization performance of the decision tree. On the other hand, the accuracy rate of decision tree is much higher than those of theoretical models commonly used in nuclear structure research, such as Skyrme-Hartree-Fock-Bogoliubov, covariant density functional theory, and finite range droplet model. Next, by taking all spin-determined odd-<i>Z</i> nuclei and odd-<i>N</i> nuclei as a learning set, the ground-state spin values for 254 spin undetermined but recommended odd-<i>Z</i> nuclei and 268 spin undetermined but recommended odd-<i>N</i> nuclei are predicted, with the predicted set coincidence rates reaching 68.5% and 69.0%, respectively. Finally, four odd-mass number chains, i.e. <i>Z</i> = 59, <i>Z</i> =77, <i>N</i> = 41, and <i>N</i> = 59, are selected to compare the learning (prediction) results of the decision tree with the experimental (recommended) values of the corresponding nuclei, and to discuss the differences and similarities in the results given by the three theoretical models, thereby further demonstrating the research and application value of the decision tree in the ground-state spin of nuclei.

Crystal designing and magneto-chemical characterization of unusual nickel(II) MOFs

Here, we have reported crystal designing and magneto-chemical characterization of two new complexes [Ni(3,5-dnba)2(hmp)2] (1) and [Ni3(Py)8(µ-CH3COO)4](I3)2(2) employed by 3,5-dinitro benzoic acid (dnba), 2-Pyridine methanol (hmpH) and pyridine. Complex 1 consists of an unusual NiII octahedral MOF-like monomeric structure, whereas 2 comprises of planar three Ni asymmetric “distorted hexagonal planar” units linked by alternating syn, syn, anti, a (μ-O2CCH3) and syn, syn, (μ-O2CCH3)2 units. Variable-temperature, solid-state magnetic susceptibility studies in the 3.0–300 K temperature range in a 0.33 T (333 Hz) direct-current (dc) magnetic field reveal the paramagnetic and ferromagnetic behavior with calculated ground-state spin (S) values are 1 and 3/2 of complex 1 and 2, respectively. Interesting, complex 2 have weak antiferromagnetic intra-Ni3 exchange couplings. Alternating current magnetic susceptibility studies, both the complex did not belong to the SMM category.

Multiresponsive Spin Crossover Driven by Rotation of Tetraphenylborate Anion in an Iron(III) Complex

Dynamic molecular materials, which involve mechanical motions in crystals, usually exhibit tunable properties related to conformational polymorphs. Herein, we describe a solvent-free molecular crys...

Sandglass-Shaped LnIII9 Cluster Containing Two Quadrangular Pyramids (Ln5O5) Shared by Vertices: Structure, Magnetic and Photoresponsive Metal Ion Sensing

Based on the large ground state spin value and orbital quenching angular momentum of Dy(III) ions, significant magnetic anisotropy is generated. Most of the related studies of single-molecule magnets are carried out around Dy(III) ions, from single core to 24 core. There are reports, but the number of single-molecule magnets with high core (eight cores and above) is still very limited. We have obtained three hourglass-shaped Ln-exclusive nine-nuclear complexes [Ln9(C8H9N2O)4(μ4-OH)2(μ3-OH)8(NO3)8(CH3OH)2(H2O)2]·(NO3)·xMeOH·yH2O (Ln = Dy (1, x = 4, y = 7), Ho (2, x = 1, y = 8), Gd (3, x = 3, y = 0)) with 2-pyridine acetalamine Schiff base as a ligand, and studied the relationship between their structure and magnetic properties. The AC magnetic susceptibility of complex 1 exhibits obviously single-molecule magnetic behavior. Further, the photoresponse test of cluster 2 in a variety of different metal ion solutions showed that it can efficiently recognize Y(III) ions. This is one of the rare examples of selective photoresponsive Y(III) ions of lanthanide complexes. The AC magnetic susceptibility of complex 1 exhibits obviously single-molecule magnetic behavior. Further, the photoresponse test of cluster 2 in a variety of different metal ion solutions showed that it can efficiently recognize Y(III) ions. This is one of the rare examples of selective photoresponsive Y(III) ions of lanthanide complexes.

Molecular spin frustration in mixed-chelate Fe5 and Fe6 oxo clusters with high ground state spin values

The synthesis, structures, and magnetic properties are reported of three new polynuclear FeIII complexes containing the anions of picolinic acid (picH) and triethanolamine (teaH3) as chelates. The complexes [Fe6O2(OH)2(O2CR)4(pic)4(teaH)2] (R = Me (1), Ph (2)) and [Fe5O2(O2CBut)4(pic)3(teaH)2] (3) were obtained from the reaction of [Fe3O(O2CR)6(H2O)3](NO3) (R = Me, Ph, But) with picH and teaH3 in a 1:2:1 ratio in MeCN. The core of 1 and 2 consists of an [Fe4(µ3-O)2]8+ ‘planar-butterfly’ unit to which is attached an Fe atom on either side by bridging O atoms. The core of 3 consists of an [Fe5(µ3-O)2]11+ unit comprising two near-perpendicular vertex-sharing [Fe3(µ3-O)]7+ triangular units. Variable-temperature (T) and -field (H) solid-state dc and ac magnetization (M) studies in the 5.0–300 K temperature range revealed that 1 and 2 have an S = 5 ground state spin whereas 3 has an S = 5/2 ground state. Jij exchange couplings were calculated by DFT and a magnetostructural correlation (MSC) for polynuclear FeIII/O complexes. This allowed rationalization of the observed ground states from the analysis of the spin frustration effects operative, and provided good input values for fits of the experimental χMT vs T data to obtain the Jij values.

Hexanuclear manganese(III) single-molecule magnets based on oxime and azole-type ligands

Two novel hexanuclear manganese(III) complexes belonging to the Mn6 family of single-molecule magnets (SMMs), of formulae [Mn6(μ3-O)2(H2N-sao)6(bta)2(EtOH)6]·2EtOH·4H2O (1) and [Mn6(μ3-O)2(H2N-sao)6(pta)2(EtOH)6]·4EtOH (2) [H2N-saoH2 = salicylamidoxime, bta = 1,2,3-benzotriazolate anion, pta = 5-phenyl-tetrazolate anion], have been synthesized and characterized structurally and magnetically. Both compounds crystallize in the triclinic system with space group P1¯ (1 and 2). In their crystal packing, adjacent Mn6 complexes are connected through non-coordinating solvent molecules, which are H-bonded to N atoms of azole rings and –NH2 groups of salicylamidoxime ligand. The study of the magnetic properties of 1 and 2 through magnetic susceptibility measurements reveals as predominant interaction an antiferromagnetic coupling between the MnIII metal ions in both compounds. A ground state spin value of S = 4 for 1 and 2 was confirmed through variable temperature-variable field dc magnetization data, and the occurrence of slow relaxation of the magnetization in both 1 and 2 indicates single-molecule magnet behavior.

Giant Heterometallic [Mn36Ni4]0/2- and [Mn32Co8] "Loops-of-Loops-and-Supertetrahedra" Molecular Aggregates.

We report the synthesis, crystal structures and magnetic properties of the giant heterometallic [Mn36Ni4]2−/0 (compounds 1, 2)/[Mn32Co8] (compound 3) “loops-of-loops-and-supertetrahedra” molecular aggregates and of a [Mn2Ni6]2+ compound (cation of 4) that is structurally related with the cation co-crystallizing with the anion of 1. In particular, after the initial preparation and characterization of compound [Mn2Ni6(μ4-O)2(μ3-OH)3(μ3-Cl)3(O2CCH3)6(py)8]2+[Mn36Ni4(μ4-O)8(μ3-O)4(μ3-Cl)8Cl4(O2CCH3)26(pd)24(py)4]2− (1) we targeted the isolation of (i) both the cationic and the anionic aggregates of 1 in a discrete form and (ii) the Mn/Co analog of [Mn36Ni4]2− aggregate. Our synthetic efforts toward these directions afforded the discrete [Mn36Ni4] “loops-of-loops-and-supertetrahedra” aggregate [Mn36Ni4(μ4-O)8(μ3-O)4(μ3-Cl)8Cl2(O2CCH3)26(pd)24(py)4(H2O)2] (2), the heterometallic Mn/Co analog [Mn32Co8(μ4-O)8(μ3-O)4(μ3-Cl)8Cl2(μ2-OCH2CH3)2(O2CCH3)28(pd)22(py)6] (3) and the discrete [Mn2Ni6]2+ cation [Mn2Ni6(μ4-O)2(μ3-OH)4(μ3-Cl)2(O2CCH3)6(py)8](ClO4)(OH) (4). The structure of 1 consists of a mixed valence []2− molecular aggregate that contains two loops separated by two supertetrahedral units and a []2+ cation based on two [MnIII(μ4-O)(μ3-OH)1.5(μ3-Cl)1.5]4+ cubane sub-units connected through both mono- and tri-atomic bridges provided by the μ4-O2− and carboxylate anions. The structures of 2–4 are related to those of the compounds co-crystallized in 1 exhibiting however some differences that shall be discussed in detail in the manuscript. Magnetism studies revealed the presence of dominant ferromagnetic interactions in 1–3 that lead to large ground state spin (ST) values for the “loops-of-loops-and-supertetrahedra” aggregates and antiferromagnetic exchange interactions in 4 that lead to a low (and possibly zero) ST value. In particular, dc and ac magnetic susceptibility studies revealed that the discrete [Mn36Ni4] aggregate exhibits a large ST value ~ 26 but is not a new SMM. The ac magnetic susceptibility studies of the [Mn32Co8] analog revealed an extremely weak beginning of an out-of-phase tail indicating the presence of a very small relaxation barrier assignable to the anisotropic Co2+ions and a resulting out-of-phase ac signal whose peak is at very low T.

Theoretical Studies on Hexanuclear [M3(μ3-O/OH)]2 (M = Fe(III), Mn(III), and Ni(II)) Clusters: Magnetic Exchange, Magnetic Anisotropy, and Magneto-Structural Correlations.

Controlling spin Hamiltonian parameters such as magnetic exchange and magnetic anisotropy of polynuclear clusters is of great interest in the area of single molecule magnets (SMMs). Among large polynuclear clusters, hexanuclear clusters offer the best compromise in terms of size as they are often rigid, solution stable, and chemically amenable. The {M6O2} core is one of the common architectures known for many hexanuclear clusters and generally reported to possess a diamagnetic ST = 0 spin ground state, barring a few exceptions. In these clusters, there are several open questions that are poorly understood: (a) What controls the nature of magnetic exchange, which in turn dictates the ground state spin values? (b) For clusters possessing a nonzero spin ground state, what dictates the magnetic anisotropy? Here, using density functional methods, we have attempted to shed light on these two question by evaluating the exchange coupling constants in [Fe6IIIO2(OH)2{(C4N2H2SMe)2C(OH)O}2( tBuCO2)10] (1), [Fe6III(O)2(O2CH2)(O2CCH2 tBu)12(py)2] (2), [Fe6III(O2)(O)2(O2CCMe3)12(py)2] (3), [FeIII6O3(O2CMe)9(OEt)2(bpy)2]ClO4 (4), [MnIII6O2(O2CH2)(O2CPe t)11(HO2CPe t)2(O2CMe)] (5), and [NiII6(OH)4(O2C tBu)8( tBuCO2H)4] (6) complexes. We have estimated all the eight near-neighbor exchange coupling constants in these clusters. Our calculations not only agree with the experimental results but also offer insight on the origin of the spin ground state. Extensive magneto-structural correlations developed by varying M-O-M angles and M-O distances reveal that J values are extremely sensitive to small structural distortions. Correlations developed indicate that both the parameters are important for Fe(III), but for Mn(III) and Ni(II), the angles were found to play a dominant role. Quite interestingly, the computed zero-field splitting parameter D S=5 of complex 1 reveals that the exchange contribution to the anisotropy controls the sign of the ground state D value-an observation which differs from the general perception that the ground state D is controlled by the single-ion zero-field splitting parameter.

Reversible On-Off Switching of a Single-Molecule Magnet via a Crystal-to-Crystal Chemical Transformation.

Dynamic molecular crystals are of high interest due to their potential applications. Herein we report the reversible on-off switching of single-molecule magnet (SMM) behavior in a [Mo(CN)7]4- based molecular compound. Upon dehydration and rehydration, the trinuclear Mn2Mo molecule [Mn(L)(H2O)]2[Mo(CN)7]·2H2O (1) undergoes reversible crystal-to-crystal transformation to a hexanuclear Mn4Mo2 compound [Mn(L)(H2O)]2[Mn(L)]2[Mo(CN)7]2 (2). This structural transformation involves the breaking and reforming of coordination bonds which leads to significant changes in the color and magnetic properties. Compound 1 is an SMM with an energy barrier of 44.9 cm-1, whereas 2 behaves as a simple paramagnet despite its higher ground state spin value. The distortion of the pentagonal bipyramidal geometry of [Mo(CN)7]4- in 2 disrupts the anisotropic exchange interactions that lead to SMM behavior in 1.

Heterometallic MnIII4Ln2 (Ln = Dy, Gd, Tb) Cross-Shaped Clusters and Their Homometallic MnIII4MnII2 Analogues.

The employment of di-2-pyridyl ketone, (py)2CO, in heterometallic Mn/4f and homometallic Mn cluster chemistry has yielded six MnIII4Ln2 and two MnIII4MnII2 structurally related clusters, namely, [Mn4Ln2O2{(py)2CO2}4(NO3)2(RCO2)2(H2O)6](NO3)2 (Ln = Gd, 1, 5; Dy, 2; Tb, 3; R = Et, 1-3; Me, 5), [Mn4Dy2O2{(py)2CO2}4(NO3)4(EtCO2)2(H2O)3(MeOH)]·0.7MeOH·0.8H2O (4·0.7MeOH·0.8H2O), [Mn4Gd2O2{(py)2CO2}4(NO3)4(C6H4ClCO2)2(MeOH)2(py)2]·2MeOH (6·2MeOH), [Mn6O2{(py)2CO2}4(py)4(H2O)4](ClO4)4·4H2O (7·4H2O), and [Mn6O2{(py)2CO2}4(NO3)4(py)4] (8), where (py)2CO22- is the dianion of the gem-diol derivative of (py)2CO. The compounds possess a new type of cross-shaped structural core, which in the case of 1-6 is essentially planar, whereas in 7 and 8 it deviates from planarity. Clusters 1-6 are rare examples of Mn/4f species bearing (py)2CO or its derivatives, despite the fact that this ligand has been well-studied and proven a rich source of more than 200 metal compounds so far. Variable-temperature, solid-state direct-current and alternating-current magnetization studies were performed on complexes 1-5, 7, and 8 revealing that the dominant exchange interactions between the metal ions are antiferromagnetic and indicating ground-state spin values of S = 5 (for 1), 6 (for 5), and 2 (for 7 and 8).

Cyanate groups in higher oxidation state metal cluster chemistry: Mixed-valence (II/III) Mn16 and Mn18 clusters

The employment of cyanato (OCN−) group in high oxidation state manganese cluster chemistry, in conjunction with carboxylate ions and the organic chelating/bridging ligand 2-(hydroxymethyl)pyridine (hmpH), is reported. The syntheses, crystal structures, and magnetochemical characterization are described for [Mn16O8(OR)4(OCN)4(O2CMe)12(hmp)6(ROH)2] (R=Me (1), Et (2)) and [Mn18O14(O2CR)18(hmp)4(hmpH)2(H2O)2] (R=Me (3), Et (4)). The 2:1:1:1 reactions of Mn(O2CMe)2·4H2O, hmpH, NaOCN and NEt3 in solvent MeOH or EtOH afford the isostructural complexes [Mn16O8(OR)4(OCN)4(O2CMe)12(hmp)6(ROH)2] (R=Me (1), Et (2)). The [Mn16(μ4-O)4(μ3-O)4(μ-OMe)4(μ3-OR)6(μ-OR)6]10+ core of representative complex 1 comprises a MnII4MnIII4 double-cubane subunit attached on either side to two symmetry-related MnIIMnIII3 defective dicubanes. A similar reaction of Mn(O2CR)2·4H2O, hmpH, NaOCN and NEt3, but in solvent MeCN, led instead to the formation of [Mn18O14(O2CR)18(hmp)4(hmpH)2(H2O)2] (R=Me (3), Et (4)). Compounds 3 and 4 are very similar to each other and can be described as a central [MnIII4(μ-O)6] rodlike subunit attached on either side to two symmetry-related [Mn7O9] subunits. Variable-temperature, solid-state dc and ac magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions in all compounds, and possible S=2 or 1 (for 1 and 2) and S=0 (for 3 and 4) ground state spin values. The combined results demonstrate the ability of cyanato groups to facilitate the formation of new polynuclear MnII/III complexes with structures different than these obtained from the use of the related azides.

New structural types of Mn16 single-molecule magnets: W-shaped topology from reductive aggregation.

Two new Mn16 clusters are reported: [Mn16O10(OH)3(OMe)8(O2CPhBut)17(MeOH)5] (2) and [Mn16O16(OMe)6(O2CPh)12(NO3)4(MeOH)2(H2O)4] (3). The complexes were obtained by reductive aggregation of MnO4– in CH2Cl2/MeOH, and oxidation of MnII and preformed (NnBu4)[Mn4IIIO2(O2CPh)9(H2O)] with CeIV, respectively. The core of 2 has a Mn16III core with an unusual 1:2:3:4:3:2:1 layer structure and a W-shaped pleated topology, whereas 3 contains a central 2 × 3 Mn6IV planar grid held within a nonplanar Mn10III loop and is a rare example of a complex with nitrate ions bridging like carboxylate ions. Variable-temperature, solid-state dc susceptibility, and ac susceptibility studies reveal that 2 and 3 possess S = 12 and S = 8 ground states, respectively. Fits of dc magnetization data collected over a temperature range of 1.8–4.0 K and a magnetization range of 0.1–4 T were fit to give S = 12, D = −0.16(2) cm–1, g = 1.98(3) for 2 and S = 8, D = −0.22(1) cm–1, g = 1.99(2) for 3, where D is the axial zero-field splitting parameter. The ac in-phase (χM′T) susceptibility below 15 K confirmed the ground-state spin values of 2 and 3, as determined from dc data, and the appearance of frequency-dependent out-of-phase (χM″) signals revealed that both complexes are new single-molecule magnets (SMMs). Fits of the ac data gave Ueff = 49.7(1) K and τ0 = 4.32 × 10–9 s for 2 and Ueff ≈ 14.0 ± 2 cm–1 and τ0 ≈ 3.2 ± 0.5 × 10–8 s for 3, where Ueff is the effective barrier to magnetization relaxation and τ0 is the pre-exponential factor. Thus, complexes 2 and 3 are two new members of a growing family of Mn16 clusters, and two new examples of high-nuclearity SMMs, with the Ueff for 2 approaching the value for the prototypical SMM family, [Mn12O12(O2CR)16(H2O)4].

Black holes as gases of punctures with a chemical potential: Bose-Einstein condensation and logarithmic corrections to the entropy

We study the thermodynamical properties of black holes when described as gases of indistinguishable punctures with a chemical potential. In this picture, which arises from loop quantum gravity, the black hole microstates are defined by finite families of half-integers spins coloring the punctures, and the near-horizon energy measured by quasilocal stationary observers defines the various thermodynamical ensembles. The punctures carry excitations of quantum geometry in the form of quanta of area, and the total horizon area ${a}_{\mathrm{H}}$ is given by the sum of these microscopic contributions. We assume here that the system satisfies the Bose-Einstein statistics, and that each microstate is degenerate with a holographic degeneracy given by $\mathrm{exp}(\ensuremath{\lambda}{a}_{\mathrm{H}}/{\ensuremath{\ell}}_{\mathrm{Pl}}^{2})$ and $\ensuremath{\lambda}>0$. We analyze in detail the thermodynamical properties resulting from these inputs, and in particular compute the grand canonical entropy. We explain why the requirements that the temperature be fixed to the Unruh temperature and that the chemical potential vanishes do not specify completely the semiclassical regime of large horizon area, and classify in turn what the various regimes can be. When the degeneracy saturates the holographic bound ($\ensuremath{\lambda}=1/4$), there exists a semiclassical regime in which the subleading corrections to the entropy are logarithmic. Furthermore, this regime corresponds to a Bose-Einstein condensation, in the sense that it is dominated by punctures carrying the minimal (or ground state) spin value $1/2$.

Chimiothérapie (CT) de maintenance par bevacizumab/pemetrexed chez des patients (pts) avec un cancer bronchique non à petites cellules non épidermoïdes (CBNPCne) avancé : survie globale actualisée de l’essai randomisé de phase III AVAPERL

For a selective excitation of spin-flip strength, (6Li,6He) reactions can be a useful tool, because: a) 6Li and 6He have ground-state spin and parity values Jπ = 1+ and 0+, respectively; b) 6He has no particle-stable excited state, thus effects from ejectile excitation can be avoided. The (6Li,6He) experiments were performed at 100 MeV/nucleon, at which incident energy the reaction is expected to be single-step dominant. Through the analysis of the good-resolution (6Li,6He) data on 13C, 26Mg, 27Al and 58Ni targets, the evidence for a proportional relationship between 0° cross sections and the corresponding Gamow-Teller transition strengths is examined. Suppression of non-spin flip excitations is discussed based on the hindrance of the excitation of the isobaric analog state.

Molecular Nanoscale Magnetic Refrigerants: A Ferrimagnetic {CuII15GdIII7} Cagelike Cluster from the Use of Pyridine-2,6-dimethanol

The employment of pyridine-2,6-dimethanol in 3d/4f metal cluster chemistry has afforded a new {Cu(II)15Gd(III)7} cagelike molecule with a beautiful structure built by fused triangular subunits; the compound exhibits an overall ferrimagnetic behavior with an appreciable ground-state spin value and shows promise as a low-temperature magnetic refrigerant.

Mn8Cluster with Ferrocene-1,1′-Dicarboxylate Ligation: Single-Molecule Magnetism with Multiple External Redox Centers

The syntheses, structures, and magnetic properties are reported of a new Mn8 cluster obtained from the reaction of ferrocene-1,1'-dicarboxylic acid (fdcH2) with [Mn12O12(O2CMe)16(H2O)4] and mononuclear Mn salts under different conditions and limited light exposure. The product was obtained in two forms: [Mn8O4(fdc)6(DMF)2(H2O)2] (1) and [Mn8O4(fdc)6(DMF)4] (2), differing in the bound solvent ligands. The structures are otherwise almost identical, comprising very similar cores that both contain 4Mn(III) and 4Mn(II) atoms bridged by four O(2-) ions and six fdc(2-) groups. The [Mn(III)4Mn(II)4(μ4-O)4] cores have virtual Td symmetry and can be described as a central [Mn(III)4(μ4-O)4](4+) cubane unit whose four O(2-) ions are μ4, because they each attach to an external Mn(II) atom. Peripheral ligation about the core is provided by six bridging fdc(2-) groups and the terminal solvent ligands, one each on the Mn(II) atoms. The differences in solvent ligands between 1 and 2, and different packing from the different crystal space groups, lead to significant differences in metric parameters within the core, which are reflected in significantly different magnetic properties. Variable-temperature, solid-state dc and ac susceptibility measurements reveal the clusters to be predominantly antiferromagnetically coupled, and to possess ground state spin values of S = 5 and S = 2 for 1 and 2, respectively. The difference in ground states is assigned to the small but distinct structural differences seen in the central cubane. Alternating current (AC) susceptibility data indicate 1 and 2 to be new single-molecule magnet, and this was confirmed by magnetization versus direct current (DC) field scans on a single crystal of 1·4DMF·4H2O, which exhibited hysteresis.

Mn<sup>III</sup> <sub>2</sub>Ln<sup>III</sup> <sub>2</sub> (Ln = Gd, Dy, Ho) Complexes From The Initial Employment of 1,3-Propanediol In Mixed 3d/4f Metal Cluster Chemistry

The initial employment of 1,3-propanediol (pdH2) in the synthesis of 3d/4f metal clusters has afforded a new family of tetranuclear [Mn2Ln2O2{(CH3)3CCO2}8{(CH3)3CCO2H}2(pdH2)2] (Ln = Dy, 1; Gd, 2; Ho, 3) complexes. Compounds 1-3 represent new additions to the small family of MnIII 2Ln2 clusters possessing planar or diamond-like cores. Variable-temperature, dc and ac magnetization measurements were performed on compounds 1-3 and revealed the existence of very weak antiferromagnetic exchange interactions between the metal centers leading to a ground state spin value S = 5 in case of 2·2(CH3)3CCO2H·2H2O. Keywords: 1, 3-propanediol, 3d/4f clusters, crystal structures, magnetic properties.