Molar Magnetic Susceptibility Research Articles

Magnetic properties of a linear trinuclear manganese compound [Mn3(PhCO2)6(Bipy)2] · H2O

The reaction of the trinuclear oxo-centered mixed-valence complex [Mn3O(O2CPh)6(Py)2(H2O)] with 2,2′-bipyridyl (Bipy) and another potential tripodal ligand affords the title compound [Mn3(PhCO2)6(Bipy)2] · H2O in good yield. The X-ray crystallographic diffraction study reveals that three mangenese ions are arranged in a linear mode with Mncenter-Mnterminal and Mnterminal-Mnterminal diatances of 3.588 and 7.176 A, respectively. Molar magnetic susceptibility of the compound gradually decreases from 12.23 (300 K) to 4.45 cm3 K mol−1 (2 K). Taking into account the structure of this compound, the data in the 2.0–300 K range were fit to the appropriate theoretical expression to give J = −2.73 cm−1, ρ = 2.07%, Na = −0.0004 cm3 mol−1, g = 1.992, and R2 = 0.99996. The magnetization versus external magnetic field measurements at 2 K shows that the ground state is ST = 5/2.

Transport (Electrical Resistivity/Magnetoresistance) and Specific Heat Measurements of Cu2 LnNbO8Sr2 with Ln = Er, Dy

The magnetic, transport and specific heat measurements of 1212-type compounds crystallized in tetragonal symmetry with starting composition, Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy have been investigated. The Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy compounds showed non-superconducting properties down to 1.8 K in the magnetic susceptibility measurements. The magnetic parameter (μeff) obtained from the linear region of inverse molar magnetic susceptibility curves agrees with the calculated values for the respective free trivalent Er and Dy ions in Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy compounds. Though there is no strong evidence of magnetic ordering seen from magnetic susceptibilities, the hysteresis, M(H) curve obtained at 1.8 K looks like a canted antiferromagnet. The S-shaped (slightly curved) magnetization curve suggests weak ferromagnetic interactions that exist in the Ln = Er compound. A small hysteresis is observed with the coercive field (Hc) of 49 Oe and the remnant magnetization (Mr) of about 0.06 μB/f.u. for Ln = Er. Interestingly, such a hysteresis loop opening is not seen for the Ln = Dy compound. While specific heat anomaly (λ-like transition) was observed for Ln = Dy compound at low temperature (around 6 K), for Ln = Er compound such an anomaly was not seen in the specific heat measurements. The electrical resistivity versus temperature, ρ(T), data showed that the compounds Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy are not in metallic state and they are really semiconducting-in-nature. Interestingly, rather large magnetoresistance, MR (∼18%) was observed at low temperature ∼2 K for Er-based niobio-cuprate.

Impact of High Pressure and High Temperature on Annealed Oxygen-deficient CoSrO3−δ Perovskites: Structural and Magnetization Studies

In this brief article, structural, magnetization studies of oxygen deficient perovskite cobalt oxides CoSrO3−δ synthesized in two different ways are reported. The structural refinements (JANA2006) of X-ray powder diffraction data indicate that the sample prepared under ambient pressure (stage-1) shows a hexagonal structure with P63/mmc (194) as a possible space group. The stage-1 sample subsequently sintered at 1450 °C for 1–2 h under high-pressure 6 GPa conditions (stage-2) crystallizes in tetragonal symmetry with I4/mcm (140) space group having a=5.444(7) A and c=7.68(2) A. While the stage-1 sample exhibits a paramagnetic nature in the magnetic susceptibility, M(T), measurements, interestingly the sample annealed under high-pressure conditions shows ferromagnetism in the magnetic susceptibility, M(T) and field dependence magnetization, M(H) measurements. The high-pressure annealed sample shows hysteresis opening with a quite large coercive field of 7.3 kOe at 1.8 K. The temperature dependence of the inverse molar susceptibility curves exhibits linear behavior in the high-temperature regime and could be fitted to the Curie–Weiss expression, χ(T)=C/(T−θW). The experimental values of θW and peff obtained from the linear region of the inverse molar magnetic susceptibility curves are found to be: −210.7(5) K and 2.38(2) μB/Co for stage-1 and 260.2(7) K and 1.87(3) μB/Co for stage-2 samples, respectively. A negative sign of θW indicates rather strong antiferromagnetic correlations in the stage-1 sample. Apart from these results, the structural parameters reported by various groups for the strontium-based perovskite cobalt oxides are also presented in the form of literature collections.

Effect of chromium ion substitution on the electromagnetic properties of nickel ferrite

Polycrystalline ferrites with general formula NiFe 2− x Cr x O 4 (0 ≤ x ≤ 1) were prepared through oxalate impregnation method. The samples were characterized using DTA–TG, XRD, FT-IR, AC conductivity, VSM and magnetic susceptibility measurements. All compositions show cubic Spinel structure. Lattice constant slightly decreases with increasing chromium content. Average crystallite size lays in the range 147–170 nm. FT-IR studies show two absorption bands ( ν 1 and ν 2) near about 600 cm −1 and 400 cm −1 for tetrahedral and octahedral sites, respectively. No shift was observed in band position at frequency ν 1 by increasing Cr content, meanwhile the frequency ν 2 is shifted to higher frequencies with increasing Cr content. AC conductivity measurements as a function of temperature showed that the samples behave like semiconductors. The decrease in the conductivity with increasing Cr content is due to limiting the degree of Fe 2+–Fe 3+ conduction in the octahedral site by introducing Cr which has preference to substitute octahedral Fe 3+ ions. The saturation magnetization decreases linearly with increasing Cr content, whereas coercivity increases. Nèel's magnetic moments calculated from expected cation distributions in comparison with that from hysteresis loop gives satisfactory results up to x = 0.8. Magnetic susceptibility measurements revealed that all the samples have ferrimagnetic properties which changed to paramagnetic materials by increasing temperature. The Curie temperature and molar magnetic susceptibility were observed to decrease with increasing Cr content.

Effective Transition Probability for the Faraday Effect of Lanthanide(III) Ion Solutions

The Faraday effects of 14 lanthanide(III) ion solutions were systematically analyzed on the basis of the Faraday C term. The effective transition probability, K, which measures the magneto-optical contribution of the 4f(n) --> 4f(n-1)5d transition to the molar Verdet constant, was determined. Linear correlations between K and the square root of the molar magnetic susceptibility of the lanthanide(III) ions, chi(m)(1/2), were obtained. From the observed new regularity, K for promethium(III) was estimated.

Synthesis and Characterization of two Closed Side Oxadiazole ligands with their Related Complexes Cu( II ) and Pd(II)

The two oxadiazole new ligands of bis oxadiazol derivatives, have been synthesized by the reaction of (L1)and , oxadiazol-2yl] methane (L2.) with adibic acid in presence of ethnolic solution of potassium hydroxide. The mixture was refluxed for eight hours. The ligands were characterized using IR 1H.NMR13C-NMR and mass spectroscopies .The ( L3 ) was used to synthesize complexes with metals Cu( II ) and pd(II ) . The complexes were studied and identified using IR, UV-VIS spectra and molar conductivity, magnetic susceptibility and atomic absorption techniques. The results exhibited that all complexes have an octahedral structure

Topological research on the molar magnetic susceptibility of alkali metal compounds with support vector regression

According to the experimental dataset on the molar magnetic susceptibility χm of 45 alkali metal compounds and the topological descriptor?——magnetic connectivity index mF， which is extracted by the magnetic valence gi of simple ion deduced from classical electrodynamics， support vector regression （SVR） combined with particle swarm optimization for its parameter optimization is proposed to establish a model for predicting the molar magnetic susceptibility of alkali metal compound via 0F and 1F. The performance of SVR model is compared with that of multivariate linear regression （MLR） model. The results show that the mean absolute error， the mean absolute percentage error and the root mean square error for 9-fold cross validation test of SVR models are all smaller than those achieved by MLR models. It is revealed that the generalization ability of SVR model is superior to that of MLR model. This study suggests that magnetic connectivity index is an effective descriptor and the SVR is a powerful approach to the prediction of the molar magnetic susceptibility of alkali metal compounds.

SYNTHESIS, CHARACTERIZATION AND SELECTIVITY STUDIES OF POLY(ACRYLAMIDE) INCORPORATING SCHIFF BASES

Three novel polymers incorporating Schiff bases, derived from condensation reactions of poly(acrylamide) with 5-chloro-2-hydroxybenzaldehyde, 5-bromo-2-hydroxybenzaldehyde and 5-methyl-2-hydroxybenzaldehyde, have been synthesized, and their Cu(II) and Ni(II) complexes have been prepared. The 1H-NMR signals of the –CH=N– and –NH2 groups have been utilized to determine the relative abundances of Schiff base and acrylamide groups in the polymers containing Schiff bases. Poly(acrylamide) incorporating Schiff bases and metal complexes thereof have been characterized by molar conductance, magnetic susceptibility and electronic and IR spectral studies. The selectivity of poly(acrylamide) incorporating Schiff bases in forming Ni(II)-aldehyde and Cu(II)-aldehyde complexes has been studied. The Cu(II) and Ni(II) contents in the metal-bearing polymer complexes were determined by the ICP-MS technique.

Structure of 2:1 cobalt(III) complexes derived from arylazocitrazinic acid

1H, 13C NMR and MS spectra of the 2:1 cobalt(III) complexes, the azo coupling products of 2-aminophenol or 2-aminobenzoic acid with the citrazinic acid, were measured and analysed. It was found that the cobalt atom is six-coordinated being bound to two oxygens (one from primary and one from secondary component) and the nitrogen of 2-aminophenol or 2-aminobenzoic acid. Molar magnetic susceptibility data proved the presence of Co(III). Diazotisation of 2-aminophenol or 2-aminobenzoic acid and subsequent coupling reaction with citrazinic acid and complexation of the formed azo product proceeded on standard way.

Band structure of a new (16–18 K) superconductor LiFeAs compared to Li0.5FeAs and LiCoAs

The band structure of a new (16–18 K) superconductor LiFeAs, as a possible first representative of the third (the so-called 111) group of phases, which, along with the groups of four-component 1111 oxyarsenides LnOFeAs and three-component 122 arsenides AFe2As2, belong to the family of new high-temperature (26–56 K) FeAs superconductors, has been studied using the ab initio full-potential augmented-plane-wave method and the generalized-gradient approximation. The structure, energy bands, densities of state, Fermi surface, low-temperature electron specific heat γ, and molar Pauli magnetic susceptibility for LiFeAs are discussed and compared to similar data for the systems simulating the hole (Li0.5FeAs) and electron (LiCoAs) doping of LiFeAs.

Homoleptic Permethylpentalene Complexes: “Double Metallocenes” of the First-Row Transition Metals

The synthesis of the bimetallic permethylpentalene complexes Pn*2M2 (M = V, Cr, Mn, Co, Ni; Pn* = C8Me6) has been accomplished, and all of the complexes have been structurally characterized in the solid state by single-crystal X-ray diffraction. Pn*2V2 (1) and Pn*2Mn2 (3) show very short intermetallic distances that are consistent with metal-metal bonding, while the cobalt centers in Pn*2Co2 (4) exhibit differential bonding to each side of the Pn* ligand that is consistent with an eta(5):eta(3) formulation. The Pn* ligands in Pn*2Ni2 (5) are best described as eta(3):eta(3)-bonded to the metal centers. (1)H NMR studies indicate that all of the Pn*2M2 species exhibit D(2h) molecular symmetry in the solution phase; the temperature variation of the chemical shifts for the resonances of Pn*2Cr2 (2) indicates that the molecule has an S = 0 ground state and a thermally populated S = 1 excited state and can be successfully modeled using a Boltzmann distribution (DeltaH(o) = 14.9 kJ mol(-1) and DeltaS(o) = 26.5 J K(-1) mol(-1)). The solid-state molar magnetic susceptibility of 3 obeys the Curie-Weiss law with mu(eff) = 2.78 muB and theta = -1.0 K; the complex is best described as having an S = 1 electronic ground state over the temperature range 4-300 K. Paradoxically, attempts to isolate the "double ferrocene" equivalent, Pn*2Fe2, led only to the isolation of the permethylpentalene dimer Pn*2 (6). Solution electrochemical studies were performed on all of the organometallic compounds; 2-5 exhibit multiple quasi-reversible redox processes. Density functional theory calculations were performed on this series of complexes in order to rationalize the observed structural and spectroscopic data and provide estimates of the M-M bond orders.

Electric and magnetic susceptibilities of gaseous oxygen: Present data and modern theory compared

We used a cross capacitor to measure the relative dielectric permittivity ${\ensuremath{\epsilon}}_{r}$ of ${\mathrm{O}}_{2}$ at 273, 293, and $323\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and at pressures up to $6.5\phantom{\rule{0.3em}{0ex}}\mathrm{MPa}$. Simultaneously we measured oxygen's complex refractive index $n$ using a quasispherical cavity resonator at frequencies between 2.4 and $7.3\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. The combined results from these measurements determine oxygen's frequency-dependent, relative magnetic permeability ${\ensuremath{\mu}}_{r}(f,p,T)$ with an uncertainty of less than 1% of $({\ensuremath{\mu}}_{r}\ensuremath{-}1)$ at pressures above $2\phantom{\rule{0.3em}{0ex}}\mathrm{MPa}$. Regression of these data to a model for oxygen's impact---broadened microwave spectrum allowed us to determine two quantities that are, in principle, amenable to calculation: the molar magnetic susceptibility in the limits of zero pressure and zero frequency ${\ensuremath{\chi}}_{M00}^{\mathrm{meas}}\ensuremath{\equiv}{\ensuremath{\chi}}_{M}(0,0,293.15\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and the second magnetic virial coefficient ${b}_{\ensuremath{\mu}}$. With oxygen's electronic $g$ factor constrained to $2.0039\ifmmode\pm\else\textpm\fi{}0.0003$ (the value known from laser magnetic resonance, EPR, and molecular beam experiments) we obtained ${\ensuremath{\chi}}_{M00}^{\mathrm{meas}}=(42.92\ifmmode\pm\else\textpm\fi{}0.06)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}$ and ${b}_{\ensuremath{\mu}}=\ensuremath{-}1.8\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}$. The result for ${\ensuremath{\chi}}_{M00}^{\mathrm{meas}}$ is consistent with a recent ab initio calculation ${\ensuremath{\chi}}_{M00}^{\mathrm{meas}}∕{\ensuremath{\chi}}_{M00}^{\mathrm{calc}}=0.9998\ifmmode\pm\else\textpm\fi{}0.0014$. Our measurements of oxygen's magnetic susceptibility are the first made relative to the susceptibility of helium calculated ab initio. All previous measurements were made relative to the diamagnetic susceptibility of water. These previous measurements, published in 1943 or earlier, span the wider range $0.975<{\ensuremath{\chi}}_{M00}^{\mathrm{meas}}∕{\ensuremath{\chi}}_{M00}^{\mathrm{calc}}<1.019$. Our measurements of ${\ensuremath{\epsilon}}_{r}$ determine the static molecular dielectric polarizability of oxygen: $(1.7456\ifmmode\pm\else\textpm\fi{}0.0003)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}40}\phantom{\rule{0.3em}{0ex}}\mathrm{F}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{2}$, which deviates by $+0.7$ and $\ensuremath{-}0.1%$ from two recent ab initio calculations.

Structural, magnetic and photomagnetic study of the [Fe(PM–NEA)2(NCS)2] spin crossover complex

The new spin-crossover compound [Fe(PM–NEA)2(NCS)2] with PM–NEA = N-(2-pyridylmethylene)-4-(naphthalene-1-ethynyl)aniline has been synthesized. The temperature dependence of χMT (χM = molar magnetic susceptibility and T = temperature) has revealed a very gradual complete spin conversion between LS (S = 0) and HS (S = 2) states with T1/2 of about 204 K. At 10 K the well-known LIESST (light-induced excited spin state trapping) effect has been observed within the SQUID cavity, by irradiating a powder sample with a Kr+ laser coupled with an optical fibre. The HS → LS relaxation after LIESST has been analyzed with a stretched exponential behaviour. This is consistent with structural analysis, since the presence of naphthalene rings induces a less compact crystal packing than in already reported [Fe(PM–L)2(NCS)2] crystal structures. In particular, the intermolecular interaction network shows a noteworthy dissymmetry on each side of the complex. Furthermore, the structure–property relationship confirms the important role of the metal coordination sphere distortion on the T1/2 value.

Synthesis, spectroscopic characterization and antibacterial studies of some derivatives of chlorodimethylsulphoxide/tetramethylenesulphoxide ruthenium(II) and ruthenium(III) with 4-aminoantipyrine

We report the synthesis of five complexes of three different formulations viz. [cis-RuCl2(4-antp)2], [trans-RuCl2(4-antp)2] and [X]+[trans-RuCl4(4-antp)2]− (X+ = [(DMSO)2H]+, Na+, or [(TMSO)H]+ and 4-antp = 4-aminoantipyrine) from different routes. These complexes were characterized on the basis of elemental analyses, molar conductance measurements, magnetic susceptibility, electronic spectra, FTIR, 1H-NMR and 13C{1H}-NMR spectroscopy. Complexes were screened for antibacterial activity and found to be potent against gram negative bacteria Escherichia coli. ¶This paper is dedicated to my teacher, Dr. H. Singh, Ex. Professor, D.D.U. University, Gorakhpur, UP, India.

Synthesis, structure and magnetic property of [Ce(DMSO)2(H2O)Fe(CN)6

The title complex, [Ce(DMSO)2(H2O)Fe(CN)6] (1), was obtained by solution reactions and structurally characterized by X-ray diffraction. The title complex is characteristic of a novel cyano-bridged two-dimensional stair-like layered structure. The magnetic property of the title complex is reported herein. The χMT value at 300 K is ca. 0.92 emu K mol−1. The temperature dependence behavior of molar magnetic susceptibility of the complex clearly indicates the presence of an antiferromagnetic interaction.

Synthesis, crystal structure, and magnetic properties of a cobalt(II) complex with (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol

AbstractA novel bridging ligand, (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol (I), and its cobalt(II) complex, [Co(I)2(NCS)2]n (II), were prepared. The structures of ligand I and complex II were determined by single crystal X-ray analysis. Magnetic susceptibility measurements were performed for cobalt (II) complex II. Compound I crystallised in orthorhombic space group Pbca with a = 7.6585(14) Å, b = 12.209(2) Å, c = 23.207(4) Å, V= 2170.0(7) Å3 and Z=8. Complex II crystallised in monoclinic space group P21/n with a = 13.223(8) Å, b = 16.959(10) Å, c = 13.948(8) Å, β = 115.395(10)°, V= 2826(3) Å3 and Z = 4. Each cobalt(II) ion is surrounded by two NCS− anions and four pyridyl moieties from two bridging ligands. Each bridging ligand connects two neighbouring Co(II) ions to form a 2-dimensional structure. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K revealed that magnetic interactions between the cobalt ions are weak.

Syntheses, Structure, and a Mössbauer and Magnetic Study of Ba4Fe2I5S4

The compound Ba4Fe2I5S4 has been prepared at 1223-1123 K by the "U-assisted" reaction of FeS, BaS, S, and U with BaI2 as a flux. A more rational synthesis was also found; however, the presence of U appears to be essential for the formation of single crystals suitable for X-ray diffraction studies. Ba4Fe2I5S4 crystallizes in a new structure type with two formula units in space group I4/m of the tetragonal system. The structure consists of a Ba-I network penetrated by (1)infinity[Fe2S4] chains. Each Fe atom, which is located on a site with 4 symmetry, is tetrahedrally coordinated to four S atoms. The FeS4 tetrahedra edge-share to form linear (1)infinity[Fe2S4] chains in the [001] direction. The Fe-Fe interatomic distance in these chains is 2.5630(4) A, only about 3% longer than the shortest Fe-Fe distance in -Fe metal. Charge balance dictates that the average formal oxidation state of Fe in these chains is +2.5. The Mössbauer spectra obtained at 85 and 270 K comprise a single quadrupole doublet that has hyperfine parameters consistent with an average Fe oxidation state of +2.5. The Mössbauer spectrum obtained at 4.2 K consists of a single magnetic sextet with a small hyperfine field of -15.5 T. This spectrum is also consistent with rapid electron delocalization and an average Fe oxidation state of +2.5. The molar magnetic susceptibility of Ba4Fe2I5S4, obtained between 3.4 and 300 K, qualitatively indicates the presence of weak pseudo-one-dimensional ferromagnetic exchange within a linear chain above 100 K and weak three-dimensional ordering between the chains at lower temperatures.

Synthesis of Unsymmetrical Bissalicylaldimine Ligands and bis‐Schiff Base Cobalt Complexes with Benzo‐10‐aza‐15‐crown‐5 Pendant

AbstractNovel unsymmetrical bissalicylaldimine bis‐Schiff bases with a benzo‐10‐aza‐15‐crown‐5 pendant and their cobalt complexes have been synthesized via condensation of 3 or 5‐[(benzo‐10‐aza‐15‐crown‐5)‐10‐ylmethyl] salicylaldehyde with the half unit Schiff bases and characterized by 1H NMR, IR, mass spectroscopy, elemental analysis, molar conductances and molar magnetic susceptibility.

Use of the Sulfato Ligand in 3d‐Metal Cluster Chemistry: A Family of Hexanuclear Nickel(II) Complexes with 2‐Pyridyl‐Substituted Oxime Ligands

AbstractThe initial use of 2‐pyridyl‐substituted oximes [(py)C(R)NOH; R = Me, Ph]/sulfate blend in nickel(II) chemistry has yielded a family of hexanuclear clusters. The syntheses, structures and magnetic properties are reported of [Ni6(SO4)4(OH){(py)C(Me)NO}3{(py)C(Me)NOH}3(MeOH)2(H2O)] (1),[Ni6(SO4)4(OH){(py)C(ph)NO}3{(py)C(ph)NOH}3(MeOH)3] (2)and [Ni6(SO4)4(OH){(py)C(ph)NO}3{(py)C(ph)NOH}3(H2O)3] (3), where (py)C(Me)NOH is methyl 2‐pyridyl ketone oxime and (py)C(ph)NOH is phenyl 2‐pyridyl ketone oxime. The hexanuclear molecules present in the three complexes have similar structures which contain the [Ni6(μ3‐OH)(μ3‐SO4)3(μ3‐ONR)3]2+ core. The core consists of six NiII ions arranged as two parallel equilateral triangular subunits, one small (Ni···Ni ca. 3.3 Å) and the other larger (Ni···Ni ca. 6.0 Å). Characteristic IR bands are discussed in terms of the known structures of 1–3. The magnetic properties of 1 and 2 have been studied by variable‐temperature dc magnetic susceptibility techniques which indicate antiferromagnetic interactions. A simple 2‐J model was found to be adequate to describe the similar thermal variation of the molar magnetic susceptibilities of 1 and 2.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Thermal behaviour of Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pd(II) complexes with isatin-β-thiosemicarbazone

The isatin-β-thiosemicarbazone (ITC) complexes of Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pd(II) were prepared and characterized by elemental analysis, as well as molar conductivity, magnetic susceptibility, FTIR, UV-Vis and 1H NMR spectroscopic methods. The complexes were also studied for its thermal stability. They all behaviour as anhydrous complexes and its thermolysis passes through the stages of deamination (517–547 K) and complete thermal decomposition (619–735 K).