Octahedral Mn Research Articles

Self-Assembly of a New 1D Coordination Polymer Built of [Nb6Cl12(CN)6]4− and Mn(III) Complexes

A new 1D coordination polymer [Me4N]3{[Mn(L)][Nb6Cl12(CN)6]}·3MeCN·H2O (1) (L = acacen 2− = N,N′-bis(acetylacetone)-1,2-ethylenediimine) was synthesized from reaction between [Me4N]4[Nb6Cl12(CN)6] and [Mn(L)]Cl in acetonitrile. The crystal structure of 1 was determined from single-crystal X-ray diffraction analysis. Compound 1 crystallizes in the tetragonal system, space group I41/a (No. 88), a = 30.585(4), c = 27.348(6) A, V = 25582(7) A3, Z = 16. Its 1D framework consists of chains formed of metal clusters and Mn(L) complexes linked to each other by Nb–C≡N–Mn–N≡C–Nb linkages. The chains extend along the a and b crystallographic axes and are related to each other by 41 screw axis. The chains are held together by [Me4N]+ cations and solvent molecules located in channels running between the chains. 1 and the previously reported 1D coordination polymer [Me4N]3{[Mn(5-MeO-salen)][Nb6Cl12(CN)6]} (3) differ from each other in terms of their synthesis and their structural characteristics. Octahedral metal clusters and Mn(III) complexes with tetradentate schiff base ligands self assemble in solution to form the 1D cluster-based coordination polymer shown below.

A Porous Coordination Polymer Exhibiting Reversible Single-Crystal to Single-Crystal Substitution Reactions at Mn(II) Centers by Nitrile Guest Molecules

The porous coordination polymer {[Mn(L)(H(2)O)](H(2)O)(1.5)(DMF)}(n) (1) containing a water molecule coordinated at the apical position of each distorted octahedral Mn(II) center has been synthesized using the solvothermal technique by reacting Mn(NO(3))(2) x 4 H(2)O with a new flexible ligand (LH(2)) having isophthalic fragment and pyridine donors at the two ends. The coordinated water molecule could be substituted by nitrile guest molecules such as acetonitrile, acrylonitrile, allylnitrile, and crotononitrile (affording compounds 2-5, respectively) without loss of crystallinity. Interestingly, compound 1 selectively captures cis-crotononitrile into its cavity from a mixture of cis and trans isomers. Hence, the cis isomer can be separated from the trans isomer. In each case, 1.5 lattice water molecules and a dimethylformamide (DMF) molecule are also simultaneously replaced by certain numbers of these guest molecules. When these first-generation compounds 2-5 are dipped in DMF at room temperature with the lid of the vial open to the atmosphere, the mother crystal 1 is regenerated in each case. Thus, all of these substitution reactions are completely reversible. Also, the first-generation compounds 2-5 can be interconverted among one another by dipping them in appropriate nitrile guests. All of these phenomena could be observed in single-crystal to single-crystal fashion.

Cationic behavior and the related magnetic and magnetotransport properties of manganese ferrite thin films

Manganese ferrite (Mn x Fe 3− x O 4) thin films have been prepared by a sol–gel method. The samples ( x≤1.25) are polycrystalline containing well-defined grains and maintain cubic spinel structure with increasing lattice constant with x. The substituting Mn ions were found to have multi-valence, +2 and +3, by X-ray photoelectron spectroscopy. The saturation magnetization of the Mn-substituted films measured by vibrating sample magnetometry was found to increase from that of Fe 3O 4 at low x and then gradually decreases as x increases further. Such magnetic behavior can be explained in terms of the dominance of Mn 2+ species over Mn 3+ at low x and the gradual decrease in the population ratio Mn 2+/Mn 3+ as x increases. The observed decrease in the coercivity with increasing x implies the increase in octahedral Mn 2+ population. The Mn-substituted samples exhibit magnetoresistance (MR) effect the maximum intensity of which is gradually reduced with x from that of Fe 3O 4. All samples show increasing MR with increasing external field ( H), while their magnetization curves start to saturate near H=2 kOe. Such increasing MR with H can be explained in terms of the tunneling of spin-polarized carriers across grain boundaries. The reduction in the MR intensity with x can be partly explained in terms of the decrease in spin-polarized carrier density associated with octahedral occupation of Mn 2+ ions.

Conformation control of a flexible 1,4-phenylenediacetate ligand in coordination complexes: a rigidity-modulated strategy

Five coordination complexes based on the flexible ligand 1,4-phenylenediacetic acid (H2pda), formulated as Zn(trans-pda) (1a), Mn(H2O)2(trans-pda) (1b), [M(cis-pda)(4,4′-bipy)]·H2O (M = Zn (2a), Co (2b), Cd (2c); H2pda = 1,4-phenylenediacetic acid; 4,4′-bipy = 4,4′-bipyridine), are reported. The crystal structures of the as-synthesized complexes were determined by single-crystal X-ray diffraction analyses. Complexes 1a and 1b have similar three-dimensional (3-D) network structures built by tetrahedral Zn nodes (for 1a) or octahedral Mn nodes (for 1b) and trans-pda2− bridges. Complexes 2a, 2b, and 2c possess similar two-dimensional (2-D) layered structures constructed from interconnecting metal-cis-pda2− double chains by 4,4′-bipy ligands. It is interesting that conformation of the flexible pda2− ligand is modulated in presence of the rigid 4,4′-bipy ligand. The trans-pda2− ligand was typically isolated in a single pda2− system whereas the cis-pda2− ligand was observed in a mixed pda2−/4,4′-bipy system. Furthermore, the dimensionalities of the complexes vary from 3-D (1a and 1b) to 2-D (2a, 2b, and 2c) when auxiliary 4,4′-bipy ligands were introduced. The photoluminescent studies on solid-state samples of complexes 1a, 2a and 2c indicate that the complexes exhibit intense fluorescent emissions at room temperature.

Selective Sorption of Co<SUP>2+</SUP> over Ni<SUP>2+</SUP> Using Biogenic Manganese Oxides

Preferential sorption of Co 2+ ions over Ni Z+ ions was achieved using biogenic Mn oxides produced by the Mn-oxidizing fungus Paraconiothyrium sp. WL-2 strain with a maximum selectivity coefficient (α Co ) of 18. The selective sorption was based on different sorption mechanism for Co z+ and Ni 2+ and unique properties of biogenic Mn oxides. The octahedral Co 2+ ions occupy vacancies of central metal sites and edge sites in the octahedral Mn oxide unit structures of biogenic Mn oxides, where they are immobilized by oxidation to CoOOH by Mn(III). In contrast, Ni 2+ ions are sorbed primarily on layer edges at circumneutral pHs without oxidation. Selective sorption of Co 2+ over Ni 2+ on the biogenic Mn oxides results from more vacant sites, higher Mn(III) contents, and larger specific surface areas compared to synthetic Mn oxides.

EPR investigation of local structure for [Mn(H 2O) 6] 2+ cluster in [M(H 2O) 6]XCl 6:Mn 2+ (M = Zn, Mg, Cd, Ca; X = Pt, Sn) systems at different temperatures

A theoretical method for studying the inter-relation between the local structure and EPR spectra is established by diagonalizing the complete energy matrices. For [M(H 2O) 6]XCl 6:Mn 2+ (M = Zn, Mg, Cd, Ca; X = Pt, Sn) systems, the calculated results demonstrate that the local structures around the octahedral Mn 2+ centers in the doped systems are very similar despite of the host crystals being different. Furthermore, it is shown that the EPR zero-field parameter D depends simultaneously on the local structure parameters R and θ while ( a − F) depends mainly on R, whether the doped systems are at liquid-nitrogen temperature or room temperature.

Diaqua[5-(2-pyridyl)tetrazolato-κ2N1,N5]manganese(II)

The title compound, [Mn(C6H4N5)2(H2O)2], was synthesized by the hydro­thermal reaction of Mn(NO3)2 with picolino­nitrile in the presence of NaN3. The Mn atom lies on an inversion centre. The distorted octa­hedral Mn environment contains two planar trans-related N,N′-chelating 5-(2-pyrid­yl)­tetra­zolate ligands in the equatorial plane and two axial water mol­ecules. O—H⋯N hydrogen bonds generate an infinite three-dimensional network.

Triply Interpenetrated Structure of {MnII(L)2[AgI(CN)2]2}{MnII(H2O)2[AgI(CN)2]2} (L = 4-CNpy or py-4-aldoxime)

Abstract Two novel 3D network coordination polymers {Mn(L)2[Ag(CN)2]2}{Mn(H2O)2[Ag(CN)2]2} (L = 4-CNpy (1) or py-4-aldoxime (2)) (4-CNpy = 4-cyanopyridine; py-4-aldoxime = pyridine-4-aldoxime) were synthesized and characterized by using single-crystal X-ray analysis and magnetic measurements. Both complexes have two distinct octahedral manganese atoms, Mn(1) and Mn(2), linked by a [Ag(CN)2]− unit. The pyridine ring of two Ls coordinate at the apical positions of Mn(1). On the other hand, at the apical positions of Mn(2), two H2O are coordinated. The apical axis of Mn(1) is not parallel to the apical axis of Mn(2). Therefore, {Mn[Ag(CN)2]2} networks in 1 and 2 are distorted and form three-dimensional (3D) frameworks. There are large channels in the 3D networks; however, triple interpenetration was found in 1 and 2. From the temperature dependence of magnetic susceptibility, there is very weak antiferromagnetic interaction between the Mn atoms bridged by a [Ag(CN)2]− unit in 1 and 2.

Soft-Chemical Synthesis and Electrochemical Characterization of Multicomponent Mn1–x–yCoxNiyO2 Nanostructures

Nanostructured Mn(1-x-y)Co(x)Ni(y)O2 metal oxides are synthesized by one-pot hydrothermal reaction at low temperature. From powder X-ray diffraction and field emission-scanning electron microscopic analyses, it is found that the crystal structure and crystal morphology of the present materials are tunable by the control of the composition of precursor. 1D nanowires with alpha-MnO2-type structure are prepared with low substitution rate of Co and Ni, while the increase of substituent contents leads to the formation of delta-MnO2-structured 3D nanospheres consisting of 2D nanoplates. According to X-ray absorption near edge spectroscopy and chemical analyses, mixed valent Co(III)/Co(IV) and divalent Ni(II) ions are stabilized in the octahedral Mn sites of alpha-MnO2- and delta-MnO2-structures. The electrochemical measurements clearly demonstrate that the present nanostructured materials show promising electrode performances for lithium secondary batteries.

An Antiferromagnetic Mn(II)‐Azido Chain: Synthesis and Characterization

A new polymeric compound, [Mn(N3)2(1)2]n (2) where 1=N(phenyl)isonicotinamide (NPI), has been synthesized and characterized by X‐ray crystallography and low‐temperature magnetic study. Compound 2 consists of a one‐dimensional chain of octahedral Mn(II) bridged by azide anions in end‐to‐end fashion. In this compound, the Mn(II) ions are linked by 4 azide bridging ligands and 2 monodentate ligands 1. Variable temperature magnetic susceptibility measurements in the temperature range 300–4 K reveal the existence of weak antiferromagnetic interactions (J=−14.6 cm−1).

Syntheses, structures and magnetic properties of Mn(II) containing 3D polymeric networks

Two novel 3D coordination polymers {[Mn(aip)(DMF)]} n , CPO-9, and {[Mn 3(Hatp) 2(atp) 2](H 2O) 2(DEF) 4} n CPO-10 (aip = 5-aminoisophthalate, atp = 2-aminoterephthalate, DMF = dimethylformamide, DEF = diethylformamide) have been synthesized by solvothermal methods. Their properties have been studied by single-crystal X-ray diffraction, thermogravimetric analysis, high-temperature powder X-ray diffraction and magnetic susceptibility measurements. The crystal structure of CPO-9 is based on infinite chains of carboxylato-bridged five-coordinated Mn(II) ions that are crosslinked via the aip ligands to form a 3D structure. CPO-10 is based on linear trinuclear building units of carboxylato-bridged octahedral Mn(II) ions that are crosslinked by the atp ligands into a 3D structure. Both compounds have 1D channels that contain solvent molecules. The solvent accessible void volume for CPO-10 is 51.9% of the unit cell volume. For both compounds, however, the solvent molecules cannot be removed without the collapse of the structures into amorphous phases at 250 °C. The magnetic susceptibility measurements indicate antiferromagnetic couplings between the Mn(II) ions in both compounds. The magnetic data have been fitted using theoretical approaches.

Tridentate Facial Ligation of Tris(pyridine-2-aldoximato)nickel(II) and Tris(imidazole-2-aldoximato)nickel(II) To Generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiIIand the Electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIIISpecies: A Magnetostructural, Electrochemical, and EPR Spectroscopic Study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.

Tetrahedral versus octahedral Mn site coordination in wurtzite and rocksalt Zn1−xMnxO investigated by means of XAS experiments under high pressure

Abstract We present the results of x-ray absorption measurements carried out in Zn 1− x Mn x O thin films under high pressure. The Mn environment remains essentially the same for nominal Mn concentrations given by x = 0.05 , 0.1, 0.15 and 0.25. Both the XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) indicate that Mn occupies the Zn site, being surrounded by four oxygen atoms at 2.02±0.01 A. The substitutional hypothesis is reinforced by comparing the differences between the ambient (wurtzite) and high pressure (rocksalt) spectra, which correspond to tetrahedral and octahedral Mn environments.

Structure−Property Relationships of the 10H Hexagonal-Type Perovskite BaMn0.4Fe0.6O2.73

The crystal structure of BaMn0.4Fe0.6O2.73, a recently identified oxygen-deficient 10H-type hexagonal perovskite in the system BaMn1-xFexO3-y, has been established by a combination of electron microdiffraction and neutron diffraction. The structure (space group P63/mmc, a = 5.74435(5) Å, and c = 24.0331(3) Å) can be described by a stacking sequence (hch‘ch)2 along the c-axis with the anion deficiency located exclusively in the h‘-BaO3-type layers. The anion distribution in the h‘-BaO3 layers differs significantly from that observed for 10H BaFeO2.8 and results in a 70:30 random distribution of corner-sharing tetrahedral Fe2O7 dimers and face-sharing octahedral (Mn,Fe)2O9 dimers as opposed to the exclusive Fe2O7 dimers in 10H BaFeO2.8. The difference is attributed to the preference of Mn for octahedral coordination. The compound is a “leaky” insulator at room temperature with a permittivity of ∼20. The conduction mechanism has low activation energy, ∼0.3 eV, and is consistent with polaronic hopping associated with the Fe and/or Mn ions.

Origin of the Zero-Field Splitting in Mononuclear Octahedral Dihalide MnII Complexes: An Investigation by Multifrequency High-Field Electron Paramagnetic Resonance and Density Functional Theory

The synthesis, structural characterization, and electronic properties of a new series of high-spin six-coordinate dihalide mononuclear MnII complexes [Mn(tpa)X2] (tpa=tris-2-picolylamine; X=I (1), Br (2), and Cl (3)) are reported. The analysis of the crystallographic data shows that in all investigated complexes the manganese ion lies in the center of a distorted octahedron with a cis configuration of the halides imposed by the tpa ligand. By a multifrequency high-field electron paramagnetic resonance investigation (95-285 GHz), the electronic properties of 1-3 were determined (DI=-0.600, DBr=-0.360, DCl=+0.115 cm-1), revealing the important effect of (i) the nature of the halide and (ii) the configuration (cis/trans) of the two halides on the magnitude of D. The spin Hamiltonian parameters obtained by density functional theory calculations initiated from the crystal structure of 1-3 are in reasonable agreement with the experimental values. The absolute value of D is consistently overestimated, but the sign and the trend over the chemical series is well reproduced. Theoretical models (cis- and trans-[Mn(NH3)4X2], X=I, Br, Cl and F) have been used to investigate the different contributions to D and also to understand the origin of the experimentally observed changes in D within the series reported here. This study reveals that the spin-spin coupling contributions to the D tensor are non-negligible for the lighter halides (F, Cl) but become insignificant for the heavier halides (I, Br). The four different types of excitations involved in the spin-orbit coupling (SOC) part of the D tensor contribute with comparable magnitudes and opposing signs. The general trend observed for halide MnII complexes (DI>DBr>DCl) can be explained by the fact that the halide SOC dominates the D value in these systems with a major contribution arising from interference between metal- and halide-SOC contributions, which are proportional to the product of the SOC constants of Mn and X.

The crystal structure of ingersonite, Ca3Mn2+Sb45+O14, and its relationships with pyrochlore

The crystal structure of ingersonite, (Ca2.93Mn 2+ 1.06Fe 2+ 0.01)(Sb 5+ 3.95Mg0.05)F0.15O13.85, has been solved and refi ned in the space group P3121 (a = 7.282(2), c = 17.604(4) A, V = 808.4(3) A 3 , Z = 3) to R = 2.32% for 2219 Fo > 4σ(Fo) using MoKα X-ray data. The structure of ingersonite is isostructural with the synthetic weberite-3T polytype and related to the pyrochlore structure type. Both ingersonite and pyrochlore structures can be described as a sequence of pairs of polyhedral layers (named M and N), stacked along (111) and (001), respectively. In terms of the cation sites, M and N layers have general formula AB3 and A3B, respectively, where B are the octahedral cations forming the B2X6 framework of the pyrochlore structure and A are the larger, interstitial cations forming eightfold polyhedra in pyrochlore. In ingersonite, the M layers occur at z ~ 1/6, 1/2, and 5/6: The B octahedra are occupied by Sb 5+ and share corners to form a pseudohexagonal tungsten bronze (HTB) motif with the A position occupied by octahedral Mn 2+ at the center of the pseudohexagonal rings. N layers occur at z ~ 0, 1/3, and 2/3, with A = Ca and B = Sb 5+ : Isolated B octahedra share 6 edges with 6 eightfold A polyhedra, to form a continuous sheet similar to the analogous layer in pyrochlore. The stacking of successive pairs of M and N layers in ingersonite is the same as in pyrochlore. Nonetheless, a difference in the relative position between M and N layers in ingersonite and pyrochlore is observed. The crystal-chemical relationships with other pyrochlore-related minerals are outlined. Keywords: Ingersonite, crystal structure, chemical data, weberite-3T polytype, pyrochlore-related structure, X-ray diffraction data

Armbrusterite, K5Na6Mn3+Mn142+[Si9O22]4(OH)10{middle dot}4H2O, a new Mn hydrous heterophyllosilicate from the Khibiny alkaline massif, Kola Peninsula, Russia

Armbrusterite, ideally K5Na6Mn3+Mn2+14[Si9O22]4(OH)10·4H2O, is a new silicate of potassium, sodium, and manganese found in a thin cancrinite-aegirine-microcline vein within urtite at Mt. Kukisvumchorr. The mineral occurs in intimate association with raite. Other associated minerals are lamprophyllite, mangan-neptunite, pectolite, vinogradovite, calcite, molybdenite, galena, sphalerite, and fluorite. Armbrusterite occurs as split, curved crystals and spherulites (≤2 mm diameter). The mineral is translucent (transparent in thin fragments), dark reddish-brown. It has vitreous luster and light-brown streak. Cleavage is perfect on (001) and the fracture is uneven. Mohs hardness is about 3.5. In transmitted light, the mineral is reddish-brown, with strong pleochroism: X = light yellowish-brown, Y and Z = dark reddish-brown; dispersion r > v, weak. Armbrusterite is biaxial (.): α = 1.532(2), β = 1.560(2), γ = 1.564(2) (for λ = 589 nm), 2V varies from 10° to 20°. Optical orientation: X is perpendicular to (001). The mean chemical composition determined by electron microprobe and the Penfield method (for H2O) is (wt%): Na2O 5.26, MgO 0.19, Al2O3 0.04, SiO2 56.02, K2O 6.13, CaO 0.26, TiO2 0.04, MnO 23.62, Mn2O3 2.07, FeO 0.65, ZnO 0.20, H2O 4.1, sum. 98.58. Empirical formula calculated on the basis of Si = 36 is K5.03Na6.55(Mn2+12.86Mn3+1.01Fe2+0.35Mg0.18 Ca0.18Zn0.09Al0.03Ti0.02)Σ=14.72[Si36O88](OH)10.10 ·3.75 H2O. Armbrusterite is monoclinic, C2/m, a = 17.333(2), b = 23.539(3), c = 13.4895(17) Å, β = 115.069(9)°, V = 4985.4(11) Å3, Z = 2. The strongest X-ray powder-diffraction lines are [d in Å, (I), (hkl)]: 12.28 (100) (001), 4.10 (10) (003), 3.562 (10) (113, 261), 3.260 (18) (114), 3.117 (13) (203), 3.077 (54) (004), 2.622 (10) (371). The crystal structure of armbrusterite was refined to R1 = 0.085 on the basis of 3960 unique observed reflections. The structure is based upon double silicate [Si9O22] layers consisting of 5-, 6-, 7-, and 8-membered tetrahedra rings. The layers are linked via octahedral sheets formed by Na and Mn octahedra. The interior of the double silicate layers is occupied by K+ cations and H2O molecules. The mineral is named in honor of Thomas Armbruster (b. 1950; University of Berne) for his outstanding contribution to structural mineralogy and crystallography, especially to the study of Mn-rich minerals.

Coordination properties of the diethyl 2-pyridylmethylphosphonate ligand (2-pmpe) with chloride transition-metal salts: X-ray crystal structure of Cd 4(2-pmpe) 4Cl 8

A new series of the chloride transition-metal complexes containing the ligand diethyl 2-pyridylmethylphosphonate (2-pmpe) of general formula M(2-pmpe) 2Cl 2 (M = Ni, Co, Mn) and M(2-pmpe)Cl 2 (M = Co, Zn,) were prepared. The complexes were identified and characterized by elemental analysis, spectroscopic and magnetic studies. For Cd 4(2-pmpe) 4Cl 8 X-ray crystal structure was determined. The structure is based on a chloro-bridged tetranuclearcadmium quasi cubane cluster, in which each cadmium atom is chelated by one N,O-chelate 2-pmpe ligand and coordinated with four bridging chloride atoms. The ligand containing two donor atoms, heterocyclic pyridyl nitrogen and phosphoryl oxygen atoms binds in a didentate chelate manner in all complexes. Two compounds were obtained with cobalt chloride salt, exhibiting tetrahedral (1:1) and octahedral (1:2 metal to ligand molar ratio) arrangements of cobalt ions. The octahedral Ni(II), Co(II) and Mn(II) complexes are izostructural. Geometry of Zn(2-pmpe)Cl 2 is consistent with a pseudotetrahedral environment of Zn(II) ion. The spectroscopic properties of Zn(II), and magnetic behavior of Ni(II), Co(II) and Mn(II) complexes indicate mononuclear structure of all compounds.

Theoretical study of local lattice structure of Mn 2+ in perovskite fluorides A 2MF 4 (A=K, Rb; M=Mg, Zn, Cd) series

A theoretical method for investigating the inter-relation between the molecular structure and electronic structure has been established on the basis of the 252×252 complete energy matrices for a 3d 5 configuration ion in a tetragonal ligand field. By means of this method, which is independent of the X-ray diffraction, the local structure of the paramagnetic Mn 2+ ion in perovskite fluorides A 2MF 4 (A=K, Rb; M=Zn, Mg, Cd) are determined directly by analyzing the EPR spectrum of octahedral Mn 2+ center in A 2MF 4 crystals and the optical absorption spectrum of the (MnF 6) 4− cluster. It is shown that, comparing with the octahedral cubic structure, the local micro-structure in the vicinity of Mn 2+ displays an elongated distortion when b 2 0 > 0 and a compressed distortion when b 2 0 < 0 , and Δ R vs. 1 0 4 b 2 0 as well as Δ R vs. 1 0 4 b 4 0 in the distortion region is, respectively, approximately linear. Simultaneously, the theoretical zero-field-splitting parameters b 2 0 , b 4 0 and b 4 4 are in good agreement with the experimental values.

Synthesis and Characterization of Mixed‐Valent Manganese Phosphonate Cage Complexes

The reaction of phenylphosphonic acid (PhPO(3)H(2)) with the mixed-valent basic oxo-centered manganese triangle [Mn(3)O(O(2)CCMe(3))(6)(py)(3)] (1; where py=pyridine) in the presence of a suitable base gives four different manganese clusters depending on the identity of the base. The syntheses and structural characterization of [Mn(18)(mu(3)-O)(8)(PhPO(3))(14)(O(2)CCMe(3))(12)(py)(6)(H(2)O)(2)] (2), [Mn(7)(mu(3)-O)(3)(O(3)PPh)(3)(O(2)CCMe(3))(8)(py)(3)] (3), [Mn(9)Na(mu(3)-O)(4)(mu(4)-O)(2)(O(3)PPh)(2)(O(2)CCMe(3))(12)(H(2)O)(2)(H(2)O)(0.67)(Py)(0.33)] (4), and [Mn(13)(mu(3)-O)(8)(OMe)(8)(O(3)PPh)(4)(O(2)CCMe(3))(10)] (5) are described. Complexes 4 and 5 are homovalent Mn(III) cages, while 2 and 3 contain divalent, trivalent, and/or tetravalent ions. All the manganese centers are valence-localized, the octahedral Mn(III) sites being recognizable by marked Jahn-Teller distortions. The magnetic properties of compounds 2-5 have been investigated in the polycrystalline state by magnetic susceptibility and high-field magnetization measurements, which reveal that spin ground states vary from 0< or =S > or =8. AC susceptibility measurements performed on 4 and 5, in the 1.6-10.0 K ranges show the presence of out of AC susceptibility signal (chi(M)'') for 4, and an effective energy barrier (U(eff)) for the re-orientation of the magnetization is found to be 17 K, but for 5, the chi(M)'' maximum is found to be below 1.5 K.