Synthesis, physical properties, multitemperature crystal structure, and 20 K synchrotron X-ray charge density of a magnetic metal organic framework structure, Mn3(C8O4H4)3(C5H11ON)2

A new magnetic metal organic framework material has been synthesized, Mn3(C8O4H4)3(C5H11ON)2, 1. Magnetic susceptibility measurements from 2 to 400 K reveal anti-ferromagnetic ordering at approximately 4 K and a total magnetic moment of 6.0 micro(B). The magnetic phase transition is confirmed by heat capacity data (2-300 K). The crystal structure is studied by conventional single-crystal X-ray diffraction data at 300, 275, 250, 225, 200, 175, 150, 125, and 100 K, and synchrotron data at 20 K. There is a phase transition between 100 and 20 K due to ordering of the diethylformamide molecules. The X-ray charge density is determined based on multipole modeling of a second 20 K single-crystal synchrotron radiation data set. The electron distributions around the two unique Mn centers are different, and both have substantial anisotropy. Orbital population analysis reveals large electron donation (1.7 e) to each Mn atom and the maximum possible number of unpaired electrons is 3.2 for both Mn sites. Thus, there is a considerable orbital component to the magnetic moment. Bader topological analysis shows an absence of Mn-Mn bonding, and the magnetic ordering is via super-exchange through the oxygen bridges. Formal electron counting suggests Mn2+ sites, but this is not supported by the Bader atomic charges, Mn1 = +0.11 e, Mn2 = +0.17 e. The topological measures show the dominant metal-ligand interactions to be electrostatic, and a simple exponential correlation is derived between Mn-O bond lengths and the values of nabla2rho at the bond critical points.     

Cs2K[Mn(CN)6] at 293, 85 and 10 K

The crystal structure of dicaesium potassium hexacyanomanganese(III) has been determined by X‐ray diffraction at 293, 85 and 10 K. The Mn and K atoms lie on inversion centres and the Cs atom is in a general position. The accurate and extensive data sets collected should be suitable for charge–density analysis studies.     

Experimental and theoretical electron density distribution and magnetic properties of the butterfly-like complex [Fe(4)O(2)(O(2)CCMe(3))(8)(NC(5)H(4)Me)(2)].2CH(3)CN

The structure and electron density distribution (EDD) of the carboxylate-bridge iron complex [Fe(III)(4)(micro(3)-O)(2)(O(2)CCMe(3))(8)(NC(5)H(4)Me)(2)].2CH(3)CN, 1, has been determined from synchrotron X-ray diffraction data (R(int) = 0.025) collected with the crystal cooled to 16(5) K. At this temperature complex 1 crystallized in the triclinic space group P with cell parameters a = 12.6926(7) A, b = 12.9134(8) A, c = 13.4732(8) A, alpha = 115.372(2) degrees, beta = 107.702(3) degrees, and gamma = 102.731(2) degrees. The theoretical EDD determined from a density functional theory (DFT) single point calculation of an entire molecule of 1 at the experimental geometry has been analyzed and compared to the experimental EDD. The latter is expressed in the framework of a multipolar model with parameters determined by least-squares refinement (R(w)(F(2)) = 0.024) based on the X-ray diffraction data. The central micro(3)-oxygen atom in 1 is significantly out of the plane spanned by the three Fe atoms coordinated to this oxygen. Comparison of measures for the bonding geometry around the iron atoms in 1 with the corresponding values for the iron atoms in relevant trinuclear complexes suggests that there are significant differences in the Fe-(micro(3)-O) bonds in the two cases. Analyses of both the experimental and theoretical EDDs reveal very significant differences between the two Fe-(micro(3)-O) bonds in 1, with one bond being much more directed and stronger than the other bond. A topological analysis of the EDDs using the atoms in molecules approach also reveals very distinct differences between the properties of the two Fe(III) atoms. A clear exponential relationship is found between the Laplacian of the experimental density at the bond critical points in the Fe-ligand bonds and their bond lengths. M?ssbauer spectroscopy of 1 shows two easily separable doublets corresponding to the two different iron sites. Magnetic susceptibility measurements between 4.2 and 300 K indicate antiferromagnetically coupled Fe(III) atoms constituting an S = 0 ground state.     

Interpenetrating three-dimensional diamondoid lattices and antiferromagnetic ordering (T(c) = 73 K) of Mn(II)(CN)2

Thermolysis of either the 3-D, bridged-layered [NEt(4)]Mn(II)(3)(CN)(7) or 2-D, layered [NEt(4)](2)Mn(II)(3)(CN)(8) forms Mn(II)(CN)(2). Rietveld analysis of the high-resolution synchrotron powder X-ray diffraction data determined that Mn(II)(CN)(2) is cubic [a = 6.1488(3) ?] (space group = Pn3m) consisting of two independent, interpenetrating networks having the topology of the diamond lattice. Each tetrahedrally coordinated Mn(II) is bonded to four orientationally disordered cyanide ligands. Mn(II)(CN)(2) magnetically orders as an antiferromagnet with a T(c) = 73 K determined from the peak in d(χT)/dT. Exchange coupling estimated via the mean field Heisenberg model from the transition temperature (J/k(B) = -4.4 K) and low temperature magnetic susceptibility of the ordered phase (J/k(B) = -7.2 K) indicate that Mn(II)(CN)(2) experiences weak antiferromagnetic coupling. The discrepancy between those estimates is presumably due to local anisotropy at the Mn(II) sites arising from the CN orientational disorder or interactions between the interpenetrating lattices.     

Frequency-domain Fourier-transform terahertz spectroscopy of the single-molecule magnet (NEt4)[Mn2(5-Brsalen)2(MeOH)2Cr(CN)6

We have investigated the novel single-molecule magnet (NEt(4))[Mn(2)(5-Brsalen)(2)(MeOH)(2)Cr(CN)(6)] (1; 5-Brsalen = N,N'-ethylenebis(5-bromosalicylidene)iminato anion) using spectroscopic as well as magnetization and susceptibility measurements. Frequency-domain Fourier-transform terahertz electron paramagnetic resonance (FDFT THz-EPR) based on the generation of THz radiation from a synchrotron in combination with inelastic neutron scattering (INS) allows for the discrimination between intermultiplet and intramultiplet transitions. Together with ac/dc magnetic susceptibility measurements the obtained set of data provides a complete characterization of the lowest energetic magnetic excitations. We find that the new compound 1 exhibits much weaker intermolecular interactions than found in the closely related compound: K[Mn(2)(5-Brsalen)(2)(H(2)O)(2)Cr(CN)(6)] (2). Furthermore, two phonon lines in the vicinity of the magnetic excitations are detected.     

Weak ferromagnetism in chiral diamond-like neutral networks: Mn(2-pymS)2 and Co(2-pymS)2 (2-pymSH = 2-mercaptopyrimidine)

The reactions of 2-mercatopyrimidine with MCl(2) (M = Mn(2+) or Co(2+)) in solvothermal conditions result single crystals of Mn(2-pymS)(2)1 and Co(2-pymS)(2)2. The two complexes both have the diamond-like topology frameworks, which could be traced back to the similar way of pyrimidine rings acting as the asymmetric bridging ligands. Interestingly, although they have similar chemical formulas, structural analysis by single-crystal X-ray diffraction studies reveals that the sulfur atoms play different roles in 1 and 2. For 1, the Mn ion lies in a distorted octahedral environment bonded to four nitrogen atoms and two sulfur atoms, whereas the Co ion in a distorted tetrahedral environment only coordinates to nitrogen atoms of pyrimidine ligands in the case of Co(2-pymS)(2)2. More interestingly, although magnetic measurements for both complex 1 and 2 indicate long range magnetic ordering and spin canting below the critical temperature (20 K for 1 and 42.9 K for 2), a hysteresis loop can be observed even at 40 K, which is just below the T(C) for complex 2, which is distinctly harder than 1.     

Experimental X-ray charge density studies on the binary carbonyls Cr(CO)6, Fe(CO)5, and Ni(CO)4

The experimental charge densities in the binary carbonyls Cr(CO)(6) (1), Fe(CO)(5) (2), and Ni(CO)(4) (3) have been investigated on the basis of high-resolution X-ray diffraction data collected at 100 K. The nature of the metal-ligand interactions has been studied by means of deformation densities and by topological analyses using the Atoms in Molecules (AIM) approach of Bader. A detailed comparison between the experimental results and theoretical results from previous work and from gas-phase and periodic DFT/B3LYP calculations shows excellent agreement, both on a qualitative and quantitative level. An examination of the kappa-restricted multipole model (KRMM) for Cr(CO)(6), using theoretically derived structure factors, showed it to provide a somewhat worse fit than a model with freely refined kappa' values. The experimental atomic graphs for the metal atoms in 2 and 3 were found to be dependent on the multipole model used for that atom. In the case of compound 2, restriction of the multipole populations according to idealized site symmetry of D(3h) gave an atomic graph in essential agreement with the theoretical gas-phase study. For compound 3, all multipole models fail to reproduce the atomic graph obtained from the theoretical gas-phase study. The atomic quadrupole moments for the C atoms in all compounds were consistent with significant pi back-donation from the metal atoms.     

Temperature and pressure evolution of the crystal structure of A(x)(Fe(1-y)Se)2 (A = Cs, Rb, K) studied by synchrotron powder diffraction

Temperature-dependent synchrotron powder diffraction on Cs(0.83)(Fe(0.86)Se)(2) revealed first-order I4/m to I4/mmm structural transformation around 216 °C associated with a disorder of the Fe vacancies. Irreversibility observed during the transition is likely associated with a mobility of the intercalated alkali atoms. Pressure-dependent synchrotron powder diffraction on Cs(0.83)(Fe(1-y)Se)(2), Rb(0.85)(Fe(1-y)Se)(2), and K(0.8)(Fe(1-y)Se)(2) (y ~ 0.14) indicated that the I4/m superstructure reflections are present up to pressures of 120 kbar. This may indicate that the ordering of the Fe vacancies is present in both superconducting and nonsuperconductive states.     

Experimental and theoretical charge distribution in (Z)-N-methyl-C-phenylnitrone

The total experimental charge density in (Z)-N-methyl-C-phenylnitrone (1) has been determined using high-resolution X-ray diffraction data in combination with neutron diffraction data measured at 100 K in terms of the rigid pseudoatom model. Multipole refinement converged at R = 0.03 for 7163 reflections with I > 2 sigma(I). Topological analysis of the total experimental charge density rho(r) and its Laplacian, -[symbol: see text]2 rho(r) and a comparison with high level theoretical gas-phase calculations reveals an unexpected electron distribution in the N-O group, both atoms having negative atomic charges, contrary to that commonly assumed in nitrone species. This observation is confirmed on examination of both the theoretical charges and the molecular electrostatic potential. Compound 1 contains a large number of hydrogen bonds and these are analysed using the atoms in molecules approach leading to quantitative values for bond strength, ranging from medium to very weak.     

Experimental and theoretical charge density study of chemical bonding in a Co dimer complex

The charge density of Co2(CO)6(HC[triple bond]CC6H10OH) (1) in the crystalline state has been determined using multipolar refinement of single-crystal X-ray diffraction data collected (i) with a synchrotron source at very low temperatures (15 K) and (ii) using a conventional source with the crystal at intermediate temperature (100 K). The X-ray charge density model is augmented by complete active space and density functional theory calculations. Topological analyses of the different charge distributions show that the two Co atoms are not bonded to each other in the quantum theory of atoms in molecules (QTAIM) sense of the word. However, the behavior of the source function and the total energy density indicate that there is some bond-like character in the Co-Co interaction. The bridging alkyne fragment provides an unusual bonding situation, with extremely small electron density differences between the two Co-C bond critical points and the "CoC2" ring critical point. Thus, the structure is close to a topological catastrophe point. Comparison of the results obtained from the two diffraction data sets and ab initio theory suggests that the topology of the experimental electron density in this special atomic environment is highly sensitive to subtle effects of measurement errors and potential shortcomings of the multipole model, or to effects of the crystal field. Thus, even the two identical molecules in the asymmetric unit show altered bonding patterns.     

High-spin- and low-spin-state structures of [Fe(chloroethyltetrazole)6](ClO4)2 from synchrotron powder diffraction data

The spin-crossover complex [Fe(teec)(6)](ClO(4))(2) (teec = chloroethyltetrazole) exhibits a 50 % incomplete spin crossover in the temperature range 300-30 K. Time-resolved synchrotron powder diffraction experiments have been carried out to elucidate its structural behavior. We report crystal structure models of this material at 300 K (high spin) and 90 K (low spin), as solved from synchrotron powder diffraction data by using Genetic Algorithm and Parallel Tempering techniques and refined with Rietveld refinement. During short synchrotron powder diffraction experiments (five minutes duration) two distinguishable lattices were observed the quantities of which vary with temperature. The implication of this phenomenon, that is interpreted as a structural phase transition associated with the high-to-low spin crossover, and the structural characteristics of the high-spin and low-spin models are discussed in relation to other compounds showing a similar type of spin-crossover behavior.     

Synthesis, nuclear, and magnetic structures and magnetic properties of [Mn3(OH)2(SO4)2(H2O)2

[Mn(3)(OH)(2)(SO(4))(2)(H(2)O)(2)] and its deuterated analogue were synthesized by a hydrothermal technique and characterized by differential thermal analysis, thermogravimetric analysis, and IR spectroscopy. Its nuclear structure, determined by single-crystal X-ray analysis and Rietveld analysis of neutron powder-diffraction data, consists of a 3D network of chains of edge-sharing Mn(1)O(6), running along the c axis, connected by the apices of Mn(2)O(6) and SO(4) units. It is isostructural to the nickel analogue. Determination of the magnetic structure and measurements of magnetization and heat capacity indicate the coexistence of both magnetic long-range ordering (LRO) and short-range ordering (SRO) below a Néel temperature of 26 K, while the SRO is retained at higher temperatures. The moments of the two independent Mn atoms lie in the bc plane, and that of Mn(1) rotates continuously by 54 degrees towards the c axis on decreasing the temperature from 25 to 1.4 K. While the SRO may be associated with frustration of the moments within a Mn(3) trimer, the LRO is achieved by antiparallel alignment of the four symmetry-related trimers within the magnetic unit cell. A spin-flop field, measured by dc and ac magnetization on a SQUID, is observed at 15 kOe.     

Electron density distribution of an oxamato bridged Mn(II)-Cu(II) bimetallic chain and correlation to magnetic properties

The electron density distribution of the ferrimagnetic MnCu(pba)(H2O)3.2H2O chain compound, where pba stands for 1,3-propylenebis(oxamato), has been derived from high resolution X-ray diffraction measurements at 114 K using a multipolar model. The analysis of the chemical bonding has been carried out through the "Atoms in Molecules" formalism and thoroughly interpreted with regards to the strong intrachain and weak interchain magnetic couplings. The topological properties of the electron density on the oxamato bridge indicate large electron delocalization and conjugation effects, in addition to high charge transfer from both metals to the bridge. The resulting positive charges on Mn (+1.45 e) and Cu (+1.56 e) induce charge polarization of the bridge, leading to a shift of electron density from the central C atoms to the metal coordinating O and N atoms. The Mn-bridge interactions are mainly closed-shell interactions with low electron density at the corresponding bond critical points, whereas the Cu-bridge interactions exhibit significant covalent character. The Cu-N bonds are moreover stronger than the Cu-O bonds. The 3d Cu and Mn orbital populations are consistent with pyramidal and regular octahedral environments, respectively, in agreement with the loss of degeneracy due to ligand field effects. Interchain interaction pathways are evidenced by the existence of four bond critical points in hydrogen bond regions. Finally, these intrachain and interchain bonding features are correlated to the results of experimental and theoretical spin density distributions, as well as magnetic measurements.     

Structural and magnetic investigations of the mixed-valence Fe(II,III) two-dimensional layer complex, [Fe2(II) Fe2(III)(HCOO)10(C6H7N)6]n.

The structure of the complex, [Fe2(II)Fe2(III)(HCOO)10(C6H7N6)n, (1) exhibits a neutral two-dimensional layer network of alternating iron(II) and iron(III) ions, bridged equatorially by formate groups. All iron atoms are octahedrally coordinated, with iron(III) coordinating axially to one gamma-picoline and one formate group, while the iron(II) centers interact axially with two gamma-picoline groups, above and below the layer plane. The complex crystallizes in the triclinic space group P1 at all studied temperatures [at 120 K, the cell dimensions are: a = 10.228(1), b = 12.071(1), c = 12.072(1) A, alpha = 89.801(2), beta = 71.149(2), gamma = 73.371(2) degrees]. An intralayer antiferromagnetic exchange interaction of J = -2.8 cm(-1) between iron(II) and iron(III) was observed in the magnetic studies. Decreasing the temperature to close to 20 K causes a magnetic-ordering phenomenon to occur and a low-temperature phase with a long-range antiferromagnetic spin orientation appears. The magnetic phase transition was confirmed by M?ssbauer spectroscopic studies at temperatures above and below the critical temperature. Structural information of 1 from synchrotron X-ray diffraction data collected at room temperature and 16 K suggests that the antiferromagnetic ordering is caused by an enhanced pi-pi interaction between chi-picoline groups from adjacent layers.     

Hydrothermal synthesis in the system Ni(OH)(2)-NiSO(4): nuclear and magnetic structures and magnetic properties of Ni(3)(OH)(2)(SO(4))(2)(H(2)O)(2)

We present the synthesis, characterization by DT-TGA and IR, single crystal X-ray nuclear structure at 300 K, nuclear and magnetic structure from neutron powder diffraction on a deuterated sample at 1.4 K, and magnetic properties as a function of temperature and magnetic field of Ni(3)(OH)(2)(SO(4))(2)(H(2)O)(2). The structure is formed of chains, parallel to the c-axis, of edge-sharing Ni(1)O(6) octahedra, connected by the corners of Ni(2)O(6) octahedra to form corrugated sheets along the bc-plane. The sheets are connected to one another by the sulfate groups to form the 3D network. The magnetic properties measured by ac and dc magnetization, isothermal magnetization at 2 K, and heat capacity are characterized by a transition from a paramagnet (C = 3.954 emu K/mol and theta = -31 K) to a canted antiferromagnet at T(N) = 29 K with an estimated canting angle of 0.2-0.3 degrees. Deduced from powder neutron diffraction data, the magnetic structure is modeled by alternate pairs of Ni(1) within a chain having their moments pointing along [010] and [010], respectively. The moments of Ni(2) atoms are oppositely oriented with respect to their adjacent pairs. The resulting structure is that of a compensated arrangement of moments within one layer, comprising one ferromagnetic and three antiferromagnetic superexchange pathways between the nickel atoms.     

Structural study of the thermal and photochemical spin states in the spin crossover complex [Fe(phen)2(NCSe)2

The first structural data for [Fe(phen)(2)(NCSe)(2)] (obtained using the extraction method of sample preparation) in its high-spin, low-spin and LIESST induced metastable high-spin states have been recorded using synchrotron radiation single crystal diffraction. The space group for all of the spin states was found to be Pbcn. On cooling from the high-spin state (HS-1) at 292 K through the spin crossover at about 235 K to the low-spin state at 100 K (LS-1) the iron coordination environment changed to a more regular octahedral geometry and the Fe-N bond lengths decreased by 0.216 and 0.196 A (Fe-N(phen)) and 0.147 A (Fe-N(CSe)). When the low-spin state was illuminated with visible light at about 26 K, the structure of this LIESST induced metastable high-spin state (HS-2) was very similar to that of HS-1 with regards to the Fe-phen bond lengths, but there were some differences in the bond lengths in the Fe-NCSe unit between HS-1 and HS-2. When HS-2 was warmed in the dark to 50 K, the resultant low-spin state (LS-2) had an essentially identical structure to LS-1. In all spin states, all of the shortest intermolecular contacts (in terms of van der Waals radii) involved the NCSe ligand, which may be important in describing the cooperativity in the solid state. The quality of the samples was confirmed by magnetic susceptibility and IR measurements.     

Electron density distributions of redox active mixed valence carboxylate bridged trinuclear iron complexes

The electron density distributions (EDD) of the redox active mixed valence trinuclear oxo-centered iron carboxylate, [Fe(3)O(CH(2)ClCOO)(6)(H(2)O)(3)].3H(2)O, 1, and the oxidized form of 1, [Fe(3)O(CH(2)ClCOO)(6)(H(2)O)(2)(CH(2)ClCOO)].1H(2)O, 2, as well as of [Fe(3)O(C(CH(3))(3)COO)(6) (NC(5)H(5))(3)], 3, have been determined from accurate single-crystal X-ray diffraction data measured at 100 K (1, 2) and from extensive synchrotron radiation X-ray diffraction data measured at 28 K (3). Analysis of the EDDs shows that the central oxygen atom has a very different EDD in the mixed valence complexes (1 and 3) compared with the oxidized complex (2). Furthermore, in 1 and 3 the chemical bonds between formally identical trivalent Fe atoms and the central oxygen are fundamentally different. This is in direct contrast to the Fe(IIImicro(3)-O) bonds in the oxidized complex, which are practically identical. Analysis of the d-orbital populations on the metal sites in the three complexes shows that the extra electron density on the Fe(II) site primarily is distributed in a d(yz) orbital (z-axis toward the central oxygen, y-axis perpendicular to the Fe(3)O-plane). Presence of extra charge in the d(yz) orbital correlates with a decrease in the d(xy) population, i.e., with a depletion of charge in the equatorial region of coordination to carboxylate oxygen. The d(xy) charge depletion appears to be of importance for determining the active versus trapped Fe(III) site, and the equatorial ligands therefore have a considerable influence on the ET process. Bader topological analysis of the EDDs corroborates the conclusions drawn from the orbital population analysis, but it also provides additional knowledge about the chemical bonding in the structures. For comparison with the X-ray results, theoretical calculations were carried out for 3 in the experimental geometry. The present information about ET processes in trinuclear oxo-centered iron complexes cannot be deduced from analysis of the molecular structures (i.e., bond lengths and angles), and thus it is demonstrated that X-ray charge density analysis is able to reveal subtle new features of significant physical and chemical importance on complex molecular systems.     

Tetranuclear manganese(II) complexes of sulfonylcalix[4]arene macrocycles: synthesis, structure, spectroscopic and magnetic properties

Two tetranuclear manganese(II) complexes {K(+)[Mn(4)(ThiaSO(2))(2)(OH)](-)} (1) and {K(+)[Mn(4)(ThiaSO(2))(2)(F)](-)} (2) have been synthesized under solvothermal conditions in methanol with p-tert-butylsulfonylcalix[4]arene (ThiaSO(2)). For both complexes, the structure has been established from single-crystal X-ray diffraction. The two complexes are best described as manganese squares sandwiched between two thiacalixarene macrocycles. In both complexes, in the center of the square formed by the four manganese(II) atoms, the unexpected presence of μ(4)-OH(-) or μ(4)-F(-) gives a negative charge to the cluster. The two tetranuclear complexes exhibit strong orange luminescence behavior resulting from the symbiosis between the ThiaSO(2) and the Mn(2+). Despite similar chemical formulation, (1) and (2) present difference in emission intensity and lifetime τ.