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A series of seven novel salts of tetrachloro- and tetrabromosemiquinone radical anions with organic cations is prepared and structurally characterised by single-crystal X-ray diffraction. Four types of stacks of radical anions have been identified: i) stacks of pancake-bonded dimers (Peierls-distorted stacks), ii) stacks of pancake-bonded trimers, iii) stacks of equidistant radicals and iv) a novel type of equidistant stacks of partially charged radicals (charge: −1/2, imposed by a stoichiometry of 1 : 2). Cations play an important role in stabilisation of the stacks of radical anions; the structures with stacks of equidistant radicals include columns of cations. However, the structures having pancake-bonded dimers and trimers are accompanied by isolated pairs of cations. [ABSTRACT FROM AUTHOR]

The covalent nature of strong N−Br⋅⋅⋅N halogen bonds in a cocrystal (2) of N‐bromosuccinimide (NBS) with 3,5‐dimethylpyridine (lut) was determined from X‐ray charge density studies and compared to a weak N−Br⋅⋅⋅O halogen bond in pure crystalline NBS (1) and a covalent bond in bis(3‐methylpyridine)bromonium cation (in its perchlorate salt (3). In 2, the donor N−Br bond is elongated by 0.0954 Å, while the Br⋅⋅⋅acceptor distance of 2.3194(4) is 1.08 Å shorter than the sum of the van der Waals radii. A maximum electron density of 0.38 e Å−3 along the Br⋅⋅⋅N halogen bond indicates a considerable covalent contribution to the total interaction. This value is intermediate to 0.067 e Å−3 for the Br⋅⋅⋅O contact in 1, and approximately 0.7 e Å−3 in both N−Br bonds of the bromonium cation in 3. A calculation of the natural bond order charges of the contact atoms, and the σ*(N1−Br) population of NBS as a function of distance between NBS and lut, have shown that charge transfer becomes significant at a Br⋅⋅⋅N distance below about 3 Å. [ABSTRACT FROM AUTHOR]

Three heterometallic one-dimensional (1D) coordination polymers {A[CrCu2(bpy)2(C2O4)4]·H2O}n [A = K+ (1) and NH4+ (2); bpy = 2,2′-bipyridine] and [(Cr2O7)Cu2(C2O4)(phen)2]n (3; phen = 1,10-phenanthroline) with uncommon topology have been synthesized using a building block approach and characterized by single-crystal X-ray diffraction, IR and impedance spectroscopies, magnetization measurements, and DFT calculations. Due to the partial decomposition of the building block [Cr(C2O4)3]3−, all three compounds contain oxalate-bridged [Cu2(L)2(μ-C2O4)]2+ units [L = bpy (1 and 2) and phen (3)]. In compounds 1 and 2 these cations are mutually connected through oxalate groups from [Cr(C2O4)3]3−, thus forming ladder-like topologies. Unusually, three different bridging modes of the oxalate ligand are observed in these chains. In compound 3 copper(ii) ions from cationic units are bridged through the oxygen atoms of Cr2O72− anions in a novel ladder-like mode. Very strong antiferromagnetic coupling observed in all three compounds, determined from the magnetization measurements and confirmed by DFT calculations (J = −343, −371 and −340 cm−1 for 1, 2 and 3, respectively), appears between two copper(ii) ions interacting through the oxalate bridge. [ABSTRACT FROM AUTHOR]

Three heterometallic one-dimensional (1D) coordination polymers {A[CrCu2(bpy)2(C2O4)4]·H2O}n [A = K+ (1) and NH4+ (2); bpy = 2,2′-bipyridine] and [(Cr2O7)Cu2(C2O4)(phen)2]n (3; phen = 1,10-phenanthroline) with uncommon topology have been synthesized using a building block approach and characterized by single-crystal X-ray diffraction, IR and impedance spectroscopies, magnetization measurements, and DFT calculations. Due to the partial decomposition of the building block [Cr(C2O4)3]3−, all three compounds contain oxalate-bridged [Cu2(L)2(μ-C2O4)]2+ units [L = bpy (1 and 2) and phen (3)]. In compounds 1 and 2 these cations are mutually connected through oxalate groups from [Cr(C2O4)3]3−, thus forming ladder-like topologies. Unusually, three different bridging modes of the oxalate ligand are observed in these chains. In compound 3 copper(ii) ions from cationic units are bridged through the oxygen atoms of Cr2O72− anions in a novel ladder-like mode. Very strong antiferromagnetic coupling observed in all three compounds, determined from the magnetization measurements and confirmed by DFT calculations (J = −343, −371 and −340 cm−1 for 1, 2 and 3, respectively), appears between two copper(ii) ions interacting through the oxalate bridge. [ABSTRACT FROM AUTHOR]

The charge density of the Zundel cation in the crystal of 2[H5O2]+[C6O8N2]2−·4H2O is studied by X-ray diffraction and periodic DFT calculations. The covalent nature of the central O–H–O bonds in the Zundel cation is revealed: the electron density at the two O–H critical points is about 1.0 e Å−3, corresponding to a three-centre, two-electron system. The bond orders derived from the topology of the electron density are 0.27–0.41, which are more similar to those of single O–H bonds (bond order 0.45–0.51) than those of H…O hydrogen bonds (bond orders = 0.05–0.10). [ABSTRACT FROM AUTHOR]

A series of eight novel complexes of chloranilic acid (CA) with the first-row transition metals (M = Mn, Cr, Ni, Co) were prepared and characterised by single-crystal X-ray diffraction, IR spectroscopy and polycrystalline X-band electron spin resonance (ESR) spectroscopy. All studied complexes revealed distorted octahedral arrangements. Three coordination modes of the chloranilate ligand are observed: bidentate, bis(bidentate) and, a novel one, mono+bidentate bridging, which can easily be distinguished by IR spectra. The size of the metal atom and different modes of chloranilate coordination affect crystal-packing topologies: 0D (mononuclear or dinuclear) and 1D (zig-zag chains or ladder-like chains). However, the ancillary ligands have a minor influence on the topology of the systems studied. [ABSTRACT FROM AUTHOR]

A new method for the synthesis of marine alkaloids leucettamines B and C from Leucetta sp. sponges is described. The key step is the base-promoted rearrangement of β -lactam into imidazolone ring. Leucettamines B and C as well as their N-benzoyl derivatives were obtained in high yields. Single-crystal structures of both leucettamines B and C were determined by X-ray diffraction confirming Z-configuration of double bond at 4-position of imidazolone. [ABSTRACT FROM AUTHOR]

A heterometallic coordination polymer {[Cu(bpy)3][Mn2(C2O4)3]·H2O}n (1; bpy = 2,2′-bipyridine) was synthesized using a building-block approach and characterized by IR spectroscopy, single-crystal X-ray diffraction, magnetization measurement, and X-band ESR spectroscopy both on a single crystal and a polycrystalline sample. The molecular structure of 1 is made of a three-dimensional (3D) anionic network [Mn2(C2O4)3]n2n− and tris-chelated cations [Cu(bpy)3]2+ occupying the vacancies of the framework. In compound 1 magnetic order is confirmed below 12.8 K – magnetization measurements reveal an antiferromagnetic-like network of canted Mn2+ spins with incorporated paramagnetic Cu2+ centres. The ESR spectroscopy distinctly shows the phase transition; above T≈ 13 K, single isotropic Lorentzian lines of Mn2+ ions in the high spin state S = 5/2 were observed, while below this temperature, only characteristic Cu2+ signals from cations were detected. Thermal decomposition residues of 1 at different temperatures (800–1000 °C) were analyzed by powder X-ray diffraction; by heating the sample up to 1000 °C the spinel oxide CuMn2O4 [94.1(2) wt%] was formed. From the refined structural parameters, it could be seen that the obtained spinel is characterized by the inversion parameter δ∼ 0.8, and therefore the structural formula at room temperature can be written as tet[Cu0.17Mn0.83]oct[Mn1.17Cu0.83]O4. [ABSTRACT FROM AUTHOR]

The nature of interactions between face-to-face staggered stacked quinoid rings with π-systems, observed with a short inter-ring centroid…centroid distance, is analyzed by experimental and theoretical methods. Charge density studies based on X-ray diffraction and DFT calculations, complemented by impedance spectroscopy, were employed to define the electronic and structural characteristics of the quinoid rings responsible for their interactions within the crystal packing. The crystal packing is mainly stabilized by strong electrostatic interactions between the K+ cation and the hydrogen chloranilate anion. The proximity and orientation of the stacked quinoid rings in parallel glide-plane arrangement are partly governed by the non-covalent interactions within the dimer. The estimated contribution of dispersion energy to the stacking of the rings about −10 kcal mol−1, as calculated by DFT methods, is comparable to medium–strong hydrogen bonding. The electronic structure of 3,6-dichloro-2,5-dihydroxyquinone monoanion exhibits alternating electron-rich and electron-poor regions. The calculated electrostatic energy shows variations with the relative orientation of rings within dimers reaching ca. 10–15 kcal mol−1. Thus, the nature of interactions between π-systems of quinoid rings can be described by a polar/π model where electrostatic complementarity plays a determinant role in π-stacking orientation. These interactions have great potential in crystal engineering and may be employed in the design of functional materials. [ABSTRACT FROM AUTHOR]

2012/2013 mark the 100th anniversary of von Laue's diffraction of X‐rays from single crystals of copper sulfate, the postulation of Bragg's law, and the solution of the first X‐ray structure. However, even before 1912, the study of crystals was an integral part of chemistry and it played a major role in development of modern chemical science, including key concepts such as atoms, molecules, isomerism, and chirality. [ABSTRACT FROM AUTHOR]

A series of alkali salts of hydrogen bromanilic acid trihydrates (K+, Rb+ and Cs+, potassium, rubidium and caesium 2,5-dibromo-4-hydroxy-3,6-dioxocyclohexa-1,4-dien-1-olate trihydrate), bromanilic acid tetrahydrate (Na+, disodium 2,5-dibromo-3,6-dioxocyclohexa-1,4-diene-1,4-diolate tetrahydrate) and bromanilic acid dihydrates (K+, Rb+ and Cs+, dipotasium, dirubidium and dicaesium 2,5-dibromo-3,6-dioxocyclohexa-1,4-diene-1,4-diolate dihydrate) were prepared and studied by single-crystal X-ray diffraction. Their crystal packings are dominated by quinoid ring stacking. The monoanionic quinoid rings pack face-to-face without offset and with short centroid separations (3.25-3.30 Å), while the dianionic rings form offset stacks (1.4-1.8 Å) with a larger centroid separation (3.8-4.1 Å). [ABSTRACT FROM AUTHOR]

Similarities and differences between the structures of two solvates, heterometallic complex salts, [CuCl(phen) 2 ][Cu(H 2 O)(phen) 2 ][Cr(C 2 O 4) 3 ]· n H 2 O [ n = 5 (1) and n = 8 (2); phen = 1,10-phenanthroline] prepared using [Cr(C 2 O 4) 3 ]3- as a building block were reported. The degree of trigonality, τ, was calculated for the copper(II) atoms in compounds 1 and 2. In the presence of [NBu 4 ]+ partial decomposition of the building block [Cr(C 2 O 4) 3 ]3− occurred, and the homobinuclear oxalate-bridged complex [{Cu(bpy)Cl} 2 (µ -C 2 O 4)]·CH 3 OH (3 ; bpy = 2,2 ' -bipyridine) was formed. Compounds 1–3 were characterized by IR spectroscopy and single-crystal X-ray diffraction. [Display omitted] Two heterometallic complex salts, as polymorphs of a solvate, consisting of three different mononuclear units, [CuCl(phen) 2 ][Cu(H 2 O)(phen) 2 ][Cr(C 2 O 4) 3 ]· n H 2 O [ n = 5 (1) and n = 8 (2); phen = 1,10-phenanthroline] were obtained in reactions in which [Cr(C 2 O 4) 3 ]3− was used as a building unit. The polymorphs of a solvate are obtained in crystalline forms that differ in type or stoichiometry of included solvent molecules, mostly obtained under different conditions. In this [CuIICrIII] system, the used solvents and crystallization method influence the final product, i.e., the formation of a specific solvatomorph. From the reaction of an aqueous solution of K 3 [Cr(C 2 O 4) 3 ]·3H 2 O and acetonitrile solutions containing phen and CuCl 2 ·2H 2 O, compound 1 was formed when the layering technique is used; and compound 2 can be obtained from the mixture of these reactants, but using methanol instead of acetonitrile. Based on the index parameter for the degree of trigonality, τ , the geometry of copper(II) atoms of the [Cu(H 2 O)(phen) 2 ]2+ cations in 1 and 2 are distorted from square pyramidal toward trigonal bipyramidal conformation, while those of [CuCl(phen) 2 ]+ have a trigonal bipyramidal geometry. Interestingly, in the presence of [NBu 4 ]+ cations, and applying slow liquid diffusion, partial decomposition of the building block [Cr(C 2 O 4) 3 ]3− occurred and the homobinuclear oxalate-bridged complex [{Cu(bpy)Cl} 2 (µ -C 2 O 4)]·CH 3 OH (3 ; bpy = 2,2 ′ -bipyridine) was formed. Consequently, the oxalate ligand released from the coordination sphere of CrIII was coordinated to CuII ions during the crystallization process. The obtained oxalate-based compounds 1 – 3 were characterized by IR spectroscopy and single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

Semiquinone ( p-benzosemiquinone), a transient organic radical, was detected in the solid state by EPR spectroscopy revealing four symmetrically equivalent protons. A variable-temperature X-ray diffraction analysis (293 and 90 K) and EPR data support a dynamical disorder of the proton. A low-barrier O—H···O hydrogen bond stabilizes the radical. The C—O bond length is 1.297 (4) Å, corresponding to a bond order of ca 1.5. The geometry of the radical implies an electron delocalization throughout the benzenoid ring. Two polymorphs of semiquinone, monoclinic and triclinic, were observed and their structures determined. Their crystal packings were compared with those of quinhydrone polymorphs. [ABSTRACT FROM AUTHOR]

Abstract: In this article we present a detailed structural investigation for the configurational isomers of PCU-hydrazones. The structural characterization of these hydrazones was performed using NMR spectroscopy, X-ray diffraction analysis and theoretical calculations. The single crystal X-ray structures of PCU-hydrazones 6B and 6C have been solved and used to conclusively confirm the characterization obtained via NMR spectra of a particular isomer. Nuclear magnetic shielding values calculated for 6A–C using DFT calculations were correlated with the experimentally determined chemical shifts. The computed results were found to be in good agreement with the observed 13C NMR values. The computed NMR results helped to ascertain the isomers of PCU-hydrazones 4A–C. [Copyright &y& Elsevier]

A series of doubly cyclopalladated complexes of azobenzene and its unsymmetrical substituted derivatives, namely, (LPdCI(u-AZB)LPdCI), where AZB is azobenzene, 4-methylazobenzene, 4-aminoazobenzene, or 4-(dimethylamino)- 4'-nitroazobenzene, while L is N,N-dimethylformamide, dimethylsulfoxide, or pyridine, have been prepared. Their structural and spectroscopic properties were determined by X-ray diffraction analysis as well as by 1H NMR, IR, UV-vis, and fluorimetric studies. Experimental results were rationalized by quantum chemical calculations. Crystal structures of several complexes have been resolved, and for the first time, it was demonstrated that the cyclopalladation may take place at the azobenzene aromatic ring having the strong electron-withdrawing substituent at the para position. In all cases, the metalated carbon and N,N-dimethylformamide or dimethylsulfoxide ligands are mutually trans, whereas the pyridine ligands are in the cis arrangement. cis/trans isomerism in the isolated compounds is explained by comparing the calculated energies of isomeric structures. All of the complexes absorb strongly in the visible region, and according to time-dependent density functional theory calculations, most of the absorptions can be attributed to intraligand c or metal-to-ligand charge-transfer transitions. The fluorescence emission was observed for the complexes with 4-aminoazobenzene or 4-(dimethylamino)-4'-nitroazobenzene. The aromaticity of palladacycles is evaluated by several aromaticity indices and related to relevant experimental findings. [ABSTRACT FROM AUTHOR]

A heterometallic coordination polymer {[Cu(bpy)3][Mn2(C2O4)3]·H2O}n (1; bpy = 2,2′-bipyridine) was synthesized using a building-block approach and characterized by IR spectroscopy, single-crystal X-ray diffraction, magnetization measurement, and X-band ESR spectroscopy both on a single crystal and a polycrystalline sample. The molecular structure of 1 is made of a three-dimensional (3D) anionic network [Mn2(C2O4)3]n2n− and tris-chelated cations [Cu(bpy)3]2+ occupying the vacancies of the framework. In compound 1 magnetic order is confirmed below 12.8 K – magnetization measurements reveal an antiferromagnetic-like network of canted Mn2+ spins with incorporated paramagnetic Cu2+ centres. The ESR spectroscopy distinctly shows the phase transition; above T≈ 13 K, single isotropic Lorentzian lines of Mn2+ ions in the high spin state S = 5/2 were observed, while below this temperature, only characteristic Cu2+ signals from cations were detected. Thermal decomposition residues of 1 at different temperatures (800–1000 °C) were analyzed by powder X-ray diffraction; by heating the sample up to 1000 °C the spinel oxide CuMn2O4 [94.1(2) wt%] was formed. From the refined structural parameters, it could be seen that the obtained spinel is characterized by the inversion parameter δ∼ 0.8, and therefore the structural formula at room temperature can be written as tet[Cu0.17Mn0.83]oct[Mn1.17Cu0.83]O4. [ABSTRACT FROM AUTHOR]

A novel heterometallic oxalate-based compound of the formula {[Co(bpy)3][Mn2(C2O4)3]·H2O}n (1; bpy = 2,2'-bipyridine) was synthesized and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), and magnetization measurement. The molecular structure of 1 is made of a three-dimensional (3D) anionic network, [Mn2(C2O4)3]n2n-, and tris-chelated cations [Co(bpy)3]2+ occupying the vacancies of the framework. Splitting between the zero-field-cooled (ZFC) and field-cooled (FC) branches of susceptibility below the small peak at 13 K indicates magnetic ordering. Compound 1 was used as a single-source precursor for the formation of the mixed-metal oxide CoMn2O4. This conversion via thermal decomposition was explored by thermal analysis (TGA and DTA), IR spectroscopy, powder XRD, and magnetic susceptibility measurement. From refined structural parameters, it could be seen that the spinel obtained by the thermal treatment of 1 at 800 °C is characterized by the inversion parameter ε = 21%, and therefore the structural formula at room temperature can be written as tet[Co0.79Mn0.21]oct[Co0.105Mn0.895]2O4. The temperature dependence of magnetization for CoMn2O4 points to at least three magnetic phases: the ferrimagnetic state is observed below 83 K, and up to 180 K blocking of the magnetic moments of nanocrystallites of 31 nm appears, transforming to paramagnetic-like behavior above 180 K. Microstructural characterization of the CoMn2O4 sample was carried out by means of XRD line-broadening analysis. [ABSTRACT FROM AUTHOR]