Synthesis and X-ray structural characterization of tris(l-glycinato)vanadium(III) and trans-tetraquadichlorovanadium(III) chloride

Despite the importance of V^III in biology, only three V^III complexes of naturally occurring amino acids have been structurally characterized. We report the structure of the first vanadium complex incorporating a glycine ligand, [V(Gly)₃] · 2DMSO, which crystallizes in a monoclinic system with space group Cc, a = 8.9186(5) Å, b = 21.5347(9) Å, c = 9.9064(5) Å and β = 110.536(3)°. The X-ray structural data show the central V^III metal octahedrally coordinated by three bidentate glycinato ligands arranged a mer configuration, with both Δ and Λ enantiomers present in the unit cell. The bulk sample was isolated as [V(Gly)₃] · DMSO · NaCl. Structural comparisons are made with the corresponding homoleptic glycinato complexes of Co^III, Cr^III and Ni^II. The structure of trans-[V(OH₂)₄Cl₂]Cl · 2H₂O has also been re-determined. This latter complex crystallizes in a monoclinic system in the P2(1)/c space group, a = 6.4381(9) Å, b = 6.3843(9) Å, c = 11.7980(17) Å and β = 98.057(2)°. The vanadium atom lies at a crystallographic inversion centre within the distorted octahedron formed by the four water and two chloride ligands.     

On the structure of the N,N′-dimethylpropyleneurea and dimethylsulfoxide solvated gallium(III) and indium(III) ions and bromide complexes in solution and solid state, and the complex formation of the gallium(III) and indium(III) bromide systems in N,N′-dimethylpropyleneurea

The structures of the N,N′-dimethylpropyleneurea (DMPU) solvated gallium(III) and indium(III) ions have been determined in DMPU solution by means of EXAFS. The gallium(III) ion is five-coordinate with a mean Ga-O bond distance of 1.924(5) Å, while the larger indium(III) ion is octahedrally coordinated with a mean In-O bond distance of 2.146(3) Å. The complex formation equilibria in DMPU for the gallium(III) and indium(III) bromide systems have been studied calorimetrically at 298 K. Three relatively strong complexes are formed in the indium(III) bromide system in DMPU, whereas no stability constants could be established in the gallium(III) bromide system as the heats of complex formation were very close to zero. Gallium(III) bromide is present as DMPU solvated GaBr₃ complexes in solution with three equatorial Ga-Br bonds at 2.328(3) Å, and two Ga-O bonds at 1.92(3) Å in the apical positions of a distorted trigonal bipyramid. The DMPU solvated indium(III) bromide has the same configuration with a mean In-Br bond distance of 2.510(3) Å, and two In-O bonds at 2.201(6) Å. Indium(III) binds three bromides and three Me₂SO molecules through the oxygen atoms in octahedral fac-configuration with mean In-Br and In-O bond distances of 2.630(3) and 2.211(15) Å, respectively.     

A tridentate bis(pyrazolyl) ligand binds to Cu(II), without using the pyrazole group: a very unusual coordination mode of the ligand Hbdmpb, 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid

A new pyrazole-based ligand, namely 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid (Hbdmpb) was synthesised together with its copper complex Na[Cu(bdmpb)₂(OOCCH₃)H₂O] · 4H₂O. Both the free ligand and its Cu compound were fully characterised and their crystal structures were determined by X-ray analysis. The free-ligand molecular structure is uneventful. The Cu compound is highly unusual, as the pyrazole nitrogen atoms do not bind to the Cu ion. The copper(II) ion is coordinated by four nearly coplanar oxygen atoms from two dehydronated ligands bdmpb (CuO(1a) 1.942(4), CuO(1b) 1.933(4) Å), a monodentate acetate group (CuO(1) 1.927(3) Å) and a water molecule (CuO(1w) 1.937(4) Å). The nitrogen atoms of the pyrazole rings do not coordinate to the metal center, but instead are involved in strong intramolecular hydrogen bonds. The coordinated water molecule is strongly H-bonded to two pyrazole N atoms from two bdmpb ligands (N(12a) ? HO(1w) 2.762(7), N(12b) ? HO(1w) 2.774(7) Å). The other two pyrazole N atoms with a lone pair are hydrogen-bonded to water molecules in the lattice (N(22a) ? HO(2w) 2.763(7), N(22b) ? HO(6w) 2.892(7) Å). The sodium ion is six-coordinated by the oxygen atom O(2) of the acetato ligand and by five water molecules. The EPR spectrum recorded in the solid state shows a characteristic signal for an axial anisotropic S = 1/2 species. The spectrum recorded in methanol glass confirms the absence of the coordination of pyrazole nitrogen atoms to the copper centers.     

Manganese(II) complexes with croconate and 2-(2-pyridyl)imidazole ligands: Syntheses, X-ray structures and magnetic properties

The mixed-ligand complexes of manganese(II) of formula [Mn(pyim)₂(C₅O₅)] (1) and [Mn(pyim)(H₂O)(C₅O₅)]_n · 2.5nH₂O (2) [pyim = 2-(2-pyridyl)imidazole and  = croconate (dianion of 4,5-dihydroxy-4-cyclopentene-1,2,3-trione)] have been prepared and their structures determined by X-ray crystallographic methods. Compound 1 is a tris-chelated mononuclear complex where the manganese atom is six-coordinate: four nitrogen atoms from two pyim molecules and two oxygen atoms from a croconate group build a somewhat distorted octahedral surrounding around the metal atom. The resulting neutral mononuclear units are linked to each other through double bridges which are constituted by the imidazole N-H and the metal-coordinated croconate-oxygen atom, the metal-metal separation through this supramolecular pathway being 7.6856(11) Å. Compound 2 is a croconato-bridged manganese(II) uniform chain with an intrachain metal-metal distance of 7.5118(9) Å. A bidentate pyim group, a water molecule and four oxygen atoms from two bis-bidentate croconate ligands build an irregular seven-coordination polyhedron around each manganese atom in 2. The investigation of the magnetic properties of 2 in the temperature range 1.9-295 K has shown the occurrence of a weak antiferromagnetic interaction [J = −0.066 cm⁻¹ with the Hamiltonian defined as H = −J ∑_i S_i · S_i+1] through the bis-bidentate croconate. The ability of the bis-chelating croconate to mediante magnetic interactions between paramagnetic first-row transition metal ions is discussed and compared to that of the related oxalate ligand.     

Vanadium K-edge absorption spectrum of bromoperoxidase from Ascophyllum nodosum

With synchrotron radiation from the Bonn 2.5 GeV synchrotron, high-resolution absorption spectra have been measured at the vanadium K-edge of bromoperoxidase from the marine brown alga Ascophyllum nodosum and several model compounds. The near-edge structure (XANES) of these spectra was used to determine the charge state and the coordination geometry around the vanadium atom. For the active enzyme a coordination charge of 2.7 was found which is compatible with a formal valence of +5, assuming coordination by atoms with a high electronegativity such as oxygen or nitrogen. For the reduced enzyme the coordination charge value of 2.15 indicates the reduction of the valency by 1 unit. Our results suggest that the coordination sphere of the vanadium atom in the native enzyme consists of at least seven oxygen atoms in a distorted octahedral environment with an average bond length of about 2 A. Through the reduction process, the coordination sphere of the vanadium atom changes with a simultaneous decrease of the coordination cage. These results agree with those deduced from previous EPR and 51V-NMR measurements.     

Synthesis, crystal structure and electroluminescent properties of a Schiff base zinc complex

A new complex of zinc with a Schiff base, zinc(N,N′-bis(salicylidene)-3, 6-dioxa-1, 8-diaminooctane monohydrate) (ZnBSO · H₂O), was synthesized and characterized by means of elemental analyses, IR spectra and DTA-TG. Its structure was determined by X-ray single crystal analysis. It was demonstrated that the zinc atom is coordinated by the two oxygen atoms in phenolate and two nitrogen atoms in imine of the ligand in a slightly distorted tetrahedral geometry, while the two oxygen atoms from the oxa-alkyl chain are not coordinated to Zn(II) atom. The energy levels of the HOMO, LUMO and the electrochemical band gap were determined by cyclic voltammeter. The electroluminescent devices with the complex as the emitter showed bright blue emission with a peak at 450 nm, which is same as the fluorescence of the complex in both solution and solid states.     

Crystal structures of native and inactivated cis-3-chloroacrylic acid dehalogenase: Implications for the catalytic and inactivation mechanisms

The isomeric mixture of cis- and trans-1,3-dichloropropene constitutes the active component of a widely used nematocide known as Telone II®. The mixture is processed by various soil bacteria to acetaldehyde through the 1,3-dichloropropene catabolic pathway. The pathway relies on an isomer-specific hydrolytic dehalogenation reaction catalyzed by cis- or trans-3-chloroacrylic acid dehalogenase, known respectively as cis-CaaD and CaaD. Previous sequence analysis and crystallographic studies of the native and covalently modified enzymes identified Pro-1, His-28, Arg-70, Arg-73, Tyr-103, and Glu-114 as key binding and catalytic residues in cis-CaaD. Mutagenesis of these residues confirmed their importance to the dehalogenation reaction. Crystal structures of the native enzyme (2.01 Å resolution) and the enzyme covalently modified at the Pro-1 nitrogen by 2-hydroxypropanoate (1.65 Å resolution) are reported here. Both structures are at a resolution higher than previously reported (2.75 Å and 2.1 Å resolution, respectively). The conformation of the covalent adduct is strikingly different from that previously reported due to its interaction with a 7-residue loop (Thr-32 to Leu-38). The participation of another active site residue, Arg-117, in catalysis and inactivation was also examined. The implications of the combined findings for the mechanisms of catalysis and inactivation are discussed.     

Synthesis and crystal structure of a cobalt(II) coordination polymer constructed from 2,6-pyridinedicarboxylate anion and 1,3-bis(4-pyridyl)propane nitrogen ligand

The coordination polymer named {[Co(H₂O)₄(BPP)][Co(dipic)₂]·H₂O}_n (dipic = 2,6-pyridinedicarboxylate and BPP = 1,3-bis(4-pyridyl)propane) has been synthesized by the diffusion method and characterized by thermal analysis, vibrational spectroscopy and single crystal X-ray diffraction analysis. The compound is formed by an one-dimensional polymeric cationic chain, in which the BPP ligands connect the Co2 sites, and an anionic moiety formed by Co1 center and two dipic²⁻ anions. Both crystallographic independent metal sites adopt a distorted octahedral geometry. Co2 center is coordinated by two nitrogen atoms from BPP ligands and four oxygen atoms from aqua ligands, while Co1 center is coordinated by two nitrogen atoms and four oxygen atoms from two dipic²⁻ anions. The cationic and anionic moieties are connected through hydrogen bonding interactions leading to a 3D supramolecular array.     

A ferromagnetically coupled tetranuclear pseudo-cubane copper(II) cluster: magnetic and ESR studies

A tetranuclear copper(II) complex [Cu₄(NSI)₄] · 2C₂H₅OH · 2H₂O (NSI=hydroxethylsalicydeneimine) has been synthesized and characterized by X-ray diffraction analysis. The compound crystallizes in the monoclinic system, space group P2(1), a=9.494(3) Å, b=18.687(5) Å, c=13.149(4) Å, β=110.162(5)°, Z=2, R₁=0.0482 and wR₂=0.0978. The crystal structure contains a tetranuclear pseudo-cubane core based on an approximately cubane array of alternating copper and oxygen atoms. Each copper atom resides in a distorted square planar coordination environment with one nitrogen and three oxygen atoms from two NSI ligands. The tetranuclear units are linked in the crystal by O-H?O hydrogen bonds and weak Cu?O co-ordination bonds into one-dimensional structure. Variable temperature (5-300 K) magnetic measurements indicate the existence of ferromagnetic interactions among copper atoms. The IR and ESR spectra have also been investigated.     

Reactions and structures in the gallium(III)/indium(III)-N,N-dimethylthioformamide systems

The structure of the N,N-dimethylthioformamide (DMTF) solvated gallium(III) ion has been determined in solution by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. The gallium(III) ion is four-coordinate in tetrahedral fashion with a mean Ga-S bond distance of 2.233(2) Å in DMTF solution. At the dissolution of indium(III) perchlorate or trifluoromethanesulfonate in DMTF coordinated solvent molecules are partly reduced to sulfide ions, and a tetrameric complex with the composition [In₄S₄(SHN(CH₃)₂)₁₂]⁴⁺ is formed. The structure of the solid tetrameric complex in the perchlorate salt was solved with single crystal X-ray diffraction. Four indium(III) ions and four sulfide ions form a highly symmetric heterocubane structure where each indium binds three bridging sulfide ions and each sulfide ion binds three indium(III) ions with a mean In-S bond distance of 2.584(1) Å, and S-In-S angles of 90.3(1)°. Each indium(III) additionally binds three DMTF molecules at significantly longer mean In-S bond distance, 2.703(1) Å; the S-In-S angles are in the range 80.3-90.4°. Large angle X-ray scattering data on a DMTF solution of indium(III) trifluoromethanesulfonate show that the same tetrameric species characterized in the solid state is also present in solution, whereas the EXAFS measurements only give information about the In-S bond distances due to the short core hole lifetime.     

Silver dichloroacetate: A compound with weak Ag-Cl bonding interactions and an extraordinary range of Cl NQR frequencies

Silver complexes of halocarbons and silver salts of halogenated organic acids (for example, silver chloroacetate) often show secondary Ag?X bonding interactions and unusually low ³⁵Cl NQR frequencies, due to secondary bonding of chlorines to silver atoms. The crystal structure of silver dichloroacetate has been determined at 100 K and shows six crystallographically-inequivalent chlorines. The structure is built from Ag₂(OOCCHCl₂)₂ dimers, similar to those found in silver chloroacetate; in both compounds the dimers are linked by additional Ag-O and Ag-Cl bonds. In the structure of silver dichloroacetate, two distinct conformations of the dichloromethyl groups are present. Two chlorines have no silver neighbors closer than 3.50 Å; two bridge to one Ag atom each, at Ag?Cl secondary bond distances of 2.8203(4) and 3.0196(4) Å, and two are apical, coordinating to at least two Ag neighbors each, at longer bond distances of 3.1401 (3)-3.3704(4) Å. Such very long distances are nevertheless shorter than the sum of the van der Waals radii of silver and chlorine, ca. 3.45 Å.The ³⁵Cl NQR spectrum of silver dichloroacetate at 77 K shows six signals scattered over the broad range from 35.600 to 38.498 MHz. Their EFG asymmetry parameters η were measured by the Fourier analysis of the slow beats in the spin echo envelope of the NQR signal of polycrystalline samples. The two highest-frequency chlorines have relatively low η values, 0.075 and 0.106, as befits Cl atoms not coordinated to Ag, and are placed by their conformations far from the carboxylate plane. The two middle-frequency chlorines have higher η values, 0.167 and 0.168, as expected for bridging Cl atoms. The two low-frequency chlorines have lower η values of 0.114 and 0.129, as expected for apical Cl atoms. For purposes of comparison, η values for Ag₂(OOCCH₂Cl)₂, Na(OOCCH₂Cl), and Ca(OOCCH₂Cl)₂ · H₂O were also recorded. So far, we have not observed any significant effect on the ³⁵Cl NQR parameters of halogenated organic anions coordinated to hard-acid metal ions (K⁺, Rb⁺, Ca²⁺). The effects of the different conformations of the Cl₂CH groups on the broad NQR frequency range are also discussed.     

Synthesis, structure and redox properties of an unexpected trinuclear copper(II) complex with aspartame: [Cu(apm)2Cu(μ-N,O:O′-apm)2(H2O)Cu(apm)2(H2O)] · 5H2O

Structural, magnetic and spectroscopic data of a new trinuclear copper(II) complex with the ligand aspartame (apm) are described. [Cu(apm)₂Cu(μ-N,O:O′-apm)₂(H₂O)Cu(apm)₂(H₂O)] · 5H₂O crystallizes in the triclinic system, space group P1 (#1) with a = 7.3300(1) Å, b = 15.6840(1) Å, c = 21.5280(1) Å, α = 93.02(1)°, β = 93.21(1)°, γ = 92.66(1)° and Z = 1. Aspartame coordinates to Cu(II) through the carboxylate and β-amino groups. The carboxylate groups of the two central ligands act as bidentate bridges in a syn-anti conformation while the carboxylate groups of the four peripheral ligands are monodentate in a syn conformation. The central copper ion is in a distorted square pyramidal geometry with the apical position being occupied by one oxygen atom of the water molecule. The two terminal copper(II) atoms are coordinated to the ligands in the same position but their coordination sphere differs from each other due to the fact that one copper atom has a water molecule in an apical position leading to an octahedral coordination sphere while the other copper atom is exclusively coordinated to aspartame ligands forming a distorted square pyramidal coordination sphere. Thermal analysis is consistent with the X-ray structure. EPR spectra and CV curves indicate a rupture of the trinuclear framework when this complex is dissolved in ethanol or DMF, forming a mononuclear species, with a tetragonal structure.     

The synthesis and characterization of a cationic technetium nitrosyl complex: The X-ray crystal structure of [TcCl(NO)(DPPE)2](PF6) · CH2Cl2

The reaction of the ammonium pertechnetate with a stochiometric excess of hydroxylamine hydrochloride in methanol yields a nitrosyl containing intermediate which can subsequently be reacted with reducing ligands to form nitrosyl complexes in various oxidation states. The reaction with a sixfold excess of diphenyl-phosphinoethane (DPPE) yields the Tc(I) cation [TcCl(NO)(DPPE)₂]⁺ which can be precipitated cleanly with tetraphenylborate. The infrared spectrum displays an absorption at 1728 cm⁻¹ which corresponds to the nitrosyl group. The ESI(+) mass spectrum displays the parent ion [TcCl(NO)(DPPE)₂]⁺ as the only signal at 960 m/z.The X-ray crystal structure of the hexafluorophosphate salt shows a mutually trans arrangement of the nitrosyl and chloride ligands with the two bidentate phosphine ligands coordinated in the equatorial plane. The nitrosyl and chloride ligands display the usual site disorder which makes discussion of bond lengths tenuous. However, the Tc-N-O bond angle of 179.0(2)° reflects the sp hybridization of the nitrosyl nitrogen atom. The Tc-P bonds are somewhat elongated at 2.3810(6), 2.3947(6), 2.4096(5) and 2.4321(6) Å, due to the steric congestion around the metal ion. The Tc-Cl bond is unexceptional at 2.3262(7) Å. The coordination geometry of this complex is best described as a distorted octahedron.     

Coordination chemistry of acrylamide 3: Synthesis, crystal structure and IR spectroscopic properties of dichloro-tetrakis(O-acrylamide)copper(II), [Cu(O-OC(NH2)CHCH2)4Cl2]

The molecular structure of copper(II) chloride complex with acrylamide (AAmCH₂CHCONH₂), [Cu(AAm)₄Cl₂], was determined using X-ray diffraction analysis. The complex crystallizes in the cubic space group I-43d with a = 17. 8310(2) Å, β = 90°, and V = 5669.27(11) ų for Z = 12. The acrylamide molecules bind to the metal center via the carbonyl oxygen atom (Cu-O 1.996 Å). The coordination geometry of the metal center in the complex involves a tetragonally distorted octahedral structure with four O-donor atoms of acrylamide bonded in the equatorial positions and two chlorides in the apical positions. Comparison of crystal structure data of acrylamide and metal acrylamide complexes of those formed with divalent transition metal chlorides has been summarized.     

Synthesis, crystal structure and magnetic properties of a polynuclear Cu(II) complex: catena-poly[aqua(di-2-pyridylamine)copper(II)(μ-formato-O,O′)nitrate]

The synthesis, X-ray structure, spectroscopic and magnetic properties of a zig-zag formato-bridged chain complex with the formula [Cu(dpyam)(μ-O₂CH)(OH₂)]_n(NO₃)_n (1) (in which dpyam = di-2-pyridylamine) is described.The geometry of the copper(II) ion is distorted square pyramidal with a basal plane consisting of two nitrogen atoms of the dpyam ligand (Cu-N distances 1.987(3) and 2.010(3) Å) and two oxygen atoms of two different formato ligands (Cu-O distances 1.974(2) and 1.975(2) Å). A coordinated water molecule occupies the axial position at a distance of 2.222(3) Å. The copper atoms are bridged unsymmetrically by a formato anion in a syn-anti arrangement, resulting in a polymeric zig-zag chain structure.The magnetic susceptibility measurements (5-280 K) agree with a very weak ferromagnetic chain interaction between the Cu centres with a J value of 0.75 cm⁻¹.     

Pseudohalide supported mononuclear trans-Ni complexes of cationic and neutral dinitrogen heterocycles

Two mixed ligand complexes trans-[Ni(NCS)₄(PpzH)₂] (1) and trans-[Ni(NCO)₂(Imd)₄] (2) (where Ppz = piperazine; Imd = imidazole) were synthesized from one-pot reactions, and their crystal and molecular structures were determined. The reaction of NiCl₂·4H₂O with piperazine and KSCN in a 1:2:4 mole ratio in aqueous MeOH at room temperature under stirring condition affords 1. Whereas the reaction of NiCl₂·6H₂O with imidazole and NaOCN in a 1:4:2 mole ratio in aqueous MeOH at room temperature under stirring condition yields 2 quantitatively. The nickel ions are hexacoordinated by six nitrogen donor atoms of two different origin, thiocyanate and piperazinium ions in case of 1 and cyanate ion and neutral imidazole in case of 2, to form tetragonally elongated and quite regular octahedral arrangements. In 1, the average Ni-N_ppz distance is 2.198 Å is longer than the average Ni-N_thc distance at 2.070 Å, whereas, in case of 2, the average Ni-N_imd distance at 2.112 Å and is close to the average Ni-N_cyt distance at 2.107 Å. The reactions in other varying stoichiometries failed to provide the hitherto unknown complexes [Ni(NCS)₂(Ppz)₄] and [Ni(NCO)₄(ImdH)₂] confirming the ease of protonation on non-bonding of piperazine is more compared to that of imidazole.     

Synthesis, crystal structure and quantum study of organoammonium polyoxomolybdate with one-dimension chain containing face-shared molybdenum-oxygen octahedra

Organoammoinium polyoxomolybdate [(enH)₂(H₂Mo₆O₂₀)]_∞ was formed in autogeneous pressure at 160 °C for 120 h. The colorless crystals of polyoxomolybdate were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. The crystals are in monoclinic system with a space group P2₁/n and a = 8.0844(16), b = 14.413(3), c = 8.9153(18) Å, β = 98.12(3)°, V = 1013.8(4) ų, Z = 4. The final R = 0.0375, wR = 0.0706 for 2370 reflections [I > σ(I₀)].The crystals are constructed by one-dimension infinite inorganic chains with Mo₆O₂₀ unit as building block and protonated ethylenediamine cations located in between the inorganic chains. There are many hydrogen bonds between the chains and between the chains and the cations. IR spectrum of the title compound exhibited the vibration absorption of MoO, Mo-O-Mo bonds and protonated ethylenediamine cations, and suggests the presence of N-H-O and O-H-O hydrogen bonds. Quantum calculation gives the distribution of charges and the composition of frontier molecular orbits. From the calculation results, it can be inferred that protonation must have occurred on the terminal oxygen atom (O3) due to its smallest charge value and the terminal oxygen atom (O3) forms hydrogen bonds with the O12 atoms of the adjacent chain (2.936 Å); and that Mo1 atom will first receive the reduced electron. The electron transition taking place between HOMO and LUMO belongs basically to O → Mo charge transfer transition.     

Elucidations of the Catalytic Cycle of NADH-Cytochrome b5 Reductase by X-ray Crystallography: New Insights into Regulation of Efficient Electron Transfer

NADH-Cytochrome b₅ reductase (b5R), a flavoprotein consisting of NADH and flavin adenine dinucleotide (FAD) binding domains, catalyzes electron transfer from the two-electron carrier NADH to the one-electron carrier cytochrome b₅ (Cb5). The crystal structures of both the fully reduced form and the oxidized form of porcine liver b5R were determined. In the reduced b5R structure determined at 1.68 Å resolution, the relative configuration of the two domains was slightly shifted in comparison with that of the oxidized form. This shift resulted in an increase in the solvent-accessible surface area of FAD and created a new hydrogen-bonding interaction between the N5 atom of the isoalloxazine ring of FAD and the hydroxyl oxygen atom of Thr66, which is considered to be a key residue in the release of a proton from the N5 atom. The isoalloxazine ring of FAD in the reduced form is flat as in the oxidized form and stacked together with the nicotinamide ring of NAD⁺. Determination of the oxidized b5R structure, including the hydrogen atoms, determined at 0.78 Å resolution revealed the details of a hydrogen-bonding network from the N5 atom of FAD to His49 via Thr66. Both of the reduced and oxidized b5R structures explain how backflow in this catalytic cycle is prevented and the transfer of electrons to one-electron acceptors such as Cb5 is accelerated. Furthermore, crystallographic analysis by the cryo-trapping method suggests that re-oxidation follows a two-step mechanism. These results provide structural insights into the catalytic cycle of b5R.     

Asymmetric chlorine-bridged zig-zag Cu(II) chains linked together in 2D sheets by strong Watson-Crick type intermolecular double hydrogen bonds of bis(pyrimidin-2-yl)amine ligands: synthesis, structure and antiferromagnetism

A novel polymeric, asymmetric chloro-bridged copper chain with general formula [μ-Cl-CuCl(dipm]_n (in which dipm = bis(pyrimidin-2-yl)amine) has been synthesized and characterised by X-ray crystallography and infrared spectroscopy. The chains are organized in 2D sheets by intermolecular double H bonds between pairs of dipm molecules. In addition, EPR and magnetic measurements have been performed, and these have been related to the dinuclear structural details.The geometry around the copper(II) ion is distorted square pyramidal with the basal plane formed by the two nitrogen atoms of the dipm ligand and two chloride atoms, one of which is bridging. The Cu-N distances are 2.0342(15) and 2.0125(15) Å and Cu-Cl distances are 2.2899(6) and 2.2658(6) Å. The apical position of Cu is occupied by a chloride atom of a neighbouring unit atom at a distance of 2.6520(6) Å, resulting in the polynuclear array in which one chloride anion and the copper ion forms a zig-zag chain. The magnetic interaction between the Cu-Cu atoms is weak antiferromagnetic with a singlet-triplet separation (J) of −3.2(1) cm⁻¹.     

A structural study of the hydrated and the dimethylsulfoxide, N,N′-dimethylpropyleneurea, and N,N-dimethylthioformamide solvated iron(II) and iron(III) ions in solution and solid state

The structures of the solvated iron(II) and iron(III) ions have been studied in solution and solid state by extended X-ray absorption fine structure (EXAFS) in three oxygen donor solvents, water, dimethylsulfoxide (Me₂SO), N,N′-dimethylpropyleneurea (DMPU), and one sulfur donor solvent, N,N-dimethylthioformamide (DMTF); these solvents have different coordination and solvation properties. In addition, the structure of hexakis(dimethylsulfoxide)iron(III) perchlorate has been determined crystallographically to support the determination of the corresponding solvate in solution. The hydrated, the dimethylsulfoxide and N,N-dimethylthioformamide solvated iron(II) ions show regular octahedral coordination in both solution and solid state with mean Fe-O, Fe-O, and Fe-S bond distances of 2.10, 2.10, and 2.52 Å, respectively, whereas the N,N′-dimethylpropyleneurea iron(II) solvate is five-coordinated, d(Fe-O) = 2.06 Å. The compounds vary in color from light green (hydrate) to dark orange or red (DMPU). The hydrated iron(III) ion in aqueous solution and the dimethylsulfoxide solvated iron(III) ions in solution and solid state show the expected octahedral coordination, the Fe-O bond distances are 2.00 Å for both, whereas the N,N′-dimethylpropyleneurea iron(III) solvate is found to be five-coordinated with a mean Fe-O bond distance of 1.99 Å. The N,N-dimethylthioformamide solvated iron(III) ion in the solid perchlorate salt is tetrahedrally four-coordinated, the mean Fe-S bond distance is 2.20 Å. Iron(III) is reduced with time to iron(II) in N,N-dimethylthioformamide solution. The compounds vary in color from pale yellow (hydrate) to blackish red (DMPU).