Agnieszka Wojciechowska

Systematic investigation of the [Ni2+–phen–CrO42−] system; dichromate species isolated from alkaline solutions

Abstract Nickel(II) dichromate and chromate complexes with 1,10-phenanthroline were isolated from basic (pH 8–9) solutions. [Ni(phen)3]Cr2O7·8H2O (1), NiCrO4 (2), [Ni(phen)3]Cr2O7·3H2O (3) and [Ni(phen)(OCrO3)(H2O)3]·H2O (4) were characterized with spectroscopic (UV–Vis, IR, FIR) methods and one (4), additionally, with X-ray data. In the complex (4) the chromate ion is monodentately coordinated to nickel ion. This complex crystallizes in the triclinic crystal system (space group P 1 ). The single crystal electronic spectrum of complex (4) at 4 K reveals a rare feature when the structured second d–d band (Oh symmetry) is unsplit in spite of lowering symmetry. The filtration process has revealed that this band is vibronically structured in the νs NiOCr quantum. A new broad low intensity band at approximately 14 000 cm−1 was assigned to the forbidden transition in the bridge. An attempt to explain precipitation of dichromates from alkaline solutions has been given.

Synthetic models for the glucose tolerance factor: the spectroscopic characterization and toxicity studies of monomeric and dimeric Cr(III) species

Abstract A number of chromium(III) complexes with glycine, cysteine, glutamic and nicotinic acids-models for biologically active Cr(III) species have been prepared and characterized with physicochemical methods (UV\Vis, IR spectra, magnetic moments). Four of them have been also tested for their toxicity. On the basis of CF calculation it was found that only the nicotinates were octahedral Cr(III) species. Other complexes exhibited a tetragonal deformations. Based upon 10 Dq values, the sequence of the ligand field strength was found to be: glycine>cysteine≈glutamic acid>nicotinic acid. The likely structures were proposed for the isolated compounds. The preliminary toxicity studies showed that all tested complexes appeared to be non-toxic and can be potentially applied as chromium nutrition products.

Synthesis, crystal structure and spectroscopic characterisation of double salt [Zn(bpy)3](CrO4)0.5NO36.5H2O

Abstract A new Zn(II) complex with 2,2′bipyridine (bpy), chromate and nitrate groups, [Zn(bpy)3](CrO4)0.5NO36.5H2O has been prepared and characterised with crystallographic and spectroscopic methods. The orthorhombic complex crystallises in the space group Ccc2 with the lattice constants a=13.992(3) A , b=24.483(5) A , c=21.556(4) A and Z=8. The coordination environment about Zn(II) ion is nearly octahedral. The CrO42− and NO3− entities exhibit anionic position in the crystal. The electronic spectra enhanced with mathematical methods (filtration and deconvolution) exhibit the presence of vibrational fine structure in the CrO42− entity on the spin-forbidden 3T1 transition.

Dinuclear Metallacycles with Single M–X–M Bridges (X = Cl–, Br–; M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)): Strong Antiferromagnetic Superexchange Interactions

A series of monochloride-bridged, dinuclear metallacycles of the general formula [M2(μ-Cl)(μ-L)2](ClO4)3 have been prepared using the third-generation, ditopic bis(pyrazolyl)methane ligands L = m-bis[bis(1-pyrazolyl)methyl]benzene (Lm), M = Cu(II), Zn(II), and L = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*), M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II). These complexes were synthesized from the direct reactions of M(ClO4)2·6H2O, MCl2, and the ligand, Lm or Lm*, in the appropriate stoichiometric amounts. Three analogous complexes of the formula [M2(μ-Cl)(μ-L)2](BF4)3, L = Lm, M = Cu(II), and L = Lm*, M = Co(II), Cu(II), were prepared from the reaction of [M2(μ-F)(μ-L)2](BF4)3 and (CH3)3SiCl. The bromide-bridged complex [Cu2(μ-Br)(μ-Lm*)2](ClO4)3 was prepared by the first method. Three acyclic complexes, [Co2(μ-Lm)μ-Cl4], [Co2(μ-Lm*)Cl4], and [Co2(μ-Lm*)Br4], were also prepared. The structures of all [M2(μ-X)(μ-L)2]3+ (X = Cl-, Br-) complexes have two ditopic bis(pyrazolyl)methane ligands bridging two metals in a metallacyclic arrangement. The fifth coordination site of the distorted trigonal bipyramidal metal centers is filled by a bridging halide ligand that has an unusual linear or nearly linear M-X-M angle. The NMR spectra of [Zn2(μ-Cl)(μ-Lm*)2](ClO4)3 and especially [Cd2(μ-Cl)(μ-Lm*)2](ClO4)3 demonstrate that the metallacycle structure is maintained in solution. Solid state magnetic susceptibility data for the copper(II) compounds show very strong antiferromagnetic exchange interactions, with -J values of 536 cm-1 for [Cu2(μ-Cl)(μ-Lm)2](ClO4)3·xCH3CN, 720 cm-1 for [Cu2(μ-Cl)(μ-Lm*)2](ClO4)3, and 945 cm-1 for [Cu2(μ-Br)(μ-Lm*)2](ClO4)3·2CH3CN. Smaller but still substantial antiferromagnetic interactions are observed with other first row transition metals, with -J values of 98 cm-1 for [Ni2(μ-Cl)(μ-Lm*)2](ClO4)3, 55 cm-1 for [Co2(μ-Cl)(μ-Lm*)2](ClO4)3, and 34 cm-1 for [Fe2(μ-Cl)(μ-Lm*)2](ClO4)3. EPR spectra of [Cu2(μ-Cl)(μ-Lm*)2](BF4)3 confirm the dz2 ground state of copper(II). In addition, the sign of the zero-field splitting parameter D was determined to be positive for [Cu2(μ-F)(μ-Lm*)2](BF4)3. Electronic spectra of the copper(II) complexes as well as Mössbauer spectra of the iron(II) complexes were also studied in relation with the EPR spectra and magnetic properties, respectively. Density functional theory calculations were performed using ORCA, and exchange integral values were obtained that parallel but are slightly higher than the experimental values by about 30%.

Structural, spectroscopic, magnetic behavior and DFT investigations of L-tyrosinato nickel(II) coordination polymer

New 1D-coordination polymer {[Ni(L-Tyr)2(μ-4,4′-bpy)]·4H2O}n (1) (L-Tyr = L-tyrosine, 4,4′-bpy = 4,4′-bipyridine) is composed of L-tyrosinate anions chelated nickel(II) centres via N amino and O carboxylate atoms, whereas the apices of the elongated octahedral coordination sphere are occupied by the N atoms of 4,4′-bipyridine. Its molecular structure was determined by single-crystal X-ray diffraction and characterized using vibrational (FT-IR), Raman spectroscopy (FT-Raman), electronic (NIR-Vis-UV) and high field electron paramagnetic resonance (HF-EPR) spectroscopy and thermal (TG-DTA, DSC) and magnetic methods. The tetragonality distortion parameter (T) equals 0.945. The gx, gy and gz parameters (HF-EPR spectra) are slightly temperature dependent and the set gx = 2.178(5), gy = 2.156(4), gz = 2.19(1), D = −5.76(2) cm−1, E = −0.41(1) cm−1 was found at 5 K. The analysis of the temperature and field dependent magnetization shows the weakness of magnetic interactions in 1.

1–D Framework l-arginine zinc(II) units bridged by oxalate: synthesis, structure, properties, and theoretical studies

Abstract We synthesized a l-arginine containing Zn2+ complex and oxalate ions. {[Zn2(l-Arg)2(ox)2]·8H2O}n (1) (l-Arg  =l-arginine, ox  =  oxalate) crystallize in the monoclinic space group P21 with a  =  8.979(2), b  =  9.840(2) (Å), c  =  18.509(3) (Å), β  =  95.58(3) (Å), V  =  1627.6(6) Å3, and Z  =  2. The zinc centers are six-coordinate via one l-arginine zwitterion and two bridging oxalates. The binuclear [Zn2(l-Arg)2(ox)2] units are linked via oxalate and form 1-D “stair-like” linear chains. The complex was characterized using FT-IR, FT-Raman, UV–vis spectroscopy, and thermal analysis techniques, as well as DFT methods. Electronic bands above 31,000 cm−1 originate in 1,3Au (n→π*) transitions within oxalate ions. Theoretical studies were performed for the model compound {[Zn(l-Arg)(Hox)2]·4H2O} using the fragment of the crystallographic structure of 1. The interaction energy (ΔE) values for l-arginine and two oxalate ions are comparable at -145 kcal mol−1. Natural bond orbital (NBO) analysis of the electronic structure and bonding is also discussed.

Metal–organic framework in an L-arginine copper(II) ion polymer: structure, properties, theoretical studies and microbiological activity

A novel 1D polymeric copper(II) complex with L-arginine and a linear bridged 4,4′-bipyridine with a formula of {[Cu(L-Arg)2(μ-4,4′-bpy)]Cl2·3H2O}∞ (1) (where L-Arg = L-arginine, 4,4′-bpy = 4,4′-bipyridine) was synthesized. The crystal structure and properties of the product were characterized using X-ray diffraction, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), spectroscopic techniques (FT-IR, Raman, NIR-vis-UV electronic and EPR), magnetic methods, and microbiological examinations. The crystals of 1 crystallized in a trigonal system and a space group of P3221 was characterized with a = b = 12.31 A, c = 18.45 A, V = 2420 A3, Z = 3, α = β = 90° and γ = 120°. The N and O donor atoms of trans-chelated L-Arg zwitterions and two N atoms of the 4,4′-bpy molecule form a tetragonal distorted octahedral geometry around the copper(II) ions with static character (T = 0.748). The diffuse-reflectance electronic spectrum of 1 is characteristic of the [CuN2N′2O2] chromophore. The EPR spectrum of frozen 1 (at 77 K) dissolved in water is related to the N2O2 set (g⊥ = 2.057, g‖ = 2.258 and A‖ = 169 G). The structure of the [Cu(L-Arg)2(μ-4,4′-bpy)]2+ model complex was optimized at the B3LYP and B3LYP-D3 levels. The calculations of the atomic spin densities on the atoms in the doublet state of the model complex revealed that, with regard to the ligands, the spin population is distributed mainly over the oxygen and nitrogen atoms of L-arginine. The antimicrobial activities were examined against the Gram-positive and Gram-negative bacteria strains: Streptococcus mutans, Enterococcus hirae, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica, Shigella flexneri; and fungi: Saccharomyces cerevisiae, Candida albicans. Complex 1 exhibited strong antimicrobial activity against bacteria and fungi, both in their growth inhibition as well as in microbial killing.

Structural, spectroscopic and magnetic properties of a novel copper(II) L-tyrosinato complex

The complex [Cu(L-Tyr)2(H2O)]·H2O (1) (L-Tyr = L-tyrosine) was obtained as crystals and characterized by X-ray, spectroscopic (FT-IR, FT-Raman, NIR-vis-UV, and EPR) and magnetic methods. The monomeric complex crystallized in the monoclinic P21 symmetry with a = 11.967 (1) A, b = 5.9986 (4) A, c = 14.936 (1) A. The amino N and carboxylate O atoms of chelating L-tyrosinate anions together with the O atom of water molecules create a slightly distorted square pyramidal environment around the Cu(II) ions (τ = 0.11). The distance of about 5.998(1) A [Cu(L-Tyr)2(H2O)] units is involved in a polymeric chain based on N(1)–H⋯O(4)vi and N(2)–H⋯O(5)vi hydrogen bonds. The d–d band found in the polycrystalline-reflectance spectrum at 15 700 cm−1 is composed of three 2B1(dx2–y2) → 2A1 (dz2), 2B1 → 2B2(dxy) and 2B1 → 2E (dxz ≈ dyz) transitions with energies 14 880, 15 800 and 19 950 cm−1, respectively. In DMSO solution the complex preserves its square pyramidal geometry as evidenced by an intensive band at ca. 16 400 cm−1. The EPR spectral parameters for powder (g‖ = 2.236 and g⊥ = 2.063) and DMSO frozen solution (g‖ = 2.250, g⊥ = 2.055, and A‖ = 180 G) correspond to an axial symmetry of the Cu(II) coordination geometry with the dx2–y2 orbital as a ground state of the unpaired electron. Furthermore, the frozen solution spectrum revealed signals corresponding to S = 1 spin states of Cu(II) ions coupled by dipole–dipole interactions with distinctly resolved hyperfine splitting due to two copper nuclei (|D| = 0.0468 cm−1, g‖ = 2.238, g⊥ = 2.06 and A‖ = 85 G). The variable-temperature magnetic susceptibility measurements revealed the existence of a weak ferromagnetic interaction between neighboring copper(II) ions through the N–H⋯O hydrogen bonds.

1D Co(II) coordination polymers based on cyclobutyl- and cyclopentyl-substituted zoledronate analogues: synthesis, structural comparison, thermal stability and magnetic properties

Two novel derivatives of zoledronic acid (1-hydroxy-2-[1-(1H-imidazol-1-yl)cyclobutyl]ethylidene-1,1-diphosphonic acid (H4cbtZol) and 1-hydroxy-2-[1-(1H-imidazol-1-yl)cyclopentyl]ethylidene-1,1-diphosphonic acid (H4cptZol)) were synthesized, crystallized from water solutions as H4cbtZol·H2O (1) and H4cptZol·4H2O (2), and characterized by single-crystal X-ray diffraction. The reactions of H4cbtZol and H4cptZol with acetate or sulphate Co(II) salts, carried out under hydrothermal conditions, afforded Co3(HcbtZol)2(H2O)6·6H2O (1a), being isomorphous with recently reported Co(II)/Ni(II) complexes based on HdmtZol3− and HcppZol3− anions, and Co3(HcptZol)2(H2O)4·2H2O (2a). Both 1a and 2a were characterized by means of X-ray crystallography, IR and NIR-Vis-UV spectroscopic methods. Furthermore, their thermal stabilities and magnetic properties were compared. Compounds 1a and 2a comprise 1D polymeric chains with crystallographically and spectroscopically distinct six-coordinated Co1 and Co2 centers, which differ in architectures. In 1a, the chains feature alternately arranged [Co2(HcbtZol)(H2O)2]2 and {Co1O6} units. The chains of 2a are constructed from dinuclear [Co2(HcptZol)(H2O)2]2 units built up from symmetry related edge-sharing {Co2O6} octahedrons, extended by corner-sharing {Co1O6} octahedrons, which results in higher rigidity imposed on trinuclear units and shorter Co2⋯Co2 and Co1⋯Co2 distances as compared to 1a. The crystal field parameters Dq, Ds, Dt and B of 798 cm−1, 450 cm−1, −75 cm−1 and 857 cm−1 for 1a and 644 cm−1, 509 cm−1, −146 cm−1 and 902 cm−1 for 2a revealed that the {Co2O6} octahedron of 2a exhibits a larger tetragonal distortion as compared to 1a, despite the nearly identical values of the tetragonality T parameter (1.07 for 2a and 1.06 for 1a). These differences are reflected in the thermal and magnetic behaviors of 1a and 2a. In particular, compound 2a is more stable than 1a, retaining thermal stability up to 208 °C. On the other hand, its dehydration is a one-stage process, accompanied by simultaneous destruction of its 1D architecture and immediate elimination and decomposition of ligands. The analysis of magnetic properties revealed the existence of competing interactions, with the predominant participation of antiferromagnetic interactions in 1a (spin-3/2 Heisenberg trimer chain) and ferromagnetic interactions in 2a (spin-1/2 Ising diamond chain).