X-ray K-absorption spectrum of cobalt in some cobalt complexes

The X-ray K-absorption edge of cobalt in some cobalt (II) and cobalt (III) complexes has been investigated using a 400 mm bent crystal spectrometer. The structure associated with the absorption edge has been used to deduce information regarding the bond lengths, the mode of bonding and the coordination of cobalt in complexes. On the basis of the results obtained, it has been concluded that Co ions are surrounded by distorted octahedra in Co^II(Saltn)(H₂O)₂, Co^III(acac)(Saltn) whereas Co ions in Co^II(Salbn) have a tetrahedral structure and Co ions in Co^II(SalHn) have pseudotetrahedral structure. All the compounds exhibit slight ionic character.     

Synthesis,crystal structure,and magnetic properties of a new end-to-end thiocyanato-bridged dicobalt(II) complex CoII(dien)(H2O)(NCS)(μ1,3-NCS)CoII(dien)(NCS)2 (dien = diethylenetriamine)

Synthesis, characterization, crystal structure, and magnetic properties of the first single µ_1,3-thiocyanato-bridged dicobalt(II) compound, [Co^II(dien)(H₂O)(NCS)(µ_1,3-NCS)Co^II(dien)(NCS)₂] (1; dien = diethylenetriamine), are described. In 1, cobalt(II) is six coordinate with distorted-octahedral geometry. The Co(1) ··· Co(2) distance is 5.99 Å. The magnetic properties of 1 have been investigated by variable-temperature magnetic susceptibility measurements. The metal centers are coupled by weak ferromagnetic interaction (J = 1.14 cm^?1). The structure and magnetic properties are compared with related thiocyanate-bridged compounds.     

Cobalt(II) and Cobalt(III) Tri‐tert‐butoxysilanethiolates. Synthesis,Properties, Crystal and Molecular Structures of [Co{μ‐SSi(OBut)3}{SSi(OBut)3}(NH3)]2 and [Co{SSi(OBut)3}2(NH3)4][SSi(OBut)3] Complexes

The heteroleptic neutral tri‐tert‐butoxysilanethiolate of cobalt(II) incorporating ammonia as additional ligand ( 1 ) has been prepared by the reaction of a cobalt(II) ammine complex with tri‐tert‐butoxysilanethiol in water. Complex 1 , dissolved in hexane, undergoes oxidation in an ammonia saturated atmosphere to the ionic cobalt(III) compound 2 . Molecular and crystal structures of 1 and 2 have been determined by single crystal X‐ray structural analysis. 1 forms a dimeric molecule [Co{μ‐SSi(OBu^t)₃}{SSi(OBu^t)₃}(NH₃)]₂ with a folded central Co₂S₂ ring and distorted tetrahedral ligand arrangement at both Co^II atoms (CoNS₃ core). The product 2 is composed of the octahedral Co^III complex cation [Co{SSi(OBu^t)₃}₂(NH₃)₄]⁺ and the tri‐tert‐butoxysilanethiolate anion. Within the crystal two pairs of ions interact by hydrogen bonds forming well separated entities. 1 and 2 are the first structurally characterized cobalt thiolates where metal is also bonded to ammonia and 2 is the first cobalt(III) silanethiolate.     

Breathing Effect in a Cobalt Phosphonate upon Dehydration/Rehydration: A Single‐Crystal‐to‐Single‐Crystal Study

Two cobalt phosphonates, [Co₂(2,2′‐bpy)₂(H₂O)(pbtcH)] ( 1 ) and [Co₂(H₂O)(pbtcH)(phen)₂] ( 2 ; pbtcH₅=5‐phosphonatophenyl‐1,2,4‐tricarboxylic acid, 2,2′‐bpy=2,2′‐bipyridine, phen=1,10‐phenanthroline), with layer structures are reported. Compound 1 contains O‐C‐O and O‐P‐O bridged tetramers of Co₄, which are further connected by pbtcH^4? units to form a layer. In compound 2 , the cobalt tetramers made up of water‐bridged Co₂ dimers and O‐P‐O linkages are connected into a layer by pbtcH^4? units. Upon dehydration, compounds 1 and 2 experience single‐crystal‐to‐single‐crystal (SC–SC) structural transformations to form [Co₂(2,2′‐bpy)₂(pbtcH)] ( 1 a ) and [Co₂(pbtcH)(phen)₂] ( 2 a ), respectively. The process is reversible in each case. Notably, a breathing effect is observed for 1 , accompanied by pore opening and closing due to the reorientation of the coordinated 2,2′‐bpy molecules. The transformation was also monitored by in situ IR measurements. Magnetic studies reveal that antiferromagnetic interactions are mediated between the magnetic centers in compounds 1 and 1 a , whereas ferromagnetic interactions are dominant in compound 2 .     

Synthesis,growth, structure and characterization of nickel(II)-doped hexaaquacobalt(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate crystals

Single crystals of K₂[Co_(1−x)Ni_x(H₂O)₆] (C₈H₅O₄)₄·4H₂O (x = 0.25) (PCNHP), a semiorganic black colored transparent crystal of size ∼20 × 13 × 4 mm³, are grown from an aqueous solution of potassium hydrogen phthalate enriched with cobalt chloride and nickel chloride by slow evaporation solution growth technique at room temperature. Structural analysis by single crystal X-ray diffraction reveals that the crystal belongs to monoclinic system with space group P2₁/c and the cell parameters are a = 10.41(3) Å, b = 6.84(2) Å, c = 29.46(9) Å, Z = 4. Incorporation of both Co(II) and Ni(II) into the potassium hydrogen phthalate (KHP) crystal lattice is well confirmed by EDS and chemical tests. Powder XRD profiles indicate the crystallinity and FT-IR studies reveal the vibrational patterns. The UV–vis optical absorption spectrum of PCNHP shows the lower optical cut-off at ∼300 nm and the crystal was transparent in the entire visible region. The crystalline perfection of the grown crystal analysed by high-resolution X-ray diffraction (HRXRD) analysis reveals that the diffraction curve (DC) contains multi-peaks with low angular spread indicating the possibility of low angle structural grain boundaries. Scanning electron microscope (SEM) studies indicate the structure defect centers. The dielectric, thermal and mechanical behaviors of the specimen were also investigated.     

Synthesis and crystal structure of a neutral open framework cobalt(II) phosphate Co6(PO4)4·7H2O with a channel structure

Using tri-ethyl phosphate as a phosphate source, the hydrothermal reaction of cobalt(II) oxalate di-hydrate, zinc oxide and 1,8 di-amino octane at 200°C gave purple crystals of Co₆(PO₄)₄?·?7H₂O (1), along with a mixture of open-framework zinc–cobalt phosphates Co–Zn–HPO₄, and Co₃(HPO₄)₂(2OH). Compound 1, has been characterized by thermal analysis, FTIR and single crystal X-ray diffraction. The single crystal structure of Co₆(PO₄)₄?·?7H₂O reveals cobalt in four, five and six-fold coordination with linkages through the bridging water molecules and the oxygen atoms of the phosphate in the subunits. Four subunits are connected together through the oxygen atoms (PO₄), to form the three dimensional open framework structure, with a 20-member ring channel that hosts two uncoordinated water molecules. Thermal removal of the water molecules occurs between 400–600°C, with the collapse of the structure above 600°C.     

Synthesis,structure, photophysical properties and biological activity of a cobalt(II) coordination complex with 4,4′-bipyridine and porphyrin chelating ligands

A new bioactive material of cobalt(II) with 5,10,15,20-tetrakis[4 (benzoyloxy)phenyl] porphyrin (TPBP) and bpy ligands ([Co^II(TPBP)(bpy)₂] 1) has been synthesized and characterized by Single-crystal X-ray diffraction (SCXRD), spectroscopic methods and quantum-chemistry calculations. In the crystalline structures of six coordinated Co(II) [Co^II(TPBP)(bpy)₂] 1, linear 1D polymeric chains were observed in which all the porphyrin units are aligned parallel to each other. The crystal packing is stabilized by inter-and intramolecular C–H⋯O and C–H⋯N hydrogen bonds, and by weak C–H⋯Cg π interactions. Interestingly, NBO–Second-order perturbation theory analysis, carried out at the UB3LYP/6-31G(d)/SDD DFT level of theory, demonstrated that a two-center bond between the nitrogen atoms and the cobalt ions (Co) was not found, the Co–N_py/bp interactions are coming from an electronic delocalization between the N_py/N_bp filled orbitals to the anti-bonding LP*(4) and LP*(5) metal NBOs. Mass spectroscopy, and elemental analysis were also investigated to confirm the molecular structure. The downfield shift and the peak broadening of the axial ligand resonances observed in the ¹H NMR indicated the contiguity to the paramagnetic Co(II) center. Additionally, the photophysical properties have been evaluated by UV–visible absorption, and fluorescence emission spectroscopies. Finally, bioactivity investigations revealed that free porphyrin TPBP, Co^IITPBP and complex 1 could be used as potential antioxidant agents.     

Synthesis, crystal structures and catalytic properties of two 1D cobalt(II) coordination polymers

Two new cobalt(II) coordination polymers, namely [Co_1.5(PhCOO)₃(bbbm)_1.5(H₂O)] _n (1) and [Co(chdc)(bbbm)] _n (2) (bbbm = 1,1′-(1,4-butanediyl)bis-1H-benzimidazole, H₂chdc = 1,4-cyclohexanedicarboxylic acid), have been synthesized and structurally characterized by single crystal X-ray diffraction. The cobalt(II) centers display different environments, with trigonal–bipyramidal and octahedral geometries in 1 and a tetrahedral geometry in 2. The 1D linear chains of complex 1 and ladder-like chains of complex 2 are bridged by bbbm in bis-monodentate coordination mode; the variation of the carboxylate co-ligand effectively tunes the resulting framework architecture. The degradation of methyl orange in a photochemical Fenton-like process using complexes 1 and 2 as catalysts was investigated.     

A supramolecular polymeric chain in the cobalt(II) complex with diclofenac: synthesis,crystal structure,spectroscopic, thermal and antioxidant activity

Abstract

A cobalt(II) complex with empirical formula [Co(dicl)₂·(H₂O)₃]·MeOH (where dicl?=?diclofenac) was synthesized and characterized by elemental analysis, flame atomic absorption spectroscopy (FAAS), infrared spectroscopy (FTIR) and thermal decomposition techniques (TGA). The crystal structure of the complex was determined by single crystal X-ray diffraction technique. The compound crystallizes in the monoclinic space group I2/a. Apical water molecules link adjacent cobalt(II) ions forming polymeric chains along the crystal a axis. The thermal behavior of the complex was studied by TG/DTG/DTA, TG/MS and TG/FTIR methods under non-isothermal conditions in air. Upon heating [Co(dicl)₂·(H₂O)₃]·MeOH decomposes progressively to metal oxides, which are the final products of pyrolysis. Furthermore, antioxidant activity of the complex was examined.     

Synthesis,Crystal Structure,and Magnetic Properties of a New Coordination Polymer Framework [CoII(4,4′‐bpy)(N3)2]n

A new cobalt(II) coordination polymer containing 4,4′‐bipyridine and azide as bridging ligand, [Co^II(4,4′‐bpy)(N₃)₂]_n ( 1 ) was synthesized under mild hydrothermal conditions and was characterized by single‐crystal X‐ray diffraction studies and magnetic susceptibility measurements. It exhibits an acentric structure, in which cobalt(II) ions are linked through end‐to‐end (EE) azido groups. The 4,4′‐bpy ligands are coordinated on the axial positions of the octahedral environment reinforcing the intermetallic connections and resulting in a network. Circular dichroism spectra of the compound exhibit a maximum negative Cotton effect at 260 nm, which indicates the chiral nature of 1 . Variable temperature magnetic susceptibility measurements in the temperature range 2–300 K reveal the existence of antiferromagnetic couplings in the framework.     

Field‐Induced Single‐Ion Magnetic Behavior in Two Mononuclear Cobalt(II) Complexes

The employment of a new rigid N‐tridentate ligand, bis(1‐chloroimidazo[1,5‐a]pyridin‐3‐yl)pyridine (bcpp), in the construction of cobalt(II) single‐ion magnets is reported. Two cobalt(II) complexes, [Co(bcpp)Cl₂] ( 1 ) and [Co(bcpp)Br₂] ( 2 ), have been prepared and characterized. Single‐crystal XRD analyses reveal that complexes 1 and 2 are isostructural. They are pentacoordinated mononuclear cobalt(II) compounds with expected trigonal bipyramidal geometry. Both analysis of the magnetic data and ab initio calculations reveal easy‐plane magnetic anisotropy (D>0) for 1 and 2 . Detailed alternating current magnetic susceptibility measurements reveal the occurrence of slow magnetic relaxation behavior for the cobalt(II) centers of 1 and 2 ; thus indicating that both complexes are field‐induced single‐ion magnets.     

Synthesis,crystal structure,and magnetism properties of coordination polymer: Co(2-mpac)2(H2O)2 as molecular building block

Utilizing Co(2-mpac)₂(H₂O)₂ as molecular building block, a coordination polymer, [Co₂(2-mpac)₄(4,4′-bpy) · 2H₂O] _n (1) (2-mpac = 5-methyl-2-pyrazinecarboxylic acid; 4,4′-bpy = 4,4′-bipyridine), was synthesized and structurally characterized by X-ray single crystal diffraction. Elemental analysis, infrared, and magnetism are presented. Variable temperature magnetic susceptibility measurements exhibit weak antiferromagnetic interaction between Co centers in 1.     

Structural characterization of a new cobalt(II) complex of 1-benzyl-5-methyl-1<Emphasis Type="Italic">H</Emphasis>-imidazole

The preparation of a cobalt(II) chloride complex with a N-donor ligand 1-benzyl-5-methyl-1H-imidazole of formula [CoCl₂(1-benzyl-5-methyl-1H-imidazole)₂] is described. The isolated complex was characterized by UV, IR spectroscopy and crystallographic studies. Single crystal X-ray diffraction analysis of the complex reveals its monomeric tetra-coordinated nature. The coordination polyhedron around the cobalt center can be described as a quasi-regular tetrahedron. The Co–N distances for this compound are 2.0111(17) Å and 2.0118(17) Å, while the Co–Cl distances are 2.2582(7) Å and 2.2549(7) Å. The crystal packing can be described as layers parallel to (101) plane alternating along the b axis, and it is stabilized by π–π stacking between the imidazole and phenyl rings. The shortest centroid–centroid distance is 3.6002(14) Å.     

Synthesis,crystal structure and luminescent property of a novel H<Subscript>2</Subscript>O-bridged cobalt(II) polymer with one-dimensional chain structure

The coordination compound [Co(C₁₀H₇COO)₂(H₂O)₃]_2n · 4nH₂O was prepared by the reaction of 1-naphthoic acid and cobalt(II) acetate tetrahydrate in basic solution, and was fully characterized by X-ray diffraction, element analysis, FTIR, TG-DTA and luminescent spectra. In the crystal the six-coordinated Co(II) centers are linked into one-dimensional zigzag chains by water molecules, which are further assembled into a two-dimensional network through weak inter-chain C–H···π interactions. The solid complex exhibits favorable fluorescent properties similar to those of free ligand at room temperature, which can be assigned to the intraligand electronic transfer.     

Le phosphate de cobalt et de lithium à valence mixte Li4+xCo2−x(P2O7)2 (x = 0,03): étude structurale et analyse de distribution de charge

The title compound, namely lithium cobalt(II/III) bis(diphosphate), Li_4.03Co_1.97(P₂O₇)₂, is a new mixed‐valent lithium/cobalt(II/III) phosphate. Three metal sites out of seven are occupied simultaneously by Li⁺ and Co^II/III ions. This disorder was established both from an analysis of the atomic displacement ellipsoids and Li/Co—O bond distances, and by means of a charge‐distribution (CHARDI) model, which provides satisfactory agreement on the computed charges (Q) for all the cations.     

Syntheses,crystal structures and thermodecomposition behaviors of three energetic compounds

Three new energetic compounds, nickel(II) 3,5-dinitro-2-pyridonate (Ni(2DNPO)₂(H₂O)₄, 1), copper(II) 3,5-dinitro-4-pyridonate (Cu(4DNPO)₂(H₂O)₄, 2) and cobalt(II) 3,5-dinitro-4-pyridone-N-hydroxylate ([Co(4DNPOH)₂(H₂O)₄] · 2DMF, 3 · 2DMF), were characterized by elemental analysis, FT–IR, TG-DSC and X-ray single crystal diffraction analysis. Complexes 1 and 2 are similar in structure with the metal ion coordinated by oxygen donors of four water molecules on the equatorial position and two nitrogen donors of the pyridone rings of two ligands in the axial positions. The cobalt(II) complex 3 · 2DMF is a heavily distorted octahedral geometry. The Co(II) has equatorial positions defined by oxygens of four water molecules. Its axial positions are filled with two oxygen atoms of the pyridone-N-hydroxylate of two ligands. The TG-DSC results reveal that 1 is the most stable, with higher initial thermal decomposition temperature and enthalpy. Based on the thermoanalyses, the nickel compound is a promising candidate as a component in catalyzed RDX-CMDB propellants in comparison with our earlier lead(II) analogs.     

Study of the electronic structure of polynuclear cobalt trimethylacetate complexes by Co3<Emphasis Type="Italic">s</Emphasis> and Co3<Emphasis Type="Italic">p</Emphasis> X-ray photoelectron spectroscopy

The electronic structure of mono-, hexa-, and nonanuclear cobalt trimethylacetate complexes was studied by XPS. The Co3s- and Co3p X-ray photoelectron spectra of the complexes were recorded. The Co3p spectrum of bivalent cobalt was calculated in the isolated-ion intermediate-coupling approximation. Spectrum analysis showed that the [Co(N-Phobsqdi)2(η′-N-Ph-opda)(OOCCMe₃)] complex is a strong-field complex with Co(III) in the diamagnetic state; the [Co(dipy)₂(OOCCMe₃)₂], [Co(dipyam)(OOCCMe₃)₂], and [Co₉(μ₃-OH)₆(μ-OOCCMe₃)₁₂(OCMe₂)₄] are high-spin weak-field Co(II) complexes; and the [Co₆(μ₄-O)₂(OOCCMe₃)₁₀(THF)₄] complex contains both the Co(II) and Co(III) atoms. The energy position of major Co3s- and Co3p spectral maxima were found to be sensitive to the nature of the nearest environment of cobalt atoms. The data correlate well with X-ray crystallographic data.     

Syntheses,Characterization, and Antibacterial Property of Polynuclear Cobalt(III) and Copper(II) Complexes Derived from Similar Tridentate Schiff Bases

An end-on azido-bridged trinuclear cobalt(III) complex [Co₃(L¹)₂(μ_1,1-N₃)₄(N₃)₂(OMe)(MeOH)] (I) and a phenolato-bridged dinuclear copper(II) complex [Cu₂(L²)₂(NCS)₂] (II), where L¹ is the deprotonated form of 2-((2-(dimethylamino)ethylimino)methyl)-4-fluorophenol, and L² is the deprotonated form of 2-((3-(dimethylamino)propylimino)methyl)-4-fluorophenol, have been prepared and characterized by elemental analyses, IR and UV-Vis spectra, and single crystal X-ray diffraction (CIF files CCDC nos. 1023376 (I); 1023377 (II)). The Co atoms in complex I are in octahedral coordination, and the Cu atoms in complex II are in square pyramidal coordination. The antibacterial properties have been tested on some bacteria and yeast.     

Synthesis and Magnetic Properties of Two New Cobalt Complexes Constructed by Semirigid V‐shaped 5‐(4‐Carboxyphenoxy)‐pyridine‐2‐carboxylic Acid

Two cobalt complexes, [Co₃(L)₂(CH₃OH)₂(μ₃‐OH)₂] ( 1 ) and [Co(L)(bpe)_0.5] · H₂O ( 2 ) [H₂L = 5‐(4‐carboxyphenoxy)‐pyridine‐2‐carboxylic acid; bpe = 1, 2‐bis(4‐pyridyl)ethylene] were synthesized and fully characterized by elemental analyses, IR spectroscopy, single‐crystal X‐ray diffraction, thermogravimetric analysis (TGA), and magnetic analysis. Complex 1 has a two‐dimensional (2D) structure with puckered Co–O–Co chains, and 2 displays a three‐dimensional (3D) network containing one‐dimensional rectangular channels with dimensions of 9.24 × 13.84 Å. In complex 1 , variable‐temperature magnetic susceptibility measurements indicate antiferromagnetic interactions between cobalt magnetic centers.     

Front Cover: Water-Solvation-Dependent Spin Transitions in Cobalt(II)-Octacyanidometallate Complexes (Eur. J. Inorg. Chem. 30/2023)

The spin-crossover (SCO) and charge-transfer (CT) phenomena, the switching processes between two distinguishable magnetic states, are promising for developing materials capable of sophisticated memory and sensing functionalities. The majority of SCO systems are based on iron(II) complexes. However, cobalt(II)-2,2′:6′,2′′-terpyridine (terpy) systems emerge as a promising alternative. In this work, new complex salts [Co^II(terpy)₂]₂[Mo^IV(CN)₈] ⋅ 15H₂O, Co₂Mo (H₂O), and [Co^II(terpy)₂]₃[W^V(CN)₈]₂ ⋅ 12H₂O, Co₃W₂ (H₂O) were synthesized and physiochemically characterized. Structural studies for both compounds revealed [Co(terpy)₂]²⁺ layers pillared by octacyanidometallate anions and completed with water molecules between them. Magnetic studies confirmed that the (de)solvated phases of both complexes exhibit partial SCO on the cobalt(II) centers: Co^II−LS (S_Co(II)-LS=¹/₂)↔Co^II−HS (S_Co(II)-HS=³/₂). Moreover, handling dehydrated samples in a high-humidity environment leads to partial recovery of previous magnetic properties via humidity-induced SCO for Co₂Mo : Co^II−HS→Co^II−LS, and the new phenomenon of isothermal humidity-activated charge-transfer-induced spin transition, which we define here as HACTIST, for Co₃W₂ : Co^II−HS⋅⋅⋅W^V (S_Co(II)-HS=³/₂ and S_W(V)=¹/₂)→Co^III−LS⋅⋅⋅W^IV (S_W(IV)=0 and S_Co(III)-LS=0). These comprehensive studies shed light on the water-solvation-dependent spin transitions in Co(II)-octacyanidometallate(IV/V) complexes.