Isostructural Nickel Research Articles

Valence tautomeric interconversion of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety in solid solutions with isostructural nickel analogue: phase transitions and monocrystal destruction.

Valence tautomeric complexes (VT) are promising systems for creating molecular devices. From this viewpoint, valence tautomeric complexes with a hysteresis loop on the magnetic curve are of special interest as potential memory elements. The hysteresis loop is a consequence of retarded structural rearrangements which investigation is an actual problem. Recently, we have described a new VT transition taking place in a bis-dioxolene cobalt complex with imino-pyridine having a TEMPO substituent (A. A. Zolotukhin, et al., Inorg. Chem., 2017, 56, 14751-14754). Valence tautomeric transformation occurs with a hysteresis loop and is accompanied by a phase transition. The phase transition taking place during cooling is accompanied by crystal destruction. This fact makes it impossible to monitor the structural changes responsible for the hysteresis loop. The current research attempts to resolve this problem. A nickel compound of the same composition (TEMPO-imino-pyridine)Ni(3,6-DBSQ)2 was synthesized and characterized. It was established to be isostructural with the cobalt complex. It was used as an inert matrix for the dilution of the VT cobalt complex. The number of solid solutions with Co/Ni ratios of 1 : 1, 1 : 2, 1 : 4, and 1 : 8 was obtained. Variable temperature magnetic susceptibility measurements show that VT transformation with a hysteresis loop takes place in all solid solutions. The hysteresis loop is shifted to low temperatures primarily due to the shifting of its low-temperature boundary with dilution. The hysteresis width does not change significantly with dilution. DSC detected that transformations are accompanied by phase transitions at different temperatures at cooling and heating. The phase transition at the first cooling occurs at slightly lower temperatures compared with subsequent cycles. These temperatures correspond to the transition temperatures detected from the magnetic curves. The phase transition during the first cooling is accompanied by crystal destruction. Physical destruction takes place in the crystals of all solid solutions. X-ray diffraction powder patterns confirm that phase transition is accompanied by considerable reorganization of the crystal structure typical for the first order transitions. The unit cell volume of solid solutions is larger than that of pure complexes. Especially calculated crystal invariom indicated that the "lattice energy" in a solid solution is the lowest compared with that in "pure" nickel and cobalt complexes.

Expression of concern: Valence tautomeric interconversion of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety in solid solutions with isostructural nickel analogue: phase transitions and monocrystal destruction

Expression of concern for ‘Valence tautomeric interconversion of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety in solid solutions with isostructural nickel analogue: phase transitions and monocrystal destruction’ by Michael P. Bubnov et al., Dalton Trans., 2024, 53, 9151–9160, https://doi.org/10.1039/D4DT00453A.

Engineering the magnetic coupling and anisotropy at the molecule-magnetic surface interface in molecular spintronic devices.

A challenge in molecular spintronics is to control the magnetic coupling between magnetic molecules and magnetic electrodes to build efficient devices. Here we show that the nature of the magnetic ion of anchored metal complexes highly impacts the exchange coupling of the molecules with magnetic substrates. Surface anchoring alters the magnetic anisotropy of the cobalt(II)-containing complex (Co(Pyipa)2), and results in blocking of its magnetization due to the presence of a magnetic hysteresis loop. In contrast, no hysteresis loop is observed in the isostructural nickel(II)-containing complex (Ni(Pyipa)2). Through XMCD experiments and theoretical calculations we find that Co(Pyipa)2 is strongly ferromagnetically coupled to the surface, while Ni(Pyipa)2 is either not coupled or weakly antiferromagnetically coupled to the substrate. These results highlight the importance of the synergistic effect that the electronic structure of a metal ion and the organic ligands has on the exchange interaction and anisotropy occurring at the molecule–electrode interface.

Template metal-organic frameworks: solvent-free synthesis, characterization and powder X-ray diffraction studies of [Cu(NO3)2(bipy)2](py)2

A solid-state synthetic method was used for the preparation of template metal-organic frameworks [Cu(NO3)2(bipy)2](py)2] (1a). The compound was prepared by grinding stoichiometric amount of [Cu(NO3)2]·3H2O, 4,4-bipyridine and pyrene in absence of any solvent. Solvent based synthesis of [Cu(NO3)2(bipy)2](py)2 (1b) was also carried out by the reaction of the metal salt and the two ligands by refluxing in methanol for 2 h for comparison purpose. The materials were characterized by elemental analysis, FT-IR, UV–visible spectroscopies and EI-MS, TGA and powder X-ray diffraction (PXRD) analysis. In order to understand the geometry and structure of the compound, the PXRD patterns of the compounds 1a and 1b were compared with the simulated patterns of the single crystal X-ray diffraction data of the analogous isostructural nickel compound [Ni(NO3)2(bipy)2](py)2 obtained from the Cambridge structural database. The PXRD patterns of the synthesized metal-organic frameworks (MOFs) 1a and 1b were in close agreement with the simulated pattern of the single crystal X-ray diffraction data of the nickel compound [Ni(NO3)2(bipy)2](py)2 suggesting that both compounds are isostructural. This study suggests that template MOFs that afford controllable cavities are suitable for accommodating organic guest molecules which can be synthesized by manual grinding of the starting materials. It was also revealed that neutral solids can be effective templates during the formation of square-grid coordination networks with pyrene as guest under mechanochemical conditions.

Temperature Dependence of the Crystal Structure and g-Values of trans-Diaquabis(methoxyacetato)Copper(II): Evidence for a Thermal Equilibrium Between Complexes with Tetragonally Elongated and Compressed Geometries

The crystal structures of trans-diaquabis(methoxyacetato)copper(II) and the isostructural nickel(II) complex have been determined over a wide temperature range. In conjunction with the reported behavior of the g-values, the structural data suggest that the copper(II) compound exhibits a thermal equilibrium between three structural forms, two having orthorhombically distorted, tetragonally elongated geometries but with the long and intermediate bonds to different atoms, and the third with a tetragonally compressed geometry. This is apparently the first reported example of a copper(II) complex undergoing an equilibrium between tetragonally elongated and compressed forms. The optical spectrum of single crystals of the copper(II) compound is used to obtain metal-ligand bonding parameters which yield the g-values of the compressed form of the complex and hence the proportions of the complex in each structural form at every temperature. When combined with estimates of the Jahn-Teller distortions of the different forms, the latter produce excellent agreement with the observed temperature dependence of the bond lengths. The behavior of an infrared combination band is consistent with such a thermal equilibrium, as is the temperature dependence of the thermal ellipsoid parameters and the XAFS. The potential surfaces of the different forms of the copper(II) complex have been calculated by a model based upon Jahn-Teller coupling. It is suggested that cooperative effects may cause the development of the population of tetragonally compressed complexes, and the crystal packing is consistent with this hypothesis, though the present model may oversimplify the diversity of structural forms present at high temperature.

{3,3′,5,5′-Tetramethoxy-2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}copper(II)

In the title square-planar copper complex, [Cu(C20H22N2O6)], the Cu—N and Cu—O bond lengths are significantly longer than those of its isostructural nickel analog. The title structure is related to that of the corresponding monohydrate. There are significant differences in the conformations of the two complexes. While the monohydrate is mainly planar, in the title compound there is a slight twist in the two benzene rings at each end of the complex [dihedral angle = 13.14 (6)°]. All the atoms of the meth­oxy substitutents are in the plane of the ring to which they are attached (r.m.s. deviation = 0.0079 Å) except for one of the meth­oxy C atoms, which deviates slightly [0.309 (4) Å]. In the crystal, weak C—H⋯O inter­molecular inter­actions link the mol­ecules.

{3,3′,5,5′-Tetramethoxy-2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}nickel(II)

The title square-planar nickel complex, [Ni(C20H22N2O6)], has Ni—N and Ni—O bond lengths of 1.8448 (14)/1.8478 (14) and 1.8536 (12)/1.8520 (12) Å. There is a slight twist in the two benzene rings at each end of the complex [dihedral angle = 11.11 (5)°]. All the atoms of the meth­oxy substitutents are in the plane of the ring to which they are attached except for one which deviates slightly [0.365 (3) Å]. In the crystal, weak C—H⋯O inter­molecular inter­actions connect the mol­ecules.

Building Metallacrown Topology around a Discrete [M3(μ3-O)] (M = Ni(II) and Pd(II)) Core Using Oximato Oxygen Linkers: Synthesis, Structures, and Spectroscopic Characterization of a New Family of Compounds with an Inverse-9-MC-3 Motif

A family of trinuclear oximato complexes [(M(II)L)(3)(mu(3)-O)]ClO(4) (M = Ni, 1-3; Pd, 4 and 5) (HL = 2-alkylamino-3-oximobutane) involving a discrete [M(3)(mu(3)-O)](4+) core have been synthesized in moderate to high yields by a simple one-pot reaction. The products were characterized by ESI-mass and (1)H NMR spectroscopy as well as by single-crystal X-ray diffraction analysis of representative compounds viz., 1, 2, and 4. The oximato oxygen atoms from the ligands and the central mu(3)-O atom connect the metal centers, forming an inverse metallacrown topology in these complexes. In the isostructural nickel compounds (1, 2), the metal centers are situated at the vertices of an equilateral triangle with its centroid position being occupied by the mu(3)-O atom; the Ni-O-Ni angles vary in the range 119.0(2)-120.2(2) degrees . In the palladium complex 4, the geometry of the Pd(3)O core is better described as a regular trigonal pyramid with the metal centers and the mu(3)-O atom occupying the apexes; the Pd-O-Pd angles are close to 109 degrees . The coordination square planes around the individual palladium centers bend appreciably from each other (dihedral angles vary in the range 28.62-34.53 degrees ), providing more of a bowl shape compared to the overall metallacrown topology that remains virtually planar in the nickel complexes. The mu(3)-oxygen atom in 4 is displaced by 0.687 A from the center of the triangular plane with corners occupied by the Pd(II) ions. The protons of the metallacrown peripheral rings in 4 and 5 are more deshielded compared to their nickel(II) counterparts, as revealed from their (1)H NMR spectra in dichloromethane-d(2) solution.

Base‐Induced Formation of Two Magnesium Metal‐Organic Framework Compounds with a Bifunctional Tetratopic Ligand

AbstractTwo coordination polymers constructed from magnesium and the tetratopic organic linker 2,5‐dihydroxyterephthalic acid are reported, denominated CPO‐26‐Mg and CPO‐27‐Mg. The organic component carries two different types of protic functional groups. The degree of deprotonation of the organic component can be regulated by the amount of sodium hydroxide employed in the synthesis, thus determining which of the compounds forms. In CPO‐26‐Mg, only the carboxylic acid groups of the linker are deprotonated and take part in the construction of the three‐dimensional framework. The structure is non‐porous, and its topology is based on the PtS net. In CPO‐27‐Mg, both the carboxylic acid and the hydroxy groups are deprotonated and involved in the construction of a microporous three‐dimensional framework which is based on a honeycomb motif containing large solvent‐filled channels. The metal atoms are arranged in chiral chains along the intersection of the honeycomb and contain one water molecule in their coordination sphere, which allows for the creation of coordinatively unsaturated metal sites upon dehydration. CPO‐27‐Mg is a potentially useful lightweight adsorbent with a pore volume of 60 % of the total volume of the structure and an apparent Langmuir surface area of up to 1030 m2 g–1. Its thermal stability was investigated by thermogravimetry and variable‐temperature powder X‐ray diffraction, which shows framework degradation to commence at 160 °C in air, at 235 °C under nitrogen, and at 430 °C in a dynamic vacuum. Thermogravimetric dehydration and re‐hydration experiments at miscellaneous temperatures indicate that it is possible to obtain open metal sites in CPO‐27‐Mg, but the water is more tightly bound in this material than in the previously reported isostructural nickel compound.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

An array-based study of reactivity under solvent-free mechanochemical conditions—insights and trends

An array-based approach is put forward to obtain insight into reactivity under mechanochemical solvent-free conditions. We describe a survey of sixty potential reactions between twelve metal salts MX2 {(M = Cu, X2 = (OAc)2, (HCO2)2, (F3CCO2)2, (acac)2, (F6acac)2, (NO3)2, SO4; M = Ni, X2 = (OAc)2, (NO3)2, SO4; M = Zn, X2 = (OAc)2, (NO3)2} and five bridging organic ligands {isonicotinic acid (HINA), 1,4-benzenedicarboxylic acid (H2BDC), acetylenedicarboxylic acid (H2ADC), 1,3,5-benzenetricarboxylic acid (H3BTC), 4,4′-bipyridyl (BIPY). Reaction conditions involved a ball mill, applied for 15 min at 30 Hz, without external heating. When examined by XRPD, forty of the combinations gave detectable reactions, thirty-eight with crystalline products. Of these, twenty-nine reactions were quantitative (consuming all of at least one reactant). Comparison of XRPD patterns with patterns simulated from single crystal X-ray diffraction data in the Cambridge Structural Database allowed structural identification of six products. Of particular interest are the microporous framework materials [Cu(INA)2] and [Cu3(BTC)2] (HKUST-1) obtained by reaction of the corresponding carboxylic acids with copper acetate. Other non-porous polymers with 3-dimensional connectivity, [Ni(ADC)(H2O)4], or 1-dimensional connectivity, [Cu(acac)2(BIPY)] and [Cu(F6acac)(BIPY)] were also obtained. Reaction between zinc acetate and H2ADC gave a new product which had not previously been characterised by single-crystal X-ray crystallography, but whose XRPD pattern suggests that it is isostructural with the known nickel polymer [Ni(ADC)(H2O)4]. Two further isostructural nickel and zinc products were obtained in reactions between HINA and nickel nitrate and zinc nitrate. Trends observed within the array are discussed. Copper acetate and copper formate were the most effective starting materials for reaction with carboxylic acids, potentially related to the basicity of their anions and the solvating effects of the formic and acetic acid byproducts. Amongst the ligands there was a general negative corelation between melting point and reactivity. The issue of pore templating in microporous phases and the generation of new structures is also discussed in relation to the Cu(INA)2, Cu3(BTC)2 and nickel nitrate-BIPY systems. Overall, the study suggests that mechanochemical reactivity between metal salts and organic ligands under solvent free conditions is remarkably general. Use of array-based approaches as demonstrated here is advocated a useful way to reveal underlying trends in reactivity under solvent free mechanochemical conditions and to highlight particular cases for more detailed study.

Comparative crystal field study of Ni 2+ energy levels in NiCl 2, NiBr 2, and NiI 2 crystals

The exchange charge model of crystal field theory has been used to analyze systematically the ground state absorption spectra of octahedrally coordinated Ni 2+ ion in isostructural nickel halide crystals NiCl 2, NiBr 2, and NiI 2. The parameters of the crystal field acting on the Ni 2+ ion are calculated from the available crystal structure data. The obtained energy level schemes are compared with experimental absorption spectra; a good agreement with experimental data is demonstrated. Dependencies of the crystal field invariants and covalence effects on the type of ligands are considered. It is shown numerically that the overlap effects between Ni 2+ ion and ligands increase with an increase of the ligands’ atomic number resulting in the following order of the degree of covalence: NiI 2>NiBr 2>NiCl 2.

Structural characterization and intramolecular aliphatic C-H oxidation ability of M(III)(mu-O)2M(III) complexes of Ni and Co with the hydrotris-(3,5-dialkyl-4-X-pyrazolyl)borate ligands TpMe2,X (X = Me, H, Br) and TpiPr2.

Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.

Spectroscopic and magnetic properties of a new class of two-dimensional bitriazole compounds: The X-ray structure of poly-bis(thiocyanato- N)-bis-μ-(4,4′-bis-1,2,4-triazole- N1, N1′)-cobalt(II) monohydrate

The synthesis of a new class of two-dimensional triazole compounds is described, including the crystal structure of [Co(NCS) 2(btr) 2]H 2O [btr stands for 4,4′-bis-1,2,4-triazole (C 4H 4N 6)]. Crystals are monoclinic, space group C2/ c, a = 11.159(1) Å, b = 13.047(4) Å, c = 12.993(3) Å, β = 91.81(2)°, Z = 4. The structure has been solved by Fourier and direct methods and refined by full-matrix least squares to R = 0.0229, R w = 0.0283. The structure consists of layers of six-coordinated cobalt atoms, each having two trans-oriented N-bonded thiocyanate groups [CoNCS 2.098(2) Å] and linked together in the equatorial plane by single bridges of btr to a two-dimensional network. The btr ligand coordinates through its N(1) and N(1′) atoms [CoN 2.128(1) and 2.142(1) Å]. The intralayer CoCo distance is 9.207(2) Å, and the inter-layer CoCo distance is 8.584(1) Å. The magnetic susceptibilities of the compound and of the isostructural nickel and iron compounds are discussed. The iron compound exhibits a high-spin-low-spin crossover at liquid-nitrogen temperatures, as shown by magnetic susceptibility.

The crystal and molecular structures of hexaquocobalt(II) diisonicotinate N-oxide and its isostructural nickel(II) homologue

Abstract In this experiment the crystal and molecular structures of hexaaquocobalt(II)diisonicotinate N-oxide were determined from three-dimensional X-ray diffraction dat. The crystals belong to the monoclinic space group P2 1 /c. The cell parameters are a = 7.74(2), b = 9.826(2), c = 11.474(2) A , β = 91.08(2)°, V = 873.2(3) A 3 for the Co-complex, and a = 7.765(2), b = 9.725(6), c = 11.363 A , β = 91.20(3)°, V = 857.9(7) A 3 for the Ni-complex. Both structures were refined to a final R-value of 0.045. The X-ray structure analysis showed that there are metal(II)hexaquo cations and isonicotinate N-oxide anions formulated as Co(H 2 O) 6 2+ 2L − and Ni(H 2− O) 6 2+ 2L − in the structures. The strong hydrogen bonds between aqua ligands and all three oxygens of the isonicotinate N-oxide ions.