Structure and Magnetic Properties of a 1D Alternating Cu(II) Monomer―Paddlewheel Chain

One-dimensional metal–organic coordination polymers make up a class of compounds with potential towards the development of practical, new magnetic materials. Herein, a rare example of an ABBABB coupled linear chain comprised of alternating dicopper(II) tetraacetate units bridged to copper(II) acetate monomer units via axial η2:η1:µ2 coordinated acetate is reported. Examination of the structure, determined by small molecule X-ray crystallography, shows that each Cu(II) ion is in a dx2–y2 magnetic ground state. Magnetic susceptibility and magnetization data were collected and, consistent with the structural interpretation, demonstrate that the Cu(II) dimer (paddlewheel) exhibits classic antiferromagnetic exchange, while the S = 1/2 Cu(II) monomer is uncompensated in the ground state (low temperature regime.) Data were therefore fitted to a modified Bleaney-Bowers model, and results were consistent with the only other reported chain in this class for which magnetic data are available

μ-1,6-Dioxo-1,6-diphenylhexane-3,4-diolato-bis[(2,2′-bipyridine)chloridocopper(II)] dihydrate a; b; a

The reaction of CuCl2 with 1,6-diphenyl-1,3,5,6-hexanetetrone and 2,2′-bipyridine (bipy) in ethanol gave crystals of the corresponding bimetallic complex, [Cu2(C18H12O4)Cl2(C10H8N2)2]·2H2O. The molecule is centrosymmetric with each CuII ion coordinated to two oxygen atoms from the tetronediate, two nitrogen atoms from a bipy ligand and one coordinated chloride ion. A water molecule of crystallization forms hydrogen bonds to the chloride ions, linking the molecules into a chain parallel to the bc-face diagonal. © 2023 The Author(s)

Platinum(II) phosphonate complexes derived from endo-8-camphanylphosphonic acid

The reactions of cis-[PtCl₂L₂] [L = PPh₃, PMe₂Ph or L₂ = Ph₂P(CH₂)₂PPh₂ (dppe)] with endo-8-camphanylphosphonic acid (CamPO₃H₂) and Ag₂O in refluxing dichloromethane gave platinum(II) phosphonate complexes [Pt(O₃PCam)L₂]. The X-ray crystal structure of [Pt(O₃PCam)(PPh₃)₂]•₂CHCl₃ shows that the bulky camphanyl group, rather than being directed away from the platinum, is instead directed into a pocket formed by the Pt and the two PPh₃ ligands. This allows the O₃P–CH₂ group to have a preferred staggered conformation. The complexes were studied in detail by NMR spectroscopy, which demonstrates non-fluxional behaviour for the sterically bulky PPh₃ and dppe derivatives, which contain inequivalent phosphine ligands in their ³¹P NMR spectra. These findings are backed up by theoretical calculations on the PPh₃ and PPhMe₂ derivatives, which show, respectively, high and low energy barriers to rotation of the camphanyl group in the PPh₃ and PPhMe₂ complexes. The X-ray crystal structure of CamPO₃H₂ is also reported, and consists of hydrogen-bonded hexameric aggregates, which assemble to form a columnar structure containing hydrophilic phosphonic acid channels surrounded by a sheath of bulky, hydrophobic camphanyl groups

Synthesis, characterization and magnetic properties of four new organically templated metal sulfates [C5H14N2][M(II)(H2O)6](SO4)2, (M(II) = Mn, Fe, Co, Ni).

International audienceA series of novel organically templated metal sulfates, [C(5)H(14)N(2)][M(II)(H(2)O)(6)](SO(4))(2) with (M(II) = Mn (1), Fe (2), Co (3) and Ni (4)), have been successfully synthesized by slow evaporation and characterized by single-crystal X-ray diffraction as well as with infrared spectroscopy, thermogravimetric analysis and magnetic measurements. All compounds were prepared using a racemic source of the 2-methylpiperazine and they crystallized in the monoclinic systems, P2(1)/n for (1, 3) and P2(1)/c for (2,4). Crystal data are as follows: [C(5)H(14)N(2)][Mn(H(2)O)(6)](SO(4))(2), a = 6.6385(10) Å, b = 11.0448(2) Å, c = 12.6418(2) Å, β = 101.903(10)°, V = 906.98(3) Å(3), Z = 2; [C(5)H(14)N(2)][Fe(H(2)O)(6)](SO(4))(2), a = 10.9273(2) Å, b = 7.8620(10) Å, c = 11.7845(3) Å, β = 116.733(10)°, V = 904.20(3) Å(3), Z = 2; [C(5)H(14)N(2)][Co(H(2)O)(6)](SO(4))(2), a = 6.5710(2) Å, b = 10.9078(3) Å, c = 12.5518(3) Å, β = 101.547(2)°, V = 881.44(4) Å(3), Z = 2; [C(5)H(14)N(2)][Ni(H(2)O)(6)](SO(4))(2), a = 10.8328(2) Å, b = 7.8443(10) Å, c = 11.6790(2) Å, β = 116.826(10)°, V = 885.63(2) Å(3), Z = 2. The three-dimensional structure networks for these compounds consist of isolated [M(II)(H(2)O)(6)](2+) and [C(5)H(14)N(2)](2+) cations and (SO(4))(2-) anions linked by hydrogen-bonds only. The use of racemic 2-methylpiperazine results in crystallographic disorder of the amines and creation of inversion centers. The magnetic measurements indicate that the Mn complex (1) is paramagnetic, while compounds 2, 3 and 4, (M(II) = Fe, Co, Ni respectively) exhibit single ion anisotropy

The potential for circular dichroism as an additional facile and sensitive method of monitoring low-molecular-weight heparins and heparinoids

The ultraviolet circular dichroism (CD) spectra of commercial low-molecular-weight heparins, heparinoids and other anticoagulant preparations have been recorded between 180 and 260 nm. Principal component analysis of the spectra allowed their differentiation into a number of groups related to the means of their production reflecting the structural changes introduced by each process. The findings suggest that CD provides a complementary technique for the rapid analysis of heparin preparations

Interplay Between Magnetic Frustration and Quantum Criticality in the Unconventional Ladder Antiferromagnet C9H18N2CuBr4

Quantum fluctuation in frustrated magnets and quantum criticality at the transition between different quantum phases of matter are two of the cornerstones in condensed matter physics. Here we demonstrate the nontrivial interplay between them in the spin-1/2 coupled two-leg ladder antiferromagnet C9H18N2CuBr4. Employing the high-resolution neutron spectroscopy, we unambiguously identify a weakly first-order hydrostatic pressure-driven quantum phase transition, which arises from fluctuations enhanced by the frustrating interlayer coupling. An exotic pressure-induced quantum disordered state is evidenced by the broad spectral linewidth observed near the phase transition. Interestingly, we find that the gapped transverse excitations in the Neel-ordered phase at ambient pressure cannot be described by the conventional S=1 magnons, i.e., the spin wave quanta, associated with explicit symmetry breaking, and thus the three-dimensional magnetic order ought to emerge in an unconventional way. We further apply the quantum Fisher information to show the presence of bipartite entanglement at criticality at least up to 1.1 K in the same material.Comment: 10 pages and 6 figures. We call for theoretical understanding of the nontrivial interplay observed in this materia

Synthesis, Structural, Magnetic and Computational Studies of a One-Dimensional Ferromagnetic Cu(II) Chain Assembled from a New Schiff Base Ligand

A new asymmetrically substituted ONOO Schiff base ligand N-(2′-hydroxy-1′-naphthylidene)-3-amino-2-naphthoic acid (nancH2) was prepared from the condensation of 2–hydroxy–1–naphthaldehyde and 3–amino–2–naphthoic acid. nancH2 reacts with Cu2(O2CMe)4·2H2O in the presence of Gd(O2CMe)3·6H2O to afford a uniform one-dimensional homometallic chain, [CuII(nanc)]n (1). The structure of 1 was elucidated via single crystal X-ray diffraction studies, which revealed that the Cu(II) ions adopt distorted square planar geometries and are coordinated in a tridentate manner by an [ONO] donor set from one nanc2− ligand and an O− of a bridging carboxylate group from a second ligand. The bridging carboxylato group of the nanc2− ligand adopts a syn, anti-η1:η1:μ conformation linking neighboring Cu(II) ions, forming a 1D chain. The magnetic susceptibility of 1 follows Curie–Weiss law in the range 45–300 K (C = 0.474(1) emu K mol-1, θ = +7.9(3) K), consistent with ferromagnetic interactions between S = ½ Cu(II) ions with g = 2.248. Subsequently, the data fit well to the 1D quantum Heisenberg ferromagnetic (QHFM) chain model with g = 2.271, and J = +12.3 K. DFT calculations, implementing the broken symmetry approach, were also carried out on a model dimeric unit extracted from the polymeric chain structure. The calculated exchange coupling via the carboxylate bridge (J = +13.8 K) is consistent with the observed ferromagnetic exchange between neighbouring Cu(II) centres. © 2023 by the authors. This article belongs to the Special Issue Coordination Chemistry: Current Developments and Future Perspectives — a Themed Issue in Honor of Professor Spyros P. Perlepes on the Occasion of His 70th Birthday) This article contains supplementary material. It is available for download as a supplementary file

Satellite ligand effects on magnetic exchange in dimers. A structural, magnetic and theoretical investigation of Cu2L2X4 (L = methylisothiazolinone and X = Cl−, Br−)

Halide-bridged polymers have gained significant interest due to their diverse properties and potential applications. Stacked Cu2L2X4 dimers, where L is an organic ligand and X can be Cl− or Br−, are of interest because a chloride analogue where L = 2-pyridone, had previously been reported to exhibit bulk ferromagnetism, which augured great potentiality for this class of compounds. The synthesis, structural characterization, magnetic susceptibility measurements, and computational studies of two isostructural CuClMI (MI = methylisothiazolinone) and CuBrMI polymers of Cu(ii), along with a related CuClPYR (PYR = 2-pyridone) is reported. CuClMI and CuBrMI were found to exhibit AFM bulk properties, due to FM/AFM alternating chains along the halide-bridged polymer axis, while FM bulk properties were confirmed for CuClPYR exhibiting a FM spin ladder. In combination with a benzamide analogue, CuClBA, three O-donor amides, CuClMI, CuClBA and CuClPYR were analyzed and revealed that the kinetic exchange is affected by the identity, but more importantly, the orientation of the satellite ligands. The torsional angle of the ligand with the dimer plane is shown to significantly affect the magnetic exchange in the dimer, and between dimers, explaining the reported FM bulk properties of CuClPYR. This finding is exceedingly important, as it suggests that a spin device can be constructed to flip between singlet/triplet states by manipulating the orientation of the satellite/terminal ligand. © 2023 The Royal Society of Chemistry. This article includes supplementary data, also available for download

The Effects of Nitrogen Fertilisation on Plant Species Richness in European Permanent Grasslands: A Systematic Review and Meta-Analysis

Nitrogen fertilisation is a common form of agricultural intensification, aimed at increasing biomass, which can affect plant species diversity and ecosystem functioning. Using a systematic review and meta-analysis of nitrogen fertilisation studies in European permanent grasslands, we asked: (i) what relationship form exists between nitrogen application rate and change in plant diversity, compared to zero fertilisation controls; and (ii) how grassland, management and study characteristics affect this relationship. Meta-analysis of 34 control-treatment effects from 14 studies conducted across nine European countries revealed a negative linear relationship between nitrogen fertilisation rate and change in plant species richness, equivalent to approximately 1.5 species/m(2) lost for every 100 Kg ha(-1) yr(-1) of nitrogen added. Fertilisation induced reductions in plant species richness were greater when defoliation rates were lower. We found some evidence that grasslands with a higher baseline plant diversity lost more species when fertilised compared to more species poor grasslands, although uncertainty was high. Due to the diverse grassland types included in the analysis, the variability in fertilisation-driven changes in plant diversity was high. We identified several remaining limitations to our understanding, including uncertainty about non-linear effects, which could aid efforts to optimise the trade-off of plant diversity and increasing grassland yields

Bistability in organic magnetic materials: a comparative study of the key differences between hysteretic and non-hysteretic spin transitions in dithiazolyl radicals

Dithiazolyl (DTA)- based radicals have furnished many examples of organic spin- transition materials, some of them occurring with hysteresis and some others without. Herein, we present a combined computational and experimental study aimed at deciphering the factors controlling the existence or absence of hysteresis by comparing the phase transitions of 4- cyanobenzo- 1,3,2- dithiazolyl and 1,3,5trithia- 2,4,6- triazapentalenyl radicals, which are prototypical examples of non- bistable and bistable spin transitions, respectively. Both materials present low- temperature diamagnetic and high- temperature paramagnetic structures, characterized by dimerized (center dot center dot center dot A-A center dot center dot center dot A-A center dot center dot center dot) n and regular (center dot center dot center dot A center dot center dot center dot A center dot center dot center dot A center dot center dot center dot A center dot center dot center dot) n pi- stacks of radicals, respectively. We show that the regular pi-stacks are not potential energy minima but average structures arising from a dynamic inter-conversion between two degenerate dimerized configurations: (center dot center dot center dot A-A center dot center dot center dot A-A center dot center dot center dot)n (-A center dot center dot center dot A-A center dot center dot center dot A-)n. The emergence of this intrastack dynamics upon heating gives rise to a second-order phase transition that is responsible for the change in the dominant magnetic interactions of the system. This suggests that the promotion of a (center dot center dot center dot A-A center dot center dot center dot A-A center dot center dot center dot)n (-A center dot center dot center dot A-A center dot center dot center dot A-) n dynamics is a general mechanism for triggering spin transitions in DTA-based materials. Yet, this intra-stack dynamics does not suffice to generate bistability, which also requires a rearrangement of the intermolecular bonds between the pstacks via a first-order phase transition