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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. [ABSTRACT FROM AUTHOR]

Bisdithiazolyl radicals have furnished in recent years multiple examples of molecular materials with promising conductive and magnetic properties. The electronic band structure and magnetic ordering in four different isostructural pyridine-bridged bisdithiazolyl and Selenium substituted compounds have been studied by means of hybrid DFT based methods as implemented in the CRYSTAL code. The full rationalization of the properties of these multifunctional magnetic molecular materials requires a careful description of their complex open-shell electronic structure. The results describe the systems as narrow band (0.2–0.3 eV dispersion) open-shell semiconductors with a gap of 1.15–1.40 eV between the valence and conducting bands. The bands defining the insulating gap are dominated by orbital contributions arising from the heteroatoms sitting in the outer rings. A low energy closed-shell metallic solution is found at 0.25–0.35 eV above the magnetic solutions thus suggesting a complex mechanism for electric conduction with band and hopping contributions. The observed trend of the conductivity is in line with the variation of the insulating gap but more rigorous modelling is required to take into account the details of the band structure of the systems. For all the systems the spin density is well localised on the molecular units and is independent of the magnetic solution. Thus the system can be described as an ensemble of well-defined S = 1/2 magnetic centres using a two-body Heisenberg–Dirac–van Vleck spin Hamiltonian. The lowest energy electronic solutions are in line with the observed magnetic behaviour at low temperature. The set of competing magnetic exchange interactions that emerges from using a suitable mapping to consistently describe the low energy magnetic solutions explains the variety of magnetic responses (absence of long-range magnetic order, antiferromagnetism or ferromagnetism) of the four studied compounds at low temperatures. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties of two all-pyrazine-bridged antiferromagnetic spin ladders are reported. The complexes, catena-(bis(3-X-4-pyridone)(μ-pyrazine)copper(II)(-μ-pyrazine)diperchlorate ([Cu(pz)1.5(L)2](ClO4)2 where L = 3-X-4-pyridone and X = Br (1) or Cl (2)), contain copper(II)-based ladders in which both the rung and rail bridges are pyrazine molecules bonded through the x2–y2 orbital of the copper(II) ions. This structural scaffold is proposed to approach the isotropic spin-ladder regime. 1 and 2 crystallize in the monoclinic space group P21/c. Due to the bulk of the 3-X-4-HOpy ligands, the ladders are well isolated in the a-direction (1, 15.6 Å; 2, 15.5 Å). The ladders, which run in the b-direction, are stacked in the c-direction with the separation (1, 7.87 Å; 2, 7.82 Å) between copper(II) ions caused by the bulk of a semi-coordinate perchlorate ion coordinated in the axial position. Computational evaluation of magnetic JAB couplings between Cu-moieties of 2 supports the experimentally proposed magnetic topology and agrees with an isolated isotropic spin-ladder (Jrail = −4.04 cm−1 (−5.77 K) and Jrung = −3.89 cm−1 (−5.56 K)). These complexes introduce a convenient scaffold for synthesizing isotropic spin-ladders with modest superexchange interactions, the strength of which may be tuned by variations in L. The magnetic susceptibility down to 1.8 K, for both compounds, is well described by the strong-rung ladder model giving nearly isotropic exchange with Jrung ≈ Jrail ≈ −5.5 K (1) and −5.9 K (2) using the Hamiltonian. Theoretical simulations of the magnetic response of 2 using the isotropic ladder model are in excellent agreement with experiment. The measured magnetization to 5 T indicates a quantum-dominated magnetic spectrum. Again, calculated lower and saturation (4.3 and 24 T, respectively) critical fields for 2 are consistent with experimental measurements, and magnetization data at very low temperatures indeed suggest the presence of quantum effects. Further, the computational study of short- and long-range spin ordering indicates that a 2D-to-3D crossover might be feasible at lower temperatures. Analysis of the Boltzmann population corroborates the presence of accessible triplet states above the singlet ground state enabling the aforementioned 2D-to-3D crossover. [ABSTRACT FROM AUTHOR]