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Two new coordination polymers, [Cu(pz)(L)2(H2O)2](ClO4)2 (L = 2-Cl- (1) or 2-Br-4-pyridone (2); pz = pyrazine), have been synthesized and characterized by X-ray diffraction, EPR and variable temperature magnetic measurements. Both compounds crystallize as well isolated pyrazine-bridged chains with the heterocyclic ligands in the pyridone tautomer and coordinated via the oxygen atom. The Cu ions possess Jahn-Teller elongated octahedral geometries with the Jahn-Teller axis along the Cu-O axis. The water molecules in 2 are inequivalent with one molecule semi-coordinate (dCu...O = 3.225(6) Å) at an occupancy of 0.72. Both compounds exhibited axial powder EPR spectra, as expected. Variable temperature magnetic measurements are well fit by the uniform chain Heisenberg antiferromagnetic model with J = −10.74(4) K (1) or = −10.64(2) K (2). Comparison with the known 3-halo-4-pyridone compounds suggests an inverse relationship between the Cu-pz-Cu distance and the strength of the magnetic exchange. [ABSTRACT FROM AUTHOR]

Reaction of isoquinoline (iQuin) with cobalt(II) and nickel(II) chloride and bromide produced a family of neutral coordination complexes: (iQuin)2CoX2 [X = Cl (1), Br (2)], (iQuin)4CoX2 (X = Cl (3), X = Br (4)], (iQuin)4NiX2 [X = Cl, (5), X = Br, (6)], and (iQuin)2NiBr2(CH3CN)2 (7). The crystal structures of 1–5 and 7 are reported. The majority of the compounds crystallize with some of the iQuin ligands undergoing a ∼2-fold rotational disorder, likely caused by the nearly equivalent space occupied by the two positions. The disorder is temperature independent and ∼50:50 in all cases but one. Magnetic measurements for all seven compounds indicate that their behavior is dominated by single-ion anisotropy effects with indications of antiferromagnetic exchange also present in 1 and 2. [ABSTRACT FROM AUTHOR]

The understanding of magnetic properties of hybrid compounds is important for the design of magnetic devices. In this contribution a prominent odd–even effect in both the structural characteristics and magnetic properties of four new hybrid compounds comprised of n-carboxyalkylammonium cations and perchloridomanganate anions is reported. When the n-carboxyalkylammonium cations contain an even number of carbon atoms, compounds of the formula (NH3(CH2)nCOOH)2[MnCl4], with n = 3 and 5, are formed, which display the two-dimensional (2D) hybrid halide perovskite structure in which bridging chlorido ligands link Mn2+ ions. Compounds containing n-carboxyalkylammonium cations with an odd number of carbon atoms have the formula (NH3(CH2)nCOOH)2[MnCl4(H2O)2], with n = 2 and 4, and display a zero-dimensional (0D) structure with hydrogen bonding interactions linking neighbouring [MnCl4(H2O)2]2− anions. The odd–even effect is also evident in the magnetic properties of the compounds, which are linked to the structural differences observed in these compounds. Compounds containing an even number of carbon atoms show antiferromagnetic (AFM) interactions and spin canting at temperature TN, with 2JK = −8.28(5) K and TN = 45.0(5) K when n = 3 and 2JK = −7.72(4) K and TN = 43(1) K when n = 5. Much weaker AFM interactions and no spin canting is observed in compounds containing an odd number of carbon atoms, with 2JK = −0.14(2) K when n = 2 and 2JK = −0.14(2) K when n = 4. [ABSTRACT FROM AUTHOR]

A new tetracopper(II) coordination compound, [Cu4Cl6O(iQuin)4] (1, iQuin = isoquinoline), with an adamantane-like structure is reported. The compound crystallizes in the tetragonal space group P4/n with one crystallographically unique Cu(II) and oxide ions, and two chloride ions. Variable temperature magnetic measurements reveal dominant antiferromagnetic interactions, but the crystal structure suggests the likelihood of magnetic frustration in the compound. Modeling results indicate the presence of two competing interactions, J a p / k B = − 61.1 (7) K and J e q / k B = 41.2 (3) K (ap = apical; eq = equatorial), as well as a Zeeman coupling of the Cu(II) ions with the external magnetic field. All data were fit using the Hamiltonian H ^ = J 1 ∑ i = 1 6 S ^ γ i (1) ⋅ S ^ γ 2 (2) + J 2 ∑ i = 1 6 ( S ^ α i (1) ⋅ S ^ α i (2) + S ^ β i (1) + S ^ β i (2) ) + g μ B H → ⋅ ∑ j = 1 4 S ^ j [ABSTRACT FROM AUTHOR]

The effect of halogen bonding interactions on polymorphism in Cu(2I5YP)2X2 has been investigated, where 2I5YP = 2-iodo-5-halopyridine, Y = Br or Cl and X = Cl or Br; these complexes are abbreviated as 2I5Y-X. Two conformers are possible for 2I5Y-X complexes: the syn-conformer where the two iodine atoms are located on the same side of the coordination sphere and the anti-conformer where the iodine atoms are located on the opposite side of the coordination sphere. The anti-conformers are more stable than the corresponding syn-conformer by 4.0 kJ mol−1 in 2I5Y-Br, whereas, in 2I5Y-Cl the syn- and anti- have almost the same stability (energy difference = 0.45 kJ mol−1). In 2I5Br-Cl, crystals of the syn- and anti-conformers were characterized using single crystal X-ray diffraction. However, only the anti-conformer of 2I5Br-Br was produced. The syn-conformer crystallizes in the monoclinic space group C2/c. Two packing polymorphs of anti-2I5Cl-Cl were characterized; they crystallized in the P1¯ and P21/n space groups. On the molecular level, the syn-conformer is stabilized by C6–H⋯X hydrogen bonding interactions and the anti-conformer is stabilized by I2⋯Cu interactions. On the supramolecular level, the C–I⋯Cl and C–Y⋯Cl interactions are stronger in the C2/c phase than the corresponding interactions in the P21/n phase as indicated by Y⋯Cl and I⋯Cl distances. The possibility of crystallizing the syn-conformer depends on the nature of the halogens atoms in the complex; the lighter the halogen on position two of the pyridine ring and the heavier the halogen on position five of the pyridine ring, the higher the possibility of crystallizing the syn-conformer. syn-Conformers are not observed in 2I5Y-Br complexes. These conclusions were supported by density functional theory calculations and analyzing the electron density using quantum theory of atoms in molecules (QTAIM). Both conformers of 2I5Br-Cl and 2I5I-Cl complexes show antiferromagnetic interactions; the data were fit to a 1D-uniform AFM chain model. The interactions are stronger in the syn-conformer than the corresponding anti-conformer as indicated by J/kB values, which are −3.77(8) K, −1.88(6) K, −1.75(6) K and −1.5(4) K for syn-2I5Br-Cl, anti-2I5Br-Cl, syn-2I5I-Cl and anti-2I5I-Cl, respectively. [ABSTRACT FROM AUTHOR]