A series of end-to-end azido-bridged perovskite-type compounds [(CH3)nNH4-n][Mn(N3)3] (n = 1-4) were synthesized and characterized. Structural phase transitions indicating the general lattice flexibility were observed and confirmed by the crystal structures of different phases. These materials show cation-dependent magnetic ordering at up to 92 K and magnetic bistability near room temperature.
Recently Bi-CGSTAB as a variant of Bi-CG has been proposed for solving nonsymmetric linear systems, and its attractive convergence behavior has been confirmed in many numerical experiments. Bi-CGSTAB can be characterized by its residual polynomial which consists of the product of the residual polynomial of Bi-CG with other polynomials generated from two-term recurrence relations. In this paper, we propose a unified way to generalize a class of product-type methods whose residual polynomials can be factored by the residual polynomial of Bi-CG and other polynomials with standard three-term recurrence relations. Such product-type methods which are based on Bi-CG can be regarded as generalizations of Bi-CGSTAB. From the unified way, the well-known variants of the product-type methods, like CGS, Bi-CGSTAB, Bi-CGSTAB2, are reacquired again.
We herein reported the synthetic, structural, computational, and magnetic studies of four air-stable heptacoordinated mononuclear cobalt(II) complexes, namely, [Co(tdmmb)(HO)][BF] (1), [Co(tdmmb)(CN)]·2HO (2), [Co(tdmmb)(NCS)] (3), and [Co(tdmmb)(SPh)] (4) (tdmmb = 1,3,10,12-tetramethyl-1,2,11,12-tetraaza[[3](2,6)pyridino[3](2,9)-1,10-phenanthrolinophane-2,10-diene; SPh = thiophenol anion). Constrained by the rigid pentadentate macrocyclic ligand tdmmb, the Co centers in all of these complexes are in the heptacoordinated pentagonal-bipyramidal geometry. While the equatorial environments of these complexes remain very similar to each other, the axial ligands are systematically modified from C to N to O to S atoms. Analyses of the magnetic data and the ab initio calculations both reveal large easy-plane magnetic anisotropy (D > 0) for all four complexes. While the experimentally obtained D values do not show any clear tendency when the axial coordinated atoms change from C to N to O atoms (complexes 1-3), the largest value is for the heavier and softer S-atom-coordinated complex 4. Because of significant magnetic anisotropy, all four complexes are field-induced single-ion magnets. This work represents a delicate modification of the magnetic anisotropy by tuning the chemical environment of the metal centers.
Spin canting, antiferromagnetic ordering, metamagnetism and single-chain magnetism were verified in a cyano-bridged Fe(II) compound synthesized from the pentagonal bipyramidal Fe(II) starting material in the presence of excessive BF4(-) anions.
We discuss the shifted conjugate-orthogonal-conjugate-gradient (COCG) method, which can be used to solve a series of linear equations generated by a number of scalar shifts, without performing timeconsuming matrix-vector operations, except at a single reference energy. This is a type of CG method and is robust and has an expression of the accuracy of the calculated result that requires no additional calculation cost. The shifted COCG is useful for calculating the Green's function of a many-electron Hamiltonian, which has a very large dimension. We applied the shifted COCG method to the double orbital extended Hubbard model with twelve electrons on a periodic ffiffi ffi 8 p  ffiffi ffi 8 p site system, with the dimension of the Hamiltonian equal to 64,128,064, and we found that the ground state is an insulator. We also discuss the main points of reducing the amount of memory required to apply COCG algorithm.
We herein report the syntheses, structures, and magnetic properties of two isostructural two-dimensional (2D) coordination polymers based on a pentagonal bipyramidal Co unit [Co(TODA)] and two hexacyanometallates, namely [M(CN)][Co(TODA)]·9HO (M = Cr (1), Co (2), TODA = 1,4,10-trioxa-7,13-diazacyclopentadecane). Structure analyses show that both complexes have 2D honeycomb structures where the [Co(TODA)] units are bridged by the [M(CN)] groups through three cyano groups in the facial positions. Magnetic investigation reveals ferromagnetic coupling between the Cr and Co centres through cyanides in 1. Due to the antiferromagnetic interaction between the layers, compound 1 exhibits an antiferromagnetic ordering below 11.4 K, and shows a metamagnetic phase transition under an external dc field. Due to the disorder of the TODA ligands, compound 1 shows a spin glass behavior, which leads to slow magnetic relaxation in 1. A butterfly-shaped hysteresis loop at 1.8 K can be observed with a coercive field of 720 Oe, which is quite large for cyano-bridged Cr-Co molecular magnets. For compound 2 containing the diamagnetic [Co(CN)] unit, field-induced slow magnetic relaxation was also verified, which makes compound 2 a rare example of an SIM assembled in a 2D network. An easy-plane magnetic anisotropy with a positive D value (29.9 cm by PHI and 26.5 cm by Anisofit2.0) was deduced for hepta-coordinated Co centers. These results show the efficiency of the strategy of combining cyanometallates and pentagonal bipyramidal precursors for novel molecular magnetic materials.
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