Search

The synthesis, and structural and magnetic characterization of three [Cu.sup.2+]-containing coordination polymers, [Cu(H[F.sub.2])[(pyrazine).sub.2]]Sb[F.sub.6], [[Cu.sub.2]F(HF)(H[F.sub.2])[(pyrazine).sub.4]][(Sb[F.sub.6]).sub.2], and [CuAg([H.sub.3][F.sub.4])[(pyrazine).sub.5]][(Sb[F.sub.6]).sub.2] are presented. The polymers are found to crystallize in either tetragonal or orthorhombic space groups, have structures consisting of 2D square layers of [[M[(pyz).sub.2]].sup.n+] that are linked in the third dimension by either H[F.sub.2.sup.-] or [H.sub.3][F.sub.4.sup.-] and the variations observed in magnetic behaviors are driven by differences in the H***F hydrogen-bonding motifs.

X-ray powder diffraction and magnetic susceptibility measurements have shown that Ag[(pyz).sub.2]([S.sub.2][O.sub.8]) has 2-dimensional square nets of [Ag.sup.2+] ions resulting from the corner-sharing of axially elongated Ag[N.sub.4][O.sub.2] octahedral and have displayed characteristic 2D antiferromagnetism. [[mu].sup.+]SR measurements have shown that Ag[(pyz)([S.sub.2][O.sub.8]) has undergone 3D magnetic ordering below 7.8(3) K.

The article discusses a study that examined the antiferromagnetism in Ag(pyz)2(S2O8)(pyz = pyrazine)4. Results have shown that the compound consists of two-dimensional (2D) square nets of Ag2+ ions, which resulted from the corner-sharing of axially elongated AgN4O2 octahedra. It indicate that the bridging S2O82- ligands mediates weak interlayer spin exchange interactions.

Three Cu2+-containing coordination polymers were synthesized and characterized by experimental (X-ray diffraction, magnetic susceptibility, pulsed-field magnetization, heat capacity, and muon-spin relaxation) and electronic structure studies (quantum Monte Carlo simulations and density functional theory calculations). [Cu(HF2)(pyz)2]SbF6 (pyz = pyrazine) (1a), [Cu2F(HF)(HF2)(pyz)4](SbF6)2 (1b), and [CuAg(H3F4)(pyz)5](SbF6)2 (2) crystallize in either tetragonal or orthorhombic space groups; their stwctures consist of 2D square layers of [M(pyz)2]n+ that are linked in the third dimension by either HF2- (1a and 1b) or H3F4- (2). The resulting 3D frameworks contain charge-balancing SbF6- anions in every void. Compound lb is a defective polymorph of 1a, with the difference being that 50% of the HF2- links are broken in the former, which leads to a cooperative Jahn-Teller distortion and dx²-y² orbital ordering. Magnetic data for 1a and 1b reveal broad maxima in χ at 12.5 and 2.6 K and long-range magnetic order below 4.3 and 1.7 K, respectively, while 2 displays negligible spin interactions owing to long and disrupted superexchange pathways. The isothermal magnetization, M(B), for 1a and 1b measured at 0.5 K reveals contrasting behaviors: la exhibits a concave shape as B increases to a saturation field, Bc, of 37.6 T, whereas 1b presents an unusual two-step saturation in which M(B) is convex until it reaches a step near 10.8 T and then becomes concave until saturation is reached at 15.8 T. The step occurs at two-thirds of Msat, suggesting the presence of a ferrimagnetic structure. Compound 2 shows unusual hysteresis in M(B) at low temperature, although χ vs T does not reveal the presence of a magnetic phase transition. Quantum Monte Carlo simulations based on an anisotropic cubic lattice were applied to the magnetic data of la to afford g= 2.14, J= -13.4 K(Cu-pyz-Cu), and J⊥ = -0.20 K(Cu-F⋯:H⋯:F-Cu), while χ vs T for 1b could be well reproduced by a spin-1/2 Heisenberg uniform chain model for g = 2.127(1), J1 = -3.81(1), and zJ2 = -0.48(1) K, where J1 and J2 are the intra- and interchain exchange couplings, respectively, which considers the number of magnetic nearest-neighbors (z). The M(B) data for 1b could not be satisfactorily explained by the chain model, suggesting a more complex magnetic structure in the ordered state and the need for additional terms in the spin Hamiltonian. The observed variation in magnetic behaviors is driven by differences in the H⋯F hydrogen-bonding motifs. [ABSTRACT FROM AUTHOR]