Synthesis, Structure, Magnetic Behavior, and Theoretical Analysis of Diazine-Bridged Magnetic Ladders: Cu(quinoxoline)X₂ and Cu(2,3-dimethylpyrazine)X₂ (X = Cl, Br)

Abstract

The synthesis, structure, and magnetic behavior of the complexes Cu(qnx)Br(2) (1), Cu(2,3-dmpz)Br(2) (2), Cu(qnx)Cl(2) (3), and Cu(2,3-dmpz)Cl(2) (4) (qnx = quinoxaline, dmpz = dimethylpyrazine) are described. Both X-ray structural data and fitting of the magnetic data suggest that the compounds are well-described as strong-rung, two-leg magnetic ladders with J(rung) ranging from -30 K to -37 K, and J(rail) ranging from -14 K to -24 K. An unexpected decrease in the exchange constant for J(rail) (through the diazine ligand) is observed when the halide ion is changed from bromide to chloride, along with a small decrease in the magnetic exchange through the halide ion. Theoretical calculations on 2 and 4 via a first-principles bottom-up approach confirmed the description of the complexes as two-leg magnetic ladders. Furthermore, the calculations provide an explanation for the experimentally observed change in the value of the magnetic exchange through the dmpz ligand when the halide ion is changed from bromide to chloride, and for the very small change observed in the exchange through the different halide ions themselves via a combination of changes in geometry, bond lengths, and anion volume.

Synthesis, Structure and Properties of a New Strong‐Rung Spin Ladder Compound Cu(2‐Ethylpyrazine)Br2

“…In this structure, each copper (II) ion coordinates with its neighboring two N atoms and three bromine ions, similar to the case of Cu(2,3dimethylpyrazine)Br 2 . [15] The CuÀ N bond lengths (2.072 Å for Cu(1)-N(1) and 2.023 Å for Cu(1)-N(2)) are similar to that in several other spin ladder compounds such as Cu-(quinoxoline)Cl 2 [15] (2.0676 Å). On the other hand, the CuÀ Br bond lengths range from 2.3754 Å to 2.4305 Å, close to that in its analog compound Cu(2-methylthiopyrazine)Br 2 .…”

“…[24] It can be seen that the exchange parameters are distinct between difference compounds, enabling detailed studies on the properties of spin ladders. The exchange couplings of Cu(2-ethylpyrazine)Br 2 are most close to that in Cu(quinox)Cl 2 which has J rail /k B = À 30.3 K and J rung /k B = À 35.0 K. [15]…”

“…[10] The strong-rail spin ladder compounds include (cpaH) 2 CuBr 4 , [11] Cu(2,3-dmpyH) 2 Br 4 [12] and (dmaH)(3,5dmcpH)CuBr 4 . [13] The strong-rung spin ladder compounds include (pipH) 2 CuBr 4 , [14] Cu(quinox)Cl 2 , [15] Cu(2,3dmpz)Cl 2 , [15] and Cu(2-methylthiopyrazine)Br 2 . [16] The nearly isotropic spin ladders with J rung /J rail = 1.04 and 1.16 were found in (5napH) 2 CuBr 4 • H 2 O [17] and Cu(quinox)Br 2 .…”

A Definition of the Magnetic Transition Temperature Using Valence Bond Theory

“…A variety of real magnetic topologies have been examined (column 2 in Table 1), including regular and alternating 1D chains, strong-rail and strong-rung spin-ladders, 2D AFM layer, 3D AFM interacting honeycomb layers and 3D FM diamond-type (see column 3 in Table 1 for most significant calculated J ij values). 19, [45][46][47][48][49][50] The maximum of ∂[χT (T )]/∂T , the so called Fisher's heat capacity, has also been obtained by numerical differentiation from experimental data (see column 4 for T Table 1). The critical temperature of the magnetic capacity C s (T ), namely T µ C , of seven real systems has been calculated applying equation (18) (see column 5 in Table 1) Table 1: Comparison between computed characteristic temperatures for seven studied prototypical crystals.…”

Magnetic properties of a quantum spin ladder in proximity to the isotropic limit

“…Among others, the strong-leg ladder compound DIMPY (chemical formula (C 7 H 10 N) 2 CuBr 4 ; γ = 0.58) [13][14][15][16][17][18][19][20][21][22] and strong-rung ladder material BPCB (chemical formula (C 5 H 12 N) 2 CuBr 4 ; γ ≈ 3.6) [23][24][25][26][27][28][29][30] are the most intensively studied. The exchange-coupling ratio of another strong-rung ladder compound, Cu(quinoxoline)Cl 2 , γ = 1.58 is much closer to unity [31]. The case of an isotropic ladder (γ ∼ 1) has been less studied, presented currently only by the compound (5-NAP) 2 CuBr 4 •H 2 O with γ = 1.04 [32,33].…”