A Reply to the Comment by T. Vogt et al.Received 31 January 1995DOI:https://doi.org/10.1103/PhysRevLett.75.2629©1995 American Physical Society

A Reply to the Comment by E. M. Forgan, et al.Received 20 October 1994DOI:https://doi.org/10.1103/PhysRevLett.74.1698©1995 American Physical Society

The magnetic properties of the powdered layered structures of 3-ammoniumpyridinium tetrabromocuprate(II) and 3-ammoniumpyridinium tetrachlorocuprate(II) have been studied from 4.2 to 150 K. The data were interpreted using both 1D and 2D series expansions for the Heisenberg model, combined with the appropriate mean-field corrections, yielding interlayer exchanges with J2h/k values of (−11±2) K for the chloride salt and (−52±7) K for the bromide salt. The intralayer exchange (J1h/k) values were found to be (14±2) K and (20±2.5) K for the chloride and bromide salts, respectively. The new results are compared with previous results for the eclipsed layered structure series NH3(CH2)nNH3CuX4, where X=Br or Cl and n=2, 3, 4, or 5. As the halide-halide separation distance decreases the transition from magnetic isolation of the layers to a strong interlayer exchange is observed. The new study allows confirmation of the power dependence on the halide-halide separation.

Magnetic resonance spectra at 12–36 GHz are reported for Fe2+(3d6, S=2) in the 1D Ising ferromagnet [(CH3)3NH]FeCl3⋅2H2O, known as FeTAC, between 2.5 and 13 K. The main signal was identified as a spin-cluster resonance (SCR) because of its characteristic temperature dependence below 6 K and the linear dependence of the resonance field on the microwave frequency for H parallel to the easy axis at 4.2 K. The temperature dependence of the line intensity was fitted to the function exp[−(2J+hν)/kBT], with 2J/kB=(41±1) K, and the linear field dependence was explained by the value gz=8.26±0.05 in the S=1/2 representation and a demagnetization field of several hundred gauss, which depended on the sample shape. A frequency-dependent satellite structure observed on the low field side of the main line, which appeared as a broad line below 15 GHz, is tentatively associated with energy shifts of the lower-lying spin-cluster states produced by the magnetic dipole interaction and other terms in the Hamiltonian.

The EPR linewidths of (C3H7NH3)2Mn1−xCdxCl4 have been measured in the paramagnetic region as a function of temperature. An Arrhenius behavior exp(b/T) is observed with b strongly dependent on Cd concentration. This behavior in the pure compound is characteristic of soliton-like (skyrmion) excitations with b related to the excitation energy. In the doped compound, gapless nonlinear excitations are possible, resulting in a much different temperature-dependent linewidth. It is concluded that skyrmions dominate the low-temperature thermodynamics of two-dimensional magnets.

The syntheses, crystal structures, and powder magnetic studies of several new quasi-planar bibridged Cu(n)X(2n+2)(2-) oligomers (n = 3, 4, 6, and 7; X = Cl or Br) are reported, based on the 1-methylpyridinium (C6H8N)(+) and 1,2-dimethylpyridinium (C7H10N)(+) cations. These include (C7H10N)(2)Cu3Br8, (C6H8N)(2)Cu4Cl10, (C7H10N)(2)Cu6Cl14, and (C7H10N)(2)Cu7Br16. Crystallographic data: (C7H10N)(2)Cu3Br8, triclinic, space group P (1) over bar, a = 7.947(2) Angstrom, b = 8.799(2) Angstrom, c = 9.840(2) Angstrom, alpha = 86.95(2)degrees, beta = 76.23(2)degrees, gamma = 71.54(2)degrees, V = 633.6(3) Angstrom(3), Z = 2, d(x) = 2.78 g/cm(3), and R = 0.0483; (C6H8N)(2)Cu4Cl10, monoclinic, space group P2(1)/n, a = 11.759(2) Angstrom, b = 9.056(2) Angstrom, c = 12.048(3) Angstrom, beta = 106.21(2)degrees, V = 1232.1(5) Angstrom(3), Z = 2, d(x) = 2.15 g/cm(3), and R = 0.0321; (C7H10N)(2)Cu6Cl14, triclinic, P (1) over bar, a = 8.997(3) Angstrom, b = 9.288(3) Angstrom, c = 11.540(4) Angstrom, alpha = 80.53(2)degrees, beta = 67.82(2)degrees, gamma = 60.22(2)degrees, V = 714.7(4) Angstrom(3), Z = 1, d(x) = 2.34 g/cm(3), and R = 0.0363; (C6H8N)(2)Cu7Br16, triclinic, P (1) over bar, a = 7.237(2) Angstrom, b = 10.880(2) Angstrom, c = 12.880(2) Angstrom, alpha = 89.47(2) Angstrom, beta = 75.08(2)degrees, gamma = 79.48(2)degrees, V = 962.7(3) Angstrom(3), Z = 1, d(x) = 3.35 g/cm(3), and R = 0.0520. A common feature of the structures is the existence of oligomers containing quasi-planar symmetric bibridged finite chains of edge-sharing CuX(4), (X = halide) monomeric units. The n = 3 oligomers aggregate into chains through the formation of asymmetric bibridged linkages between terminal copper ions on adjacent trimers. In the n = 4 salt, the oligomers aggregate into stacks in which pairs of the copper ions extend their coordination sphere by forming a long, semicoordinate bond to a halide ion from a neighboring oligomer. For both the n = 3 and n = 4 salts, the pyridinium cations lie parallel to and directly above and below the anionic oligomers, separating the chains. In the n = 6 rind n = 7 salts, the stacks formed in this manner interdigitate, forming two-dimensional slabs. The slabs are separated by the organic cations. The magnetic properties of compounds are dominated by antiferromagnetic intraoligomer interactions. Thus, the n = 4 and n = 6 salts depopulate into singlet ground states at low temperature. In contrast, the n = 3 and n = 7 oligomers have S = 1/2 ground states. Expressions for the magnetic susceptibility of the n = 6 and n = 7 oligomers were obtained by diagonalization of a nearest neighbor Heisenberg Hamiltonian. The data were fit to these expressions, with inclusion of a mean field correction for interoligomer exchange. The intra-oligomer exchange coupling constants are J(1)/k = -153 K for n = 3; J(1)/k = -60 K, J(2)/k = -40 K for n = 3; J(1)/k = -23 K, J(2)/k = -30 K, and J(3)/k = -52 K for n = 5 and J(1)/k = -90 K, J(2)/k = -90 K and J(3)/k = -120 K.At low temperature, the n = 3 oligomer exhibits ferromagnetic behavior. Since the oligomer has depopulated to a spin 1/2 ground state, the system can be modeled as a spin 1/2 ferromagnetic chain with J'/k = 22.8 K.

The structure and magnetic properties and EPR spectra are reported for two copper chloride complexes of CuCl64-stoichiometry. (1-Methylpiperazinium)2CuCl6 belongs to the triclinic space group P1BAR with a = 12.448 (8) angstrom b = 11.891 (8) angstrom, c = 6.577 (4) angstrom, a = 84.16 (1)-degrees, beta = 86.74 (1)-degrees, gamma = 93.56 (1)-degrees, and Z = 2. The structure contains isolated cations, CuCl42- anions, and lattice Cl- ions. The CuCl42- anions have nearly D2d symmetry with an average trans Cl-Cu-Cl angle of 145.8-degrees. The crystals of (piperazinium)2CuCl6.MeOH are tetragonal, of space group P4(2)/n, with a = 13.597 (8) angstrom, c = 11.376 (8) angstrom, and Z = 4. The structure is composed of isolated piperazinium cations, Cl- ions, and methanol molecules and chains of nearly square pyramidal CuCl53- anions. The primary distortion of the CuCl53- species away from idealized C4v symmetry involves a small C2v distortion im basal plane (trans Cl-Cu-Cl angles = 166.8 (1) and 178.2 (1)-degrees, respectively). The basal Cu-Cl distances average 2.313 angstrom, while the apical Cu-Cl distance is 2.641 (3) angstrom. These anions are linked together in chains via extremely long interactions of 3.936 (3) angstrom between the apical Cl of one anion and the Cu atom of its neighbor. Magnetic susceptibility data are indicative of weak antiferromagnetic coupling in this latter compound. Analysis of the EPR line widths is consistent with a two-dimensional magnetic system. These results are interpreted in terms of a two-halide exchange pathway of the type Cu-Cl...Cl-Cu between chains.

Powder magnetic susceptibility measurements on two new, low-dimensional copper-halide systems are reported: (piperazinium)2CuCl6·CH3OH, and (1,2-dimethylpyridinium)2Cu3Br8. The data are analyzed using the high- and low-temperature series expansions for a 1D,S = ½, Heisenberg Hamiltonian, with a mean-field correction to model the interaction between chains. The piperazinium system shows very weak antiferromagnetism with a possibility of two-dimensional behavior. The pyridinium trimer system shows more strongly ferromagnetically coupled doublet ground states between trimers, which comprise the chain.

A theoretical study of the exchange coupling in a series of copper(II) halide compounds containing quasi-planar bi-bridged dimers is reported. The exchange, antiferromagnetic for the parent Cu2X62− (X = Cl, Br), becomes less antiferromagnetic as terminal halide ions are replaced by more electronegative O- or N-based ligands. The trend is attributed to the reduction in electron density on the bridging halide ions induced by these more electronegative ligands. Theoretical calculations of the exchange coupling are presented to compare with the experimental results.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructural, EPR, and magnetic characterization of bis(piperazinium) hexachlorocuprate-methanol and bis(1-methylpiperazinium) hexachlorocuprateA. Bonamartini-Corradi, L. P. Battaglia, J. Rubenacker, R. D. Willett, T. E. Grigereit, P. Zhou, and J. E. DrumhellerCite this: Inorg. Chem. 1992, 31, 18, 3859–3863Publication Date (Print):September 1, 1992Publication History Published online1 May 2002Published inissue 1 September 1992https://pubs.acs.org/doi/10.1021/ic00044a032https://doi.org/10.1021/ic00044a032research-articleACS PublicationsRequest reuse permissionsArticle Views104Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

AbstractThe structures of the title salts (Ia)‐(Id) ((Ia): space group P21/c, Z=4; (Ib): C2/c, Z=4; (Ic), (Id): P21/n, Z=4 and 2) are determined and discussed.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructures and magnetic properties of trinuclear copper(II) halide saltsTodd E. Grigereit, B. L. Ramakrishna, Helen Place, Roger D. Willett, Gian Carlo Pellacani, Tiziano Manfredini, Ledi Menabue, Anna Bonomartini-Corradi, and Luigi Pietro BattagliaCite this: Inorg. Chem. 1987, 26, 14, 2235–2243Publication Date (Print):July 15, 1987Publication History Published online1 May 2002Published inissue 15 July 1987https://doi.org/10.1021/ic00261a015RIGHTS & PERMISSIONSArticle Views162Altmetric-Citations39LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (893 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The magnetic susceptibilities of five trinuclear pseudoplanar bibridged copper(II) chloride species have been measured from approximately 5 to 300 K. The compounds all show antiferromagnetic intratrimer and generally weaker ferromagnetic intertrimer spin coupling. These compounds show systematic deviations from the susceptibility as calculated from an isotropic Heisenberg Hamiltonian with nearest-neighbor coupling. The deviations arise from intertrimer interactions through the formation of semicoordinate bonds and result in a spin-frustrated state at low temperatures. The results of a phenomenological mean field theory model support spin-frustration occurrence by accurately modeling the non-Boltzmann depopulation of the excited quartet state. Preliminary cluster expansion calculations have not lent support to the postulate but more extended calculations may be necessary to include a sufficient number of intermolecular interactions in order to accurately describe the crystalline state.