A Highly Anisotropic Cobalt(II)-Based Single-Chain Magnet: Exploration of Spin Canting in an Antiferromagnetic Array Andrei V. Palii,* ,† Oleg S. Reu, † Sergei M. Ostrovsky, † Sophia I. Klokishner, † Boris S. Tsukerblat,* ,‡ Zhong-Ming Sun, § Jiang-Gao Mao, § Andrey V. Prosvirin, | Han-Hua Zhao, | and Kim R. Dunbar* ,| Institute of Applied Physics of the Academy of Sciences of MoldoVa, Academy str. 5, Chisinau MD-2068, MoldoVa, Chemistry Department, Ben-Gurion UniVersity of the NegeV, Beer-SheVa 84105, Israel, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, People’s Republic of China, and Department of Chemistry, Texas A&M UniVersity, P.O. Box 30012, College Station, Texas 77843-3012 Received June 30, 2008; E-mail: andrew.palii@uv.es; tsuker@bgu.ac.il; dunbar@mail.chem.tamu.edu Abstract: In this article we report for the first time experimental details concerning the synthesis and full characterization (including the single-crystal X-ray structure) of the spin-canted zigzag-chain compound [Co(H 2 L)(H 2 O)] ∞ [L ) 4-Me-C 6 H 4 -CH 2 N(CPO 3 H 2 ) 2 ], which contains antiferromagnetically coupled, highly magnetically anisotropic Co(II) ions with unquenched orbital angular momenta, and we also propose a new model to explain the single-chain magnet behavior of this compound. The model takes into account (1) the tetragonal crystal field and the spin-orbit interaction acting on each Co(II) ion, (2) the antiferromagnetic Heisenberg exchange between neighboring Co(II) ions, and (3) the tilting of the tetragonal axes of the neighboring Co units in the zigzag structure. We show that the tilting of the anisotropy axes gives rise to spin canting and consequently to a nonvanishing magnetization for the compound. In the case of a strong tetragonal field that stabilizes the orbital doublet of Co(II), the effective pseudo-spin- 1 / 2 Hamiltonian describing the interaction between the Co ions in their ground Kramers doublet states is shown to be of the Ising type. An analytical expression for the static magnetic susceptibility of the infinite spin- canted chain is obtained. The model provides an excellent fit to the experimental data on both the static and dynamic magnetic properties of the chain. Introduction One-dimensional (1D) systems that exhibit magnetic bista- bility, which are commonly called single-chain magnets (SCMs), are of great interest because of their unusual physical properties and their potential importance for high-density data storage and quantum-computing applications. 1,2 During the past few years, this branch of molecular magnetism dealing with 1D magnets has become an area of intense research activity. 3-16 In contrast to single-molecule magnets, 1,2 the slow relaxation of magnetiza- tion in SCMs is due to the exchange interaction between rapidly relaxing units. The theoretical background for the description of SCM behavior is provided by Glauber’s stochastic ap- proach. 17 Glauber predicted the presence of slow relaxation of magnetization in a chain composed of ferromagnetically coupled spins that can be described by the Ising Hamiltonian: † Academy of Sciences of Moldova. ‡ Ben-Gurion University of the Negev. § Fujian Institute of Research on the Structure of Matter. | Texas A&M University. (1) Gatteschi, D.; Sessoli, R.; Villain, J. Molecular Nanomagnets; Oxford University Press: Oxford, U.K., 2006. (2) Gatteschi, D.; Sessoli, R. Angew. Chem., Int. Ed. 2003, 42, 268. (3) Caneschi, A.; Gatteschi, D.; Lalioti, N.; Sangregorio, C.; Sessoli, R.; Venturi, G.; Vindigni, A.; Rettori, A.; Pini, M. G.; Novak, M. A. Angew. Chem., Int. Ed. 2001, 40, 1760. (4) Caneschi, A.; Gatteschi, D.; Lalioti, N.; Sessoli, R.; Sorace, L.; Tangoulis, V.; Vindigni, A. Chem.sEur. J. 2002, 8, 286. 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