Experimental and theoretical characterization of the magnetic properties of CuF{sub 2}(H{sub 2}O){sub 2}(pyz) (pyz = pyrazine) : a two-dimensional quantum magnet arising from super-superexchange interactions through hydrogen bonded paths.
The structural, electronic, and magnetic properties of the new linear chain coordination polymer CuF{sub 2}(H{sub 2}O){sub 2}(pyz) (pyz = pyrazine) were determined by single crystal X-ray diffraction at various temperatures, SQUID magnetometry, pulsed-field magnetization, ESR, muon-spin relaxation ({mu}SR), and electronic structure calculations. Each Cu{sup 2+} ion of CuF{sub 2}(H{sub 2}O){sub 2}(pyz) is located at a distorted CuF{sub 2}O{sub 2}N{sub 2} octahedron with axial elongation along the Cu?N bonds. These octahedra are tethered together by strong F...H-O hydrogen bonds to yield two-dimensional (2D) square nets in the bc-plane that are linked along the a-direction by pyrazine linkages. Measurements of the g-factor by ESR along with first principles density functional theory electronic structure calculations show that the magnetic orbital of the Cu{sup 2+} ion lies in the CuF{sub 2}O{sub 2} plane thus forming a 2D antiferromagnetic square lattice. A broad maximum observed in x(T) at 10 K indicates a modest spin exchange interaction through the Cu-F...H-O-Cu supersuperexchange paths, and a theoretical fit of x(T) to a 2D square model gives J{sub 2D}/k{sub B} = ?5.58(1) K (in the convention where J rather than 2J is used for spin exchange). At lower temperatures, x(T) shows a sharp peak at 2.6 K, which signals a transition to a long-range magnetic ordering as confirmed by coherent precession of implanted muons. Isothermal M(B) measurements made at 0.5 K on an aligned single crystal reveal magnetic saturation, M{sub sat}, at 28.8 T (B{sub {parallel}}a) while a higher field of 33.1 T is required to saturate the spins when B is applied perpendicular to the a-axis thus showing clear anisotropy in these orientations. The presence of strong hydrogen bonds in CuF{sub 2}(H{sub 2}O){sub 2}(pyz) causes the chains to adopt a tilted packing arrangement, thus leading to a novel ground-state likely characterized by spin-canting within the 2D layers and a markedly increased critical temperature relative to the well-known Cu(NO{sub 3}){sub 2}(pyz) polymer chain compound.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); Royal Commission; Engineering and Physical Sciences Research Council (EPSRC)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 961716
- Report Number(s):
- ANL/MSD/JA-61851; JACSAT; TRN: US200923%%247
- Journal Information:
- J. Am. Chem. Soc., Vol. 20, Issue 24 ; Nov. 24, 2008; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- ENGLISH
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