Importance of halogen---halogen contacts for the structural and magnetic properties of CuX{<_2}(pyrazine-N,N'-dioxide)(H{<_2}O){<_2} (x = Cl & Br).
The structural and magnetic properties of the newly crystallized CuX{sub 2}(pyzO)(H{sub 2}O){sub 2} (X = Cl, Br; pyzO = pyrazine-N,N{prime}-dioxide) coordination polymers are reported. These isostructural compounds crystallize in the monoclinic space group C2/c with, at 150 K, a = 17.0515(7) {angstrom}, b = 5.5560(2) {angstrom}, c = 10.4254(5) {angstrom}, {beta} = 115.400(2){sup o}, and V = 892.21(7) {angstrom}{sup 3} for X = Cl and a = 17.3457(8) {angstrom}, b = 5.6766(3) {angstrom}, c = 10.6979(5) {angstrom}, {beta} = 115.593(2){sup o}, and V = 950.01(8) {angstrom}{sup 3} for X = Br. Their crystal structure is characterized by one-dimensional chains of Cu{sup 2+} ions linked through bidentate pyzO ligands. These chains are joined together through OH {hor_ellipsis} O hydrogen bonds between the water ligands and pyzO oxygen atoms and Cu-X {hor_ellipsis} X-Cu contacts. Bulk magnetic susceptibility measurements at ambient pressure show a broad maximum at 7 (Cl) and 28 K (Br) that is indicative of short-range magnetic correlations. The dominant spin exchange is the Cu-X {hor_ellipsis} X-Cu supersuperexchange because the magnetic orbital of the Cu{sup 2+} ion is contained in the CuX{sub 2}(H{sub 2}O){sub 2} plane and the X {hor_ellipsis} X contact distances are short. The magnetic data were fitted to a Heisenberg 1D uniform antiferromagnetic chain model with J1D/kB = -11.1(1) (Cl) and -45.9(1) K (Br). Magnetization saturates at fields of 16.1(3) (Cl) and 66.7(5) T (Br), from which J1D is determined to be -11.5(2) (Cl) and -46.4(5) K (Br). For the Br analog the pressure dependence of the magnetic susceptibility indicates a gradual increase in the magnitude of J1D/kB up to -51.2 K at 0.84 GPa, suggesting a shortening of the Br {hor_ellipsis} Br contact distance under pressure. At higher pressure X-ray powder diffraction data indicates a structural phase transition at 3.5 GPa. Muon-spin relaxation measurements indicate that CuCl{sub 2}(pyzO)(H{sub 2}O){sub 2} is magnetically ordered with TN = 1.06(1) K, while the signature for long-range magnetic order in CuBr{sub 2}(pyzO)(H{sub 2}O){sub 2} was much less definitive down to 0.26 K. The results for the CuX{sub 2}(pyzO)(H{sub 2}O){sub 2} complexes are compared to the related CuX{sub 2}(pyrazine) materials.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 1036441
- Report Number(s):
- ANL/MSD/JA-70958; INOCAJ; TRN: US201206%%314
- Journal Information:
- Inorganic Chemistry, Vol. 51, Issue 4; ISSN 0020-1669
- Country of Publication:
- United States
- Language:
- ENGLISH
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