title: Importance of halogen···halogen contacts for the structural and magnetic properties of CuX2(pyrazine-N,N′-dioxide)(H2O)2 (X = Cl and Br).
abstract: The structural and magnetic properties of the newly crystallized CuX(2)(pyzO)(H(2)O)(2) (X = Cl, Br; pyzO = pyrazine-N,N'-dioxide) coordination polymers are reported. These isostructural compounds crystallize in the monoclinic space group C2/c with, at 150 K, a = 17.0515(7) Å, b = 5.5560(2) Å, c = 10.4254(5) Å, β = 115.400(2)°, and V = 892.21(7) Å(3) for X = Cl and  a = 17.3457(8) Å, b = 5.6766(3) Å, c = 10.6979(5) Å, β = 115.593(2)°, and V = 950.01(8) Å(3) for X = Br. Their crystal structure is characterized by one-dimensional chains of Cu(2+) ions linked through bidentate pyzO ligands. These chains are joined together through OH···O hydrogen bonds between the water ligands and pyzO oxygen atoms and  Cu-X···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···X-Cu supersuperexchange because the magnetic orbital of the Cu(2+) ion is contained in the CuX(2)(H(2)O)(2) plane and  the X···X contact distances are short. The magnetic data were fitted to a Heisenberg 1D uniform antiferromagnetic chain model with J(1D)/k(B) = -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 J(1D) 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 J(1D)/k(B) up to -51.2 K at 0.84 GPa, suggesting a shortening of the Br···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(2)(pyzO)(H(2)O)(2) is magnetically ordered with T(N) = 1.06(1) K, while the signature for long-range magnetic order in CuBr(2)(pyzO)(H(2)O)(2) was much less definitive down to 0.26 K. The results for the CuX(2)(pyzO)(H(2)O)(2) complexes are compared to the related CuX(2)(pyrazine) materials.
authors.affiliation: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States. JASchlueter@anl.gov
authors.forename: John A
authors.initials: JA
authors.lastname: Schlueter
authors.forename: Hyunsoo
authors.initials: H
authors.lastname: Park
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Halder
authors.forename: William R
authors.initials: WR
authors.lastname: Armand
authors.forename: Cortney
authors.initials: C
authors.lastname: Dunmars
authors.forename: Karena W
authors.initials: KW
authors.lastname: Chapman
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Manson
authors.forename: John
authors.initials: J
authors.lastname: Singleton
authors.forename: Ross
authors.initials: R
authors.lastname: McDonald
authors.forename: Alex
authors.initials: A
authors.lastname: Plonczak
authors.forename: Jinhee
authors.initials: J
authors.lastname: Kang
authors.forename: Chaghoon
authors.initials: C
authors.lastname: Lee
authors.forename: Myung-Hwan
authors.initials: MH
authors.lastname: Whangbo
authors.forename: Tom
authors.initials: T
authors.lastname: Lancaster
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Steele
authors.forename: Isabel
authors.initials: I
authors.lastname: Franke
authors.forename: Jack D
authors.initials: JD
authors.lastname: Wright
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Blundell
authors.forename: Francis L
authors.initials: FL
authors.lastname: Pratt
authors.forename: Joseph
authors.initials: J
authors.lastname: deGeorge
authors.forename: Mark M
authors.initials: MM
authors.lastname: Turnbull
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Landee