Elsevier

Polyhedron

Volume 64, 12 November 2013, Pages 110-121
Polyhedron

Crystallographic and magnetic studies of the 2-pyridone/copper halide system

Dedicated to Prof. George Christou on the occasion of his 60th birthday. May there be many more.
https://doi.org/10.1016/j.poly.2013.03.066Get rights and content

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  • The syntheses of [(2-pyridone)2CuX2]2 (X = Cl, Br), [(2-pyridone)CuCl2]2, (2-pyridone)3CuCl2, and (2-pyridone)2 [CuCl2(H2O)2] are reported.

  • The [(2-pyridone)2CuX2]2 (X = Cl, Br) complexes crystallize as O-bridged dimers and show significant antiferromagnetic exchange (J = −38.2(1), −41.7(1) K).

  • [(2-pyridone)CuCl2]2 exhibits ferromagnetic exchange (J = +9(1) K) via a bichloride bridge. The dimers interact antiferromagnetically.

  • In spite of a similar bichloride bridge, (2-pyridone)2 [CuCl2(H2O)2] exhibits only weak ferromagnetic exchange.

Abstract

A series of copper halide complexes have been prepared employing 2-pyridone as a ligand. The compounds [CuBr2(2-pyridone)2]2 (1), [CuCl2(2-pyridone)2]2 (2), [CuCl2(2-pyridone)]2 (3), [CuCl2(2-pyridone)3] (4), and [CuCl2·2H2O]2[(2-pyridone)2] (5) were prepared and their structures and magnetic properties studied. Compounds 1 and 2 are dimeric species with the Cu(II) ions bridged by a pair of O-atoms from 2-pyridone molecules. Compound 3 is also a dimer, but in this case bridged by a pair of chloride ions. Only compound 4 is monomeric with fairly well isolated copper(II) ions, while compound 5 is a coordination polymer with the Cu(II) ions linked into chains via pairs of bridging chloride ions. Analysis of the magnetic data reveals that 1 and 2 exhibit significant antiferromagnetic interactions, while 4 is very weakly antiferromagnetic. Compounds 3 and 5 show weak ferromagnetic interactions. Data for 1 and 2 were fit to the antiferromagnetic dimer model with a Curie–Weiss correction to account for interdimer interactions: 1, J = −41.7(1) K, θ = −0.8(1) K; 2, J = −38.2(1) K, θ = −0.7(1) K. Data for 3 were fit to the ferromagnetic dimer model with a Curie–Weiss correction for interdimer interactions:); 2, J = 9.4(6), θ = −3.2(3). Interactions in both 4 and 5 were sufficiently weak that data were fit only to the Curie–Weiss expression resulting in θ-values of −0.50(7) and 0.58(4) K respectively.

Graphical abstract

Copper(II) bromide and chloride complexes of 2-pyridone of the formula CuX2(2-pyridone)n(H2O)m (X = Cl, Br; n = 1, 2,3; m = 0, 2) have been prepared and studied magnetically and crystallographically. Three of the complexes form dimers linked either via bichloride bridges, or via bridging 2-pyridone O-atoms, while one forms an isolated species and one forms a chloride bibridged coordination polymer. The complexes exhibit a mixture of ferromagnetic and antiferromagnetic interactions.

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Introduction

The study of coordination complexes as molecular magnets has the potential to allow for the construction of materials that have designed physical and magnetic properties depending upon the structure of the compound. Through choice of metal ion and ligand, the complex can potentially be modified to have different opacities, densities, and pathways of magnetic exchange. Studying the mechanism through which magnetic exchange occurs and how the structure of the transition metal complexes affects the magnitude and sign of the exchange will allow for the design of materials with specific magnetic properties.

The focus of our research has been to create a catalog of metal–organic copper halide complexes and salts through which crystal packing and magnetic exchange can be classified based on specific properties such as size, electronic nature of substituents, and hydrogen bonding properties of the organic material used. In recent years, much work has been done related to complexes of substituted 2-aminopyridine compounds with copper halides [1]. By altering the substituents on the 2-aminopyridine ring, a variety of structural motifs and therefore a variety of magnetic properties were obtained.

It is important to note the hydrogen bonding properties of the 2-aminopyridine/2-aminopyridinium moieties in these complexes. Hydrogen bond donation via both the amino group and pyridinium ion were significant in controlling the structure of the crystal [1]. If such a ligand, when substituted with different functional groups, is able to form transition metal complexes with a wide variety of structural and magnetic properties, what additional effects could be observed by replacing the hydrogen bond donating amino group with a substituent which could serve as both a hydrogen bond donor and acceptor? Although the amino substituent is in principle a hydrogen-bond acceptor, in practice the conjugation of the lone pair on the amino-N atom to the aromatic ring makes it a poor acceptor at best. However, 2-hydroxypyridine can serve as both a hydrogen bond donor (at the O atom) and a hydrogen bond acceptor (at both N and O atoms), either of which could aid in the packing and stabilization of complexes. It readily tautomerizes to the 2-pyridone form (Scheme 1) which is a hydrogen bond donor only at the N atom while the O atom may now serve only as a hydrogen bond acceptor.

Both the X-ray [2] and neutron [3] scattering studies indicate that the preferred form for the compound in the solid state is that of the 2-pyridone tautomer. A number of coordination complexes have been isolated showing coordination to the O-atom of 2-pyridone to Cu(II) [4], as well as Fe(II) [5], Mn(II) [6], second and third row transition metals [7], and lanthanide ions [8] and a significant number of Cu(II), Co(II), and Ni(II) complexes of the 6-chloro- and 6-methyl-2-pyridone compounds (many heterobimetallics incorporating lanthanide ions) have been reported [9]. Far fewer structures have been reported with coordination to the N-atom of the 2-hydroxypyridine tautomer, and all are of second and third row transition metals [10]. To date, only two 2-pyridone copper chloride compounds have been reported in the literature [11], [12], including the room temperature crystal structure of [(C5H5NO)2CuCl2]2, but magnetic studies had not been completed on these compounds. Here, we report the synthesis and characterization of structural and magnetic properties of five complexes of 2-pyridone with copper halides: [(C5H5NO)2CuBr2]2 (1) [(C5H5NO)2CuCl2]2 (2), [(C5H5NO)CuCl2]2 (3), [(C5H5NO)3CuCl2] (4) and [(C5H5NO)2][CuCl2·2H2O]2 (5).

Section snippets

Experimental

2-Hydroxypyridine was purchased from the Aldrich Chemical Company and used without further purification. Copper chloride and copper bromide were obtained from Baker and used without further purification. IR spectra were recorded on a Paragon 500 spectrometer. Elemental analyses were carried out by the Marine Science Institute, University of California, Santa Barbara, CA. Repeated combustion analyses consistently showed a low percent composition of hydrogen in compounds 13. However, powder

Results

Reaction of CuBr2 in acidic THF/H2O yielded crystals of 1, [CuBr2(2-pyridone)2]2 in good yield. Although the yield varied slightly, complex 1 was obtained as the product under a variety of conditions, included changes of solvent and pH. However, the chemistry of the CuCl2/2-pyridone system is substantially more complex. Although previous reports of the synthesis of 2, [CuCl2(2-pyridone)2]2, [12] were unsuccessful in our hands, direct combination of copper(II) chloride and 2-pyridone in

Discussion

Reaction of 2-hydroxypyridine with CuBr2 in water, acetonitrile, and ethanol at a variety of temperatures consistently produced [CuBr2(2-pyridone)2]2 (1), with yields near 80%. Reaction of 2-hydroxypyridine with CuCl2 yielded a variety of products depending upon the reaction conditions. When the reaction takes place in water at room temperature, [CuCl2(H2O)2]·2(2-pyridone) (5) is consistently the major product. However, when the reaction occurs in acetonitrile, the products are temperature

Acknowledgments

Financial assistance from the NSF (IMR-0314773), the Kresge Foundation, and PCISynthesis Inc. toward the purchase of the MPMS SQUID magnetometer and powder diffractometer are gratefully acknowledged. K.C.S. is grateful for a James and Ada Bickman Summer Science Internship. The authors thank M.Sc. T. González (IVIC-Venezuela) for technical support with the structure of 5.

References (38)

  • R.M. Gaura et al.

    Inorg. Chim. Acta

    (1982)
    U. Geiser et al.

    Inorg. Chem.

    (1986)
    A. Luque et al.

    J. Chem. Soc., Dalton Trans.

    (1997)
    G. Pon et al.

    Inorg. Chim. Acta

    (1997)
    F.M. Woodward et al.

    Inorg. Chim. Acta

    (2001)
    S.H. Liu et al.

    Inorg. Chem.

    (2001)
    F.M. Woodward et al.

    Phys. Rev. B

    (2002)
    M. Deumal et al.

    Eur. J. Inorg. Chem.

    (2005)
    D.K. Kumar et al.

    Cryst. Growth Des.

    (2005)
    S.F. Haddad et al.

    Inorg. Chim. Acta

    (2006)
    L. Li et al.

    Inorg. Chem.

    (2007)
    R.H. Al-Far et al.

    Acta Crystallogr., Sect. E

    (2008)
    R.H. Al-Far et al.

    Acta Crystallogr., Sect. E

    (2009)
    K.C. Shortsleeves et al.

    Inorg. Chim. Acta

    (2009)
  • L. Glazar et al.

    Acta Crystallogr., Sect. C

    (2005)
    H. Sun et al.

    Beijing Dax. Xue., Zir. Kex. (Chin.) (Acta Sci. Nat. Univ. Pek)

    (1994)
    B. Kozlevcar et al.

    Polyhedron

    (2007)
    S.R. Breeze et al.

    Inorg. Chem.

    (1993)
    D. Taylor

    Aust. J. Chem.

    (1975)
    V. Selmani et al.

    Inorg. Chem. Commun.

    (2010)
  • S. Supriya et al.

    J. Am. Chem. Soc.

    (2007)
    S. Supriya et al.

    New J. Chem.

    (2003)
  • L.S. Hollis et al.

    Inorg. Chem.

    (1983)
    L.S. Hollis et al.

    J. Am. Chem. Soc.

    (1981)
    K. Fujita et al.

    Org. Lett.

    (2007)
    P.L. Andreu et al.

    J. Organomet. Chem.

    (1991)
    A. Schreiber et al.

    Inorg. Chem.

    (1994)
    Q.-W. Chang et al.

    Z. Kristallogr. New Cryst. Struct.

    (2011)
  • P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, R. de Gelder, R. Israel, J.M.M. Smits, dirdif99, The dirdif-99...
  • D.J. Watkin et al.

    crystals Issue 10

    (1996)
  • G.H. Keller et al.

    Can. J. Chem.

    (1968)
  • F. van Bolhuis et al.

    Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem.

    (1978)
  • R.D. Willett et al.

    Inorg. Chem.

    (1986)
  • H.D. Arman et al.

    Acta Crystallogr., Sect. E: Struct. Rep. Online

    (2009)
    H.W. Yang et al.

    Acta Crystallogr., Sect. B

    (1998)
  • U. Ohms et al.

    Z. Kristallogr.

    (1984)
  • A. Escuer et al.

    Inorg. Chem.

    (1998)
    N. Berg et al.

    Chem. Eur. J.

    (2012)
  • G.A. Bowmaker et al.

    Inorg. Chim. Acta

    (2005)
    A.R. Chakravarty et al.

    Inorg. Chem.

    (1985)
    H.D. Arman et al.

    Acta Crystallogr., Sect. E: Struct. Rep. Online

    (2010)
  • A.J. Blake et al.

    Angew. Chem., Int. Ed.

    (1991)
  • A.J. Blake et al.

    Angew. Chem., Int. Ed.

    (1994)
    A.J. Blake et al.

    J. Chem. Soc., Dalton Trans.

    (1994)
    A.J. Blake et al.

    J. Chem. Soc., Dalton Trans.

    (1997)
  • C.C. Houk et al.

    Inorg. Nucl. Chem.

    (1968)
  • A.J. Blake et al.

    Acta Crystallogr., Sect. C

    (1993)
  • G.M. Sheldrick

    Acta Crystallogr., Sect. A

    (2008)
  • P. Muller et al.

    Crystal Structure Refinement: A Crystallographer’s Guide to shelxl

    (2006)
  • Cited by (0)

    View full text