[Cu(HF2)(pyz)2]BF4 (pyz = pyrazine): long-range magnetic ordering in a pseudo-cubic coordination polymer comprised of bridging HF2? and pyrazine ligands

Manson, Jamie L.; Conner, Marianne M.; Schlueter, John A.; Lancaster, Tom; Blundell, Stephen J.; Brooks, Michael; Pratt, F. L.; Papageorgiou, Thomas; Bianchi, A D; Wosnitza, J.; Whangbo, Myung‐Hwan

doi:10.1039/b608791d

Cited by 65 publications

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“…However, thermodynamic probes are known to be less sensitive to transitions driven by interplanar couplings [S11] while local probes such as muon-spin relaxation (µ + SR) are much more effective at determining the antiferromagnetic transition temperature, T N [22]. Our µ + SR data on this compound, shown in Fig.…”

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confidence: 88%

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Dimensionality Selection in a Molecule-Based Magnet

et al. 2012

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Gaining control of the building blocks of magnetic materials and thereby achieving particular characteristics will make possible the design and growth of bespoke magnetic devices. While progress in the synthesis of molecular materials, and especially coordination polymers, represents a significant step towards this goal, the ability to tune the magnetic interactions within a particular framework remains in its infancy. Here we demonstrate a chemical method which achieves dimensionality selection via preferential inhibition of the magnetic exchange in an S = 1/2 antiferromagnet along one crystal direction, switching the system from being quasi-two-to quasi-one-dimensional while effectively maintaining the nearest-neighbour coupling strength.Coordination polymers are self-organising materials consisting of arrays of metal ions linked via molecular ligands, with non-coordinated counterions supplying charge neutrality. The choice of initial components permits a high level of control over the final product, enabling many different polymeric architectures to be obtained [1]. These materials provide a route to successful crystal engineering, and a number of functionalities are being actively studied, including gas storage [2-4], optoelectronic [5,6], ferroelectric [7,8] and magnetic properties [9-14].Although it is now possible to generate an assortment of disparate magnetic lattices using this method [15,16], true control of magnetic exchange interactions implies an ability to adjust selected parameters while keeping others constant. To this end, a series of coordination polymers based on Cu(II) ions bridged by pyrazine (C 4 H 4 N 2 ) molecules have proven to be highly versatile. In these systems it has been shown that it is possible to alter significantly the primary exchange energies via adjustment of the ligands [17] and the counterions [18, S9], or fine-tune the exchange by a few percent via isotopic substitution [20], all the while maintaining the same basic metal-pyrazine network. In this paper we demonstrate the power of this strategy by chemically engineering a reduction in the dimensionality of a magnetic system. After first designing a material based on coordinated planes of Cu(II), we adapt the recipe such that the ligand bridges are broken along a specific crystal direction, resulting in a chain-like compound. Because the ligand mediating the magnetic interactions in both cases is unchanged, the nearest-neighbour exchange energies of the two materials are found to be equal to each other to within 5%. The difference in numbers of nearest-neighbours, however, means that the strength of the combined exchange interactions acting on each magnetic ion in the quasitwo-dimensional material is twice that of its quasi-onedimensional cousin.Figs. 1(a) and (b) show the crystal structure of orthorhombic [Cu(pyz) 2 (pyO) 2 ](PF 6 ) 2 (where pyz = pyrazine and pyO = pyridine-N -oxide, C 5 H 5 NO) determined using single-crystal x-ray diffraction [21]. S = 1/2 Cu ions are linked by pyz molecules into nearly square planar ...

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“…1(b), magnetic exchange energies are likely to be very small along the c-direction. In contrast, Cu-pyz-Cu bridges are known to be good mediators of antiferromagnetic superexchange [22,23] and so the magnetic properties of this material are expected to be quasi-two-dimensional. This is confirmed by the magnetic measurements described below.…”

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Dimensionality Selection in a Molecule-Based Magnet

et al. 2012

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“…[10][11][12] [ À and SbF 6 À , respectively. [10,12] Our efforts to utilize HF 2 À as a synthon much like CN À , N 3 À , and NCS À [13][14][15] have now led to the synthesis of a two-dimensional (2D) rectangular coordination polymer, namely, [Cu(HF 2 ) 2 (pyz)] n , in which the adjacent Cu 2+ ions are linked by a pyz ligand in one direction, and by two HF 2 À ions with two different bridging modes (m 1,1 and m 1,3 modes, Scheme 1 c) in the other direction (Figure 1 a). We establish that the m 1,1 -mode HF 2 À ion is close in nature to F À ···HF, and that the magnetic properties of [Cu(HF 2 ) 2 (pyz)] n are described by a 2D rectangular antiferromagnetic (AFM) lattice with a weaker spin exchange through the pyz bridge.…”

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“…Various diamagnetic salts of HF 2 À ions have been structurally characterized. [3][4][5][6][7][8] The only known paramagnetic compounds containing HF 2 À ions are the [pipzH 2 ][MnF 4 (HF 2 )] (pipz = piperazine) [9] and [Cu(HF 2 )(pyz) 2 ]X (X = BF 4 À , [10] ClO 4 À , PF 6 À , [11] AsF 6 À , SbF 6 À , [12] pyz = pyrazine) coordination polymers. [10][11][12] [ À and SbF 6 À , respectively.…”

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“…[3][4][5][6][7][8] The only known paramagnetic compounds containing HF 2 À ions are the [pipzH 2 ][MnF 4 (HF 2 )] (pipz = piperazine) [9] and [Cu(HF 2 )(pyz) 2 ]X (X = BF 4 À , [10] ClO 4 À , PF 6 À , [11] AsF 6 À , SbF 6 À , [12] pyz = pyrazine) coordination polymers. [10][11][12] [ À and SbF 6 À , respectively. [10,12] Our efforts to utilize HF 2 À as a synthon much like CN À , N 3 À , and NCS À [13][14][15] have now led to the synthesis of a two-dimensional (2D) rectangular coordination polymer, namely, [Cu(HF 2 ) 2 (pyz)] n , in which the adjacent Cu 2+ ions are linked by a pyz ligand in one direction, and by two HF 2 À ions with two different bridging modes (m 1,1 and m 1,3 modes, Scheme 1 c) in the other direction (Figure 1 a).…”

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[Cu(HF₂)₂(pyrazine)]_n: A Rectangular Antiferromagnetic Lattice with a Spin Exchange Path Made Up of Two Different FHF⁻ Bridges

et al. 2011

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The two‐dimensional antiferromagnet [Cu(HF2)2(pyz)]n (pyz=pyrazine) has a rectangular lattice (see picture) displaying two types of FHF− bridging modes. The spin exchange through Cu‐(FHF)2‐Cu is about 90 % stronger than through Cu‐pyz‐Cu, and the μ1,1‐coordinated FHF−, which is close in nature to F−⋅⋅⋅HF, is largely responsible for the exchange. C black, Cu red, F green, H cyan.

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Constructing Magnetic Molecular Solids by Employing Three‐Atom Ligands as Bridges

Wang

Gao

2009

Design and Construction of Coordination Polymers

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The combination of some three-atom bridges with paramagnetic 3d transition metal ions results in the systematic isolation of molecular magnetic materials, ranging from single-molecule and singlechain magnets to layered weak ferromagnets and three-dimensional porous magnets. The design strategy and role of secondary components, such as co-ligands, templates and other mixed short ligands are discussed.

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[Cu(HF2)(pyz)2]BF4 (pyz = pyrazine): long-range magnetic ordering in a pseudo-cubic coordination polymer comprised of bridging HF2? and pyrazine ligands

Abstract: [Cu(HF2)(pyz)2]BF4 consists of rare mu(1,3) bridging HF2- anions and micro-pyrazine ligands leading to a 3D pseudo-cubic framework that antiferromagnetically orders below 1.54(1) K.

Cited by 65 publications

References 24 publications

Dimensionality Selection in a Molecule-Based Magnet

Dimensionality Selection in a Molecule-Based Magnet

[Cu(HF₂)₂(pyrazine)]_n: A Rectangular Antiferromagnetic Lattice with a Spin Exchange Path Made Up of Two Different FHF⁻ Bridges

Constructing Magnetic Molecular Solids by Employing Three‐Atom Ligands as Bridges

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[Cu(HF2)(pyz)2]BF4 (pyz = pyrazine): long-range magnetic ordering in a pseudo-cubic coordination polymer comprised of bridging HF2? and pyrazine ligands

Abstract: [Cu(HF2)(pyz)2]BF4 consists of rare mu(1,3) bridging HF2- anions and micro-pyrazine ligands leading to a 3D pseudo-cubic framework that antiferromagnetically orders below 1.54(1) K.

Cited by 65 publications

References 24 publications

Dimensionality Selection in a Molecule-Based Magnet

Dimensionality Selection in a Molecule-Based Magnet

[Cu(HF2)2(pyrazine)]n: A Rectangular Antiferromagnetic Lattice with a Spin Exchange Path Made Up of Two Different FHF− Bridges

Constructing Magnetic Molecular Solids by Employing Three‐Atom Ligands as Bridges

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[Cu(HF₂)₂(pyrazine)]_n: A Rectangular Antiferromagnetic Lattice with a Spin Exchange Path Made Up of Two Different FHF⁻ Bridges