Enhanced Ion Anisotropy by Nonconventional Coordination Geometry: Single-Chain Magnet Behavior for a [{Fe^IIL}₂{Nb^IV(CN)₈}] Helical Chain Compound Designed with Heptacoordinate Fe^II

Abstract

Nonconventional heptacoordination in combination with efficient magnetic exchange coupling is shown to yield a 1-D heteronuclear {Fe(II)Nb(IV)} compound with remarkable magnetic features when compared to other Fe(II)-based single chain magnets (SCM). Cyano-bridged heterometallic {3d-4d} and {3d-5d} chains are formed upon assembling Fe(II) bearing a pentadentate macrocycle as the blocking ligand with octacyano metallates, [M(CN)(8)](4-) (M = Nb(IV), Mo(IV), W(IV)). X-ray diffraction (single-crystal and powder) measurements reveal that the [{(H(2)O)Fe(L(1))}{M(CN)(8)}{Fe(L(1))}](infinity) architectures consist of isomorphous 1-D polymeric structures based on the alternation of {Fe(L(1))}(2+) and {M(CN)(8)}(4-) units (L(1) stands for the pentadentate macrocycle). Analysis of the magnetic susceptibility behavior revealed cyano-bridged {Fe-Nb} exchange interaction to be antiferromagnetic with J = -20 cm(-1) deduced from fitting an Ising model taking into account the noncollinear spin arrangement. For this ferrimagnetic chain a slow relaxation of its magnetization is observed at low temperature revealing a SCM behavior with Delta/k(B) = 74 K and tau(0) = 4.6 x 10(-11) s. The M versus H behavior exhibits a hysteresis loop with a coercive field of 4 kOe at 1 K and reveals at 380 mK magnetic avalanche processes, i.e., abrupt reversals in magnetization as H is varied. The origin of these characteristics is attributed to the combination of efficient {Fe-Nb} exchange interaction and significant anisotropy of the {Fe(L(1))} unit. High field EPR and magnetization experiments have revealed for the parent compound [Fe(L(1))(H(2)O)(2)]Cl(2) a negative zero field splitting parameter of D approximately = -17 cm(-1). The crystal structure, magnetic behavior, and Mossbauer data for [Fe(L(1))(H(2)O)(2)]Cl(2) are also reported.

A toolbox of building blocks, linkers and crystallisation methods used to generate single-chain magnets

“…Simple salts of metal ions have been extensively used as building blocks (mostly Ising centres) to produce SCMs, which, when combined with short and efficient linkers, have provided highly interesting families of SCMs [72]. The use of bulkier linkers and ligands has also facilitated the production of intriguing SCMs -in particular the use of macrocycles provides a lot of control over the final architecture [107] and such systems could be more widely developed. Multifunctional SCMs are another interesting target [137].…”

“…20), another SCM by linking the axial sites of an heptacoordinated Fe(II) macrocycle, reported by Sutter, Paulsen, Barra, Ramasesha and co-workers [107], and another SCM by -stacking of a Mn(III) corrole macrocycle, reported by Wang, Gao and co-workers [108].…”

“…Amongst the linkers reported in the literature, some are 'pure' cyanide complexes, others are 'modified' cyanide complexes, meaning that some of the cyanides have been replaced by an organic ligand in order to ensure a certain connectivity is favoured. Nearly fifty of the SCMs reported feature cyanide complexes as linkers, making them the most commonly employed linker type to date ( [22,82], as well as using 'pure' octacyanides [M(CN) 8 ] n+ with M = Mo V and W V (n = 3) and M = Nb IV (n = 4), reported by the groups of Sutter, Andruh, Chibotaru, Paulsen and Ramasesha [90,107] and by Hong and co-workers [86,87].…”

Neutral Low-Dimensional Assemblies of a Mn(III) Schiff Base Complex and Octacyanotungstate(V): Synthesis, Characterization, and Magnetic Properties

“…Some of them are 1D polymers [53][54][55][56]; others possess layered [57][58][59][60][61][62][63] or 3D network structures [64][65][66][67][68]. The paramagnetic cyanotungstate(V) tectones have been used to build discrete molecules [69][70][71], chains [53][54][55][56], 2D [57] and 3D networks [64][65][66][67][68], and some of them have displayed variable magnetic properties such as high ordering temperatures [72], photo-induced magnetism [73,74], SMMs [75], and SCMs [17,54,55].…”

Neutral Low-Dimensional Assemblies of a Mn(III) Schiff Base Complex and Octacyanotungstate(V): Synthesis, Characterization and Magnetic Properties

“…Some of them are 1D polymers [53][54][55][56]; others possess layered [57][58][59][60][61][62][63] or 3D network structure [64][65][66][67][68]. The paramagnetic cyanotungstate(V) tectones have been used to build discrete molecules [69][70][71], chains [53][54][55][56], 2D [57] and 3D networks [64][65][66][67][68] and some of them have displayed variable magnetic properties such as high ordering temperatures [72], photo-induced magnetism [73,74], SMMs [75], and SCMs [17,54,55].…”