Azido-Cyanide Mixed-Bridged FeIII-NiII Complexes

The successful introduction of azide ions as secondary bridges into the Fe^III-Ni^II cyanide system afforded two clusters and one unique 4(3),2-ribbon chain: [(bpzpy)₂Ni₂(μ₂-1,1-N₃)₂{(pzTp)Fe(CN)₃}₂]·3H₂O [1; bpzpy = 2,6-bis(pyrazol-1-yl)pyridine, and pzTp = tetrakis(pyrazolyl)borate], [(L1)₂Ni₄(μ₃-1,1,1-OCH₃)₂(μ₂-1,1-N₃)₂(H₂O)₂{(Tp)Fe(CN)₃}₂]·2CH₃OH·H₂O [2; Tp = hydrotris(pyrazolyl)borate, and HL1 = 2,6-bis{(2-hydroxypropylimino)methyl}-4-methylphenol], and [(L2)₂Ni₃(μ₂-1,1-N₃)₄{(pzTp)Fe(CN)₃}₂]_n (3; L2 = 2-{[phenyl(pyridin-2-yl)methylene]amino}ethan-1-amine). Both 1 and 2 feature the centrosymmetric {Fe^III-Ni^II₂-Fe^III} and {Fe^III-Ni^II₄-Fe^III} rodlike structures in which the two peripheral [(Tp^R)Fe(CN)₃]^- anions act as monodentate ligands via one cyanide group to link the central azide-bridged [Ni₂] and [Ni₄] subunit, respectively, while 3 displays an extended structure of the double-zigzag (4,2-ribbon) chain in which the double end-on azide-bridged trinuclear [Ni₃] subunits serve as the 4-connected nodes. Magnetic study revealed that intramolecular ferromagnetic coupling is dominated by the azide or cyanide bridges in all of the complexes. Remarkably, complex 1 behaves as a single-molecule magnet with an effective energy barrier of 16.5 cm^-1 at zero dc field, while complex 3 exhibits metamagnetism with a hidden spin canting property below 12 K.

Octacyanidometallates for multifunctional molecule-based materials

Octacyanidometallates have been successfully employed in the design of heterometallic coordination systems offering a spectacular range of desired physical properties with great potential for technological applications. The [M(CN)8]n- ions comprise a series of complexes of heavy transition metals in high oxidation states, including NbIV, MoIV/V, WIV/V, and ReV. Since the discovery of the pioneering bimetallic {MnII4[MIV(CN)8]2} and {MnII9[MV(CN)8]6} (M = Mo, W) molecules in 2000, octacyanidometallates were fruitfully explored as precursors for the construction of diverse d-d or d-f coordination clusters and frameworks which could be obtained in the crystalline form under mild synthetic conditions. The primary interest in [M(CN)8]n--based networks was focused on their application as molecule-based magnets exhibiting long-range magnetic ordering resulting from the efficient intermetallic exchange coupling mediated by cyanido bridges. However, in the last few years, octacyanidometallate-based materials proved to offer varied and remarkable functionalities, becoming efficient building blocks for the construction of molecular nanomagnets, magnetic coolers, spin transition materials, photomagnets, solvato-magnetic materials, including molecular magnetic sponges, luminescent magnets, chiral magnets and photomagnets, SHG-active magnetic materials, pyro- and ferroelectrics, ionic conductors as well as electrochemical containers. Some of these materials can be processed into the nanoscale opening the route towards the development of magnetic, optical and electronic devices. In this review, we summarise all important achievements in the field of octacyanidometallate-based functional materials, with the particular attention to the most recent advances, and present a thorough discussion on non-trivial structural and electronic features of [M(CN)8]n- ions, which are purposefully explored to introduce desired physical properties and their combinations towards advanced multifunctional materials.

Two three-dimensional [MoIII(CN)7]4−-based magnets showing new topologies and ferrimagnetic ordering below 80 K

Two 3D [Mo^III(CN)₇]⁴⁻-based magnets with new topologies and ferrimagnetic ordering below 80 K have been prepared using different amides as auxiliary ligands.

How to Make a Better Magnet? Insertion of Additional Bridging Ligands into a Magnetic Coordination Polymer

A three-dimensional cyanide-bridged coordination polymer based on FeII (S = 2) and NbIV (S = 1/2) {[FeII(H2O)2]2[NbIV(CN)8]·4H2O}n (Fe2Nb) was modified at the self-assembly stage by inserting an additional formate HCOO− bridge into its cyanide framework. The resulting mixed-bridged {(NH4)[(H2O)FeII-(μ-HCOO)-FeII(H2O)][NbIV(CN)8]·3H2O}n (Fe2NbHCOO) exhibited additional FeII-HCOO-FeII structural motifs connecting each of the two FeII centers. The insertion of HCOO− was possible due to the substitution of some of the aqua ligands and crystallization water molecules in the parent framework by formate anions and ammonium cations. The formate molecular bridge not only shortened the distance between FeII ions in Fe2NbHCOO from 6.609 Å to 6.141 Å, but also created additional magnetic interaction pathways between the magnetic centers, resulting in an increase in the long range magnetic ordering temperature from 43 K for Fe2Nb to 58 K. The mixed-bridged Fe2NbHCOO also showed a much broader magnetic hysteresis loop of 0.102 T, compared to 0.013 T for Fe2Nb.

Magnetic percolation in CN-bridged ferrimagnetic coordination polymers

A series of diluted molecular magnets {[MnII(H2O)2]2[MIV(CN)8]·4H2O}n (M = Nb/Mo) exhibiting a ferrimagnetic phase have been synthesized and investigated to demonstrate the first example of site percolation in magnetic coordination polymers. It is the first case of a magnetic percolation study with selective site substitution, where magnetic ions of only one type are replaced by their diamagnetic analogues leaving the other magnetic sublattice untouched. By modifying the molecular field model the NbIV concentration dependence of the magnetic ordering temperature was reproduced and the percolation threshold was determined.