Synthesis, Crystal Structures, and Magnetic Properties of Cyanide-Bridged WVMnIII Anionic Coordination Polymers Containing Divalent Cationic Moieties: Slow Magnetic Relaxations and Spin Crossover Phenomenon

Reversible Photo- and Thermo-Induced Spin-State Switching in a Heterometallic {5d-3d} W2Fe2 Molecular Square Complex

Following the complex-as-a-ligand strategy, self-assembly of [W(CN)₈]^3- and iron(II) with bidentate nitrogen donor ligand bik (bik = bis(1-methyl-1H-imidazol-2-yl)ketone) ligand affords a cyanide-bridged [W₂Fe₂] molecular square complex [HNBu₃]₂{[W(CN)₈]₂[Fe(bik)₂]₂}·6H₂O·CH₃OH (1). The complex was characterized by single-crystal X-ray diffraction analyses, (photo)magnetic studies, optical reflectivity, electrochemical studies, and spectroscopic studies. Structural analyses revealed that in the [W₂Fe₂] square motif tungsten(V) and iron(II) centers reside in an alternate corner of the square and are bridged by the cyanide ligands. Complex 1 exhibits thermo-induced spin crossover (SCO) between {W^V (S = 1/2) - Fe^II_LS (S = 0)} and {W^V (S = 1/2) - Fe^II_HS (S = 2)} pairs near room temperature and photoinduced spin-state switching with T_LIESST = 70 K under light irradiation at low temperature. To the best of our knowledge, 1 represents the first complex containing iron(II) and [W^V(CN)₈]^3- units exhibiting both SCO and photomagnetic effect.

Crystal structures and magnetic properties of one-dimensional compounds constructed from Mn2(salen)2 building blocks and organic selenite acid ligands

Two new compounds composed of MnIII salen building blocks and organic selenite acid with ClO4− counter anions, namely [Mn2(salen)2(C6H5SeO2)](ClO4)(1) and [Mn2(salen)2(C6H4FSeO2)](ClO4)(2) [salen = N,N′-bis(salicylidene)-ethylenediamine], were synthesized through a one-pot reaction and characterized structurally and magnetically.

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.

Slow magnetic relaxation in O–Se–O bridged manganese(iii) Schiff base complexes

Two new chain complexes consisting of a Mn(salen) building block bridged by O–Se–O units, [Mn₂(salen)₂(L)](ClO₄) (1) and {[Mn(salen)]₂(L)₂}·Y (2) (salen = N,N′-bis(salicylidene)-ethylenediamine, L = 3,4,5-trifluorobenzeneseleninic acid, Y = salicylaldehyde) have been synthesized and characterized structurally and magnetically.

Auxiliary ligand-induced structural diversities of octacyanometalate-based heterobimetallic coordination polymers towards diverse magnetic properties

Three octacyanometalate-based bimetallic coordination polymers (CPs), {[μ₄-M^V(CN)₈][Co(DMF)₄]₂(ClO₄)}_n (M = W CP-1, Mo CP-2) and {[μ₄-W^IV(CN)₈]Co₂(azpy)₄}_n CP-3, were synthesized in the absence (for CPs 1 and 2) or presence (for CP-3) of auxiliary ligand 4,4'-azopyridine (azpy), respectively. CPs 1 and 2 exhibit the same three-dimensional (3D) polymeric cation frameworks with [ClO₄]^- as the counterions, while CP-3 displays a porous 3D framework in an unusual 2-nodal (4,6)-connected 4,6T155 topology with point symbol as {4²·6⁴}{4⁶·6⁴·7·8⁴}₂. Notably is that octacyanometalate [W^V(CN)₈]^3- has been reduced into [W^IV(CN)₈]^4- during the synthetic process of CP-3. The magnetic investigations indicate that CP-1 exhibits the typical ferromagnetic property due to the ferromagnetic coupling between W(v) and Co(ii) spin centers, while CP-3 displays the weak ferromagnetic interaction at low temperature, which is consistent with the valence change of W center in CP-3.

In Situ Ligand Transformation for Two-Step Spin Crossover in FeII[MIV(CN)8]4- (M = Mo, Nb) Cyanido-Bridged Frameworks

We report a unique synthetic route toward the multistep spin crossover (SCO) effect induced by utilizing the partial ligand transformation during the crystallization process, which leads to the incorporation of three different Fe^II complexes into a single coordination framework. The 3-acetoxypyridine (3-OAcpy) molecules were introduced to the self-assembled Fe^II-[M^IV(CN)₈]^4- (M = Mo, Nb) system in the aqueous solution which results in the partial hydrolysis of the ligand into 3-hydroxypyridine (3-OHpy). It gives two novel isostructural three-dimensional {Fe^II₂(3-OAcpy)₅(3-OHpy)₃[M^IV(CN)₈]}· nH₂O (M = Mo, n = 0, FeMo; M = Nb, n = 1, FeNb) coordination frameworks. They exhibit an unprecedented cyanido-bridged skeleton composed of {Fe₃M₂} _n coordination nanotubes bonded by additional Fe complexes. These frameworks contain three types of Fe sites differing in the attached organic ligands, [Fe1(3-OAcpy)₄(μ-NC)₂], [Fe2(3-OHpy)₄(μ-NC)₂], and [Fe3(3-OAcpy)₃(3-OHpy)(μ-NC)₂], which lead to the thermal two-step Fe^II SCO, as proven by X-ray diffraction, magnetic susceptibility, UV-vis-NIR optical absorption, and ⁵⁷Fe Mössbauer spectroscopy studies. The first step of SCO, going from room temperature to the 150-170 K range with transition temperatures of 245(5) and 283(5) K for FeMo and FeNb, respectively, is related to Fe1 sites, while the second step, occurring at the 50-140 K range with transition temperatures of 70(5) and 80(5) K for FeMo and FeNb, respectively, is related to Fe2 sites. The Fe3 site with both 3-OAcpy and 3-OHpy ligands does not undergo the SCO at all. The observed two-step SCO phenomenon is explained by the differences in the ligand field strength of the Fe complexes and the role of their alignment in the coordination framework. The simultaneous application of two related pyridine derivatives is the efficient synthetic route for the multistep Fe^II SCO in the cyanido-bridged framework which is a promising step toward rational design of advanced spin transition molecular switches.

A heterotrimetallic synthetic approach in versatile functionalization of nanosized {MxCu13–xW7}3+ and {M1Cu8W6} (M = Co, Ni, Mn, Fe) metal–cyanide magnetic clusters

The addition of 3d metal heteroatom into Cu^II(Me₃tacn)[W(CN)₈]ⁿ⁻ cluster system governs its structural and magnetic features.