Search

The change of the oxidation state from WIV to WV in isotopological CoII–[W(CN)8]n− chains leads to the appearence of pronounced single-chain magnet behaviour.

A unique family of three-dimensional (3D) luminescent SrII-ReV metal-organic frameworks (MOFs), {[SrII(MeOH)5][ReV(CN)4(N)(bpen)0.5]·MeOH}n [1·MeOH; N3- = nitrido ligand, bpen = 1,2-bis(4-pyridyl)ethane, and MeOH = methanol], {[SrII(MeOH)4][ReV(CN)4(N)(bpee)0.5]·2MeOH}n [2·MeOH; bpee = 1,2-bis(4-pyridyl)ethylene], and {[SrII(bpy)0.5(MeOH)2][ReV(CN)4(N)(bpy)0.5]}n (3·MeOH; bpy = 4,4'-bipyridine), is reported. They are obtained by the molecular self-assembly of Sr2+ ions with tetracyanidonitridorhenate(V) metalloligands, [ReV(CN)4(N)]2-, and pyridine-based organic spacers (L = bpen, bpee, bpy). Such a combination of molecular precursors results in bimetallic SrII-ReV cyanido-bridged layers further bonded by organic ligands into pillared Hofmann-type coordination skeletons. Because of the formation of {ReV-(L)-ReV} moieties providing emissive metal-to-ligand charge-transfer states, 1·MeOH-3·MeOH exhibit solid-state room-temperature photoluminescence tunable from green to orange by the applied organic ligand. The most stable MOF of 3·MeOH, based on the alternating {ReV-(bpy)-ReV} and {SrII-(bpy)-SrII} linkages, exhibits three interconvertible, variously solvated phases, methanol-solvated 3·MeOH, hydrated {[SrII(bpy)0.5(H2O)2][ReV(CN)4(N)(bpy)0.5]·0.6H2O}n (3·H2O), and desolvated {[SrII(bpy)0.5][ReV(CN)4(N)(bpy)0.5]}n (3). Their formation was correlated with water and methanol vapor sorption properties investigated for 3·H2O. The solvent content affects the luminescence mainly by tuning the emission energy within the series of 3·MeOH, 3·H2O, and 3. All of the obtained compounds exhibit temperature-driven modulation of luminescence, including the shift of the emission maximum and lifetime. The thermochromic luminescent response was found to be sensitive to the presence and type of solvent in the crystal lattice. This work shows that the construction of [ReV(CN)4(N)]2--based MOFs is an efficient route toward advanced solid luminophores tunable by external stimuli such as solvent or temperature.

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 inc...

Self-assembly of lanthanide(III) complexes of 2,2':6',2″-terpyridine (terpy) with dicyanidoargentate(I) and dicyanidoaurate(I) anions in water results in the formation of six isostructural dinuclear systems [Ln

Rare-earth (RE) metal complexes exhibit attractive magnetic and optical properties related to their strong magnetic anisotropy and efficient photoluminescence. Due to the accessibility of high coordination numbers, they are useful molecular building blocks for the construction of bimetallic coordination systems. Therefore, they can be readily combined with hexacyanidometallate ions of transition metals into the d–f cyanido-bridged frameworks. This leads to the rich family of molecule-based materials varying from purely inorganic 3-D REIII–[MII/III(CN)6]4−/3− (RE = La–Lu, Y; M = Cr, Fe, Ru, Co) networks, through coordination polymers of lower dimensionality obtained with supporting organic ligands, up to strictly molecular species. The past decade brought intensive interest in the design and synthesis of rare-earth hexacyanidometallate frameworks with particular attention paid to their magnetic, optical, electronic, and mechanical properties. In this review, we discuss the most important results of this research area, including remarkable thermal expansion properties, magnetic ordering effects, single-molecule magnetism, luminescent functionalities, electrochemical activity for applications in alkali ion batteries and electroanalytical sensing, and efficient NMR relaxivity for magnetic resonance imaging, as well as photo- and pressure-induced switching of magnetic and optical characteristics. We focus on the recent advances, emphasizing also the general advantages and the future perspectives in the combination of RE(III) complexes and hexacyanidometallates within the d–f coordination frameworks towards the generation of diverse physical functionalities.

Luminescent single-molecule magnets (SMMs) constitute a class of molecular materials offering optical insight into magnetic anisotropy, magnetic switching of emission, and magnetic luminescent thermometry. They are accessible using lanthanide(III) complexes with advanced organic ligands or metalloligands. We present a simple route to luminescent SMMs realized by the insertion of well-known organic cations, tetrabutylammonium and tetraphenylphosphonium, into dysprosium(III) borohydrides, the representatives of metal borohydrides investigated due to their hydrogen storage properties. We report two novel compounds, [n-Bu4N][DyIII(BH4)4] (1) and [Ph4P][DyIII(BH4)4] (2), involving DyIII centers surrounded by four pseudo-tetrahedrally arranged BH4– ions. While 2 has higher symmetry and adopts a tetragonal unit cell (I41/a), 1 crystallizes in a less symmetric monoclinic unit cell (P21/c). They exhibit yellow room-temperature photoluminescence related to the f–f electronic transitions. Moreover, they reveal DyIII-centered magnetic anisotropy generated by the distorted arrangement of four borohydride anions. It leads to field-induced slow magnetic relaxation, well-observed for the magnetically diluted samples, [n-Bu4N][YIII0.9DyIII0.1(BH4)4] (1@Y) and [Ph4P][YIII0.9DyIII0.1(BH4)4] (2@Y). 1@Y exhibits an Orbach-type relaxation with an energy barrier of 26.4(5) K while only the onset of SMM features was found in 2@Y. The more pronounced single-ion anisotropy of DyIII complexes of 1 was confirmed by the results of the ab initio calculations performed for both 1–2 and the highly symmetrical inorganic DyIII borohydrides, α/β-Dy(BH4)3, 3 and 4. The magneto-luminescent character was achieved by the implementation of large organic cations that lower the symmetry of DyIII centers inducing single-ion anisotropy and separate them in the crystal lattice enabling the emission property. These findings are supported by the comparison with 3 and 4, crystalizing in cubic unit cells, which are not emissive and do not exhibit SMM behavior.

The interest in the generation of photoluminescence in lanthanide(III) single-molecule magnets (SMMs) is driven by valuable magneto-optical correlations as well as perspectives toward magnetic switching of emission and opto-magnetic devices linking SMMs with optical thermometry. In the pursuit of enhanced magnetic anisotropy and optical features, the key role is played by suitable ligands attached to the 4f metal ion. In this context, cyanido complexes of d-block metal ions, serving as expanded metalloligands, are promising. We report two novel discrete coordination systems serving as emissive SMMs, {[DyIII(H2O)3(tmpo)3]2[PtIVBr2(CN)4]3}·2H2O (1) and {[DyIII(H2O)(tmpo)4]2[PtIVBr2(CN)4]3}·2CH3CN (2) (tmpo = trimethylphosphine oxide), obtained by combining DyIII complexes with uncommon dibromotetracyanidoplatinate(IV) ions, [PtIVBr2(CN)4]2−. They are built of analogous Z-shaped cyanido-bridged {Dy2Pt3} molecules but differ in the coordination number of DyIII (C.N. = 8 in 1, C.N. = 7 in 2) and the number of coordinated tmpo ligands (three in 1, four in 2) which is related to the applied solvents. As a result, both compounds reveal DyIII-centred slow magnetic relaxation but only 1 shows SMM character at zero dc field, while 2 is a field-induced SMM. The relaxation dynamics in both systems is governed by the Raman relaxation mechanism. These effects were analysed using ac magnetic data and the results of the ab initio calculations with the support of magneto-optical correlations based on low-temperature high-resolution emission spectra. Our findings indicate that heteroligand halogeno-cyanido PtIV complexes are promising precursors for emissive SMMs with the further potential of sensitivity to external stimuli that may be related to the lability of the axially positioned halogeno ligands.

The self-assembly of lanthanide(3+) ions with pyrazine N,N′-dioxide (pzdo) and bis(triphenylphosphine)iminium (PPN+) salts of diamagnetic octacyanidometallates of MoIV and WIV results in one-dimensional (PPN)[LnIII(pzdo)2(MeOH)0.3(H2O)3.7][MIV(CN)8]·7.7H2O·2MeOH (Ln = Er and Yb; M = Mo and W) coordination networks. They are constructed of zigzag metal–organic {LnIII(μ-pzdo)}n chains with terminal [MIV(CN)8]4− metalloligands attached to the LnIII centres. Both Er- and Yb-containing frameworks exhibit field-induced slow magnetic relaxation originating from the field-dependent equilibrium between quantum tunnelling of magnetization and the direct process along with the temperature-dependent Raman and Orbach relaxation processes. Transition metal substitution on [MIV(CN)8]4− sites modifies the intrinsic magnetic anisotropy of lanthanides, as depicted by the subtle change of thermal energy barriers of Orbach relaxation in Er-based systems, while it significantly affects Raman relaxation due to the modulated phonon mode scheme. All reported compounds exhibit strong visible light absorption due to a series of electronic transitions of pzdo ligands and [M(CN)8]4− ions and the appearance of low energy anion–π charge transfer band involving pzdo and octacyanidometallates. These charge transfer states were utilized in achieving the sensitized near-infrared photoluminescence of ErIII and YbIII centers; thus, the energy transfer process is strongly dependent on the nature of the metal centre in the [MIV(CN)8]4− ion. The W(IV)-pzdo system is a good sensitizer for ErIII, while the Mo(IV)-pzdo unit is better for YbIII emission which can be rationalized in terms of the positions of energy levels of their respective donor states. Therefore, we report NIR emissive ErIII and YbIII single-molecule magnets with tunable magnetic and optical properties, uncovering the crucial role of octacyanidometallates and their anion–π interactions with pzdo ligands.

A near-infrared emissive and magnetically anisotropic Nd(iii) complex is formed within a hybrid organic-inorganic {[NdIII(pzdo)(H2O)4][CoIII(CN)6]}·0.5(pzdo)·4H2O (1) (pzdo = pyrazine-N,N'-dioxide) ladder chain built of coexisting Nd-pzdo-Nd and Nd-NC-Co molecular bridges. 1 reveals two NdIII-centered properties, a field-induced slow magnetic relaxation of a single-ion origin with a thermal energy barrier of ΔE/kB = 51(2) K at Hdc = 1 kOe, and a near-infrared fluorescence sensitized by organic and inorganic linkers.

We report an efficient pathway toward sensitization of red room temperature EuIII emission by the charge-transfer (CT) states related to d8-d10 heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of PtII/PdII and dicyanidometallates of AuI/AgI in the construction of a trimetallic d-d-f assembly. The combination of Eu3+, [MII(CN)4]2- (M = Pt, Pd), and [MI(CN)2]- (M = Au, Ag) ions along with 4,4'-bipyridine N,N'-dioxide (4,4'-bpdo) results in four novel isostructural 2D {[EuIII(4,4'-bpdo)(H2O)2][MII(CN)4]}·[MI(CN)2]·H2O (MII/MI = Pt/Au, 1; Pt/Ag, 2; Pd/Au, 3; Pd/Ag, 4) coordination networks. They are built of hybrid coordination layers, based on cyanido-bridged {EuIII[MII(CN)4]}n square grids coexisting with metal-organic {EuIII(4,4'-bpdo)}n chains, with the further attachment of [MI(CN)2]- ions through metallophilic {MII-MI} interactions. This results in dinuclear {MIIMI} units generating an orange emissive metal-to-metal-to-ligand charge-transfer (MMLCT) state, whose energy is tuned by the applied d8-d10 metal centers. Thanks to these CT states, 1-4 exhibit room temperature red EuIII photoluminescence enhanced by energy transfer from {MIIMI} units, with the additional role of 4,4'-bpdo also transferring the energy to lanthanides. These donor CT states lying in the visible range successfully broaden the available efficient excitation range up to 500 nm. The overall emission quantum yield ranges from 8(1)% for 4 to 15(2)% for 1, with the intermediate values for 2 and 3 relatively high among the reported EuIII-based compounds with tetracyanido- and dicyanidometallates. We found that the sensitization efficiency is equally high for all compounds because of the similar energies of the CT states, while the main differences are related to the observed emission lifetimes ranging from ca. 80 μs for 4 to 120-130 μs for 2 and 3 to ca. 180 μs for 1. This phenomenon was correlated with the energies of the vibrational states, e.g., cyanide stretching vibrations, responsible for nonradiative deactivation of EuIII excited states, which are the highest for the Pd/Ag pair of 4 and the lowest for the Pt/Au pair in 1. Thus, the heaviest pair of PtII/AuI cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature EuIII luminescence.

Spin crossover (SCO) materials, revealing the externally tunable transition between two different spin states, arouse great scientific interest due to their perspective application in information storage, display devices and sensing. Of special importance are the molecular systems offering the possibility of multimodal switching within many spin centers. This is achievable in polynuclear clusters consisting of several SCO-active complexes, however, such molecules are very rare. Herein, we report a unique pair of nanometric pentadecanuclear {Fe9[M(CN)8]6(Me3tacn)8}·14MeOH (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, M = Re, 1; M = W, 2) clusters exhibiting a thermally induced spin crossover effect on Fe(ii) complexes, that is on both central and external Fe sites embedded in the cyanido-bridged cluster core. The spin transition occurs gradually in the 120-300 K range, and it is not fully completed even at room temperature. We show that facial coordination of an N,N,N-tridentate Me3tacn ligand dramatically modifies the character of the spin transition phenomenon when confronted with the previously reported {Fe9[M(CN)8]6(MeOH)24}·nMeOH (M = Re, W) clusters by (i) engaging, for the first time, not only central but also external Fe intracluster units in the SCO effect, (ii) cancelling the Fe-W charge transfer pathway, and (iii) decreasing the cooperativity within the supramolecular network.

An inorganic three-dimensional [NiII(H2O)2]2[WIV(CN)8]·4H2O (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase NiII2[WIV(CN)8] (1d). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While 1 reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, 1d is the first ever reported octacyanido-based solid revealing negative thermal expansion, also exhibiting a deep red color and diamagnetism. Such drastic shift in the physical properties is explained by the removal of water molecules, leaving the exclusively cyanido-bridged bimetallic network, which is accompanied by the transformation of the octahedral paramagnetic [NiII(H2O)2(NC)4]2– to the square-planar diamagnetic [NiII(NC)4]2– moieties.

The self-assembly of Dy(III) -3-hydroxypyridine (3-OHpy) complexes with hexacyanidocobaltate(III) anions in water produces cyanido-bridged {[Dy(III) (3-OHpy)2 (H2 O)4 ] [Co(III) (CN)6 ]}⋅H2 O (1) chains. They reveal a single-molecule magnet (SMM) behavior with a large zero direct current (dc) field energy barrier, ΔE=266(12) cm(-1) (≈385 K), originating from the single-ion property of eight-coordinated Dy(III) of an elongated dodecahedral geometry, which are embedded with diamagnetic [Co(III) (CN)6 ](3-) ions into zig-zag coordination chains. The SMM character is enhanced by the external dc magnetic field, which results in the ΔE of 320(23) cm(-1) (≈460 K) at Hdc =1 kOe, and the opening of a butterfly hysteresis loop below 6 K. Complex 1 exhibits white Dy(III) -based emission realized by energy transfer from Co(III) and 3-OHpy to Dy(III) . Low temperature emission spectra were correlated with SMM property giving the estimation of the zero field ΔE. 1 is a unique example of bifunctional magneto-luminescent material combining white emission and slow magnetic relaxation with a large energy barrier, both controlled by rich structural and electronic interplay between Dy(III) , 3-OHpy, and [Co(III) (CN)6 ](3-) .

Polynuclear coordination clusters (PCCs) provide considerable design capabilities towards various functions based on structural non-rigidity and spin state transitions, optical performance, catalytic properties and porosity. The elaboration of new synthetic pathways is fundamental towards advanced switchable and sensing materials, however, the recognition of the structure–property correlations and their optimization is also a key issue. In this context, the current review underlines the role of internal and external functionalization of recognized discrete cluster cores, as the basis for well-designed performance. In particular, we present here the essential update on the recent advances in the overall functionalization of polycyanido-bridged cores (chapter 2). Moreover, we discuss the polymetallic coordination cores constructed with other ligands (short oxido-, hydroxido-, chalcogenido- and other bridges as well as by long multitopic panelling ligands) by indicating the examples of solid-solutions and site selective occupation along the mixed-metal cluster cores (chapter 3), and external decoration of such clusters with ligands, complexes and polynuclear fragments (chapter 4). We also highlight the key properties, indicate the structure–property correlations, and show the power and limitations of the methods used in the presented studies. Finally, we provide the comparison between cyanido-bridged systems and other systems, and indicating possible future research pathways towards the development of PCCs based multicomponent functional systems.

Trivalent lanthanide ions combined with two molecular linkers, organic 4,4′-azopyridine-1,1′-dioxide (apdo), and inorganic hexacyanidocobaltate(III), gave a series of magnetoluminescent coordination polymers, [{LnIII(apdo)(H2O)4}{CoIII(CN)6}]·2H2O (Ln = Nd, 1; Tb, 2; Dy, 3; Er, 4; Tm, 5; Yb, 6). They are hybrid organic–inorganic layered frameworks composed of cyanido-bridged {Ln2(μ-NC)4Co2} squares linked by Ln–apdo–Ln bridges into a coordination network of a mixed 4- and 8-metal ring topology. Lanthanide(III) complexes, [LnIII(μ-apdo)2(H2O)4(μ-NC)2]+, of a distorted dodecahedral geometry are isolated by diamagnetic [CoIII(CN)6]3– and apdo linkers. As a result, 1–6 reveal field-induced slow relaxation of magnetization, with typical temperature-dependent relaxation of a single-ion origin for NdIII-containing 1, DyIII-containing 3, and YbIII-containing 6. The related alternate-current magnetic data were precisely analyzed, indicating the multiple magnetic relaxation pathways, including a direct process, str...

Heterotrimetallic twenty-metal-centred {[MIIxCuII13–x(Me3tacn)12(H2O)][WIV(CN)8]2[WV(CN)8]5}·[WV(CN)8]·n(solvent) (M = Co, x = 1, 1; M = Ni, x = 1.5, 2; M = Mn, x = 1.5, 3; M = Fe, x = 1.5, 4; solvent = MeOH, H2O) and fifteen-metal-centred {CoII[CuII(Me3tacn)]8[WV(CN)8]6}·18MeOH (5) metal–cyanide clusters have been synthesized and characterized. They were obtained by the combination of Cu(II) complexes of 1,4,7-trimethyl-1,4,7-triazacyclonane (Me3tacn) with octacyanidotungstate(V) ions with the addition of other transition metal ions. Using nitrates of Co(II), Ni(II) and Mn(II), or a perchlorate of Fe(II), twenty-metal-centred 1–4 were generated while the application of Co(II) perchlorate gave fifteen-metal centred 5. 1–4 exhibit an open-winged cage topology with octahedral sites partially occupied by non-copper 3d metal centers while five-coordinated sites are occupied only by Cu(II). In 5, Co(II) occupies the centre of a six-capped body-centred cube topology while Cu(II) remains at the external sites. The added transition metal ions enhance the stability of W(V), partially hampering the reduction to W(IV) in 1–4 when compared with the bimetallic {Cu13W7} analogue. It also enables a straightforward synthesis of 5 involving only W(V) without the electrochemical stabilization of this oxidation state. As a result, 1–5 exhibit enhanced magnetic properties when compared with their Cu–W analogues. The addition of Co, Ni, Mn and Fe into the {Cu13W7} clusters produces also the (+3) charge of trimetallic molecules, and breaks the molecular and crystal symmetry, which is reflected by the crystallization of a chiral cluster core with [WV(CN)8]3– counterions in the chiral P21212 space group. Our work shows efficient control over the nuclearity, charge, chirality and magnetism of metal–cyanide clusters achieved by anion-assisted incorporation of various 3d metal ions into the CuII(Me3tacn)[W(CN)8]n− system.

A gel crystallization technique was successfully applied in the pioneering preparation of a single-crystalline form of the three-dimensional copper(II) octacyanidomolybdate(IV) network, which is a photomagnetic material. This assembly crystallizes with the formula {[CuII(H2O)]2[MoIV(CN)8]}·2H2O in the tetragonal crystal system and reveals a three-dimensional cyanido-bridged framework constructed of five-coordinate square-pyramidal [CuII(H2O)(NC)4]2– complexes and [MoIV(CN)8]4– ions of square-antiprismatic geometry. First-principles calculations by the GGA + U method indicate that the visible-light absorption band, crucial for the observation of a photomagnetic effect, is interpreted in terms of MoIV to CuII charge transfer, which is enabled owing to the accompanying pz spx transition of the nitrogen atoms of the bridging cyanido ligands. The optical transitions in the visible range are anisotropic, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges.

Ytterbium (3+) ions combined with 3-pyridone and hexacyanido-cobaltate(III) anions in a concentrated aqueous solution produce cyanido-bridged {[YbIII(3-pyridone)2(H2O)2][CoIII(CN)6]} (1) chains. The resulting YbIII complexes of an elongated octahedral geometry reveal two coexisting functionalities: a field-induced slow magnetic relaxation with an energy barrier of ΔE/kB = 45(1) K at Hdc = 1 kOe, and an YbIII-centered near-infrared fluorescence in the 950–1100 nm range sensitized by 3-pyridone and [CoIII(CN)6]3−.

Cyanide-bridged {MnII9[WV(CN)8]6} clusters with the ground state spin SSG = 39/2 were connected by a 4,4′-dipyridyl disulfide (4,4′-dpds) linker into 2-D double-connected coordination layers of the I0O2 type, {MnII9(4,4′-dpds)4(MeOH)16[WV(CN)8]6}·12MeOH (1). The intercluster contacts are controlled by the bridging MnII–(4,4′-dpds)–MnII coordination modes and direct hydrogen bonds W–CN···HOMeOH–Mn in three crystallographic directions, with the vertex-to-vertex contact unprecedented in {Mn9W6}-based networks dominating over the typical edge-to-edge contacts. The resulting 3D supramolecular network of high-spin clusters was subjected to a thorough magnetic characterization in context of two critical issues. First, the intracluster WV–CN–MnII exchange coupling and intercluster interaction were successfully modeled through the combination of dc measurements, Quantum Monte Carlo simulations, and mean-field calculations, yielding a reasonable Jap = −8.0 cm–1, Jeq = −19.2 cm–1 (related to apical and equatorial CN...

The rotating magnetocaloric effect (RMCE) is a new issue in the field of magnetic refrigeration. We have explored this subject on the two-dimensional (2D) enantiopure {[MnII(R-mpm)2]2[NbIV(CN)8]}·4H2O (where mpm = α-methyl-2-pyridinemethanol) coordination ferrimagnet. In this study, the magnetic and magnetocaloric properties of single crystals were investigated along the bc//H easy plane and the a*//H hard axis. The observed small easy plane anisotropy is due to the dipole–dipole interactions. For fields higher than 0.5 T, no significant difference in the magnetocaloric effect between both geometries was noticed. The maximal magnetic entropy change for conventional effect was observed at 32 K and the magnetic field change μ0ΔH = 5.0 T attaining the value of ∼5 J mol–1 K–1. The obtained maximal value of −ΔSm is comparable to previously reported results for polycrystalline octacyanidoniobate-based bimetallic coordination polymers. A substantial anisotropy of magnetocaloric effect between the easy plane and ...

Coordination compounds built of trivalent lanthanide ions have been demonstrated as promising solid-state materials for diverse photoluminescent applications and as attractive magnetic objects with the prospective application in information storage and spintronics. We present a synthetic methodology in which both luminescent and magnetic functionalities are induced within lanthanide-based coordination polymers by the application of hexacyanocobaltate(III) anions and 3-hydroxypyridine (3-OHpy), both coordinated to 4f-metal ions modulating the lanthanide-centered properties. We report a series of trimetallic cyanido-bridged chains {[EuIIIxTbIII1–x(3-OHpy)2(H2O)4][CoIII(CN)6]}·H2O (x = 1, 0.8, 0.5, 0.4, 0.3, 0.2, 0.1, 0; compounds 1, 2, ..., 7, 8). They reveal tunable visible photoluminescence ranging from green, through yellow and orange, to red color depending on the composition of material and the wavelength of UV excitation light. Such multicolored emission is realized by the adjusted ratio between red e...

Precisely controlled stoichiometric mixtures of Co(2+) and Fe(2+) metal ions were combined with the [W(V)(CN)8](3-) metalloligand in a methanolic solution to produce a series of trimetallic cyanido-bridged {Fe(9-x)Co(x)[W(CN)8]6(MeOH)24}·12MeOH (x = 0, 1, ..., 8, 9; compounds 0, 1, ..., 8, 9) clusters. All the compounds, 0-9, are isostructural, and consist of pentadecanuclear clusters of a six-capped body-centered cube topology, capped by methanol molecules which are coordinated to 3d metal centers. Thus, they can be considered as a unique type of a cluster-based molecular solid solution in which different Co/Fe metal ratios can be introduced while preserving the coordination skeleton and the overall molecular architecture. Depending on the Co/Fe ratio, 0-9 exhibit an unprecedented tuning of magnetic functionalities which relate to charge transfer assisted phase transition effects and slow magnetic relaxation effects. The iron rich 0-5 phases exhibit thermally induced reversible structural phase transitions in the 180-220 K range with the critical temperatures being linearly dependent on the value of x. The phase transition in 0 is accompanied by (HS)Fe(II) W(V) ↔ (HS)Fe(III) W(IV) charge transfer (CT) and the additional minor contribution of a Fe-based spin crossover (SCO) effect. The Co-containing 1-5 phases reveal two simultaneous electron transfer processes which explore (HS)Fe(II) W(V) ↔ (HS)Fe(III) W(IV) CT and the more complex (HS)Co(II) W(V) ↔ (LS)Co(III) W(IV) charge transfer induced spin transition (CTIST). Detailed structural, spectroscopic, and magnetic studies help explain the specific role of both types of CN(-)-bridged moieties: the Fe-NC-W linkages activate the molecular network toward a phase transition, while the subsequent Co-W CTIST enhances structural changes and enlarges thermal hysteresis of the magnetic susceptibility. On the second side of the 0-9 series, the vanishing phase transition in the cobalt rich 6-9 phases results in the high-spin ground state, and in the occurrence of a slow magnetic relaxation process at low temperatures. The energy barrier of the magnetic relaxation gradually increases with the increasing value of x, reaching up to ΔE/kB = 22.3(3) K for compound 9.

The self-assembly of iron(II) ions with rare octacyanidorhenate(V) metalloligands in a methanolic solution results in the formation of a nanometric pentadecanuclear $\{ Fe^{II}_{9}[Re^{V}(CN)_{8}]_{6}(MeOH)_{24}\}⋅10 MeOH$ (1) molecule with a six-capped body-centered cubic topology. The cluster demonstrates a thermally-induced spin-crossover phase transition at $T_{1/2}=195 K$ which occurs selectively for a single $Fe^{II}$ ion embedded in the center of a cluster core.

Octacyanidometallates make an important branch of cyanide-based molecular magnets that not only follow the trends in modern magnetochemistry and materials science but also have stimulated these fields from the very beginning and still blaze a trail by introducing new concepts such as heterotrimetallic systems, new functionalities and cross-effects like photo-switching of magneto-optical properties and setting new records in magnetic ordering temperatures or magnetic exchange interactions. The following paper focuses on a special class of molecular magnets which, to the best of our knowledge, have not been reviewed so far: octacyanide-based magnetic clusters. A complete list of all known molecules incorporating octacyanides with an extensive discussion of their structures, topologies and magnetic properties, with special attention paid to multifunctional systems, is provided. Several milestone-clusters are discussed thoroughly to emphasize their particular importance in the development of crystal engineering and molecular magnetism.

The unique enantiopure {[Λ-Co(II)((R)-mpm)2]3[W(V)(CN)8]2}·9H2O [(R)-1] and {[Δ-Co(II)((S)-mpm)2]3[W(V)(CN)8]2}·9H2O [(S)-1], where mpm = α-methylpyridinemethanol, magnetic spongelike materials, crystallizing in the chiral P21 space group, are constructed of cyanido-bridged {Co3W2} trigonal bipyramids with three cis-[Co(II)(mpm)2(μ-NC)2] moieties in equatorial sites and two [W(V)(CN)8](3-) units in apical positions. The arrangement of {Co3W2} clusters in the crystal lattice is controlled by interactions with crystallization H2O molecules, resulting in two independent hydrogen-bonding systems: the first weaving along open channels in the a direction (weakly bonded H2O) and the second closed in the cages formed by the surrounding [W(CN)8](3-) and mpm fragments (strongly bonded H2O). The strong optical activity of (R)- and (S)-1 together with continuous chirality measure (CCM) analysis confirms the chirality transfer from enantiopure (R)- and (S)-mpm to [Co(mpm)2(μ-NC)2] units, a cyanido-bridged skeleton, and to the whole crystal lattice. Magnetic properties confronted with ab initio calculations prove the ferromagnetic couplings within Co(II)-NC-W(V) linkages inside {Co3W2} molecules, accompanied by weak antiferromagnetic intermolecular interactions. The reversible removal of weakly bonded H2O above 50 °C induces the structural phase transition 1 ⇄ 1deh and strongly affects the magnetic characteristics. The observed changes can be interpreted in terms of the combined effects of the decreasing strength of ferromagnetic Co(II)-W(V) coupling and the increasing role of antiferromagnetic intermolecular correlation, both connected with dehydration-induced structural modifications in the clusters' core and supramolecular network of 1.

Complexes of lanthanides(III) (Ce-Yb) with 2,2'-bis(2-oxazoline) (Box) combined with octacyanidomolybdate(V) gave a series of magneto-luminescent coordination polymers, {[Ln(III)(Box)n(DMF)m][Mo(V)(CN)8]}·x(solvent) (1-12). They are built of cyanido-bridged layers of a mixed 4- and 8-metal rings topology and show unique sliding of layers dependent on a 4f metal ion. For light lanthanides, dominant phase A, {[Ln(III)(Box)2(DMF)2][Mo(V)(CN)8]}·1.5MeCN (Ln = Ce, 1; Pr, 2; Nd, 3), consists of ideally aligned, not shifted layers, giving large channels (13.7 × 14.0 Å). Intermediate lanthanides reveal phase B, {[Ln(III)(Box)2(DMF)2] [Mo(V)(CN)8]}·H2O (Ln = Sm, 4; Eu, 5; Gd, 6; Tb, 7; Dy, 8), of smaller pores (8.4 × 10.6 Å) due to layer-H2O hydrogen bonding, which induces sliding of CN(-)-bridged layers. Heavy lanthanides show phase C, {[Ln(III)(Box)(DMF)3][Mo(V)(CN)8]}·MeCN (Ln = Ho, 9; Er, 10; Tm, 11; Yb, 12), with large channels (13.7 × 13.7 Å) of a similar size to light lanthanides. This effect comes from the changes in Ln(III) coordination sphere affecting solvent-layer interactions. Compounds 1-12 reveal diverse emission depending on the interaction between Ln(III) and Box luminophors. For 2-5, 9, and 12, the ligand-to-metal energy-transfer-induced visible f-centered emission ranging from green for Ho(III)-based 9, orange from Sm(III)-based 4, to red for Pr(III)- and Eu(III)-containing 2 and 5, respectively. Near-infrared emission was found for 2-4, 9, and 12. Red phosphorescence of Box was detected for Gd(III)-based 6, whereas the selective excitation of ligand or Ln(III) excited states resulting in the switchable red to green emission was found for Tb(III)-based 7. The materials revealed Ln(III)-Mo(V) magnetic coupling leading to ferromagnetism below 2.0 and 2.2 K for 4 and 7, respectively. The onset of magnetic ordering at low temperatures was found for 6 and 8. Compounds 1-12 form a unique family of cyanido-bridged materials of a bifunctional magneto-luminescence character combined with dynamic structural features.