Metallosupramolecular Coordination Complexes: The Design of Heterometallic 3d–4f Gridlike Structures

Fine-Tuning the Anisotropies of Air-Stable Single-Molecule Magnets Based on Macrocycle Ligands

Air-stable single-molecule magnets (SMMs) can be obtained by confining DyIII ion in a D6h coordination environment; however, most of the current efforts were focused on modifying the rigidity of the macrocycle ligand. Herein, we attempt to assemble air-stable SMMs based on macrocycles with a replaceable coordination site. By using an in situ 1 + 1 Schiff-base reaction of dialdehyde with diamine, three air-stable SMMs have been obtained in which one of the equatorial coordination sites can be varied from -NH- (for Dy-NH), -O- (for Dy-O), and -NMe- (for Dy-NMe). Complex Dy-NH shows a less distorted D6h symmetry and an anisotropy energy barrier of 1270 K. For complex Dy-O, the coordination site of -O- gives a relatively longer coordination bond but a comparable energy barrier in contrast with that of Dy-NH. In the case of complex Dy-NMe, although the -NMe-group gives a very long coordination bond, the large steric effect on the -NMe- group enforces a larger distortion of the D6h coordination geometry, resulting in the fast quantum tunneling of the magnetization that shortcuts the thermal relaxation process; therefore, Dy-NMe shows a lower energy barrier. This study provides a new strategy for modifying the coordinate site on the equatorial plane of D6h symmetry to fine-tune the structure and magnetic anisotropy of SMMs.

Elevating the Performance of Heterometallic 3d/4f SMMs: The Role of Diamagnetic CoIII and ZnII Ions in Magnetization Dynamics

Recent advances in the synthesis of 3d/4f Single-Molecule Magnets (SMMs) have revealed the effective role of incorporating diamagnetic CoIII or ZnII ions to enhance the magnetic properties of LnIII ions. This concept highlights notable examples of CoIII/LnIII and ZnII/LnIII SMMs documented in the recent literature, illustrating how the selection of various peripheral and/or bridging ligands can modulate the magnetic anisotropy of 4f metal ions, thereby increasing their energy barriers.

Self-Assembly Bifunctional Tetranuclear Ln2Ni2 Clusters: Magnetic Behaviors and Highly Efficient Conversion of CO2 under Mild Conditions

A series of heterometallic tetranuclear clusters, Ln₂Ni₂(NO₃)₄L₄(μ₃-OCH₃)₂·2(CH₃CN) (Ln = Gd(1), Tb(2), Dy(3), Ho(4), Er(5); HL = methyl 3-methoxysalicylate), were synthesized solvothermally. The intramolecular synergistic effect of two metal centers of Ln(III) and Ni(II) and the exposed multimetallic sites serving as Lewis acid activators greatly increase the efficiency of the CO₂ conversion, and the yield for cluster 3 can be achieved at 96% at atmospheric pressure and low temperature. In particular, the self-assembly multimetal center with polydentate ligand shows good generality and enhanced recyclability. The design of such 3d-4f heterometallic clusters provides an effective strategy for the conversion of CO₂ under greener conditions. Meanwhile, magnetic investigations indicate that cluster 1 is a good candidate for magnetic refrigerant materials with a relatively large magnetocaloric effect (MCE) (-ΔS_m = 28.5 J kg^-1 K^-1 at 3.0 K and 7.0 T), and cluster 3 shows single-molecular magnet behavior under zero dc field. Heterometallic clusters with special magnetic properties and good catalytic behavior for the conversion of CO₂ are rare. Thus, they are potential bifunctional materials applied in practice.

Self-assembly of fish-bone and grid-like CoII-based single-molecule magnets using dihydrazone ligands with NNN and NNO pockets

Three Co^II complexes, [Co₂(H₂L¹)₂](ClO₄)₄·4CH₃OH (1), [Co₂(H₄L²)₂](ClO₄)₄ (2) and [Co₄(H₄L²)₄](ClO₄)₈ (3), were constructed by the self-assembly of the symmetrical dihydrazone ligands H2L1 and H4L2 with Co^II ions under different synthetic conditions. The fish-bone-like complex 1 was obtained using the ligand H2L1 in methanol via the solvothermal method, while the self-assembly of H4L2 with Co^II ions is solvent-dependent, producing the fish-bone-like complex 2 and [2 × 2] grid-like complex 3. Magnetic susceptibility measurements and theoretical calculations reveal that the large negative D values for the three complexes stem from their easy-axis magnetic anisotropy. Ac magnetic susceptibility measurements disclosed field-induced slow magnetic relaxation behaviors and the presence of Raman and/or direct processes of the three complexes at various applied dc fields.

Experimental and theoretical insights into Co-Ln magnetic exchange and the rare slow-magnetic relaxation behavior of [CoII2Pr]2+ in a series of linear [CoII2Ln]2+ complexes

We herein report a series of near-linear trinuclear complexes [Co₂Ln(HL)₄(NO₃)](NO₃)₂ (where HL = (2-methoxy-6-[(E)-2'-hydroxymethyl-phenyliminomethyl]-phenolate) with Ln(III) = La (1), Ce (2), Pr (3)). For the comparative study, we have also included the recently reported analogous complexes of Gd(III), Tb(III), and Dy(III) (complexes 4-6) with the same H₂L ligand. The experimental nature of the dc magnetic susceptibilities profile and an empirical approach revealed that the magnetic exchange interaction between Co(II) and Ln(III) having <4f⁷ (complexes 2 and 3) is antiferromagnetic while the dominant interaction between Co(II) and Ln(III) having ≥4f⁷ (complexes 4-6) is ferromagnetic. Dynamic magnetic relaxation studies on complexes 1-3 revealed the field induced single-molecule magnetic (SMM) behavior of 1 and 3 with effective energy barriers of 10.65 K and 15.03 K respectively, for magnetic relaxation. To the best of our knowledge, 3d-Pr(III) based zero or field induced SMMs have not been reported to date. CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations on the X-ray structures of complexes 1-6, followed by POLY_ANISO simulations, estimated the magnetic exchange coupling constants J_Co-Ln and J_Co-Co and also rationalized our experimental findings for the dynamic magnetic properties.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (Ln^III). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Self-assembly of non-macrocyclic triangular Ni3Ln clusters

The synthesis and structural characterisation of four new heterometallic tetranuclear complexes is reported. Three L₃Ni₃Ln type complexes, where Ln = La (C1), Eu (C2), and Gd (C3), have been fully characterised including DC and AC magnetic measurements. A fourth complex featuring a diamagnetic Ba^II ion at its centre is also reported with structural characterisation. Structural elucidation showed that all four complexes successfully self-assembled from a stoichiometric mixture of the acyclic ligand, 1,4-diformylnaphthalene-2,3-diol, with nickel(II) nitrate and the appropriate heavy metal salt to produce the same near planar Ni₃MO₁₂ core. Ferromagnetic interactions were found to dominate the ground state of C3, exhibiting a maximal spin ground state of 13/2. The exchange coupling is quantitatively discussed along with the nickel(II) zero-field splitting effect. AC magnetic susceptibility experiments were carried out, but no frequency dependent signals were observed and thus no observable slow relaxation of magnetisation.

Coupling 6-chloro-3-methyluracil with copper: structural features, theoretical analysis, and biofunctional properties

As nucleobases in RNA and DNA, uracil and 5-methyluracil represent a recognized class of bioactive molecules and versatile ligands for coordination compounds with various biofunctional properties. In this study, 6-chloro-3-methyluracil (Hcmu) was used as an unexplored building block for the self-assembly generation of a new bioactive copper(II) complex, [Cu(cmu)₂(H₂O)₂]·4H₂O (1). This compound was isolated as a stable crystalline solid and fully characterized in solution and solid state by a variety of spectroscopic methods (UV-vis, EPR, fluorescence spectroscopy), cyclic voltammetry, X-ray diffraction, and DFT calculations. The structural, topological, H-bonding, and Hirshfeld surface features of 1 were also analyzed in detail. The compound 1 shows a distorted octahedral {CuN₂O₄} coordination environment with two trans cmu^- ligands adopting a bidentate N,O-coordination mode. The monocopper(II) molecular units participate in strong H-bonding interactions with water molecules of crystallization, leading to structural 0D → 3D extension into a 3D H-bonded network with a tfz-d topology. Molecular docking and ADME analysis as well as antibacterial and antioxidant activity studies were performed to assess the bioactivity of 1. In particular, this compound exhibits a prominent antibacterial effect against Gram negative (E. coli, P. aeruginosa) and positive (S. aureus, B. cereus) bacteria. The obtained copper(II) complex also represents the first structurally characterized coordination compound derived from 6-chloro-3-methyluracil, thus introducing this bioactive building block into a family of uracil metal complexes with notable biofunctional properties.

Influence of the Different Types of Auxiliary Noncarboxylate Organic Ligands on the Topologies and Magnetic Relaxation Behavior of Zn-Dy Heterometallic Single Molecule Magnets

In this work, we first synthesized a Zn-Dy complex, [Zn₆Dy₂(L)₆(tea)₂(CH₃OH)₂]·6CH₃OH·8H₂O (H₂L = N-3-methoxysalicylidene-2-amino-3-hydroxypyridine, teaH₃ = triethanolamine, 1), by employing H₂L, anhydrous ZnCl₂, and Dy(NO₃)₃·5H₂O reacting with auxiliary ligand teaH₃ in the mixture of CH₃OH and DMF. When teaH₃ and the solvent CH₃OH in the reaction system of 1 were replaced by the auxiliary ligand 2,6-pyridinedimethanol (pdmH₂) and the solvent MeCN, another Zn-Dy complex, [Zn₄Dy₄(L)₆(pdm)₂(pdmH)₄]·10CH₃CN·5H₂O (2), was obtained. For 1, its crystal structure can be viewed as a dimer of two Zn₃Dy^III units. However, for 2, four Dy^III form a zigzag arrangement, and each of its terminals linked two Zn^II ions. Interestingly, although the structural topologies of 1 and 2 are different, the coordination geometries of Dy^III in 1 and 2 are all triangular dodecahedron (TDD-8). The difference is that the continuous shape measure (CShM) values of Dy^III in 1 are larger than the corresponding values in 2. Magnetic investigation revealed that the diluted sample 1@Y exhibits two magnetic relaxation processes, while 2 only exhibits a single relaxation process. Ab initio calculations indicated that, in the crystal lattice of 1, two complexes exhibiting slightly different CShM values of Dy^III result in the double relaxation behavior of 1@Y. However, for 2, one of two Dy^III fragments possesses a fast quantum tunneling of magnetization (QTM), resulting in its magnetic process presented at T < 1.8 K, so 2 exhibits single relaxation behavior. More importantly, the theoretical calculations also clearly indicated that the weak ligation at equatorial sites of Dy^III in 1 and 2 ensure 1@Y and 2 possess SMM behavior, although the coordination geometry of Dy^III (TDD-8) in 1 and 2 severely deviates from the ideal polyhedron and its axial symmetry is low.

Further synthetic investigation of the general lanthanoid(iii) [Ln(iii)]/copper(ii)/pyridine-2,6-dimethanol/carboxylate reaction system: {CuLn} coordination clusters (Ln = Dy, Tb, Ho) and their yttrium(iii) analogue

In addition to previously studied {CuGd₆}, {CuGd₄}, {CuLn₇} and {CuLn₈} coordination clusters (Ln = trivalent lanthanide) containing pdm^2- or Hpdm^- ligands (H₂pdm = pyridine-2,6-dimethanol) and ancillary carboxylate groups (RCO₂^-), the present work reports the synthesis and study of three new members of a fifth family of such complexes. Compounds [Cu₅Ln₄O₂(OMe)₄(NO₃)₄(O₂CCH₂Bu^t)₂(pdm)₄(MeOH)₂] (Ln = Dy, 1; Ln = Tb, 2; Ln = Ho, 3) were prepared from the reaction of Ln(NO₃)₃·xH₂O (x = 5, 6), CuX₂·yH₂O (X = ClO₄, Cl, NO₃; y = 6, 2 and 3, respectively), H₂pdm, Bu^tCH₂CO₂H and Et₃N (2 : 2.5 : 2 : 1 : 9) in MeCN/MeOH. Rather surprisingly, the copper(ii)/yttrium(iii) analogue has a slightly different composition, i.e. [Cu₅Y₄O₂(OMe)₄(NO₃)₂(O₂CCH₂Bu^t)₄(pdm)₄(MeOH)₂] (4). The structures of 1·4MeCN·1.5MeOH and 4·2MeOH were solved by single-crystal X-ray crystallography. The five Cu^II and four Dy^III centres in 1 are held together by two μ₅-O^2-, four μ-MeO^-, two syn,synη¹:η¹:μ Bu^tCH₂CO₂^-, four η²:η¹:η²:μ₃ pdm^2- (each of these groups chelates a Cu^II atom and simultaneously bridges two Dy^III atoms through its two -CH₂O^- arms) and two μ-MeOH ligands. The four terminal nitrato groups each chelate (η¹:η¹) a Dy^III centre. The five Cu^II atoms are co-planar (by symmetry) forming a bow-tie arrangement; the four outer Cu^II atoms form a rectangle with edges of 3.061(1) and 6.076(1) Å. The four Dy^III centres also form a rectangle that lies above and below the plane of the Cu^II centres, with edges of 3.739(1) and 5.328(1) Å. The two strictly planar rectangles are almost perpendicular. Two trigonal bipyramidal μ₅-O^2- groups link the perpendicular Cu₅ and Dy₄ frameworks together. The molecule 4 has a very similar structure to that of 1, differences being the replacement of the two chelating nitrato groups of 1 by two chelating Bu^tCH₂CO₂^- ligands in 4 and the coordination polyhedra of the Ln^III and Y^III atoms (Snub diphenoids in 1 and biaugmented trigonal prisms in 4). Dc magnetic susceptibility data (χ_M) on analytically pure samples of 1-3, collected in the 300-2 K range, indicate that ferromagnetic exchange interactions dominate leading to large spin ground states. The χ_MT vs. T data for 4 suggest moderately strong antiferromagnetic Cu^IICu^II exchange interactions. Studies of the dynamic magnetic properties of the {Cu₅Ln₄} clusters show that 1 behaves as a SMM at zero field and 2 is a very weak field-induced SMM, while 3 exhibits only weak tails in the χ''_Mvs. T plots at various ac frequencies at zero dc field.

Magnetic investigation in di- and tetranuclear lanthanide complexes

Dinuclear and tetranuclear dysprosium-based complexes have been constructed by using a crab-like hydrazone ligand, with the former acting as a typical single-molecule magnet and the later showing diamagnetic ground state.

Multifunctional ZnII–LnIII (Ln = Tb, Dy) complexes based on the amine-phenol ligand with field-induced slow magnetic relaxation, luminescence, and proton conduction

Two new isomorphic Zn^II–Ln^III–Zn^II trinuclear complexes based on the amine-phenol ligand have been prepared.

Structure, assembly mechanism and magnetic properties of heterometallic dodecanuclear nanoclusters DyIII4MII8 (M = Ni, Co)

Two isostructural heterometallic dodecanuclear nanoclusters [Dy4Co8(μ3-OH)8(L)8(OAc)4(H2O)4]·3EtOH·3CH3CN·H2O (1) and [Dy4Ni8(μ3-OH)8(L)8(OAc)4(H2O)4]·3.5EtOH·0.5CH3CN·5H2O (2) with different assembly mechanisms are presented here.

Heterometallic {DyIII2FeII2} grids with slow magnetic relaxation and spin crossover

The self-assembly of a Dy^III ion, an Fe^II ion and a multitopic H₂L ligand produces novel [2 × 2] {DyIII2FeII2} grids exhibiting slow magnetic relaxation and spin crossover.

3d–4f Metallacrown complexes with a new sandwich core: synthesis, structures and single molecule magnet behavior

Two heterometallic metallacrown complexes, [Er{Cu₄(butyrat)₄}₂]·Cl₃·MeOH·26H₂O (1) and [Yb{Cu₄(butyrat)₄}₂]·Cl₃·MeOH·26H₂O (2) (H₂butyrat = 3-aminobutyric hydroxamic acid), have been reported.

Heterometallic Ru2Co2 [2 × 2] Grid with Localized Single Molecule Magnet Behavior

Metal complexes with a [n × n] gridlike structure are discussed as attractive building blocks for various materials chemistry applications in molecular nanotechnology and electronics, which often rely on the grids' magnetic and redox properties. Most of the known metallogrids are homometallic, though heterometallic systems that comprise two or more different metals promise higher level functionalities. However, heterometallic [n × n] grids are relatively rare, mostly because of the more challenging synthetic strategies. To that end a new heterometallic [2 × 2] grid complex [L₄Ru₂Co₂](BF₄)₄ (2) based on a known pyrazolate-bridged bis(tridentate) compartmental N-donor ligand [L]^- is presented in this work, along with its doubly oxidized congener [L₄Ru₂Co₂](BF₄)₆ (3). In order to prevent scrambling of the different metal ions, a stepwise synthetic approach was implemented in which an inert Ru^II "corner complex" [(HL)₂Ru](BF₄)₂ (1) was isolated first, followed by addition of the more labile Co^II. This exclusively yields the desired [L₄Ru₂Co₂]⁴⁺ with anti-topology, viz., with the Ru^II and Co^II ions situated at opposite corners of the [2 × 2] grid, as confirmed by single crystal X-ray diffraction. 2 can be sequentially oxidized four times, first at the Co vertices and then at the Ru vertices. ¹H NMR spectroscopy as well as ESI mass spectrometry evidenced integrity of the [L₄Ru₂Co₂]^4+/6+ grids in solution. Structural and magnetic analyses revealed that paramagnetic 2 features LS-Ru^II and HS-Co^II ions (LS = low-spin, HS = high-spin) whereas LS-Ru^II and LS-Co^III ions are present in diamagnetic 3. The LS-Ru^II ions in 2 serve to magnetically isolate the HS-Co^II whose coordination geometry is strongly distorted from octahedral. A large and negative axial zero-field splitting value (D = -64 cm^-1) for the local S = 3/2 ions is shown to lead to single molecule magnetic (SMM) properties characterized by a barrier to spin inversion of U_eff = 8.8 cm^-1 and a single relaxation process with τ_o = 3.1 × 10^-5 s. Transition metal [2 × 2] grid complexes showing SMM behavior are extremely rare, and this is the first heterometallic 3d/4d grid system featuring such a magnetic signature.

Heterometallic grids: synthetic strategies and recent advances

Supramolecular metallogrid complexes are metalloclusters involving metal ions in planar array arrangements and organic ligands in perpendicular arrangements at each corner of the metal sites. Such essentially metal ion arrays have attracted great attention in the last three decades owing to their variety of interesting optical, electronic and magnetic properties. Among them, metallogrids containing more than one type of metal, that is heterometallic grids, are rare but have more potential to engineer a higher level functionality into one molecule. However, until now, only dozens of heterometallic grids have been reported without any specific review. Herein, we aim to give an overview of the assembly strategies, the physicochemical properties, and finally some perspectives on the future development of heterometallic grids.

A pair of homochiral trinuclear Zn(ii) clusters exhibiting unusual ferroelectric behaviour at high temperature

A pair of homochiral trinuclear Zn(ii) clusters exhibit unusual ferroelectric behaviour at high temperature.

Oximato-Based Ligands in 3 d/4 f-Metal Cluster Chemistry: A Family of {Cu3Ln} Complexes with a "Propeller"-like Topology and Single-Molecule Magnetic Behavior

The organic chelating and bridging ligands 9,10-phenanthrenedione-9-oxime (phenoxH) and 9,10-phenanthrenedione-9,10-dioxime (phendoxH₂) were synthesized and subsequently employed for the first time in heterometallic 3 d/4 f-metal cluster chemistry. The general reaction between CuCl₂·2H₂O, LnCl₃·6H₂O, phenoxH, and NEt₃ in a 1:2:2:4 molar ratio, in a solvent mixture comprising MeCN and MeOH, afforded brown crystals of a new family of [Cu₃LnCl₃(phenox)₆(MeOH)₃] clusters (Ln = Gd (1), Tb (2), Dy (3)) that possess an unprecedented [Cu₃Ln(μ-NO)₆]³⁺ "propeller"-like core. Complexes 1-3 are the first {Cu₃Ln} clusters in which the outer Cu^II and the central Ln^III atoms are solely bridged by diatomic oximato bridges. The {Cu-N-O-Ln} bridging units are very distorted with torsion angles spanning the range 35.5-48.9° and 25.2-55.6° in 1 and 2, respectively. As a result, complexes 1-3 are antiferromagnetically coupled, in agreement with previously reported magnetostructural criteria for oximato-bridged Cu/Ln complexes. The magnetic susceptibility data for all complexes were nicely fit to an isotropic spin Hamiltonian (for 1) or a Hamiltonian that accounts for the spin of the Cu^II atoms, the spin component of the Ln^III, the spin-orbit coupling (λ), an axial ligand-field component around the Ln^III atoms (Δ), and the Zeeman effect (for the anisotropic 2 and 3). The resulting fit parameters were J = -1.34 cm^-1 and g = 2.10 (1), J = -1.42 cm^-1, g_Cu = 2.10, and Δ = -26.3 cm^-1 (2), and J = -1.70 cm^-1, g_Cu = 2.05, and Δ = -38.1 cm^-1 (3). The reported fitting procedure, implemented in the PHI program, is here used for the first time. Even if this method is only valid in high-symmetry Ln environments, when it is properly used allows a very simple and efficient method to obtain the exchange parameters. In light of the negative anisotropy, compounds 2 and 3 were found to exhibit frequency-dependent tails of out-of-phase signals in the presence of a small external dc field, characteristic of the slow magnetization relaxation of a single-molecule magnet. By using the Kramers-Kronig equations, the effective energy barriers ( U_eff) were derived and reported as U_eff = 10.1 and 5.4 cm^-1 for 2 and 3, respectively.

Heterometallic Octanuclear NiII 4LnIII 4 (Ln = Y, Gd, Tb, Dy, Ho, Er) Complexes Containing NiII 2LnIII 2O4 Distorted Cubane Motifs: Synthesis, Structure, and Magnetic Properties

The reaction of 2-methoxy-6-[{2-(2-hydroxyethylamino)ethylimino}methyl] phenol (LH₃) with lanthanide metal salts followed by the addition of nickel acetate allowed isolation of a family of octanuclear complexes, [Ni₄Ln₄(μ₂-OH)₂(μ₃-OH)₄(μ-OOCCH₃)₈(LH₂)₄]·(OH)₂·xH₂O. Single crystal X-ray diffraction studies of these complexes reveal that their central metallic core consists of two tetranuclear [Ni₂Ln₂O₄] cubane subunits fused together by acetate and hydroxide bridges. The magnetic study of these complexes reveals a ferromagnetic interaction between the Ln^III and the Ni^II center. The magnitude of exchange coupling between the Ni^II and Ln^III center, parametrized from the magnetic data of the Gd analogue, gives J = +0.86 cm^-1. The magneto caloric effect, studied for the Ni^II ₄Gd^III ₄ complex, shows a maximum of magnetic entropy change, -ΔS _m = 22.58 J kg^-1 K^-1 at 3 K for an applied external field of 5 T.

Realization of toroidal magnetic moments in heterometallic 3d–4f metallocycles

Toroidal arrangements of magnetic moments are realized in Tb^III and Dy^III based heterometallic macrocycles thanks to the magnetic coupling between lanthanide and 3d metal ions.

Heterometallic lanthanide-centred [NiII6LnIII] rings

The syntheses, structures and magnetic properties of three new hetero-heptametallic [Ni₆Ln] complexes are reported.

From double-shelled grids to supramolecular frameworks

Double-shelled 4f and 3d–4f supramolecular grids were assembled by the combination of two different tritopic hydrazone ligands, and further stacked into supramolecular HOFs through sharing the hydrogen bonding donors of halide ions. This study provides the first lanthanide-based double-shelled supramolecular grids and functionalized HOFs.

New fluorescent compounds based on zinc thiocyanate: influence of structure on spectral properties

New coordination compounds based on zinc thiocyanate, namely (acetone thiosemicarbazone-κ²N¹,S)bis(isothiocyanato-κN)zinc(II) monohydrate, [Zn(NCS)₂(C₄H₉N₃S)]·H₂O, (I), and diaquatetrakis(urea-κO)zinc(II) tetrakis(isothiocyanato-κN)zinc(II), [Zn(CH₄N₂O)₄(H₂O)₂][Zn(NCS)₄], (II), were synthesized and studied by UV-Vis, fluorescence and IR spectroscopy. Coordination salt (II) forms a rare system composed of two different coordination units of the same metal and it is the first example of a compound with two completely different zinc coordination units, of which one contains a tetrakis(urea)zinc unit. Both (I) and (II) possess fluorescence properties and produce blue and green emissions, respectively, upon irradiation with violet light. The spectral properties were correlated with the observed molecular and supramolecular structures. The acetone thiosemicarbazone ligand of (I) exhibits (upon coordination) red shifts of bands corresponding to N=C and C=S stretching vibration frequencies, which is not typical for chelating molecules.

Heterometallic Heptanuclear [Cu5Ln2] (Ln = Tb, Dy, and Ho) Single-Molecule Magnets Organized in One-Dimensional Coordination Polymeric Network

The reaction of a multisite coordination ligand, LH₃, with Cu(II) salts and Ln(NO₃)₃·nH₂O in a 1:2:1 stoichiometric ratio in the presence of triethylamine was found to afford a series of one-dimensional heterometallic [{Cu₅Ln₂(L)₂(μ₃-OH)₄(ClO₄)(NO₃)₃(OH₂)₅}(ClO₄)₂(H₂O)_x]_∞ [Ln = Tb(1), Dy(2) and Ho(3), x = 4.25, 5.5, and 5 for 1-3, respectively] coordination polymers. Complexes 1-3 have been characterized by single crystal X-ray crystallography. The detailed study of the magnetic properties has also been performed and compared with the parent [Cu₅Ln₂] molecular analogues. The ac susceptibility measurements for complexes 1-3 confirm their SMM behavior with the following characteristics: Δ_eff/k_B = 23.4 K, τ₀ = 1.1 × 10^-6 s and Δ_eff/k_B = 27.9 K, τ₀ = 6.6 × 10^-7 s under 0 and 1200 Oe dc fields, respectively for 1; Δ_eff/k_B = 8.3 K, τ₀ = 3.1 × 10^-6 s for 2 under 0 dc field. For 3, the fast QTM below 4 K prevents the estimation of the SMM energy barrier. Remarkably, the magnetic and SMM properties of the previously reported molecular [Cu₅Ln₂] analogues are preserved after their assembly in these coordination networks.