Magneto-structural correlation in a metamagnetic cobalt(II)-based pillared trilayer motif constructed by mixed pyridyl-type carboxylate ligands

Utilization of a trinuclear Cu-pyrazolate inorganic motif to build multifunctional MOFs

The current work aims to generate multifunctional MOFs by incorporating a well-known inorganic motif, a trinuclear Cu-pyrazolate [Cu3(μ3-OH)(μ-Pyz)3] (T-CuP) unit, as a node of the network. Accordingly, we report herein the synthesis and properties of five new compounds using five V-shaped dicarboxylic acids as auxiliary ligands. The structural features are consistent with the theme of grafting T-CuP units as nodal points of architectures whose chassis are primarily made of bent acids. V-shaped acids also induce a helical nature inside resulting frameworks. Beside their structural and physical features, T-CuP unit-based MOFs also vindicate our thematic approach of the trinuclear Cu-pyrazolate unit imparting specific physicochemical properties, such as magnetic, electrical, and catalytic properties, to resultant MOFs. The MOFs show excellent catalytic properties in reducing 4-nitrophenol, which could be attributed to the porous nature of the network along with the presence of metal centres with unsaturated coordination within the T-CuP unit. Furthermore, efficient photocatalytic degradation of harmful organic dyes confirms their importance for environmental remediation. The presence of a T-CuP unit and various functional groups also make some of the MOFs suitable candidates for electrical applications, which is indeed manifested in encouraging proton conductivity. Finally, the potential of current MOFs, fitted with a magnetically important trinuclear Cu-pyrazolate motif, as magnetic materials has also been thoroughly investigated.

3D Metal-Organic Frameworks Based on Co(II) and Bithiophendicarboxylate: Synthesis, Crystal Structures, Gas Adsorption, and Magnetic Properties

Three new 3D metal-organic porous frameworks based on Co(II) and 2,2′-bithiophen-5,5′-dicarboxylate (btdc²⁻) [Co₃(btdc)₃(bpy)₂]·4DMF, 1; [Co₃(btdc)₃(pz)(dmf)₂]·4DMF·1.5H₂O, 2; [Co₃(btdc)₃(dmf)₄]∙2DMF∙2H₂O, 3 (bpy = 2,2′-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformamide) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co₃(RCOO)₆}, connected either by btdc^2– ligands (1, 3) or by both btdc^2– and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N₂, O₂, CO, CO₂, CH₄ adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m²⋅g⁻¹ and promising gas separation performance with selectivity factors up to 35.7 for CO₂/N₂, 45.4 for CO₂/O₂, 20.8 for CO₂/CO, and 4.8 for CO₂/CH₄. The molar magnetic susceptibilities χ_p(T) were measured for 1 and 2 in the temperature range 1.77–330 K at magnetic fields up to 10 kOe. The room-temperature values of the effective magnetic moments for compounds 1 and 2 are μ_eff (300 K) ≈ 4.93 μ_B. The obtained results confirm the mainly paramagnetic nature of both compounds with some antiferromagnetic interactions at low-temperatures T < 20 K in 2 between the Co(II) cations separated by short pz linkers. Similar conclusions were also derived from the field-depending magnetization data of 1 and 2.

Selective Metal-Ligand Bond-Breaking Driven by Weak Intermolecular Interactions: From Metamagnetic Mn(III)-Monomer to Hexacyanoferrate(II)-Bridged Metamagnetic Mn2Fe Trimer

Metal-ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare example where metal-ligand bonds dissociate in an irreversible way, helped by a large number of weak intermolecular interactions that surpass the energy of the metal-ligand bond. Thus, we describe the design and synthesis of trinuclear Mn₂Fe complex {[Mn(L)(H₂O)]₂Fe(CN)₆},^2- starting from a mononuclear Mn(III)-Schiff base complex: [Mn(L)(H₂O)Cl] (1) and [Fe(CN)₆]^4- anions. This reaction implies the dissociation of Mn(III)-Cl coordination bonds and the formation of Mn(III)-NC bonds with the help of several intermolecular interactions. Here, we present the synthesis, crystal structure, and magnetic characterization of the monomeric Mn(III) complex [Mn(L)(H₂O)Cl] (1) and of compound (H₃O)[Mn(L)(H₂O)₂]{[Mn(L)(H₂O)]₂Fe(CN)₆}·4H₂O (2) (H₂L = 2,2'-((1E,1'E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(4-methoxyphenol)). Complex 1 is a monomer where the Schiff base ligand (L) is coordinated to the four equatorial positions of the Mn(III) center with a H₂O molecule and a Cl^- ion at the axial sites and the monomeric units are assembled by π-π and hydrogen-bonding interactions to build supramolecular dimers. The combination of [Fe(CN)₆]^4- with complex 1 leads to the formation of linear Mn-NC-Fe-CN-Mn trimers where two trans cyano groups of the [Fe(CN)₆]^4- anion replace the labile chloride from the coordination sphere of two [Mn(L)(H₂O)Cl] complexes, giving rise to the linear anionic {[Mn(L)(H₂O)]₂Fe(CN)₆}^2- trimer. This Mn₂Fe trimer crystallizes with an oxonium cation and a mononuclear [Mn(L)(H₂O)₂]⁺ cation, closely related to the precursor neutral complex [Mn(L)(H₂O)Cl]. In compound 2, the Mn₂Fe trimers are assembled by several hydrogen-bonding and π-π interactions to frame an extended structure similar to that of complex 1. Density functional theoretical (DFT) calculations at the PBE1PBE-D3/def2-TZVP level show that the bond dissociation energy (-29.3 kcal/mol) for the Mn(III)-Cl bond is smaller than the summation of all the weak intermolecular interactions (-30.1 kcal/mol). Variable-temperature magnetic studies imply the existence of weak intermolecular antiferromagnetic couplings in both compounds, which can be can cancelled with a critical field of ca. 2.0 and 2.5 T at 2 K for compounds 1 and 2, respectively. The magnetic properties of compound 1 have been fit with a simple S = 2 monomer with g = 1.959, a weak zero-field splitting (|D| = 1.23 cm^-1), and a very weak intermolecular interaction (zJ = -0.03 cm^-1). For compound 2, we have used a model with an S = 2 monomer with ZFS plus an S = 2 antiferromagnetically coupled dimer with g = 2.009, |D| = 1.21 cm^-1, and J = -0.42 cm^-1. The metamagnetic behavior of both compounds is attributed to the weak intermolecular π-π and hydrogen-bonding interactions.

A novel three-dimensional copper(I) cyanide coordination polymer constructed from various bridging ligands: synthesis, crystal structure and characterization

The cyanide ligand can act as a strong σ-donor and an effective π-electron acceptor that exhibits versatile bridging abilities, such as terminal, μ₂-C:N, μ₃-C:C:N and μ₄-C:C:N:N modes. These ligands play a key role in the formation of various copper(I) cyanide systems, including one-dimensional (1D) chains, two-dimensional (2D) layers and three-dimensional (3D) frameworks. According to the literature, numerous coordination polymers based on terminal, μ₂-C:N and μ₃-C,C,N bridging modes have been documented so far. However, systems based on the μ₄-C:C:N:N bridging mode are relatively rare. In this work, a novel cyanide-bridged 3D Cu^I coordination framework, namely poly[(μ₂-2,2'-biimidazole-κ²N³:N^3')(μ₄-cyanido-κ⁴C:C:N:N)(μ₂-cyanido-κ²C:N)dicopper(I)], [Cu₂(CN)₂(C₆H₆N₄)]_n, (I), was synthesized hydrothermally by reaction of environmentally friendly K₃[Fe(CN)₆], CuCl₂·2H₂O and 2,2'-biimidazole (H₂biim). It should be noted that cyanide ligands may act as reducing agents to reduce Cu^II to Cu^I under hydrothermal conditions. Compound (I) contains diverse types of bridging ligands, such as μ₄-C:C:N:N-cyanide, μ₂-C:N-cyanide and μ₂-biimidazole. Interestingly, the [Cu₂] dimers are bridged by rare μ₄-C:C:N:N-mode cyanide ligands giving rise to the first example of a 1D dimeric {[Cu₂(μ₄-C:C:N:N)]ⁿ⁺}_n infinite chain. Furthermore, adjacent dimer-based chains are linked by μ₂-C:N bridging cyanide ligands, generating a neutral 2D wave-like (4,4) layer structure. Finally, the 2D layers are joined together via bidentate bridging H₂biim to create a 3D cuprous cyanide network. This arrangement leads to a systematic variation in dimensionality from 1D chain→2D sheet→3D framework by different types of bridging ligands. Compound (I) was further characterized by thermal analysis, solid-state UV-Vis diffuse-reflectance and photoluminescence studies. The solid-state UV-Vis diffuse-reflectance spectra show that compound (I) is a wide-gap semiconductor with band gaps of 3.18 eV. The photoluminescence study shows a strong blue-green photoluminescence at room temperature, which may be associated with metal-to-ligand charge transfer.

New Topologically Unique Metal-Organic Architectures Driven by a Pyridine-Tricarboxylate Building Block

Two new three-dimensional (3D) coordination compounds, namely a lead(II) coordination polymer (CP) {[Pb3(µ5-cpta)(µ6-cpta)(phen)2]·2H2O}n (1) and a zinc(II) metal-organic framework (MOF) {[Zn2(µ4-cpta)(µ-OH)(µ-4,4′-bipy)]·6H2O}n (2), were hydrothermally assembled from 2-(5-carboxypyridin-2-yl)terephthalic acid (H3cpta) as an unexplored principal building block and aromatic N,N-donors as crystallization mediators. Both products were isolated as air-stable microcrystalline solids and were fully characterized by IR spectroscopy, elemental and thermogravimetric analysis, and powder and single-crystal X-ray diffraction. Structural and topological features of CP 1 and MOF 2 were analyzed in detail, allowing to identify a topologically unique 4,5,5,6-connected net in 1 or a very rare 4,4-connected net with the isx topology in 2. Thermal stability and solid-state luminescent behavior of 1 and 2 were also investigated. Apart from revealing a notable topological novelty, both compounds also represent the first structurally characterized Pb(II) and Zn(II) derivatives assembled from H3cpta, thus opening up the application of this unexplored pyridine-tricarboxylate block in the design of new metal-organic architectures.

The construction, structures, and functions of pillared layer metal–organic frameworks

Pillared layer metal–organic frameworks (PL-MOFs), belonging to one representative of porous materials, have witnessed major advances in the past few years.

The concept of mixed organic ligands in metal–organic frameworks: design, tuning and functions

The mixed organic ligand strategy is significant for the rational construction of MOFs, and furthermore for their functionality and tunability.

4-Substituent pyridine directed cobalt(ii) azides: solvothermal synthesis, structure, and magnetic properties

Azido-bridged magnetic complexes: Different 4-substituent groups of pyridine co-ligands directed the linkages between azide and Co(ii) ions, to give three azide–Co(ii) complexes with different structures and magnetic properties.

Structural diversification and photocatalytic properties of zinc(ii) polymers modified by auxiliary N-containing ligands

Four zinc coordination polymers with different architectures based on 5-(1H-benzoimidazol-2-ylsulfanylmethyl)-isophthalic acid have been prepared. Their photoluminescence and photocatalytic properties were also investigated.

Bilayer architecture based on hexanuclear heterometal cluster units

An unprecedented bilayer architecture based on “head-to-head” hexanuclear heterometal clusters and linked by parallel [Cu^IL₂] motifs has been hydrothermally made.