Solid-State Aggregation of Metallacyclophane-Based MnIICuII One-Dimensional Ladders

Building-up host-guest helicate motifs and chains: a magneto-structural study of new field-induced cobalt-based single-ion magnets

In this work, we present the synthetic pathway, a refined structural description, complete solid-state characterization and the magnetic properties of four new cobalt(ii) compounds of formulas [Co(H₂O)₆][Co₂(H₂mpba)₃]·2H₂O·0.5dmso (1), [Co(H₂O)₆][Co₂(H₂mpba)₃]·3H₂O·0.5dpss (2), [Co₂(H₂mpba)₂(H₂O)₄]_n·4nH₂O (3), and [Co₂(H₂mpba)₂(CH₃OH)₂(H₂O)₂]_n·0.5nH₂O·2ndpss (4) [dpss = 2,2'-dipyridyldisulfide and H₄mpba = 1,3-phenylenebis(oxamic) acid], where 2 and 4 were obtained from [Co(dpss)Cl₂] (Pre-I) as the source of cobalt(ii). All four compounds are air-stable and were prepared under ambient conditions. 1 and 2 were obtained from a slow diffusion method [cobalt(ii) : H₂mpba^2- molar ratio used 1 : 1] and their structures are made up of [Co₂(H₂mpba)₃]^2- anionic helicate units and [Co(H₂O)₆]²⁺ cations, exhibiting supramolecular three-dimensional structures. Interestingly, a supramolecular honeycomb network between the helicate units interacting with each other through R₂²(10) type hydrogen bonds occurs in 2 hosting one co-crystallized dpss molecule. On the other hand, for the first time, linear (3) and zigzag (4) cobalt(ii) chains were isolated by slow evaporation of stirred solutions of mixed solvents with cobalt(ii) : H₂mpba^2- in 1 : 2 molar ratio at room temperature. Magnetic measurements of Pre-I revealed a quasi magnetically isolated S = 3/2 spin state with a significant second-order spin-orbit contribution as expected for tetrahedrally coordinated cobalt(ii) ions. The analysis of the variable temperature static (dc) magnetic susceptibility data through first- (1 and 3) and second-order spin-orbit coupling models (2 and 4) reveals the presence of magnetically non-interacting high-spin cobalt(ii) ions with easy-axis (1 and 4)/easy-plane magnetic anisotropies (2 and 4) with low rhombic distortions. Dynamic (ac) magnetic measurements for Pre-I and 1-4 below 8.0 K show that they are examples of field-induced Single-Ion Magnets (SIMs).

Synthetic ability of dinuclear mesocates containing 1,3-bis(diazinecarboxamide)benzene bridging ligands to form complexes of increased nuclearity. Crystal structures, magnetic properties and theoretical studies

Triple stranded Ni-metallacyclic complexes Na_2.5[Ni₂(bpcb)₃]·0.5OH·18.5H₂O (1) and Na₂[Ni₂(bpzcb)₃]·16H₂O (2), and double stranded Cu-metallacyclic complexes [Cu₂(bpcb)₂(H₂O)₂]·8H₂O (3) and [Cu₂(bpzcb)₂(H₂O)₂]·4H₂O (4) have been assembled from the tailored bisbidentate bridging ligands, 1,3-bis(pyrimidine-2-carboxamide)benzene (H₂bpcb) and 1,3-bis(pyrazine-2-carboxamide)benzene (H₂bpzcb), and the corresponding nitrate salts of the metal ions. Following the "complex as ligand" strategy, 1 can be assembled with either Ni²⁺, Co²⁺ ions or the [Mn(acen)Cl] complex to afford unique, neutral, bent trinuclear molecules [M^IINi(bpcb)₃]·xH₂O (5 and 6) and the 2D honeycomb-like complex (PPh₄){[Ni₂(bpcb)₃]₂[Mn(acen)]₃} (7), respectively. In these cases, the Ni₂ units are linked to the corresponding metal ions through amidate oxygen atoms and the outward nitrogen atom of one of the pyrimidine rings of the bcpb ligand. The assembly of 2 with Ln³⁺ ions (Ln³⁺ = Tb, Gd) leads to one dimensional complexes of formula [{[Ni₂(bpzcb)₃]Tb(H₂O)₅}(CF₃SO₃)·THF·5H₂O]_n (8) and [{[Ni₂(bpzcb)₃]Ln(H₂O)₄(NO₃)}·2THF·nH₂O]_n (9 and 10) (Ln³⁺ = Gd and Tb), where the dinuclear Ni₂ units are joined to two Ln³⁺ ions exclusively through amidate oxygen atoms of two different ligands. The analyses of the magnetic data indicate that 1-4 exhibit intradinuclear ferromagnetic interactions between the metal ions through a spin polarisation mechanism, as supported by DFT calculations. Trinuclear complexes 5 and 6 show predominant antiferromagnetic coupling, which is a result of an antiferromagnetic interaction between one of the Ni²⁺ ions of the Ni₂ unit and the M²⁺ ion through the pyrimidine bridging fragment that is stronger than the polarised ferromagnetic interaction between the Ni²⁺ ions through the bpcb ligand in the dinuclear [Ni₂(bpcb)₃]^2- moiety. Complex 7 shows a dominant antiferromagnetic interaction between the Ni²⁺ and Mn²⁺, whereas the Ni₂Ln (Ln³⁺ = Gd, Tb) chain complexes present ferromagnetic interactions inside the Ni₂ mesocate unit as well as between the Ni²⁺ ions of the Ni₂ unit and the Ln³⁺ ions. The magnetic exchange interactions in these new materials have been experimentally analysed and supported by theoretical DFT studies.

Dicopper(II) Metallacyclophanes with N,N'-2,6-Pyridinebis(oxamate): Solution Study, Synthesis, Crystal Structures, and Magnetic Properties

The complexing ability of copper(II) in solution by the ligand N,N'-2,6-pyridinebis(oxamic acid) (H4mpyba, H4L) was determined through potentiometric and UV-vis spectroscopy at 25 °C and 0.15 M NaCl. The logarithms of the equilibrium constants for its copper(II) complexes according to the eqs 2H2L + 2Cu ⇆ [Cu2(H2L)2], 2H2L + 2Cu ⇆ [Cu2(H2L) (HL)] + H, 2H2L + 2Cu ⇆ [Cu2(HL)2] + 2H, 2H2L + 2Cu ⇆ [Cu2(HL)(L)] + 3H, and 2H2L + 2Cu ⇆ [Cu2L2] + 4H were 12.02(7), 8.04(5), 1.26(6), -7.51(6), and -16.36(6), respectively. The knowledge of the solution behavior has supported the synthesis of three new compounds bearing the common building block Cu2L2(4-). Their formulas are (Me4N)4[Cu2(mpyba)2(H2O)2]·H2O (1), (Me4N)4[K2Na2Cu4(mpyba)4(H2O)6.8]·1.6H2O (2), and [Na6Cu2(mpyba)2Cl2(H2O)8]·7H2O (3) (Me4N(+) = tetramethylammonium cation). The [Cu2(mpyba)2(H2O)2](4-) tetraanionic unit, which is present in 1, has a [3,3] metallacyclophane-type motif connected by two N-Cu-N bonds. In 2, a heterotrimetallic decanuclear nanocage is formed through front-to-front assembly of two [Cu2(mpyba)2](4-) units, which also coordinate to potassium(I) and sodium(I) cations by means of carboxylate oxygens from oxamate. The structure of 3 consists of heterobimetallic layers of formula [Na6Cu2(mpyba)2Cl2(H2O)8] and crystallization water molecules, which are interlinked by hydrogen bonds leading to a supramolecular three-dimensional network. The investigation of the magnetic properties of 1-3 in the temperature range 1.9-300 K shows the occurrence of ferromagnetic interactions between the dicopper(II) metallacyclophane unit [J = +6.85 (1), +7.40 (2), and +7.90 cm(-1) (3); H = -JSCu1·SCu2, where SCu1 = SCu2 = 1/2]. Theoretical calculations on 1-3 were carried to substantiate the nature and magnitude of the involved magnetic interactions and to support the occurrence of a spin polarization mechanism accounting for them.

Self-assembly, binding ability and magnetic properties of dicopper(ii) pyrazolenophanes

The nature of the blocking α-diimine ligand controls of the molecular folding and binding ability of the resulting “butterfly-shaped”, antiferromagnetically coupled dicopper(ii) pyrazolenophanes in the solid state.

Oxamato-based coordination polymers: recent advances in multifunctional magnetic materials

The design and synthesis of novel examples of multifunctional magnetic materials based on the so-called coordination polymers (CPs) have become very attractive for chemists and physicists due to their potential applications in nanoscience and nanotechnology.