A biphenyl-spaced bis-pyrazolylpyridine ligand interacts with ferrous ions to engender a dimetallic helical coordination cage that encapsulates an Fe³⁺ tris-anilate complex. The host-guest interaction breaks the symmetry of the Fe²⁺ centers causing a differential spin crossover behavior in them that can be followed in great detail crystallographically.

A new bis(pyrazolylpyridine) ligand (H2 L) has been prepared to form functional [Fe2 (H2 L)3 ](4+) metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅xCH3 OH (1, x=5.7 and X=Cl; 2, x=4 and X=Br), X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅yCH3 OH⋅H2 O (1 a, y=3 and X=Cl; 2 a, y=1 and X=Br) and X@[Fe2 (H2 L)3 ](I3 )2 ⋅3 Et2 O (1 b, X=Cl; 2 b, X=Br). Their structure and functional properties are described in detail by single-crystal X-ray diffraction experiments at several temperatures. Helicates 1 a and 2 a are obtained from 1 and 2, respectively, by a single-crystal-to-single-crystal mechanism. The three possible magnetic states, [LS-LS], [LS-HS], and [HS-HS] can be accessed over large temperature ranges as a result of the structural nonequivalence of the Fe(II) centers. The nature of the guest (Cl(-) vs. Br(-) ) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS-HS] or [HS-HS] states are generated through irradiation. All helicates (X@[Fe2 (H2 L)3 ])(3+) persist in solution.

The anion SiF₆^2- exerts a strong template effect, driving the exclusive assembly of two different bispyridylpyrazolyl ligands into a triple stranded Fe(II) dinuclear heteroleptic helicate, engendering a new class within the large family of coordination helicates.

The combination of two different β-diketone ligands facilitates the size-controlled assembly of pure heterometallic [LnLn'Ln] linear compounds thanks to two different coordination sites present in the molecular scaffold. [HoCeHo], [ErCeEr], and [YbCeYb] analogues are presented here and are characterized both in the solid state and in solution, demonstrating the selectivity of this unique method to produce heterometallic 4f molecular entities.

A new bis-(β-diketone) ligand featuring built-up structural asymmetry yields non-symmetric Fe(iii) and Ga(iii) dinuclear, triple-stranded helicates by design. Their structural properties have been studied, both in solid state and in solution, and compared with their corresponding symmetric analogues. The robustness observed shows the potential of this synthetic strategy to develop non-symmetric helicoidal motifs with specific functional groups.

The solid-state and solution configurations of the heterodimetallic complexes (Hpy)[LaEr(HL)₃ (NO₃ )(py)(H₂ O)] (1), (Hpy)[CeEr(HL)₃ (NO₃ )(py)(H₂ O)] (2), (Hpy)[CeGd(HL)₃ (NO₃ )(py)(H₂ O)] (3), (Hpy)[PrSm(HL)₃ (NO₃ )(py)(H₂ O)] (4), and (Hpy)₂ [LaYb(HL)₃ (NO₃ )(H₂ O)](NO₃ ) (5), in which H₃ L is 6-(3-oxo-3-(2-hydroxyphenyl)propionyl)pyridine-2-carboxylic acid and py is pyridine, were analyzed experimentally and by using DFT calculations. Complexes 3, 4, and 5 are described here for the first time, and were analyzed by using single-crystal X-ray diffraction and mass spectrometry. The theoretical study was also extended to the [LaCe] and [LaLu] analogues. The results are consistent with a remarkable selectivity of the metal distribution within the molecule in the solid state, enhanced by the size difference between the different ions. This selectivity was reduced in solution, particularly for ions with the most similar radii. This unique entry into 4f-4f'' heterometallic chemistry establishes for the first time the difference between the selectivity in solution and that in the solid state, as a result of changes to the coordination that follow the dissociation of terminal ligands upon dissolution of the complexes.

A new bis-(β-diketone) ligand featuring built-up structural asymmetry yields non-symmetric Fe(iii) and Ga(iii) dinuclear, triple-stranded helicates by design. Their structural properties have been studied, both in solid state and in solution, and compared with their corresponding symmetric analogues. The robustness observed shows the potential of this synthetic strategy to develop non-symmetric helicoidal motifs with specific functional groups.

Ditopic bis-pyrazolylpyridine ligands usually react with divalent metal ions (M²⁺) to produce dinuclear triple-stranded helicates [M₂L₃]⁴⁺ or, via π⋯π interactions, dimers of monoatomic complexes ([ML₃]₂)⁴⁺. The introduction of an additional benzene ring at each end of ligand L increases the number of aromatic contacts within the supramolecular aggregate by 40%, driving the self-recognition process in an irreversible manner. Consequently, the mixing of new bis-pyrazolylquinoline L2 with FeX₂ salts leads to crystallization of the tripartite high-spin assemblies (X@[Fe(L2)₃]₂)³⁺ (X = Cl, Br or I). The aggregates exhibit exceptional stability, as confirmed by a combination of paramagnetic ¹H NMR techniques, demonstrating their persistence in solution. Our investigations further reveal that the guests Br^- and I^- are retained inside the associate in solution but Cl^- is immediately released, resulting in the formation of the empty supramolecular dimer ([Fe(L2)₃]₂)⁴⁺.