[Mn^III₆Mn^IINa^I₂], [Mn^III₃Mn^IINa^I], and [Mn^III₃] Clusters Derived from Schiff Bases: Syntheses, Structures, and Magnetic Properties ^†

Abstract

The reaction of manganese halides with polydentate Schiff bases obtained by the condensation of 3-ethoxysalicylaldehyde and different amino alcohols, resulting in a NO₃ set of donors, yielded a series of manganese clusters with {Mn^III₆Mn^IINa₂}, {Mn^III₃Mn^IINa}, and {Mn^III₃} metallic cores. The influence of the ligand substituents and the halide on the final nuclearity has been studied. Analysis of their static magnetic behaviour confirms the ground states of 19/2 for the {Mn^III₆Mn^IINa₂} complexes, 7/2 for the {Mn^III₃Mn^IINa} clusters, and 12/2 for the triangular {Mn^III₃} systems, and a weak field induced a slow relaxation of the magnetization for the trinuclear complexes.

1. Introduction

The condensation of a primary amine with aldehydes or ketones yields Schiff bases, which are a class of highly tunable ligands as a function of the R–NH₂ and the R–C=O precursors. The design, taking into account shape, chirality, and the number and kind of donors, can induce the selective coordination of only one cation or to generate polynuclear systems with the desired properties after coordination to the adequate cations. The enormous variety of available amines and aldehydes that can be employed as precursors can generate ligands with specific topologies or donor atoms that can link either 3d or 4f cations that demonstrated to be of application in many fields like syntheses, [1] catalysis [2], luminescence [3], or pharmaceuticals [4]. Salicyl and o-vanillin are the most employed aldehyde precursors to reach tetradentate two-pocket ligands with a NO₃ set of donors.

The condensation of 3-ethoxysalicylaldehyde with substituted 2-aminoethanol, such 2-phenylglycinol or 2-Amino-1-phenylethanol, gives the polytopic ligands H₂L1 and H₂L2, respectively, see Scheme 1—top. Each ligand has a NO₃ set of donors able to link up to three cations, generating medium and large clusters.

Manganese chemistry with these ligands is dominated by the {Mn^III₃M’M″} metallic cores that consist of a triangular bipyramid formed by one triangular arrangement of Mn^III cations, linked through a μ₃-O donor, and two apical M’ and M″ cations, see Scheme 1—bottom. The most common structure consists of pentanuclear {Mn^III₃Mn^IINa^I} units [5,6,7,8,9,10,11,12] but some {Mn^III₃Mn^IICa^II} [5,7,10], {Mn^III₃Mn^IIMn^II} [7,10], or {Mn^III₃Ln^IIINa^I} [13] cores have also been reported. This pentanuclear unit is very versatile and larger nuclearities have been reported when one of the apical cations is shared by two units, resulting in a nonanuclear {Mn^III₆Mn^IINa^I₂} [8,10,12,14,15] or {Mn^III₆Ln^IIINa^I₂} [16,17] skeleton or decanuclear {Mn^III₆Mn^II₂Na^I₂} systems when the Mn^II cations from two or more units are linked by halides, pseudohalides, or methoxides [9,11,12,18,19,20].

During the last years, we explored the reactivity of a family of related ligands derived from o-vanillin and 2-amino-1-ethanol in Mn^II,III, [8,9,10,12,17], Ni^II [21,22], and Fe^III chemistry [23], trying to elucidate the effect of the substituents on the C-atoms of amino alcohol. From this previous work, we realized that the size and position of the substituents (Me, Ph, isopropyl) is hardly insignificant and largely induces different shapes and nuclearities in the resulting clusters.

Following our previous work in this field, we have explored the influence of the ethoxo substituent on the salicylaldehyde ring and the position of the phenyl ring on the alcoxo arm of the Schiff base. The reaction of manganese(II) halides with ligands H₂L1 and H₂L2 yielded a series of clusters with different nuclearities ranging from tri- to nonanuclear with formulas [Mn^III₆Mn^IINa₂(O)₂(L1)₆Cl₆] (1R), [Mn^III₆Mn^IINa₂(O)₂(L1)₆I₆] (2Ra, 2Rb), [Mn^III₃(L2)₃(O)(H₂O)₂(EtOH)]Cl (3), [Mn^III₃(L2)₃(O)(H₂O)(MeOH)₂]Br (4), and [Mn^III₃Mn^IINa(O)(L2)₃Cl₃(CH₃CN)]₂[Mn^IIBr₄] (5). Structural characterization shows a variety of metallic cores as function of minor changes on the Schiff bases, such as the rare trinuclear topology found in complexes 3–4 and the unusual Mn^III-I-Mn^III linkage found in complexes 2Ra and 2Rb. The study of their magnetic properties shows Mn^III–Mn^III ferromagnetic interactions and Mn^II–Mn^III antiferromagnetic coupling yielding S ground states between 7/2 and 19/2.

2. Materials and Methods

2.1. Physical Measurements

Magnetic susceptibility measurements were carried out on pressed polycrystalline samples at the Mesures Magnètiques Unit from Scientific and Technological Centers (CCiTUB), Universitat de Barcelona, using a MPMS5 Quantum Design susceptometer (Quantum Design, Pfungstadt, Germany), working in the range 30–300 K under magnetic fields of 0.3 T and under a field of 0.03 T in the 30–2 K range to avoid saturation effects at low temperature. Diamagnetic corrections were estimated from Pascal tables. The fit of the magnetic experimental data were performed with the PHI programme [24]. CHN analyses were performed on vacuum dried samples. Infrared spectra (4000–400 cm^–1) were recorded from KBr pellets on a Bruker IFS-125 FT-IR spectrophotometer (Bruker-Spain, Madrid, Spain).

2.2. X-ray Crystallography

Red prism-like specimens of 1R, 2Ra, 2Rb, 3, 4, and 5 were employed for the single crystal X-ray crystallographic analysis. The X-ray intensity data were measured on a D8 Venture system equipped with a multilayer monochromator and a Mo microfocus. The frames were integrated with the Bruker SAINT software package using a narrow-frame algorithm. The structures were solved and refined using the Bruker SHELXTL-2014/7 Software [25]. Crystal data and refinement details for complexes 1 to 5 are summarized in Table S1. Complete crystallographic information can be found in the corresponding CIF files with the following CCDC numbers: 2382107 (for 1R), 2382108 (for 2Ra), 2382109 (for 2Rb), 2382110 (for 3), 2382111 (for 4), and 2382112 (for 5), which contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures accessed on 9 May 2024.

2.3. Synthesis

H₂L1 and H₂L2 Schiff bases. The ligands were synthesized by the reaction of 3-ethoxysalicylaldehyde with R-2-phenylglycinol or the rac-2-Amino-1-phenylethanol, respectively, following previously reported methods [12]. Methanolic or ethanolic solutions (20 mL) obtained mixing 0.605 g (3.65 mmol) of 3-ethoxysalicylaldehyde and 0.5 g (3.65 mmol) of 2-phenylglycinol or 2-amino-1-phenylethanol were heated at 80° for 30 min in a microwave Anton Parr Monowave-300 furnace and diluted to 100 mL of volume. Fractions of 10 mL (0.0365 mmol) were employed in the syntheses of the corresponding complexes.

[Mn^III₆Mn^IINa₂(O)₂(L1)₆Cl₆] (1R) was synthesized. A solution of MnCl₂·4H₂O (0.072 g, 0.365 mmol) and 0.024 g (0.365 mmol) of sodium azide in 15 mL of acetonitrile was mixed with 10 mL of the previously prepared methanolic solution of (R)-H₂L1 (0.365 mmol). The resulting yellow mixture was maintained at open air with vigorous stirring and after 10 min, the colour changed to dark brown. After 30 more minutes, the clear solution was layered with diethyl ether and well-formed dark crystals, adequate for X-ray diffraction, and these were collected after three days with a 50% yield (~0.12 g). Because the azide anion was not coordinated, the same product was obtained employing Na(OH) (0.015 g, 0.364 mmol) as the base. CHN for C₁₀₂H₁₀₂Cl₆Mn₇N₆Na₂O₂₀: calcd. (%): C, 51.58; H, 4.33; N, 3.54. Found: C, 51.0; H, 4.5; N, 3.4.

[Mn^III₆Mn^IINa₂(O)₂(L1)₆I₆] (2Ra) and [Mn^III₆Mn^IINa₂(O)₂(L1)₆I₆]·11 CH₃CN (2Rb) were synthesized. The synthesis was performed following the same procedure employed in 1R but using 0.112 g (0.364 mmol) of manganese iodide instead the chloride salt. Crystallization of the complex, either from the layers with diethyl ether or slow evaporation, yielded a mixture of well-formed prismatic crystals and bars in a similar amount, and these were manually separated. Structural determination proved the identity of the prismatic crystals (2Ra) and the bars (2b). Yield: 25% for both complexes (~0.10 g). CHN for C₁₀₂H₁₀₂I₆Mn₇N₆Na₂O₂₀: calcd. (%): C, 41.90; H, 3.52; N, 2.87. Found 2Ra: C, 42.1; H, 3.4; N, 2.9. Found 2Rb: C, 42.3; H, 3.6; N, 2.8.

[Mn^III₃(L2)₃(O)(H₂O)₂(EtOH)]Cl·0.5 CH₃CN·0.25EtOH (3) was synthesized. To a solution of MnCl₂·4H₂O (0.072 g, 0.365 mmol) in acetonitrile (10 mL) was added Cs(OH) (0.109 g, 0.728 mmol). To the resulting brown suspension, 10 mL of the previously prepared ethanolic solution of rac-H₂L (0.364 mmol) was added. The solid was redissolved after some minutes of stirring, resulting a dark brown solution. Crystals adequate for X-ray diffraction were obtained after one week from the slow diffusion of diethyl ether. Yield: 50% (~0.08 g). CHN for C₅₃H₆₁ClMn₃N₃O₁₃: calcd. (%): C, 55.43; H, 5.35; N, 3.66. Found C, 55.8; H, 5.2; N, 3.5.

[Mn^III₃(L2)₃(O)(H₂O)(MeOH)₂]Br·CH₃CN·MeOH (4) was synthesized. The complex was obtained following the same procedure employed for the synthesis of complex 4, but starting from MnBr₂·H₂O (0.104 g, 0.364 mmol), Et₃N (0.036 g, 0.364 mmol), and a methanolic solution of rac-H₂L2 (0.364 mmol). The slow diffusion of diethyl ether yields crystalline complex 4 in a 60% yield (~0.09 g). CHN for C₅₃H₆₁BrMn₃N₃O₁₃: calcd. (%): C, 53.37; H, 5.15; N, 3.52. Found C, 53.0; H, 5.3; N, 3.7.

[Mn^III₃Mn^IINa(O)(L2)₃Cl₃(CH₃CN)]₂[Mn^IIBr₄]·0.5 H₂O (5) was synthesized. The synthesis of this complex was performed following the same procedure employed for compound 1 starting from MnBr₂·4H₂O (0.104 g, (0.364 mmol) and 10 mL of the previously prepared ethanolic solution of rac-H₂L2. Layering the resulting dark solution with diethyl ether, hexagonal crystals of 5 were collected in a 70% yield (~0.09 g). CHN for C₁₀₆H₁₀₈Br₁₀Mn₉N₈Na₂O₂₀: calcd. (%): C, 40.37; H, 3.45; N, 3.55. Found C, 39.9; H, 3.6; N, 3.4.

Representative IR spectra (complexes 1R, 3, and 5) are shown in Figure S1.

3. Results and Discussion

3.1. Description of the Structures

The oxidation states of the manganese cations have been assigned with respect to the shape of the coordination sphere, charge valence of the resulting formulas, and BSV calculations, as shown in Table S2.

3.1.1. Crystal Structure of [Mn^III₆Mn^IINa₂(O)₂(L1)₆Cl₆] (1R), [Mn^III₆Mn^IINa₂(O)₂(L1)₆I₆] (2Ra), and [Mn^III₆Mn^IINa₂(O)₂(L1)₆I₆] (2Rb)

The three structures have a common core consisting in two {Mn₃^IIIMn^IINa} pentanuclear units sharing the Mn^II cation. Selected bond parameters are reported in

Table 1. Main bond distances (Å) and angles (deg.) for complexes 1R and 2Ra.

	1R	2Ra
Mn1–O2	1.900(3)	1.880(4)
Mn1–O3	1.899(3)	1.903(3)
Mn1–O7	1.8810(8)	1.8780(9)
Mn1–X1	2.595(1)	2.942(1)
Mn1′–X1	2.701(1)	3.021(1)
Mn2–O5	1.914(3)	1.891(5)
Mn2–O6	1.886(3)	1.900(4)
Mn2–O8	1.8761(9)	1.872(1)
Mn2–X2	2.637(1)	3.023(1)
Mn2′–X2	2.735(1)	3.105(1)
Mn3–O3	2.201(3)	2.202(3)
Mn3–O6	2.196(3)	2.193(4)
Mn1–O7–Mn1′	119.2(5)	119.17(5)
Mn2–O8–Mn2′	118.82(6)	119.04(7)
Mn1–O3–Mn3	122.9(2)	123.8(2)
Mn2–O6–Mn3	125.4(2)	126.5(2)
Mn1–X1–Mn1′	75.54(4)	65.79(3)
Mn2–X2–Mn2′	73.89(4)	63.51(3)

. To avoid repetitive plots, the structure of one of them (2Ra) is shown in Figure 1 as a representative core. The pentanuclear units show a trigonal bipyramid arrangement with the Mn^III cations in the equatorial plane with the sodium and the divalent manganese in the apical positions. One μ₃-O donor is placed in the centre of the triangular arrangement of Mn^III cations. Each pentanuclear fragment is assembled by three L1²⁻ ligands linking the Mn^III cations with the Mn^II by means of alcoxo bridges and with the sodium cation by means of phenoxo bridges. The coordination sphere of the Mn^III cations is formed by one tridentate L1²⁻ ligand linking the alcoxo, phenoxo, and N-iminic donors, as well as the central oxo ligand and two bridging halide atoms. In all cases, the sodium cations are hexacoordinated and placed in the cavity formed by the three bidentate fragments composed by the phenoxo and the ethoxo O donors of the three L1²⁻ ligands, resulting in an intermediate polyhedron between the octahedral and trigonal prism.

Complexes 1R and 2Ra possesses a C₃ axis that relates the Mn^III and the L1²⁻ ligands, but the lack of an inversion centre imposed by the chiral ligand (R3 space group) determines that the two pentanuclear subunits are not equivalent and there are small differences in the bond parameters around Mn(1) and Mn(2), as shown in Table 1. Complex 2Rb shows the same core as 1R and 2Ra, but the loss of symmetry (from R3 to P2₁ space group) has the consequence that despite the bond parameters being very similar to those of 2Ra, all the cations are not equivalent, see Table S3.

3.1.2. Crystal Structure of [Mn^III₃(L2)₃(O)(H₂O)₂(EtOH)]Cl (3) and [Mn^III₃(L2)₃(O)(H₂O)(MeOH)₂]Br (4)

The two compounds have a common structure that consist of a triangular arrangement of Mn^III cations linked by one μ₃-O bridge and three L2²⁻ ligands, three solvent molecules, and one halide counterion. The representative molecular structure of complex 3 is shown in Figure 2 and the main bond parameters for the two complexes are listed in

Table 2. Main bond distances (Å) and angles (deg.) for the triangular complexes 3 and 4.

	3	4
Mn1–O3	2.255(2)	2.227(1)
Mn1–O5	1.902(2)	1.911(1)
Mn1–O6	1.882(1)	1.877(1)
Mn1–O10	1.926(1)	1.929(1)
Mn1–O11	2.293(3)	2.278(2)
Mn1–N1	1.987(2)	1.979(2)
Mn2–O2	1.910(2)	1.908(1)
Mn2–O2w	2.270(2)	2.316(1)
Mn2–O3	1.889(1)	1.868(1)
Mn2–O9	2.234(2)	2.240(1)
Mn2–O10	1.921(1)	1.915(1)
Mn2–N2	1.969(2)	1.978(1)
Mn3–O3w	2.266(2)	2.279(2)
Mn3–O6	2.253(2)	2.231(1)
Mn3–O8	1.902(2)	1.890(1)
Mn3–O9	1.864(2)	1.878(1)
Mn3–O10	1.929(1)	1.921(1)
Mn3–N3	1.993(2)	1.978(2)
Mn1–O3–Mn2	92.22(6)	93.38(5)
Mn1-O6-Mn3	92.62(6)	92.83(5)
Mn2–O9–Mn3	93.14(6)	92.29(5)
Mn1–O10–Mn2	102.36(6)	102.13(6)
Mn1–O10–Mn3	102.24(6)	101.69(6)
Mn2–O10–Mn3	101.74(6)	101.96(5)

. The μ₃-O donor is placed 0.85 Å over the plane defined by the manganese cations and the Mn-O-Mn bond angles lie in the short interval of 101.69(6)°–102.36(6)°. Each L2²⁻ ligand acts as tridentate by means of the deprotonated O-donors and the iminic nitrogen, whereas the O-ethoxy atoms remain uncoordinated. The coordination sphere of the Mn^III cations is formed by the three donors from one L2²⁻ ligand, two O-alcoxo donors, and one solvent molecule (water or alcohol). The L2²⁻ ligand contains a chiral C-atom and the main plane of the (R) and (S) isomers are disordered and tilted around 50° with respect to the plane defined by the three cations, resulting a helical arrangement.

3.1.3. Crystal Structure of [Mn^III₃Mn^IINa(O)(L2)₃Cl₃(CH₃CN)]₂[Mn^IIBr₄] (5)

The structure of 5 consists in two non-equivalent {Mn^IIIMn^IINa} cationic pentanuclear units and one [Mn^IIBr₄]²⁻ counteranion. Bond parameters are similar in both molecules forming the global system (

Table 3. Main bond distances (Å) and angles (deg.) for the two non-equivalent clusters present in the unit cell of compound 5.

	5A	5B
Mn1–O1	1.914(2)	1.931(3)
Mn1–O2	1.867(3)	1.883(3)
Mn1–O10	1.920(2)	1.903(2)
Mn1–Br1	2.7608(7)	2.7261(7)
Mn1–Br3	2.7725(7)	2.7938(7)
Mn3–O7	1.921(2)	1.920(3)
Mn3–O8	1.887(2)	1.889(3)
Mn3–O10	1.895(2)	1.890(2)
Mn3–Br1	2.8260(6)	2.8403(7)
Mn3–Br2	2.7777(7)	2.7730(7)
Mn4–O4	1.903(2)	1.906(3)
Mn4–O5	1.890(2)	1.889(3)
Mn4–O10	1.897(2)	1.887(3)
Mn4–Br2	2.9163(6)	2.7651(7)
Mn4–Br3	2.7785(6)	2.8431(7)
Mn2–O1	2.061(2)	2.036(3)
Mn2–O4	2.052(2)	2.050(3)
Mn2–O7	2.054(2)	2.064(3)
Mn2–N4	2.135(4)	2.113(5)
Mn1–O10–Mn3	120.0(1)	119.8(1)
Mn1–O10–Mn4	119.9(1)	120.0(1)
Mn3–O10–Mn4	120.1(1)	119.9(1)
Mn2–O1–Mn1	109.3(1)	113.8(1)
Mn2–O7–Mn3	110.3(1)	112.7(1)
Mn2–O4–Mn4	111.8(1)	113.4(2)
Mn1–Br1–Mn3	72.50(2)	72.22(3)
Mn1–Br3–Mn4	73.09(2)	71.21(3)
Mn3–Br2–Mn4	70.41(2)	72.36(3)

), which is shown in Figure 3.

The position of the cations and the linkage provided by the L2²⁻ ligands in the pentanuclear units are similar to those described for complexes 1R and 2Ra/2Rb. However, in this case, the divalent manganese is tetracoordinated with a coordination sphere composed of three O-alcoxo donors from the corresponding Schiff bases and one acetonitrile ligand, resulting in a NO₃ environment. The tetrahedral arrangement around the Mn^II imposes larger Mn^II-O-Mn^III bond angles than the octahedral environment that takes values in the 109.3(1)°–113.8(1)° range.

3.2. Structural and Synthetic Comments

The chemistry of the manganese halides and the reported ligands is sensitive to the specific halide and the topology of the ligand. The substituents in the vicinity of the O-alkoxo donor induce steric hindrance that becomes the determinant for the final nuclearities of the clusters. In fact, the {Mn₆^IIIMn^II} core becomes not possible for the L2²⁻ ligand and the products tend to lower nuclearities such as {Mn₃^III} or {Mn₃^IIIMn^IINa} found in complexes 3–5. It is remarkable that the characterization of clusters 3 and 4 had a triangular topology, which was unprecedented for the analogous ligand with a methoxy substituent. Ligand H₂L2 is able to give the usual {Mn₃^IIIMn^IINa} core, but probably due to small differences in solubility with respect to the methoxy-related ligand, can generate different cores.

Complexes 2Ra and 2Rb exhibit the unusual Mn^III-I linkage that a priori is poorly compatible due to the oxidant character of the trivalent manganese. Most of the reported complexes exhibiting this bond are mononuclear phthalocyanine derivatives [26,27,28,29], in which the Mn^III cation is placed in a square pyramidal environment with the iodide donor in the apical elongated site. Also, some iodide–phosphine complexes [30,31] and some other mononuclear complexes with the Schiff base 2,2′-bis(3,5-di-t-butylsalicylaldimino)-6,6′-dimethylbiphenyl [32] show a square pyramidal environment or the macrocyclic cyclam [33] derivative with an elongated octahedral environment, which have been reported.

Due to the apparent instability of the Mn^III/I⁻ system, this ligand has not been usually employed in manganese cluster chemistry. The only structurally characterized clusters combining Mn^III and iodide are those reported by Brechin et al. in some {Mn^II₄Mn^III₆I₄} derivatives of 2-Amino-2-methyl-1,3-propanediol and 2-Amino-2-ethyl-1,3-propanediol [34], as well as one hexanuclear complex derived from ethyl-salicyaldoxime that were the only clusters with Mn^III-I bonds, including one μ₃-I bridge [35]. It is remarkable that complexes 2Ra and 2Rb become the second clusters characterized with this kind of bond.

The configuration of the complexes built from chiral ligands is determined by the ligand chirality, which can be transferred to the coordination sphere of the cations to the complex or to the crystal. This “predetermined chirality” is usually propagated in an opposite sense by the corresponding enantiomeric ligands, resulting in mirror image clusters or networks for each enantiomer [36,37]. Thus, starting from the racemic H₂L2 ligand, it could be expected that complexes 3, 4, or 5, containing three ligands in their structures, must show the RRR and SSS arrangements related by inversion centres in the network. However, as was summarized in a previous work, this family of clusters often exhibits an unexpected mixing of enantiomers in the same molecule [12].

Complex 3 shows a complete disorder for the three ligands and complex 4 shows a helical arrangement of the three Schiff bases with respect to the plane defined by the manganese cations and a mixture of enantiomers, with one R enantiomer and two disordered R/S enantiomers, or one S enantiomer and two disordered R/S ligands, see Figure 4. Complex 5 exhibits an unusual mixture of enantiomers in the same molecule, with one of the molecules containing two R enantiomers and one R/S disordered ligand, and the molecule related by the inversion centre in the network contains two S enantiomers and one disordered R/S ligand, as shown in Figure 4.

3.3. Magnetic Properties

Susceptibility measurements were performed in the 2–300 K temperature range on powdered pressed samples for complexes 1R, 2Ra, 4, and 5. Complexes 1R and 2Ra show χ_MT values of 17.49 and 18.48 cm³·mol⁻¹·K at room temperature, lower than the expected values for six Mn^III and one Mn^II isolated cations (22.375 cm³·mol⁻¹·K) that decrease slightly down to a minimum of 16.86 cm³·mol⁻¹·K at 150 K and 17.68 cm³·mol⁻¹·K at 110 K for 1R and 2Ra, respectively. Below this minimum, the χ_MT values increase up to a maximum of 38.42 cm³·mol⁻¹·K placed at 13 K for complex 1 and 37.24 cm³·mol⁻¹·K at 10 K for complex 2Ra with a moderate decrease at lower temperatures, see Figure 5. The shape of the plot with a well-defined minimum is the signature of ferrimagnetic response for these two complexes.

Complex 4 shows the χ_MT value of 8.24 cm³·mol⁻¹·K at room temperature, slightly lower than the expected value for three isolated Mn^III cations of 9.00 cm³·mol⁻¹·K. On cooling, the χ_MT value increases slightly up to a maximum value of 10.37 cm³·mol⁻¹·K at 5.5 K, followed by a weak decrease at low temperature, suggesting a very weak ferromagnetic interaction. Finally, the room temperature χ_MT value for complex 5 is 29.97 cm³·mol⁻¹·K, very close to the expected value for six Mn^III and three Mn^II isolated cations of 31.125 cm³·mol⁻¹·K. The χ_MT value increases up to 31.62 cm³·mol⁻¹·K at 13 K and a further decrease below this temperature appears to be indicative of the presence of ferrimagnetic interactions, as shown in Figure 5.

The susceptibility plots for complexes 1R and 2Ra were fitted according the two-J Hamiltonian derived from Scheme 2.

H = −2J₁(S₁·S₂ + S₁·S₃ + S₂·S₃ + S₄·S₅ + S₄·S₆ + S₅·S₆) − 2J₂(S₁·S₇ + S₂·S₇ + S₃·S₇ + S₄·S₇ + S₅·S₇ + S₆·S₇)

This results in the best fit parameters J₁ = 1.73(8) cm⁻¹, J₂ = −3.81(6) cm⁻¹, and g = 1.859 (2) for complex 1 and J₁ = 1.47(6) cm⁻¹, J₂ = −2.30(2) cm⁻¹, and g = 1.867(3) for complex 2Ra. Magnetization measurements give unsaturated values of 14.70 and 16.50 Nμ_β for complexes 1R and 2Ra, respectively, slightly lower than the expected spin-only value of 17.7 Nμ_β, assuming a g value of 1.86 obtained in the susceptibility fit. The deviation should be attributed to weak zero-field splitting of the Mn^III cations that has not been included in the fits due to the large size of the matrix, out of the scope of usual fits.

The fit of the experimental data for complex 4 according the spin-only Hamiltonian derived from Scheme 2 can be determined as follows:

H = −2J₁(S₁·S₂ + S₁·S₃ + S₂·S₃)

This does not reproduce adequately the weak susceptibility increase and thus, a D_ion term was added. The best fit values were J₁ = 0.19(1) cm⁻¹, D_ion = 2.04(8), and g = 1.974(6). The magnetization measurement performed at 2 K reaches an unsaturated value of 11.45 Nμ_β, close to the expected value of 12 Nμ_β.

The susceptibility data for complex 5 were fitted, assuming the same set of interactions for the two non-equivalent units with the two-J Hamiltonian derived from Scheme 2.

H = 2 × (−2J₁(S₁·S₂ + S₁·S₃ + S₂·S₃) − 2J₂(S₁·S₄ + S₂·S₄ + S₃·S₄))

This includes the interactions inside the Mn^III triangles (J₁) and the interaction between the Mn^II···Mn^III inside the two tetranuclear units. The contribution of one isolated S = 5/2 from the [MnBr₄]²⁻ isolated counteranion, assumed as fully isotropic according to its high S = 5/2 spin (⁶A₁ term), has been taken into account for the total χ_MT value. The best fit parameters were J₁ = 2.38(2) cm⁻¹, J₂ = −1.32(1) cm⁻¹, and g = 1.939(1), implying a S = 7/2 spin ground state for each {NaMn^IIMn^III₃} cluster. Isothermal magnetization measurement at 2 K reaches a value of 18.54 Nμ_β under the maximum applied field, close to the expected 19 Nμ_β value, confirming the S = 7/2 ground state for the two {Mn^III₃Mn^IINa^I} units, see Figure 5—right.

The ac response of complexes 1R, 2Ra, 4, and 5 was tested under different external fields (0–0.5 T) and a constant frequency of 1000 Hz and no out-of-phase signals were observed with the exception of weak tails in the χ″M(H) plots for triangular complex 3, Figure S2, which was shown to be too weak for a further analysis. The lack of ac response despite the relatively high S ground states of 19/2 (1R, 2Ra, 2Rb), 12/2 (3, 4), and 7/2 (5) should be attributed to the unfavourable arrangement of the easy axis of the Mn^III cations, which show a triangular arrangement that results in a low or negligible total anisotropy for the whole molecules, see Figure 6.

4. Conclusions

Depending on the position of the substituents on the amino alcohol fragment of the Schiff bases obtained by condensation with 3-ethoxysalicylaldehyde with the 1 or 2-phenyl derivatives of 2-amino-1-ethanol, a series of clusters with {Mn^III₆Mn^IINa₂}, {Mn^III₃Mn^IINa}, and {Mn^III₃} nuclearity have been characterized. The magnetic response of these systems yields large S ground states comprised between 7/2 and 19/2 as a consequence of the Mn^III–Mn^III ferromagnetic and Mn^II–Mn^III antiferromagnetic coupling. The reported systems confirm that the mix of ligands with different (R)/(S) configurations in the same molecule instead of the expected separation of enantiomers is a common feature in this kind of cage with an odd number of chiral ligands.