A new topology of hexanuclear [Mn^III₄Ln^III₂] clusters: syntheses, structures, and magnetic properties

Abstract

Reactions of manganese nitrate and lanthanide nitrate hexahydrate with 2-(hydroxymethyl)pyridine (hmpH) and sodium propionate as co-ligands in the mixed solutions of acetonitrile and ethanol generated two hexanuclear Mn–Ln compounds [Mn₄Ln₂O₂(OH)(hmp)₅(EtCO₂)₃(MeCN)(NO₃)₅(H₂O)] [Ln = La (1), Nd (2)]. Compounds 1 and 2 are isostructural and possess a core of [Mn^III₄Ln^III₂(μ₃-OR)₃(μ₃-O)₂(μ₂-O)₃]⁵⁺, which comprises three face-sharing defect cubane units. The core topology represents a new core type of Mn–Ln cluster. The soild-state dc magnetic susceptibility analyses indicate antiferromagnetic interactions within the two compounds. Compound 1 possesses an S = 0 ground state spin, fitting of the dc data for a tetranuclear Mn^III₄ with the Magpack program gives parameters of J₁ = −0.50 cm⁻¹, J₂ = −5.03 cm⁻¹, J₃ = 3.77 cm⁻¹ and g = 1.95.

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Introduction

Growing attention has been given to single molecule magnets (SMMs) in recent decades due to their exotic physical properties and potential applications in information storage.¹ SMMs are molecules that exhibit magnetic hysteresis below a certain blocking temperature due to a high energy barrier which is closely related to the combination of a large ground spin state (S) and a large zero field splitting parameter (D).² Recently, 3d–4f heterometallic clusters as a kind of new SMM have received great interest. Compared with traditional 3d clusters which we have mainly focused on, mixing the transition metal and lanthanide ion in different proportions may modulate magnetic properties as the lanthanide ion often possesses large ground-state spin and significant single-ion anisotropy. Since the first 3d–4f SMM of Cu₂Tb₂ (ref. 3) was discovered in 2004, various 3d–4f clusters have been investigated, especially Mn/Ln compounds, such as Mn₂Ln₂,^4a Mn₃Ln₄,^4b Mn₅Ln₄,^4c Mn₈Ln₄,^4d Mn₁₁Gd₂,^4e and Mn₂₁Dy,^4f for manganese as a transition metal always displays high spin states as well as large zero field splitting parameters related to the Jahn–Teller effect of Mn^III. Nevertheless, the reports on Mn/Ln SMMs incorporating light lanthanide ions are limited by comparison with those containing heavy lanthanide ions.⁵ To search for new 3d–4f SMMs and further investigate the magnetic interactions within them, more Mn/Ln compounds containing light lanthanide ions need to be explored.

It is important to select an appropriate ligand to construct 3d–4f compounds, and the polydentate chelating ligand with nitrogen and/or oxygen atoms could facilitate the coordination affinities of Mn and Ln metal ions. The 2-(hydroxymethyl)pyridine (hmpH), a N/O bidentate chelate and bridging ligand, has been widely employed for the synthesis of high-nuclearity Mn clusters, such as Mn₁₀, Mn₁₂, Mn₁₈, Mn₂₁.⁶ However, only few examples of Mn/Ln clusters used hmpH as ligand have been reported to date, such as Mn^III₂Ln^III₂, Mn^III₂Ln^III₄, Mn^III₈Ln^III₄ and Mn^III₄Ce^III₂.⁷ The carboxylate ions are flexible ligands and often lead to antiferromagnetic coupling. For Mn–Ln clusters using hmpH and a carboxylate as co-ligands, variation of the carboxylate R groups, from small acetate to bulky phenyl group, generated different kinds of compounds with aesthetical structures and unusual properties.⁷ In the present work, we used pyridine-based alkoxide and sodium propionate as co-ligands to construct a new family of mixed 3d–4f hexanuclear compounds. The magnetic susceptibility study indicates the presence of antiferromagnetic interactions within the compounds. The syntheses, structures and magnetic properties of these compounds are described in this paper.

Experimental

Syntheses

All reagents and solutions were of commercially available, used without further purification.

Preparation of the compounds: Mn(NO₃)₂ (aq, 50%, 0.36 ml, 1.5 mmol) and Ln(NO₃)₃·6H₂O (1.0 mmol) were added to a colorless stirred solution of hmpH (0.10 ml, 1.0 mmol) and NEt₃ (0.14 ml, 1.0 mmol) in MeCN (15 ml) and EtOH (5 ml), which led to a rapid color change to dark red. Then sodium propionate (0.096 g, 1.0 mmol) were added to the vigorous solutions. The mixture was stirred for 5 h, then filtered, and the solution was left undisturbed in a flask. Slow evaporation of the solution at room temperature gave large black crystals in five days, which were collected by filtration, washed thoroughly with MeCN, and dried in vacuum.

[Mn₄La₂O₂(OH)(hmp)₅(EtCO₂)₃(MeCN)(NO₃)₅(H₂O)] (1). Yield: 0.16 g, 25%. Elemental analysis (%) calcd for 1: C: 30.15; N: 8.25; H: 4.02. Found: C: 30.23; N: 8.23; H: 4.11. ICP analysis calcd for La: 14.89%; found: 14.75%. Selected IR data (KBr, cm⁻¹): 3660 (w), 3394 (mb), 2977 (w), 2833 (w), 2484 (w), 2361 (w), 1766 (w), 1616 (m), 1582 (s), 1554 (m), 1465 (m), 1438 (m), 1377 (s), 1308 (s), 1226 (m), 1164 (s), 1069 (w), 884 (m), 816 (m), 809 (w), 768 (m), 727 (vs), 713 (w), 706 (w), 665 (s), 645 (vw), 638 (w), 625 (vw), 563 (s), 556 (m), 522 (m), 508 (w), 474 (m), 467 (w), 426 (w).

[Mn₄Nd₂(O)₂(OH)(hmp)₅(EtCO₂)₃(MeCN)(NO₃)₅(H₂O)] (2). Yield: 0.15 g, 24%. Elemental analysis (%) calcd for 2: C: 30.31; N: 8.28; H: 3.92. Found: C: 30.28; N: 8.31; H: 4.05. ICP analysis calcd for Nd: 15.48%; found: 15.57%. Selected IR data (KBr, cm⁻¹): 3640 (w), 3407 (mb), 2977 (w), 2847 (w), 2361 (w), 2334 (w), 1759 (w), 1616 (m), 1589 (s), 1561 (m), 1465 (m), 1452 (m), 1383 (s), 1315 (s), 1233 (m), 1158 (s), 1076 (m), 1055 (vs), 884 (m), 823 (m), 782 (w), 768 (m), 727 (vs), 713 (w), 706 (w), 665 (s), 645 (vw), 638 (w), 617 (w), 583 (w), 570 (s), 556 (m), 515 (m), 474 (m), 460 (w), 440 (w), 426 (w).

Physical measurements

Elemental analyses (C, H and N) were performed on a Vario ELIIII Elemental Analyzer and the content of lanthanide was determined by inductively coupled plasma optical emission spectrometer. IR spectra (400–4000 cm⁻¹) were recorded on a Vertex 70 FT-IR spectrometer in the solid state (KBr pellets). XRPD spectra were measured on a MiniFlexII diffractometer using a Cu-Kα rotating anode source with a wavelength of 1.542 Å (Fig. S1†). Variable temperature dc susceptibility magnetic data for compounds 1 and 2 were obtained by a PPMS-9T superconducting magnetometer with a field of 0.1 T and temperature ranging from 2 to 300 K. AC magnetic susceptibilities were collected on a Quantum Design MPMS-XL magnetometer. This magnetometer operates with an oscillating ac field of 3 G in the ac frequencies range 511–2311 Hz.

X-ray crystallography

The single crystal data of the compounds were collected by a Cu kα rotating anode source at 100 K, using a Supernova diffractometer with the ω-scan method. Absorption correction was performed with SCALE3 ABSPACK scaling algorithm, using spherical harmonics. All structures were solved with direct methods and full-matrix least-squares refinement were implemented by the SHELXTL-97 program package.⁸ The non-H atoms were refined anisotropically, while the H atoms were determined with geometrical calculations riding on the respective C atoms. The solvent molecules of complexes were disordered and could not be refined satisfactorily, which were handled with the SQUEEZE option in PLATON.⁹ The crystal data and structure refinement details of complexes are displayed in Table 1.

Table 1 Crystallographic data for compounds 1 and 2

	1 3C2H5OH·3H2O	2 3C2H5OH·2H2O
a R1 = ∑(||Fo| − |Fc||)/∑|Fo|.b wR2 = [∑w(Fo^2 − Fc^2)^2/∑w(Fo^2)^2]^0.5.
Formula	Mn4La2O36C47N11H75	Mn4Nd2O35C47N11H73
Fw	1867.56	1860.17
Crystal system	Triclinic	Triclinic
Space group	P1̄	P1̄
a, Å	11.7735(4)	11.7632(4)
b, Å	16.3609(4)	16.3266(5)
c, Å	17.8475(5)	17.7806(3)
α, deg	93.405(2)	93.1011(18)
β, deg	91.388(3)	91.1479(19)
γ, deg	108.443(3)	108.882(3)
V, Å^3	3252.21(17)	3223.77(15)
Z	2	2
T, K	100	100
ρcalcd, g cm^−3	1.727	1.724
μ, mm^−1	16.82	19.049
F(000)	1656	1668
R1^a	0.0621	0.0809
wR2^b	0.1514	0.1930

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Results and discussion

Synthesis

Reaction of Mn(NO₃)₂, Ln(NO₃)₃·6H₂O, EtCO₂Na, NEt₃ and hmpH in MeCN/EtOH (15/5, v/v) generated two hexanuclear heterobimetallic Mn₄Ln₂ compounds with general formula [Mn₄Ln₂O₂(OH)(hmp)₅(EtCO₂)₃(MeCN)(NO₃)₅(H₂O)] (Ln = La (1), Nd (2)) were successfully generated. Various reaction conditions have been explored, such as different types of alkali and solvents. The NEt₃ is assumed to be the proton acceptor, but also promoted the oxidation reaction of Mn^II to Mn^III with atmospheric O₂ by providing alkaline conditions. When KOH, NaOH, and NaN₃ were used to replace NEt₃, no crystalline products were yielded. While using MeCN, MeCN/CH₃OH as the solvent led to the same compounds in low yields. When using MeCN/CH₂Cl₂ as the solvent, no crystallized products were obtained.

To explore the effect of different carboxylate R groups to the structures and properties of compounds, sodium acetate and benzoic acid were replaced sodium propionate in the reactions. When used MeCO₂Na and hmpH as co-ligands, no crystallized products were yielded. While used PhCO₂H and hmpH as co-ligands, it generated a family of dodenuclear clusters with the formula [Mn^III₈Ln^III₄(O)₈(hmp)₄(O₂CPh)₁₂(NO₃)₄(PhCO₂H) (C₂H₅OH)], which have been reported by our group.^7c As compared to the two clusters with different R groups, the structures differ in two parts: (i) compounds with EtCO₂⁻ groups are hexanuclear clusters, when PhCO₂⁻ as an alternative group to EtCO₂⁻ it generated dodenuclear clusters; (ii) the Mn₄Ln₂ compounds comprise a core of three face-sharing defected cubane units, while the Mn₈Ln₄ compounds possess a spindle-shaped core.

Description of the crystal structures

Compounds 1 and 2 are isostructural, therefore the structure of compound 1 will be described in detail as a representative. The partially labeled structure and core of compound 1 are shown in Fig. 1. Selected interatomic distances and angles are presented in Table 2. Compound 1 crystallizes in the triclinic space group P1̄, and the core [Mn^III₄La^III₂(μ₃-OR)₃(μ₃-O)₂(μ₂-O)₃]⁵⁺ (Fig. 1) comprises three face-sharing defected cubane units of Mn1Mn2La2(μ₂-O)₂(μ₃-OH)(μ₃-OR), Mn1Mn2La1(μ₃-O)₂(μ₃-OH)(μ₃-OR) and Mn3Mn4La1(μ₃-O)₂(μ₂-OR)₂. The four Mn ions form a square plane with the distances of Mn1–Mn2 and Mn3–Mn4 being 3.18 Å and 3.35 Å respectively, which are different from the previous reported butterfly or cubane Mn₄ topology. Two La atoms are located above and below the plane. These metals are held together though eight oxygen atoms, of which three are of μ₃-O, two are of η¹:η²:μ₂ hmp⁻ groups, one is of η¹:η¹:μ₂ hmp⁻ group, one is of η¹:η³:μ₃ hmp⁻ group, and the other is of η¹:η²:μ₃ hmp⁻ group. The peripheral ligands are completed by five NO₃⁻ counterions, three EtCO₂⁻ ligands, one MeCN and one H₂O terminal groups.

Fig. 1 (Top) Partially labelled structure of compound 1. (Bottom) The core of compound 1. Color scheme: La, green; Mn, teal; O, red; N, blue. H atoms have been omitted for clarity.

Table 2 Selected bond lengths (Å) and angles (deg) for compound 1

Mn1–O1	1.894	Mn3–O6	2.134
Mn1–O2	2.137	Mn3–O7	1.943
Mn1–O11	2.253	Mn3–O8	1.926
Mn1–O28	1.838	Mn3–O10	2.462
Mn1–O29	1.992	Mn3–O30	1.824
Mn1–N1	2.047	Mn3–N3	2.052
Mn2–O4	1.899	Mn4–O3	1.927
Mn2–O5	2.198	Mn4–O7	2.374
Mn2–O11	2.154	Mn4–O10	1.917
Mn2–O29	2.044	Mn4–O28	1.823
Mn2–O30	1.841	Mn4–N4	2.043
Mn2–N2	2.069	Mn4–N6	2.283
La2–O20	2.616	La2–O21	2.629
La1–O9	2.550	La1–O10	2.637
La1–O11	2.536	La1–O12	2.594
La1–O14	2.659	La1–O15	2.723
La1–O17	2.636	La1–O28	2.496
La2–O1	2.484	La1–O30	2.464
La2–O18	2.615	La2–O4	2.488
La2–O23	2.608	Mn1–O29–Mn2	104.188
Mn1–O1–La2	109.882	Mn1–O28–La1	113.912
Mn1–O11–Mn2	92.631	Mn2–O30–La1	112.039
Mn1–O28–Mn4	126.318	Mn2–O30–Mn3	126.223
Mn1–O29–La2	103.266	Mn2–O4–La2	100.589
Mn3–O30–La1	113.282	Mn3–O10–Mn4	98.968
Mn3–O7–Mn4	101.211	Mn4–O28–La1	109.456

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The oxidation states of Mn metals and the protonation levels of O atoms were assigned by the charge balance consideration and bond valence sum (BVS)¹⁰ calculations (Tables 3 and 4, respectively). All Mn^III atoms display a coordination number of six with distorted octahedral geometries. The three Mn^III atoms exhibit distinctly Jahn–Teller axial elongations along O(carb)–Mn–O(carb) axes including O2–Mn1–O11 axes, O5–Mn2–O11 axes and O6–Mn3–O10 axes, which avoid the Mn–O²⁻ bonds as expected. The elongated Mn^III–O bonds are 0.304–0.418 Å longer than the other Mn^III–O bonds. Both La ions are ten coordinate with different types of geometries varying in the coordination environment. La1 is bound by four oxygen atoms from two NO₃⁻, two bridging μ₃-O ligands, one nitrogen atom and one oxygen atom from a η¹:η¹:μ₂ hmp⁻ group, one oxygen atom from η¹:η¹:μ₂ hmp⁻ group, one oxygen atom of η¹:η¹:μ₂ EtCO₂⁻ group. La2 coordinates with a O₁₀ donor set consisting of six η¹:η¹:μ NO₃⁻, two η¹:η¹:μ₂ hmp⁻, one μ₃-O and one terminal water. The La–O bond distances range from 2.459 Å to 2.724 Å and the La–N bond distance is 2.734 Å. There exist a hydrogen bond between the terminal water on the La2 and the EtCOO⁻ on the Mn2, the O–H⋯O distance is 2.747 Å and angle is 155.09°. There are no dominant intermolecular interactions within the compound, for the nearest metal distance between different molecules is the separation of Mn–La (7.701 Å), thus it is considered that the magnetic behaviour may be of molecular origin.

Table 3 Bond valence sums for Mn^a atoms of compound 1

Atom	Mn(II)	Mn(III)	Mn(IV)
a The italic value is the closest to the charge for which it was calculated, and the nearest whole number can be considered as the oxidation state of the atom.
Mn1	3.27	3.02	3.14
Mn2	3.19	2.94	3.05
Mn3	3.21	2.98	3.08
Mn4	3.25	3.03	3.11

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Table 4 Bond valence sums for the O atoms of compound 1^a

Atom	BVS	Assignment
a BVS values for O atoms of RO^−(μ-O^2−) and μ-OH groups are typically 1.8–2.1 and 1.0–1.2 respectively.
O10	1.99	RO^−
O11	1.94	RO^−
O28	2.07	μ3-O^2−
O29	1.26	μ3-OH
O30	2.09	μ3-O^2−

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To date, only a small amount family of hexanuclear clusters have been reported, including [Mn^IV₄Ce^III₂O₂(Me-sao)₆(NO₃)₄(OAc)₂(H₂O)₂]¹¹ and [Mn₄Ce₂O₂(Bu_tCO₂)₅(NO₃)₅(hmp)₄]¹⁴ whose cores containing two [Mn₂CeO] triangular units, [Mn^III₄Ln^III₂(μ₃-O)₂(Hbeemp)₂(OAc)₈(μ₃-OMe)₂(H₂O)₂] as well as [Mn^III₄Ln^III₂(H₂L)₂(HL)₂(CH₃COO)₄(CH₃O)₂(CH₃OH)₄] with butterfly shaped cores,¹² a face-fused double-cubane [Mn₄Ln₂O₂(O₂CBu_t)₆(edteH₂)₂(NO₃)₂],¹³ [Mn₄Ce₂O₂(O₂CMe)₆(NO₃)₄(hmp)₄] possessing an octahedral core,¹⁵ [Mn^II₂Mn^III₂Ln^III₂(Piv)₈(thme)₂(H₂tea)₂] containing four face-sharing defected cubane units.¹⁶ In addition, the core of compounds 1 and 2 is Mn^III₄Ln^III₂, which is distinct from the compound of [Mn^II₂Mn^III₂Ln^III₂(Piv)₈(thme)₂(H₂tea)₂] with a core of Mn^II₂Mn^III₂Ln^III₂. Obviously, the structures of compounds 1 and 2 are completely different from the compounds above, which represent a new topology.

Magnetic properties

The solid-state, variable-temperature dc magnetic susceptibility data of compounds 1 and 2 were measured in the 2–300 K temperature range with an applied field of 0.1 T.

Plots of χ_MT vs. T for compounds 1 and 2 are depicted in Fig. 2. The χ_MT vs. T plots of compounds 1 and 2 show similar trends. For compound 1, at room temperature, the χ_MT value is 10.66 cm³ K mol⁻¹, which is slightly lower than the expected value of 12.01 cm³ K mol⁻¹ for the uncoupled four Mn^III ions (S = 2, C = 3.00 cm³ K mol⁻¹, g = 2.00) and two diamagnetic La^III ions. The χ_MT value decreases slowly upon lowering the temperature until approximately 100 K, and then rapidly decreases down to a value close to zero at 2 K. The susceptibility data in the temperature range of 100–300 K obeys the Curie–Weiss law, and the derived Weiss constant value is −32.04 K. The above mentioned behaviour indicates dominate antiferromagnetic exchanges within compound 1, leading to an S = 0 ground state. As La^III ion is diamagnetic, the magnetic property of antiferromagnetic for compound 1 is attributed to the interactions of Mn^III–Mn^III. The curve of M versus H displays an almost linear increase without clear saturation up to 8 T at 2 K (Fig. S2†), which further confirmed this conclusion.¹⁷

Fig. 2 The χ_MT vs. T plots for compounds 1 and 2 in a 0.1 T dc field. The solid line is fit of the data of compound 1 with the Magpack program using the coupling scheme shown in the inset.

To explore the magnetic exchange interactions within Mn₄ core of compound 1, the magnetic susceptibility data in the 15–300 K range were fitted using the Magpack program.¹⁸ Data below 15 K were omitted as zero field or Zeeman effects maybe affect the fitting in the low temperature range. The isotropic Heisenberg spin Hamiltonian describing the magnetic interactions within the Mn₄ cores could be given as follows:

Ĥ = −2J₁Ŝ₁Ŝ₂ − 2J₂(Ŝ₂Ŝ₃ + Ŝ₁Ŝ₄) − 2J₃Ŝ₃Ŝ₄

where J₁ denotes the Mn1 and Mn2 coupling interaction, the exchange coupling constant of Mn1–Mn4 and Mn2–Mn3 could be considered to be the same as J₂ due to similar structural parameters, J₃ is the Mn3 and Mn4 exchange constant. The model containing atom labeling and exchange pathways are shown in Fig. 2 (inset). The solid line exhibits a satisfactory fit of the experimental data to the theoretical data (Fig. 2), giving the parameters of J₁ = −0.50 cm⁻¹, J₂ = −5.03 cm⁻¹, J₃ = 3.77 cm⁻¹, and g = 1.95. The exchange interactions within Mn4 core are all weak, and the J₃ indicates ferromagnetic interaction between Mn3 and Mn4. The Mn3 and Mn4 are bridged by two μ₂-OR⁻ atoms which coming from hmp⁻ groups. The alkoxide O atom of hmpH often supports ferromagnetic coupling between the metal atoms, and the comparison of exchange parameters for the compounds, whose Mn^III and Mn^III metals are bridged by alkoxide O atom of hmpH, are listed in Table 5.²² In addition, the Mn^III–Mn^III interaction in Mn4 rhombs with the JT axes containing μ₂-OR⁻ groups are often ferromagnetic interactions,¹⁹ thus it is reasonable for J₃ to be positive. The weak J₃ may be related to the longer Mn^III–Mn^III distance (3.35 Å), comparing with the reported Mn4 cores whose value of J average 8–9 cm⁻¹ and Mn^III–Mn^III distance span is 3.15 to 3.23 Å.²⁰

Table 5 Comparison of exchange parameters in Mn_X compounds

Compound	J1	g	Ref.
[Mn4(hmp)6(CH3CN)2(H2O)4]	8.56	1.96	22a
[Mn4(hmp)6(CCl3COO)2(H2O)2]	5.31	1.99	22b
[Mn4(hmp)4(OH)2Mn(dcn)6]	7.1	1.95	22c
[Mn4(hmp)6(NO3)2(dcn)2]	9.8	1.94	22e
[Mn4(hmp)4(Hpdm)2(dcn)2]	12.66	1.97	22e
[Mn4(hmp)6Br2(H2O)2]	12.65	1.94	22d

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For compound 2, the χ_MT value of 13.40 cm³ K mol⁻¹ at 300 K is much lower than the calculated value of 25.12 cm³ K mol⁻¹ for four independent Mn^III ions (S = 2, C = 3.00 cm³ K mol⁻¹, g = 2.00) and two uncoupled Nd^III ions (S = 3/2, L = 6, J = 9/2, g = 8/11). The χ_MT value decreases in a monotonic fashion upon cooling with a value of 0.71 cm³ K mol⁻¹ at 2 K. A negative Weiss constant value of −44.82 K was obtained according to the Curie–Weiss law above 50 K. For compound 2, modelling the magnetic susceptibility with a similar approach as compound 1 is difficult because of the complicated intrinsic magnetic properties of the Nd^III ion. In order to investigate more magnetic information of compound 2, we can subtract the plot 1 from 2 plot to explore the interactions between Mn–Nd in complex 2, the interactions of Nd–Nd can be neglected as the distance of two Nd ions being 6.35 Å. The χ_MT product decrease with decreasing temperature (Fig. S3†) suggesting the interactions between Mn–Nd are antiferromagnetic. The isothermal magnetization curves (M vs. H/T) for compound 2 are not coincide (Fig. 3), displaying the presence of magnetic anisotropy of Nd^III or low-lying excited states.²¹ Furthermore, the magnetization of compound 2 increases slowly with increasing applied field without saturation even at 8 T (Fig. S4†), which is also confirmed the presence of these effects.

Fig. 3 Plot of the magnetization versus H/T for compound 2 in the field of 1–5 T and the temperature of 2–15 K.

The ac susceptibility measurements were performed on compounds 1 and 2 in the temperature range of 2.0 K to 5.0 K with a 3.0 G ac field oscillating in the scope of 511–2311 Hz and a zero-applied dc field. There are no frequency-dependent behaviour in the in-phase signals χ′_MT and the out-of-phase signals χ′′_M for both compounds (Fig. S5 and S6†). Hence, compounds 1 and 2 do not display SMM behaviour, which may be due to small magnetic anisotropy and low ground state.

Conclusions

In summary, reactions of Mn(NO₃)₂ and Ln(NO₃)₃·6H₂O with hmpH and sodium propionate as co-ligands have yielded new examples of 3d/4f hexanuclear clusters. Compounds 1 and 2 with aesthetical core of three face-sharing defected cubanes, which are the new additions to the family of Mn₄Ln₂. Antiferromagnetic interactions within the two compounds were indicated by solid-state dc magnetic susceptibility analyses. Compound 1 has an S = 0 ground state, fitting the χ_MT versus T data with the Magpack program gives parameters of J₁ = −0.50 cm⁻¹, J₂ = −5.03 cm⁻¹, J₃ = 3.77 cm⁻¹ for the Mn^III–Mn^III interactions. The ac susceptibility data exhibit no SMM behaviour for both compounds. Further efforts to explore the same cluster with heavy lanthanide are in progress.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 21173219, 21303201 and 21203195).

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Footnote

† Electronic supplementary information (ESI) available: X-ray crystallographic data for complexes 1 and 2 in CIF format. CCDC 1439267 and 1439268. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ra25526k

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