Synthesis, Structure, and Magnetic Properties of 1D {[MnIII(CN)6][MnII

Article pubs.acs.org/IC

Synthesis, Structure, and Magnetic Properties of 1D {[MnIII(CN)6][MnII(dapsc)]}n Coordination Polymers: Origin of Unconventional Single-Chain Magnet Behavior Valentina D. Sasnovskaya,† Vyacheslav A. Kopotkov,*,† Artem D. Talantsev,† Roman B. Morgunov,† Eduard B. Yagubskii,*,† Sergey V. Simonov,§ Leokadiya V. Zorina,*,§ and Vladimir S. Mironov*,‡ †

Institute of Problems of Chemical Physics, Russian Academy of Sciences, Semenov’s av., 1, Chernogolovka, MD, Russian Federation Institute of Solid State Physics, Russian Academy of Sciences, Academician Ossipyan str., 2, Chernogolovka, MD, Russian Federation ‡ Shubnikov Institute of Crystallography of Federal Scientific Research Centre “Crystallography and Photonics”, Russian Academy of Sciences, Leninskii av. 59, Moscow, Russian Federation §

S Supporting Information *

ABSTRACT: Two one-dimensional cyano-bridged coordination polymers, namely, {[MnII(dapsc)][MnIII(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O) (I) and {[MnII(dapsc)][MnIII(CN)6][K(H2O)2(MeOH)2]}n (II), based on alternating high-spin MnII(dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of Ueff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII−CN−MnII spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [MnIII(CN)6]3−. The prospects of [MnIII(CN)6]3− complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.

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INTRODUCTION Low-dimensional magnetically bistable molecular materials, the single-molecule magnets (SMMs) and single-chain magnets (SCMs) featuring slow magnetic relaxation of purely molecular origin, super-paramagnetism, blocking, and quantum tunneling of magnetization1a−f have attracted great attention owing to their potential applications in high-density information storage, spintronic devices, and quantum computing.1g−i However, these promising technological applications are hindered by a very low blocking temperature for the reversal of magnetization (TB), which is currently limited by 20 K for SMMs2a,b and 14 K for SCMs.2c,d Magnetic bistability and slow magnetic relaxation in SMMs are due to double-well potential with the magnetization reversal barrier Ueff = Δ = |D|S2 originating from the combination of a large ground-state spin S and negative uniaxial magnetic anisotropy D. In contrast to SMMs represented by discrete zero-dimensional (0D) high-spin molecules, SCMs are built of magnetically isolated spin chains (one-dimensional © XXXX American Chemical Society

(1D) magnetic structures) with strongly dominating intrachain spin coupling. In SCMs, there is an extra energy term Δξ in the relaxation barrier Ueff arising from the exchange coupling (J) between the magnetic ions within the chain; Δξ is referred to as correlation energy.1b−e Thus, it is generally considered that it should be easier to increase the barrier and blocking temperature for SCMs than it is for SMMs. According to the Glauber’s seminal theory, in infinite ferromagnetic Ising chain the barrier is written as Ueff = 2Δξ = 8|J|S2.3 In a Heisenberg chain of spins with uniaxial single-ion magnetic anisotropy D, the correlation energy is given by Δξ = 4|J|S2 in the Ising limit (specified by |D/J| > 4/3) and Δξ = 4S2 (|JD|)1/2 in the Heisenberg limit (|D| ≪ |J|).1b−e The overall energy barrier is expressed by Ueff = Δ + 2Δξ for an infinite spin chain and Ueff = Δ + Δξ for a finite-length chain; in the latter case, the nucleation Received: April 8, 2017

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DOI: 10.1021/acs.inorgchem.7b00676 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

provides large uniaxial magnetic anisotropy of 3d ions,14b−d which is very hepful in the enhancement of the overall barrier Ueff. These complexes are usually combined with hexacyanometallates [M(3d)(CN)6]n− and octacyanometallates (NbIV(CN)84−, MoV(CN)83−, and WV(CN)83−) to form alternating heterometallic chains;9c,11i,n however, a homometallic chain built of cyano-bridged FeII(L-N5) pentagonal complexes with SCM properties has been recently reported.1−11 Besides, several heterometallic cyano-bridged chains built of high-spin MnII(L5) pentagonal complexes and orbitally degenerate pentagonal-bipyramidal [MoIII(CN)7]4− complex were obtained and magnetically characterized.17a,b In this work, we present the synthesis and crystal structure of two cyano-bridged chain coordination polymers derived from the heptacoordinated MnII(dapsc) complex based on pentadentate Schiff-base dapsc ligand (dapsc = 2,6-diacetylpyridine bis(semicarbazone), Figure 1) and magnetically anisotropic

effect of the ends of chains results in twice smaller contribution of Δξ to the barrier Ueff. In fact, at low temperatures the relaxation dynamics of SCMs is typically described by the finitelength model.1b−e Early studies on SMMs and SCMs have mainly focused on obtaining high-spin molecular species in hopes to maximize contributions to the barrier, as one might expect from Ueff = |D| S2 or Δξ = 4|J|S2 equations. However, more recently it has become increasingly apparent that controlling magnetic anisotropy is a more efficient alternative for obtaining larger barriers Ueff and blocking temperatures (TB ∝ Ueff) for molecular nanomagnets.4 As a result, in the past decade the research interest has shifted from large molecules with large ground-state spin to smaller molecules including highly anisotropic magnetic centers, such as 4d and 5d transition-metal complexes4b,5 and lanthanide2a,6 and actinide7 ions. Especially intense efforts were undertaken to develop lanthanide-based SMM complexes, which exhibit very strong single-ion magnetic anisotropy associated with large magnetic moments and unquenched first-order orbital angular momentum.6 Currently, the highest reported energy barriers and blocking temperatures for SMMs belong to lanthanide complexes.2a,b Particular attention was paid to mononuclear lanthanide complexes with SMM behavior (which are referred to as single-ion magnets, SIMs)8 as they represent the ultimate size limit for spin-based devices and exhibit unusually high barrier and blocking temperature (up to Ueff ≈ 1261 cm−1 8b and TB ≈ 20 K2a); as a result, reports for mononuclear lanthanide SIM complexes are increasing rapidly.6,8 More recently, there has been a growing interest in maximizing the magnetic anisotropy of mononuclear high-spin 3d complexes with less-common ligand coordination that produces orbitally degenerate ground state with unquenched orbital angular momentum.9 Currently, numerous 3d-based SIMs were reported.10 Among them, linear two-coordinate Fe(I) complex displayed a barrier Ueff of 246 cm−1 (354 K),10c and recently reported linear two-coordinade Co(II) imido complex has the energy barrier of 413 cm−1,10d the largest yet observed for a 3d-based SMM. Similar synthetic strategies have also been applied to SCMs.11,12 A variety of magnetically anisotropic molecular building blocks are employed for designing 1D polymer compounds with enhanced SCM properties, high-spin 3d complexes with large magnetic anisotropy,11d orbitally degenerate 3d complexes (FeII, FeIII, CoII), 4d and 5d complexes (such as ReCl4(CN)22−,11b,c ReCl62−,11d and ReF62− 11e), and lanthanide ions.11m These efforts are directed toward increasing the magnetic anisotropy parameter D and enhancing intrachain exchange interactions J, or ideally both. In this respect, the metal-radical approach is especially attractive, as it allows to integrate single-ion anisotropy of individual metal centers into the overall magnetic anisotropy of the spin chain through strong metal-radical spin coupling.12 Thus, the radical bridged chain compounds with CoII ions, namely, [Co(hfac)2PyNN]n2c and [Co(hfac)2NaphNN]n,2d display a relaxation barrier of 396 and 398 K, respectively, which is the largest presently known for SCMs. In recent years, there have been increasing reports on SCMs based on orbitally degenerate (or nearly degenerate) transitionmetal complexes with unquenched first-order orbital momentum.13 These complexes are excellent platforms for the preparation of clusters,14 chains,15 and higher-dimensional molecular magnets.16 Pentagonal-bipyramidal coordination

Figure 1. Molecular structure of the pentadentate ligand dapsc (R = NH2) and some its derivatives: dapbh (R = Ph), dapbih (R = BiPh).

orbitally degenerate hexacyanomanganate(III) complex: {[Mn(dapsc)][Mn(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O) (I) and {[Mn(dapsc)][Mn(CN)6][K(H2O)2(MeOH)2]}n (II). Compound I is magnetically characterized; analysis of its static and dynamic magnetic properties reveals an SCM behavior with an energy barrier of ∼40 K. It is important to note that in I and II the pentagonal-bipyramidal [MnII(dapsc)] complex functions as a magnetically isotropic high-spin building block (S = 5/2), not as an anisotropic spin carrier, as discussed above.9−13 Previously, similar high-spin [MnII(L5)] complexes with pentagonal macrocyclic ligands have been successfully used for preparation of heterometallic SMM clusters,5c chains,17a,b and extended heterometallic structures.17c Although the complexes of dapsc and its derivatives have long been known,18 their use for the preparation of magnetic polynuclear assemblies is currently limited only by four works. The pentanuclear [{M(II)(L)}3{W(CN)8}2(H2O)2] (M = Ni, Fe, Co; L = dapbh, dapbih, Figure 1) and [{Co(dapbh)}3{M(CN)6}2(H2O)2] (M = Cr, Fe) and trinuclear [{Mn(dapsc)}2{Mo(CN)7}(H2O)2] complexes have been described.5c,13c,14b,e Two of them with [Ni(dapbh)]2+ and [Fe(dapbih)]2+ are SMMs.13c,14e Recently, the first bimetallic chain complexes based on [Mn(dapsc)]2+ and [Fe(dapbh)]2+ planar units with diamagnetic cyanometallates [Fe(CN)5NO]2− and [Ni(CN)4]2− have been synthesized. The former exhibits photochromism associated with the presence of the nitroprusside anion,19 and the latter is an SIM and shows slow magnetic relaxation induced by the magnetic field.13d In the chain compounds I and II, the low-spin [MnIII(CN)6]3− complex (S = 1) is used as a magnetically anisotropic partner for the high-spin [MnII(dapsc)]2+ complex. It is noteworthy that, in contrast to the other 3d hexacyanometallate building blocks, the [Mn(CN)6]3− anion remains much less explored due to B


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Inorganic Chemistry difficulties in isolation of single crystals of the [Mn(CN)6]3− containing materials, because [Mn(CN)6]3− complexes tend to decompose in solution.20 Hexacyanomanganate(III) exhibits pronounced magnetic anisotropy stemming from triple orbital degeneracy of the 3T1g ground state that results in unquenched orbital momentum and strong first-order spin−orbit coupling (see below the Magnetic Section). Several SMMs and SCMs based on [Mn(CN)6]3− complexes have been previously obtained,11a,20 and some theoretical analysis of their anisotropic magnetic properties was reported.21 Below in this paper we show that the chain compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII−CN−MnII spin coupling. More specically, despite the presence of orbital degeneracy and first-order unquenched orbital momentum, the [MnIII(CN)6]3− complex has a wellisolated nonmagnetic singlet ground state resulting from the spin−orbit splitting of the ground 3T2g orbital triplet. This results in the unusual situation in which high-spin MnII ions in the chains are magnetically uncoupled with the nonmagnetic ground state of MnIII ions; their magnetic interaction can occur only through excited spin states of [MnIII(CN)6]3− complex in the second-order perturbation. Obviously, this hinders obtaining of high magnetic anisotropy and energy barrier in hexacyanomanganate(III)-based SMMs and SCMs. Herein we provide detailed theoretical analysis of magnetic properties and SCM behavior of I, and we critically discuss the prospects of [MnIII(CN)6]3− complex as a building block for designing SMMs and SCMs.

Figure 2. Asymmetric unit in I with atom numbering scheme (ORTEP drawing with 50% probability ellipsoids). Symmetry codes: (a) (−x, y − 0.5, −z), (b) (1 − x, y − 0.5, 1 − z), (c) (−x, y + 0.5, −z), (d) (1 − x, y + 0.5, 1 − z). Bonding between atoms with minor occupancy is shown by dashed lines.

fragments have a nearly planar structure. Maximal deviations from planarity within each of the semicarbazone arms [in the planes defined by seven nonmetallic atoms of two pentagonal cycles: O(1), C(1), N(3), N(5), C(4), C(5), N(7) and O(2), C(2), N(4), N(6), C(10), C(9), N(7) for dapsc at Mn(1); O(3), C(21), N(10), N(12), C(24), C(25), N(14) and O(4), C(22), N(11), N(13), C(30), C(29), N(14) for dapsc at Mn(2)] are 0.043(3) Å. The dihedral angle between the two planes is 3.35(7)° and 2.12(6)° for dapsc at Mn(1) and Mn(2), respectively. Two oxygen atoms of each dapsc are coordinated to K+ cation that is incorporated into the complex composition; K−O distances are 2.653(4)−2.900(3) Å. Coordination sphere of each K+ involves also one methanol and several water molecules. There is a strong disorder of K/solvent part in I. The K atom connected to dapsc at Mn(2) (as well as some atoms of its coordination sphere) was separated into two positions K(1) and K(1b) of 0.8 and 0.2 occupancies, respectively. The K(1) and K(2) atoms are both deviated from the dapsc plane at 1.26 Å, whereas K(1b) atom is practically in the dapsc plane. Two K+ ions from adjacent chains are located quite close to each other, at 4.126(1) Å [or 4.369(5) Å for K(1b)] and bridged through two oxygen atoms from one water and one methanol molecule. As a result, interchain coordination bonds are formed via the pair of K+ ions. These coordination bonds join adjacent infinite chains into two-dimensional corrugated plane parallel to (1 0−1) (Figure 3). The adjacent chains interact additionally by π···π stacking of dapsc moieties along the shortest cell axis a as well as by hydrogen bonding of N−Hdapsc···Owater, O−Hwater···Nanion type in the (1 0−1) plane and N−Hdapsc...Nanion in the (0 1 0) plane (Figures S3a and S4a in the Supporting Information, hydrogen bond geometry is given in the figure captions). The MnII−MnIII distances along the chain are 5.1345(7) and 5.1404(6) for Mn(1) and 5.1378(7) and 5.1854(6) Å for Mn(2). The shortest interchain intermetallic distances are 8.1757(7) and 8.2397(7) Å between the Mn(1) and Mn(2) centers connected via π−π stacking of dapsc ligands.

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RESULTS AND DISCUSSION Synthesis and Crystal Structure. The reaction of [MnII(dapsc)Cl2]·H2O with K3[MnIII(CN)6] was studied, and two types of single crystals were obtained in separate syntheses, which differ by crystallization rate (see Experimental). The rapid crystallization yielded crystals of I, while the slow one produced crystals of II. Complex I crystallizes in the monoclinic P21 space group (Table S1 in the Supporting Information). The asymmetric unit includes two [Mn(dapsc)], two [Mn(CN)6] moieties, two K+ ions, one MeOH solvent molecule, and seven water molecules, all in general positions [one K, MeOH (O(1w)) and one H2O (O(2w)) are disordered between two sites of 0.8/0.2 occupancy, another H2O (O(8w)) is disordered between two sites of 0.5/0.2 occupancy, and third H2O (O(5w)) has occupancy of 0.8], Figure 2. The key bond distances and angles are listed in Table S2 in the Supporting Information. Crystal structure of I is built of infinite chains running along the [1 0 1] direction (Figure 3). They consist of alternating cationic [MnII(dapsc)]2+ and anionic [MnIII(CN)6]3− units connected through cyanide bridges. The Mn(II) ions have a distorted pentagonal bipyramidal coordination formed by two oxygen and three nitrogen atoms of the equatorial dapsc ligand and two axial nitrogen atoms from cyanide bridges. The Mn−O and Mn−N bond distances in [MnII(dapsc)]2+ (Table S2 in the Supporting Information) agree well with similar bonds in the previously published chain complex {[Mn(dapsc)][Fe(CN)5NO]·0.5CH3OH·0.25H2O}n.19 The trans-disposed CN ligands form shorter bonds with Mn(II) than N, O atoms of the dapsc ligand. The MnIII−C distances in two independent [MnIII(CN)6]3− octahedrons are in the range of 1.981(3)−2.004(4) Å. Along the MnIII−C−N−MnII chain bridges, the MnIII−C−N angles are practically linear in contrast to nonlinear MnII−N−C ones (Table S2 in the Supporting Information). The Mn(dapsc) C


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Figure 3. Infinite chains joined via pair of K+ ions in the (1 0 −1) plane in I (only major positions of K and connecting water and methanol molecules are shown; other water molecules from K surrounding are omitted for clarity).

Complex II crystallizes in the monoclinic P21/c space group (Table S1 in the Supporting Information). The asymmetric unit includes one Mn(dapsc) fragment in general position, two independent [Mn(CN)6] moieties on the inversion centers, one K+ ion, two water and two methanol molecules in general positions. An ORTEP drawing of II is shown in Figure 4; key bond distances and angles are listed in Table S2 in the Supporting Information. Crystal structure contains infinite chains of alternating cationic [MnII(dapsc)]2+ and anionic [MnIII(CN)6]3− units running along [1 0−1] (Figure 5). Structure of the chain is very similar in I and II. Two independent [MnIII(CN)6]3− octahedrons

in II occupy the inversion centers (1/2, 0, 1/2) and (1, 0, 0). The Mn−O, N bond lengths in the MnII(dapsc) moiety and Mn−C ones in the MnIII(CN)6 octahedron are close to that in I (Table S2 in the Supporting Information). The Mn(dapsc) fragment is planar: the dihedral angle between the two semicarbazone planes defined by atoms O(1), C(1), N(3), N(5), C(4), C(5), N(7) and O(2), C(2), N(4), N(6), C(10), C(9), N(7) is 2.95(4)°. Two oxygen atoms of the dapsc ligand are coordinated to K+ cation at K−O distances of 2.761(1) Å for O(1) and 2.782(1) Å for O(2). Nitrogen atom from one of the adjacent [Mn(CN)6] units within the chain is also coordinated to the K+ ion; K(1)−N(16) distance is 2.890(2) Å. Coordination sphere of K+ is completed by two water and two methanol molecules at K−O distances of 2.771(2)−2.883(2) Å. The MnII−MnIII distances along the chain in II are 5.2429(6) Å for Mn(2) and 5.0766(6) Å for Mn(3). The shortest interchain intermetallic distance is 8.1341(9) Å between the two Mn(II) centers. Although the complexes I and II are not isostructural, they have very similar molecular packing. Both compounds form infinite chains {[MnII(dapsc)][MnIII(CN)6]}−∞ and contain K+ counterion coordinated to oxygen atoms of dapsc. The π−π stacking of the dapsc fragments along the shortest cell axis is also observed in both I and II (Figures S3a and S3b in the Supporting Information, respectively) as well as the interchain N−H···NC hydrogen bonding in the (0 1 0) plane (Figures S4a and S4b in the Supporting Information). The main difference between the two structures is in the position of K+ cations. Two nearest K+ ions in II are located in the plane of attached dapsc (in contrast to the structure of I, where they are 1.26 Å apart from this plane) and separated by 5.971(1) Å, which is more than 1.6 Å farther than in I. As a result, interchain coordination bonds via pair of K+ ions are not formed in II. The considerable disorder takes place in the structure of I related to arrangement of K+ ions and their environment, unlike II. The difference in the position of K+ cations leads to diverse mutual shift of neighbor chains and turn

Figure 4. Asymmetric unit in II with atom numbering scheme (ORTEP drawing with 50% probability ellipsoids). Symmetry codes: *(1 − x, −y, 1 − z), **(2 − x, −y, −z). D


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Inorganic Chemistry

Figure 5. Infinite chain in II. Intrachain hydrogen bonds are shown by red dashed lines.

of the chain components in I and II, as one can see from comparison of Figures S3a, S3b, S4a, and S4b in the Supporting Information, in spite of the common packing model. The question of the planar pentagonal coordination of the dapsc ligand is important in terms of the prospects for its use as a building block for the design of molecular nanomagnets. For this purpose, we specially investigated the origin of the planar structure of Mn(dapsc) in I and II and performed density functional theory (DFT) calculations for isolated [MnII(dapsc)(H2O)2]2+ and [MnII(dapsc)]2+ complexes with and without two apical H2O ligand molecules using the ORCA 3.0.3 suite of programs and employing the spin-unrestricted method at the B3LYP/SVP(TzVPP) level of theory.22 It is noteworthy that planar pentagonal coordination has been observed in a number of 3d metal complexes with dapsc and other related pentadentate macrocyclic ligands.5c,13,14,16 However, in some complexes the dapsc-type pentagonal macrocycle with unclosed N3O2 or N5 chelating ring is nonplanar, in which the terminal O or N atoms move away from the equatorial plane.23 The calculations reveal considerable difference in the DFToptimized structure of the Mn(dapsc) pentagonal unit, which is planar in [MnII(dapsc)(H2O)2]2+ and nonplanar in [MnII(dapsc)]2+ (Figure S5 in the Supporting Information). The optimized geometry of [MnII(dapsc)(H2O)2]2+ corresponds to a nearly perfect planar structure of the dapsc ligand in the equatorial plane with atomic distances and bond angles very close to the corresponding experimental values in I and II (Figure S5b in the Supporting Information). By contrast, the absence of the apical ligands in [MnII(dapsc)]2+ results in a considerable departure from planarity of the N3O2 ring of dapsc due to shifts of the terminal O atoms from the equatorial plane by ∼0.7 Å, which is followed by a reduction of the Mn−O distances by ∼0.12 Å (Figure S5c in the Supporting Information). This indicates that apical ligands play an important role in stabilization of the planar structure of the Mn(dapsc) unit. We can therefore suggest that planarity of the dapsc ligand in I and II is an inherent property of Mn(dapsc) complex with two NC apical ligands rather than the result of the crystal stacking effect or stabilizing contacts between the terminal O atoms of dapsc and K+ cations (Figures 2 and 4). Magnetic Properties. The temperature dependence of the magnetic susceptibility was measured on polycrystalline sample of I in the temperature range of 2.0−300 K under the applied magnetic field of 0.1 T. The magnetic properties of II were not studied by reason for nonuniformity of the samples (see Experimental). The μeff(T) plot for I is depicted in Figure 6.

Figure 6. Temperature dependence of effective magnetic moment (μeff) for complex I from 300 to 2.0 K under the applied magnetic field of 1 kOe. The dotted line indicates the theoretical value for system of the noninteracting spins MnII (S = 5/2) and MnIII (S = 1). (insets) The FC and ZFC magnetization under 20 Oe and μeff vs T plot from 10 to 2.0 K.

The room-temperature value of effective magnetic moment (μeff) for I is slightly larger than the spin-only value of 6.55 μB for the magnetically uncoupled MnII (S = 5/2) and MnIII (S = 1) ions; this is largely due to enhanced effective g-factor of orbitally degenerate low-spin [MnIII(CN)6]3− complexes (and eventual inaccuracy in determining spin carrier concentration in the samples of I; see below Figure 10). When cooled, μeff value gradually decreases to the minimum value at ∼20 K, then rapidly increases up to the maximum values at ∼3.5 K (Figure 6, inset), followed by a decrease to 2 K. Formally, the latter feature can be regarded as a signature of anti-ferromagnetic coupling between the chains through the hydrogen bonding network, π−π interaction, and the interchain coordination bonds via solvent molecules and K+ ions; however, our calculations in terms of a microscopic model indicate very weak interchain spin coupling suggesting the absence of threedimensional long-range magnetic ordering and pointing 1D magnetic behavior of I (see below, Figure S11). Therefore, the origin of the maximum of μeff is seemingly due to complicated (unconventional) intrachain spin coupling between the [MnIII(CN)6]3− and MnII(dapsc) units (see below the next Section). The overall behavior of the μeff versus T curve points to anti-ferromagnetic exchange interactions within chains between E


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Inorganic Chemistry MnII and MnIII spin carriers through the cyanide bridges resulting in a ferrimagnetic spin arrangement along the chains. The Curie−Weiss fit of the susceptibility data above 75 K gave the Weiss constant θ = −30.0 K. The rapid increase of μeff below 10 K suggests a ferrimagnetic ordering. Exchange interactions between MnIII and MnII ions in I are analyzed in more detail in the next Section. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization at 20 Oe were measured to test the magnetic behavior at low temperatures (Figure 6, inset). The FC and ZFC data are divergent below the critical temperature Tc = 3.5 K, which indicates the occurrence of irreversibility of magnetization below this temperature and thereby to the presence of a slowing of the magnetization relaxation. The field dependence of the magnetization measured at 2.0 K (Figure S6 in the Supporting Information) reveals the “magnet”-type behavior of the material with an abrupt increase of the magnetization at low fields. No hysteresis loop was observed at 2.0 K. To investigate the relaxation behavior, alternating current (AC) susceptibility measurements were performed in zero direct current (DC) field with an AC field of 4 Oe at frequencies in range of 1−1400 Hz. The in-phase (χ′) and out-ofphase (χ″) parts of AC susceptibility for I show clear frequency dependence below 3.5 K (Figure 7), which precludes the presence of three-dimensional long-range ordering and is an indication of a slow magnetic relaxation, as observed for SMMs and SCMs. Taking into account the 1D character of I, the present magnetization dynamics indicates the occurrence of SCM-like behavior. The relative variation of the temperature of the maximum of χ″ with respect to the frequency of the oscillating field is expressed by the so-called Mydosh parameter φ = (ΔTmax/Tmax)/Δ(log ν).24 The calculated φ value of 0.16 is in

the range expected for normal super-paramagnets or SCMs and thus excludes the possible occurrence of a spin glass state. The SCM behavior of I is also supported by the microscopic calculations of interchain exchange parameters in terms of manyelectron superexchange theory (details are described below in the Magnetic Section and in the Supporting Information, Appendix B). Calculations for the two MnII(dapsc) units of two neighboring chains contacted through the π−π stacking interactions of the planar dapcs fragments (Figure S11a) result in a very weak anti-ferromagnetic spin coupling, J = −0.006 cm−1. Similar calculations indicate that spin coupling between the two MnII(dapsc) units mediated by K+ ions and solvent molecules (water and methanol) is even weaker, J ≈ −1 × 10−4 cm−1 or less. (Figure S11b). This implies that the intrachain spin coupling between the cyano-bridged [MnII(dapsc)]2+ and [MnIII(CN)6]3− moieties (J = −6 cm−1; see below) strongly dominates in I. The frequency dependence of the position of the peak temperature in χ″ for I follows an Arrhenius law τ = τ0 exp(Ueff/kBT), (τ = 1/2πν) with an effective energy barrier Ueff/kB = 27.8 cm−1 (40.0 K) and a pre-exponential factor τ0 being 3.3 10 −10 s (Figure S7 in the Supporting Information). These parameters are in the range of those reported for SCMs and confirm that I exhibits an energy gap for the magnetization reversal.11 To further test the 1D nature of the complex I, the ln(χmT) versus 1/T plot was examined (Figure S8 in the Supporting Information). For any 1D spin system (an Ising-like or anisotropic Heisenberg spin chain), the correlation length (ξ) and χmT increase exponentially with decreasing temperature according to the equation χmT = Ceff exp(Δξ/kBT), in which Ceff is the effective Curie constant and Δξ is the energy required to create a domain wall along the chain.1b−e The curve of ln(χmT) versus 1/T is linear between 10 and 4 K with an energy gap Δξ/kB of 9.81 K confirming the 1D nature of the complex. The ln(χmT) versus T−1 curve saturates at the lowest temperatures, that is, below ca. 3 K, due to finite size effects.1b−e For an Ising-like SCM, the energy barrier for the spin reversal Δτ is Ueff = 2Δξ + Δ for the infinite chain and Ueff = Δξ + Δ for the finite-size chain, where Δ is the anisotropy energy.1b−e As the correlation length (ξ) is saturating at ∼3 K (Figure S8 in the Supporting Information) and the relaxation time of I was determined below 3 K (Figure S7 in the Supporting Information) in the finite-size chain regime, the anisotropy barrier can be estimated as Δ = Ueff − Δξ = 30.19 K. Below magnetic properties and the origin of slow magnetic relaxation in I are discussed in the light of the electronic structure of [MnIII(CN)6]3− and [MnII(dapsc)]2+ complexes and mechanism of unconventional MnIII−CN−MnII spin coupling. Analysis of Magnetic Behavior of I. Magnetic Properties of Isolated [MnIII(CN)6]3− Complexes. Analysis of magnetic properties of I is complicated by the presence of orbitally degenerate [MnIII(CN)6]3− magnetic centers with unquenched first-order orbital momentum. Electronic structure and magnetic properties of isolated [MnIII(CN)6]3− complexes were previously discussed in the literature.25−28 The ground state of [MnIII(CN)6]3− complex with the regular octahedral structure (Oh symmetry) is a low-spin (S = 1) orbital triplet 3T1g(3d4) resulting from the (t2g)4 electronic configuration with two unpaired electrons. The spin−orbit coupling (SOC) on MnIII splits the 3T1g triplet into three groups of energy levels, which formally correspond to coupling of the orbital momentum L = 1 and spin S = 1 into the total

Figure 7. Temperature dependence of the real (χ′) and imaginary (χ″) parts of the ac susceptibility for I measured at the indicated frequencies (1−1400 Hz). F


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Inorganic Chemistry

Figure 8. Orbital splitting and spin−orbit splitting of the ground 3T1g orbital triplet in (a) regular octahedral [MnIII(CN)6]3− complex (Oh symmetry) and (b) distorted [MnIII(CN)6]3− complex. Typical splitting energies are given in the actual energy scale.

Table 1. Calculated Energies (cm−1) of Orbital States 3 T1g(1−3) and Spin−Orbit States En(j) (see Figure 8) of Two Structurally Inequivalent [MnIII(CN)6]3− Complexes Mn3 and Mn4 (see Figure 2) in Compound I and in the Regular Octahedral (Oh) Complex [MnIII(CN)6]3−

angular momentum j = L + S, the ground spin−orbit singlet j = 0 and excited j = 1 and j = 2 spin states (Figure 8a).29 The ground singlet state j = 0 is nonmagnetic; it is well-isolated from excited spin levels (Figure 8a). The energy spacing between j and j − 1 energy levels obeys the conventional Lande pattern, ΔE = (ζ/2)j, where ζ is the SOC constant for the MnIII ion.29 In distorted [MnIII(CN)6]3− complexes the 3T1g state splits into three individual components 3T1g(1−3), which further undergoes SOC splitting to produce spin−orbit states, which are grouped into three series of states En(j), originating from the parent spin−orbit states j = 0, 1, and 2 (Figure 8b). In this case, electronic structure and magnetic properties of [MnIII(CN)6]3− are further complicated (Figure 8b). To relate magnetic behavior of I with the specific electronic structure of [MnIII(CN)6]3− complexes involved in I, we calculated the energy spectrum of spin states in distorted [MnIII(CN)6]3− complexes (Figure 8b) in terms of conventional ligand-field (LF) Hamiltonian combined with the angular-overlap model (AOM).30 In these calculations, we used the Racah parameters B = 675 and C = 3120 cm−1, and the SOC constant ζ = 284 cm−1 obtained in ref 28 from quantum-chemical calculations; this value is close to the SOC constant reported in ref 21. The AOM parameters for [MnIII(CN)6]3− complexes were estimated from the LF splitting energy 10 Dq ≈ 31 000 cm−1 and results of ab initio calculations for a trigonally compressed [MnIII(CN)6]3− complex involved in a [MnIII6MnIII(CN)6]3+ triplesalen-based SMM cluster,31 eσ = 11 500 cm−1 and eπ/eσ = 0.07. The radial dependence of AOM parameters is approximated by eσ, π(R) = eσ, π(R0)(R0/R)n with n = 3 at the reference distance R0 = 2.00 Å. The actual experimental geometry of two structurally inequivalent [MnIII(CN)6]3− complexes Mn3 and Mn4 in I (Figure 2) is applied. Calculated orbital energies and spin−orbit energies are presented in Table 1. Calculated temperature dependence of magnetic susceptibility of [MnIII(CN)6]3− (for powder samples averaged over two structurally inequivalent [MnIII(CN)6]3− complexes Mn3 and Mn4 in compound I, see Supporting Information for details, Appendixes C and D) shown in Figure 9a. At low temperature the χmT product rapidly increases from a nearly zero value, and then it tends to saturate above 100 K and reaches a nearly

MnIII(CN)63− (Mn3)

E1(0)

orbital 3T1g states 0 0 53.3 19.4 91.8 55.4 spin−orbit states En(j) 0 0

E1(1) E2(1) E3(1) E1(2) E2(2) E3(2) E4(2) E5(2)

130.6 149.6 171.9 398.4 407.9 427.6 459.5 460.4

3

T1g(1) 3 T1g(2) 3 T1g(3) j=0

j=1

j=2

MnIII(CN)63− (Mn4)

135.6 154.4 164.2 408.6 410.9 429.9 441.9 444.9

MnIII(CN)63− (Oh) 0 0 0 0 151.6 151.6 151.6 424.6 424.6 425.1 425.1 425.1

constant value of ca. 1.46 cm3 mol−1 K (μeff ≈ 3.4 μB) at room temperature; between 2 and 60 K χmT increases linearly with the temperature. These results are well-consistent with the experimental magnetic data for the Cs2K[Mn(CN)6] compound;26a however, magnetic measurements for the [(Ph3P)2N]3[MnIII(CN)6] compound with isolated [MnIII(CN)6]3− complexes have resulted in considerably larger effective magnetic moment at room temperature (μeff ≈ 4.0 μB) with some temperature-independent paramagnetism.26b Note that the effective magnetic moment at room temperature (μeff ≈ 3.4 μB) is considerably larger than that expected for the S = 1 spin-only value (μeff = 2.83 μB, or χmT = 1.0 cm3 mol−1 K). Such a behavior results from a nonmagnetic ground spin−orbit singlet state j = 0 and progressive thermal population of excited j = 1 and j = 2 spin−orbit states with the increasing temperature (Table 1 and Figure 8). Formally, magnetic behavior of [MnIII(CN)6]3− can be simulated in terms of a conventional G


Article

Inorganic Chemistry

Figure 9. (a) Comparison of χmT curves calculated for individual [MnIII(CN)6]3− complexes in I (for powder samples averaged over two inequivalent MnIII sites Mn3 and Mn4 in I, Figure 2) in terms of full LF Hamiltonian and in terms of the S = 1 ZFS spin Hamiltonian DSz2 + E(Sx2 − Sy2). The best correspondence is obtained at D = +115 cm−1, E = 0, and gMn(III) = 2.45. (b) Comparison of the experimental χmT data for the chain compound I (blue circles) with the sum of χmT values of isolated MnII(dapsc) and [MnIII(CN)6]3− complexes (solid blue curve).

S = 1 zero-field splitting (ZFS) spin Hamiltonian DSz2 + E(Sx2 − Sy2) with a large and positive ZFS energy D. In this approximation, ZFS with positive D mimics the energy positions of the three lowest spin−orbit states E1(0), E1(1), and E2(1); the presence of other En(j) states (Figure 8b) is simulated by larger value of gMn(III). In this way, the overall character of the χmT curve for [MnIII(CN)6]3− is reasonably reproduced with D = +115 cm−1, E = 0, and gMn(III) = 2.45 (Figure 9a, solid blue curve). On the one hand, nonmagnetic character of the ground state j = 0 may lead to conclusion that at low temperature [MnIII(CN)6]3− complexes are not magnetically coupled with other spin carriers, as has been argued for the [MnIII6MnIII(CN)6]3+ triplesalen SMM cluster.31 However, this is definitely not true for compound I, since its magnetic susceptibility is poorly described by the model of two magnetically independent [MnII(dapsc)]2+ and [MnIII(CN)6]3− spin centers (Figure 9b). This unambiguously indicates that spin coupling between MnII and MnIII ions in I cannot be neglected, and thus it should be analyzed in some detail. On the other hand, magnetic anisotropy of I is not related to the single-ion ZFS anisotropy of high-spin MnII(dapsc) complexes (S = 5/2), which is generally very low for the ground 6A1 state, regardless of the specific ligand coordination (including less-common pentagonal-bipyramidal N3O2 coordination of dapsc ligand). More quantitatively, LF/AOM calculations for MnII(dapsc) complexes in I resulted in ZFS parameters of D = −0.16 cm−1 and E ≈ 0 (see Supporting Information for detail). These values are well-consistent with the experimental data for other structurally related MnII(L5) pentagonal complexes indicating small ZFS energies.5c,32 This indicates that magnetic anisotropy of I is primarily due to magnetic anisotropy of [MnIII(CN)6]3− complexes combined with some intrachain magnetic coupling. Analysis of Spin Coupling between MnII(dapsc) and [MnIII(CN)6]3− Magnetic Centers in I. Conventional isotropic spin Hamiltonian −JSASB cannot generally be applied in the case of spin coupling between MnII(dapsc) and [MnIII(CN)6]3−

centers in I due to triple orbital degeneracy of the 3T1g ground state of [MnIII(CN)6]3− and unquenched orbital momentum with first-order SOC resulting in well-isolated ground singlet state j = 0 (Figure 8). In this case, the commonly used concept of effective (fiction) spin29 is also inapplicable to [MnIII(CN)6]3− because of the absence of the ground-state spin degeneracy. This problem is a special case of a general problem of spin coupling for orbitally degenerate octahedral magnetic centers with the ground orbital triplet 2S+1T (that occurs in d1, d2, d6, and d7 high-spin octahedral complexes and in d4, d5 low-spin complexes, such as [MnIII(CN)6]3− and [FeIII(CN)6]3− 29). For these systems, spin coupling between orbitally degenerate complex (A) and other spin center (B) is often treated in terms of a model Hamiltonian33,34,35a −JSA SB + ΔL z 2 + kλLS + μB (kL + geSA )H + μB gBSBH (1)

in which the first term represents isotropic spin coupling, and ΔLz2 describes splitting of the energy levels of the 2S+1T orbital triplet in distorted octahedral site A (where Δ is the energysplitting parameter, and Lz is the z-projection of the effective orbital momentum L = 1 associated with the 2S+1T triplet). Here kλLS is the effective SOC acting within the space of the 2S+1 T states of center A with λ and k being the many-electron SOC parameter (λ = ζ/2SA) and the orbital reduction factor, respectively. The last two terms represent Zeeman interaction for the sites A and B, where gB and ge are the isotropic g factors for the B center and a free electron, and μB is the Bohr magneton. In many cases magnetic behavior of molecular spin clusters involving triply degenerate 3d ions (with the 2S+1T ground state) is reasonably well-reproduced in terms of this approach.35 However, spin Hamiltonian (1) provides only a simplified description of the actual picture of spin coupling for magnetic centers with unquenched orbital momentum. Herein we analyze this point in more detail for the specific exchangecoupled pair [MnIII(CN)6]3−·MnII(dapsc) in compound I. First, calculations indicate an irregular character of the orbital splitting pattern of the 3T1g term of [MnIII(CN)6]3− complexes H


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Inorganic Chemistry in I (Table 1) and in other [MnIII(CN)6]3−-based compounds (Table S3 in the Supporting Information), which is inconsistent with the axial symmetry of ΔLz2 operator. Second and even more important issue concerns the use of the −JSASB spin coupling operator in (1) that corresponds to the Lines approach.36 Actually, in the absence of SOC on MnIII, spin coupling between MnII and MnIII is described by an orbitally dependent isotropic spin Hamiltonian Horb, which can be written in general form Ĥorb = A − RSA SB

for the [MnIII(CN)6]3− complex Mn3 in I (Figure 2) and ⎛−22.52 ⎜ A = ⎜ 0.55 ⎜ ⎝ 0.64 ⎛−5.15 ⎜ R = ⎜ 0.28 ⎜ ⎝−0.88

(2)

(3a)

R = J(2 − L z 2)

(3b)

for the complex Mn4; here, the matrix elements (in cm ) refer to the actual wave functions of the three split orbital components 3T1g(1−3) (Table 1) in distorted [MnIII(CN)6]3− complexes Mn3 and Mn4 involved in the chains of I (Figures 2 and 3). As can be seen from eqs 4 and 5), the structure of the spin-dependent orbital operator R differs considerably from that of the commonly used Lines approach, R = JI.36 In particular, contrary to the Lines model assuming equal eigenvalues of the R matrix (En ≡ J), the eigenvalues of the R matrix in eqs 4 and 5) are essentially different, −7.10, −5.44, −0.97 cm−1 for the site Mn3 and −7.44, −5.37, −1.63 cm−1 for Mn4 (in Figure 2); details of calculations are outlined in the Supporting Information (Appendix A). These values estimate the overall strength of spin coupling in MnIII−CN−MnII cyanobridged pairs in I. These results evidently show that there is an unconventional spin coupling in MnIII−CN−MnII exchange-coupled pairs in I resulting from the interplay of nondiagonal spin-dependent orbital operator R in eqs 4 and 5, low-symmetry splitting of the 3 T1g orbital triplet (Table 1), and first-order SOC on MnIII centers. In fact, the actual complexity of spin coupling in I goes far beyond the commonly used model based on the Lines approach and spin Hamiltonian (1). It is important to clarify that the term “unconventional” refers to a special case of spin coupling between the wellisolated singlet ground state j = 0 of [MnIII(CN)6]3− and true S = 5/2 spin of MnII(dapsc), which cannot be described by the conventional spin Hamiltonian in terms of variables of a fiction spin on MnIII due to the absence of spin degeneracy (multiplicity) of the ground j = 0 singlet state (Figure 8 and Table 1). To a first approximation, [MnIII(CN)6]3− complexes in the chains carry no first-order magnetic moment; however, [MnIII(CN)6]3− complexes cannot be regarded as true diamagnetic metal centers, and spin coupling cannot be neglected, as can be seen from Figure 9b that clearly evidences the presence of magnetic interactions in the chains. In this case, magnetic coupling between the [MnIII(CN)6]3− and MnII(dapsc) units occurs through excited j = 1 and j = 2 states of [MnIII(CN)6]3− complexes, which are mixed to the ground j = 0 state by the MnIII−CN−MnII exchange interaction; the latter is described by the orbitally dependent spin Hamiltonian (eqs 2, 4, and 5). This mixing manifests as a second-order effect, since the energy gap ΔE01 between the j = 0 ground state and excited j = 1 and 2 spin levels is much larger (ΔE01 > 100 cm−1) than the exchange parameters (J ≈ 6 cm−1). As a result, magnetic interaction between the j = 0 singlet state of MnIII and the S = 5/2 spin of MnII is described by an effective (unconventional) second-order anisotropic spin-coupling. This spin coupling scheme is illustrated graphically in Figure S10. Simulation of the Magnetic Susceptibility of I. Obviously, at the current state of the art, simulation of the χmT curve for the chain compound I in terms of orbitally dependent spin Hamiltonian Horb (eqs 2, 4, and 5) combined

where J = −t2(U(A → B)−1 + U(A ← B)−1)/5 and J1 = −t2U(A ← B)−1; here t is the electron-transfer parameter corresponding to one-electron matrix elements t = ⟨dxz(A)|h|dxz(B)⟩ = ⟨dyz(A)|h|dyz(B)⟩ connecting xz and yz magnetic orbitals on MnIII(A) and MnII(B) centers (see Supporting Information).37 With typical CT energies U(A→ B) = 65 000 cm−1 (8 eV), U(A ← B) = 80 000 cm−1 (10 eV), and electron-transfer parameter t = 835 cm−1 (estimated from extended Hückel calculations, see Supporting Information for details, Appendix A) we obtain the orbital exchange parameter J = −3.9 cm−1 for 3 T1g(mL = ±1) states and J = −7.8 cm−1 for the 3T1g(mL = 0) state. More rigorous calculations in terms of many-electron superexchange model38 performed for the [MnIII(CN)6]3−−MnII(dapsc) exchange-coupled pairs involved in I reveal a complicated nondiagonal structure of the 3 × 3 matrices A and R ⎛−25.93 2.56 1.35 ⎞ ⎜ ⎟ A = ⎜ 2.56 − 25.11 0.82 ⎟ , R ⎜ ⎟ ⎝ 1.35 0.82 − 21.68 ⎠ ⎛−4.38 2.78 1.10 ⎞ ⎜ ⎟ = ⎜ 2.78 − 4.23 0.97 ⎟ ⎜ ⎟ ⎝ 1.10 0.97 − 4.90 ⎠

(5) −1

where SA and SB are spin operators of [MnIII(CN)6]3− (SA = 1) and MnII(dapsc) (SB = 5/2) magnetic centers; A and R are, respectively, spin-independent and spin-dependent orbital operators that act on the orbital variables only. In the space of the 3T1g(A) × 6A1(B) wave functions (where × stands for antisymmetrized product) the A and R orbital operators are written as a Hermitian 3 × 3 matrix. According to the Lines approach, the matrix of the spin-dependent operator in (2) takes the form R = JI, which is always diagonal and proportional to the unit matrix I, regardless of the specific electronic structure of the orbital wave functions 3T1g(mL).36 It is therefore of interest to examine the correctness of the Lines approach for I. Primary insight into the structure of the Horb Hamiltonian (2) could be obtained from superexchange calculations for a linear MnIII−CN−MnII exchange-coupled bi-octahedral pair (see Supporting Information for detail) using a simplified approach, in which all MnIII(A) → MnII(B) and MnIII(A) ← MnII(B) charge-transfer (CT) states have the same excitation energy, U(A → B) for 3d4(A)−3d5(B) states and U(A ← B) for 3d6(A)−3d3(B) states (that corresponds to so-called closure approximation). In this case, simple analytical calculations result in A = J1 + (5J /2)(2 − L z 2)

0.55 0.64 ⎞ ⎟ − 25.41 − 2.92 ⎟ , ⎟ − 2.92 − 23.58 ⎠ 0.28 − 0.88 ⎞ ⎟ − 6.18 − 2.32 ⎟ ⎟ − 2.32 − 3.12 ⎠

(4) I


Article

Inorganic Chemistry with SOC on MnIII centers is a challenging problem. Application of the spin Hamiltonian (1) to a MnIII−CN−MnII chain is also rather difficult and complicated. In this situation, we must use a simplified approach, in which the Horb + HSOC Hamiltonian (2) for [MnIII(CN)6]3−−[MnII(dapsc)]2+ pairs is replaced by the conventional isotropic (spin-only) spin Hamiltonian −JSASB (SA = 1, SB = 5/2) with large positive ZFS energy for MnIII, that mimics magnetic behavior of isolated [MnIII(CN)6]3− complexes, as discussed above (see Figure 9a). Calculations are performed for a (−MnIII−CN−MnII−)2 fourmember segment of the chain in I with periodic boundary conditions (see insert in Figure 10) in terms of a spin Hamiltonian:

due to long-range magnetic correlations of the SCM chain, which could not be reproduced in terms of spin Hamiltonian (6) involving a short four-member segment of the (−MnII− CN−MnIII−)x chain. It is important to note that the value of J = −6.0 cm−1 agrees reasonably with the orbital exchange parameters in the R matrices (4 and 5) of the orbitally dependent spin Hamiltonian Horb (2) obtained from superexchange interactions (see previous Section). In this context, it is interesting to compare magnetic behavior of I and linear trinuclear complex [MnII(LN3O2)MnIII(CN)6MnII(LN3O2)]20b composed of the same (MnIII) and very similar (MnII) molecular building blocks as those in I; the structure of this complex is very similar to the local structure of chains in compound I (Figure 11). The overall character of the χmT curve of [Mn(LN3O2)(H2O)]2[Mn(CN)6] complex is reasonably described in terms of spin Hamiltonian

H = −J(S1 + S3)(S2 + S4) + D((S2z)2 + (S4z)2 ) + μB H

∑ i=1−4

giSi

(6)

H = −J(S1 + S3)S2 + D(S2z)2 + μB H

where S1 and S3 refer to [MnII(dapsc)]2+, and S2, S4 refer to [MnIII(CN)6]3−. Here the exchange parameter J is variable, while other parameters are fixed at g1 = g3 = 2.00 for MnII and D = 115 cm−1, g2 = g4 = 2.45 for MnIII, as obtained from the fitting of the χmT curve for isolated [MnIII(CN)6]3− complexes in terms of an S = 1 ZFS spin Hamiltonian (see Figure 9a and comments; calculation details are presented in the Supporting Information, Appendix D). At J = −6.0 cm−1, D = +115 cm−1, g1 = g3 = 2.00, and g2 = g4 = 2.45 the simulated curve reasonably reproduces the overall character of the experimental χmT curve, albeit calculated values are systematically lower (solid gray line, Figure 10). This

∑ i=1−3

giSi

(7)

with the same set of parameters as that used for I (J = −6.0 cm−1, D = 115 cm−1, gMn(II) = 2.00, and gMn(III) = 2.45; Figure 11a, solid blue curve). A good fit is obtained at smaller exchange parameter, J = −3.3 cm−1, D = 115 cm−1, gMn(II) = 2.00, and gMn(III) = 2.45 (applying a scaling factor of k = 0.962, Figure 11a, solid red curve). The calculated energy spectrum pattern of low-lying spin states of [Mn(LN3O2)(H2O)]2[Mn(CN)6] reveals the absence of double-well potential required for SMMs; in fact, the E versus MS diagram has a complicated structure, which is more compatible with a single-well pattern (Figure 11b). The lowest energy level corresponds to an MS = 0 spin state, which is followed by a dense group of excited spin states with low MS values (Figure 11b). These features do not meet the necessary conditions for a magnetic molecule to be a SMM; this accounts for the absence of SMM behavior of [Mn(LN3O2)(H2O)]2[Mn(CN)6] complex.20b Similar calculations for [MnII(tmphen)2]3[MnIII(CN)6]2 trigonal-bipyramidal cluster39 also result in reasonable agreement between simulated and experimental χmT curves with the same set of parameters as that used for I (Figure S9 and Appendix D in the Supporting Information). Calculations indicate that the ground state of [MnII(tmphen)2]3[MnIII(CN)6]2 corresponds to an MS = 1/2 Kramers doublet; some eventual manifestations of slow magnetic relaxation39 may be associated with a complicated character of the spin energy diagram with a high density of low-lying spin states. [MnIII(CN)6]3− as Magnetically Anisotropic Building Block: Critical Analysis. In recent years, it has become increasingly apparent that incorporation of molecular building blocks with a strong intrinsic magnetic anisotropy represents an efficient strategy to increase the spin-reversal barrier Ueff and the blocking temperature TB.4 In this respect, orbitally degenerate cyanometallates [M(CN)n]m− with unquenched first-order orbital momentum are especially attractive; the [MnIII(CN)6]3− complex certainly falls into this category. It is therefore of interest to compare magnetic anisotropy of [MnIII(CN)6]3− complex with that of other orbitally degenerate cyanide transitionmetal complexes [M(CN)n]m− with unquenched first-order orbital momentum (such as [FeIII(CN)6]3−, [MnII(CN)6]4−, [Ru III (CN) 6 ] 3− , [Os III (CN) 6 ] 3− , [Mo III (CN) 7 ] 4− , and [ReIV(CN)7]3−) and to estimate its prospects for designing SMMs/SCMs. Previously, magnetic anisotropy and spinreversal barrier in trigonal-bipyramidal (MnIII2MnII3) and linear

Figure 10. Experimental and simulated χmT curves of I. Simulated χmT curve (solid gray line) is calculated at J = −6.0 cm−1, D = +115 cm−1, gMn(II) = 2.00, and gMn(III) = 2.45 in terms of spin Hamiltonian (6) for a Mn4 fragment of the (−MnII−CN−MnIII−)x chain with periodic boundary conditions (shown in the inset). Corrected χmT curve (bold solid blue line) is calculated at the same set of parameters with the scaling factor k = 1.066.

difference may be due to the sampling/solvent loss aspects, which are quite common to solvent-rich samples of molecular magnets. This effect can be taken into account by applying a scaling factor k to the experimental χmT data. A good correspondence between the experimental and calculated χmT curves is obtained with k = 1.066 (bold blue line, Figure 10). In particular, a close agreement is observed above 40 K, and the simulated curve reproduces a minimum at ca. 20 K. The rapid increase of the experimental χmT product at low temperature is J


Article

Inorganic Chemistry

Figure 11. (a) Experimental20b and simulated χmT curves of trinuclear complex [MnII(LN3O2)(H2O)]2[MnIII(CN)6]. Solid blue curve is calculated in terms of the spin Hamiltonian (6) with the set of parameters obtained for I (J = −6.0 cm−1, D = 115 cm−1, gMn(II) = 2.00, and gMn(III) = 2.45; solid red curve corresponds to the best fit with variable J (J = −3.3 cm−1, D = 115 cm−1, gMn(II) = 2.00, gMn(III) = 2.45, with the scaling factor k = 0.962). (b) E vs MS diagram of low-lying spin states of MnII(LN3O2)(H2O)]2[MnIII(CN)6]. (inset) Full spin energy diagram of MnII(LN3O2)(H2O)]2[MnIII(CN)6].

(MnII−MnIII−MnII) SMM clusters with [MnIII(CN)6]3− complexes were discussed in terms of idealized (highly symmetrized) structural model and simplified superexchange calculations.21 This approach exploits the idea that in uniaxially distorted [MnIII(CN)6]3− complexes (with trigonally compressed or tetragonally elongated Mn(CN)6 octahedron) the axial LF component ΔLz2 with negative Δ parameters splits the 3 T1g orbital triplet into the upper 3T1g(mL = 0) state and two lower 3T1g(mL= ±1) degenerate orbital states. The latter are further split by SOC to produce magnetically active ground non-Kramers doublet |mL = ±1, mS = ∓1⟩ (where mL and mS are projections of the orbital momentum L = 1 and spin S = 1)

resulting in anisotropic spin coupling and spin-reversal barrier.21 Unfortunately, these assumptions are generally inconsistent with the actual electronic structure of [MnIII(CN)6]3− complexes in real molecular magnets. In fact, in axially distorted [MnIII(CN)6]3− complexes the two lowest spin−orbit states |mL = ±1, mS = ∓1⟩ are not degenerate, but they are always split into two individual singlet states |j = 0⟩ = (|mL = 1, mS = − 1⟩ + |mL = − 1, mS = 1⟩)/ 2

and |j = 1, mj = 0⟩ = (|mL = 1, mS = − 1⟩ − |mL = − 1, mS = 1⟩)/ 2 K


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Inorganic Chemistry

Figure 12. Calculated orbital splitting energy (Δ) and spin−orbit splitting energy (ΔE01) in axially distorted [MnIII(CN)6]3− complexes. (a) Trigonally distorted complexes (D3d symmetry). (b) Tetragonally distorted complexes (D4h symmetry). The tetragonal distortion corresponds to the normal coordinate Q3 = 4δ/31/2 of octahedral complex. Calculations are performed in terms of the LF/AOM approach with the set of parameters listed in the text.

(corresponding to the E1(0) and E1(1) energy levels, Figures 8b and 12). The splitting energy ΔE01 = E1(1) − E1(0) remains quite pronounced even at large values of Δ. More quantitative LF/AOM calculations (involving all 3d4 states of MnIII) for axially distorted [MnIII(CN)6]3− complexes indicate that the energy separation ΔE01 does not turn to zero at any reasonable distortions of [MnIII(CN)6]3− complexes (Figure 12). It is also of note that Δ = −251 cm−1 reported in ref 21a corresponds to a large ground-state splitting, ΔE01 ≈ 100 cm−1 (Figure 12a), which is incompatible with the basic assumption of the model that the ground non-Kramers doublet |mL = ±1, mS = ∓1⟩ is degenerate. However, closer inspection of the molecular structure of hexacyanomanganate(III)-based molecular magnets reveals that the structure of [MnIII(CN)6]3− complexes is always close to octahedral and varies insignificantly from compound to compound;20a,26,31,35,39,40 eventual Jahn−Teller distortions are also weak.28 Actually, subtle departures from the octahedral Oh symmetry are too small to produce a large and negative axial orbital splitting energy Δ required for realization of the model discussed in ref 21. Detailed comparative LF calculations for these complexes20a,26,31,35,39,40 indicate that the total orbital splitting energy E(3T1g(3)) − E(3T1g(1)) of the 3T1g triplet is small (within 200 cm−1, which is less than the SOC splitting energy, >400 cm−1; see Figure 8b), and the ground spin−orbit singlet state j = 0 is always well-isolated (ΔE01 > 100 cm−1; see

Tables S3 and S9 in the Supporting Information and Figure 8b). Moreover, the orbital splitting pattern of the 3T1g states typically reveals an irregular character incompatible with the axial symmetry of the splitting term ΔLz2 (as exemplified by Tables 1 and S3 in the Supporting Information); in particular, this is the case for two [MnIII(CN)6]3− complexes involved in the [MnII(tmphen)2]3[MnIII(CN)6]2 trigonal-bipyramidal cluster,39 which have a slightly distorted octahedral structure and reveal no true trigonal symmetry required for the basic model discussed in 21. Hence, the scenario of degenerate ground nonKramers doublet |mL = ±1, mS = ∓1⟩ is highly unlikely; in fact, it refers to an imaginary limiting case of extremely large axial orbital splitting Δ that does not occur in real [MnIII(CN)6]3− complexes invariably exhibiting well-isolated singlet ground state j = 0 (see Figures 8b and 12 and Tables 1 and S3 as well as Appendix C in the Supporting Information). On the one hand, these arguments are corroborated by experimental data on magnetic properties of structurally related trinuclear Mn−M(CN)x−Mn complexes with the central orbitally degenerate cyanometalle anions, [RuIII(CN)6]3−, [OsIII(CN)6]3−,41 [MoIII(CN)7]4−,5c,38d and [MnIII(CN)6]3−.20b All linear trinuclear complexes based on [RuIII(CN)6]3−, [OsIII(CN)6]3−, and [MoIII(CN)7]4− anions with magnetically active half-integer spin (S = 1/2, ground-state Kramers doublet) exhibit SMM behavior,5c,41 while the MnII(LN3O2)−MnIII(CN)6− MnII(LN3O2) complex is a simple paramagnet;20b this difference L


Article

Inorganic Chemistry

as its strength is estimated by J = −6 cm−1. In fact, because of the relation J ≪ ΔE01, there is a special case of the weak spin coupling regime between the SA = 1 and SB = 5/2 spins in the chains of I, in which a second-order magnetic moment on MnIII appears due to mixing of the j = 1 and j = 2 excited states to the j = 0 ground state by exchange interaction (Figure S10). As a result, there arises a special effective second-order anisotropic magnetic interaction between the j = 0 singlet state of MnIII and the S = 5/2 spin of MnII, which causes an “unconventional” SCM behavior of the {[MnIII(CN)6]-MnII(dapsc)}n chains (Figure S10). In this context, it is of interest to compare SCM characteristics of I with those of other chain compounds based on [MnIII(CN)6]3− complexes. Recently, 1D compound {[(tptz)MnII(H2O)MnIII(CN)6]2MnII(H2O)2}n·4nMeOH·2nH2O (tptz = 2,4,6-tri(2-pyridyl)-1,3,5-triazine) with tapelike chains composed of [MnII(tptz)]2+ cations and [MnIII(CN)6]3− anions has been reported.20a It exhibits an SCM behavior with the effective energy barrier of Ueff/kB = 40.5 K and with the Δξ/kB = 22.3 K and Δ/kB = 18.2 K parameters, which are comparable to those in I (Ueff/kB = 40.0 K, Δξ/kB = 9.8 K, and Δ/kB = 30.2 K). Remarkably, the overall behavior of the χmT curve of this compound is similar to that shown in Figure 6; that is, it exhibits a flat minimum at 40 K and rapidly increases at low temperature.20a On the one hand, this suggests that the underlying mechanism of SCM behavior is similar for 1D compounds based on MnII ions and [MnIII(CN)6]3− complexes, irrespective of the differences in their specific composition and the local molecular structure. On the other hand, in contrast to I, cyanobridged chains [−MnIII−NC−MnIII−CN−]n composed of [MnIII(5-TMAMsalen)]3+ cations and [MnIII(CN)6]3− anions show ferromagnetic intrachain spin coupling (J = +2.8 cm−1) and display no minimum in the χmT curve;11a the microscopic origin of ferromagnetism in this compound is unclear. It is also important to note that, in contrast to magnetically isotropic [MnII(dapsc)]2+ cations in I, [MnIII(5-TMAMsalen)]3+ cations serve as an extra source of magnetic anisotropy due to the presence of negative ZFS parameter D on MnIII ions. However, despite this difference and the opposite sign of the intrachain spin coupling (ferromagnetic vs anti-ferromagnetic in I), the SCM energy parameters (Ueff/kB = 25.0 K and Δξ/kB = 7.6 K)11a of this compound are fairly consistent with those in I. Given that the ground state of [MnIII(CN)6]3− complexes is invariably a well-isolated nonmagnetic singlet state j = 0 (Figure 12 and Table S3), similar SCM parameters of these chain polymer compounds are likely due to the same microscopic mechanism associated with the weak exchange regime (J ≪ ΔE01), in which some magnetic anisotropy arises due to exchange-induced second-order mixing of the j = 0,1,2 states of [MnIII(CN)6]3− complexes (Figure 8). However, quantitative treatment of the SCM energy parameters (Ueff, Δξ, and Δ) for [MnIII(CN)6]3−-based chain compounds in terms of the intrinsic microscopic parameters (such as J, SMn(II), SMn(III)) is a complicated problem, which is beyond the scope of this paper. In summary, a single chain magnet built of alternating cyanobridged [MnII(dapsc)]2+ and [MnIII(CN)6]3− complexes has been synthesized and characterized structurally and magnetically. We have performed detailed theoretical analysis of magnetic properties and SCM behavior of I. It has been shown that prospects of [MnIII(CN)6]3− complexes as building blocks for designing SMMs and SCMs are rather limited due to antiparallel coupling of the unquenched orbital momentum L = 1 and S = 1 spin resulting in nonmagnetic ground state j = 0.

originates from a nonmagnetic ground state j = 0 of [MnIII(CN)6]3− (see Figure 11 and comments). On the other hand, the opposite point of view that at low temperatures [MnIII(CN)6]3− complexes are not involved in magnetic coupling with other spin centers due to nonmagnetic character of its ground state j = 031 is also incorrect, as evidenced by results of our magnetic calculations for I (see Figures 9b and 10 and comments). Therefore, despite the presence of unquenched first-order orbital momentum, [MnIII(CN)6]3− complex has a severe disadvantage of nonmagnetic ground state j = 0, as opposite to other orbitally degenerate cyanocomplexes, [FeIII(CN)6]3−, [MnII(CN)6]4−, [RuIII(CN)6]3−, [OsIII(CN)6]3−, [MoIII(CN)7]4−, and [ReIV(CN)7]3−, where the ground state is a magnetically active Kramers doublet. This feature is an inherent property of [MnIII(CN)6]3− resulting from the fact that the orbital momentum L = 1 and integer spin S = 1 cancel each other due to antiparallel spin−orbit coupling resulting in a well-isolated ground spin−orbit singlet j = 0. Because of general weakness of exchange interactions in cyano-bridged molecular magnets, [MnIII(CN)6]3−-based SMMs and SCMs typically fall into weak exchange regime (J ≪ ΔE01), where magnetic anisotropy of orbitally degenerate [MnIII(CN)6]3− complex manifests only as a second-order effect with respect to the SOC energy (Figure S10). The second-order character of magnetic interactions implies that only a small fraction of the magnetic anisotropy of [MnIII(CN)6]3− orbitally degenerate complexes (measured by the full spin−orbit splitting energy of the ground orbital triplet 3T2g(3d4), around 500 cm−1; see Figure 8 and Table S3) contributes to the overall molecular magnetic anisotropy of [MnIII(CN)6]3−-based SMMs and SCMs. Generally, this situation cannot be improved considerably due to large energy separation ΔE01 between the j = 0 and j = 1 spin states in regular or moderately distorted [MnIII(CN)6]3− complexes (Figure 12 and Tables 1 and S3 in the Supporting Information). This hinders prospects of [MnIII(CN)6]3− complexes for engineering high molecular magnetic anisotropy; actually, [MnIII(CN)6]3− complex is definitely not among the most promising magnetically anisotropic molecular building blocks for designing advanced SMMs/SCMs.

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CONCLUSIONS AND OUTLOOK The static and dynamic magnetic measurements reported in this paper clearly indicate an SCM behavior of the heterospin chain compound I, {[Mn(dapsc)][Mn(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O). However, detailed theoretical interpretation of SCM characteristics of I is rather difficult owing to complicated electronic structure of orbitally degenerate complexes [MnIII(CN)6]3− and unconventional character of the MnIII−CN−MnII spin coupling. Presently, theoretical knowledge on SCMs is mainly based on two models associated with the Ising and Heisenberg limits.1d Obviously, the situation with our compound I is distinctively different from these two SCM regimes. Indeed, our previous analysis indicates that the MnIII−CN−MnII spin coupling is not described in terms of the conventional spin Hamiltonian technique (employed in the isotropic Heisenberg model −JSASB and in the anisotropic Ising model −JSAzSBz) due to the absence of spin degeneracy of the well-isolated j = 0 ground state of [MnIII(CN)6]3− complexes. To a first approximation, magnetic moment of [MnIII(CN)6]3− is absent at low temperatures due to a large energy gap ΔE01. At the same time, our results indicate that spin coupling between MnIII and MnII ions in I cannot be ignored (Figures 9b and 10), M


Article

Inorganic Chemistry To the best of our knowledge, I represents the first example of SCM based on planar pentagonal complexes of the dapsc ligand. Our results demonstrate that planar pentagonal structure of M(dapsc) complexes is favorable for designing chains, especially in combination with specially selected bridging anionic complexes, such as cyanometallates. Although [MnII(dapsc)]2+ complex in I is magnetically isotropic (due to spin-only nature of the ground 6A1 state of MnII), the use of M(dapsc) complexes with other 3d transition-metal ions (M = TiIII, CrIII, FeII, CoII, and NiII) can create strong singleion magnetic anisotropy imposed by pentagonal coordination of dapsc and related macrocyclic ligands.14−16 Currently, we have synthesized a few more new 1D coordination polymers derived from the M(dapsc) complexes and hexacyanometallates: {[Mn(dapsc)][Fe(CN)6][K(H2O)5]]}n, {[M(dapsc)][Cr(CN)6][K(H2O)3.75C2H5OH)0.5]}n, M = Mn, Co, and lanthanide complex {[Ho(dapsc)(H2O)2][M(CN)6]}n· 3n(H2O), M = Cr, Fe. Thus, the M(dapsc) building blocks really provide a versatile route to a wide variety of 3d−3d and 4f−3d 1D chains. The study of their structure and magnetic properties is underway.

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{[Mn(dapsc)][Mn(CN)6][K(H2O)2(MeOH)2]}n (II). To prepare the crystals of II, the reaction between [Mn(dapsc)Cl2]·H2O and K3[Mn(CN)6] was performed in H-shaped tubes. One compartment of the H-tube was filled with solution of [Mn(dapsc)Cl2]·H2O (0.071 mmol in 10 mL of CH3OH + 3.0 mL of H2O), and the second compartment was filled with solution of K3[Mn(CN)6] (0.071 mmol in 3 mL of H2O). The tube was filled with methanol and left to stand undisturbed in a refrigerator. In two weeks, the crystals grew on the walls of the tube. The crystals for X-ray analysis were kept in contact with the mother liquid. XRPD patterns of the dried samples of the complex II are in rather poor agreement with simulated pattern calculated from single-crystal diffraction data for II. Therefore, the magnetic properties of polycrystalline samples of II were not studied. Physical Measurements. Analyses of C, H, and N were performed on a vario MICRO cube analyzing device. Infrared spectra (500−4000 cm−1) were recorded using a Varian 3100 FTIR Excalibur Series spectrometer. The thermogravimetric analysis was performed in argon atmosphere with a heating rate of 5.0 °C min−1 using a NETZSCH STA 409 C Luxx thermal analyzer, interfaced to a QMS 403 Aelos mass spectrometer, which allows simultaneous thermogravimetry (TG), differential scanning calorimetry (DSC), and massspectrometry measurements. The DC and AC magnetic susceptibility of powder samples I was measured by a Quantum Design MPMS-5 SQUID magnetometer. The experimental data were corrected for the sample holder and for the diamagnetic contribution calculated from Pascal constants. Effective magnetic moment was calculated using the equation μeff = 2.828(χM × T)1/2. X-ray Crystallography. X-ray single-crystal diffraction data were collected at low temperatures on an Oxford Diffraction Gemini-R CCD diffractometer equipped with an Oxford cryostream cooler [λ(Mo Kα) = 0.710 73 Å, graphite monochromator, ω-scans]. Single crystals were taken from the mother liquid using a nylon loop with paratone oil and immediately transferred into cold nitrogen stream of the diffractometer. Data reduction with empirical absorption correction of experimental intensities (Scale3AbsPack program) was made with the CrysAlisPro software.42 The structures were solved by direct method and refined by a full-matrix least squares method using SHELX97 program.43 All non-hydrogen atoms were refined anysotropically. The positions of H atoms were calculated geometrically and refined in a riding model with isotropic displacement parameters depending on Ueq of connected atom. Torsion angles for CH3 hydrogens were refined using HFIX137. The hydrogen atoms bonded to oxygen of solvent water and methanol molecules were found from difference Fourier map and refined isotropically with Uiso(H) = 1.5Ueq(O); additional geometrical restraints (SADI/DFIX) were applied for H−O bonds in H2O. For disordered methanol and water molecules in I with occupancy of 0.5 or less hydrogen atoms were not found. Main crystal data and the X-ray data collection and refinement statistics are listed in Table S1 in the Supporting Information.

EXPERIMENTAL SECTION

Synthesis and Preparation of the Single Crystals. {[Mn(dapsc)][Mn(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O) (I). Method A. The crystals of I were obtained by slow diffusion of water solution of K3[Mn(CN)6] (23 mg, 0.07 mmol in 3 mL) through frit with a pore diameter of 10−20 μm into water−alcohol (H2O/CH3OH = 1:2) solution [Mn(dapsc)Cl2]·H2O18j (29.5 mg, 0.07 mmol in 7 mL) for a day at 8−10 °C. K3[Mn(CN)6] decomposes gradually on dissolving in water at room temperature with formation of a flaky product. The diffusion of the K3[Mn(CN)6] solution through dense frit into [Mn(dapsc)Cl2]·H2O solution allows to prevent contamination of reaction product by products of K3[Mn(CN)6] decomposition. The resulting crystals were filtered, washed with methanol, and dried in vacuum. Yield: 0.023 g (51%). Anal. found: C, 32.27%; H, 3.39%; N, 28.68%. Calc. for [Mn(dapsc)][Mn(CN) 6 ][K(H 2 O) 2 . 7 5 ]} n (C17H20.5KMn2N13O4.75): C, 32.31%; H, 3.27%; N, 28.81%. Characteristic IR data (cm−1): (νC≡N), 2149, 2120, 2111; (νC=N), 1661 (imine). The crystals for X-ray analysis were kept in contact with the mother liquid, since they easily lose the coordinate methanol (0.5 mol) and solvent water (0.5 mol) during drying in accordance with the data of elemental and thermogravimetric analyses. The thermogram of the complex after drying in vacuum demonstrates a mass loss of 8.4% in the temperature range of 90−150 °C with endothermic peak at 121.6 °C, which corresponds to the loss of coordinate water molecules (2.75 H2O, 7.83%; Figure S1 in the Supporting Information). In the mass spectrum recorded in the gas phase, the peaks are observed at m/z 18 and 17 from H2O molecules, while the peaks at m/z 15, 29, 30, and 31 relating to the fragments of methanol molecule (CH3: m/z = 15; CHO: m/z = 29; CH2O: m/z = 30; CH3O: m/z = 31) are not observed. The decomposition of complex starts above 150 °C (DSCpeak at 232.9 °C) and accompanies by the release of CN-fragments (m/z = 26). X-ray powder diffraction (XRPD) patterns of the dried samples of the complex I were compared with simulated pattern calculated from single-crystal diffraction data (Figure S2 in the Supporting Information). It has been found that the complex preserves crystallinity after drying and gives an XRPD pattern that is very similar to that of the simulated one for the single crystal of I. Method B. The complex I was also obtained by the classical one-pot synthesis: to a stirred water (6.0 mL)−methanol (11 mL) solution of [Mn(dapsc)Cl2]·H2O (46 mg, 0.11 mmol) was added solid K3[Mn(CN)6] (36 mg, 0.11 mmol). The initial K3[Mn(CN)6] quickly dissolves, and the solution takes on orange color. After it was stirred for ∼30 min, the mixture was kept in the refrigerator for a day. The resulting precipitate was filtered, washed with water and methanol, and dried in vacuum. Yield: 0.033 g (47%). The polycrystalline samples of I obtained by methods A and B were identical.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00676. Supplementary tables, structure figures, some magnetic data, additional theoretical analysis of magnetic behavior. CCDC 1448515 (I) and 1426621 (II) (PDF) Accession Codes

CCDC 1426621 and 1448515 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. N


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Inorganic Chemistry

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: *E-mail: *E-mail: *E-mail:

[email protected]. (V.A.K.) [email protected]. (L.V.Z.) [email protected]. (V.S.M.) [email protected]. (E.B.Y.)

ORCID

Vyacheslav A. Kopotkov: 0000-0002-7654-232X Author Contributions

All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Program No. 1 of the Presidium of Russian Academy of Sciences and partially supported by the RFBR Grant No. 15-03-07904-a.

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Inorganic Chemistry

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Magnetic Properties of {[MnII(tmphen)2]3[MnIII(CN)6]2}. Angew. Chem., Int. Ed. 2003, 42, 1523−1526. (40) (a) Figgis, B. N.; Sobolev, A. N.; Kucharski, E. S.; Broughton, V. Cs2K[Mn(CN)6] at 293, 85 and 10K. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2000, 56, 735−737. (b) Vannerberg, N. G.; et al. The OD-Structure of K3Mn(CN)6. Acta Chem. Scand. 1970, 24, 2335− 2348. (41) Dreiser, J.; Pedersen, K. S.; Schnegg, A.; Holldack, K.; Nehrkorn, J.; Sigrist, M.; Tregenna-Piggott, P.; Mutka, H.; Weihe, H.; Mironov, V. S.; Bendix, J.; Waldmann, O. Three-Axis Anisotropic Exchange Coupling in the Single-Molecule Magnets NEt4[MnIII2(5Brsalen)2(MeOH)2MIII(CN)6] (M = Ru, Os). Chem. - Eur. J. 2013, 19, 3693−3701. (42) CrysAlisPro, Version 1.171.33; Oxford Diffraction Ltd: Oxford, UK, 2010. (43) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122.

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Synthesis, Structure, and Magnetic Properties of 1D {[MnIII(CN)6][MnII

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