or Mer-tricyanidoferrate building blocks: Syntheses, crystal structures and magnetic properties

Polyhedron 85 (2015) 457–466

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Low dimensional magnetic assemblies based on MnIII(Schiff base) and/or Mer-tricyanidoferrate building blocks: Syntheses, crystal structures and magnetic properties Hongbo Zhou a, Yingying Wang a, Fangyou Mou a, Xiaoping Shen a,⇑, Yashu Liu b a b

School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China

a r t i c l e

i n f o

Article history: Received 16 July 2014 Accepted 7 September 2014 Available online 18 September 2014 Keywords: MnIII(Schiff base) Cyanometalate Tricyanidoferrate Supramolecular Magnetism

a b s t r a c t Four new MnIII(Schiff base) and/or [FeIII(L)(CN)3] (L = mpzcq, qcq) based complexes, PPh4[FeIII(mqzcq) (CN)3]4H2O (1), {[MnIII(5-CH3O-salen)(H2O)]2[FeIII(mqzcq)(CN)3]2}2H2O (2), {[MnIII(5-CH3-salen)] [FeIII(mqzcq)(CN)3]}H2OCH3CN (3) and {[MnIII(4-CH3O-salcy)] [FeIII(qcq)(CN)3]}2CH3CN (4) (mqzcq = 8-(5-methylpyrazine-2-carboxamido)quinoline; qcq = 8-(2-quinoline-2-carboxamido)quinoline; salen = N,N0 -ethylenebis(salicylideneiminato) dianion; salcy = N,N0 -(1,2-cyclohexanediylethylene)bis(salicylideneiminate) were synthesized and characterized structurally and magnetically. The results reveal that 1 and 2 are discrete 0-D structures while 3 and 4 are 1-D zigzag neutral chains. Notably, the out-of-plane III  are both presented in 2 with the Mn2 dimer, {[MnIII(5-CH3O-salen)(H2O)]2+ 2 and [Fe (mpzcq)(CN)3] Mn2 dimer being further organized into 1-D supramolecular chain arrangement via hydrogen bonds interactions. Magnetic investigation indicates that weak intradimer ferromagnetic coupling exists in 2 while dominant intrachain antiferromagnetic couplings in 3 and 4. Moreover, slow magnetic relaxations were also observed for 2 and 3. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Nanosize magnetic materials (for example: single-molecule magnets (SMMs) and single-chain magnets (SCMs)) derived from coordination complexes have been attracting people’s attention since the 1990s [1]. The researchers’ great enthusiasm has been fueled by the quest for new nanosize magnetic materials with enhanced properties and the quest for deeper understanding of the magneto-structural correlation [2]. In this field, several groups including us have been focusing on investigating the magnetic systems based on MnIII(Schiff base) (Scheme 1) because of the large ground state spin (ST) and strong anisotropy of MnIII ions as well as the flexibility in tuning the structural fashions and magnetism in these systems [2–11]. For MnIII(Schiff base) cations, the mononuclear [MnIII(Schiff-base)]+ 2+ and out-of-plane dimer of [MnIII (Hereinafter refer 2 (Schiff-base)2] to as Mn2 dimer) are in equilibrium in the solution [3g], and the latter forms are often of great interest because they can show SMM properties with the ST = 4 ground state [3a,5c]. Notably, Miyasaka and co-workers firstly introduced such dimers into the 1-D assemblies using hexacyanometalates building blocks and successfully ⇑ Corresponding author. Fax: +86 511 8879180. E-mail address: [email protected] (X. Shen). http://dx.doi.org/10.1016/j.poly.2014.09.003 0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

constructed a SCM, (NEt4)[Mn2(5-MeO-salen)2Fe(CN)6] [4c]. Then they reported another example of 1-D supramolecular organization of the Mn2 dimers with an intermediate behavior between SMM and SCM properties [5d]. However, the Mn2 dimers are often easily dissociated into mononuclear form of [MnIII(Schiff-base)]+ during the synthesis process [3g,3l–n]. In most cases, the complexes consisting of Mn2 dimers are obtained by chance rather than by a clear strategy. The experimental facts indicate that the structural fashions of these complexes are influenced by a combination of factors from Schiff-base ligands and the electron donors as well as the reaction microenvironment. For the electron donors, hexacyanometalates are the most famous and these building blocks have recently evolved into the so-called modified hexacyanometalates [(L)M(CN)p]q (M = Fe, Cr; etc. L = blocking group), which have contributed to a large number of magnetic complexes till now [3c,3e,6e,7g, 9d,9e,12–14]. The introducing of organic ligands into the cyanometalates facilitates researchers to fine tune the architectures and topologies of the complexes. More importantly, the modified hexacyanometalates can possibly enhance the magnetic anisotropy in comparison to the pristine hexacyanometalates. In this work, the building block of [FeIII(L)(CN)3] (L = mqzcq, qcq; mqzcq = 8-(5-methylpyra-zine-2-carboxamido)quinoline; qcq = 8-(2-quinoline-2-carboxamido)quinoline) was used instead of [Fe(CN)6]3 to assemble with MnIII(Schiff-base) cations. The

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[Fe(CN)6]3 was replaced by mer-[FeIII(L)(CN)3] because the latter could facilitate tuning the ligand field and magnetic orbits around FeIII ion, which further influence the versatility for reactivity and availability of structures. Furthermore, the blocking groups introduced on FeIII could also affect the intermolecular short contacts which are proved to be important factors for final magnetic properties. The experimental goal is to connect the Mn2 dimers into 1-D chain arrangement through [FeIII(L)(CN)3] anions so that enhanced SCM properties can be expected. Unfortunately, we failed to obtain the target complex but got four new [FeIII(L)(CN)3] based magnetic complexes, PPh4[FeIII(mqzcq)(CN)3]4H2O (1), {[MnIII(5-CH3O-salen) (H2O)]2[FeIII(mqzcq)(CN)3]2}2H2O (2), {[MnIII(5-CH3-salen)] [FeIII(mqzcq)(CN)3]}H2OCH3CN (3), {[MnIII(4-CH3O-salcy)][FeIII(qcq) (CN)3]}2CH3CN (4) (salen = N,N0 -ethylenebis(salicylideneiminato) dianion; salcy = N,N0 -(1,2-cyclohexanediylethylene)bis(salicylideneiminate). Interestingly, the Mn2 dimer of {[MnIII(5-CH3O-salen) III  (H2O)]2+ 2 and [Fe (mpzcq)(CN)3] are both presented in 2 with the Mn2 dimer being further organized into 1-D supramolecular chain arrangement via hydrogen bond interactions. So, complex 2 can be regarded as another example of 1-D supramolecular organization of Mn2 dimers. Different from 2, complexes 3 and 4 show 1-D zigzag chain arrangements, which imply the mononuclear forms of [MnIII(5-CH3-salen)]+ and [MnIII(4-CH3O-salcy)]+ dominate in a competitive situation and induce the reaction routes from supramolecular organized Mn2 dimers to zigzag bimetallic chains. Herein, we report the syntheses, crystal structures and magnetic properties of these four complexes. 2. Experimental 2.1. Reagents and materials All chemicals and solvents are commercial available and used as received without further purification. The reaction precursors of K[FeIII(mqzcq)(CN)3]H2O, PPh4[FeIII(mqzcq)(CN)3]H2O [7b], PPh4[FeIII(qcq)(CN)3]H2O [3h], [MnIII(5-CH3-salen)(H2O)]ClO4, [MnIII(5-CH3O-salen)(H2O)]ClO4 and [MnIII(4-CH3O-salcy)(H2O)] ClO4 [15], were synthesized according to the literatures. Caution! Cyanides are very toxic and perchlorate salts of metal complexes are potentially explosive. So it is highly suggested to hand them carefully with small quantities for the safety consideration. 2.2. Synthesis 2.2.1. PPh4[FeIII(mqzcq)(CN)3]4H2O (1) A methanol solution (10 mL) of PPh4[FeIII(mqzcq)(CN)3]H2O (0.1 mmol) was slowly added to an aqueous solution (10 mL) of

La(NO3)36H2O (0.033 mmol). The resulting solution was filtered and the filtrate was left to allow slow evaporation in dark at room temperature. Black block crystals of complex 1 were formed in 2 weeks, which were washed with methanol and water, respectively, and dried in air. Anal. Calc. for C42H39FeN7O5P: C, 62.38; H, 4.86; N, 12.13. Found: C, 62.45; H, 4.83; N, 12.18%. IR: mmax/cm1: 3475(m), 3050(w), 2118(m), 1637(s), 1535 (m), 1502 (m), 1463(m), 1130(m), 762(m). 2.2.2. {[MnIII(5-CH3O-salen)(H2O)]2[FeIII(mqzcq)(CN)3]2}2H2O (2) An aqueous solution (10 mL) of K[FeIII(mqzcq)(CN)3]H2O (0.05 mmol) was slowly added to a methanol solution (10 mL) of [MnIII(5-CH3O-salen)(H2O)]ClO4 (0.05 mmol). The resulting solution was filtered and the filtrate was left to allow slow evaporation in dark at room temperature. Black rod crystals of complex 2 were formed in 2 weeks, which were washed with methanol and water, respectively, and dried in air. Anal. Calc. for C72H66Fe2Mn2N18O14: C, 53.09; H, 4.08; N, 15.48. Found: C, 53.29; H, 4.33; N, 15.27%. IR: mmax/cm1 3416(s), 2120(m), 1623(s), 1542(m), 1504(w), 1463(m), 1436(m), 1384(m), 1342(m), 1284(s), 1220(m), 808(w), 723(m). 2.2.3. {[MnIII(5-CH3-salen)][FeIII(mqzcq)(CN)3]}H2OCH3CN (3) An aqueous solution (10 mL) of K[FeIII(mqzcq)(CN)3]H2O (0.05 mmol) was slowly added to a acetonitrile solution (10 mL) of [MnIII(5-CH3-salen)(H2O)]ClO4 (0.05 mmol). The resulting solution was filtered and the filtrate was left to allow slow evaporation in dark at room temperature. Black block crystals of complex 3 were formed in 2 weeks, which were washed with acetonitrile and water, respectively, and dried in air. Anal. Calc. for C38H34FeMnN10O4: C, 56.66; H, 4.25; N, 17.39. Found: C, 56.35; H, 4.42; N, 17.25%. IR: mmax/cm1 3418(s), 2134(m), 2119(m), 1618(s), 1550(m), 1504(m), 1463(m), 1438(m), 1388(m), 1309(m), 1249(m), 1220(m), 848(w), 734(m). 2.2.4. {[MnIII(4-CH3O-salcy)][FeIII(qcq)(CN)3]}2CH3CN (4) A methanol solution (10 mL) of PPh4[FeIII(qcq)(CN)3]H2O (0.05 mmol) was slowly added to a acetonitrile solution (10 mL) of [MnIII(4-CH3O-salcy)(H2O)]ClO4 (0.05 mmol), then an aqueous solution (10 mL) of Pr(NO3)36H2O (0.033 mmol) was added into the mixture. The resulting solution was filtered and the filtrate was left to allow slow evaporation in dark at room temperature. Black block crystals of complex 4 were formed in 2 weeks, which were washed with methanol/ acetonitrile and water, respectively, and dried in air. Anal. Calc for C48H42FeMnN10O5: C, 60.71; H, 4.46; N, 14.75. Found: C, 60.55; H, 4.52; N, 14.35%. IR:

O

O

[MnIII(5-CH3-salen)]+

[MnIII(5-CH3O-salen)]+

[MnIII(4-CH3O-salcy)]+ O

O

N

CNN

O Mn N N

O

H3CO

O Mn N N

O

O Mn N N

O

N

N

N Fe CN CN

[FeIII(mpzcq)(CN)3]-

N

CNN

Fe CN

CN

[FeIII(qcq)(CN)3]-

Scheme 1. MnIII(Schiff-base) cations and [FeIII(L)(CN)3] anions used in this work.

OCH3

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mmax/cm1 3420(m), 2140(m), 2120(m), 1630(s), 1530(m), 1510(m), 1460(m), 1390(s), 1340(m), 1210(m), 850(m), 729(m).

summarized in Table 1, and selected bond lengths and angles are listed in Table 2. 3. Results and discussion

2.3. Physical measurement Elemental analyses for C, H and N were conducted at a Perkin– Elmer 240C analyzer. Infrared spectra were measured on KBr pellets with a Nicolet FT-170SX spectrometer in the range from 4000 to 400 cm1. Magnetic susceptibility of the microcrystalline samples was measured with the use of a Quantum Design SQUID magnetometer (MPMP-XL7). Direct current (dc) measurements were performed from 300 to 1.8 K and from 0 to 70 kOe applied dc fields. The alternating current (ac) susceptibility measurements were carried out at frequencies ranging from 1 to 1500 Hz with an ac field amplitude of 3 Oe with no dc field applied. Susceptibilities were corrected considering sample holder as the background and the diamagnetic contribution calculated from Pascal constants according to Pascal’s tables [16]. 2.4. X-ray structure determination Single crystal X-ray crystallographic data were collected on a Bruker SMART APEX CCD detector diffractometer with graphitemonochromated Mo Ka radiation (k = 0.71073 Å). Diffraction data analysis and reduction were carried out with SMART, SAINT and XPREP [17]. The structures were solved by direct methods and refined by a full-matrix least-squares method based on F2 using the SHELXL crystallographic software package [18]. All the non-hydrogen atoms were refined anisotropically, whereas hydrogen atoms except the water–H atoms were calculated at idealized positions as fixed contributors. H atoms on water molecules were located from the residual peaks and included in the refinement with isotropic thermal parameters derived from the parent atoms. For complex 4, the group of 1,2-diaminocyclohexane is slightly disordered and the C39 atom is unequally disordered over two sites (C39, C390 ). Thus, the H atoms at the adjacent C40, C41 sites were similarly modeled as disorder and appear as two pairs of partial-occupancy H atoms. Crystallographic data for 1–4 are

3.1. Synthesis and characterization The complex of PPh4[FeIII(mqzcq)(CN)3]H2O (1a) was firstly synthesized by Hong group and the crystal structure was then determined [7b]. Surprisingly, the PPh+4 and [FeIII(mqzcq)(CN)3] could be crystallized in two different forms, as shown by Scheme 2a. Our purpose of introducing La(NO3)36H2O into the system is to construct a 3d–4f complex, and unexpectedly the lanthanide metal ion does not appear in the final product but induce the formation of complex 1. Moreover, we also failed to obtain 1 with routine recrystallization method if the La(NO3)36H2O was not added into the solution. So, it is believed that the PPh+4 and [FeIII(mqzcq)(CN)3] could be crystallized in two or even more different forms depending on the crystallization environment. Complex 2 and 3 were both prepared by direct reaction of K[FeIII(mqzcq)(CN)3]H2O and MnIII(Schiff base) cations using the mixed solvent of methanol/water or acetonitrile/water. However, they show quite different molecular structures, as shown in Scheme 2b. Such differences in structural arrangement reveal the subtle balance of mononuclear [MnIII(Schiff-base)]+ cation and out-of-plane Mn2 dimer that are potentially affected by a combination of factors such as coordination field, electron effect, solvent polarity and so on. For 4, we failed to prepare the suitable single crystals when using the similar procedure with the syntheses of 2 and 3. Being inspired by the synthesis method used for complex 1, the lanthanide metal salt was then added, and the single crystals of 4 were formed. The mechanism is not clear yet. The infrared spectra of 1–4 all show the characteristic m(CN) bands in the range from 2110 to 2140 cm1. For 3 and 4, two m(CN) stretching peaks at 2134 and 2119 cm1 for 3, 2140 and 2120 cm1 for 4 correspond to the bridging and terminal cyanide groups, respectively [19]. Other characteristic absorption bands in the infrared spectra of 1–4 are also in agreement with their structures determined by X-ray diffraction.

Table 1 Details of the crystal data and structural refinement parameters of 1–4.

Formula M (g mol1) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V(Å3) Z dcalc (g cm3) F(0 0 0) Reflections collected Observed reflections Independent reflections Rint Data/restraints/parameter Goodness-of-fit (GOF)c on F2 R1a (I > 2 r(I)) wR2b(all data) a b c

1

2

3

4

C42H39FeN7O5P 808.62 monoclinic P21/c 15.654(3) 13.622(3) 18.605(4) 90.00 104.18(3) 90.00 3846.4(14) 4 1.396 1684 16 438 6779 4880 0.0560 6779/6/506 1.035 0.0761 0.1445

C72H66Fe2Mn2N18O14 1629.01 monoclinic C2/c 29.730(2) 17.168(3) 14.363(2) 90.00 108.49(3) 90.00 6953(2) 4 1.556 3352 26 416 6795 5417 0.0326 6795/0/494 1.009 0.0345 0.0763

C38H34FeMnN10O4 805.54 orthorhombic P212121 12.175(3) 13.545(2) 22.344(3) 90.00 90.00 90.00 3684.8(12) 4 1.452 1660 27 320 7070 6835 0.0233 6835/0/491 1.006 0.0248 0.0589

C48H42FeMnN10O5 949.71 monoclinic P21/c 18.065(4) 15.139(3) 16.363(3) 90.00 93.25(3) 90.00 4467.9(15) 4 1.412 1964 19 977 7703 5899 0.0460 5899/15/599 1.078 0.0744 0.1669

P R1 = = Fo|  |Fc||/66Fo|. wR2 = [Rw(F2o  F2c )2/Rw(F2o)2]1/2; w = 1/r2(|Fo|). Goodness of fit: GOF = [Ow(F2o  F2c )2/(n  p)]1/2, where n is the number of reflections and p is the number of parameters.

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Table 2 Selected bond lengths (Å) and angles (°) for 1–4. 1 C1–Fe1 C2–Fe1 C3–Fe1 Fe1–N5 Fe1–N4 Fe1–N6 N1–C1–Fe1 N2–C2–Fe1 N3–C3–Fe1

2 1.938(5) 1.967(5) 1.962(5) 1.855(4) 1.946(4) 1.982(4) 177.5(5) 176.3(5) 177.0(5)

C1–Fe1 C2–Fe1 C3–Fe1 Fe1–N14 Fe1–N15 Fe1–N13 Mn1–O3 Mn1–O4 Mn1–N18 Mn1–N17 Mn1–O2 Mn1–O4#1 N10–C1–Fe1 N11–C2–Fe1 N12–C3–Fe1

3 1.962(3) 1.949(3) 1.959(3) 1.895(2) 1.958(2) 1.977(2) 1.872(2) 1.887(2) 1.972(2) 1.980(2) 2.159(2) 2.469(2) 178.1(2) 175.1(2) 176.6(2)

4

C1–Fe1 C2–Fe1 C3–Fe1 Fe1–N4 Fe1–N5 Fe1–N3 Mn1–O3 Mn1–O2 Mn1–N7 Mn1–N8 Mn1–N9 Mn1–N1 N1–C1–Fe1 N2–C2–Fe1 N9#2–C3–Fe1 C1–N1–Mn1– C3#3–N9–Mn1

1.952(2) 1.961(2) 1.965(2) 1.886(2) 1.945(2) 1.965(2) 1.891(2) 1.891(2) 1.988(3) 1.989(3) 2.280(2) 2.323(3) 177.0(2) 175.7(2) 175.9(2) 148.7(2) 151.3(2)

C1–Fe1 C2–Fe1 C3–Fe1 Fe1–N5 Fe1–N6 Fe1–N4 Mn1–O2 Mn1–O1 Mn1–N7 Mn1–N8 Mn1–N3#4 Mn1–N1 N1–C1–Fe1 N2–C2–Fe1 N3–C3–Fe1 C1–N1–Mn1 C3–N3–Mn1#5

1.940(6) 1.953(5) 1.950(5) 1.886(4) 2.005(4) 2.028(4) 1.884(3) 1.884(3) 1.975(4) 1.989(4) 2.265(4) 2.343(4) 174.0(4) 176.6(5) 173.9(5) 151.2(4) 158.2(4)

Symmetry transformations used to generate equivalent atoms: #1: 2  x, 1  y, 1 – z; #2: 0.5 + x, 0.5  y, 2 – z; #3: 0.5 + x, 0.5  y, 2 – z; #4: x, 0.5  y, 0.5 + z; #5: x, 0.5  y, 0.5 + z.

(a)

PPh4+

[FeIII(mqzcq)(CN)3]-

(b) [MnIII(5-CH3O-salen)]+

methanol/ether

PPh4[FeIII(mqzcq)(CN)3]·H2 O (1a) (Space group C2/c)

methanol/water PPh4[FeIII(mqzcq)(CN)3]·4H2 O (1) (Space group P21/c) LaNO3·6H2O

methanol [FeIII(mpzcq)(CN)3]-

water 1-D supramolecular organization

[MnIII(5-CH3-salen)]+

acetonitrile water 1-D zigzag chain

Scheme 2. (a) The two different crystallized forms for PPh+4 and [FeIII(mqzcq)(CN)3]; (b) the different structural styles for the complexes derived from the reaction of [MnIII(Schiff-base)]+ cations and [FeIII(L)(CN)3] anions. (The black and white balls represent the [MnIII(Schiff-base)]+ cation and [FeIII(L)(CN)3] anion, respectively.)

3.2. Crystal structures of 1–4 The important bond distances and angles of 1–4 are listed in Table 2. The crystal structures are shown in Figs. 1 and 2. The packing structures of the four complexes are depicted in Figs. S1–S4 in Supplementary data. Complex 1 (Fig. 1a) crystallized in P21/c space group and the asymmetric unit is composed of one [FeIII(mqzcq)(CN)3] anion, one PPh+4 cation and four lattice water molecules. As mentioned in the syntheses and characterization section, complex 1 is a new crystalline form (P21/c) of PPh+4 and [FeIII(mqzcq)(CN)3] in comparison to the previously reported complex 1a (C2/c) [7a]. For the [FeIII(mqzcq)(CN)3] unit, the center FeIII ion is coordinated by three N atoms from the tridentate ligand of mqzcq and three C atoms from three terminal CN group, affording the distorted octahedron geometry. The Fe–C and0 Fe–N bond lengths are0 in the range of 1.938(5)–1.967(5) Å A and 1.855(4)–1.982(4) Å A, respectively. The shorter bond distance of 0 0 Fe–N5 (amide) [1.855(4) Å A] than Fe–N4/N6 [1.946(4), 1.982(4) Å A] are typical of this class of complexes [3h,7a,8c]. As shown by most cyanometalates, the Fe–C„N angles are nearly linear with the values falling in the narrow region of 176.3(5)–177.5(5)°. The main

differences between 1 and 1a are their packing structures. For 1, the [FeIII(mqzcq)(CN)3] anions contact with each other via p–p stacking inducing the formation of 2-D supramolecular network, where the PPh+4 cations are well located between the layers, as shown in Fig. S1. In contrast to 1, the PPh+4 and [FeIII(mqzcq)(CN)3] in 1a are both included in the formed layers in which p–p stacking contacts between PPh+4 and [FeIII(mqzcq)(CN)3] are found. The shortest intra- and interlayer metal–metal distances of 1 are 0 6.566 and 15.04 Å A, respectively. Complex 2 (Fig. 1b) can be described as ion-pair structure and the molecular unit is composed of one [MnIII(5-CH3O-salen) III  (H2O)]2+ 2 dimer, two free [Fe (mqzcq)(CN)3] anions and two lattice water molecules. From the magnetic point of view, the Mn2 dimers often behave as an important structural unit in various MnIII(Schiff base) based compounds, and Miyasaka et al. have firstly systematically studied them and called them as out-of-plane Mn2 dimers [3a,3i,5c]. In previous relevant works, the out-of-plane Mn2 dimers have been isolated or included in the assembly with cyanometalate anions, affording a series of low dimensional systems [3j,3k,8b]. However, to the best of our knowledge, such structural style of 2 in which the out-of-plane Mn2 dimers and the free uncoordinated

H. Zhou et al. / Polyhedron 85 (2015) 457–466

461

Fig. 1. ORTEP (30%) diagrams of molecular structures with selected atom-labeling schemes for 1 (a), 2 (b), 3(c) and 4 (d). Hydrogen atoms and crystallized solvent molecules are omitted for clarity.

[FeIII(L)(CN)3] anions are coexisted in one system is still no report. The structural characteristic of [FeIII(mqzcq)(CN)3] anion in 2 is quite comparable to that in complex 1. For the out-of-plane [MnIII(5-CH3O-salen)(H2O)]2+ 2 dimer, it lies on an inversion center and thus only one MnIII site that assumes an six-coordination geometry is found in the asymmetric unit. The MnIII center is surrounded by N2O2 atoms from the Schiff base ligand of [5-CH3O-salen]2 in the equatorial plane and two axial oxygen atoms, O2 and O4#1 (#1: 2  x, 1  y, 1  z), from the coordinated water molecule and the neighboring [MnIII(5-CH3O-salen)(H2O)]+ moiety, respectively. The two [MnIII(5-CH3O-salen)(H2O)]+ moieties are then well combined together through the axial connection of each MnIII center with the phenolate oxygen atoms (O4, O4#1) (#1: 2  x, 1  y, 1  z) from the neighboring Schiff base ligands and lead to the centrosymmetric dinuclear Mn2 entity. Due to the Jahn–Teller effect, the two MnIII centers both adopt an axialelongated octahedral geometry with axial Mn–O bond lengths 0 [2.159(2)–2.469(2) Å A0 ] longer than the equatorial Mn–N/O distances [1.872(2)–1.980(2) Å A]. Interestingly, the formed out-of-plane dimmers of [MnIII(5-CH3O-salen)(H2O)]2+ 2 are further organized into 1-D supramolecular chain arrangement (Mn2)n along c axis via the hydrogen bond interaction, as shown in Fig. 2a. For the packing structure of 2, the [FeIII(mqzcq)(CN)3] anions are well arranged into the anion layers through p–p stacking interactions, and then each formed 1-D supramolecular chain of (Mn2)n is parallelly located between the anion layers, as shown in Fig. S2. Complexes 3 and 4 (Fig. 1c, d) show similar zigzag chain styles and so they are discussed together. The two complexes crystallized in P212121 and P21/c space group, respectively. In their structures, the [MnIII(Schiff base)]+ cation and [FeIII(L)(CN)3] anion are alternately linked into 1-D neutral zigzag chain via the cyanide bridges. Within the chain, each [FeIII(L)(CN)3] anions coordinate axially to two MnIII(Schiff-base) cations in cis-mode, while each of MnIII(Schiff-base) cations links to two [FeIII(L)(CN)3] anions in trans-mode. For the [FeIII(L)(CN)3] moiety, the structural

parameters are also quite similar to those of the uncoordinated free [FeIII(L)(CN)3] anions described in complexes 1 and 2. For the [MnIII(Schiff base)]+ part, the MnIII ion locates in the center of highly elongated octahedron (Jahn–Teller effect) with the equatorial plane occupied by four N2O2 donor atoms [Mn–N/O distances 0 ranging from 1.884(3) to 1.989(4) Å A/O distathe Schiff base ligand and apical positions coordinated by two N atoms [Mn–Ncyanide dis0 tances ranging from 2.265(4) to 2.343(4) Å A] from the cyanide groups of two neighboring [FeIII(L)(CN)3] units. For the bond angle aspect, \Mn–N–Ccyanide in the bridging pathways are equal to 148.7(2)° and 151.32(2)° for 3, 151.2(4)° and 158.2(4)° for 4, respectively. These angles deviate significantly from the linearity and the values fall in the range expected for typical FeIII–CN–MnIII systems [8c,9e,14a,14c]. Furthermore, the chain styles of 3 and 4 are quite different, which may be related to the presence or absence of 1,2-diaminocyclohexaneon group on the Schiff base ligands, that might affect geometric features of the chains. The shortest intrachain metal–metal distance is 5.205 Å for 3 and 5.244 Å for 4, respectively. For the extended structures of 3 and 4 (Figs. S3 and S4), the zigzag chains stack parallelly through the p–p interaction between the aromatic ring on [FeIII(L)(CN)3], leading to the formation of 3-D supramolecular networks, where the solvent molecules are located in the formed channels along a or b axis. In this way, the shortest interchain metal  metal distances are 8.529 Å for 3 and 8.715 Å for 4, respectively. 3.3. Magnetic properties The magnetic susceptibilities data of 1–4 were collected at 2 kOe in the temperature range of 1.8–300 K and plotted as the thermal dependence for the vMT products. The field dependence of magnetizations of 2–4 was measured up to 70 kOe at 1.8 K. For complex 1 (Fig. S5), the room-temperature vMT value is 0.53 cm3 K mol1, which is higher than the spin only value [0.375 cm3 K mol1] for a isolated FeIII (s = 1/2) ions, suggesting

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2+ Fig. 2. The 1-D supramolecular organization of [MnIII dimers for 2 (a), and the 1-D zigzag chain structures for 3 (b) and 4 (c). Hydrogen atoms and crystallized 2 (Schiff-base)2] solvent molecules are omitted for clarity.

the presence of significant orbital contributions to the magnetic moment [20]. Upon cooling, the vMT value decreases quasi-linearly and then drop more rapidly in the low temperature region until reach the value of 0.35 cm3 K mol1 at 1.8 K. The magnetic thermal behavior of 1 are typical for magnetically isolated low-spin distorted octahedral iron(III) system with spin–orbital coupling of the 2T2g ground term [20a]. The rapidly drop tendency of the vMT versus T plots at very low temperature might be caused by weak intermolecular antiferromagnetic interactions mediated through the p–p stacking contacts. The magnetic data of 2 is shown in Fig. 3a. The room-temperaIII 3 1 ture vMT value for per MnIII , which 2 Fe2 unit in 2 is 6.87 cm K mol corresponds to the spin-only value of 6.76 cm3 K mol1 expected for III non-interacting MnIII 2 Fe2 unit (SMn = 2, SFe = 1/2, assuming g = 2). Upon cooling, the value remains nearly constant in the temperature range from 300 to 30 K, and then it exhibits an abrupt decrease with further cooling and reaches 3.49 cm3 K mol1 at 1.8 K. No maximum was observed in the vM versus T plot (Inset of Fig. 3a). As revealed by most FeIII–MnIII systems [8c,9e,14a,14c], the rapidly decrease of vMT values at very low temperature might be caused by an overall antiferromagnetic interaction, the spin–orbit coupling effects of the

low-spin FeIII ion [20a] and/or the zero-field splitting (D) of the MnIII ions [15]. The fit of the experimental data of 2 to a Curie–Weiss law, vM = C/(T  h), can be carried out between 20 and 300 K, affording C = 7.01 cm3 K mol1, h = 0.95 K. The very small negative Weiss constant cannot be used to identify the intramolecular magnetic coupling nature of 2 owing to the complicated structure of 2. To evaluate the magnetic coupling parameters of 2, it is necessary to take into account the structure factors and the possible pathways. The X-ray structure determination reveals that complex 2 is composed of one out-of-plane Mn2 dimer and two free [FeIII(mqzcq)(CN)3] anions. Therefore, a first model [3i] is easily devised considering the contribution from both Mn2 dimer and the two paramagnetic FeIII ions. The following spin Hamiltonian has been considered:

H ¼ 2JðSMn1 SMn2 Þ þ DMn ðS2z;Mn1 þ S2z;Mn2 Þ þ 2g lB HðSMn þ sFe Þ where J is the intradimer MnIII. . .MnIII magnetic exchanges mediated via the two phenolate oxygen bridges. DMn refers to the zero-field splitting (ZFS) parameter originated from a single MnIII ion, and Sz,Mn is the z component of the SMn operators. The magnetic

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50

100

Fe

Fe

0 50 100 150 200 250 300

T/K

150

200

250

300

-1

3

Mn

1

0

0

Mn

2

3

J

6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0

1

χM / cm mol

2

χMT / cm K mol

-1

-1

(b) 7.0

3

6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0

χM / cm mol

3

χMT / cm K mol

-1

(a) 7.0

0

50

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0

3.0

Mn

50 100 150 200 250 300

T/K

3.0 2.5

-1

Fe

0.0

3.5

2.5

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0.4

2.0 1.5 1.0

200

250

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Fe

Fe

0.3

J

0.2

Mn

Mn

0.1 0.0 0 50 100150200250300 T/K

0.5

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Mn

χM / cm mol

Fe

0.8

4.0

150

T/K

(d) 3.5

)

) J(1-

-1

3

1.6

+

3

3

χMT / cm K mol

-1

4.5

J(1

χMT / cm K mol

χM / cm mol

2.4

50 100 150 200 250 300

T/K

-1

5.0

Mn

0 0

T/K

(c)

J Mn

0

50

100

150

200

250

300

T/K

Fig. 3. (a) Temperature dependence of vMT and vM (Inset) for 2 measured at 2 kOe; (b) The vMT and vM (Inset) curves for out-of-plane Mn2 dimer obtained by subtracting the contribution of [FeIII(mqzcq)(CN)3] unit; (c) Temperature dependence of vMT and vM (Inset) for 3 measured at 2 kOe; (d) Temperature dependence of vMT and vM (Inset) for 4 measured at 2 kOe. (The red solid lines represent the best fits to the models described in the text.) (Colour online.)

susceptibility was calculated using MAGPACK program [21], but unfortunately this model led to multiple solutions of the variable parameters without satisfactory match between the calculated and the experimental plot. The previous works have shown that the magnetic anisotropy and the intermolecular interactions (J0 ) might produce the similar effects on magnetic properties at very low temperature, and thus it is not reasonable to estimate them independently. To avoid over parametrization, the contribution brought by magnetic anisotropy is neglected but taking account of the intermolecular interactions (J0 ) in the frame of the mean-field approximation [22]:

v¼

h

v

 i 1  2zj = Ng 2 l2B v 0

The experimental susceptibility data in the whole temperature region explored was fitted using the described model, giving the set of parameters: J = 0.72 cm1, g = 2.0, J0 = 0.26 cm1. The negative value of J0 value confirms the presence of intermolecular antiferromagnetic interactions in 2. It deserves to be noted that the values of D for MnIII in Schiff base complexes are found in the usual range of 1 to 4 cm1 in the literatures [3i,15], and thus the evaluated intermolecular antiferromagnetic interactions should be overestimated because the contribution brought by magnetic anisotropy of MnIII ions are not considered. Nevertheless, it is still insufficient to claim that the intradimer MnIII. . .MnIII magnetic exchange is ferromagnetic because the Weiss constant is negative (0.95 K) but exchange coupling J is positive (0.72 cm1). In previous reports, the ferromagnetic intradimer MnIII. . .MnIII interactions were often found to be typical of this type of out-of-plane Mn2 dimers [3a]. Therefore, The MnIII. . .MnIII magnetic coupling constant J should be indeed ferromagnetic but is probably underestimated because the spin orbit coupling contribution of the [FeIII(mqzcq)(CN)3] anions are not considered in the model. To estimate the magnetic exchange of the out-of-plane Mn2 dimers with a better accuracy, an alternative approach is used for treating

the data of 2. From the structural section, it is revealed that the [FeIII(mqzcq)(CN)3] units presented in complexes 1 and 2 feature the comparable structural parameters, and hence it is reasonable to subtract the contribution of spin orbit coupling brought by [FeIII(mqzcq)(CN)3] anions using the magnetic data of 1. After subtraction, the final magnetic property will depend only on the out-of-plane Mn2 dimers. On the basis of these considerations, the modified plot of vMT versus T (Fig. 3b) could be refitted using the Curie–Weiss law and the dinuclear Mn2 model, affording the new set of parameters, h = 1.79 K, J = 1.5 cm1, g = 1.97, J0 = 0.35 cm1. The parameters extracted from the second model indicate the presence of dominant intradimer ferromagnetic interaction in 2, which is consistent with the result observed for most outof-plane Mn2 dimers [3i] and could be explained by the Goodenough–Kanamori rule [23]. The intramolecular ferromagnetic nature of complex 2 can be further confirmed by the fielddependent magnetization measured up to 70 kOe at 1.8 K, as shown in Fig. 4. As the external field increases, the magnetization of 2 continuously increases until reaches a value of 3.9 NlB at 70 kOe, which corresponds to ferromagnetic coupled MnIIIFeIII state but with the theoretical saturation value (5 NlB) (calculated form MS = gSMn + gsFe with g = 2) unattained. The unsaturated magnetization even at 70 kOe is also typical for MnIII(Schiff base) based complexes, which should be due to the magnetic anisotropy brought by MnIII ion [3i,15]. As mentioned in Section 1, the outof-plane Mn2 dimers can behave possibly as a SMM, and thus the measurement of the alternating current (ac) magnetic susceptibility at low temperature was carried out on polycrystalline samples. As shown in Fig. S6a, Complex 2 show frequency independent v0M versus T curves but the vM00 versus T curves (where v0M is the inphase susceptibility and v00M is the out-of-phase susceptibility) are rather frequency dependent, indicating the presence of slow magnetic relaxations originated from the out-of-plane Mn2 dimers. However, the frequency dependent imaginary part signal for 2 is rather weak and so it is impossible to conduct the dynamic investigation in detail though the out-of-phase maxima peaks seems to

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4

M / NμB

3 2

complex 2 complex 3 complex 4

1 0 -10

0

10

20

30

40

50

60

70

80

H / KOe Fig. 4. Field dependence of the magnetization for 2–4 measured at 1.8 K calculated for FeIIIMnIII unit. (The solid lines are eye guideline.)

be observable. Considering that the out-of-plane Mn2 dimers often exhibit strong slow magnetic relaxations [4g,5c,5d], the weak imaginary part signal for 2 should be ascribed to the significant intermolecular interactions, as proved by the structure analysis. The magnetic properties of 3 and 4 were depicted in Fig. 3c and d, respectively. At room temperature, the vMT values of 3 and 4 are equal to 3.22 and 3.37 cm3 K mol1, respectively, which is in accord with the spin only value (3.37 cm3 K mol1, calculated for one SMn = 2, one SFe = 1/2, with g = 2) anticipated for uncoupled MnIIIFeIII unit. As the temperature decreased, the vMT value of 3 continuously decrease until reaching a minimum of 2.49 cm3 K mol1 at around 16 K, then the value stop decreasing but increase up to 4.35 cm3 K mol1 at 1.8 K. The vMT versus T plot of 3 reveal the typical ferrimagnetic behavior expected for ferrimagnetic AB chains with the local spins SA – SB [16]. However, 4 exhibits quite different behavior that the vMT products keep decreasing upon cooling until down to 0.73 cm3 K mol1 at 1.8 K. The rapidly decrease of the vMT value at low temperature is probably due to the significant interchain antiferromagnetic interactions. Curie– Weiss law, vM = C/(T  h), was applied to fit experimental data between 20 and 300 K, affording C = 3.11 cm3 K mol1, h = 5.53 K for 3 and C = 3.45 cm3 K mol1, h = 6.14 K for 4, respectively. The negative Weiss constants indicate that the intramolecular magnetic exchanges through FeIII–CN–MnIII pathway in 3 and 4 might be antiferromagnetic nature. For the chain structure of 3 and 4, an approximate model firstly introduced by Seiden [24] can be used for simulating their magnetic behaviors. From the magnetic point of view, the SMn  SFe is large and thus, it is reasonable to treating SMn = 2 as a classical spin and SFe = 1/2 as a quantum spin. Then, the data of 3 and 4 can be modeled using an isotropic Heisenberg Hamiltonian (SMn,i = SMn,i+1 = 2 and SFe,i = 1/2, J being the magnetic coupling constant between Mn(III) and Fe(III) centers):

H ¼ 2J

þ1 X ðSMn;i sFe;i þ sFe;i SMn;iþ1 Þ 1

For both complexes, this model failed to fit the experimental data down to 1.8 K. In fact, the structures of both complexes reveal that each FeIII–CN–MnIII pathway in the chain are not equivalent, and hence an alternative modified model that considers 3 and 4 as alternating ferromagnetic chains [with two independent magnetic coupling constant J(1 + a) and J(1  a)] was used to fit the experimental data [25]. The isotropic Heisenberg Hamiltonian could be expressed as:

H ¼ 2J

þ1 X

  ð1 þ aÞSMn;i sFe;i þ ð1  aÞsFe;i SMn;iþ1

1

Using this model, the vMT versus T plot of 3 could be satisfactorily reproduced down to 1.8 K, affording the set of parameters: J(1 + a) = 5.5 cm1, J(1  a) = 1.0 cm1, g = 1.98. However, the fit of experimental data of 4 failed to produce satisfactory result in particular for the data in low temperature region. It is obvious that significant magnetic anisotropy and/or the interchain antiferromagnetic contributions are coexisted together. To avoid over parametrization, the magnetic anisotropy is not considered but taking account of the intermolecular interactions (J0 ) in the frame of the mean-field approximation [22]. In this way, we performed the fit to experimental data of 4 only in the limited temperature region from 300 to 20 K based on the first described model, giving J = 3.1 cm1, g = 2.02, J0 = 0.4 cm1. Nevertheless, the parameters should be taken with caution because the effect of the magnetic anisotropy brought by the Mn(III) ions are not considered. The negative values of exchange coupling for 3 and 4 confirm that antiferromagnetic interactions are operative between the MnIII and FeIII centers, which is typical of these FeIII–CN–MnIII systems and the magnitude of the intrachain Fe. . .Mn interactions are also comparable to other analogous compounds [3h,4f,7b]. The intrachain Fe. . .Mn antiferromagnetic interactions for 3 and 4 were further supported by the M versus H measurements at 1.8 K, as shown in Fig. 4. The magnetization of 3 increases rapidly as the dc field increases, revealing the expected ferrimagnetic characteristic behavior. In contrast, the magnetization of 4 increases nearly linearly at low field, which corresponds to the overall antiferromagnetic nature of 4 at very low temperature and is consistent with the susceptibility data. For both 3 and 4, the saturation magnetizations reach 2.8 NlB at 70 kOe, which is in agreement with the theoretical value (3 NlB) [calculated from MS = g(SMn  SFe) with g = 2)] anticipated for an antiferromagnetic arrangement of the MnIII and FeIII spins along the chain. From the analysis, the quite different vMT versus T curves shown by 3 and 4 could be ascribed to the different coupling strength of both intra- and interchain antiferromagnetic interactions. For 3, the chain seems to be better isolated from each other and the significant intrachain antiferromagnetic interactions induce the 1-D ferromagnetic chain behavior. However, the coupling strength of both intra- and interchain antiferromagnetic interactions in 4 were found to be close to each other and thus, producing significant interchain interactions that destroy the 1-D ferromagnetic chain properties in low temperature region. However, it is still not possible to fully clarified such obvious differences considering that the magnetic behaviors are a simple function of neither the Mn–Ncyanide distances nor the Mn–N–Ccyanide angles nor the torsion angles but together these structural variables. Temperature dependences of the ac susceptibility for 3 and 4 were also measured, as shown in Figs. S6b and S6c. For 3, the in-phase susceptibility v0M and out-of-phase susceptibility v00M both are frequency independent upon cooling, but a frequency dependent signal is then detected at temperatures lower than 2 K, revealing the presence of slow relaxation of the magnetization. Different from 3, no frequency dependent signal was observed for 4 in the whole temperature region down to 1.8 K. Obviously, the low dimensional dynamic properties are influenced by intermolecular interaction, and in most cases, the slow magnetic relaxations originated from the anisotropy of spin clusters or chains are weakened when the intermolecular interactions are significant. However, there are still some exception examples in which the low dimensional properties are even contributed by the intermolecular contacts [5d,26].

4. Conclusions In summary, four new [FeIII(L)(CN)3] based complexes featuring different structures and magnetism have been discussed in this

H. Zhou et al. / Polyhedron 85 (2015) 457–466

work. Interestingly, the out-of-plane Mn2 dimers are 1-D supramolecular organized (2) with the [FeIII(mpzcq)(CN)3] acting as the counter anions, and then these type of structural moieties can be even rearranged into 1-D zigzag chains (3, 4). Undoubtedly, 2+ the introduction of out-of-plane dimer of [MnIII 2 (Schiff-base)2] into the low dimensional magnetic assemblies (clusters or chains) is very interesting and more importantly, the high ground state spin and anisotropy of such Mn2 units are most likely to contribute to the slow magnetic relaxations that are required for designing new SMMs and SCMs. Unfortunately, none of our constructed systems present ideal SMMs and SCMs behaviors though the slow magnetic relaxations were detected for 2 and 3. Even though, it is still deserved to perform further research to designing new 0-D or 1-D systems in which the important magnetically anisotropic spin units (like out-of-plane Mn2 dimers or other clusters with higher nuclearity) are involved as structural subunits.

[4]

Acknowledgments The authors are grateful for financial support from the National Natural Science Foundation of China (Nos. 1601310042 and 51072071), Doctoral Innovation Program Foundation of China (No. 1721310119) and the Startup Foundation for Advanced Talents of Jiangsu University (No. 11JDG106).

[5]

Appendix A. Supplementary data CCDC 998551–998554 contain the supplementary crystallographic data for compounds 1–4, respectively. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.poly.2014.09.003.

[6]

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