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N,N′-donor reaction system
Inorganica Chimica Acta 432 (2015) 64–70
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Structural diversity and magnetic properties of the manganese/carbazol9-ylpropanate/N,N0 -donor reaction system Yunsheng Ma ⇑, Yuan Yuan, Hui Miao, Qixuan Zhong, Xiaoyan Tang, Hongjian Cheng, Rongxin Yuan ⇑ School of Chemistry and Material Engineering, Jiangsu Key Laboratory of Advanced Functional Materials, Changshu Institute of Technology, Changshu, Jiangsu 215500, China
a r t i c l e
i n f o
Article history: Received 3 February 2015 Received in revised form 24 March 2015 Accepted 26 March 2015 Available online 3 April 2015 Keywords: Carbazol-9-ylpropanate Manganese Porous structure Magnetic property
a b s t r a c t Reactions of carbazol-9-ylpropanate (carbp) with manganese perchlorate in the presence of 2,20 -bipy and 4,40 -bipy yield four compounds, namely, [Mn2(carbp)2(2,20 -bipy)4](ClO4)2 (1), [Mn2(carbp)2(4,40 II III 0 bipy)4](ClO4)2 (2), [MnII4MnIII 2 (l4-O)2(carbp)10(DMF)4] (3) and [Mn4 Mn2 (l4-O)2(carbp)10(4,4 -bipy)2] (4). Compound 1 and 2 have dinuclear structures, in which the MnII ions are linked by two carbp bridges. Compound 3 has a hexanuclear structure, in which two MnIII ions are surrounded by four MnII ions to form 10+ core. While, compound 4 has a two edge-sharing OMn4 tetrahedra giving rise to the [MnII4MnIII 2 (l4-O)2] 0 ( l -O) (carbp) ] as node and 4,4 -bipy as spacer. Magnetic susceptibil3-D porous structure with [MnII4MnIII 4 2 10 2 ity measurements show the presence of dominant antiferromagnetic interactions in compounds 1–4. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction (Carboxylato)metal compounds have received considerable attention for their applications in the fields of sorption, separation, magnetism and so on [1]. Terephthalic acid, isophthalic acid, trimesic acid and other polycarboxylic acids have been used to construct metal–organic frameworks (MOFs) such as MOF-5, which can be used in the fields of sorption and separation [2]. Monocarboxylato ligands RCO 2 (R = alkyl or aryl) are employed to build clusters especially manganese-based cluster that can function as singlemolecule magnets (SMMs) [3,4]. For example, CH3CO 2 was used to construct a giant SMMs Mn84 torus [5]. (CH3)3CCO 2 was chosen to produce Mn18 and Mn6 clusters [6]. It is interesting to find that this type of Mn6 cluster can be used as tectonic fragments for the building of cluster-based networks [7]. If R is aryl such as Ph and Fc (Fc = ferrocenyl), Mn30 and Mn4 were separated, respectively [8]. Clearly, the R groups have impacts on the formation of the final clusters. We are interested in the construction of manganese based coordination clusters for the searching of SMMs [9]. It is found that the structures are sensitive to the alkyl groups of the ligand. Carbazole has a conjugated aryl group that can form p–p interactions in the structures; hence stabilize the coordination compounds [10]. We studied the manganese-carbazolylacetato reaction system and obtained two dinuclear and two one- dimensional compounds in the presence of ancillary 2,20 -bipy and 4,40 -bipy ligands. The ⇑ Corresponding authors. E-mail addresses: [email protected] (Y. Ma), [email protected] (R. Yuan). http://dx.doi.org/10.1016/j.ica.2015.03.032 0020-1693/Ó 2015 Elsevier B.V. All rights reserved.
structures of these compounds are sensitive to the ratio of reactants and ancillary ligands [11]. Changing carboxylate to phosphonate group, we constructed two manganese phosphonate clusters with pentanuclear and decanuclear structures [12]. It can be found that the carbazole based ligands are promising for the construction of coordination clusters. Based on the previous work, it is necessary to study the effects of the chain length between carbazolyl and carboxylate group on the formation of the coordination clusters. Here, we report the progress of our research on the construction of manganese-based compounds by using carbazol-9-ylpropanate (carbp) as main ligand. Four manganese carboxylato compounds with dinuclear, hexanuclear and Mn6 based 3D porous structures were isolated and characterized. 2. Experimental 2.1. Materials and methods All the starting materials were reagent grade and were used as purchased. The N-carbazol-9-ylpropanic acid (Hcarbp) (Scheme 1) was prepared according to the literature method [13]. Elemental analyses were performed on a PE 240C elemental analyzer. The IR spectra were recorded on a NICOLET 380 spectrometer with pressed KBr pellets. TG was measured on Rigaku TG plus 8120. All the magnetic studies were performed on microcrystalline state. The magnetic susceptibilities were measured on a Quantum Design MPMS SQUID-XL7 magnetometer. Diamagnetic corrections were made for both the sample holder and the compound estimated from Pascal’s constants [14].
Y. Ma et al. / Inorganica Chimica Acta 432 (2015) 64–70
Scheme 1. Carbazol-9-ylpropanic acid.
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Brown block-shaped crystals formed after slow evaporation of the solution at room temperature for 3 days. Yield: 0.193 g, 38% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C188H186N20O32Mn6: C, 63.30; H, 5.26; N, 7.85%. Found: C, 63.21; H, 5.11; N, 7.63%. FTIR (KBr): 3046.1(w), 2925.8(w), 1665.0(m), 1595.1(vs), 1486.6(m), 1453.5(m), 1407.8(s), 1383.9(vs), 1324.9(m), 1233.6(m), 752.5(m), 611.5(s). Thermogravimetric analysis shows the weight loss (15.2%) in the temperature range of 30–100 °C, in agreement with the calculated value 14.3% for the removal of lattice molecules.
2.2. Synthesis of [Mn2(carbp)2(2,20 -bipy)4](ClO4)2 (1) A CH3OH solution (10 mL) of 2,20 -bipy (0.312 g, 2 mmol) and Nacarbp (0.261 g, 1 mmol) was added to a CH3OH solution (10 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The solution was stirred for 1 h to give yellow precipitate which was recrystallized from hot CH3OH. Yellow block-shaped crystals formed after slow evaporation of the solution at room temperature for 4 days. Yield: 0.388 g, 55% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C70H56Mn2N10O12Cl2: C, 59.63; H, 4.00; N, 9.93%. Found: C, 59.81; H, 3.74; N, 9.87%. FTIR (KBr): 3049.6(w), 1632.8(vs), 1600.1(vs), 1484.7(m), 1447.6(s), 1403.2(s), 1315.6(s), 1206.3(m), 1093.2(s), 751.8(vs), 631.4(s). The two very strong bands centered at 1600 and 1403 cm1, attributed to the mas(COO) and ms(COO) of carbp with D = 197 cm1 confirm the carboxylate ligand adopts bidentate-bridging coordination mode [15]. 2.3. Synthesis of [Mn2(carbp)2(4,40 -bipy)4(H2O)3](ClO4)22CH3OH (22CH3OH) A CH3OH solution (5 mL) of 4,40 -bipy (0.312 g, 2 mmol) and Nacarbp (0.261 g, 1 mmol) was added to a CH3OH solution (5 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The solution was stirred for 1 h gave white precipitate which was recrystallized from CH3OH/H2O (V:V = 1:1). Colorless block-shaped crystals formed after slow evaporation of the solution at room temperature for 7 days. Yield: 0.343 g, 45% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C72H70Mn2N10O17Cl2: C, 56.59; H, 4.62; N, 9.17%. Found: C, 56.33; H, 4.23; N, 9.37%. FTIR (KBr): 3049.0(w), 2930.0(w), 1658.5(s), 1595.8(vs), 1486.6(m), 1455.8(s), 1414.8(s), 1384.2(vs), 1329.0(m), 1323.2(m), 751.3(s), 614.4(m). 2.4. Synthesis of [MnII4MnIII 2 (l4-O)2(carbp)10(DMF)4]5.5DMF2H2O (35.5DMF2H2O) A DMF solution (3 mL) of Nacarbp (0.261 g, 1 mmol) was added to a DMF solution (3 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The resulting solution was stirred for 3 h at 60 °C to give brown solution, which was filtrated. Brown block-shaped crystals formed after slow evaporation of the solution at room temperature for 2 days. Yield: 0.185 g, 32% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C357H381Mn12N39O67: C, 61.70; H, 5.53; N, 7.86. Found: C, 61.08; H, 5.22; N, 7.46%. FTIR (KBr): 3052.0(w), 2930.0(w), 1660.6(s), 1597.4(vs), 1486.7(m), 1453.5(s), 1415.5(s), 1332.6(m), 1240.2(w), 751.5(s), 604.8(s). Thermogravimetric analysis shows the weight loss (13.2%) in the temperature range of 30–120 °C, in agreement with the calculated value 12.6% for the removal of lattice molecules.
2.6. X-ray crystallographic analysis Single crystals were selected for indexing and intensity data collection on a Rigaku SCX mini CCD diffractometer using graphite-monochromated Mo Ka radiation (k = 0.71073 Å) at room temperature. A hemisphere of data was collected in the h range 3.05–25.00° for 1, 1.77–25.00° for 2, 0.82–26.00° for 3 and 2.18– 25.00° for 4 using a narrow-frame method with scan widths of 0.03° in x and an exposure time of 10 s frame1. Cell parameters were refined by using the program CrystalClear [16] on all observed reflections. The collected data were reduced by using the program CrystalClear, and an absorption correction (multi-scan) was applied. The reflection data were also corrected for Lorentz and polarization effects. The structures were solved by direct methods and refined on F2 by full matrix least squares using SHELXTL [17]. All the non-hydrogen atoms were located from the Fourier maps, and were refined anisotropically. All H atoms were refined isotropically, with the isotropic vibration parameters related to the non-H atom to which they are bonded. The SQUEEZE [18] command in PLATON was used in the structure refinement for compound 4. The void volume and number of electrons are 7189 Å3 and 1119 per unit. Crystallographic and refinement details of 1–4 are listed in Table 1. Selected bond lengths and angles are given in Tables S1–S4 for 1–4, respectively. 3. Results and discussion 3.1. Syntheses The reactions of MnII with carbp in the presence of 4,40 -bipy in CH3OH and DMF give 2 and 4, respectively. During the formation of compound 4, the starting MnII ions were oxidized by oxygen because of the lower MnIII/MnII electrode potential in basic DMF. Actually, we observed the color changes from colorless to light brown during the recrystallization process. Compound 4 can also be obtained by recrystallizing compound 2 in DMF, indicating the transformation process is very complicate. It is interesting to find that compound 3 and 4 contain the same [MnII4MnIII 2 (l4-O)2 (carbp)10] core. We used compound 3 as starting material to react with 4,40 -bipy in DMF, however, only got brown precipitate. This means compound 3 cannot transform to 4 directly. Comparatively, the present carbazolylpropanate/manganese shows different results from carbazolylacetate/manganese system [11]. This indicates that the chain length between carbazolyl and carboxylate affects the formation of the final compounds. 3.2. Crystal structures
0 2.5. Synthesis of [MnII4MnIII 2 (l4-O)2(carbp)10(4,4 -bipy)2] 6DMF4H2O (46DMF4H2O)
A DMF solution (3 mL) of 4,40 -bipy (0.156 g, 1 mmol) and Nacarbp (0.261 g, 1 mmol) was added to a DMF solution (3 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The resulting solution was stirred for 2 h at 60 °C to give brown solution, which was filtrated.
The Compound 1 crystallizes in the triclinic space group P1. asymmetric unit consists of one MnII ion, one carbazol-9-ylII propanate, two 2,20 -bipy ligands and one ClO 4 anion. The Mn ion locates in a distorted octahedral environment. Four of the six coordination sites are filled by N atoms (N2, N3, N4, N5) from two 2,20 -bipy ligands. The remaining sites are filled by O atoms
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Table 1 Crystal data and structure refinements for 1–4.
a
Compounds
1
2
3
4
Empirical formula M Crystal system Space group a (Å) b (Å) c (Å) a () b () c () V (Å3) Z qcal (g cm3) l (mm1) F(0 0 0) Total, unique data (Rint) Goodness-of-fit (GOF) on F2 R1, wR2a R1, wR2 (all data) (Dq)max, (Dq)min (e Å3)
C70H56Mn2N10O12Cl2 1410.03 triclinic P1
C72H70Mn2N10O17Cl2 1528.16 orthorhombic Pna21 19.299(4) 14.308(3) 25.382(5) 90 90 90 7009(2) 4 1.448 0.515 3168 44 741, 10 168, 0.055 1.07 0.0629, 0.1538 0.0715, 0.1622 1.02, 0.55
C357H381Mn12N39O67 6949.29 triclinic P1
C94H93Mn3N10O16 1783.62 monoclinic C2/c 43.211(9) 17.597(4) 22.718(7) 90 129.74(3) 90 19,716(7) 8 1.232 0.429 7632 63 859, 17 244, 0.03 1.168 0.0528, 0.1389 0.0592, 0.1411 0.923, 0.55
R1 =
P
||Fo| |Fc|/
10.427(2) 12.599(3) 14.334(3) 69.39(3) 76.79(3) 70.85(3) 1651.3(7) 1 1.418 0.534 726 14 250, 5807, 0.051 1.09 0.0631, 0.1424 0.0957, 0.1606 0.721, 0.445
17.9334(17) 24.1581(13) 27.8398(16) 112.663(2) 98.128(3) 105.3960(3) 10320.2(13) 1 1.118 0.422 3632 73 195, 40 105, 0.018 1.07 0.0552, 0.1354 0.0688, 0.1384 0.601, 0.339
P P P |Fo|; wR2 = { w(Fo2 Fc2)2/ w(Fo2)2}1/2.
(O1, O2A) from two carbazol-9-ylpropanate ligands (Fig. 1). The Mn–O and Mn–N distances fall in the range of [2.105(3)–2.337(4) Å], which are consistent with those in [Mn2(C6H11CO2)2(2,20 -bipy)4] (ClO4)2 and other dinuclear manganese compounds with carboxylate and 2,20 -bipy ligands [19]. Two MnII ions are connected by two syn-anti l2-carbazol-9-ylpropanate (g1,g1-l2) ligands with the Mn Mn separation of 4.721(2) Å, which is close to that in [Mn2(2-ClC6H4CO2)2(2,20 -bipy)4](ClO4)2 (4.711 Å) [20]. The molecules are packed together through p–p stacking interactions between carbazolyl groups. The shortest centroid–centroid distance between the phenyl groups is 3.516(1) Å (Fig. S1). The packing mode is different from that observed in [Mn2(cabo)2 (2,20 -bipy)4](ClO4)2 (cabo = carbazol-9-ylacetate), in which the stacking interaction comes from the 2,20 -bipy ligands [11]. This difference may due to the presence of longer alkyl chain in carbazol-9-ylpropanate ligand that lead to the extension of the carbazolyl group in the crystal.
Compound 2 crystallizes in the orthorhombic space group Pna21. The asymmetric unit consists of two Mn(II) ions, two carbazol-9-ylpropanato ligands, four 4,40 -bipy ligands, three coordinating H2O molecules and two ClO 4 anion (Fig. 2). The Mn1 atom are coordinated by [O1, O3, O4, O6] from two carbp ligands, one water and [N1, N5] from two 4,40 -bipy ligands and in a distorted octahedral coordination geometry. The Mn2 atom also adopts octahedral coordination geometry. The six sites are filled with oxygen atoms [O2, O4, O5, O18] from two carbp ligands and two water molecules and nitrogen atoms [N3, N7] from two 4,40 -bipy ligands. The Mn–O and Mn–N bond lengths fall in the range of [2.082(4)–2.342(4) Å], which are close to that in [Mn(cabo)2(4,40 -bipy)2]n [11]. One carbp serves as syn-anti l2-carbazol-9-ylpropanato (g1,g1-l2) ligand, while the other adopts bridging and chelating mode (g1,g2-l3) to coordinate with two Mn ions leading to the Mn Mn separation of 3.880(2) Å. This distance is shorter than that in compound 1. The Mn1–O4–Mn2 bond angle is 119.32(16)°. The molecules are packed by p–p stacking
Fig. 1. ORTEP drawing of 1 (30% probability ellipsoids). Hydrogen atoms and ClO 4 anions are omitted for clarity.
Fig. 2. ORTEP drawing of 2 (30% probability ellipsoids). Hydrogen atoms and ClO 4 anions are omitted for clarity.
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interactions between the 4,40 -bipy groups. The shortest centroid– centroid distance between the pyridinyl rings is 3.606(1) Å (Fig. S2). In Compound 3 crystallizes in the monoclinic space group P1. the asymmetric unit, there are six Mn ions. The Mn atoms are located in the vertex of two MnII2–MnIII 2 tetrahedra sharing their MnIII–MnIII edge with a l4-O2 in the center of each tetrahedron, giv10+ ing rise to a [MnII4MnIII unit. Peripheral ligation consists of 2 (l4-O)2] ten bridging carbp ions and four terminal DMF molecules (Fig. 3). Four carbp ions are coordinating in g1,g2-l3 mode whereas the remaining ligands show the g1,g2-l2 coordination mode. The Mn ions locates in the octahedral environment, each MnII ion is of the type MnO6 with four O atoms from four carboxylate groups, one O from the central l4-O bridge, and one O from a DMF. The Mn–O distances are in the range of 2.101(2)–2.307(2) Å, which are in accordance with those in [Mn6O2(PhCO2)10(DMF)4] [21]. The coordination geometry around the inner MnIII ions (Mn5, Mn6) is elongated octahedral for the Jahn–Teller effects, where the six positions are occupied by O atoms from four carbp bridging groups and two l4-O2 ions. The axial bond lengths Mn5–O6, Mn5–O14 are equal to 2.241(2) and 2.247(2) Å, respectively. For Mn6, the Mn6–O7 and Mn6–O15 bond lengths are 2.239(2) and 2.233(2) Å. The Mn–O bond lengths in the equatorial position are shorter than the axial positions. The Mn5 Mn6 separation is equal to 2.814(1) Å. The bond
angles for Mn5–O25–Mn6 and Mn5–O26–Mn6 are 95.96(10)° and 95.23(10)°, respectively. BVS confirms that both Mn5 and Mn6 have the +3 oxidation state. Compound 3 is the first known example of [Mn6O2(RCO2)10] cluster bearing the carbazolyl group. The Mn6 molecules are packed together through weak hydrogen bonding interactions among Mn6 and guest molecules (Fig. S3). It should be noted that, this kind of Mn6 cluster can also be constructed by using CH3CO 2 [22a], CHCl2CO2 [22b], CCl3CO2 [22c], CBr3CO2 [22d], CH3CH2CO2 [22e], (CH3)3CCO2 [22b], PhCO2 [21], F4PhCO 2 [22f] and (NO2)2PhCO 2 [22g] anions as ligands. Compound 4 crystallizes in monoclinic space group C2/c. The 10+ [MnII4MnIII core locates on a 2-fold axis, which passes 2 (l4-O)2] through Mn1 and Mn2 along the b-axis, and hence the asymmetric unit contains only half of the cluster. The central core structure is very similar to that in compound 3 (Fig. 4). The bond lengths and angles are close to that in 3. The 4,40 -bipy molecules act as bridging ligands connecting the [Mn6O2(RCO2)10] clusters with its four neighbors through the peripheral MnII ions. Thus each 4,40 -bipy connects two Mn4 atoms of adjacent clusters or two Mn3 atoms, forming a 3D distorted porous diamond-like framework that can be described as a (6,4) net (Fig. 5). The solvent-accessible volume per unit cell is 36.5% as calculated by the PLATON program. The 3D structure is different from [Mn2L2(4,40 bpy)2][Mn2L2(H2O)2]2H2O that has 2Dlayer + 1Dchain ? 3D framework [23]. To our knowledge, polymeric frameworks based on [Mn6] cores are scarce. The title compound [Mn6O2(carbp)10(4,40 -bipy)2] can be compared with other 3D diamond-like polymers such as [Mn6O2(tBuCO2)10(NIT-Me)2] [24a] and [Mn6O2(C6H5CH2CO2)10(pyz)2] [24b] with 2,4,4,5,5-pentamethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1oxyl (NIT-Me) and pyrazine (pyz) as bridges. While, only one 1D polymeric [Mn6O2(t-BuCO2)10(t-BuCO2H)(4,40 -bipy)] with 4,40 -bipy as bridge was reported [24c]. This study gives us the signal that monocarboxylate ligand bearing bulky group may be employed to construct 3D porous coordination polymer.
3.3. Magnetic properties The temperature-dependent molar magnetic susceptibilities of 1–4 were measured at 1000 Oe in the temperature range of 1.8– 300 K. The vM and vMT versus T plots for 1 are shown in Fig. 6. At room temperature, vMT is equal to 8.92 cm3 K mol1, which is close to the expected spin-only value for two isolated magnetic
Fig. 3. (a) Structure of compound 3, C and N atoms from DMF were omitted for clarity; (b) Core structure of compound 3, hydrogen and aromatic rings were omitted for clarity.
Fig. 4. Structure of compound 4.
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Fig. 5. (a) View of the diamond structure; (b) view of an equivalent fragment in the distorted 3D diamond-like topology in compound 4. (C atoms are replaced by 10+ [MnII4MnIII clusters and the C–C bonds by 4,40 -bipy bridges). Hydrogen atoms and carbazolyl groups are omitted for clarity. 2 (l4-O)2]
centers (S = 5/2). When the temperature is lowered, vM increases and passes through a rounded maximum at Tmax = 7 K. This indicates that antiferromagnetic exchange interactions prevail in solid compound. The magnetic data can be analyzed using a dinuclear model [14]. The exchange Hamiltonian is H = 2JS1S2, where S = 5/2, J is the coupling constant. Take the interdimer exchange interactions (zj0 ) into account. The best fitting parameters obtained are g = 2.0, J = 0.86 cm1, and zj0 = 0.027 cm1. The result shows that the antiferromagnetic interaction is very weak, which is in consistent with that observed in other dinuclear manganese compounds bearing dicarboxylate bridges [19]. For 2, the room temperature vMT is equal to 8.59 cm3 K mol1, which is close to the spin only value for two isolated MnII ions. Upon cooling, vMT decreases to 0.62 cm3 K mol1 at 1.8 K (Fig. 7). The data were fitted by using the dinuclear model to give g = 2.0, J = 0.95 cm1, and zj0 = 0.14 cm1. Clearly, the MnII–MnII (d5–d5) magnetic exchange interaction is more antiferromagnetic than that in 1. This is due to the presence of g1,g2-l2 bridging carboxylate in 2 that can transfer stronger magnetic interaction than the g1,g1-l2 bridging carboxylate in 1. For 3, the room temperature vMT is 17.27 cm3 K mol1, which is lower than the expected spin-only value for isolated magnetic centers (23.5 cm3 K mol1 for four MnII and two MnIII). When the temperature is lowered, the vMT product shows a progressive decrease down to about 50 K and a more abrupt decrease at lower temperature to reach a value of 0.42 cm3 K mol1 at 1.8 K (Fig. 8). The profile of this magnetic behavior indicates that antiferromagnetic interactions are propagated between the metal centers. This observation can be compared with other clusters with identical 10+ [MnII4MnIII cores [22]. 2 (l4-O)2]
Fig. 7. Plots of vM (s) and vMT (h) for 2. Solid lines show the best fit of the data according to the proposed model.
Fig. 8. Thermal variation of the vMT product per [Mn6] cluster for compound 3. The solid lines correspond to the best-fit curve using the parameters described in the text.
As shown in Fig. 9, a model is used to simulate four pairwise coupling on the basis of the bond lengths and angles between the Mn atoms. The Heisenberg spin Hamiltonian is thus given as:
H ¼ J 1 ðS1 S2 þ S3 S4 Þ J 2 ðS1 S5 þ S2 S6 þ S3 S5 þ S4 S6 Þ J 3 ðS1 S6 þ S2 S5 þ S3 S6 þ S4 S5 Þ J 4 S5 S6
Fig. 6. Plots of vM (s) and vMT (h) for 1. Solid lines show the best fit of the data according to the proposed model.
J1 and J4 represent the MnII–MnII (d5–d5) and MnIII–MnIII (d4–d4) exchange interaction, while J2 and J3 represent the MnII–MnIII (d5–d4) exchange interaction. The susceptibility data were fitted by using the magnetism package MAGPACK based on the
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4. Conclusions The reactions of carbazol-9-ylpropanate and MnII ions in the presence of chelating 2,20 -bipy and bridging 4,40 -bipy ligands yield four different compounds. The results indicate the bulky carbazolyl substituent group has good crystallinity in the construction of coordination compounds. We found solvent plays a key role for the formation of special compound such as 2 and 4. In addition, DMF is one ideal solvent for the construction of mixed valence state manganese clusters such as 3. Magnetic measurements of 1–4 revealed that all of the compounds mediate antiferromagnetic interactions between the metal ions. Further work is in progress to study new manganese phosphonates with bulky carbazole groups. Acknowledgements
Fig. 9. Model of magnetic exchange pathway in the [Mn6] cluster.
This work is supported by NSFC (Nos. 21001018, 21201025) and NSF of Jiangsu Provence (Nos. BK2012643, 12KJA150001, 14KJA150001, 14KJB150001). Appendix A. Supplementary material CCDC 1022151, 1022152, 1022153 and 1022154 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica. 2015.03.032. References
Fig. 10. Thermal variation of the vMT product per [Mn6] cluster for compound 4. The solid lines correspond to the best-fit curve using the parameters described in the text.
corresponding Hamiltonian [25]. The best fitting can be achieved above 10 K with parameters: g = 2, J1 = 3.8 cm1, J2 = J3 = 8.0 cm1, J4 = 99.6 cm1 (R = 1.2 103). The larger J2 than J1 indicates that the (d5–d4) interaction is more antiferromagnetic than the (d5–d5) interaction as observed in [MnII4MnIII [26]. This simulation 3 (teaH)3(tea)3](ClO4)23MeOH results are consistent with the previous analysis of the similar metallic core cluster [22f,24b]. For 4, the room temperature vMT is 18.63 cm3 K mol1, which is smaller than the expected spin-only value for isolated magnetic centers. Upon cooling, the value of vMT gradually decreases to 0.58 cm3 K mol1 at 1.8 K (Fig. 10). The result indicates the presence of overall antiferromagnetic interactions between the metal centers. Although the structure of 4 shows that Mn6 clusters are connected through 4,40 -bipy bridges. The magnetic coupling through these bridges can be neglected since the shortest Mn–Mn distance through 4,40 -bipy is about 11.63 Å. Therefore, the susceptibility data were analyzed in a similar way to 3 and the best fitting parameters obtained are g = 2, J1 = 3.6 cm1, J2 = J3 = 7.7 cm1, J4 = 99.6 cm1 (R = 8.2 104). The J values for compound 4 are closely related to that for 3 due to the similar bond angles and distances.
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Structural diversity and magnetic properties of the manganese/carbazol9-ylpropanate/N,N0 -donor reaction system Yunsheng Ma ⇑, Yuan Yuan, Hui Miao, Qixuan Zhong, Xiaoyan Tang, Hongjian Cheng, Rongxin Yuan ⇑ School of Chemistry and Material Engineering, Jiangsu Key Laboratory of Advanced Functional Materials, Changshu Institute of Technology, Changshu, Jiangsu 215500, China
a r t i c l e
i n f o
Article history: Received 3 February 2015 Received in revised form 24 March 2015 Accepted 26 March 2015 Available online 3 April 2015 Keywords: Carbazol-9-ylpropanate Manganese Porous structure Magnetic property
a b s t r a c t Reactions of carbazol-9-ylpropanate (carbp) with manganese perchlorate in the presence of 2,20 -bipy and 4,40 -bipy yield four compounds, namely, [Mn2(carbp)2(2,20 -bipy)4](ClO4)2 (1), [Mn2(carbp)2(4,40 II III 0 bipy)4](ClO4)2 (2), [MnII4MnIII 2 (l4-O)2(carbp)10(DMF)4] (3) and [Mn4 Mn2 (l4-O)2(carbp)10(4,4 -bipy)2] (4). Compound 1 and 2 have dinuclear structures, in which the MnII ions are linked by two carbp bridges. Compound 3 has a hexanuclear structure, in which two MnIII ions are surrounded by four MnII ions to form 10+ core. While, compound 4 has a two edge-sharing OMn4 tetrahedra giving rise to the [MnII4MnIII 2 (l4-O)2] 0 ( l -O) (carbp) ] as node and 4,4 -bipy as spacer. Magnetic susceptibil3-D porous structure with [MnII4MnIII 4 2 10 2 ity measurements show the presence of dominant antiferromagnetic interactions in compounds 1–4. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction (Carboxylato)metal compounds have received considerable attention for their applications in the fields of sorption, separation, magnetism and so on [1]. Terephthalic acid, isophthalic acid, trimesic acid and other polycarboxylic acids have been used to construct metal–organic frameworks (MOFs) such as MOF-5, which can be used in the fields of sorption and separation [2]. Monocarboxylato ligands RCO 2 (R = alkyl or aryl) are employed to build clusters especially manganese-based cluster that can function as singlemolecule magnets (SMMs) [3,4]. For example, CH3CO 2 was used to construct a giant SMMs Mn84 torus [5]. (CH3)3CCO 2 was chosen to produce Mn18 and Mn6 clusters [6]. It is interesting to find that this type of Mn6 cluster can be used as tectonic fragments for the building of cluster-based networks [7]. If R is aryl such as Ph and Fc (Fc = ferrocenyl), Mn30 and Mn4 were separated, respectively [8]. Clearly, the R groups have impacts on the formation of the final clusters. We are interested in the construction of manganese based coordination clusters for the searching of SMMs [9]. It is found that the structures are sensitive to the alkyl groups of the ligand. Carbazole has a conjugated aryl group that can form p–p interactions in the structures; hence stabilize the coordination compounds [10]. We studied the manganese-carbazolylacetato reaction system and obtained two dinuclear and two one- dimensional compounds in the presence of ancillary 2,20 -bipy and 4,40 -bipy ligands. The ⇑ Corresponding authors. E-mail addresses: [email protected] (Y. Ma), [email protected] (R. Yuan). http://dx.doi.org/10.1016/j.ica.2015.03.032 0020-1693/Ó 2015 Elsevier B.V. All rights reserved.
structures of these compounds are sensitive to the ratio of reactants and ancillary ligands [11]. Changing carboxylate to phosphonate group, we constructed two manganese phosphonate clusters with pentanuclear and decanuclear structures [12]. It can be found that the carbazole based ligands are promising for the construction of coordination clusters. Based on the previous work, it is necessary to study the effects of the chain length between carbazolyl and carboxylate group on the formation of the coordination clusters. Here, we report the progress of our research on the construction of manganese-based compounds by using carbazol-9-ylpropanate (carbp) as main ligand. Four manganese carboxylato compounds with dinuclear, hexanuclear and Mn6 based 3D porous structures were isolated and characterized. 2. Experimental 2.1. Materials and methods All the starting materials were reagent grade and were used as purchased. The N-carbazol-9-ylpropanic acid (Hcarbp) (Scheme 1) was prepared according to the literature method [13]. Elemental analyses were performed on a PE 240C elemental analyzer. The IR spectra were recorded on a NICOLET 380 spectrometer with pressed KBr pellets. TG was measured on Rigaku TG plus 8120. All the magnetic studies were performed on microcrystalline state. The magnetic susceptibilities were measured on a Quantum Design MPMS SQUID-XL7 magnetometer. Diamagnetic corrections were made for both the sample holder and the compound estimated from Pascal’s constants [14].
Y. Ma et al. / Inorganica Chimica Acta 432 (2015) 64–70
Scheme 1. Carbazol-9-ylpropanic acid.
65
Brown block-shaped crystals formed after slow evaporation of the solution at room temperature for 3 days. Yield: 0.193 g, 38% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C188H186N20O32Mn6: C, 63.30; H, 5.26; N, 7.85%. Found: C, 63.21; H, 5.11; N, 7.63%. FTIR (KBr): 3046.1(w), 2925.8(w), 1665.0(m), 1595.1(vs), 1486.6(m), 1453.5(m), 1407.8(s), 1383.9(vs), 1324.9(m), 1233.6(m), 752.5(m), 611.5(s). Thermogravimetric analysis shows the weight loss (15.2%) in the temperature range of 30–100 °C, in agreement with the calculated value 14.3% for the removal of lattice molecules.
2.2. Synthesis of [Mn2(carbp)2(2,20 -bipy)4](ClO4)2 (1) A CH3OH solution (10 mL) of 2,20 -bipy (0.312 g, 2 mmol) and Nacarbp (0.261 g, 1 mmol) was added to a CH3OH solution (10 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The solution was stirred for 1 h to give yellow precipitate which was recrystallized from hot CH3OH. Yellow block-shaped crystals formed after slow evaporation of the solution at room temperature for 4 days. Yield: 0.388 g, 55% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C70H56Mn2N10O12Cl2: C, 59.63; H, 4.00; N, 9.93%. Found: C, 59.81; H, 3.74; N, 9.87%. FTIR (KBr): 3049.6(w), 1632.8(vs), 1600.1(vs), 1484.7(m), 1447.6(s), 1403.2(s), 1315.6(s), 1206.3(m), 1093.2(s), 751.8(vs), 631.4(s). The two very strong bands centered at 1600 and 1403 cm1, attributed to the mas(COO) and ms(COO) of carbp with D = 197 cm1 confirm the carboxylate ligand adopts bidentate-bridging coordination mode [15]. 2.3. Synthesis of [Mn2(carbp)2(4,40 -bipy)4(H2O)3](ClO4)22CH3OH (22CH3OH) A CH3OH solution (5 mL) of 4,40 -bipy (0.312 g, 2 mmol) and Nacarbp (0.261 g, 1 mmol) was added to a CH3OH solution (5 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The solution was stirred for 1 h gave white precipitate which was recrystallized from CH3OH/H2O (V:V = 1:1). Colorless block-shaped crystals formed after slow evaporation of the solution at room temperature for 7 days. Yield: 0.343 g, 45% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C72H70Mn2N10O17Cl2: C, 56.59; H, 4.62; N, 9.17%. Found: C, 56.33; H, 4.23; N, 9.37%. FTIR (KBr): 3049.0(w), 2930.0(w), 1658.5(s), 1595.8(vs), 1486.6(m), 1455.8(s), 1414.8(s), 1384.2(vs), 1329.0(m), 1323.2(m), 751.3(s), 614.4(m). 2.4. Synthesis of [MnII4MnIII 2 (l4-O)2(carbp)10(DMF)4]5.5DMF2H2O (35.5DMF2H2O) A DMF solution (3 mL) of Nacarbp (0.261 g, 1 mmol) was added to a DMF solution (3 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The resulting solution was stirred for 3 h at 60 °C to give brown solution, which was filtrated. Brown block-shaped crystals formed after slow evaporation of the solution at room temperature for 2 days. Yield: 0.185 g, 32% based on Mn(ClO4)26H2O. Elemental Anal. Calc. for C357H381Mn12N39O67: C, 61.70; H, 5.53; N, 7.86. Found: C, 61.08; H, 5.22; N, 7.46%. FTIR (KBr): 3052.0(w), 2930.0(w), 1660.6(s), 1597.4(vs), 1486.7(m), 1453.5(s), 1415.5(s), 1332.6(m), 1240.2(w), 751.5(s), 604.8(s). Thermogravimetric analysis shows the weight loss (13.2%) in the temperature range of 30–120 °C, in agreement with the calculated value 12.6% for the removal of lattice molecules.
2.6. X-ray crystallographic analysis Single crystals were selected for indexing and intensity data collection on a Rigaku SCX mini CCD diffractometer using graphite-monochromated Mo Ka radiation (k = 0.71073 Å) at room temperature. A hemisphere of data was collected in the h range 3.05–25.00° for 1, 1.77–25.00° for 2, 0.82–26.00° for 3 and 2.18– 25.00° for 4 using a narrow-frame method with scan widths of 0.03° in x and an exposure time of 10 s frame1. Cell parameters were refined by using the program CrystalClear [16] on all observed reflections. The collected data were reduced by using the program CrystalClear, and an absorption correction (multi-scan) was applied. The reflection data were also corrected for Lorentz and polarization effects. The structures were solved by direct methods and refined on F2 by full matrix least squares using SHELXTL [17]. All the non-hydrogen atoms were located from the Fourier maps, and were refined anisotropically. All H atoms were refined isotropically, with the isotropic vibration parameters related to the non-H atom to which they are bonded. The SQUEEZE [18] command in PLATON was used in the structure refinement for compound 4. The void volume and number of electrons are 7189 Å3 and 1119 per unit. Crystallographic and refinement details of 1–4 are listed in Table 1. Selected bond lengths and angles are given in Tables S1–S4 for 1–4, respectively. 3. Results and discussion 3.1. Syntheses The reactions of MnII with carbp in the presence of 4,40 -bipy in CH3OH and DMF give 2 and 4, respectively. During the formation of compound 4, the starting MnII ions were oxidized by oxygen because of the lower MnIII/MnII electrode potential in basic DMF. Actually, we observed the color changes from colorless to light brown during the recrystallization process. Compound 4 can also be obtained by recrystallizing compound 2 in DMF, indicating the transformation process is very complicate. It is interesting to find that compound 3 and 4 contain the same [MnII4MnIII 2 (l4-O)2 (carbp)10] core. We used compound 3 as starting material to react with 4,40 -bipy in DMF, however, only got brown precipitate. This means compound 3 cannot transform to 4 directly. Comparatively, the present carbazolylpropanate/manganese shows different results from carbazolylacetate/manganese system [11]. This indicates that the chain length between carbazolyl and carboxylate affects the formation of the final compounds. 3.2. Crystal structures
0 2.5. Synthesis of [MnII4MnIII 2 (l4-O)2(carbp)10(4,4 -bipy)2] 6DMF4H2O (46DMF4H2O)
A DMF solution (3 mL) of 4,40 -bipy (0.156 g, 1 mmol) and Nacarbp (0.261 g, 1 mmol) was added to a DMF solution (3 mL) of Mn(ClO4)26H2O (0.362 g, 1 mmol). The resulting solution was stirred for 2 h at 60 °C to give brown solution, which was filtrated.
The Compound 1 crystallizes in the triclinic space group P1. asymmetric unit consists of one MnII ion, one carbazol-9-ylII propanate, two 2,20 -bipy ligands and one ClO 4 anion. The Mn ion locates in a distorted octahedral environment. Four of the six coordination sites are filled by N atoms (N2, N3, N4, N5) from two 2,20 -bipy ligands. The remaining sites are filled by O atoms
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Table 1 Crystal data and structure refinements for 1–4.
a
Compounds
1
2
3
4
Empirical formula M Crystal system Space group a (Å) b (Å) c (Å) a () b () c () V (Å3) Z qcal (g cm3) l (mm1) F(0 0 0) Total, unique data (Rint) Goodness-of-fit (GOF) on F2 R1, wR2a R1, wR2 (all data) (Dq)max, (Dq)min (e Å3)
C70H56Mn2N10O12Cl2 1410.03 triclinic P1
C72H70Mn2N10O17Cl2 1528.16 orthorhombic Pna21 19.299(4) 14.308(3) 25.382(5) 90 90 90 7009(2) 4 1.448 0.515 3168 44 741, 10 168, 0.055 1.07 0.0629, 0.1538 0.0715, 0.1622 1.02, 0.55
C357H381Mn12N39O67 6949.29 triclinic P1
C94H93Mn3N10O16 1783.62 monoclinic C2/c 43.211(9) 17.597(4) 22.718(7) 90 129.74(3) 90 19,716(7) 8 1.232 0.429 7632 63 859, 17 244, 0.03 1.168 0.0528, 0.1389 0.0592, 0.1411 0.923, 0.55
R1 =
P
||Fo| |Fc|/
10.427(2) 12.599(3) 14.334(3) 69.39(3) 76.79(3) 70.85(3) 1651.3(7) 1 1.418 0.534 726 14 250, 5807, 0.051 1.09 0.0631, 0.1424 0.0957, 0.1606 0.721, 0.445
17.9334(17) 24.1581(13) 27.8398(16) 112.663(2) 98.128(3) 105.3960(3) 10320.2(13) 1 1.118 0.422 3632 73 195, 40 105, 0.018 1.07 0.0552, 0.1354 0.0688, 0.1384 0.601, 0.339
P P P |Fo|; wR2 = { w(Fo2 Fc2)2/ w(Fo2)2}1/2.
(O1, O2A) from two carbazol-9-ylpropanate ligands (Fig. 1). The Mn–O and Mn–N distances fall in the range of [2.105(3)–2.337(4) Å], which are consistent with those in [Mn2(C6H11CO2)2(2,20 -bipy)4] (ClO4)2 and other dinuclear manganese compounds with carboxylate and 2,20 -bipy ligands [19]. Two MnII ions are connected by two syn-anti l2-carbazol-9-ylpropanate (g1,g1-l2) ligands with the Mn Mn separation of 4.721(2) Å, which is close to that in [Mn2(2-ClC6H4CO2)2(2,20 -bipy)4](ClO4)2 (4.711 Å) [20]. The molecules are packed together through p–p stacking interactions between carbazolyl groups. The shortest centroid–centroid distance between the phenyl groups is 3.516(1) Å (Fig. S1). The packing mode is different from that observed in [Mn2(cabo)2 (2,20 -bipy)4](ClO4)2 (cabo = carbazol-9-ylacetate), in which the stacking interaction comes from the 2,20 -bipy ligands [11]. This difference may due to the presence of longer alkyl chain in carbazol-9-ylpropanate ligand that lead to the extension of the carbazolyl group in the crystal.
Compound 2 crystallizes in the orthorhombic space group Pna21. The asymmetric unit consists of two Mn(II) ions, two carbazol-9-ylpropanato ligands, four 4,40 -bipy ligands, three coordinating H2O molecules and two ClO 4 anion (Fig. 2). The Mn1 atom are coordinated by [O1, O3, O4, O6] from two carbp ligands, one water and [N1, N5] from two 4,40 -bipy ligands and in a distorted octahedral coordination geometry. The Mn2 atom also adopts octahedral coordination geometry. The six sites are filled with oxygen atoms [O2, O4, O5, O18] from two carbp ligands and two water molecules and nitrogen atoms [N3, N7] from two 4,40 -bipy ligands. The Mn–O and Mn–N bond lengths fall in the range of [2.082(4)–2.342(4) Å], which are close to that in [Mn(cabo)2(4,40 -bipy)2]n [11]. One carbp serves as syn-anti l2-carbazol-9-ylpropanato (g1,g1-l2) ligand, while the other adopts bridging and chelating mode (g1,g2-l3) to coordinate with two Mn ions leading to the Mn Mn separation of 3.880(2) Å. This distance is shorter than that in compound 1. The Mn1–O4–Mn2 bond angle is 119.32(16)°. The molecules are packed by p–p stacking
Fig. 1. ORTEP drawing of 1 (30% probability ellipsoids). Hydrogen atoms and ClO 4 anions are omitted for clarity.
Fig. 2. ORTEP drawing of 2 (30% probability ellipsoids). Hydrogen atoms and ClO 4 anions are omitted for clarity.
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interactions between the 4,40 -bipy groups. The shortest centroid– centroid distance between the pyridinyl rings is 3.606(1) Å (Fig. S2). In Compound 3 crystallizes in the monoclinic space group P1. the asymmetric unit, there are six Mn ions. The Mn atoms are located in the vertex of two MnII2–MnIII 2 tetrahedra sharing their MnIII–MnIII edge with a l4-O2 in the center of each tetrahedron, giv10+ ing rise to a [MnII4MnIII unit. Peripheral ligation consists of 2 (l4-O)2] ten bridging carbp ions and four terminal DMF molecules (Fig. 3). Four carbp ions are coordinating in g1,g2-l3 mode whereas the remaining ligands show the g1,g2-l2 coordination mode. The Mn ions locates in the octahedral environment, each MnII ion is of the type MnO6 with four O atoms from four carboxylate groups, one O from the central l4-O bridge, and one O from a DMF. The Mn–O distances are in the range of 2.101(2)–2.307(2) Å, which are in accordance with those in [Mn6O2(PhCO2)10(DMF)4] [21]. The coordination geometry around the inner MnIII ions (Mn5, Mn6) is elongated octahedral for the Jahn–Teller effects, where the six positions are occupied by O atoms from four carbp bridging groups and two l4-O2 ions. The axial bond lengths Mn5–O6, Mn5–O14 are equal to 2.241(2) and 2.247(2) Å, respectively. For Mn6, the Mn6–O7 and Mn6–O15 bond lengths are 2.239(2) and 2.233(2) Å. The Mn–O bond lengths in the equatorial position are shorter than the axial positions. The Mn5 Mn6 separation is equal to 2.814(1) Å. The bond
angles for Mn5–O25–Mn6 and Mn5–O26–Mn6 are 95.96(10)° and 95.23(10)°, respectively. BVS confirms that both Mn5 and Mn6 have the +3 oxidation state. Compound 3 is the first known example of [Mn6O2(RCO2)10] cluster bearing the carbazolyl group. The Mn6 molecules are packed together through weak hydrogen bonding interactions among Mn6 and guest molecules (Fig. S3). It should be noted that, this kind of Mn6 cluster can also be constructed by using CH3CO 2 [22a], CHCl2CO2 [22b], CCl3CO2 [22c], CBr3CO2 [22d], CH3CH2CO2 [22e], (CH3)3CCO2 [22b], PhCO2 [21], F4PhCO 2 [22f] and (NO2)2PhCO 2 [22g] anions as ligands. Compound 4 crystallizes in monoclinic space group C2/c. The 10+ [MnII4MnIII core locates on a 2-fold axis, which passes 2 (l4-O)2] through Mn1 and Mn2 along the b-axis, and hence the asymmetric unit contains only half of the cluster. The central core structure is very similar to that in compound 3 (Fig. 4). The bond lengths and angles are close to that in 3. The 4,40 -bipy molecules act as bridging ligands connecting the [Mn6O2(RCO2)10] clusters with its four neighbors through the peripheral MnII ions. Thus each 4,40 -bipy connects two Mn4 atoms of adjacent clusters or two Mn3 atoms, forming a 3D distorted porous diamond-like framework that can be described as a (6,4) net (Fig. 5). The solvent-accessible volume per unit cell is 36.5% as calculated by the PLATON program. The 3D structure is different from [Mn2L2(4,40 bpy)2][Mn2L2(H2O)2]2H2O that has 2Dlayer + 1Dchain ? 3D framework [23]. To our knowledge, polymeric frameworks based on [Mn6] cores are scarce. The title compound [Mn6O2(carbp)10(4,40 -bipy)2] can be compared with other 3D diamond-like polymers such as [Mn6O2(tBuCO2)10(NIT-Me)2] [24a] and [Mn6O2(C6H5CH2CO2)10(pyz)2] [24b] with 2,4,4,5,5-pentamethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1oxyl (NIT-Me) and pyrazine (pyz) as bridges. While, only one 1D polymeric [Mn6O2(t-BuCO2)10(t-BuCO2H)(4,40 -bipy)] with 4,40 -bipy as bridge was reported [24c]. This study gives us the signal that monocarboxylate ligand bearing bulky group may be employed to construct 3D porous coordination polymer.
3.3. Magnetic properties The temperature-dependent molar magnetic susceptibilities of 1–4 were measured at 1000 Oe in the temperature range of 1.8– 300 K. The vM and vMT versus T plots for 1 are shown in Fig. 6. At room temperature, vMT is equal to 8.92 cm3 K mol1, which is close to the expected spin-only value for two isolated magnetic
Fig. 3. (a) Structure of compound 3, C and N atoms from DMF were omitted for clarity; (b) Core structure of compound 3, hydrogen and aromatic rings were omitted for clarity.
Fig. 4. Structure of compound 4.
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Fig. 5. (a) View of the diamond structure; (b) view of an equivalent fragment in the distorted 3D diamond-like topology in compound 4. (C atoms are replaced by 10+ [MnII4MnIII clusters and the C–C bonds by 4,40 -bipy bridges). Hydrogen atoms and carbazolyl groups are omitted for clarity. 2 (l4-O)2]
centers (S = 5/2). When the temperature is lowered, vM increases and passes through a rounded maximum at Tmax = 7 K. This indicates that antiferromagnetic exchange interactions prevail in solid compound. The magnetic data can be analyzed using a dinuclear model [14]. The exchange Hamiltonian is H = 2JS1S2, where S = 5/2, J is the coupling constant. Take the interdimer exchange interactions (zj0 ) into account. The best fitting parameters obtained are g = 2.0, J = 0.86 cm1, and zj0 = 0.027 cm1. The result shows that the antiferromagnetic interaction is very weak, which is in consistent with that observed in other dinuclear manganese compounds bearing dicarboxylate bridges [19]. For 2, the room temperature vMT is equal to 8.59 cm3 K mol1, which is close to the spin only value for two isolated MnII ions. Upon cooling, vMT decreases to 0.62 cm3 K mol1 at 1.8 K (Fig. 7). The data were fitted by using the dinuclear model to give g = 2.0, J = 0.95 cm1, and zj0 = 0.14 cm1. Clearly, the MnII–MnII (d5–d5) magnetic exchange interaction is more antiferromagnetic than that in 1. This is due to the presence of g1,g2-l2 bridging carboxylate in 2 that can transfer stronger magnetic interaction than the g1,g1-l2 bridging carboxylate in 1. For 3, the room temperature vMT is 17.27 cm3 K mol1, which is lower than the expected spin-only value for isolated magnetic centers (23.5 cm3 K mol1 for four MnII and two MnIII). When the temperature is lowered, the vMT product shows a progressive decrease down to about 50 K and a more abrupt decrease at lower temperature to reach a value of 0.42 cm3 K mol1 at 1.8 K (Fig. 8). The profile of this magnetic behavior indicates that antiferromagnetic interactions are propagated between the metal centers. This observation can be compared with other clusters with identical 10+ [MnII4MnIII cores [22]. 2 (l4-O)2]
Fig. 7. Plots of vM (s) and vMT (h) for 2. Solid lines show the best fit of the data according to the proposed model.
Fig. 8. Thermal variation of the vMT product per [Mn6] cluster for compound 3. The solid lines correspond to the best-fit curve using the parameters described in the text.
As shown in Fig. 9, a model is used to simulate four pairwise coupling on the basis of the bond lengths and angles between the Mn atoms. The Heisenberg spin Hamiltonian is thus given as:
H ¼ J 1 ðS1 S2 þ S3 S4 Þ J 2 ðS1 S5 þ S2 S6 þ S3 S5 þ S4 S6 Þ J 3 ðS1 S6 þ S2 S5 þ S3 S6 þ S4 S5 Þ J 4 S5 S6
Fig. 6. Plots of vM (s) and vMT (h) for 1. Solid lines show the best fit of the data according to the proposed model.
J1 and J4 represent the MnII–MnII (d5–d5) and MnIII–MnIII (d4–d4) exchange interaction, while J2 and J3 represent the MnII–MnIII (d5–d4) exchange interaction. The susceptibility data were fitted by using the magnetism package MAGPACK based on the
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4. Conclusions The reactions of carbazol-9-ylpropanate and MnII ions in the presence of chelating 2,20 -bipy and bridging 4,40 -bipy ligands yield four different compounds. The results indicate the bulky carbazolyl substituent group has good crystallinity in the construction of coordination compounds. We found solvent plays a key role for the formation of special compound such as 2 and 4. In addition, DMF is one ideal solvent for the construction of mixed valence state manganese clusters such as 3. Magnetic measurements of 1–4 revealed that all of the compounds mediate antiferromagnetic interactions between the metal ions. Further work is in progress to study new manganese phosphonates with bulky carbazole groups. Acknowledgements
Fig. 9. Model of magnetic exchange pathway in the [Mn6] cluster.
This work is supported by NSFC (Nos. 21001018, 21201025) and NSF of Jiangsu Provence (Nos. BK2012643, 12KJA150001, 14KJA150001, 14KJB150001). Appendix A. Supplementary material CCDC 1022151, 1022152, 1022153 and 1022154 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica. 2015.03.032. References
Fig. 10. Thermal variation of the vMT product per [Mn6] cluster for compound 4. The solid lines correspond to the best-fit curve using the parameters described in the text.
corresponding Hamiltonian [25]. The best fitting can be achieved above 10 K with parameters: g = 2, J1 = 3.8 cm1, J2 = J3 = 8.0 cm1, J4 = 99.6 cm1 (R = 1.2 103). The larger J2 than J1 indicates that the (d5–d4) interaction is more antiferromagnetic than the (d5–d5) interaction as observed in [MnII4MnIII [26]. This simulation 3 (teaH)3(tea)3](ClO4)23MeOH results are consistent with the previous analysis of the similar metallic core cluster [22f,24b]. For 4, the room temperature vMT is 18.63 cm3 K mol1, which is smaller than the expected spin-only value for isolated magnetic centers. Upon cooling, the value of vMT gradually decreases to 0.58 cm3 K mol1 at 1.8 K (Fig. 10). The result indicates the presence of overall antiferromagnetic interactions between the metal centers. Although the structure of 4 shows that Mn6 clusters are connected through 4,40 -bipy bridges. The magnetic coupling through these bridges can be neglected since the shortest Mn–Mn distance through 4,40 -bipy is about 11.63 Å. Therefore, the susceptibility data were analyzed in a similar way to 3 and the best fitting parameters obtained are g = 2, J1 = 3.6 cm1, J2 = J3 = 7.7 cm1, J4 = 99.6 cm1 (R = 8.2 104). The J values for compound 4 are closely related to that for 3 due to the similar bond angles and distances.
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