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Two new azido bridging Mn(II) 1D systems: Synthesis and characterization of trans-[Mn(N3)2(2-aminopyridine)2]n and trans-[Mn(N3)2(4-azidopyridine)2]n
Journal of Molecular Structure 969 (2010) 192–196
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Two new azido bridging Mn(II) 1D systems: Synthesis and characterization of trans-[Mn(N3)2(2-aminopyridine)2]n and trans-[Mn(N3)2(4-azidopyridine)2]n Franz A. Mautner a,*, Andreas Egger a, Beate Sodin a, Mohamed A.S. Goher b, Morsy A.M. Abu-Youssef b, Alshima’a Massoud b, Albert Escuer c, Ramon Vicente c a b c
Institut für Physikalische und Theoretische Chemie, Technische Universität Graz, A-8010 Graz, Austria Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321, Egypt Department de Quimica Inorganica and Institut de Nanociencia i Nanotecnologia, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain
a r t i c l e
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Article history: Received 7 December 2009 Received in revised form 2 February 2010 Accepted 4 February 2010 Available online 10 February 2010 Keywords: Pyridine derivative ligands Manganese(II) Azido bridging Spectra Crystal structure Magnetic properties
a b s t r a c t Two new manganese(II) azido complexes [Mn(L)2(N3)2]n with L = 2-aminopyridine (1) and 4-azidopyridine (2) have been synthesized and structurally characterized by spectroscopic and crystallographic methods. Both complexes 1 and 2 crystallize in the triclinic system, space group P-1, and their structures are featuring six-coordinate manganese centres, chains of [Mn(N3)2]n, and two trans 2-aminopyridine or 4-azidopyridine ligands giving 1D systems. In the [Mn(N3)2]n-chains of 1 each manganese atom is connected by double di end-on (EO) azido bridges forming cyclic Mn2N2 units, whereas in 2, the metal centers are alternatively bridged by double di-end-to-end (EE) and double di end-on (EO) azido ligands. The intra-chain Mn. . .Mn distances are 3.5350(12) in 1, and 3.3701(18) and 5.032(3) Å, in 2, respectively. In 1 the polymeric chains of polyhedra are connected by hydrogen bonds of type N–H. . .N to generate a 2D supramolecular network. Magnetic susceptibility measurements were performed only for complex 1 which shows weak ferromagnetic interactions with a J value of 1.2 cm1. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction A large number of uncommon magnetic systems have been reported as a consequence of the growing research on the magnetic properties of azido-bridged compounds in the last decade [1]. This is in fact resulted from the versatility of the azido ion which has the ability to connect two metal atoms in the end-to-end fashion (l-1,3, EE), which is generally associated with antiferromagnetic (AF) coupling or end-on (l-1,1, EO) predominantly associated with ferromagnetic (F) coupling, and this bridging nature of the azido ion leads to the formation of molecular compounds with a wide range of nuclearities [1,2] as well as extended systems including 1D, 2D and 3D dimensionalities [1,3]. Such versatility of the bridging azido ion allows alternating EE and EO, as well as variable ratios of both types to exist simultaneously in the same compound [4,5]. With the above flexibility, a series of compounds of the general formula [Mn(N3)2(R-py)2]n, where R-py is a substituted pyridine ligand with a R group in meta or para position, having 1D systems in which the alternance of EE and EO azido bridges exist have been studied and found to form a complete series with gradual changes in the topology and magnetic responses [1]. This series include compounds containing only EO or only EE with F or AF magnetic responses, respectively, as well as systems with variable ratios of * Corresponding author. Tel.: +43 316 873 8234; fax: +43 316 873 8225. E-mail address: [email protected] (F.A. Mautner). 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.02.012
EE to EO bridges. This graduation provides interesting material to study unusual topologies and magnetic properties. As an extension of our research on the Mn(II)/azide/pyridine derivative systems, we have synthesized and characterized two new compounds using L = 2-aminopyridine (2-ampy) and 4-azidopyridine (4-azpy) to obtain the 1D systems trans-[Mn(N3)2(2-ampy)2]n (1) and trans-[Mn(N3)2(4-azpy)2]n (2). 2. Experimental 2.1. Materials and instrumentation Infrared spectra were recorded in a Bruker IFS-125 model FT-IR spectrophotometer as KBr pellets. Elemental analyses were carried out using a Perkin-Elmer analyzer. 2-Aminopyridine has been purchased from Aldrich and other chemicals were of analytical grade quality and used without further purification. Caution: Metal azido complexes are potentially explosives. Only a small amount of material should be prepared and should be handled with caution. 2.2. Synthesis 2.2.1. Preparation of [Mn(N3)2(2-ampy)2]n (1) (a) Mn(II) nitrate tetrahydrate (0.25 g, 1.0 mmol), sodium azide (0.13 g, 2.0 mmol) and 2-aminopyridine (0.19 g, 2.0 mmol) were
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dissolved in a minimum amount of aqueous hydrazoic acid (2.5 mL) [6,7]. After warming to 65 °C a clear solution was obtained and subsequent slow cooling of the solution to 4 °C gave after two weeks compound 1 as yellow crystals (yield: 0.20 g, 60%). (b) Alternatively single crystals of 1 were also obtained by the H-tube technique. An aqueous solution of (20 cm3) of Mn(NO3)24H2O (0.50 g, 2.0 mmol) and 0.10 g of L-ascorbic acid was prepared and placed inside the H-tube until its connection has been covered, followed by dropwise addition of both 2-aminopyridine (0.38 g, 4.0 mmol) in (10 cm3) methanol and an aqueous solution of NaN3 (0.65 g, 10.0 mmol), each in one arm, at the same time. The final clear mixture was allowed to stand undisturbed in a dark place at room temperature for several weeks. Analysis: Found: C 36.6; H 3.5; N 43.0. Calcd. for C10H12MnN10: C 36.7; H 3.7; N 42.8. IR (KBr, cm1): 2078 vs mas(N3) 1337 s, 1276 s, mas(N3), 1620 s. 2.2.2. Preparation of [Mn(N3)2(4-azpy)2]n (2) To a methanolic solution of 0.50 g, 2 mmol of manganese(II) nitrate tetrahydrate, 15 ml, 0.60 g, 4 mmol of 4-chloropyridine hydrochloride solid were added. Further, 0.65 g, 10 mmol of sodium azide aqueous solution were added dropwise with constant stirring, the clear solution was allowed to stand in dark place for several days. Transparent crystals suitable for X-ray measurements were collected, dried in air with a yield of 60% with respect to the metal. Analysis: Found: C, 31.7; H, 2.4; N, 51.5. Calcd. for C10H8MnN14: C, 31.7; H, 2.1; N, 51.7. IR (KBr, cm1): 2419 ms, 2265 s, (4-N3py) 2127, 2107, 2082 vs, mas(N3). 1597 vs, 1560 vs, 1500 vs, 1469 s, 1450 s, 1423 vs, 1412 vs, 1134 vs, 1109 vs, 1010 vs, 816 vs, (pyridine moiety), 1334 s, 1289 vs, (msym N3) 592 vs, 507 vs, (d N3) 314 vs, 294 vs, 269 vs (M–N(L) and M–N(N3) vibrations).
Table 1 Crystallographic data and processing parameters. Compound
1
2
Empirical formula Formula mass System Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z T (K) l(MoKa) (mm1) Dcalc (Mg/m3) Crystal size (mm) h range (°) Reflections collected Independ. refl./Rint Parameters Goodness-of-Fit on F2 R1/wR2 (all data) Residual extrema (e/Å3)
C10H12MnN10 327.24 Triclinic P-1 3.5350(10) 9.038(3) 10.139(3) 82–84(2) 89.56(2) 87.96(2) 321.2(2) 1 99(2) 1.039 1.692 0.25 0.20 0.16 3.23–30.00 2217 1846/0.0252 103 1.096 0.0254/0.0676 0.410/0.352
C10H8MnN14 379.24 Triclinic P-1 8.252(3) 8.313(2) 11.927(6) 82.71(3) 69.88(3) 80.83(3) 765.1(6) 2 92(2) 0.903 1.666 0.30 0.24 0.12 2.97–26.00 3424 2977/0.0258 226 1.095 0.0380/0.0905 0.491/0.435
aqueous/methanolic solutions afforded the title complexes [Mn(N3)2(2-aminopy)2]n, 1, and [Mn(N3)2(4-azidopy)2]n, 2. The 4azidopyridine ligand in 2 was formed in situ by the reaction of the 4-chloropyridine with excess sodium azide. Complex 2 is a new polymorph with 1D chain system, whereas the previously reported polymorph forms a 2D layer system and exhibits ferrimagnetic behaviour [12].
2.3. Magnetic measurements 3.1. Structures Magnetic susceptibility measurements under a magnetic field of 1 T in the temperature range 2–300 K and magnetization measurements in the field range of 0–5 T were performed with a Quantum Design MPMS-XL SQUID magnetometer at the Magnetochemistry Service of the University of Barcelona. All measurements were performed on polycrystalline samples. Pascal’s constants were used to estimate the diamagnetic corrections [8] which were subtracted from the experimental susceptibilities to give the corrected molar magnetic susceptibilities. 2.4. X-ray crystal structure analysis The X-ray single-crystal data were collected on a modified STOE 4-circle diffractometer with graphite-monochromatized Mo-Ka radiation (k = 0.71069 Å). The crystallographic data, conditions retained for the intensity data collection and some features of the structure refinements are listed in Table 1. Lorentz-polarisation and absorption corrections were made using the DIFABS computer program [9]. The structures were solved by direct methods using the SHELXS-86 [10a] computer program and refined by full-matrix least-squares methods on F2, using the SHELXL-93 [10b] program incorporated in the SHELXTL/PC V 5.03 [11] program package. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were assigned with isotropic displacement factors and included in the final refinement cycles by use of geometrical restraints. 3. Results and discussion The interaction between manganese(II) nitrate tetrahydrate, sodium azide and 2-aminopyridine or 4-chloropyridine in aqueous or
Compound 1 crystallizes in the triclinic space group P-1. Relevant bond distances and angles are listed in Table 2, the structure is illustrated in Fig. 1. Each Mn is located at a center of inversion and is coordinated octahedrally by six N atoms of which two are part of the trans-coordinated 2-aminopyridine ligands and the remaining four N atoms belong to azido groups. The Mn centers are arranged in linear chains [angle Mn(1C). . .Mn(1). . .Mn(1B) = 180°] along the a-axis by means of azido groups which double-bridge two adjacent Mn
Table 2 Selected bond lengths (Å) and angles (°) for (1). Mn(1). . .Mn(1C) Mn(1)–N(11A) Mn(1)–N(1A) Mn(1)-N(11B) N(11)–N(12) N(12)–N(13) H(7). . .N(11C) N(2)–H(6) N(2). . .N(13D) N(11A)–Mn(1)–N(11) N(11)–Mn(1)–N(1A) N(11)–Mn(1)–N(1) N(11A)–Mn(1)–N(11B) N(1A)–Mn(1)–N(11B) N(11A)–Mn(1)–N(11C) N(1A)–Mn(1)–N(11C) N(11B)–Mn(1)–N(11C) N(12)–N(11)–Mn(1B) N(13)–N(12)–N(11) N(2)–H(7). . .N(11C)
3.5350(12) 2.2495(12) 2.2889(12) 2.2901(12) 1.2060(14) 1.154(2) 2.35 0.89 3.255(2) 180.0 90.75(4) 89.25(4) 102.28(4) 93.17(4) 77.72(4) 86.83(4) 180.0 134.70(8) 179.24(12) 158.9
N(11). . .N(11B) Mn(1)–N(11) Mn(1)–N(1) Mn(1)–N(11C) N(11)–Mn(1B) N(2)–H(7) N(2). . .N(11C) H(6). . .N(13D) N(11A)–Mn(1)–N(1A) N(11A)–Mn(1)–N(1) N(1A)–Mn(1)–N(1) N(11)–Mn(1)–N(11B) N(1)–Mn(1)–N(11B) N(11)–Mn(1)–N(11C) N(1)–Mn(1)–N(11C) N(12)–N(11)–Mn(1) Mn(1)–N(11)–Mn(1B) N(11B). . .N(11)–N(12) N(2)–H(6). . .N(13D)
2.848(2) 2.2495(12) 2.2889(12) 2.2901(12) 2.2901(12) 0.88 3.1871(18) 2.41 89.25(4) 90.75(4) 180.0 77.72(4) 86.83(4) 102.28(4) 93.17(4) 121.74(8) 102.28(4) 168.80(10) 159.3
Symmetry codes: (A) x + 1,y + 1,z; (B) x + 2,y + 1,z; (C) x1,y,z; (D) x + 1,y + 2,z.
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F.A. Mautner et al. / Journal of Molecular Structure 969 (2010) 192–196 Table 3 Selected bond lengths (Å) and angles (°) for (2). Mn(1). . .Mn(1A) Mn(1)–N(11) Mn(1)–N(21) Mn(1)–N(1) Mn(1)–N(2) N(21)–N(22) N(31)–N(32) N(41)–N(42) N(11A)–Mn(1)–N(11) N(11A)–Mn(1)–N(1) N(11A)–Mn(1)–N(23) N(11)–Mn(1)–N(21) N(1)–Mn(1)–N(21) N(11)–Mn(1)–N(2) N(1)–Mn(1)–N(2) N(21)–Mn(1)–N(2) N(12)–N(11)–Mn(1A) N(13)–N(12)–N(11) N(21)–N(22)–N(23B) N(31)–N(32)–N(33) N(41)–N(42)–N(43)
3.3701(18) 2.235(2) 2.244(2) 2.240(2) 2.271(2) 1.177(3) 1.245(3) 1.246(3) 82.20(9) 94.27(8) 170.81(8) 171.83(8) 86.91(8) 93.78(8) 171.26(8) 86.61(8) 126.4(2) 179.1(3) 178.3(2) 170.7(3) 171.2(3)
Mn(1). . .Mn(1B) Mn(1)–N(11A) Mn(1)–N(23) N(11)–N(12) N(12)–N(13) N(22)–N(23B) N(32)–N(33) N(42)–N(43) N(11)–Mn(1)–N(1) N(11)–Mn(1)–N(23) N(1)–Mn(1)–N(23) N(11A)–Mn(1)–N(21) N(23)–Mn(1)–N(21) N(11A)–Mn(1)–N(2) N(23)–Mn(1)–N(2) N(12)–N(11)–Mn(1) Mn(1)–N(11)–Mn(1A) N(11A). . .N(11)–N(12) Mn(1)–N(23)–N(22B) Mn(1)–N(21)–N(22)
5.032(3) 2.237(2) 2.241(2) 1.167(3) 1.165(3) 1.181(3) 1.122(3) 1.129(3) 93.47(8) 88.96(8) 88.74(9) 89.64(8) 99.21(8) 91.54(8) 86.53(8) 126.2(2) 97.80(9) 152.2(3) 119.7(2) 123.5(2)
Symmetry codes: (A) x,1y,1z; (B) x,y,1z; (C) x,1 + y,z. Fig. 1. Molecular geometry and atom labeling scheme of 1.
atoms in an end-on coordination mode (EO) giving rise to centrosymmetric Mn2N2 units. Each unit defines a plane with one azido group of the unit above and the other one below the plane by an angle of 168.80(10)° [N(11B). . .N(11)–N(12)]. The azido groups are linear (179.24(12)°) and the Mn–N(azido) distances are 2.2495(12) and 2.2901(12) Å for Mn(1)–N(11) and Mn(1B)–N(11), respectively. The ligands are coordinated via the pyridinic N atom with a Mn–N distance of 2.2889(12) Å and the pyridine ring tilted with a torsion angle of 163.8(1)° for Mn(1)–N(1)–C(5)–C(4). The NH2-groups of the ligands establish two different types of hydrogen bonds: an intramolecular H-bond to a coordinated N(azido) atom belonging to the same octahedron as the ligand and an inter-molecular H-bond to the terminal N atom of an azido group in the adjacent chain. Due to the latter one the Mn(N3)2-chains are connected to layers extending
along the ab-plane of the unit cell (Fig. 2). Along the chain direction the pyridine rings form p–p stacking interactions with a separation of 3.5350(10) Å between their centroids. Compound 2 crystallizes also in the triclinic space group P-1. Relevant bond distances and angles are collected in Table 3 and a perspective view together with the atom numbering scheme is shown in Fig. 3. The structure of 2 consists of octahedrally coordinated Mn atoms in which the coordination sites are occupied by two 4-azidopyridine ligands in trans arrangement and four azido ligands which form double bridges between neighbouring Mn centers. The azido groups in the double bridges are alternately in the EE and EO modes, giving an alternating chain, oriented along the b-axis of the unit cell (Fig. 4). The Mn2(l1,3-N3)2 ring is quite regular: bond lengths are Mn(1)–N(21) = 2.244(2) Å, and Mn(1)–N(23) = 2.241(2) Å, and bond angles are Mn(1)–N(21)–N(22) = 123.5(2)° and Mn(1)– N(23)–N(22B) = 119.7(2)°. The Mn–(l1,3-N3)2–Mn ring shows the
Fig. 2. Packing view of 1. Along the chain direction the 2-aminopyridine molecules form p–p stacking interactions with a separation of 3.5350(10) Å between centroids of their pyridine rings.
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Fig. 3. Ortep view and atom labeling scheme of 2.
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typical distortion from the planar to the chair conformation, evaluated as a d parameter = 34.3° [13]. The Mn(1B)–N(23B). . .N(21)– Mn(1) torsion angle = 51.3(3)°. The centrosymmetric Mn2N2 ring is strictly planar, as is usual for double EO bridges, and shows a bond angle Mn(1)–N(11)–Mn(1A) = 97.80(9)° and bond lengths Mn(1)– N(11) and Mn(1)–N(11A) of 2.235(2) and 2.237(2) Å, respectively. The Mn. . .Mn intra-chain distances are asymmetric, the longer corresponding to the EE ring, Mn(1). . .Mn(1B) = 5.032(3) Å, and the shorter to the EO ring, Mn(1). . .Mn(1A) = 3.3701(18) Å. The polymeric chain is slightly corrugated with a Mn(1B). . .Mn(1). . .Mn(1A) angle of 162.9°. The N(1)–Mn(1)–N(2) bond angle of the axial pyridine ligand is 171.26(8)°. This deviation from 180° has the effect of moving away the axial ligands on the EO ring. The terminal azido groups bonded to the pyridine rings in para-positions have strong asymmetric bond geometries with Dd(N–N) [difference of the N–N bond lengths within the azide group] of 0.121(3) and 0.117(3) Å, respectively, and N(31)–(N32)–N(33) and N(41)–N(42)–N(43) bond angles of 170.7(3)° and 171.2(3)°, respectively. These values are in good agreement with corresponding parameters observed for the covalent azide group N(51)–N(52)–N(53) in the 2D polymorph of [Mn(N3)2(4-azidopy)2]n: Dd(N–N) = 0.136(9) Å, N–N–N bond angle = 170.2(7)° [12]. As far as we know no other metal complexes with 4-azidopyridine are known, whereas 2-aminopyridine is a common ligand: e.g. Oxalato-bridged chains of octahedra with trans-coordinated 2aminopyridines are reported in a series of transition metal compounds [14]. Cis-coordinated 2-aminopyridine molecules and l(NCS)2 double bridges are observed in the polymeric chains of [Ni(NCS)2(2-ampy)2]n [15]. Methoxide and chloride bridging units are present in the polymeric chains of [Cu2(2-ampy)2(l-OMe)2Cl2]n [16]. The dimeric form of [Cu(benzoato)2(2-ampy)]2 reveals a ‘‘paddle-wheel” type structure where 2-aminopyridine acts as axial ligand via pyridine N atom [17]. The core of the cubic zinc phosphonate [tBuPO3Zn(2-ampy)]4 resembles a ‘‘zeolite”-like arrangement [18]. In the dinuclear Cu(II) complex with 2,6-pyridinedicarboxlyate the 2-ampy molecules act as N,N0 -bridging ligands [19]. 3.2. Magnetic properties The variable temperature magnetic susceptibility data for complex 1 were recorded between 300 and 2 K. The plot of vMT versus T is shown in Fig. 5. Compound 1 shows a vMT room temperature value of 4.74 cm3 mol1 K, greater than the expected value of 4.375 cm3 mol1 K for an isolated manganese atom. vMT increases
Fig. 4. Packing view of 2.
Fig. 5. Plot of vMT (dot circles) vs T in the 300–2 K range of temperatures for 1 measured on cooling under external magnetic field of 0.3 T. The solid line shows the best fit as uniform ferromagnetic chain (see text).
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gradually as the temperature decreases to a maximum value of 25.81 cm3 mol1 K at 4 K and then decreases quickly to 9.59 cm3 mol1 K at 2 K. The magnetic susceptibility behaviour of 1 indicates bulk ferromagnetic coupling in good agreement with magnetization experiments which show a quasi-saturated value of MNb equivalent to five electrons (4.96) under an external field of 5 T at 2 K. Taking into account the 1D structure of 1, the fit of the magnetic data was made by using the appropriate equation [20] for homogeneous S = 5/2 chains derived from the Hamiltonian H = JSiSi+1 in the range 300–5 K for 1 due to the decrease of the vMT values after the maximum. The best fit parameters were J = 1.2(1) cm1, g = 2.13(2). The positive J value is in accordance with the ferromagnetic coupling expected for end-on azido bridges with Mn–N–Mn bond angles around 100° (the Mn(1)–N(11)– Mn(10 ) bond angle is 102.28(4)°). The J value for 1 is similar to that reported for the related compounds cis-[Mn(l1,1-N3)2(2-bzpy)2]n (2-bzpy = 2-benzoylpyridine) [21] and trans-[Mn(l1,1-N3)2(pyzamid)2]n (pyzamid = pyrazineamide) [22] with J values of 0.8 and 1.1 cm1 for Mn–N–Mn angles of 100.5° (mean angle) and 97.1°, respectively. The structure of cis-[Mn(l1,1-N3)2(2-bzpy)2]n shows well isolated chains but as in the case of trans-[Mn(l1,1-N3)2(pyzamid)2]n, 1 forms H bonds between chains which are the cause of the weak antiferromagnetic interactions at low temperature as can be seen in the decrease of vMT in the low temperature region. In summary we have synthesized and characterized two new azido-bridged Mn 1D systems: [Mn(N3)2(2-aminopy)2]n, 1, and [Mn(N3)2(4-azidopy)2]n, 2. In 1 the polymeric chains of polyhedra are formed by di-EO azido bridges and further connected by hydrogen bonds of type N–H. . .N to generate a 2D supramolecular network. Magnetic susceptibility measurements for 1 show weak ferromagnetic interactions with a J value of 1.2 cm1. The 1D complex 2 is a new polymorph with composition [Mn(N3)2(4-azidopy)2]n. As its previously reported 2D polymorph, complex 2 exhibits, EO and EE azido bridging groups as well as ‘‘covalent” azido groups in the trans-coordinated 4-azidopyridine ligands. Acknowledgements This research was partially supported by CICYT (Grant CTU2006/01759/BQU) through the Grant CTQ2005-08123-C02/ BQU. F.A.M. thanks Prof. C. Kratky and F. Belaj (Univ. Graz) for technical support. Appendix A. Supplementary data Supplementary data are available from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK on request, quoting the deposition numbers: CCDC-643272 and CCDC-756797 for 1 and 2, respectively. 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
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Two new azido bridging Mn(II) 1D systems: Synthesis and characterization of trans-[Mn(N3)2(2-aminopyridine)2]n and trans-[Mn(N3)2(4-azidopyridine)2]n Franz A. Mautner a,*, Andreas Egger a, Beate Sodin a, Mohamed A.S. Goher b, Morsy A.M. Abu-Youssef b, Alshima’a Massoud b, Albert Escuer c, Ramon Vicente c a b c
Institut für Physikalische und Theoretische Chemie, Technische Universität Graz, A-8010 Graz, Austria Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321, Egypt Department de Quimica Inorganica and Institut de Nanociencia i Nanotecnologia, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain
a r t i c l e
i n f o
Article history: Received 7 December 2009 Received in revised form 2 February 2010 Accepted 4 February 2010 Available online 10 February 2010 Keywords: Pyridine derivative ligands Manganese(II) Azido bridging Spectra Crystal structure Magnetic properties
a b s t r a c t Two new manganese(II) azido complexes [Mn(L)2(N3)2]n with L = 2-aminopyridine (1) and 4-azidopyridine (2) have been synthesized and structurally characterized by spectroscopic and crystallographic methods. Both complexes 1 and 2 crystallize in the triclinic system, space group P-1, and their structures are featuring six-coordinate manganese centres, chains of [Mn(N3)2]n, and two trans 2-aminopyridine or 4-azidopyridine ligands giving 1D systems. In the [Mn(N3)2]n-chains of 1 each manganese atom is connected by double di end-on (EO) azido bridges forming cyclic Mn2N2 units, whereas in 2, the metal centers are alternatively bridged by double di-end-to-end (EE) and double di end-on (EO) azido ligands. The intra-chain Mn. . .Mn distances are 3.5350(12) in 1, and 3.3701(18) and 5.032(3) Å, in 2, respectively. In 1 the polymeric chains of polyhedra are connected by hydrogen bonds of type N–H. . .N to generate a 2D supramolecular network. Magnetic susceptibility measurements were performed only for complex 1 which shows weak ferromagnetic interactions with a J value of 1.2 cm1. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction A large number of uncommon magnetic systems have been reported as a consequence of the growing research on the magnetic properties of azido-bridged compounds in the last decade [1]. This is in fact resulted from the versatility of the azido ion which has the ability to connect two metal atoms in the end-to-end fashion (l-1,3, EE), which is generally associated with antiferromagnetic (AF) coupling or end-on (l-1,1, EO) predominantly associated with ferromagnetic (F) coupling, and this bridging nature of the azido ion leads to the formation of molecular compounds with a wide range of nuclearities [1,2] as well as extended systems including 1D, 2D and 3D dimensionalities [1,3]. Such versatility of the bridging azido ion allows alternating EE and EO, as well as variable ratios of both types to exist simultaneously in the same compound [4,5]. With the above flexibility, a series of compounds of the general formula [Mn(N3)2(R-py)2]n, where R-py is a substituted pyridine ligand with a R group in meta or para position, having 1D systems in which the alternance of EE and EO azido bridges exist have been studied and found to form a complete series with gradual changes in the topology and magnetic responses [1]. This series include compounds containing only EO or only EE with F or AF magnetic responses, respectively, as well as systems with variable ratios of * Corresponding author. Tel.: +43 316 873 8234; fax: +43 316 873 8225. E-mail address: [email protected] (F.A. Mautner). 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.02.012
EE to EO bridges. This graduation provides interesting material to study unusual topologies and magnetic properties. As an extension of our research on the Mn(II)/azide/pyridine derivative systems, we have synthesized and characterized two new compounds using L = 2-aminopyridine (2-ampy) and 4-azidopyridine (4-azpy) to obtain the 1D systems trans-[Mn(N3)2(2-ampy)2]n (1) and trans-[Mn(N3)2(4-azpy)2]n (2). 2. Experimental 2.1. Materials and instrumentation Infrared spectra were recorded in a Bruker IFS-125 model FT-IR spectrophotometer as KBr pellets. Elemental analyses were carried out using a Perkin-Elmer analyzer. 2-Aminopyridine has been purchased from Aldrich and other chemicals were of analytical grade quality and used without further purification. Caution: Metal azido complexes are potentially explosives. Only a small amount of material should be prepared and should be handled with caution. 2.2. Synthesis 2.2.1. Preparation of [Mn(N3)2(2-ampy)2]n (1) (a) Mn(II) nitrate tetrahydrate (0.25 g, 1.0 mmol), sodium azide (0.13 g, 2.0 mmol) and 2-aminopyridine (0.19 g, 2.0 mmol) were
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dissolved in a minimum amount of aqueous hydrazoic acid (2.5 mL) [6,7]. After warming to 65 °C a clear solution was obtained and subsequent slow cooling of the solution to 4 °C gave after two weeks compound 1 as yellow crystals (yield: 0.20 g, 60%). (b) Alternatively single crystals of 1 were also obtained by the H-tube technique. An aqueous solution of (20 cm3) of Mn(NO3)24H2O (0.50 g, 2.0 mmol) and 0.10 g of L-ascorbic acid was prepared and placed inside the H-tube until its connection has been covered, followed by dropwise addition of both 2-aminopyridine (0.38 g, 4.0 mmol) in (10 cm3) methanol and an aqueous solution of NaN3 (0.65 g, 10.0 mmol), each in one arm, at the same time. The final clear mixture was allowed to stand undisturbed in a dark place at room temperature for several weeks. Analysis: Found: C 36.6; H 3.5; N 43.0. Calcd. for C10H12MnN10: C 36.7; H 3.7; N 42.8. IR (KBr, cm1): 2078 vs mas(N3) 1337 s, 1276 s, mas(N3), 1620 s. 2.2.2. Preparation of [Mn(N3)2(4-azpy)2]n (2) To a methanolic solution of 0.50 g, 2 mmol of manganese(II) nitrate tetrahydrate, 15 ml, 0.60 g, 4 mmol of 4-chloropyridine hydrochloride solid were added. Further, 0.65 g, 10 mmol of sodium azide aqueous solution were added dropwise with constant stirring, the clear solution was allowed to stand in dark place for several days. Transparent crystals suitable for X-ray measurements were collected, dried in air with a yield of 60% with respect to the metal. Analysis: Found: C, 31.7; H, 2.4; N, 51.5. Calcd. for C10H8MnN14: C, 31.7; H, 2.1; N, 51.7. IR (KBr, cm1): 2419 ms, 2265 s, (4-N3py) 2127, 2107, 2082 vs, mas(N3). 1597 vs, 1560 vs, 1500 vs, 1469 s, 1450 s, 1423 vs, 1412 vs, 1134 vs, 1109 vs, 1010 vs, 816 vs, (pyridine moiety), 1334 s, 1289 vs, (msym N3) 592 vs, 507 vs, (d N3) 314 vs, 294 vs, 269 vs (M–N(L) and M–N(N3) vibrations).
Table 1 Crystallographic data and processing parameters. Compound
1
2
Empirical formula Formula mass System Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z T (K) l(MoKa) (mm1) Dcalc (Mg/m3) Crystal size (mm) h range (°) Reflections collected Independ. refl./Rint Parameters Goodness-of-Fit on F2 R1/wR2 (all data) Residual extrema (e/Å3)
C10H12MnN10 327.24 Triclinic P-1 3.5350(10) 9.038(3) 10.139(3) 82–84(2) 89.56(2) 87.96(2) 321.2(2) 1 99(2) 1.039 1.692 0.25 0.20 0.16 3.23–30.00 2217 1846/0.0252 103 1.096 0.0254/0.0676 0.410/0.352
C10H8MnN14 379.24 Triclinic P-1 8.252(3) 8.313(2) 11.927(6) 82.71(3) 69.88(3) 80.83(3) 765.1(6) 2 92(2) 0.903 1.666 0.30 0.24 0.12 2.97–26.00 3424 2977/0.0258 226 1.095 0.0380/0.0905 0.491/0.435
aqueous/methanolic solutions afforded the title complexes [Mn(N3)2(2-aminopy)2]n, 1, and [Mn(N3)2(4-azidopy)2]n, 2. The 4azidopyridine ligand in 2 was formed in situ by the reaction of the 4-chloropyridine with excess sodium azide. Complex 2 is a new polymorph with 1D chain system, whereas the previously reported polymorph forms a 2D layer system and exhibits ferrimagnetic behaviour [12].
2.3. Magnetic measurements 3.1. Structures Magnetic susceptibility measurements under a magnetic field of 1 T in the temperature range 2–300 K and magnetization measurements in the field range of 0–5 T were performed with a Quantum Design MPMS-XL SQUID magnetometer at the Magnetochemistry Service of the University of Barcelona. All measurements were performed on polycrystalline samples. Pascal’s constants were used to estimate the diamagnetic corrections [8] which were subtracted from the experimental susceptibilities to give the corrected molar magnetic susceptibilities. 2.4. X-ray crystal structure analysis The X-ray single-crystal data were collected on a modified STOE 4-circle diffractometer with graphite-monochromatized Mo-Ka radiation (k = 0.71069 Å). The crystallographic data, conditions retained for the intensity data collection and some features of the structure refinements are listed in Table 1. Lorentz-polarisation and absorption corrections were made using the DIFABS computer program [9]. The structures were solved by direct methods using the SHELXS-86 [10a] computer program and refined by full-matrix least-squares methods on F2, using the SHELXL-93 [10b] program incorporated in the SHELXTL/PC V 5.03 [11] program package. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were assigned with isotropic displacement factors and included in the final refinement cycles by use of geometrical restraints. 3. Results and discussion The interaction between manganese(II) nitrate tetrahydrate, sodium azide and 2-aminopyridine or 4-chloropyridine in aqueous or
Compound 1 crystallizes in the triclinic space group P-1. Relevant bond distances and angles are listed in Table 2, the structure is illustrated in Fig. 1. Each Mn is located at a center of inversion and is coordinated octahedrally by six N atoms of which two are part of the trans-coordinated 2-aminopyridine ligands and the remaining four N atoms belong to azido groups. The Mn centers are arranged in linear chains [angle Mn(1C). . .Mn(1). . .Mn(1B) = 180°] along the a-axis by means of azido groups which double-bridge two adjacent Mn
Table 2 Selected bond lengths (Å) and angles (°) for (1). Mn(1). . .Mn(1C) Mn(1)–N(11A) Mn(1)–N(1A) Mn(1)-N(11B) N(11)–N(12) N(12)–N(13) H(7). . .N(11C) N(2)–H(6) N(2). . .N(13D) N(11A)–Mn(1)–N(11) N(11)–Mn(1)–N(1A) N(11)–Mn(1)–N(1) N(11A)–Mn(1)–N(11B) N(1A)–Mn(1)–N(11B) N(11A)–Mn(1)–N(11C) N(1A)–Mn(1)–N(11C) N(11B)–Mn(1)–N(11C) N(12)–N(11)–Mn(1B) N(13)–N(12)–N(11) N(2)–H(7). . .N(11C)
3.5350(12) 2.2495(12) 2.2889(12) 2.2901(12) 1.2060(14) 1.154(2) 2.35 0.89 3.255(2) 180.0 90.75(4) 89.25(4) 102.28(4) 93.17(4) 77.72(4) 86.83(4) 180.0 134.70(8) 179.24(12) 158.9
N(11). . .N(11B) Mn(1)–N(11) Mn(1)–N(1) Mn(1)–N(11C) N(11)–Mn(1B) N(2)–H(7) N(2). . .N(11C) H(6). . .N(13D) N(11A)–Mn(1)–N(1A) N(11A)–Mn(1)–N(1) N(1A)–Mn(1)–N(1) N(11)–Mn(1)–N(11B) N(1)–Mn(1)–N(11B) N(11)–Mn(1)–N(11C) N(1)–Mn(1)–N(11C) N(12)–N(11)–Mn(1) Mn(1)–N(11)–Mn(1B) N(11B). . .N(11)–N(12) N(2)–H(6). . .N(13D)
2.848(2) 2.2495(12) 2.2889(12) 2.2901(12) 2.2901(12) 0.88 3.1871(18) 2.41 89.25(4) 90.75(4) 180.0 77.72(4) 86.83(4) 102.28(4) 93.17(4) 121.74(8) 102.28(4) 168.80(10) 159.3
Symmetry codes: (A) x + 1,y + 1,z; (B) x + 2,y + 1,z; (C) x1,y,z; (D) x + 1,y + 2,z.
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F.A. Mautner et al. / Journal of Molecular Structure 969 (2010) 192–196 Table 3 Selected bond lengths (Å) and angles (°) for (2). Mn(1). . .Mn(1A) Mn(1)–N(11) Mn(1)–N(21) Mn(1)–N(1) Mn(1)–N(2) N(21)–N(22) N(31)–N(32) N(41)–N(42) N(11A)–Mn(1)–N(11) N(11A)–Mn(1)–N(1) N(11A)–Mn(1)–N(23) N(11)–Mn(1)–N(21) N(1)–Mn(1)–N(21) N(11)–Mn(1)–N(2) N(1)–Mn(1)–N(2) N(21)–Mn(1)–N(2) N(12)–N(11)–Mn(1A) N(13)–N(12)–N(11) N(21)–N(22)–N(23B) N(31)–N(32)–N(33) N(41)–N(42)–N(43)
3.3701(18) 2.235(2) 2.244(2) 2.240(2) 2.271(2) 1.177(3) 1.245(3) 1.246(3) 82.20(9) 94.27(8) 170.81(8) 171.83(8) 86.91(8) 93.78(8) 171.26(8) 86.61(8) 126.4(2) 179.1(3) 178.3(2) 170.7(3) 171.2(3)
Mn(1). . .Mn(1B) Mn(1)–N(11A) Mn(1)–N(23) N(11)–N(12) N(12)–N(13) N(22)–N(23B) N(32)–N(33) N(42)–N(43) N(11)–Mn(1)–N(1) N(11)–Mn(1)–N(23) N(1)–Mn(1)–N(23) N(11A)–Mn(1)–N(21) N(23)–Mn(1)–N(21) N(11A)–Mn(1)–N(2) N(23)–Mn(1)–N(2) N(12)–N(11)–Mn(1) Mn(1)–N(11)–Mn(1A) N(11A). . .N(11)–N(12) Mn(1)–N(23)–N(22B) Mn(1)–N(21)–N(22)
5.032(3) 2.237(2) 2.241(2) 1.167(3) 1.165(3) 1.181(3) 1.122(3) 1.129(3) 93.47(8) 88.96(8) 88.74(9) 89.64(8) 99.21(8) 91.54(8) 86.53(8) 126.2(2) 97.80(9) 152.2(3) 119.7(2) 123.5(2)
Symmetry codes: (A) x,1y,1z; (B) x,y,1z; (C) x,1 + y,z. Fig. 1. Molecular geometry and atom labeling scheme of 1.
atoms in an end-on coordination mode (EO) giving rise to centrosymmetric Mn2N2 units. Each unit defines a plane with one azido group of the unit above and the other one below the plane by an angle of 168.80(10)° [N(11B). . .N(11)–N(12)]. The azido groups are linear (179.24(12)°) and the Mn–N(azido) distances are 2.2495(12) and 2.2901(12) Å for Mn(1)–N(11) and Mn(1B)–N(11), respectively. The ligands are coordinated via the pyridinic N atom with a Mn–N distance of 2.2889(12) Å and the pyridine ring tilted with a torsion angle of 163.8(1)° for Mn(1)–N(1)–C(5)–C(4). The NH2-groups of the ligands establish two different types of hydrogen bonds: an intramolecular H-bond to a coordinated N(azido) atom belonging to the same octahedron as the ligand and an inter-molecular H-bond to the terminal N atom of an azido group in the adjacent chain. Due to the latter one the Mn(N3)2-chains are connected to layers extending
along the ab-plane of the unit cell (Fig. 2). Along the chain direction the pyridine rings form p–p stacking interactions with a separation of 3.5350(10) Å between their centroids. Compound 2 crystallizes also in the triclinic space group P-1. Relevant bond distances and angles are collected in Table 3 and a perspective view together with the atom numbering scheme is shown in Fig. 3. The structure of 2 consists of octahedrally coordinated Mn atoms in which the coordination sites are occupied by two 4-azidopyridine ligands in trans arrangement and four azido ligands which form double bridges between neighbouring Mn centers. The azido groups in the double bridges are alternately in the EE and EO modes, giving an alternating chain, oriented along the b-axis of the unit cell (Fig. 4). The Mn2(l1,3-N3)2 ring is quite regular: bond lengths are Mn(1)–N(21) = 2.244(2) Å, and Mn(1)–N(23) = 2.241(2) Å, and bond angles are Mn(1)–N(21)–N(22) = 123.5(2)° and Mn(1)– N(23)–N(22B) = 119.7(2)°. The Mn–(l1,3-N3)2–Mn ring shows the
Fig. 2. Packing view of 1. Along the chain direction the 2-aminopyridine molecules form p–p stacking interactions with a separation of 3.5350(10) Å between centroids of their pyridine rings.
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Fig. 3. Ortep view and atom labeling scheme of 2.
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typical distortion from the planar to the chair conformation, evaluated as a d parameter = 34.3° [13]. The Mn(1B)–N(23B). . .N(21)– Mn(1) torsion angle = 51.3(3)°. The centrosymmetric Mn2N2 ring is strictly planar, as is usual for double EO bridges, and shows a bond angle Mn(1)–N(11)–Mn(1A) = 97.80(9)° and bond lengths Mn(1)– N(11) and Mn(1)–N(11A) of 2.235(2) and 2.237(2) Å, respectively. The Mn. . .Mn intra-chain distances are asymmetric, the longer corresponding to the EE ring, Mn(1). . .Mn(1B) = 5.032(3) Å, and the shorter to the EO ring, Mn(1). . .Mn(1A) = 3.3701(18) Å. The polymeric chain is slightly corrugated with a Mn(1B). . .Mn(1). . .Mn(1A) angle of 162.9°. The N(1)–Mn(1)–N(2) bond angle of the axial pyridine ligand is 171.26(8)°. This deviation from 180° has the effect of moving away the axial ligands on the EO ring. The terminal azido groups bonded to the pyridine rings in para-positions have strong asymmetric bond geometries with Dd(N–N) [difference of the N–N bond lengths within the azide group] of 0.121(3) and 0.117(3) Å, respectively, and N(31)–(N32)–N(33) and N(41)–N(42)–N(43) bond angles of 170.7(3)° and 171.2(3)°, respectively. These values are in good agreement with corresponding parameters observed for the covalent azide group N(51)–N(52)–N(53) in the 2D polymorph of [Mn(N3)2(4-azidopy)2]n: Dd(N–N) = 0.136(9) Å, N–N–N bond angle = 170.2(7)° [12]. As far as we know no other metal complexes with 4-azidopyridine are known, whereas 2-aminopyridine is a common ligand: e.g. Oxalato-bridged chains of octahedra with trans-coordinated 2aminopyridines are reported in a series of transition metal compounds [14]. Cis-coordinated 2-aminopyridine molecules and l(NCS)2 double bridges are observed in the polymeric chains of [Ni(NCS)2(2-ampy)2]n [15]. Methoxide and chloride bridging units are present in the polymeric chains of [Cu2(2-ampy)2(l-OMe)2Cl2]n [16]. The dimeric form of [Cu(benzoato)2(2-ampy)]2 reveals a ‘‘paddle-wheel” type structure where 2-aminopyridine acts as axial ligand via pyridine N atom [17]. The core of the cubic zinc phosphonate [tBuPO3Zn(2-ampy)]4 resembles a ‘‘zeolite”-like arrangement [18]. In the dinuclear Cu(II) complex with 2,6-pyridinedicarboxlyate the 2-ampy molecules act as N,N0 -bridging ligands [19]. 3.2. Magnetic properties The variable temperature magnetic susceptibility data for complex 1 were recorded between 300 and 2 K. The plot of vMT versus T is shown in Fig. 5. Compound 1 shows a vMT room temperature value of 4.74 cm3 mol1 K, greater than the expected value of 4.375 cm3 mol1 K for an isolated manganese atom. vMT increases
Fig. 4. Packing view of 2.
Fig. 5. Plot of vMT (dot circles) vs T in the 300–2 K range of temperatures for 1 measured on cooling under external magnetic field of 0.3 T. The solid line shows the best fit as uniform ferromagnetic chain (see text).
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gradually as the temperature decreases to a maximum value of 25.81 cm3 mol1 K at 4 K and then decreases quickly to 9.59 cm3 mol1 K at 2 K. The magnetic susceptibility behaviour of 1 indicates bulk ferromagnetic coupling in good agreement with magnetization experiments which show a quasi-saturated value of MNb equivalent to five electrons (4.96) under an external field of 5 T at 2 K. Taking into account the 1D structure of 1, the fit of the magnetic data was made by using the appropriate equation [20] for homogeneous S = 5/2 chains derived from the Hamiltonian H = JSiSi+1 in the range 300–5 K for 1 due to the decrease of the vMT values after the maximum. The best fit parameters were J = 1.2(1) cm1, g = 2.13(2). The positive J value is in accordance with the ferromagnetic coupling expected for end-on azido bridges with Mn–N–Mn bond angles around 100° (the Mn(1)–N(11)– Mn(10 ) bond angle is 102.28(4)°). The J value for 1 is similar to that reported for the related compounds cis-[Mn(l1,1-N3)2(2-bzpy)2]n (2-bzpy = 2-benzoylpyridine) [21] and trans-[Mn(l1,1-N3)2(pyzamid)2]n (pyzamid = pyrazineamide) [22] with J values of 0.8 and 1.1 cm1 for Mn–N–Mn angles of 100.5° (mean angle) and 97.1°, respectively. The structure of cis-[Mn(l1,1-N3)2(2-bzpy)2]n shows well isolated chains but as in the case of trans-[Mn(l1,1-N3)2(pyzamid)2]n, 1 forms H bonds between chains which are the cause of the weak antiferromagnetic interactions at low temperature as can be seen in the decrease of vMT in the low temperature region. In summary we have synthesized and characterized two new azido-bridged Mn 1D systems: [Mn(N3)2(2-aminopy)2]n, 1, and [Mn(N3)2(4-azidopy)2]n, 2. In 1 the polymeric chains of polyhedra are formed by di-EO azido bridges and further connected by hydrogen bonds of type N–H. . .N to generate a 2D supramolecular network. Magnetic susceptibility measurements for 1 show weak ferromagnetic interactions with a J value of 1.2 cm1. The 1D complex 2 is a new polymorph with composition [Mn(N3)2(4-azidopy)2]n. As its previously reported 2D polymorph, complex 2 exhibits, EO and EE azido bridging groups as well as ‘‘covalent” azido groups in the trans-coordinated 4-azidopyridine ligands. Acknowledgements This research was partially supported by CICYT (Grant CTU2006/01759/BQU) through the Grant CTQ2005-08123-C02/ BQU. F.A.M. thanks Prof. C. Kratky and F. Belaj (Univ. Graz) for technical support. Appendix A. Supplementary data Supplementary data are available from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK on request, quoting the deposition numbers: CCDC-643272 and CCDC-756797 for 1 and 2, respectively. 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
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