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Synthesis, crystal structure and magnetic properties of a novel iron(III) 18-azametallacrown-6 compound
www.elsevier.com/locate/ica Inorganica Chimica Acta 328 (2002) 69 – 73
Synthesis, crystal structure and magnetic properties of a novel iron(III) 18-azametallacrown-6 compound Shen Lin a,b, Shi-Xiong Liu a,c,*, Bi-Zhou Lin d a
Department of Chemistry, Fuzhou Uni6ersity, Fuzhou 350002, China Department of Chemistry, Fujian Normal Uni6ersity, Fuzhou 350007, China c State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, Fuzhou 350002, China d Institute of Material Physical Chemistry, Huaqiao Uni6ersity, Quanzhou, Fujian 362011, China b
Received 9 April 2001; accepted 3 September 2001
Abstract A novel macrocyclic hexanuclear iron(III) 18-azametallacrown-6 compound, [Fe6(C9H7N2O3)6(CH3OH)6]·8CH3OH·2H2O, has been prepared using a trianionic pentadentate ligand N-acetylsalicylhydrazide (ashz3 − ) and characterized by X-ray diffraction. Due to the meridional coordination of the ligand to the Fe3 + ion, the ligand enforces the stereochemistry of the Fe3 + ions as a propeller configuration with alternating L/D forms. The disc-shaped hexanuclear ring shows about 6.20 A, in diameter at entrance, about 9.31 A, at its largest diameter at the center of the cavity, respectively. There are many kinds of intramolecular and intermolecular hydrogen bonds in the title compound. The OH···O hydrogen bond distances range from 2.609(5)– 2.901(5) A, . The magnetic susceptibility (4–275K) study indicates antiferromagnetic exchange interactions between the adjacent Fe3 + ions around the ring. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Metallacrown; Iron complexes; Crystal structures; Magnetic properties; Supramolecular chemistry
1. Introduction Polynuclear metal complexes with a ring structure have been the subject of numerous structural and spectroscopic studies. Metallacrown and its analogies have attracted considerable attention since the first report of metallacrown ether [1]. The presence of transition metal ions in the metallacrown ring leads to a class of molecules with features distinct from the simple organic crowns, such as strong visible absorption spectra, redox activity, magnetism and molecular recognition. Metallacrowns have been characterized with V(V)O [2], Mn(III) [3,4], Fe(III) [1,5], Cu(II) [6], Zn(II) [7], Ni(II) [8] and Ga(III) [9] in the ring position utilizing hydroxamic acid ligands as shown in Scheme 1(a). This kind of metallacrown is a rich variety of compounds in 9-metal-
* Corresponding author. Tel./fax: + 86-591-3729860. E-mail address: [email protected] (S.-X. Liu).
lacrowns-3 [1,2], 12-metallacrowns-4 [3,6 –9] and 15metallacrowns-5 [4,6c] with a [MNO]n repeat unit that forms cyclic structure. Recently, several azametallacrowns with a [MNN]n repeat unit were reported including a Mn(III)18-azametallacrown-6 [10], the first two Mn(III)/Fe(III) 30-azametallacrowns-10 [11a] and the two cobalt 18-azametallacrowns-6 [11b]. In the azametallacrown, the nitrogen atoms are replacing the all oxygen atoms in the cyclic structure. In the present paper, we report a new potential pentadentate ligand N-acetylsalicylhydrazidate (1) (H3ashz, Scheme 1(b)) and a novel iron(III) 18-azametallacrown-6 compound, [Fe6(N-acetylsalicylhydrazide)6(MeOH)6]·8CH3OH·2H2O (2) (Scheme 1(c)). The triply deprotonated N-acetylsalicylhydrazide(ashz3 − ) of the title compound 2 may bridge the neighboring ions through its hydrazide NN group shown in Scheme 1(c). In addition, the meridional coordination of the ashz3 − to the Fe3 + cation forces the neighboring Fe3 + cations into a propeller configuration. The existence of intramolecular and intermolecular hydrogen bonds makes the title
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 6 6 4 - 8
S. Lin et al. / Inorganica Chimica Acta 328 (2002) 69–73
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Scheme 1. Basic biding sites of shi3 − (a), ligand H3bzshz (b), and basic biding sites in compound 2 (c).
compound 2 more stable in the air than the reported azametallacrown [11a]. The title compound 2 is the first example of 18-metallacrown-6 compounds with [MNN]n repeat unit containing iron(III) as ring ion.
2. Experimental
2.1. General procedures Reagents were purchased commercially and used without further purification. Infrared spectra were measured on a Perkin–Elmer FT-IR 2000 spectrometer as KBr pellets in the 4000– 400 cm − 1 region. The magnetic susceptibility data were obtained using a Quantum Design PPMS 6000 magnetometer in the temperature range from 4 to 275 K at an applied magnetic field of 10 kG whereby the diamagnetic contributions were estimated from Pascal’s constants.
2.2. Synthesis 2.2.1. Ligand H3ashz (1) Acetic anhydride (3.41 g, 33.4 mmol) and salicylhydrazide (4.24 g, 27.9 mmol) were added to 60 ml of chloroform at 0 °C. The reaction mixture was slowly warmed to room temperature (r.t.) and stirred for 4 h. After staying for overnight at refrigerator, the resulting white precipitate was filtered and rinsed with chloroform and diethyl ether (5.1 g, 95.0% yield). m.p.: 179– 181 °C. 2.2.2. [Fe6(MeOH)6(ashz)6] ·8CH3OH·2H2O (2) H3ashz (0.194 g, 1.0 mmol) was dissolved in 20 ml of methanol, and 0.404 g (1.0 mmol) of ferric nitrate decahydrate was dissolved in 20 ml of methanol in another flask. The two solutions were mixed and stirred and the color of the mixture changed to black– violet, then filtered. After staying for 2 days, black– violet rhombohedral crystals were obtained from the filtrate (0.26 g, 60.0% yield). Anal. Calc. for C68H102Fe6N12O34: C, 41.5; H, 5.2; N, 8.5; O, 27.7. Found: C, 40.4; H, 3.8; N, 9.1; O, 28.5%.
2.3. X-ray crystallography A crystal of the title compound 2 with dimensions of 0.50× 0.39× 0.28 mm was mounted in a glass capillary with the mother liquor to prevent the loss of the structural solvents during X-ray diffraction data collection. The data were recorded on a Siemens Smart CCD areadetector diffractometer with graphite-monochromated Mo Ka radiation (u= 0.71073 A, ), the scan mode being . The structure was solved by direct methods using SHELXS-86 and refined by full-matrix leastsquares calculations with SHELXL-97. All non-hydrogen atoms were refined with anisotropic thermal parameters. All hydrogen atoms were located in calculated positions and/or in the positions from difference Fourier map. The crystallographic data are given in Table 1. Table 1 Crystallographic data Empirical formula Formula weight Crystal system Space group a (A, ) b (A, ) c (A, ) i (°) V (A, 3) Z Dcalc (mg m−3) v (mm−1) F(000) Crystal size (mm) qmax, qmin (°) Index ranges Observed reflections Independent reflections Variables R wR Goodness-of-fit Largest difference peak a (e A, −3)
C68H102Fe6N12O34 1966.72 monoclinic P21/n 16.038(2) 19.467(3) 16.157(4) 118.19(2) 4446(2) 2 1.469 1.040 2044 0.50×0.40×0.28 25.11, 1.77 −175h519, −195k523, −195l513 5162 7848 [Rint =0.0357] 560 0.0445 0.0951 0.962 and hole 0.346 and −0.306
a Fourier map: R= Fo − Fc / Fo ; wR={ [w(F o2−F c2)2]/ [ w(F o2)2]}1/2.
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3.2. Structure of compound 2
Fig. 1. Perspective view of compound 2, solvent molecules and all hydrogen atoms have been omitted for clarity.
3. Results and discussion
3.1. Spectral characterization In the IR spectra, the ligand 1 shows stretching bands attributed to CO, CN, COH (phenolic) and NH at 1670, 1632, 1157 and 1236, and 3319 cm − l, respectively [12]. Bands at 3196 and 2708 cm − 1 are assigned to w(OH) vibrations involving intramolecular hydrogen bonding, while band at 1237 cm − 1 is attributed to l(OH) (phenolic) [13]. In addition, a strong band found at 1606 cm − 1 is assigned to CNNC group [12,13]. In the title compound 2, the absence of the NH and CO stretching vibration bands is consistent with the deprotonation of the CONH groups and coordination to the Fe(III) ion. The peaks at 1256 and 1034 cm − 1 are attributed to FeO linkage formed through methanol coordination [14]. The CNNC framework seen at l606 cm − 1 in the ligand sifted to 1600 cm − 1 upon coordination to Fe atom. The disappearance of the bands at 3196 and 2708 m − 1 and the appearance of the bands at 1316 and 1256 cm − 1 support the involvement of phenolic oxygen in coordination through deprotonation. This is confirmed by the band at 445 cm − 1 assigned to FeO (phenolic). Raman spectrum of the title compound 2 exhibited peaks at 1598 and 1515 cm − 1 corresponding to symmetric and asymmetric stretching of CNNC framework [12].
The title compound 2 crystallizes in the monoclinic system and space group P21/n. The structure exhibits a hexanuclear ring of iron atoms linked by six hydrazide NN groups. The deprotonated ligand ashz3 − acts as a trianionic pentadentate ligand, one phenolate oxygen, one carbonyl oxygen and one hydrazide nitrogen in the ligand are bound to one Fe3 + cation, and the other carbonyl oxygen plus the other hydrazide nitrogen in the same ligand are chelated to an adjacent Fe3 + cation. Therefore, the ligand is forcing all Fe3 + cations into a propeller configuration with alternating L/D stereochemistry as DLD or LDL forms (Fig. 1). Three methanol groups coordinated at the metal centers with L configuration are found on one face of the azametallacrown, and the remaining three methanol groups coordinated to the other metal centers with D configuration are found on the other face of the azametallacrown. The two faces of the disc-shaped hexanuclear ring have opposite chiralities to each other. This organization results in the 18-membered hexanuclear core ring system with an [FeNN]n repeat unit that is similar to that recently reported for the [MnIII 6 (Nformylsalicylhydrazidate)6(MeOH)6] (3) [10]. However, the cavity sizes of 2 and 3 are different. The approximate dimensions of the oval-shaped cavity are about 6.20 A, in diameter at entrance, about 9.31 A, at its largest diameter at the center of the cavity in compound 2, which are greater than those of compound 3. The change of the cavity size is probably caused by the steric effect of the different bridging multidentate ligands in the compound 2 and 3. It is also observed that the all atoms in the ligand are almost in co-plane and the all iron atoms in title compound 2 are in an octahedral FeN2O4 environment. The Jahn–Teller distortion is not observed because of the high-spin d5 iron(III) ion configuration compared with some Mn(III) azametallacrown compounds [10,11a]. The average neighboring Fe···Fe separation of 4.881 A, seems to be slightly longer than that of Fe(III)[Fe(III)(salicylhydroximato)(MeOH)(acetate)]3 [1] but shorter than that of [Fe(N-phenylsalicylhydrazidate)(MeOH)]10·3CH2Cl2·12.5CH3OH·5H2O [11a] with Fe···Fe distance of 4.848 and 4.946 A, , respectively. The average M···M···M interatomic angle in the 18-membered core ring of compound 2 is 117.6°, which is close to interior angle in n-hexagon of 120° (Table 2). There are not any solvent molecules in the ‘host’ cavity of azametallcrown in the title compound and [Co6(C9H7N2O3)6(CH3OH)6]·6CH3OH [11b], while one of the solvent methanol molecules is encapsulated within the cobalt metallacrown ‘host’ cavity in [Co6(C8H5N2O3)6(CH3OH)6]·5CH3OH 11b. As listed in Table 3, there are many kinds of intramolecular and intermolecular hydrogen bonds in the title compound 2.
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The first kind is between the OH group from coordinated methanol and the oxygen atom from solvent Table 2 Selected bond lengths (A, ) and angles (°) in compound 2 Bond lengths Fe(1)O(1) Fe(1)O(3) Fe(2)O(5) Fe(2)N(3) Fe(3)O(9) Fe(3)N(5) N(1)N(2) Fe(1)Fe(2) Fe(1)O(6) Fe(1)N(4) Fe(2)O(10) Fe(2)N(6)
1.908(3) 2.058(3) 1.918(3) 2.044(3) 1.923(3) 2.036(3) 1.405(4) 4.881(1) a 1.990(3) 2.081(3) 2.005(3) 2.089(3)
Fe(3)O(2a) Fe(3)O(12) N(3)N(4) Fe(1)Fe(3) Fe(1)N(1) Fe(1)O(4) Fe(2)O(7) Fe(2)O(8) Fe(3)O(11) Fe(3)N(2a) N(5)N(6) Fe(1)Fe(1a)
1.983(2) 2.091(3) 1.418(4) 8.349(1) b 2.046(3) 2.095(3) 2.038(3) 2.089(3) 2.008(3) 2.113(3) 1.406(4) 9.669(2) c
Bond angles O(1)Fe(1)O(6) O(6)Fe(1)N(1) O(6)Fe(1)O(3) O(1)Fe(1)N(4) N(1)Fe(1)N(4) O(1)Fe(1)O(4) N(1)Fe(1)O(4) N(4)Fe(1)O(4) O(5)Fe(2)O(7) O(5)Fe(2)N(3) O(7)Fe(2)N(3) O(10)Fe(2)N(6) N(3)Fe(2)N(6) O(10)Fe(2)O(8) N(3)Fe(2)O(8) O(9)Fe(3)O(2a) O(2a)Fe(3)O(11) O(2a)Fe(3)N(5) O(9)Fe(3)O(12) O(11)Fe(3)O(12) O(9)Fe(3)N(2a) O(11)Fe(3)N(2a) O(12)Fe(3)N(2a) C(7)O(2)Fe(3a) C(10)O(4)Fe(1) C(17)O(6)Fe(1) C(20)O(8)Fe(2) C(27)O(10)Fe(2) C(30)O(12)Fe(3) N(2)N(1)Fe(1) N(1)N(2)Fe(3a) N(4)N(3)Fe(2) N(3)N(4)Fe(1) N(6)N(5)Fe(3) N(5)N(6)Fe(2)
105.0(1) 166.6(1) 93.4(1) 93.3(1) 109.6(1) 94.7(1) 88.6(1) 160.5(1) 162.3(1) 86.7(1) 76.0(1) 76.0(1) 104.0(1) 84.1(1) 95.6(1) 100.4(1) 96.9(1) 172.2(1) 93.9(1) 89.7(1) 92.9(1) 89.7(1) 158.6(1) 117.7(2) 128.0(3) 116.7(2) 123.3(3) 116.5(2) 126.1(3) 116.7(2) 112.9(2) 115.7(2) 112.9(2) 115.4(2) 112.4(2)
O(1)Fe(1)N(1) O(1)Fe(1)O(3) N(1)Fe(1)O(3) O(6)Fe(1)N(4) O(3)Fe(1)N(4) O(6)Fe(1)O(4) O(3)Fe(1)O(4) O(5)Fe(2)O(10) O(10)Fe(2)O(7) O(10)Fe(2)N(3) O(5)Fe(2)N(6) O(7)Fe(2)N(6) O(5)Fe(2)O(8) O(7)Fe(2)O(8) N(6)Fe(2)O(8) O(9)Fe(3)O(11) O(9)Fe(3)N(5) O(11)Fe(3)N(5) O(2a)Fe(3)O(12) N(5)Fe(3)O(12) O(2a)Fe(3)N(2a) N(5)Fe(3)N(2a) C(1)O(1)Fe(1) C(8)O(3)Fe(1) C(11)O(5)Fe(2) C(18)O(7)Fe(2) C(21)O(9)Fe(3) C(28)O(11)Fe(3) C(7)N(1)Fe(1) C(8)N(2)Fe(3a) C(17)N(3)Fe(2) C(18)N(4)Fe(1) C(27)N(5)Fe(3) C(28)N(6)Fe(2) Fe(1)Fe(2)Fe(3)
86.9(1) 161.6(1) 75.1(1) 76.6(1) 89.6(1) 84.2(1) 88.5(1) 108.3(1) 89.0(1) 165.0(1) 97.0(1) 90.8(1) 87.4(1) 90.8(1) 160.1(1) 162.7(1) 86.8(1) 76.1(1) 83.0(1) 93.6(1) 75.8(1) 107.0(1) 131.4(2) 115.3(2) 133.7(2) 115.3(2) 132.6(3) 116.3(2) 130.1(2) 135.9(3) 132.6(3) 136.6(3) 131.3(3) 136.4(3) 117.6(2) d
Symmetry code: a, −x, −y, −z. a The average value of the Fe(1)Fe(2), Fe(2)Fe(3), Fe(3)Fe(1a) interatomic distances. b This is an average value of the Fe(1)Fe(3), Fe(2)Fe(1a), Fe(3)Fe(2a) interatomic distances. c This is an average value of the Fe(1)Fe(1a), Fe(2)Fe(2a), Fe(3)Fe(3a) interatomic distances. d This is an average value of the Fe(1)Fe(2)Fe(3), Fe(2)Fe(3)Fe(1a), Fe(3)Fe(1a)Fe(2a) interatomic angles.
Table 3 Hydrogen bond geometry (A, , °) DH···A
DH
H···A
D···A
DH···A
O(4)H(04)···O(15) O(8)H(08)···O(14) O(12)H(012)···O(13) O(15)H(015)···O(9A) O(13)H(013)···O(5B) O(16)H(016)···O(3) O(14)H(014)···O(17) O(17)H(171)···O(1) O(17)H(172)···O(16C)
1.053 0.987 0.966 1.017 0.978 1.076 1.080 1.036 0.972
1.674 1.631 1.616 1.845 1.970 1.713 1.672 1.904 1.925
2.677(5) 2.609(5) 2.579(5) 2.856(5) 2.851(4) 2.774(4) 2.625(6) 2.901(5) 2.816(6)
157.4 169.8 174.4 172.6 148.7 167.8 144.3 160.6 151.2
Symmetry codes: (A) −x, −y, −z; (B) 1−x, −y, −z; (C) 1/2−x, 1/ 2+y, 1/2−z.
Fig. 2. The effective magnetic moment (veff) and the inverse susceptibility m− 1 data as a function of temperature for the title compound, where open dots for observed results, and solid lines attached to m− 1 and veff for fitting curves based on the Curie – Weiss law and on an super-exchange fit, respectively.
methanol, e.g. O(4)H(04)···O(15), O(8)H(08)···O(14) and O(12)H(012)···O(13); the second is between the OH from solvent methanol and the oxygen atom (phenolic oxygen, carbonyl oxygen or water oxygen), e.g. O(13)H(013)···O(5B), O(15)H(015)···O(9A), O(16)H(016)···O(3) and O(14)H(014)···O(17); the third is between the OH from crystalline water and the phenolic oxygen or solvent methanol oxygen atom, e.g. O(17)H(171)···O(1) and O(17)H(172)···O(16C). It is worth to note that there are two hydrogen bonds for each of the solvent methanol molecules [C(31)H3O(13)H, C(32)H3O(14)H, C(33)H3O(15)H] and for water molecule.
3.3. Magnetic properties As shown in Fig. 2, the molar effective magnetic moment (veff) of the title compound shows the presence of an antiferromagnetic coupling between the Fe(III) spin 5/2 centers. The veff value at 272 K is 13.16vB, which is smaller than the sum value expected for a six spin-only paramagnetic systems with S= 2.5 (veff =
S. Lin et al. / Inorganica Chimica Acta 328 (2002) 69–73
14.49vB). With decreasing temperature, the veff values firstly decrease slightly, reaching 9.83 vB at 60 K, and then decrease rapidly after 60 K, reaching 2.19vB at 4.2 K. This is further suggested by a negative Weiss constant q = − 68.9(5) K, derived from the Curie–Weiss law fit in the temperature ranging from 68 to 272 K. Structurally, the magnetic super-exchanges would likely propagate between the neighboring centers (J1), between the near-neighboring centers (J2) and between the opposite centers (J3). When the six Fe(III) centers are simplified to be arranged in the symmetry of D6h, a least-squares fit for the data within T \ 43 K obtains the parameters J1/k= − 4.87(2) K, J2/k = − 0.96(5) K, J3/k = − 0.21(4) K and the agreement factor F= [(obs −cal)2/obs]= 9.59 ×10 − 3. The negative values of J demonstrate an antiferromagnetic coupling between the paramagnetic centers. As expected, the interactions between the neighboring centers dominate the others, which matched the derived absolute values of J1, J2 and J3. The antiferromagnetic nature of the interaction can be understood in terms of overlap through the bridging group between the single occupied metal d-orbitals.
4. Conclusion The title compound 2 is the first example of 18-azametallacrown-6 compounds containing Fe3 + as ring ions. An important structural feature in [Fe6(C9H7N2O3)6(CH3OH)6]·8CH3OH·2H2O is that there is not only a vacant cavity in the center of 18-azametallacrown-6 core ring, but also the opposite chiralities on the two faces of the metallacrown ring system. The vacant cavity and the opposite chiralities suggest that the title compound might have interesting chiral recognition properties. This novel iron 18-azametallacrown-6 compound also shows the presence of an antiferromagnetic coupling between the neighboring Fe(III) centers on the basis of overlap through the bridging group between the single occupied metal d-orbitals.
5. Supplementary material Lists of the CIF file for the title compound 2 have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 160047. Copies of this infor-
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mation may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: + 44-1223-336-033; e-mail: deposit@ ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements The authors are grateful for financial support from the National Natural Science Foundation of China and the Natural Science Foundation of Fujian Province, China.
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Synthesis, crystal structure and magnetic properties of a novel iron(III) 18-azametallacrown-6 compound Shen Lin a,b, Shi-Xiong Liu a,c,*, Bi-Zhou Lin d a
Department of Chemistry, Fuzhou Uni6ersity, Fuzhou 350002, China Department of Chemistry, Fujian Normal Uni6ersity, Fuzhou 350007, China c State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, Fuzhou 350002, China d Institute of Material Physical Chemistry, Huaqiao Uni6ersity, Quanzhou, Fujian 362011, China b
Received 9 April 2001; accepted 3 September 2001
Abstract A novel macrocyclic hexanuclear iron(III) 18-azametallacrown-6 compound, [Fe6(C9H7N2O3)6(CH3OH)6]·8CH3OH·2H2O, has been prepared using a trianionic pentadentate ligand N-acetylsalicylhydrazide (ashz3 − ) and characterized by X-ray diffraction. Due to the meridional coordination of the ligand to the Fe3 + ion, the ligand enforces the stereochemistry of the Fe3 + ions as a propeller configuration with alternating L/D forms. The disc-shaped hexanuclear ring shows about 6.20 A, in diameter at entrance, about 9.31 A, at its largest diameter at the center of the cavity, respectively. There are many kinds of intramolecular and intermolecular hydrogen bonds in the title compound. The OH···O hydrogen bond distances range from 2.609(5)– 2.901(5) A, . The magnetic susceptibility (4–275K) study indicates antiferromagnetic exchange interactions between the adjacent Fe3 + ions around the ring. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Metallacrown; Iron complexes; Crystal structures; Magnetic properties; Supramolecular chemistry
1. Introduction Polynuclear metal complexes with a ring structure have been the subject of numerous structural and spectroscopic studies. Metallacrown and its analogies have attracted considerable attention since the first report of metallacrown ether [1]. The presence of transition metal ions in the metallacrown ring leads to a class of molecules with features distinct from the simple organic crowns, such as strong visible absorption spectra, redox activity, magnetism and molecular recognition. Metallacrowns have been characterized with V(V)O [2], Mn(III) [3,4], Fe(III) [1,5], Cu(II) [6], Zn(II) [7], Ni(II) [8] and Ga(III) [9] in the ring position utilizing hydroxamic acid ligands as shown in Scheme 1(a). This kind of metallacrown is a rich variety of compounds in 9-metal-
* Corresponding author. Tel./fax: + 86-591-3729860. E-mail address: [email protected] (S.-X. Liu).
lacrowns-3 [1,2], 12-metallacrowns-4 [3,6 –9] and 15metallacrowns-5 [4,6c] with a [MNO]n repeat unit that forms cyclic structure. Recently, several azametallacrowns with a [MNN]n repeat unit were reported including a Mn(III)18-azametallacrown-6 [10], the first two Mn(III)/Fe(III) 30-azametallacrowns-10 [11a] and the two cobalt 18-azametallacrowns-6 [11b]. In the azametallacrown, the nitrogen atoms are replacing the all oxygen atoms in the cyclic structure. In the present paper, we report a new potential pentadentate ligand N-acetylsalicylhydrazidate (1) (H3ashz, Scheme 1(b)) and a novel iron(III) 18-azametallacrown-6 compound, [Fe6(N-acetylsalicylhydrazide)6(MeOH)6]·8CH3OH·2H2O (2) (Scheme 1(c)). The triply deprotonated N-acetylsalicylhydrazide(ashz3 − ) of the title compound 2 may bridge the neighboring ions through its hydrazide NN group shown in Scheme 1(c). In addition, the meridional coordination of the ashz3 − to the Fe3 + cation forces the neighboring Fe3 + cations into a propeller configuration. The existence of intramolecular and intermolecular hydrogen bonds makes the title
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 6 6 4 - 8
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Scheme 1. Basic biding sites of shi3 − (a), ligand H3bzshz (b), and basic biding sites in compound 2 (c).
compound 2 more stable in the air than the reported azametallacrown [11a]. The title compound 2 is the first example of 18-metallacrown-6 compounds with [MNN]n repeat unit containing iron(III) as ring ion.
2. Experimental
2.1. General procedures Reagents were purchased commercially and used without further purification. Infrared spectra were measured on a Perkin–Elmer FT-IR 2000 spectrometer as KBr pellets in the 4000– 400 cm − 1 region. The magnetic susceptibility data were obtained using a Quantum Design PPMS 6000 magnetometer in the temperature range from 4 to 275 K at an applied magnetic field of 10 kG whereby the diamagnetic contributions were estimated from Pascal’s constants.
2.2. Synthesis 2.2.1. Ligand H3ashz (1) Acetic anhydride (3.41 g, 33.4 mmol) and salicylhydrazide (4.24 g, 27.9 mmol) were added to 60 ml of chloroform at 0 °C. The reaction mixture was slowly warmed to room temperature (r.t.) and stirred for 4 h. After staying for overnight at refrigerator, the resulting white precipitate was filtered and rinsed with chloroform and diethyl ether (5.1 g, 95.0% yield). m.p.: 179– 181 °C. 2.2.2. [Fe6(MeOH)6(ashz)6] ·8CH3OH·2H2O (2) H3ashz (0.194 g, 1.0 mmol) was dissolved in 20 ml of methanol, and 0.404 g (1.0 mmol) of ferric nitrate decahydrate was dissolved in 20 ml of methanol in another flask. The two solutions were mixed and stirred and the color of the mixture changed to black– violet, then filtered. After staying for 2 days, black– violet rhombohedral crystals were obtained from the filtrate (0.26 g, 60.0% yield). Anal. Calc. for C68H102Fe6N12O34: C, 41.5; H, 5.2; N, 8.5; O, 27.7. Found: C, 40.4; H, 3.8; N, 9.1; O, 28.5%.
2.3. X-ray crystallography A crystal of the title compound 2 with dimensions of 0.50× 0.39× 0.28 mm was mounted in a glass capillary with the mother liquor to prevent the loss of the structural solvents during X-ray diffraction data collection. The data were recorded on a Siemens Smart CCD areadetector diffractometer with graphite-monochromated Mo Ka radiation (u= 0.71073 A, ), the scan mode being . The structure was solved by direct methods using SHELXS-86 and refined by full-matrix leastsquares calculations with SHELXL-97. All non-hydrogen atoms were refined with anisotropic thermal parameters. All hydrogen atoms were located in calculated positions and/or in the positions from difference Fourier map. The crystallographic data are given in Table 1. Table 1 Crystallographic data Empirical formula Formula weight Crystal system Space group a (A, ) b (A, ) c (A, ) i (°) V (A, 3) Z Dcalc (mg m−3) v (mm−1) F(000) Crystal size (mm) qmax, qmin (°) Index ranges Observed reflections Independent reflections Variables R wR Goodness-of-fit Largest difference peak a (e A, −3)
C68H102Fe6N12O34 1966.72 monoclinic P21/n 16.038(2) 19.467(3) 16.157(4) 118.19(2) 4446(2) 2 1.469 1.040 2044 0.50×0.40×0.28 25.11, 1.77 −175h519, −195k523, −195l513 5162 7848 [Rint =0.0357] 560 0.0445 0.0951 0.962 and hole 0.346 and −0.306
a Fourier map: R= Fo − Fc / Fo ; wR={ [w(F o2−F c2)2]/ [ w(F o2)2]}1/2.
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3.2. Structure of compound 2
Fig. 1. Perspective view of compound 2, solvent molecules and all hydrogen atoms have been omitted for clarity.
3. Results and discussion
3.1. Spectral characterization In the IR spectra, the ligand 1 shows stretching bands attributed to CO, CN, COH (phenolic) and NH at 1670, 1632, 1157 and 1236, and 3319 cm − l, respectively [12]. Bands at 3196 and 2708 cm − 1 are assigned to w(OH) vibrations involving intramolecular hydrogen bonding, while band at 1237 cm − 1 is attributed to l(OH) (phenolic) [13]. In addition, a strong band found at 1606 cm − 1 is assigned to CNNC group [12,13]. In the title compound 2, the absence of the NH and CO stretching vibration bands is consistent with the deprotonation of the CONH groups and coordination to the Fe(III) ion. The peaks at 1256 and 1034 cm − 1 are attributed to FeO linkage formed through methanol coordination [14]. The CNNC framework seen at l606 cm − 1 in the ligand sifted to 1600 cm − 1 upon coordination to Fe atom. The disappearance of the bands at 3196 and 2708 m − 1 and the appearance of the bands at 1316 and 1256 cm − 1 support the involvement of phenolic oxygen in coordination through deprotonation. This is confirmed by the band at 445 cm − 1 assigned to FeO (phenolic). Raman spectrum of the title compound 2 exhibited peaks at 1598 and 1515 cm − 1 corresponding to symmetric and asymmetric stretching of CNNC framework [12].
The title compound 2 crystallizes in the monoclinic system and space group P21/n. The structure exhibits a hexanuclear ring of iron atoms linked by six hydrazide NN groups. The deprotonated ligand ashz3 − acts as a trianionic pentadentate ligand, one phenolate oxygen, one carbonyl oxygen and one hydrazide nitrogen in the ligand are bound to one Fe3 + cation, and the other carbonyl oxygen plus the other hydrazide nitrogen in the same ligand are chelated to an adjacent Fe3 + cation. Therefore, the ligand is forcing all Fe3 + cations into a propeller configuration with alternating L/D stereochemistry as DLD or LDL forms (Fig. 1). Three methanol groups coordinated at the metal centers with L configuration are found on one face of the azametallacrown, and the remaining three methanol groups coordinated to the other metal centers with D configuration are found on the other face of the azametallacrown. The two faces of the disc-shaped hexanuclear ring have opposite chiralities to each other. This organization results in the 18-membered hexanuclear core ring system with an [FeNN]n repeat unit that is similar to that recently reported for the [MnIII 6 (Nformylsalicylhydrazidate)6(MeOH)6] (3) [10]. However, the cavity sizes of 2 and 3 are different. The approximate dimensions of the oval-shaped cavity are about 6.20 A, in diameter at entrance, about 9.31 A, at its largest diameter at the center of the cavity in compound 2, which are greater than those of compound 3. The change of the cavity size is probably caused by the steric effect of the different bridging multidentate ligands in the compound 2 and 3. It is also observed that the all atoms in the ligand are almost in co-plane and the all iron atoms in title compound 2 are in an octahedral FeN2O4 environment. The Jahn–Teller distortion is not observed because of the high-spin d5 iron(III) ion configuration compared with some Mn(III) azametallacrown compounds [10,11a]. The average neighboring Fe···Fe separation of 4.881 A, seems to be slightly longer than that of Fe(III)[Fe(III)(salicylhydroximato)(MeOH)(acetate)]3 [1] but shorter than that of [Fe(N-phenylsalicylhydrazidate)(MeOH)]10·3CH2Cl2·12.5CH3OH·5H2O [11a] with Fe···Fe distance of 4.848 and 4.946 A, , respectively. The average M···M···M interatomic angle in the 18-membered core ring of compound 2 is 117.6°, which is close to interior angle in n-hexagon of 120° (Table 2). There are not any solvent molecules in the ‘host’ cavity of azametallcrown in the title compound and [Co6(C9H7N2O3)6(CH3OH)6]·6CH3OH [11b], while one of the solvent methanol molecules is encapsulated within the cobalt metallacrown ‘host’ cavity in [Co6(C8H5N2O3)6(CH3OH)6]·5CH3OH 11b. As listed in Table 3, there are many kinds of intramolecular and intermolecular hydrogen bonds in the title compound 2.
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The first kind is between the OH group from coordinated methanol and the oxygen atom from solvent Table 2 Selected bond lengths (A, ) and angles (°) in compound 2 Bond lengths Fe(1)O(1) Fe(1)O(3) Fe(2)O(5) Fe(2)N(3) Fe(3)O(9) Fe(3)N(5) N(1)N(2) Fe(1)Fe(2) Fe(1)O(6) Fe(1)N(4) Fe(2)O(10) Fe(2)N(6)
1.908(3) 2.058(3) 1.918(3) 2.044(3) 1.923(3) 2.036(3) 1.405(4) 4.881(1) a 1.990(3) 2.081(3) 2.005(3) 2.089(3)
Fe(3)O(2a) Fe(3)O(12) N(3)N(4) Fe(1)Fe(3) Fe(1)N(1) Fe(1)O(4) Fe(2)O(7) Fe(2)O(8) Fe(3)O(11) Fe(3)N(2a) N(5)N(6) Fe(1)Fe(1a)
1.983(2) 2.091(3) 1.418(4) 8.349(1) b 2.046(3) 2.095(3) 2.038(3) 2.089(3) 2.008(3) 2.113(3) 1.406(4) 9.669(2) c
Bond angles O(1)Fe(1)O(6) O(6)Fe(1)N(1) O(6)Fe(1)O(3) O(1)Fe(1)N(4) N(1)Fe(1)N(4) O(1)Fe(1)O(4) N(1)Fe(1)O(4) N(4)Fe(1)O(4) O(5)Fe(2)O(7) O(5)Fe(2)N(3) O(7)Fe(2)N(3) O(10)Fe(2)N(6) N(3)Fe(2)N(6) O(10)Fe(2)O(8) N(3)Fe(2)O(8) O(9)Fe(3)O(2a) O(2a)Fe(3)O(11) O(2a)Fe(3)N(5) O(9)Fe(3)O(12) O(11)Fe(3)O(12) O(9)Fe(3)N(2a) O(11)Fe(3)N(2a) O(12)Fe(3)N(2a) C(7)O(2)Fe(3a) C(10)O(4)Fe(1) C(17)O(6)Fe(1) C(20)O(8)Fe(2) C(27)O(10)Fe(2) C(30)O(12)Fe(3) N(2)N(1)Fe(1) N(1)N(2)Fe(3a) N(4)N(3)Fe(2) N(3)N(4)Fe(1) N(6)N(5)Fe(3) N(5)N(6)Fe(2)
105.0(1) 166.6(1) 93.4(1) 93.3(1) 109.6(1) 94.7(1) 88.6(1) 160.5(1) 162.3(1) 86.7(1) 76.0(1) 76.0(1) 104.0(1) 84.1(1) 95.6(1) 100.4(1) 96.9(1) 172.2(1) 93.9(1) 89.7(1) 92.9(1) 89.7(1) 158.6(1) 117.7(2) 128.0(3) 116.7(2) 123.3(3) 116.5(2) 126.1(3) 116.7(2) 112.9(2) 115.7(2) 112.9(2) 115.4(2) 112.4(2)
O(1)Fe(1)N(1) O(1)Fe(1)O(3) N(1)Fe(1)O(3) O(6)Fe(1)N(4) O(3)Fe(1)N(4) O(6)Fe(1)O(4) O(3)Fe(1)O(4) O(5)Fe(2)O(10) O(10)Fe(2)O(7) O(10)Fe(2)N(3) O(5)Fe(2)N(6) O(7)Fe(2)N(6) O(5)Fe(2)O(8) O(7)Fe(2)O(8) N(6)Fe(2)O(8) O(9)Fe(3)O(11) O(9)Fe(3)N(5) O(11)Fe(3)N(5) O(2a)Fe(3)O(12) N(5)Fe(3)O(12) O(2a)Fe(3)N(2a) N(5)Fe(3)N(2a) C(1)O(1)Fe(1) C(8)O(3)Fe(1) C(11)O(5)Fe(2) C(18)O(7)Fe(2) C(21)O(9)Fe(3) C(28)O(11)Fe(3) C(7)N(1)Fe(1) C(8)N(2)Fe(3a) C(17)N(3)Fe(2) C(18)N(4)Fe(1) C(27)N(5)Fe(3) C(28)N(6)Fe(2) Fe(1)Fe(2)Fe(3)
86.9(1) 161.6(1) 75.1(1) 76.6(1) 89.6(1) 84.2(1) 88.5(1) 108.3(1) 89.0(1) 165.0(1) 97.0(1) 90.8(1) 87.4(1) 90.8(1) 160.1(1) 162.7(1) 86.8(1) 76.1(1) 83.0(1) 93.6(1) 75.8(1) 107.0(1) 131.4(2) 115.3(2) 133.7(2) 115.3(2) 132.6(3) 116.3(2) 130.1(2) 135.9(3) 132.6(3) 136.6(3) 131.3(3) 136.4(3) 117.6(2) d
Symmetry code: a, −x, −y, −z. a The average value of the Fe(1)Fe(2), Fe(2)Fe(3), Fe(3)Fe(1a) interatomic distances. b This is an average value of the Fe(1)Fe(3), Fe(2)Fe(1a), Fe(3)Fe(2a) interatomic distances. c This is an average value of the Fe(1)Fe(1a), Fe(2)Fe(2a), Fe(3)Fe(3a) interatomic distances. d This is an average value of the Fe(1)Fe(2)Fe(3), Fe(2)Fe(3)Fe(1a), Fe(3)Fe(1a)Fe(2a) interatomic angles.
Table 3 Hydrogen bond geometry (A, , °) DH···A
DH
H···A
D···A
DH···A
O(4)H(04)···O(15) O(8)H(08)···O(14) O(12)H(012)···O(13) O(15)H(015)···O(9A) O(13)H(013)···O(5B) O(16)H(016)···O(3) O(14)H(014)···O(17) O(17)H(171)···O(1) O(17)H(172)···O(16C)
1.053 0.987 0.966 1.017 0.978 1.076 1.080 1.036 0.972
1.674 1.631 1.616 1.845 1.970 1.713 1.672 1.904 1.925
2.677(5) 2.609(5) 2.579(5) 2.856(5) 2.851(4) 2.774(4) 2.625(6) 2.901(5) 2.816(6)
157.4 169.8 174.4 172.6 148.7 167.8 144.3 160.6 151.2
Symmetry codes: (A) −x, −y, −z; (B) 1−x, −y, −z; (C) 1/2−x, 1/ 2+y, 1/2−z.
Fig. 2. The effective magnetic moment (veff) and the inverse susceptibility m− 1 data as a function of temperature for the title compound, where open dots for observed results, and solid lines attached to m− 1 and veff for fitting curves based on the Curie – Weiss law and on an super-exchange fit, respectively.
methanol, e.g. O(4)H(04)···O(15), O(8)H(08)···O(14) and O(12)H(012)···O(13); the second is between the OH from solvent methanol and the oxygen atom (phenolic oxygen, carbonyl oxygen or water oxygen), e.g. O(13)H(013)···O(5B), O(15)H(015)···O(9A), O(16)H(016)···O(3) and O(14)H(014)···O(17); the third is between the OH from crystalline water and the phenolic oxygen or solvent methanol oxygen atom, e.g. O(17)H(171)···O(1) and O(17)H(172)···O(16C). It is worth to note that there are two hydrogen bonds for each of the solvent methanol molecules [C(31)H3O(13)H, C(32)H3O(14)H, C(33)H3O(15)H] and for water molecule.
3.3. Magnetic properties As shown in Fig. 2, the molar effective magnetic moment (veff) of the title compound shows the presence of an antiferromagnetic coupling between the Fe(III) spin 5/2 centers. The veff value at 272 K is 13.16vB, which is smaller than the sum value expected for a six spin-only paramagnetic systems with S= 2.5 (veff =
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14.49vB). With decreasing temperature, the veff values firstly decrease slightly, reaching 9.83 vB at 60 K, and then decrease rapidly after 60 K, reaching 2.19vB at 4.2 K. This is further suggested by a negative Weiss constant q = − 68.9(5) K, derived from the Curie–Weiss law fit in the temperature ranging from 68 to 272 K. Structurally, the magnetic super-exchanges would likely propagate between the neighboring centers (J1), between the near-neighboring centers (J2) and between the opposite centers (J3). When the six Fe(III) centers are simplified to be arranged in the symmetry of D6h, a least-squares fit for the data within T \ 43 K obtains the parameters J1/k= − 4.87(2) K, J2/k = − 0.96(5) K, J3/k = − 0.21(4) K and the agreement factor F= [(obs −cal)2/obs]= 9.59 ×10 − 3. The negative values of J demonstrate an antiferromagnetic coupling between the paramagnetic centers. As expected, the interactions between the neighboring centers dominate the others, which matched the derived absolute values of J1, J2 and J3. The antiferromagnetic nature of the interaction can be understood in terms of overlap through the bridging group between the single occupied metal d-orbitals.
4. Conclusion The title compound 2 is the first example of 18-azametallacrown-6 compounds containing Fe3 + as ring ions. An important structural feature in [Fe6(C9H7N2O3)6(CH3OH)6]·8CH3OH·2H2O is that there is not only a vacant cavity in the center of 18-azametallacrown-6 core ring, but also the opposite chiralities on the two faces of the metallacrown ring system. The vacant cavity and the opposite chiralities suggest that the title compound might have interesting chiral recognition properties. This novel iron 18-azametallacrown-6 compound also shows the presence of an antiferromagnetic coupling between the neighboring Fe(III) centers on the basis of overlap through the bridging group between the single occupied metal d-orbitals.
5. Supplementary material Lists of the CIF file for the title compound 2 have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 160047. Copies of this infor-
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mation may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: + 44-1223-336-033; e-mail: deposit@ ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements The authors are grateful for financial support from the National Natural Science Foundation of China and the Natural Science Foundation of Fujian Province, China.
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