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Structural, spectral and magnetic studies of two Co(II)-N-heterocyclic diphosphonates based on multinuclear units
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 153 (2015) 171–177
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Structural, spectral and magnetic studies of two Co(II)-N-heterocyclic diphosphonates based on multinuclear units Chen Zhao, Kui-Rong Ma ⁎, Yu Zhang, Yu-He Kan, Rong-Qing Li, Hua-You Hu Jiangsu Key Laboratory for Chemistry of Low-dimensional Materials, School of Chemistry and Chemical Engineering, Huaiyin Normal University, Huaian 223300, PR China
a r t i c l e
i n f o
Article history: Received 5 May 2015 Received in revised form 2 July 2015 Accepted 11 August 2015 Available online 13 August 2015 Keywords: Structure Co(II) diphosphonate Fluorescence Magnetism
a b s t r a c t Two examples of Co(II)-N-heterocyclic coordination polymers based on 1-hydroxyethylidenediphosphonic acid (H5L = CH3C(OH)(PO3H2)2), namely 0.5(H3NCH2CH2NH3)·[Co6(Cl2)(H3L)2(H2L)(HL)(2,2′-bipy)6] 1 and 2(NH4)·[Co3(HL)2(H2O)2(phen)2]·2(H2O) 2, have been solvothermally obtained by introducing the second ligands 2,2′-bipyridine/1,10-phenanthroline (2,2′-bipy/phen) and characterized by powder X-ray diffraction (PXRD), elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions show that compound 1 possesses a 0-D structure with hexa-nuclear cluster [Co6(O–P–O)8] built through single/double O–P–O bridges and compound 2 displays a 1-D ladder-like chain structure with magnetic topology building blocks [Co4(O–P–O)4]n. Then H-bonding and π–π stacking interactions further expand the two low-dimensional structures into threedimensional supramolecular frameworks. Fluorescent measurements reveal that both the maximum emission peaks of 1–2 are centered at 423 nm, mainly deriving from intraligand π*–π transition state of N-heterocyclic ligand 2,2′-bipy/phen, respectively. Magnetism data indicate that 1 exhibits antiferromagnetic behavior within hexa-nuclear Co(II) clusters, while 2 shows weak ferromagnetic interactions in 1-D topology Co(II)-chain, showing promising potential as magnetic materials. © 2015 Elsevier B.V. All rights reserved.
1. Introduction As a new type of functional molecular materials, coordination polymers (CPs) not only have abundant space topology, but also have huge potential applications in gas storage, separation, optics, electron, magnetism, chiral separation and catalysis and other fields. The assembly of the coordination polymers based on phosphonates is currently of significant interest [1–3]. Any material properties mainly depend on their structures. So both the structure of organic ligand and the coordination behavior of metal ion are generally dominant for the self-assembly of phosphonate CPs. In addition we don't know enough about the synthetic rules and topology. It is means that the rational synthesis of CPs with the target structure is an extremely creative and intellectually challenging task. In our work, firstly, 1-hydroxyethylidenediphosphonic acid (H5L) with a flexible hydroxyl group is often used as building block in the construction of the phosphonates. The additional –OH group attached to the organic tether not only provides a possible hydrophobic/ hydrophilic environment but also increases solubility of the resulting metal phosphonates. Importantly, it is more likely to behave as a bis(bidentate) chelating ligand using its four of six phosphonate oxygen atoms, which would be good for the construction low-dimensional CPs [4,5]. Secondly, lots of auxiliary ligands with N-heterocycle as one assistant method have been applied widely during the self-assembly of the ⁎ Corresponding author. E-mail address: [email protected] (K.-R. Ma).
http://dx.doi.org/10.1016/j.saa.2015.08.017 1386-1425/© 2015 Elsevier B.V. All rights reserved.
CPs. Polypyridyl ligands have been intensively used as ancillary building blocks in the phosphonate coordination chemistry [6], due to their interesting electronic, photonic and magnetic properties, as well as π-stacking ability and directional H-bonding when coordinating to transition metals. Although many chemists devoted to the study of self-assembly of the CPs by means of the mixed ligands [7–11], low-dimensional phosphonate CPs have not been well developed based on auxiliary N-heterocyclic ligands under the solvothermal condition. So 2,2′-bipy and phen have been selected as auxiliary ligands in our work. Finally, Co(II) ion is focused because of its unique high-spin d7 electron configuration and larger spin-orbital coupling effect for an octahedral Co(II) complex. Many great compounds of Co(II)-H5L have been resolved, but a few Co(II)-diphosphonate compounds with 2,2′-bipy/phen have been structurally determined [12]. By introducing the auxiliary ligands 2,2′-bipy/ phen, we have succeeded in winning two new diphosphonate CPs, 0.5(H3NCH2CH2NH3)·[Co6(Cl2)(H3L)2(H2L)(HL)(2,2′-bipy)6] 1 and 2(NH4)·[Co3(HL)2(H2O)2(phen)2]·2(H2O) 2. In this paper, we study crystal structures, fluorescent and magnetic properties. 2. Experimental 2.1. Materials and general methods All reagents were purchased from commercial sources and used without further purification. Element analyses were performed on a Perkin-Elmer 2400 LS elemental analyzer. IR spectra were recorded
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C. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 153 (2015) 171–177
from 4000 to 400 cm−1 with a Nicolet AVATAR360 instrument. The thermal gravimetric analyses (TG–DSC) were carried out with a NETZSCH STA 449F3 thermal analyzer with a heating rate of 10 K·min− 1. Powder X-ray diffraction patterns (PXRD) were performed on an ARL X'TRA diffractometer using Cu-Kα radiation. Emission spectra in the solid state at room temperature were taken on a Perkin-Elmer LS-55 fluorescence spectrophotometer. Magnetic susceptibility data were collected, respectively, on 0.0236 g for 1 and 0.0230 g for 2 of samples using a Quantum Design MPMS-7 SQUID magnetometer.
2.2. Syntheses 2.2.1. The preparations of 1 0.5(H3 NCH2 CH2 NH3)·[Co6 (H3 L)2 (H2 L)(HL)Cl 2(2,2′-bipy) 6 ] 1: The mixture of CoCl2 ·6H2 O (0.0714 g, 0.3 mmol), H5 L (0.0618 g, 0.3 mmol), 2,2′-bipy (0.0625 g, 0.4 mmol) and ethylenediamine (0.0060 g, 0.1 mmol) in absolute ethyl alcohol (10 mL) was stirred for 30 min, and sealed into a 15 mL Teflon-lined reactor. Solution was heated to 120 °C for 5 days, and then cooled at room temperature. Pink cluster-like crystals of 1 were collected by vacuum filtration. Then they were washed thoroughly with the absolute ethyl alcohol, and dried in air (yield 38% for 1 based on cobalt). Anal. Calc. for C137H143 Cl4Co12N25O56P16 1: C 37.53, H 3.26, N 7.99. Found C 37.58, H 3.31, N 8.02%. IR (KBr)/cm−1: 3421(w), 3345(w), 3324(w), 3164(m), 3131(m), 3106(w), 3025(w), 2931(w), 2823(w), 1600(m), 1569(w), 1525(m), 1473(m), 1315(w), 1218(w), 1165(s), 1139(s), 1110(s), 1064(s), 1024(s), 935(m), 879(w), 813(w), 775(w), 651(w), 572(m), 466(m) (see Supplementary Fig. A.1a).
Table 1 Crystallographic data and structural refinements for 1-2.
Empirical formula Formula weight T/K Crystal system Space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z Dc/g · cm−3 μ/mm−1 θ range/° Reflections collected/unique Data/restraints/ parameters GOF on F2 Final R indices [I N 2σ(I)] R indices (all data) Largest diff. peak and hole/eÅ−3
1
2
C137H143Cl4Co12N25O56P16 4380.25 296(2) Triclinic
C28H40Co3N6O18P4 1049.33 293(2) Triclinic
10.4128(1) 15.225(2) 26.935(4) 79.762(2) 85.737(2) 84.807(2) 4177.5(1) 1 1.741 1.469 1.87–25.00 29,332/14,361 [R(int) = 0.0631] 3049/3/261
6.5167(9) 11.874(2) 12.624(2) 95.531(2) 102.070(2) 91.744(2) 949.5(2) 1 1.835 1.550 1.66–25.00 6731/3311 [R(int) = 0.0316] 3311/1/269
0.911 R1 = 0.0615, wR2 = 0.1347
1.079 R1 = 0.0377, wR2 = 0.0949
R1 = 0.1303, wR2 = 0.1464 1.714, −1.911
R1 = 0.0459, wR2 = 0.1062 0.650, −0.556
Note. R1 = Σ||Fo| − |Fc||/Σ|Fo|; wR2 = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)]2}1/2.
3. Results and discussion 3.1. Description of the structures
2.2.2. The preparations of 2 2(NH4 )·[Co3(HL)2 (H2 O)2 (phen)2 ]·2(H2 O) 2: The mixture of Co(NO3 ) 2·6H2 O (0.0582 g, 0.2 mmol), H5 L (0.0412 g, 0.2 mmol), phen (0.0793 g, 0.4 mmol) and NH4F (0.0370 g, 1 mmol) in absolute ethyl alcohol (10 mL) was stirred for 30 min, and sealed into a 15 mL Teflon-lined reactor. Solution was heated to 120 °C for 5 days, and then cooled at room temperature. Pink rod-like crystals of 2 were collected by vacuum filtration. Then they were washed thoroughly with the absolute ethyl alcohol, and dried in air (yield 65% for 2 based on cobalt). Anal. Calc. for C28 H40 Co3 N6 O 18 P4 2: C 32.02, H 3.81, N 8.01. Found C 32.07, H 3.88, N 8.05%. IR (KBr)/cm−1 : 3259(w, broad), 2927(w), 2843(w), 1621(w), 1587(w), 1517(w), 1427(w), 1388(m), 1303(w), 1159(s), 1076(s), 1049(s), 977(w), 931(m), 848(w), 775(w), 727(m), 653(w), 568(m), 482(m), 458(m) (see Supplementary Fig. A.1b).
2.3. Crystallography Intensity data were collected on a Bruker SMART CCD diffractometer equipped with a graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at 296 K for 1 and 293 K for 2 using the ω-2θ scan technique. The structure was solved by direct methods and refined by full-matrix least-squares fitting on F2 by SHELXL-97. A total of 29,332 for 1 and 6731 for 2 reflections were collected, of which 14,361 (Rint = 0.0631) for 1 and 3311 (Rint = 0.0316) for 2 were unique, respectively. All non-hydrogen atoms of 1 and 2 were located from the initial solution and refined with anisotropic thermal parameters. The position of hydrogen atoms of 1 and 2 were either located by difference Fourier maps or calculated geometrically and their contributions in structural factor calculations were included. Crystallographic data and structural refinements are summarized in Table 1. Selected bond lengths [Å] and angles [°] are list in Table 2. Hydrogen bonds [Å] and angles [°] are given in Table 3.
Single-crystal X-ray diffraction analyses reveal that both 1 and 2 possess 3-D supramolecular architectures. The asymmetric unit of 1 (Fig. 1) contains six distinct Co(II) atoms, two H3L2− ligands, a H2L3− ligand, a HL4− ligand, two Cl− ligands as well as six coordinated 2,2′-bipy molecules and a half of free ethylenediamine cation. Four centers Co(1), Co(2), Co(5) and Co(6) in 1 are all in a distorted octahedral coordination environment, while the remains of two other centers Co(3) and Co(4) are in a trigonal bipyramid (TBP) environment. Four Co(II) centers are 6-coordinated to six oxygen atoms (O(5), O(7), O(8), O(11), O(14), O(15)) from three phosphonate ligands for Co(1), to six oxygen atoms (O(12), O(16), O(18), O(21), O(22), O(28)) from three phosphonate ligands for Co(2), to two oxygen atoms from a phosphonate ligand and four nitrogen atoms from two 2,2-bipy ligands (O(3), O(6), N(5), N(6), N(7), N(8)) for Co(5) and to two oxygen atoms from a phosphonate ligand and four nitrogen atoms from two 2,2-bipy ligands (O(24), O(27), N(9), N(10), N(11), N(12)) for Co(6). Both Co(3) and Co(4) are 5-coordinated to two oxygen atoms from a phosphonate ligand, two nitrogen atoms from a 2,2-bipy ligand and a Cl− ion (O(17), O(19), N(1), N(2), Cl(1)) for Co(3)/(O(10), O(13), N(3), N(4), Cl(2)) for Co(4), respectively. The equatorial planes are defined by N(2)–O(17)–Cl(1) for Co(3) and N(3)–O(13)–Cl(2) for Co(4) in trigonal bipyramid structures, and the distortion parameters (τ) are 0.63 for Co(3) and 0.79 for Co(4) based on 5-coordination description, respectively [a regular trigonal bipyramid (TBP) and square-based pyramid (SP) have τ values of 1.00 and 0.00 [13,14]]. The Co(II)–Cl distances are in the range of 2.303(2)–2.306(2) Å. The Co(II)–O/N distances in 1 are fall within the range of 1.980(4)–2.240(4) Å/2.082(6)–2.091(6) Å which are similar to those of reported 2,2′-bipy-containing Co(II) phosphonate complexes [12]. The –PO3 group in 1 displays three types of coordination modes simultaneously (Fig. A.2a). i, Monodentate mode: it links a Co(II) atom in η1η0η0 mode. ii, Bidentate mode: it chelates to two Co(II) atoms in η1η0η1 mode. iii, Tridentate mode: it chelates two Co(II) atoms and bridges a Co(II) atom in η1η1η1 mode. The H5L is role-playing the tetra-/
C. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 153 (2015) 171–177 Table 2 Selected bond lengths (Å) and angles (°) for 1–2.
Table 2 (continued) 1 2
1 Co(1)–O(15) Co(1)–O(5) Co(1)–O(8) Co(1)–O(11) Co(1)–O(7) Co(1)–O(14) Co(2)–O(12) Co(2)–O(22) Co(2)–O(16) Co(2)–O(18) Co(2)–O(28) Co(2)–O(21) Co(3)–O(17) Co(3)–O(19) Co(3)–N(2) Co(3)–N(1) Co(3)–Cl(1) P(1)–C(1) P(2)–C(1) P(3)–C(3) P(4)–C(3) O(15)–Co(1)–O(5) O(15)–Co(1)–O(8) O(5)–Co(1)–O(8) O(15)–Co(1)–O(11) O(5)–Co(1)–O(11) O(8)–Co(1)–O(11) O(15)–Co(1)–O(7) O(5)–Co(1)–O(7) O(8)–Co(1)–O(7) O(11)–Co(1)–O(7) O(15)–Co(1)–O(14) O(5)–Co(1)–O(14) O(8)–Co(1)–O(14) O(11)–Co(1)–O(14) O(7)–Co(1)–O(14) O(12)–Co(2)–O(22) O(12)–Co(2)–O(16) O(22)–Co(2)–O(16) O(12)–Co(2)–O(18) O(22)–Co(2)–O(18) O(16)–Co(2)–O(18) O(12)–Co(2)–O(28) O(22)–Co(2)–O(28) O(16)–Co(2)–O(28) O(18)–Co(2)–O(28) O(12)–Co(2)–O(21) O(22)–Co(2)–O(21) O(16)–Co(2)–O(21) O(18)–Co(2)–O(21) O(28)–Co(2)–O(21) O(17)–Co(3)–O(19) O(17)–Co(3)–N(2) O(19)–Co(3)–N(2) O(17)–Co(3)–N(1) O(19)–Co(3)–N(1) N(2)–Co(3)–N(1) O(17)–Co(3)–Cl(1) O(19)–Co(3)–Cl(1) N(2)–Co(3)–Cl(1) N(1)–Co(3)–Cl(1)
2.021(4) 2.073(4) 2.091(4) 2.106(4) 2.151(4) 2.240(4) 2.033(4) 2.086(5) 2.092(4) 2.101(4) 2.137(4) 2.261(4) 1.980(4) 2.063(4) 2.085(6) 2.133(7) 2.303(2) 1.858(7) 1.833(7) 1.840(6) 1.841(7) 95.8(2) 168.5(2) 91.4(2) 95.5(2) 102.7(2) 91.5(2) 84.1(2) 83.5(2) 87.9(2) 173.7(2) 90.3(2) 172.2(2) 81.8(2) 81.4(2) 92.4(2) 95.4(2) 94.3(2) 103.3(2) 168.5(2) 92.3(2) 92.1(2) 86.9(2) 83.0(2) 173.4(2) 85.9(2) 90.1(2) 172.5(2) 81.1(2) 81.4(2) 92.4(2) 94.2(2) 129.2(2) 93.3(2) 86.6(2) 167.0(2) 76.4(3) 119.9(1) 97.9(1) 108.6(2) 92.9(2)
Co(4)–O(13) Co(4)–O(10) Co(4)–N(3) Co(4)–N(4) Co(4)–Cl(2) Co(5)–O(3) Co(5)–O(6) Co(5)–N(5) Co(5)–N(7) Co(5)–N(6) Co(5)–N(8) Co(6)–O(27) Co(6)–O(24) Co(6)–N(11) Co(6)–N(9) Co(6)–N(10) Co(6)–N(12) P(5)–C(5) P(6)–C(5) P(7)–C(7) P(8)–C(7) O(13)–Co(4)–O(10) O(13)–Co(4)–N(3) O(10)–Co(4)–N(3) O(13)–Co(4)–N(4) O(10)–Co(4)–N(4) N(3)–Co(4)–N(4) O(13)–Co(4)–Cl(2) O(10)–Co(4)–Cl(2) N(3)–Co(4)–Cl(2) N(4)–Co(4)–Cl(2) O(3)–Co(5)–O(6) O(3)–Co(5)–N(5) O(6)–Co(5)–N(5) O(3)–Co(5)–N(7) O(6)–Co(5)–N(7) N(5)–Co(5)–N(7) O(3)–Co(5)–N(6) O(6)–Co(5)–N(6) N(5)–Co(5)–N(6) N(7)–Co(5)–N(6) O(3)–Co(5)–N(8) O(6)–Co(5)–N(8) N(5)–Co(5)–N(8) N(7)–Co(5)–N(8) N(6)–Co(5)–N(8) O(27)–Co(6)–O(24) O(27)–Co(6)–N(11) O(24)–Co(6)–N(11) O(27)–Co(6)–N(9) O(24)–Co(6)–N(9) N(11)–Co(6)–N(9) O(27)–Co(6)–N(10) O(24)–Co(6)–N(10) N(11)–Co(6)–N(10) N(9)–Co(6)–N(10) O(27)–Co(6)–N(12) O(24)–Co(6)–N(12) N(11)–Co(6)–N(12) N(9)–Co(6)–N(12) N(10)–Co(6)–N(12)
1.980(4) 2.042(5) 2.082(6) 2.131(6) 2.306(2) 2.068(5) 2.107(4) 2.122(6) 2.146(6) 2.147(7) 2.191(6) 2.067(4) 2.098(5) 2.154(6) 2.155(6) 2.162(6) 2.178(6) 1.846(7) 1.830(6) 1.839(7) 1.850(7) 96.1(2) 122.6(2) 95.2(2) 85.3(2) 170.8(2) 76.5(2) 123.3(2) 96.5(1) 110.8(2) 90.3(2) 93.4(2) 91.6(2) 97.1(2) 94.1(2) 95.7(2) 165.7(2) 166.3(2) 81.4(2) 76.6(3) 99.0(2) 94.5(2) 168.7(2) 90.8(2) 75.7(2) 92.7(2) 93.6(2) 92.9(2) 92.8(2) 167.2(2) 83.4(2) 99.7(2) 92.2(2) 99.9(2) 166.0(2) 76.0(2) 88.0(2) 168.0(2) 75.2(2) 97.5(2) 91.9(2)
2 Co(1)–O(1) Co(1)–O(3)#1 Co(1)–N(1) Co(1)–N(2) Co(1)–O(5)#1 Co(1)–O(1W) Co(2)–O(2)#2 O(1)–Co(1)–O(3)#1 O(1)–Co(1)–N(1) O(3)#1–Co(1)–N(1) O(1)–Co(1)–N(2) O(3)#1–Co(1)–N(2)
2.007(2) 2.070(2) 2.136(3) 2.150(3) 2.156(2) 2.168(2) 2.060(2) 171.60(1) 86.73(1) 85.68(1) 92.61(1) 89.27(1)
Co(2)–O(2) Co(2)–O(4) Co(2)–O(4)#2 Co(2)–O(7)#2 Co(2)–O(7) P(1)–C(1) P(2)–C(1) O(2)#2–Co(2)–O(2) O(2)#2–Co(2)–O(4) O(2)–Co(2)–O(4) O(2)#2–Co(2)–O(4)#2 O(2)–Co(2)–O(4)#2
173
2.060(2) 2.071(2) 2.071(2) 2.218(2) 2.218(2) 1.847(4) 1.846(4) 180.00(1) 91.95(9) 88.05(9) 88.05(9) 91.95(9)
N(1)–Co(1)–N(2) O(1)–Co(1)–O(5)#1 O(3)#1–Co(1)–O(5)#1 N(1)–Co(1)–O(5)#1 N(2)–Co(1)–O(5)#1 O(1)–Co(1)–O(1W) O(3)#1–Co(1)–O(1W) N(1)–Co(1)–O(1W) N(2)–Co(1)–O(1W) O(5)#1–Co(1)–O(1W)
77.46(1) 93.92(1) 94.05(9) 173.11(1) 95.65(1) 91.52(1) 86.08(9) 98.80(1) 174.26(1) 88.05(9)
O(4)–Co(2)–O(4)#2 O(2)#2–Co(2)–O(7)#2 O(2)–Co(2)–O(7)#2 O(4)–Co(2)–O(7)#2 O(4)#2–Co(2)–O(7)#2 O(2)#2–Co(2)–O(7) O(2)–Co(2)–O(7) O(4)–Co(2)–O(7) O(4)#2–Co(2)–O(7) O(7)#2–Co(2)–O(7)
180.00(1) 85.22(9) 94.79(9) 98.07(9) 81.93(9) 94.78(9) 85.22(9) 81.93(9) 98.07(9) 180.00(1)
Symmetry code: 2:#1 x + 1, y, z #2 −x + 1, −y + 2, −z + 1 #3 x − 1, y, z.
hexa-dentate chelating-bridging ligand in the structure of 1. The last two patterns of –PO3 group are usually found in the same kinds of phosphonate compounds [9–12]. However, little research on these three patterns in the same structure was reported. All the hydroxyl groups (O(7), O(14), O(21), O(28)) of four phosphonate ligands participate in the coordination with metals. The uncoordinated phosphonate oxygen atoms are all involved in hydrogen bonds. Based on the coordination environment, four hydroxyl oxygen atoms and five phosphonate oxygen atoms (O(1), O(4), O(20), O(23), O(26)) are protonated to adjust charge balance. The binuclear units [−Co–O–P–O–]2 between Co(1)⋯Co(4)/ Co(2)⋯Co(3) ions with the distances of 5.185 Å/5.270 Å are formed by a double O–P–O bridge in syn–syn mode in 1, respectively. Two binuclear units are connected with two single O–P–O bridges to give Table 3 Hydrogen bond lengths (Å) and angles (°) for 1–2. D–H⋯A
d(D–H)
d(H⋯A)
d(D⋯A)
b(DHA)
1 O(28)–H(28W)⋯O(2)#2 O(26)–H(26W)⋯O(12) O(23)–H(23W)⋯O(18) O(21)–H(21W)⋯O(11) O(20)–H(20W)⋯O(2)#2 O(14)–H(14W)⋯O(16) O(7)–H(71W)⋯O(25)#3 O(4)–H(4W)⋯O(8) O(1)–H(1W)⋯O(15) N(13)–H(13B)⋯Cl(2)#4 C(2)–H(2C)⋯O(28)#3 C(8)–H(8A)⋯O(7)#2 C(16)–H(16)⋯O(20)#5 C(17)–H(17)⋯Cl(1)#5 C(18)–H(18)⋯O(19) C(19)–H(19)⋯O(10) C(25)–H(25)⋯O(4)#6 C(29)–H(29)⋯O(3) C(45)–H(45)⋯O(9)#7 C(51)–H(51)⋯O(17)#8 C(57)–H(57)⋯O(22)#2 C(67)–H(67)⋯Cl(1)#9
0.85 0.99 0.85 0.85 0.85 0.85 0.85 0.85 0.91 0.89 0.96 0.96 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93
1.84 1.69 1.99 1.85 1.74 1.92 1.86 2.04 1.76 2.70 2.54 2.53 2.59 2.77 2.50 2.60 2.55 2.58 2.53 2.52 2.59 2.74
2.649(6) 2.650(6) 2.779(6) 2.681(6) 2.578(6) 2.690(6) 2.614(6) 2.745(6) 2.618(6) 3.240(1) 3.329(8) 3.321(8) 3.290(9) 3.690(9) 3.074(9) 3.158(9) 3.213(1) 3.138(9) 3.240(9) 3.229(1) 3.390(1) 3.385(9)
158.8 162.7 153.3 164.8 168.0 150.4 148.0 140.7 156.4 120.1 139.1 139.7 132.3 171.0 120.1 119.4 129.0 118.6 133.9 133.2 145.0 127.5
2 N(3)–H(31)⋯N(3)#4 N(3)–H(32)⋯O(2W) N(3)–H(33)⋯O(3) O(7)–H(71)⋯O(5)#1 O(1W)–H(1A)⋯O(2)#1 O(2W)–H(2W2)⋯O(2)#4 O(2W)–H(2W1)⋯N(3) O(1W)–H(1B)⋯O(4)#2 C(8)–H(8)⋯O(3)#5 C(4)–H(4)⋯O(1W)#6
0.94 0.92 0.97 0.82 0.82 0.82 0.82 0.81 0.93 0.93
2.67 2.15 1.96 2.17 2.10 2.06 2.13 2.02 2.57 2.57
3.139(7) 2.902(5) 2.916(4) 2.985(3) 2.894(3) 2.837(4) 2.902(5) 2.826(3) 3.446(5) 3.423(5)
111.9 138.9 167.6 174.2 165.5 158.5 154.9 168.8 156.4 152.9
Symmetry transformations used to generate equivalent atoms. 1:#1 −x + 2, −y + 1, −z + 1 #2 x − 1, y, z #3 x + 1, y, z #4 x + 1, y + 1, z #5 −x, −y + 1, −z #6 x, −y, −z + 1 #7 x, y + 1, z #8 −x, −y, −z #9 x − 1, y − 1, z. 2:#1 x + 1, y, z #2 −x + 1, −y + 2, −z + 1 #3 x − 1, y, z #4 -x + 1, −y + 1, −z + 1 #5 −x + 1, −y + 1, −z #6 −x + 2, −y + 1, −z + 1.
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Fig. 1. Coordination environment of Co(II) ions in 1.
rise to a ladder-like tetra-nuclear unit [Co(1)⋯Co(4)⋯Co(2)⋯Co(3)] with Co(1)⋯Co(2)/Co(1)⋯Co(3)/Co(2)⋯Co(4) distances of 4.671 Å/ 6.277 Å/6.347 Å, and then two Co(II) ions (Co(5), Co(6)) further link up with this tetra-nuclear unit by a single O–P–O bridge and a hydroxyl bridge, respectively, resulting in a hexa-nuclear Co(II)-cluster structure, which acts as the basic build motif in the structure. The hydrogen bond C(45)⋯O(9) (3.240(9) Å, 133.9°) links hexa-nuclear clusters alternatively to form a one-dimensional supramolecular chain along the baxis, along with the second ligand 2,2′-bipy standing in two rows at its sides (Fig. A.2b). The neighboring 1-D supramolecular chains are cross-linked by the hydrogen bonds [O(28)⋯O(2) (2.649(6) Å, 158.8°), O(21)⋯O(11) (2.681(6) Å, 164.8°), O(14)⋯O(16) (2.690(6) Å, 150.4°), O(20)⋯O(2) (2.578(6) Å, 168.0°), O(14)⋯O(16) (2.690(6) Å, 150.4°), O(7)⋯O(25) (2.614(6) Å, 148.0°), C(2)⋯O(28) (3.329(8) Å, 139.1°), C(8)⋯O(7) (3.321(8) Å, 139.7°), C(57)⋯O(22) (3.390(10) Å, 145.0°), C(67)⋯Cl(1) (3.385(9) Å, 127.5°)], to lead to a twodimensional supramolecular layer in the ac plane (Fig. A.2c). In 2-D layer organic groups alternate with inorganic groups along both chains, linked by hydrogen bonds. The three-dimensional supramolecular framework is created via hydrogen bonds [C(17)⋯Cl(1) (3.690(9) Å, 171.0°), C(16)⋯O(20) (3.290(9) Å, 132.3°)] along the [100] plane between the adjacent supramolecular layers (Fig. A.2d). Also the π–π stacking interactions contribute to the formation of the 3-D framework between aromatic rings R1 ↔ R2 (R1: N(5)–C(29)–C(30)–C(31)– C(32)–C(33), R2: N(3)–C(19)–C(20)–C(21)–C(22)–C(23), symmetric code 1 − x, − y, 1 − z, centroidal distance 3.4721 Å, slip distances 0.76 Å (R1 → R2)/1.235 Å (R2 → R1) and dihedral angle 12.26°). The guest ethanediamine molecules are occupied in pore spaces of the 3-D supramolecular framework. After the removal of the guest molecules, the volume of the tunnel formed by 2-D layers is 83.7 Å3 per unit cell using PLATON [15] based on the crystal structure, comprising 2.0% of the crystal volume 4177.5 Å3. Compound 2 features a one-dimensional chain structure, and there are one and a half unique Co(II) ions, a HL4− ligand, a coordinated water molecule, and a phen ligand as well as a free NH+ 4 cation and a free water molecule in its asymmetric unit (Fig. 2). The unique Co(1) and Co(2) centers in 2 are both in an octahedral coordination environment. They are 6-coordinated to three oxygen atoms (O(1), O(3), O(5)) from two phosphonate ligands, two nitrogen atoms from a phen ligand (N(1), N(2)) and a water oxygen atom O(1W) for Co(1) and to six oxygen atoms (O(2), O(4), O(7), O(2A), O(4A), O(7A)) from two
phosphonate ligands for Co(2). The Co(1)–N(1) distance is 2.136(3) Å and Co(1)–N(2) distance is 2.150(3) Å. The other Co–O bond lengths are in the range of 2.007(2)–2.218(2) Å. These distances are comparable to those reported for other Co(II) phosphonates [12]. The coordinating pattern of the ligand HL4− in 2 is the form of hexadentate chelating-bridging, affording five phosphonate oxygen atoms (O(1), O(2), O(3), O(4), O(5)) in μ3:(η1η1)(η1η1η1) mode, to chelate/ bridge with three Co(II) atoms. Each –PO3 groups of the ligand HL4− display two types of coordination modes simultaneously. i, Bidentate mode: one chelates two Co(II) atoms in μ2: η1η0η1 mode. ii, Tridentate mode: another chelates three Co(II) atoms in μ3: η1η1η1 mode. The two modes are same as the last two patterns of 1. The hydroxyl group O(7) of ligand is also coordinated to metal. The uncoordinated phosphonate oxygen atoms are all involved in hydrogen bonds. Based on the coordination environment, the hydroxyl oxygen atom is protonated and four phosphonate oxygen atoms are deprotonated to adjust charge balance. Each [Co(1)O4N2] octahedron, as the basic building unit, is bridged by a single O(3)–P(1)–O(1) bridge to yield a one-dimensional inorganic single chain along the a-axis, and then it is further joined together via [Co(2)O6] octahedron by two single O(4)–P(2)–O(5) bridges to build
Fig. 2. Coordination environment of Co(II) ions in 2.
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a ladder-like chain (Fig. A.3a). The second ligand phen stands in two rows at its sides. The 1-D ladder-like chain includes a type of 16member ring [–Co(1)–O–P–O–Co(2)–O–P–O–]2 with the distances Co(1)⋯Co(1), Co(1)⋯Co(2) and Co(2)⋯Co(2) of 7.556 Å, 4.933 Å and 6.517 Å, respectively. Importantly, the magnetic topology of 2 should come from trimer building blocks [Co(1)(O–P–O)2Co(2)(O–P– O)2Co(1)]n within the inorganic chain. The ladder-like chain structure is similar to those compounds reported by our group: [Zn1.5(H2L) (bipy)(H2O)]·3H2O [16] and [Ni3(H2L)2(H2O)4]·3H2O [17]. The free water molecules and NH+ 4 cations are located in cavities defined by 1D chain and are involved in the information of 3-D supramolecular structure. The adjacent ladder-like chains are connected with each other by hydrogen bonds formed among the free water molecules, NH+ 4 cations and phosphonate oxygen atoms, N(3)⋯N(3A) (3.139(7) Å, 111.9°), N(3)⋯O(2W) (2.902(5) Å, 138.9°), N(3)⋯O(3) (2.916(4) Å, 167.6°), O(2W)⋯O(2) (2.837(4) Å, 158.5°), O(2W)⋯N(3) (2.902(5) Å, 154.9°), C(4)⋯O(1W) (3.423(5) Å, 152.9°), to give rise to a 2-D supramolecular layer in the ab plane (Fig. A.3b). The intermolecular H-bonding C(8)⋯O(3) (3.446(5) Å, 156.4°) and π–π stacking between the aromatic ring R1 ↔ R2 (R1:N(2)–C(12)–C(11)–C(10)–C(9)–C(13)), R2: (C(6)– C(7)–C(8)–C(9)–C(13)–C(14), symmetric code 1 − x, 1 − y, −z, centroidal distance 3.6150 Å, slip distances 1.627 Å (R1 → R2)/1.581 Å (R2 → R1) and dihedral angle 1.73°) have an important role to play in controlling the formation of the 3-D supramolecular network (Fig. A.3c). All the hydrogen bonds and π–π stacking interactions in the structures of 1–2 are best propitious to stabilize the structure, as well charge transfer. 3.2. Spectral studies The powder XRD patterns of 1–2 indicate that as-synthesized products are both new materials, and the patterns are entirely consistent with the simulated those from the single-crystal X-ray diffraction, respectively (see Supplementary Fig. A.4a–b). The fluorescent spectra of both compounds and the second ligands (2,2′-bipy and phen) are shown in Fig. 3. The free H5L ligand does not emit fluorescence at room temperature in the visible region. However, the second ligand 2,2′-bipy shows a broad peak at 377 nm and a sharp peak at 422.5 nm (λex = 233 nm), and another ligand phen reveals a stronger peak at 361.5 nm with a shoulder peak at 379 nm and a weak peak at 400 nm (λex = 335 nm). The fluorescent emissions of 2,2′-bipy have a few minor variations when it coordinates with Co(II) ion, that is, weakening of fluorescent intensity at 377 and 423 nm for 1 (λex = 233 nm) (Fig. 3a). However, the fluorescent emission peaks of 2 (λex = 235 nm) have changed so much (Fig. 3b), including the maximum band shifts from 361.5 nm to the lower energy band 423 nm compared to the free phen ligand and the fluorescent intensity also weaken. With the increase of molecular rigidity, the energy loss of the nonradiative transition was decreased, and the energy gap from the excited state to the ground state was reduced. Thus, the maximal emission peak
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of 2 shows red shift effect. The emission bands of 1–2 are mainly attributed to intraligand π*–π transition states of 2,2′-bipy for 1 and phen for 2. In view of fluorescent intensity of 1 and 2, it shows its decay compared with that of the second ligand. This phenomenon is interpreted to be the result of two factors: (1) unsaturated d7 electron configuration of the central cobalt(II) ion, and (2) the geometries of the complexes. First, if the d shell of metal ion is incomplete, LMCT (ligand-to-metal charge transfer) will happen. This will lead to reductions in electron number of ligand during the transition from the lowest excited state to the ground state, which leads to the appearance of fluorescence quenching. Next, both 1 and 2 belong to the low-dimensional compounds, hexa-nuclear cluster for 1 and 1-D chain for 2. The formation of complexes with low-dimensional structures destroys the larger conjugated system of the second ligand. 3.3. Thermal characteristics TG–DSC measures were conducted to examine the stabilities of 1–2 in the temperature range of 25–800 °C (see Supplementary Fig. A.5a–b). TGA curve of 1 shows one main weight loss, attributing to the departure of the guest molecule ethanediamine with the loss of 0.71% (calc. 0.71%) at 160 °C and above 200 °C the loss of [P–OH] and [C–OH] hydroxyl groups and 2,2′-bipy ligands. This step loss is completed at 600 °C with an obvious endothermic peak centered at 395 °C and a weak exothermic peak centered at 550 °C. There is an unconspicuous weight loss process after 600 °C until the warming over with two weak exothermic peaks centered at 605 and 650 °C. This loss can be attributed to the decomposition of organic moieties of phosphonate ligand and chloridion. The final thermal decomposition residue at 800 °C is Co6(P2O7)4 based on the powder X-ray diffraction patterns. The total weight loss of 52.07% is close to the calculated value (52.08%). TGA curve of 2 indicates three main steps of weight losses. The first step with two weak endothermic peaks centered at 118 °C and 200 °C is loss of the crystal water, NH+ 4 cation and the coordinated water before 220 °C. The observed weight loss of 10.32% is in good agreement with the calculated value (10.29%). The second step from 220 to 600 °C is a continuous pyrolysis process with a weak exothermic peak at 500 °C, and the third step has a distinct weightlessness from 600 °C. The mass loss of both steps can be attributed to the decomposition of hydroxyl group [C– OH] and phen, coming with the collapse of internal skeletal structure of 2. The total weight loss is about 38.06% which means thermaldecomposition is not over at 800 °C. 3.4. Magnetism properties The temperature-dependent susceptibility data of 1–2 have been measured under a field of 2 KOe (Fig. 4). At 300 K, the χmT value of 2.62 cm3·mol−1·K for 1 is slightly larger than the expected that of 1.87 cm3·mol−1·K for a free CoII ion (g = 2.0, S = 3/2), suggesting the orbital contribution of the octahedral Co(II) ions (Fig. 4a). This
Fig. 3. Solid-state emission spectra of 1 (3a) and 2 (3b) and the second ligands 2,2′-bipy/1,10-phen.
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Fig. 4. Temperature dependence of χm and χmT for 1 (4a) and 2 (4b). The theoretical behavior is fitted by red solid lines for 1–2.
is a ubiquitous phenomenon for the high spin Co(II) compounds [18]. The χm T value with cooling decreases smoothly in the range of 300–50 K, and drops quickly below 50 K to get to a minimum 0.93 cm3·mol−1·K at 2.7 K which suggests the typical antiferromagnetic behavior. Fit of the magnetic data for 1 was done by using the Curie– Weiss law χm = Cm/(T–θ): C = 2.73 emu·K·mol−1 and θ = −13.58 K. The negative θ further confirmed antiferromagnetic interactions between Co(II) ions within six-nuclear cluster above 10 K. The magnetic behavior of 1 depends on the superexchange pathway of the O–P–O bridge in syn–anti and syn–syn modes. The distances between Co(II) centers falls in the range of 4.671–6.347 Å. On the basis of the connections and distances between Co(II) ions within hexanuclear cluster, four exchange integral are approximately equal J1 ≈ J2 ≈ J3 ≈ J4 (Scheme 1). The magnetic data of 1 were analyzed by the expression (1) [19] for isotropically coupled binuclear S = 3/2 Co(II) ions based on spin Hamiltonian (H = −JŜ1Ŝ2), in which the molecular field approximation (2) was introduced for possible interbinuclear interaction as follows: χ Co ¼
Nβ2 g 2 14 þ 5X 6 þ X 10 þ TIP kðT−θÞ 7 þ 5X 6 þ 3X 10 þ X 12
χ m ¼ χ Co
.h 0 i 1−χ Co 2zJ Ng 2 β2
ð1Þ
ð2Þ
where X = exp(−J/kT) and TIP is the temperature-independent paramagnetism (the spin-orbital coupling contributes) of the Co2+ ion. N, g, β, k and T have their usual meanings, and J is the exchange integral. χm is the measured magnetic susceptibility. zJ′ is the interdimer exchange parameter, and z is the number of nearest neighbors. The best fitted parameters above 10 K are: J = − 3.6 cm−1, g = 2.00, zJ′ = −0.3 K and TIP = −0.00024 cm3·mol−1. At 300 K, the χmT value of 2 of 8.88 cm3·mol−1·K is much greater than the expected that of 5.63 cm3·mol−1·K for a free Co3 unit (g =
2.0, S = 3/2), suggesting the orbital contribution of the octahedral Co(II) ions (Fig. 4b). The χmT value is little changed in the range of 300 K–190 K, and gradually increases with cooling to reach a maximum 9.29 cm 3·mol−1·K at 140 K. Then drops abruptly to get to a minimum 2.65 cm3·mol−1·K at 2.7 K, which may be caused by coordination field or intermolecular interaction at low temperature. Fit of the magnetic data for 2 was done by using the Curie–Weiss law χm = Cm/(T–θ): C = 8.86 emu·K·mol−1 and θ = 1.43 K. The positive θ further confirmed ferromagnetic interactions within a linear trinuclear Co(II) model above 50 K. The compound 2 exhibits a topologically weak ferromagnetic Co(II)phosphonate chain. Intrachain Co(1)⋯Co(2) distances are 5.044 Å and 4.933 Å, respectively, and the nearest interchain Co⋯Co distance is 8.348 Å. So the exchange coupling between Co(II) ions is mainly transmitted through O–P–O bridges in inorganic topological chain. Based on the above discussion, two coupling constants J are used for communicating the coupling pathways in this topological chain. The magnetic susceptibility data were fitted to a topological CoII-chain (S = 3/2), considering a temperature correction term θ and a temperatureindependent paramagnetism TIP, based on the appropriate spin Hamiltonian expression of a linear trimer as follows [20,21]: ^ ¼ −J Σ S^3n−1 S^3n þ S^3n S^3nþ1 – J Σ S^3n S^3nþ2 þ S^3nþ1 S^3nþ3 H 1 2 –gβH S^3n þ S^3n−1 þ S^3nþ1
where J1 and J2 are intra- and inter-trimer exchange constants, respectively. Best fit results were obtained: J1 = 3.94 cm−1, J2 = − 2.05 cm−1, g = 2.39, θ = −0.8 cm−1 and TIP = 0.0001. The obtained J values indicate both ferro- and antiferro-magnetic interactions between the metal Co2+ ions. 4. Conclusions
Scheme 1. The coupling pathways in 1.
We have successfully obtained two low-dimensional Co(II)-N-heterocyclic-diphosphonate CPs under solvothermal condition. Both 1 and 2 display the 3-D supramolecular structures built by hexa-nuclear clusters for 1 and 1-D ladder-like chain containing tetra-nuclear clusters for 2 via H-bonding and π–π stacking interactions, respectively. Fluorescent studies at room temperature show emission bands are mainly derived from the ancillary ligands. The correlation of the structures and magnetic properties of coordination polymers are less focused based on low-dimensional Co(II)-N-heterocyclic-diphosphonate CPs. Especially, the multinuclear CoII-unit linked through a single or double O– P–O bridges may lead to an unexpected magnetic behavior based on Co(II)-N-heterocyclic-diphosphonate CPs. In future, we will continue to make efforts to explore the related magneto-structural relationship of low-dimensional multinuclear M(II)-diphosphonate CPs.
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Acknowledgments The authors are grateful to the financial support from Jiangsu province college students innovation and entrepreneurship training programs, Open Fund of Jiangsu Key Laboratory for Chemistry of Lowdimensional Materials, Cultivation Fund of High Level Project of Huaiyin Normal University, the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province and National Natural Science Foundation of China (Projects nos. 201410323004Z, JSKC13127, 11HSGJBZ12, 12KJA15004, 14KJA150003 and 21202058). Appendix A. Supplementary data Electronic supplementary information (ESI) available: diagrams of molecular structures, FT-IR spectra, PXRD and TG–DSC curves for this paper. The CCDC (955,516 for 1, 955,517 for 2) with the supplementary crystallographic 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 doi: http://dx.doi.org/10.1016/j.saa.2015.08.017. References [1] J. Diwu, T.E. Albrecht-Schmitt, Chem. Commun. 48 (2012) 3827–3829. [2] E. Matczak-Jon, V. Videnova-Adrabińska, Coord. Chem. Rev. 249 (2005) 2458–2488.
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[3] Z.-S. Cai, S.-S. Bao, M. Ren, L.-M. Zheng, Chem. Eur. J. 20 (2014) 17137–17142. [4] J.-G. Mao, A. Clearfield, Inorg. Chem. 41 (2002) 2319–2324. [5] K.-R. Ma, F. Ma, Y.-L. Zhu, L.-J. Yu, X.-M. Zhao, Y. Yang, W.-H. Duan, Dalton Trans. 40 (2011) 9774–9781. [6] L.-M. Zheng, H.-H. Song, X.-Q. Xin, Comments Inorg. Chem. 22 (2000) 129–149. [7] R. Clarke, K. Latham, C. Rix, M. Hobday, J. White, CrystEngComm 7 (2005) 28–36. [8] M. Viciano-Chumillas, S. Tanase, L. Jos de Jongh, J. Reedijk, Eur. J. Inorg. Chem. 22 (2010) 3403–3418. [9] J.-F. Xiang, M. Li, S.-M. Wu, L.-J. Yuan, J.-T. Sun, J. Mol. Struct. 826 (2007) 143–149. [10] K.-R. Ma, Y. Zhang, Y.-H. Kan, H.-Y. Hu, M.-H. Cong, Y.-J. Zhang, Spectrochim. Acta A 115 (2013) 829–834. [11] K.-R. Ma, C.-L. Wei, Y. Zhang, M.-H. Cong, H.-Y. Hu, J. Inorg. Organomet. Polym. 23 (2013) 629–637. [12] M.-J. Zheng, Y.-Y. Zhu, Z.-G. Sun, J. Zhu, C.-Q. Jiao, W. Chu, S.-H. Sun, H. Tian, CrystEngComm 15 (2013) 1445–1453. [13] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc. Dalton Trans. (1984) 1349–1356. [14] R.R. Holmes, Prog. Inorg. Chem. 32 (1984) 119–235. [15] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7. [16] K.-R. Ma, Y. Zhang, Y.-H. Kan, R.-Q. Li, H.-Y. Hu, Chin. J. Inorg. Chem. 30 (2014) 2549–2558. [17] K.-R. Ma, Y. Zhang, Y.-H. Kan, X.-J. Yang, M.-H. Cong, Synth. Met. 182 (2013) 40–48. [18] A. Rujiwatra, C.J. Kepert, J.B. Claridge, M.J. Rosseinsky, H. Kumagai, M. Kurmoo, J. Am. Chem. Soc. 123 (2001) 10584–10594. [19] Y.-H. Liu, H.-L. Tsai, Y.-L. Lu, Y.-S. Wen, J.-C. Wang, K.-L. Lu, Inorg. Chem. 40 (2001) 6426–6431. [20] M. Drillon, E. Coronado, M. Belaiche, R.L. Carlin, J. Appl. Phys. 63 (1988) 3551–3553. [21] R. Georges, J.J. Borrás-Almenar, E. Coronado, J. Curély, M. Drillon, One-dimensional magnetism: an overview of the models in magnetism: molecules to materials, in: J.S. Miller, M. Drillon (Eds.), Wiley, Germany, 2001.
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Structural, spectral and magnetic studies of two Co(II)-N-heterocyclic diphosphonates based on multinuclear units Chen Zhao, Kui-Rong Ma ⁎, Yu Zhang, Yu-He Kan, Rong-Qing Li, Hua-You Hu Jiangsu Key Laboratory for Chemistry of Low-dimensional Materials, School of Chemistry and Chemical Engineering, Huaiyin Normal University, Huaian 223300, PR China
a r t i c l e
i n f o
Article history: Received 5 May 2015 Received in revised form 2 July 2015 Accepted 11 August 2015 Available online 13 August 2015 Keywords: Structure Co(II) diphosphonate Fluorescence Magnetism
a b s t r a c t Two examples of Co(II)-N-heterocyclic coordination polymers based on 1-hydroxyethylidenediphosphonic acid (H5L = CH3C(OH)(PO3H2)2), namely 0.5(H3NCH2CH2NH3)·[Co6(Cl2)(H3L)2(H2L)(HL)(2,2′-bipy)6] 1 and 2(NH4)·[Co3(HL)2(H2O)2(phen)2]·2(H2O) 2, have been solvothermally obtained by introducing the second ligands 2,2′-bipyridine/1,10-phenanthroline (2,2′-bipy/phen) and characterized by powder X-ray diffraction (PXRD), elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions show that compound 1 possesses a 0-D structure with hexa-nuclear cluster [Co6(O–P–O)8] built through single/double O–P–O bridges and compound 2 displays a 1-D ladder-like chain structure with magnetic topology building blocks [Co4(O–P–O)4]n. Then H-bonding and π–π stacking interactions further expand the two low-dimensional structures into threedimensional supramolecular frameworks. Fluorescent measurements reveal that both the maximum emission peaks of 1–2 are centered at 423 nm, mainly deriving from intraligand π*–π transition state of N-heterocyclic ligand 2,2′-bipy/phen, respectively. Magnetism data indicate that 1 exhibits antiferromagnetic behavior within hexa-nuclear Co(II) clusters, while 2 shows weak ferromagnetic interactions in 1-D topology Co(II)-chain, showing promising potential as magnetic materials. © 2015 Elsevier B.V. All rights reserved.
1. Introduction As a new type of functional molecular materials, coordination polymers (CPs) not only have abundant space topology, but also have huge potential applications in gas storage, separation, optics, electron, magnetism, chiral separation and catalysis and other fields. The assembly of the coordination polymers based on phosphonates is currently of significant interest [1–3]. Any material properties mainly depend on their structures. So both the structure of organic ligand and the coordination behavior of metal ion are generally dominant for the self-assembly of phosphonate CPs. In addition we don't know enough about the synthetic rules and topology. It is means that the rational synthesis of CPs with the target structure is an extremely creative and intellectually challenging task. In our work, firstly, 1-hydroxyethylidenediphosphonic acid (H5L) with a flexible hydroxyl group is often used as building block in the construction of the phosphonates. The additional –OH group attached to the organic tether not only provides a possible hydrophobic/ hydrophilic environment but also increases solubility of the resulting metal phosphonates. Importantly, it is more likely to behave as a bis(bidentate) chelating ligand using its four of six phosphonate oxygen atoms, which would be good for the construction low-dimensional CPs [4,5]. Secondly, lots of auxiliary ligands with N-heterocycle as one assistant method have been applied widely during the self-assembly of the ⁎ Corresponding author. E-mail address: [email protected] (K.-R. Ma).
http://dx.doi.org/10.1016/j.saa.2015.08.017 1386-1425/© 2015 Elsevier B.V. All rights reserved.
CPs. Polypyridyl ligands have been intensively used as ancillary building blocks in the phosphonate coordination chemistry [6], due to their interesting electronic, photonic and magnetic properties, as well as π-stacking ability and directional H-bonding when coordinating to transition metals. Although many chemists devoted to the study of self-assembly of the CPs by means of the mixed ligands [7–11], low-dimensional phosphonate CPs have not been well developed based on auxiliary N-heterocyclic ligands under the solvothermal condition. So 2,2′-bipy and phen have been selected as auxiliary ligands in our work. Finally, Co(II) ion is focused because of its unique high-spin d7 electron configuration and larger spin-orbital coupling effect for an octahedral Co(II) complex. Many great compounds of Co(II)-H5L have been resolved, but a few Co(II)-diphosphonate compounds with 2,2′-bipy/phen have been structurally determined [12]. By introducing the auxiliary ligands 2,2′-bipy/ phen, we have succeeded in winning two new diphosphonate CPs, 0.5(H3NCH2CH2NH3)·[Co6(Cl2)(H3L)2(H2L)(HL)(2,2′-bipy)6] 1 and 2(NH4)·[Co3(HL)2(H2O)2(phen)2]·2(H2O) 2. In this paper, we study crystal structures, fluorescent and magnetic properties. 2. Experimental 2.1. Materials and general methods All reagents were purchased from commercial sources and used without further purification. Element analyses were performed on a Perkin-Elmer 2400 LS elemental analyzer. IR spectra were recorded
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from 4000 to 400 cm−1 with a Nicolet AVATAR360 instrument. The thermal gravimetric analyses (TG–DSC) were carried out with a NETZSCH STA 449F3 thermal analyzer with a heating rate of 10 K·min− 1. Powder X-ray diffraction patterns (PXRD) were performed on an ARL X'TRA diffractometer using Cu-Kα radiation. Emission spectra in the solid state at room temperature were taken on a Perkin-Elmer LS-55 fluorescence spectrophotometer. Magnetic susceptibility data were collected, respectively, on 0.0236 g for 1 and 0.0230 g for 2 of samples using a Quantum Design MPMS-7 SQUID magnetometer.
2.2. Syntheses 2.2.1. The preparations of 1 0.5(H3 NCH2 CH2 NH3)·[Co6 (H3 L)2 (H2 L)(HL)Cl 2(2,2′-bipy) 6 ] 1: The mixture of CoCl2 ·6H2 O (0.0714 g, 0.3 mmol), H5 L (0.0618 g, 0.3 mmol), 2,2′-bipy (0.0625 g, 0.4 mmol) and ethylenediamine (0.0060 g, 0.1 mmol) in absolute ethyl alcohol (10 mL) was stirred for 30 min, and sealed into a 15 mL Teflon-lined reactor. Solution was heated to 120 °C for 5 days, and then cooled at room temperature. Pink cluster-like crystals of 1 were collected by vacuum filtration. Then they were washed thoroughly with the absolute ethyl alcohol, and dried in air (yield 38% for 1 based on cobalt). Anal. Calc. for C137H143 Cl4Co12N25O56P16 1: C 37.53, H 3.26, N 7.99. Found C 37.58, H 3.31, N 8.02%. IR (KBr)/cm−1: 3421(w), 3345(w), 3324(w), 3164(m), 3131(m), 3106(w), 3025(w), 2931(w), 2823(w), 1600(m), 1569(w), 1525(m), 1473(m), 1315(w), 1218(w), 1165(s), 1139(s), 1110(s), 1064(s), 1024(s), 935(m), 879(w), 813(w), 775(w), 651(w), 572(m), 466(m) (see Supplementary Fig. A.1a).
Table 1 Crystallographic data and structural refinements for 1-2.
Empirical formula Formula weight T/K Crystal system Space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z Dc/g · cm−3 μ/mm−1 θ range/° Reflections collected/unique Data/restraints/ parameters GOF on F2 Final R indices [I N 2σ(I)] R indices (all data) Largest diff. peak and hole/eÅ−3
1
2
C137H143Cl4Co12N25O56P16 4380.25 296(2) Triclinic
C28H40Co3N6O18P4 1049.33 293(2) Triclinic
10.4128(1) 15.225(2) 26.935(4) 79.762(2) 85.737(2) 84.807(2) 4177.5(1) 1 1.741 1.469 1.87–25.00 29,332/14,361 [R(int) = 0.0631] 3049/3/261
6.5167(9) 11.874(2) 12.624(2) 95.531(2) 102.070(2) 91.744(2) 949.5(2) 1 1.835 1.550 1.66–25.00 6731/3311 [R(int) = 0.0316] 3311/1/269
0.911 R1 = 0.0615, wR2 = 0.1347
1.079 R1 = 0.0377, wR2 = 0.0949
R1 = 0.1303, wR2 = 0.1464 1.714, −1.911
R1 = 0.0459, wR2 = 0.1062 0.650, −0.556
Note. R1 = Σ||Fo| − |Fc||/Σ|Fo|; wR2 = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)]2}1/2.
3. Results and discussion 3.1. Description of the structures
2.2.2. The preparations of 2 2(NH4 )·[Co3(HL)2 (H2 O)2 (phen)2 ]·2(H2 O) 2: The mixture of Co(NO3 ) 2·6H2 O (0.0582 g, 0.2 mmol), H5 L (0.0412 g, 0.2 mmol), phen (0.0793 g, 0.4 mmol) and NH4F (0.0370 g, 1 mmol) in absolute ethyl alcohol (10 mL) was stirred for 30 min, and sealed into a 15 mL Teflon-lined reactor. Solution was heated to 120 °C for 5 days, and then cooled at room temperature. Pink rod-like crystals of 2 were collected by vacuum filtration. Then they were washed thoroughly with the absolute ethyl alcohol, and dried in air (yield 65% for 2 based on cobalt). Anal. Calc. for C28 H40 Co3 N6 O 18 P4 2: C 32.02, H 3.81, N 8.01. Found C 32.07, H 3.88, N 8.05%. IR (KBr)/cm−1 : 3259(w, broad), 2927(w), 2843(w), 1621(w), 1587(w), 1517(w), 1427(w), 1388(m), 1303(w), 1159(s), 1076(s), 1049(s), 977(w), 931(m), 848(w), 775(w), 727(m), 653(w), 568(m), 482(m), 458(m) (see Supplementary Fig. A.1b).
2.3. Crystallography Intensity data were collected on a Bruker SMART CCD diffractometer equipped with a graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at 296 K for 1 and 293 K for 2 using the ω-2θ scan technique. The structure was solved by direct methods and refined by full-matrix least-squares fitting on F2 by SHELXL-97. A total of 29,332 for 1 and 6731 for 2 reflections were collected, of which 14,361 (Rint = 0.0631) for 1 and 3311 (Rint = 0.0316) for 2 were unique, respectively. All non-hydrogen atoms of 1 and 2 were located from the initial solution and refined with anisotropic thermal parameters. The position of hydrogen atoms of 1 and 2 were either located by difference Fourier maps or calculated geometrically and their contributions in structural factor calculations were included. Crystallographic data and structural refinements are summarized in Table 1. Selected bond lengths [Å] and angles [°] are list in Table 2. Hydrogen bonds [Å] and angles [°] are given in Table 3.
Single-crystal X-ray diffraction analyses reveal that both 1 and 2 possess 3-D supramolecular architectures. The asymmetric unit of 1 (Fig. 1) contains six distinct Co(II) atoms, two H3L2− ligands, a H2L3− ligand, a HL4− ligand, two Cl− ligands as well as six coordinated 2,2′-bipy molecules and a half of free ethylenediamine cation. Four centers Co(1), Co(2), Co(5) and Co(6) in 1 are all in a distorted octahedral coordination environment, while the remains of two other centers Co(3) and Co(4) are in a trigonal bipyramid (TBP) environment. Four Co(II) centers are 6-coordinated to six oxygen atoms (O(5), O(7), O(8), O(11), O(14), O(15)) from three phosphonate ligands for Co(1), to six oxygen atoms (O(12), O(16), O(18), O(21), O(22), O(28)) from three phosphonate ligands for Co(2), to two oxygen atoms from a phosphonate ligand and four nitrogen atoms from two 2,2-bipy ligands (O(3), O(6), N(5), N(6), N(7), N(8)) for Co(5) and to two oxygen atoms from a phosphonate ligand and four nitrogen atoms from two 2,2-bipy ligands (O(24), O(27), N(9), N(10), N(11), N(12)) for Co(6). Both Co(3) and Co(4) are 5-coordinated to two oxygen atoms from a phosphonate ligand, two nitrogen atoms from a 2,2-bipy ligand and a Cl− ion (O(17), O(19), N(1), N(2), Cl(1)) for Co(3)/(O(10), O(13), N(3), N(4), Cl(2)) for Co(4), respectively. The equatorial planes are defined by N(2)–O(17)–Cl(1) for Co(3) and N(3)–O(13)–Cl(2) for Co(4) in trigonal bipyramid structures, and the distortion parameters (τ) are 0.63 for Co(3) and 0.79 for Co(4) based on 5-coordination description, respectively [a regular trigonal bipyramid (TBP) and square-based pyramid (SP) have τ values of 1.00 and 0.00 [13,14]]. The Co(II)–Cl distances are in the range of 2.303(2)–2.306(2) Å. The Co(II)–O/N distances in 1 are fall within the range of 1.980(4)–2.240(4) Å/2.082(6)–2.091(6) Å which are similar to those of reported 2,2′-bipy-containing Co(II) phosphonate complexes [12]. The –PO3 group in 1 displays three types of coordination modes simultaneously (Fig. A.2a). i, Monodentate mode: it links a Co(II) atom in η1η0η0 mode. ii, Bidentate mode: it chelates to two Co(II) atoms in η1η0η1 mode. iii, Tridentate mode: it chelates two Co(II) atoms and bridges a Co(II) atom in η1η1η1 mode. The H5L is role-playing the tetra-/
C. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 153 (2015) 171–177 Table 2 Selected bond lengths (Å) and angles (°) for 1–2.
Table 2 (continued) 1 2
1 Co(1)–O(15) Co(1)–O(5) Co(1)–O(8) Co(1)–O(11) Co(1)–O(7) Co(1)–O(14) Co(2)–O(12) Co(2)–O(22) Co(2)–O(16) Co(2)–O(18) Co(2)–O(28) Co(2)–O(21) Co(3)–O(17) Co(3)–O(19) Co(3)–N(2) Co(3)–N(1) Co(3)–Cl(1) P(1)–C(1) P(2)–C(1) P(3)–C(3) P(4)–C(3) O(15)–Co(1)–O(5) O(15)–Co(1)–O(8) O(5)–Co(1)–O(8) O(15)–Co(1)–O(11) O(5)–Co(1)–O(11) O(8)–Co(1)–O(11) O(15)–Co(1)–O(7) O(5)–Co(1)–O(7) O(8)–Co(1)–O(7) O(11)–Co(1)–O(7) O(15)–Co(1)–O(14) O(5)–Co(1)–O(14) O(8)–Co(1)–O(14) O(11)–Co(1)–O(14) O(7)–Co(1)–O(14) O(12)–Co(2)–O(22) O(12)–Co(2)–O(16) O(22)–Co(2)–O(16) O(12)–Co(2)–O(18) O(22)–Co(2)–O(18) O(16)–Co(2)–O(18) O(12)–Co(2)–O(28) O(22)–Co(2)–O(28) O(16)–Co(2)–O(28) O(18)–Co(2)–O(28) O(12)–Co(2)–O(21) O(22)–Co(2)–O(21) O(16)–Co(2)–O(21) O(18)–Co(2)–O(21) O(28)–Co(2)–O(21) O(17)–Co(3)–O(19) O(17)–Co(3)–N(2) O(19)–Co(3)–N(2) O(17)–Co(3)–N(1) O(19)–Co(3)–N(1) N(2)–Co(3)–N(1) O(17)–Co(3)–Cl(1) O(19)–Co(3)–Cl(1) N(2)–Co(3)–Cl(1) N(1)–Co(3)–Cl(1)
2.021(4) 2.073(4) 2.091(4) 2.106(4) 2.151(4) 2.240(4) 2.033(4) 2.086(5) 2.092(4) 2.101(4) 2.137(4) 2.261(4) 1.980(4) 2.063(4) 2.085(6) 2.133(7) 2.303(2) 1.858(7) 1.833(7) 1.840(6) 1.841(7) 95.8(2) 168.5(2) 91.4(2) 95.5(2) 102.7(2) 91.5(2) 84.1(2) 83.5(2) 87.9(2) 173.7(2) 90.3(2) 172.2(2) 81.8(2) 81.4(2) 92.4(2) 95.4(2) 94.3(2) 103.3(2) 168.5(2) 92.3(2) 92.1(2) 86.9(2) 83.0(2) 173.4(2) 85.9(2) 90.1(2) 172.5(2) 81.1(2) 81.4(2) 92.4(2) 94.2(2) 129.2(2) 93.3(2) 86.6(2) 167.0(2) 76.4(3) 119.9(1) 97.9(1) 108.6(2) 92.9(2)
Co(4)–O(13) Co(4)–O(10) Co(4)–N(3) Co(4)–N(4) Co(4)–Cl(2) Co(5)–O(3) Co(5)–O(6) Co(5)–N(5) Co(5)–N(7) Co(5)–N(6) Co(5)–N(8) Co(6)–O(27) Co(6)–O(24) Co(6)–N(11) Co(6)–N(9) Co(6)–N(10) Co(6)–N(12) P(5)–C(5) P(6)–C(5) P(7)–C(7) P(8)–C(7) O(13)–Co(4)–O(10) O(13)–Co(4)–N(3) O(10)–Co(4)–N(3) O(13)–Co(4)–N(4) O(10)–Co(4)–N(4) N(3)–Co(4)–N(4) O(13)–Co(4)–Cl(2) O(10)–Co(4)–Cl(2) N(3)–Co(4)–Cl(2) N(4)–Co(4)–Cl(2) O(3)–Co(5)–O(6) O(3)–Co(5)–N(5) O(6)–Co(5)–N(5) O(3)–Co(5)–N(7) O(6)–Co(5)–N(7) N(5)–Co(5)–N(7) O(3)–Co(5)–N(6) O(6)–Co(5)–N(6) N(5)–Co(5)–N(6) N(7)–Co(5)–N(6) O(3)–Co(5)–N(8) O(6)–Co(5)–N(8) N(5)–Co(5)–N(8) N(7)–Co(5)–N(8) N(6)–Co(5)–N(8) O(27)–Co(6)–O(24) O(27)–Co(6)–N(11) O(24)–Co(6)–N(11) O(27)–Co(6)–N(9) O(24)–Co(6)–N(9) N(11)–Co(6)–N(9) O(27)–Co(6)–N(10) O(24)–Co(6)–N(10) N(11)–Co(6)–N(10) N(9)–Co(6)–N(10) O(27)–Co(6)–N(12) O(24)–Co(6)–N(12) N(11)–Co(6)–N(12) N(9)–Co(6)–N(12) N(10)–Co(6)–N(12)
1.980(4) 2.042(5) 2.082(6) 2.131(6) 2.306(2) 2.068(5) 2.107(4) 2.122(6) 2.146(6) 2.147(7) 2.191(6) 2.067(4) 2.098(5) 2.154(6) 2.155(6) 2.162(6) 2.178(6) 1.846(7) 1.830(6) 1.839(7) 1.850(7) 96.1(2) 122.6(2) 95.2(2) 85.3(2) 170.8(2) 76.5(2) 123.3(2) 96.5(1) 110.8(2) 90.3(2) 93.4(2) 91.6(2) 97.1(2) 94.1(2) 95.7(2) 165.7(2) 166.3(2) 81.4(2) 76.6(3) 99.0(2) 94.5(2) 168.7(2) 90.8(2) 75.7(2) 92.7(2) 93.6(2) 92.9(2) 92.8(2) 167.2(2) 83.4(2) 99.7(2) 92.2(2) 99.9(2) 166.0(2) 76.0(2) 88.0(2) 168.0(2) 75.2(2) 97.5(2) 91.9(2)
2 Co(1)–O(1) Co(1)–O(3)#1 Co(1)–N(1) Co(1)–N(2) Co(1)–O(5)#1 Co(1)–O(1W) Co(2)–O(2)#2 O(1)–Co(1)–O(3)#1 O(1)–Co(1)–N(1) O(3)#1–Co(1)–N(1) O(1)–Co(1)–N(2) O(3)#1–Co(1)–N(2)
2.007(2) 2.070(2) 2.136(3) 2.150(3) 2.156(2) 2.168(2) 2.060(2) 171.60(1) 86.73(1) 85.68(1) 92.61(1) 89.27(1)
Co(2)–O(2) Co(2)–O(4) Co(2)–O(4)#2 Co(2)–O(7)#2 Co(2)–O(7) P(1)–C(1) P(2)–C(1) O(2)#2–Co(2)–O(2) O(2)#2–Co(2)–O(4) O(2)–Co(2)–O(4) O(2)#2–Co(2)–O(4)#2 O(2)–Co(2)–O(4)#2
173
2.060(2) 2.071(2) 2.071(2) 2.218(2) 2.218(2) 1.847(4) 1.846(4) 180.00(1) 91.95(9) 88.05(9) 88.05(9) 91.95(9)
N(1)–Co(1)–N(2) O(1)–Co(1)–O(5)#1 O(3)#1–Co(1)–O(5)#1 N(1)–Co(1)–O(5)#1 N(2)–Co(1)–O(5)#1 O(1)–Co(1)–O(1W) O(3)#1–Co(1)–O(1W) N(1)–Co(1)–O(1W) N(2)–Co(1)–O(1W) O(5)#1–Co(1)–O(1W)
77.46(1) 93.92(1) 94.05(9) 173.11(1) 95.65(1) 91.52(1) 86.08(9) 98.80(1) 174.26(1) 88.05(9)
O(4)–Co(2)–O(4)#2 O(2)#2–Co(2)–O(7)#2 O(2)–Co(2)–O(7)#2 O(4)–Co(2)–O(7)#2 O(4)#2–Co(2)–O(7)#2 O(2)#2–Co(2)–O(7) O(2)–Co(2)–O(7) O(4)–Co(2)–O(7) O(4)#2–Co(2)–O(7) O(7)#2–Co(2)–O(7)
180.00(1) 85.22(9) 94.79(9) 98.07(9) 81.93(9) 94.78(9) 85.22(9) 81.93(9) 98.07(9) 180.00(1)
Symmetry code: 2:#1 x + 1, y, z #2 −x + 1, −y + 2, −z + 1 #3 x − 1, y, z.
hexa-dentate chelating-bridging ligand in the structure of 1. The last two patterns of –PO3 group are usually found in the same kinds of phosphonate compounds [9–12]. However, little research on these three patterns in the same structure was reported. All the hydroxyl groups (O(7), O(14), O(21), O(28)) of four phosphonate ligands participate in the coordination with metals. The uncoordinated phosphonate oxygen atoms are all involved in hydrogen bonds. Based on the coordination environment, four hydroxyl oxygen atoms and five phosphonate oxygen atoms (O(1), O(4), O(20), O(23), O(26)) are protonated to adjust charge balance. The binuclear units [−Co–O–P–O–]2 between Co(1)⋯Co(4)/ Co(2)⋯Co(3) ions with the distances of 5.185 Å/5.270 Å are formed by a double O–P–O bridge in syn–syn mode in 1, respectively. Two binuclear units are connected with two single O–P–O bridges to give Table 3 Hydrogen bond lengths (Å) and angles (°) for 1–2. D–H⋯A
d(D–H)
d(H⋯A)
d(D⋯A)
b(DHA)
1 O(28)–H(28W)⋯O(2)#2 O(26)–H(26W)⋯O(12) O(23)–H(23W)⋯O(18) O(21)–H(21W)⋯O(11) O(20)–H(20W)⋯O(2)#2 O(14)–H(14W)⋯O(16) O(7)–H(71W)⋯O(25)#3 O(4)–H(4W)⋯O(8) O(1)–H(1W)⋯O(15) N(13)–H(13B)⋯Cl(2)#4 C(2)–H(2C)⋯O(28)#3 C(8)–H(8A)⋯O(7)#2 C(16)–H(16)⋯O(20)#5 C(17)–H(17)⋯Cl(1)#5 C(18)–H(18)⋯O(19) C(19)–H(19)⋯O(10) C(25)–H(25)⋯O(4)#6 C(29)–H(29)⋯O(3) C(45)–H(45)⋯O(9)#7 C(51)–H(51)⋯O(17)#8 C(57)–H(57)⋯O(22)#2 C(67)–H(67)⋯Cl(1)#9
0.85 0.99 0.85 0.85 0.85 0.85 0.85 0.85 0.91 0.89 0.96 0.96 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93
1.84 1.69 1.99 1.85 1.74 1.92 1.86 2.04 1.76 2.70 2.54 2.53 2.59 2.77 2.50 2.60 2.55 2.58 2.53 2.52 2.59 2.74
2.649(6) 2.650(6) 2.779(6) 2.681(6) 2.578(6) 2.690(6) 2.614(6) 2.745(6) 2.618(6) 3.240(1) 3.329(8) 3.321(8) 3.290(9) 3.690(9) 3.074(9) 3.158(9) 3.213(1) 3.138(9) 3.240(9) 3.229(1) 3.390(1) 3.385(9)
158.8 162.7 153.3 164.8 168.0 150.4 148.0 140.7 156.4 120.1 139.1 139.7 132.3 171.0 120.1 119.4 129.0 118.6 133.9 133.2 145.0 127.5
2 N(3)–H(31)⋯N(3)#4 N(3)–H(32)⋯O(2W) N(3)–H(33)⋯O(3) O(7)–H(71)⋯O(5)#1 O(1W)–H(1A)⋯O(2)#1 O(2W)–H(2W2)⋯O(2)#4 O(2W)–H(2W1)⋯N(3) O(1W)–H(1B)⋯O(4)#2 C(8)–H(8)⋯O(3)#5 C(4)–H(4)⋯O(1W)#6
0.94 0.92 0.97 0.82 0.82 0.82 0.82 0.81 0.93 0.93
2.67 2.15 1.96 2.17 2.10 2.06 2.13 2.02 2.57 2.57
3.139(7) 2.902(5) 2.916(4) 2.985(3) 2.894(3) 2.837(4) 2.902(5) 2.826(3) 3.446(5) 3.423(5)
111.9 138.9 167.6 174.2 165.5 158.5 154.9 168.8 156.4 152.9
Symmetry transformations used to generate equivalent atoms. 1:#1 −x + 2, −y + 1, −z + 1 #2 x − 1, y, z #3 x + 1, y, z #4 x + 1, y + 1, z #5 −x, −y + 1, −z #6 x, −y, −z + 1 #7 x, y + 1, z #8 −x, −y, −z #9 x − 1, y − 1, z. 2:#1 x + 1, y, z #2 −x + 1, −y + 2, −z + 1 #3 x − 1, y, z #4 -x + 1, −y + 1, −z + 1 #5 −x + 1, −y + 1, −z #6 −x + 2, −y + 1, −z + 1.
174
C. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 153 (2015) 171–177
Fig. 1. Coordination environment of Co(II) ions in 1.
rise to a ladder-like tetra-nuclear unit [Co(1)⋯Co(4)⋯Co(2)⋯Co(3)] with Co(1)⋯Co(2)/Co(1)⋯Co(3)/Co(2)⋯Co(4) distances of 4.671 Å/ 6.277 Å/6.347 Å, and then two Co(II) ions (Co(5), Co(6)) further link up with this tetra-nuclear unit by a single O–P–O bridge and a hydroxyl bridge, respectively, resulting in a hexa-nuclear Co(II)-cluster structure, which acts as the basic build motif in the structure. The hydrogen bond C(45)⋯O(9) (3.240(9) Å, 133.9°) links hexa-nuclear clusters alternatively to form a one-dimensional supramolecular chain along the baxis, along with the second ligand 2,2′-bipy standing in two rows at its sides (Fig. A.2b). The neighboring 1-D supramolecular chains are cross-linked by the hydrogen bonds [O(28)⋯O(2) (2.649(6) Å, 158.8°), O(21)⋯O(11) (2.681(6) Å, 164.8°), O(14)⋯O(16) (2.690(6) Å, 150.4°), O(20)⋯O(2) (2.578(6) Å, 168.0°), O(14)⋯O(16) (2.690(6) Å, 150.4°), O(7)⋯O(25) (2.614(6) Å, 148.0°), C(2)⋯O(28) (3.329(8) Å, 139.1°), C(8)⋯O(7) (3.321(8) Å, 139.7°), C(57)⋯O(22) (3.390(10) Å, 145.0°), C(67)⋯Cl(1) (3.385(9) Å, 127.5°)], to lead to a twodimensional supramolecular layer in the ac plane (Fig. A.2c). In 2-D layer organic groups alternate with inorganic groups along both chains, linked by hydrogen bonds. The three-dimensional supramolecular framework is created via hydrogen bonds [C(17)⋯Cl(1) (3.690(9) Å, 171.0°), C(16)⋯O(20) (3.290(9) Å, 132.3°)] along the [100] plane between the adjacent supramolecular layers (Fig. A.2d). Also the π–π stacking interactions contribute to the formation of the 3-D framework between aromatic rings R1 ↔ R2 (R1: N(5)–C(29)–C(30)–C(31)– C(32)–C(33), R2: N(3)–C(19)–C(20)–C(21)–C(22)–C(23), symmetric code 1 − x, − y, 1 − z, centroidal distance 3.4721 Å, slip distances 0.76 Å (R1 → R2)/1.235 Å (R2 → R1) and dihedral angle 12.26°). The guest ethanediamine molecules are occupied in pore spaces of the 3-D supramolecular framework. After the removal of the guest molecules, the volume of the tunnel formed by 2-D layers is 83.7 Å3 per unit cell using PLATON [15] based on the crystal structure, comprising 2.0% of the crystal volume 4177.5 Å3. Compound 2 features a one-dimensional chain structure, and there are one and a half unique Co(II) ions, a HL4− ligand, a coordinated water molecule, and a phen ligand as well as a free NH+ 4 cation and a free water molecule in its asymmetric unit (Fig. 2). The unique Co(1) and Co(2) centers in 2 are both in an octahedral coordination environment. They are 6-coordinated to three oxygen atoms (O(1), O(3), O(5)) from two phosphonate ligands, two nitrogen atoms from a phen ligand (N(1), N(2)) and a water oxygen atom O(1W) for Co(1) and to six oxygen atoms (O(2), O(4), O(7), O(2A), O(4A), O(7A)) from two
phosphonate ligands for Co(2). The Co(1)–N(1) distance is 2.136(3) Å and Co(1)–N(2) distance is 2.150(3) Å. The other Co–O bond lengths are in the range of 2.007(2)–2.218(2) Å. These distances are comparable to those reported for other Co(II) phosphonates [12]. The coordinating pattern of the ligand HL4− in 2 is the form of hexadentate chelating-bridging, affording five phosphonate oxygen atoms (O(1), O(2), O(3), O(4), O(5)) in μ3:(η1η1)(η1η1η1) mode, to chelate/ bridge with three Co(II) atoms. Each –PO3 groups of the ligand HL4− display two types of coordination modes simultaneously. i, Bidentate mode: one chelates two Co(II) atoms in μ2: η1η0η1 mode. ii, Tridentate mode: another chelates three Co(II) atoms in μ3: η1η1η1 mode. The two modes are same as the last two patterns of 1. The hydroxyl group O(7) of ligand is also coordinated to metal. The uncoordinated phosphonate oxygen atoms are all involved in hydrogen bonds. Based on the coordination environment, the hydroxyl oxygen atom is protonated and four phosphonate oxygen atoms are deprotonated to adjust charge balance. Each [Co(1)O4N2] octahedron, as the basic building unit, is bridged by a single O(3)–P(1)–O(1) bridge to yield a one-dimensional inorganic single chain along the a-axis, and then it is further joined together via [Co(2)O6] octahedron by two single O(4)–P(2)–O(5) bridges to build
Fig. 2. Coordination environment of Co(II) ions in 2.
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a ladder-like chain (Fig. A.3a). The second ligand phen stands in two rows at its sides. The 1-D ladder-like chain includes a type of 16member ring [–Co(1)–O–P–O–Co(2)–O–P–O–]2 with the distances Co(1)⋯Co(1), Co(1)⋯Co(2) and Co(2)⋯Co(2) of 7.556 Å, 4.933 Å and 6.517 Å, respectively. Importantly, the magnetic topology of 2 should come from trimer building blocks [Co(1)(O–P–O)2Co(2)(O–P– O)2Co(1)]n within the inorganic chain. The ladder-like chain structure is similar to those compounds reported by our group: [Zn1.5(H2L) (bipy)(H2O)]·3H2O [16] and [Ni3(H2L)2(H2O)4]·3H2O [17]. The free water molecules and NH+ 4 cations are located in cavities defined by 1D chain and are involved in the information of 3-D supramolecular structure. The adjacent ladder-like chains are connected with each other by hydrogen bonds formed among the free water molecules, NH+ 4 cations and phosphonate oxygen atoms, N(3)⋯N(3A) (3.139(7) Å, 111.9°), N(3)⋯O(2W) (2.902(5) Å, 138.9°), N(3)⋯O(3) (2.916(4) Å, 167.6°), O(2W)⋯O(2) (2.837(4) Å, 158.5°), O(2W)⋯N(3) (2.902(5) Å, 154.9°), C(4)⋯O(1W) (3.423(5) Å, 152.9°), to give rise to a 2-D supramolecular layer in the ab plane (Fig. A.3b). The intermolecular H-bonding C(8)⋯O(3) (3.446(5) Å, 156.4°) and π–π stacking between the aromatic ring R1 ↔ R2 (R1:N(2)–C(12)–C(11)–C(10)–C(9)–C(13)), R2: (C(6)– C(7)–C(8)–C(9)–C(13)–C(14), symmetric code 1 − x, 1 − y, −z, centroidal distance 3.6150 Å, slip distances 1.627 Å (R1 → R2)/1.581 Å (R2 → R1) and dihedral angle 1.73°) have an important role to play in controlling the formation of the 3-D supramolecular network (Fig. A.3c). All the hydrogen bonds and π–π stacking interactions in the structures of 1–2 are best propitious to stabilize the structure, as well charge transfer. 3.2. Spectral studies The powder XRD patterns of 1–2 indicate that as-synthesized products are both new materials, and the patterns are entirely consistent with the simulated those from the single-crystal X-ray diffraction, respectively (see Supplementary Fig. A.4a–b). The fluorescent spectra of both compounds and the second ligands (2,2′-bipy and phen) are shown in Fig. 3. The free H5L ligand does not emit fluorescence at room temperature in the visible region. However, the second ligand 2,2′-bipy shows a broad peak at 377 nm and a sharp peak at 422.5 nm (λex = 233 nm), and another ligand phen reveals a stronger peak at 361.5 nm with a shoulder peak at 379 nm and a weak peak at 400 nm (λex = 335 nm). The fluorescent emissions of 2,2′-bipy have a few minor variations when it coordinates with Co(II) ion, that is, weakening of fluorescent intensity at 377 and 423 nm for 1 (λex = 233 nm) (Fig. 3a). However, the fluorescent emission peaks of 2 (λex = 235 nm) have changed so much (Fig. 3b), including the maximum band shifts from 361.5 nm to the lower energy band 423 nm compared to the free phen ligand and the fluorescent intensity also weaken. With the increase of molecular rigidity, the energy loss of the nonradiative transition was decreased, and the energy gap from the excited state to the ground state was reduced. Thus, the maximal emission peak
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of 2 shows red shift effect. The emission bands of 1–2 are mainly attributed to intraligand π*–π transition states of 2,2′-bipy for 1 and phen for 2. In view of fluorescent intensity of 1 and 2, it shows its decay compared with that of the second ligand. This phenomenon is interpreted to be the result of two factors: (1) unsaturated d7 electron configuration of the central cobalt(II) ion, and (2) the geometries of the complexes. First, if the d shell of metal ion is incomplete, LMCT (ligand-to-metal charge transfer) will happen. This will lead to reductions in electron number of ligand during the transition from the lowest excited state to the ground state, which leads to the appearance of fluorescence quenching. Next, both 1 and 2 belong to the low-dimensional compounds, hexa-nuclear cluster for 1 and 1-D chain for 2. The formation of complexes with low-dimensional structures destroys the larger conjugated system of the second ligand. 3.3. Thermal characteristics TG–DSC measures were conducted to examine the stabilities of 1–2 in the temperature range of 25–800 °C (see Supplementary Fig. A.5a–b). TGA curve of 1 shows one main weight loss, attributing to the departure of the guest molecule ethanediamine with the loss of 0.71% (calc. 0.71%) at 160 °C and above 200 °C the loss of [P–OH] and [C–OH] hydroxyl groups and 2,2′-bipy ligands. This step loss is completed at 600 °C with an obvious endothermic peak centered at 395 °C and a weak exothermic peak centered at 550 °C. There is an unconspicuous weight loss process after 600 °C until the warming over with two weak exothermic peaks centered at 605 and 650 °C. This loss can be attributed to the decomposition of organic moieties of phosphonate ligand and chloridion. The final thermal decomposition residue at 800 °C is Co6(P2O7)4 based on the powder X-ray diffraction patterns. The total weight loss of 52.07% is close to the calculated value (52.08%). TGA curve of 2 indicates three main steps of weight losses. The first step with two weak endothermic peaks centered at 118 °C and 200 °C is loss of the crystal water, NH+ 4 cation and the coordinated water before 220 °C. The observed weight loss of 10.32% is in good agreement with the calculated value (10.29%). The second step from 220 to 600 °C is a continuous pyrolysis process with a weak exothermic peak at 500 °C, and the third step has a distinct weightlessness from 600 °C. The mass loss of both steps can be attributed to the decomposition of hydroxyl group [C– OH] and phen, coming with the collapse of internal skeletal structure of 2. The total weight loss is about 38.06% which means thermaldecomposition is not over at 800 °C. 3.4. Magnetism properties The temperature-dependent susceptibility data of 1–2 have been measured under a field of 2 KOe (Fig. 4). At 300 K, the χmT value of 2.62 cm3·mol−1·K for 1 is slightly larger than the expected that of 1.87 cm3·mol−1·K for a free CoII ion (g = 2.0, S = 3/2), suggesting the orbital contribution of the octahedral Co(II) ions (Fig. 4a). This
Fig. 3. Solid-state emission spectra of 1 (3a) and 2 (3b) and the second ligands 2,2′-bipy/1,10-phen.
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Fig. 4. Temperature dependence of χm and χmT for 1 (4a) and 2 (4b). The theoretical behavior is fitted by red solid lines for 1–2.
is a ubiquitous phenomenon for the high spin Co(II) compounds [18]. The χm T value with cooling decreases smoothly in the range of 300–50 K, and drops quickly below 50 K to get to a minimum 0.93 cm3·mol−1·K at 2.7 K which suggests the typical antiferromagnetic behavior. Fit of the magnetic data for 1 was done by using the Curie– Weiss law χm = Cm/(T–θ): C = 2.73 emu·K·mol−1 and θ = −13.58 K. The negative θ further confirmed antiferromagnetic interactions between Co(II) ions within six-nuclear cluster above 10 K. The magnetic behavior of 1 depends on the superexchange pathway of the O–P–O bridge in syn–anti and syn–syn modes. The distances between Co(II) centers falls in the range of 4.671–6.347 Å. On the basis of the connections and distances between Co(II) ions within hexanuclear cluster, four exchange integral are approximately equal J1 ≈ J2 ≈ J3 ≈ J4 (Scheme 1). The magnetic data of 1 were analyzed by the expression (1) [19] for isotropically coupled binuclear S = 3/2 Co(II) ions based on spin Hamiltonian (H = −JŜ1Ŝ2), in which the molecular field approximation (2) was introduced for possible interbinuclear interaction as follows: χ Co ¼
Nβ2 g 2 14 þ 5X 6 þ X 10 þ TIP kðT−θÞ 7 þ 5X 6 þ 3X 10 þ X 12
χ m ¼ χ Co
.h 0 i 1−χ Co 2zJ Ng 2 β2
ð1Þ
ð2Þ
where X = exp(−J/kT) and TIP is the temperature-independent paramagnetism (the spin-orbital coupling contributes) of the Co2+ ion. N, g, β, k and T have their usual meanings, and J is the exchange integral. χm is the measured magnetic susceptibility. zJ′ is the interdimer exchange parameter, and z is the number of nearest neighbors. The best fitted parameters above 10 K are: J = − 3.6 cm−1, g = 2.00, zJ′ = −0.3 K and TIP = −0.00024 cm3·mol−1. At 300 K, the χmT value of 2 of 8.88 cm3·mol−1·K is much greater than the expected that of 5.63 cm3·mol−1·K for a free Co3 unit (g =
2.0, S = 3/2), suggesting the orbital contribution of the octahedral Co(II) ions (Fig. 4b). The χmT value is little changed in the range of 300 K–190 K, and gradually increases with cooling to reach a maximum 9.29 cm 3·mol−1·K at 140 K. Then drops abruptly to get to a minimum 2.65 cm3·mol−1·K at 2.7 K, which may be caused by coordination field or intermolecular interaction at low temperature. Fit of the magnetic data for 2 was done by using the Curie–Weiss law χm = Cm/(T–θ): C = 8.86 emu·K·mol−1 and θ = 1.43 K. The positive θ further confirmed ferromagnetic interactions within a linear trinuclear Co(II) model above 50 K. The compound 2 exhibits a topologically weak ferromagnetic Co(II)phosphonate chain. Intrachain Co(1)⋯Co(2) distances are 5.044 Å and 4.933 Å, respectively, and the nearest interchain Co⋯Co distance is 8.348 Å. So the exchange coupling between Co(II) ions is mainly transmitted through O–P–O bridges in inorganic topological chain. Based on the above discussion, two coupling constants J are used for communicating the coupling pathways in this topological chain. The magnetic susceptibility data were fitted to a topological CoII-chain (S = 3/2), considering a temperature correction term θ and a temperatureindependent paramagnetism TIP, based on the appropriate spin Hamiltonian expression of a linear trimer as follows [20,21]: ^ ¼ −J Σ S^3n−1 S^3n þ S^3n S^3nþ1 – J Σ S^3n S^3nþ2 þ S^3nþ1 S^3nþ3 H 1 2 –gβH S^3n þ S^3n−1 þ S^3nþ1
where J1 and J2 are intra- and inter-trimer exchange constants, respectively. Best fit results were obtained: J1 = 3.94 cm−1, J2 = − 2.05 cm−1, g = 2.39, θ = −0.8 cm−1 and TIP = 0.0001. The obtained J values indicate both ferro- and antiferro-magnetic interactions between the metal Co2+ ions. 4. Conclusions
Scheme 1. The coupling pathways in 1.
We have successfully obtained two low-dimensional Co(II)-N-heterocyclic-diphosphonate CPs under solvothermal condition. Both 1 and 2 display the 3-D supramolecular structures built by hexa-nuclear clusters for 1 and 1-D ladder-like chain containing tetra-nuclear clusters for 2 via H-bonding and π–π stacking interactions, respectively. Fluorescent studies at room temperature show emission bands are mainly derived from the ancillary ligands. The correlation of the structures and magnetic properties of coordination polymers are less focused based on low-dimensional Co(II)-N-heterocyclic-diphosphonate CPs. Especially, the multinuclear CoII-unit linked through a single or double O– P–O bridges may lead to an unexpected magnetic behavior based on Co(II)-N-heterocyclic-diphosphonate CPs. In future, we will continue to make efforts to explore the related magneto-structural relationship of low-dimensional multinuclear M(II)-diphosphonate CPs.
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Acknowledgments The authors are grateful to the financial support from Jiangsu province college students innovation and entrepreneurship training programs, Open Fund of Jiangsu Key Laboratory for Chemistry of Lowdimensional Materials, Cultivation Fund of High Level Project of Huaiyin Normal University, the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province and National Natural Science Foundation of China (Projects nos. 201410323004Z, JSKC13127, 11HSGJBZ12, 12KJA15004, 14KJA150003 and 21202058). Appendix A. Supplementary data Electronic supplementary information (ESI) available: diagrams of molecular structures, FT-IR spectra, PXRD and TG–DSC curves for this paper. The CCDC (955,516 for 1, 955,517 for 2) with the supplementary crystallographic 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 doi: http://dx.doi.org/10.1016/j.saa.2015.08.017. References [1] J. Diwu, T.E. Albrecht-Schmitt, Chem. Commun. 48 (2012) 3827–3829. [2] E. Matczak-Jon, V. Videnova-Adrabińska, Coord. Chem. Rev. 249 (2005) 2458–2488.
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