A new family of 3D heterometallic 3d–4f organodisulfonate complexes based on the linkages of 2D [Ln(nds)(H₂O)]⁺ layers and [Cu(ina)₂]⁻ chains

Abstract

Seven novel 3D heterometallic coordination compounds, LnCu(nds)(ina)₂·H₂O [Ln = Eu (1), Ce (2), Er (3), Gd (4), Sm (5), Tb(6), Dy(7); nds = 2,6-naphthanlenedisulfonate; ina = isonicotinic acid], have been synthesized under hydrothermal conditions and characterized by elemental analysis, infrared spectra, thermogravimetric analysis and single-crystal X-ray diffraction analysis. These compounds are isostructural and constructed by the linkages of 2D [Ln(nds)(H₂O)]⁺ layers and Cu(ina)₂⁻ chains, which represent the first examples of 3D heterometallic coordination polymers created by the organodisulfonate ligands. Moreover, the complexes exhibit a novel (3,6)-connected net. The luminescence properties of complexes 1, 5 and 6 and the magnetic property of 4 were also investigated.

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Introduction

Organosulfonates are typical weak-bonded ligands¹ and the coordination compounds with them are rarely reported. However, coordination compounds with organosulfonate ligands have been of great interest due to the following reasons: (i) the functionality of organosulfonate ligands is regarded with respect to multiple binding abilities of the coordinating sites and various topologies, as demonstrated by J. W. Cai.² (ii) Metal organosulfonate families show great potential for new functional materials with regards to absorption,³ catalysis,⁴ magnetism, optics, single-crystal to single-crystal conversion,⁵ and as potential analogues of metal phosphonates.⁶ (iii) The proton of the sulfonic group is easily dissociable at very low pK_a, which causes the flexible coordination modes of SO₃⁻, ranging from μ₁ to μ₆, making structural characterization, a hallmark property of MOFs, a challenge.⁷ The supramolecular chemistry of the organosulfonate group in extended solids built up by cooperative coordination and other weak intermolecular interactions has been reviewed by Côté and Shimizu.⁸ There are some examples in the literature with main group and transition metal arenesulfonates since their structural chemistry and properties have been broadly discussed in a review.⁹ Lanthanide ions have high coordination numbers and can afford enough coordination sites for different ligands, which can lead to the syntheses of lanthanide coordination polymers with unprecedented structures. Up to now, metal–organic frameworks constructed from arenedisulfonates and rare earth elements have been examined to a considerably small extent.^4a,10 However, there is only one report on 2,6-naphthalenedisulfonate coordinated to lanthanide ions by directional covalent bonds.^4a With this in mind, lanthanide s disulfonates, incorporating secondary ligands, are particularly attractive.

As is known to all, lanthanide (Ln) and transition metal (TM) ions posses different affinities for N and O donors on the basis of the hard-soft acid/base classification.¹¹ Such a characteristic provides us the impetus to construct interesting Ln–TM heterometallic coordination polymers.¹²Isonicotinic acid is a rigid ligand with carboxylate preferring to coordinate to Ln ions, the N atom on the opposite side has a strong tendency to coordinate to TM ions. Thus, it is an excellent candidate to construct high-dimensional heterometallic coordination frameworks. A characteristic of the high-dimensional frameworks is that they are entangled and the individual units cannot be separated without breaking coordination bonds.¹³ As far as we know, a 3D heterometallic organodisulfonate coordination polymer has not been reported elsewhere.

Herein, we report the synthesis, crystal structure, and characterization of seven novel heterometallic naphthanlenedisulfonate compounds, EuCu(nds)(ina)₂·H₂O (1), CeCu(nds)(ina)₂·H₂O (2), ErCu(nds)(ina)₂·H₂O (3), GdCu(nds)(ina)₂·H₂O (4), SmCu(nds)(ina)₂·H₂O (5), TbCu(nds)(ina)₂·H₂O (6) and DyCu(nds)(ina)₂·H₂O (7), which represent the first examples of 3D coordination frameworks with unique (3,6)-connected topology constructed from the linkages of 2D layers and Cu(ina)₂⁻ chains.

Experimental

Materials and methods

Solvents and starting materials were purchased commercially and used without further purification unless otherwise noted. The FT-IR spectra was recorded from KBr pellets in the 4000–400 cm⁻¹ range on a Nicolet 5DX spectrometer. The C, H, N elemental analysis was performed on a Perkin-Elmer 2400 elemental analyzer. Thermogravimetric analysis was performed on Perkin-Elmer TGA7 analyzer with a heating rate of 10 °C min⁻¹ in flowing air atmosphere. Fluorescence spectra were recorded with an F-2500 FL spectrophotometer. The magnetic susceptibility measurement was carried out on polycrystalline samples on a Quantum Design MPMS-XL5 SQUID magnetometer. Powder X-ray diffraction (PXRD) patterns were recorded on a X-pert diffractometer or Rigaku D M⁻¹-2200T automated diffractometer for Cu-Kα radiation (λ = 1.54056 Å), with a scan speed of 4° min⁻¹ and a step size of 0.02° in the 2θ range of 5–50°.

Preparation of compounds 1–7

A mixture of 2,6-naphthalenedisulfonate sodium salt (0.133 g, 0.4 mmol), isonicotinic acid (0.0984 g, 0.8 mmol), Eu(NO₃)₃·6H₂O for 1 (0.135 g, 0.3 mmol), Ce(NO₃)₃·6H₂O for 2 (0.131 g, 0.3 mmol), Er(NO₃)₃·6H₂O for 3 (0.135 g, 0.3 mmol), Gd(NO₃)₃·6H₂O for 4 (0.135 g, 0.3 mmol), Sm(NO₃)₃·6H₂O for 5 (0.135 g, 0.3 mmol), Tb(NO₃)₃·6H₂O for 6 (0.135 g, 0.3 mmol), Dy(NO₃)₃·6H₂O for 7 (0.135 g, 0.3 mmol), CuCl₂ (0.041 g, 0.3 mmol) and H₂O (10 mL) was heated to 180 °C for 72 h in a 23 mL Teflon-lined stainless-steel autoclave and then cooled to room temperature at a rate of 5 °C h⁻¹. Yellow block crystals were collected and dried in air.

EuCu(nds)(ina)₂·H₂O (1). Yield: 65% based on Eu. Anal. calcd for C₄₄H₃₂Cu₂N₄Eu₂O₂₂S₄: C 34.59, H 2.11, N 3.67%. Found: C 35.16, H 2.23, N 3.59%. IR frequencies (KBr, cm⁻¹): 3508 w, 3205 w, 1601 s, 1539 s, 1417 s, 1241 s, 1181 m, 1156 m, 1091 m, 1031 vs, 897 w, 872 w, 856 w, 824 w, 786 w, 763 w, 705 m, 658 s, 621 m, 533 w.

CeCu(nds)(ina)₂·H₂O (2). Yield: 60% based on Ce. Anal. calcd for C₄₄H₃₂Cu₂N₄Ce₂O₂₂S₄: C 35.13, H 2.14, N 3.72%. Found: C 35.56, H 2.25, N 3.74%. IR frequencies (KBr, cm⁻¹): 3445 w, 3213 w, 1592 s, 1539 s, 1416 s, 1337 w, 1244 s, 1179 m, 1144 m, 1091 m, 1028 vs, 898 w, 855 w, 788 w, 763 w, 706 m, 658 s, 623 m, 533 w.

ErCu(nds)(ina)₂·H₂O (3). Yield: 39% based on Er. Anal. calcd for C₄₄H₃₂Cu₂N₄Er₂O₂₂S₄: C 33.91, H 2.07, N 3.59%. Found: C 35.06, H 2.21, N 3.72%. IR frequencies (KBr, cm⁻¹): 3445 w, 3212 w, 1594 s, 1539 s, 1419 s, 1242 s, 1144 m, 1091 m, 1039 m, 1029 vs, 897 w, 872 w, 856 w, 824 w, 787 w, 763 w, 706 m, 658 s, 621 m, 533 w.

GdCu(nds)(ina)₂·H₂O (4). Yield: 70% based on Gd. Anal. calcd for C₄₄H₃₂Cu₂N₄Gd₂O₂₂S₄: C 34.35, H 2.10, N 3.64%. Found: C 34.57, H 2.15, N 3.70%. IR frequencies (KBr, cm⁻¹): 3510 w, 3213 w, 1603 s, 1594 m, 1541 m, 1419 s, 1377 w, 1241 s, 1181 m, 1156 m, 1144 m, 1092 w, 1042 w, 1032 vs, 897 w, 859 w, 824 w, 787 m, 713 w, 705 m, 658 s, 622 w, 563 w.

SmCu(nds)(ina)₂·H₂O (5). Yield: 62% based on Sm. Anal. calcd for C₄₄H₃₂Cu₂N₄Sm₂O₂₂S₄: C 34.66, H 2.12, N 3.67%. Found: C 35.12, H 2.14, N 3.69%. IR frequencies (KBr, cm⁻¹): 3496 w, 3213 w, 1599 s, 1540 m, 1419 s, 1242 s, 1156 w, 1180 w, 1144 m, 1091 m, 1041 m, 1030 vs, 857 w, 824 w, 787 w, 706 m, 658 s, 623 m, 531 w.

TbCu(nds)(ina)₂·H₂O (6). Yield: 61% based on Tb. Anal. calcd for C₄₄H₃₂Cu₂N₄Tb₂O₂₂S₄: C 34.27, H 2.09, N 3.63%. Found: C 34.59, H 2.16, N 3.60%. IR frequencies (KBr, cm⁻¹): 3521 w, 3212 w, 1605 s, 1541 s, 1419 s, 1241 s, 1156 m, 1144 m, 1092 m, 1032 vs, 897 w, 860 w, 824 w, 786 w, 764 w, 713 m, 658 s, 623 m, 533 w.

DyCu(nds)(ina)₂·H₂O (7). Yield: 50% based on Dy. Anal. calcd for C₄₄H₃₂Cu₂N₄Dy₂O₂₂S₄: C 34.12, H 2.08, N 3.62%. Found: C 34.36, H 2.19, N 3.70%. IR frequencies (KBr, cm⁻¹): 3436 w, 3214 w, 1591 s, 1539 s, 1416 s, 1245 s, 1179 m, 1144 m, 1091 m, 1037 vs, 899 w, 872 w, 824 w, 787 w, 706 m, 659 s, 623 m, 534 w.

X-Ray crystallography

Single-crystal X-ray diffraction data collections of 1–7 were performed on a Bruker Apex II CCD diffractometer operating at 50 kV and 30 mA using Mo-Kα radiation (λ = 0.71073 Å). Data collection and reduction were performed using the APEX II software. Multi-scan absorption corrections were applied for all the data sets using the APEX II program. All seven structures were solved by direct methods and refined by full-matrix least squares on F² using the SHELXTL program package.¹⁴ All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms attached to carbon were placed in geometrically idealized positions and refined using a riding model. Hydrogen atoms on water molecules were located from difference Fourier maps and were also refined using a riding model. The crystallographic data and refinement parameters of 1–7 are listed in Table 1, selected bonds distances and angles are listed in Table 2.

Table 1 Crystal data and structure refinement parameters of the complexes 1–7^a,b

Complex	1	2	3	4	5	6	7
a R 1 = ∑‖Fo| − |Fc‖/∑|F0|. b wR2 = {∑[W(Fo^2 − Fc^2)^2]/∑(Fo^2)^2}^1/2.
Empirical formula	C22H16CuEuN2O11S2	C22H16CuCeN2O11S2	C22H16CuErN2O11S2	C22H16CuGdN2O11S2	C22H16CuSmN2O11S2	C22H16CuTbN2O11S2	C22H16CuDyN2O11S2
Formula weight	764.03	752.18	779.32	769.31	762.42	770.99	774.56
T/K	298(2)	298(2)	298(2)	298(2)	298(2)	298(2)	298(2)
Crystal system	Triclinic	Triclinic	Triclinic	Triclinic	Triclinic	Triclinic	Triclinic
Space group	P1̄	P1̄	P1̄	P1̄	P1̄	P1̄	P1̄
a/Å	9.5144(6)	9.5770(9)	9.528(2)	9.4878(10)	9.5121(5)	9.4951(6)	9.4926(14)
b/Å	11.4162(7)	11.5117(11)	11.338(3)	11.3999(12)	11.4333(6)	11.3913(7)	11.3728(17)
c/Å	12.3690(12)	12.3980(19)	12.282(5)	12.373(2)	12.3811(10)	12.3599(13)	12.345(3)
α/°	99.4150(10)	99.6810(10)	99.109(3)	99.3880(10)	99.4600(10)	99.2940(10)	99.253(2)
β/°	100.2000(10)	100.1280(10)	100.275(3)	100.1550(10)	100.1680(10)	100.2110(10)	100.231(2)
γ/°	114.0100(10)	114.1460(10)	114.053(2)	113.9630(10)	114.0120(10)	113.9990(10)	114.0640(10)
V/Å^3	1165.63(15)	1183.2(2)	1152.1(6)	1162.1(3)	1168.14(13)	1160.68(16)	1156.5(4)
Z	2	2	2	2	2	2	2
D c/g cm^3	2.177	2.111	2.247	2.199	2.168	2.206	2.224
μ/mm^−1	3.827	3.043	4.792	3.993	3.647	4.188	4.376
F(000)	748	738	758	750	746	752	754
GOF	1.039	1.027	1.029	1.029	1.047	1.057	1.073
R indices [I > 2σ(I)]	R 1 = 0.0248	R 1 = 0.0240	R 1 = 0.0201	R 1 = 0.0215	R 1 = 0.0240	R 1 = 0.0256	R 1 = 0.0196
	wR2 = 0.0562	wR2 = 0.0551	wR2 = 0.0479	wR2 = 0.0481	wR2 = 0.0536	wR2 = 0.0649	wR2 = 0.0476
R indices (all data)	R 1 = 0.0271	R 1 = 0.0270	R 1 = 0.0217	R 1 = 0.0240	R 1 = 0.0266	R 1 = 0.0275	R 1 = 0.0209
	wR2 = 0.0577	wR2 = 0.0571	wR2 = 0.0487	wR2 = 0.0492	wR2 = 0.0552	wR2 = 0.0659	wR2 = 0.0482

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Table 2 Selected bond distances (Å) and angles (°) for 1–7^a

a Symmetry codes follow. For 1, #1 −x + 1, −y + 1, −z; #2 −x + 1, −y, −z + 1; #3 −x, −y + 1, −z + 1; #4 −x + 1, −y, −z.
Compound 1
Eu(1)–O(1)	2.357(3)	Eu(1)–O(6)#1	2.425(2)
Eu(1)–O(5)	2.371(3)	Eu(1)–O(1W)	2.454(3)
Eu(1)–O(7) #1	2.382(3)	Eu(1)–O(2)	2.556(3)
Eu(1)–O(4)	2.408(2)	Cu(1)–N(2) #2	1.882(3)
Eu(1)–O(3)	2.409(3)	Cu(1)–N(1)	1.888(3)
O(1)–Eu(1)–O(4)	144.49(10)	O(5)–Eu(1)–O(4)	73.17(9)
O(3)–Eu(1)–O(2)	52.58(9)	C(17)–O(3)–Eu(1)	95.8(2)
O(6)#1–Eu(1)–O(2)	154.06(9)	C(17)–O(2)–Eu(1)	88.8(2)
N(2)#2–Cu(1)–N(1)	172.76(15)	S(1)–O(1)–Eu(1)	164.1(2)
S(2)–O(4)–Eu(1)	143.12(16)	S(2)–O(7)–Eu(1)#1	150.32(16)
Compound 2
Ce(1)–O(1)	2.426(2)	Ce(1)–O(6)#1	2.506(2)
Ce(1)–O(5)	2.465(2)	Ce(1)–O(1W)	2.520(2)
Ce(1)–O(7)#1	2.459(2)	Ce(1)–O(2)	2.620(2)
Ce(1)–O(4)	2.480(2)	Cu(1)–N(2)#2	1.881(3)
Ce(1)–O(3)	2.484(2)	Cu(1)–N(1)	1.882(3)
O(1)–Ce(1)–O(4)	145.80(8)	O(5)–Ce(1)–O(4)	72.86(8)
O(3)–Ce(1)–O(2)	51.14(7)	C(17)–O(3)–Ce(1)	96.0(2)
N(2)#2–Cu(1)–N(1)	174.65(13)	S(1)–O(1)–Ce(1)	168.59(17)
Compound 3
Er(1)–O(1)	2.299(2)	Er(1)–O(6)#1	2.334(2)
Er(1)–O(5)	2.297(2)	Er(1)–O(1W)	2.393(2)
Er(1)–O(7)#1	2.322(2)	Er(1)–O(2)	2.505(3)
Er(1)–O(4)	2.361(2)	Cu(1)–N(1)	1.878(3)
Er(1)–O(3)	2.348(2)	Cu(1)–N(2)#2	1.878(3)
O(1)–Er(1)–O(4)	144.00(8)	O(5)–Er(1)–O(4)	73.50(8)
O(3)–Er(1)–O(2)	53.78(8)	C(17)–O(3)–Er(1)	95.3(2)
N(2)#2–Cu(1)–N(1)	171.28(13)	S(1)–O(1)–Er(1)	162.68(17)
Compound 4
Gd(1)–O(1)	2.340(2)	Gd(1)–O(6)#1	2.412(2)
Gd(1)–O(5)	2.356(2)	Gd(1)–O(1W)	2.439(2)
Gd(1)–O(7)#1	2.368(2)	Gd(1)–O(2)	2.550(2)
Gd(1)–O(4)	2.399(2)	Cu(1)–N(1)	1.882(3)
Gd(1)–O(3)	2.402(2)	Cu(1)–N(2)#2	1.877(3)
O(1)–Gd(1)–O(4)	144.11(8)	O(5)–Gd(1)–O(4)	73.39(7)
O(3)–Gd(1)–O(2)	52.83(7)	C(17)–O(3)–Gd(1)	95.3(2)
N(2)#2–Cu(1)–N(1)	172.37(12)	S(1)–O(1)–Gd(1)	163.28(16)
Compound 5
Sm(1)–O(1)	2.364(2)	Sm(1)–O(6)#1	2.439(2)
Sm(1)–O(5)	2.387(2)	Sm(1)–O(1W)	2.458(2)
Sm(1)–O(7)#1	2.393(2)	Sm(1)–O(2)	2.567(2)
Sm(1)–O(4)	2.422(2)	Cu(1)–N(1)	1.881(3)
Sm(1)–O(3)	2.426(3)	Cu(1)–N(2)#2	1.884(3)
O(1)–Sm(1)–O(4)	144.53(9)	O(5)–Sm(1)–O(4)	73.11(8)
O(3)–Sm(1)–O(2)	52.41(8)	C(17)–O(3)–Sm(1)	95.6(2)
N(2)#2–Cu(1)–N(1)	172.79(13)	S(1)–O(1)–Sm(1)	164.43(18)
Compound 6
Tb(1)–O(1)	2.337(3)	Tb(1)–O(6)#1	2.386(3)
Tb(1)–O(5)	2.345(3)	Tb(1)–O(1W)	2.428(3)
Tb(1)–O(7)#1	2.354(3)	Tb(1)–O(2)	2.541(3)
Tb(1)–O(4)	2.391(3)	Cu(1)–N(1)	1.885(3)
Tb(1)–O(3)	2.386(3)	Cu(1)–N(2)#2	1.883(3)
O(1)–Tb(1)–O(4)	144.01(11)	O(5)–Tb(1)–O(4)	73.44(10)
O(3)–Tb(1)–O(2)	53.01(9)	C(17)–O(3)–Tb(1)	95.4(2)
N(2)#2–Cu(1)–N(1)	172.02(16)	S(1)–O(1)–Tb(1)	162.8(2)
Compound 7
Dy(1)–O(1)	2.319(2)	Dy(1)–O(6)#1	2.373(2)
Dy(1)–O(5)	2.326(2)	Dy(1)–O(1W)	2.412(2)
Dy(1)–O(7)#1	2.342(2)	Dy(1)–O(2)	2.528(2)
Dy(1)–O(4)	2.380(2)	Cu(1)–N(1)	1.884(3)
Dy(1)–O(3)	2.369(2)	Cu(1)–N(2)#2	1.882(3)
O(1)–Dy(1)–O(4)	143.98(8)	O(5)–Dy(1)–O(4)	73.44(7)
O(3)–Dy(1)–O(2)	53.29(7)	C(17)–O(3)–Dy(1)	95.71(19)
N(2)#2–Cu(1)–N(1)	171.86(12)	S(1)–O(1)–Dy(1)	162.45(16)

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Results and discussion

Single-crystal X-ray analysis reveals that 1–7 crystallize in the triclinic space groupP1̄ and posses 3D coordination frameworks based on the linkages of 2D [Ln(nds)(H₂O)]⁺ sheets and [Cu(ina)₂]⁻ chains. Because these compounds are isostructural, only the structure of 1 is described in detail. An ORTEP view of 1 is shown in Fig. 1. The asymmetric unit consists of one Eu(III) ion, one Cu(I) ions, one nds ligand, two independent full deprotonated ina ligands, and one coordinated water molecule. The Eu(III) atom is eight-cooordinated in a bicapped trigonal prismatic coordination geometry by four oxygen atoms from the ina ligands, three oxygen atoms from the nds ligands and one oxygen atom from one coordinated water molecule, respectively. The Eu–O bond distances range from 2.357(3) to 2.556(3) Å. The bond angles of O–Eu–O are in the range of 52.58(9) to 144.49(10)°. It is not appropriate to use the terms syn and anti to describe the coordination mode of metal arenedisulfonate, the torsion angles of C–S–O–Eu are used.^2,15The torsion angles of C(18)–S(1)–O(1)–Eu(1), C(4)–S(2)–O(7)–Eu(1) and C(4)–S(2)–O(4)–Eu(1) are 113.443(753)°, 84.155(338)° and 76.143(282)°, respectively. The crystallographically Cu(I) center has a nearly linear coordination environment made up of two N atoms from two bridging ina ligands with a Cu–N distance which varies from 1.882(3) to 1.888(3) Å, and N–Cu–N angles of 172.76(15)°. In 2, 5, 1, 4, 6, 7 and 3, the average bond distance of Ln–O is 2.495, 2.432, 2.420, 2.408, 2.396, 2.381 and 2.357 Å, respectively, which exhibits the characteristic of lanthanide contraction.

Fig. 1 ORTEP drawing for compound 1 (50% thermal ellipsoids). All H atoms are omitted for clarity. Symmetry code: A (−x + 1, −y, −z); B (−x + 1, −y + 1, −z); C (−x, −y + 1, −z + 1).

The ina ligand adopts two kinds of bridging coordination modes: (i) the carboxylate coordinates to two europium centers with a bis-monodendate mode, while the N atom coordinates to one copper centre (Scheme 1a); (ii) the carboxylate coordinates adopt a bidendate mode while the N atom also coordinates to one copper center (Scheme 1b). The nds also acts two kinds of coordination modes: (i) each nds ligand is bonded to only two europium atoms (η¹μ¹-η¹μ¹), and leaves four free oxygen atoms (Scheme 1c). (ii) the nds-sulfonate linker adopts the η²μ²-η²μ² coordination mode, leaving two uncoordinated O atoms (Scheme 1d). Both coordination modes are proved to be crucial in constructing [Ln(nds)(H₂O)]⁺ layers and Cu(ina)₂⁻ chains. All carboxyl groups are deprotonated, in agreement with the IR data in which no strong absorption peaks around 1700 cm⁻¹ for –COOH are observed. Both v_as and v_s of the SO₃⁻groups found at 1240–1180(v_as) and 1100–1040(v_s) cm⁻¹.

Scheme 1 Coordination modes of ina and nds ligands

Two Eu(III) centres were linked, through a pair of ina ligands and nds ligands, respectively, and resulted in a dinuclear unit with a Eu⋯Eu distance of 4.5531(4) Å. The connection of adjacent dinuclear units through nds entity adopting a symmetric η¹μ¹-η¹μ¹ mode generate infinite 1D zigzag strings as shown in Fig. 2a. The nds ligand also bridging Eu₂O₁₆ dimers from one neighbouring chain in the η²μ²-η²μ² coordination mode (Fig. 2b). In doing that, the structure could be extended in terms of two-dimensional rectangle grid structure of [Ln(nds)(H₂O)]⁺ with a dimension of 11.4 × 10.9 Å, each sharing the Eu₂O₁₆ dimers with two differently coordinated nds connectors, as illustrated in Fig. 2d. Undoubtedly, the geometrical features imposed by the position of the sulfonate groups in the nds connector, to our knowledge, is the first example of 2D Ln(nds)(H₂O)⁺ sheets by directional covalent bond. It should be noticed that two different ina ligands give rise to a nearly perpendicular arrangement (dihedral angle 74.954°), which leads to the linear N–Cu–N mode in Cu(ina)₂⁻ coordination. The 2D layers are packed into a 3D framework by the bridging Cu(ina)₂⁻ chains (Fig. 2c). And the grids are packed without dislocation. From the topological point of view, each Eu/nds layer acts as a six/three-connected node, respectively, and a network is formed with the Schläfli symbol {4·8²}{4⁷·5·6⁴·7·8²}{4²·6} (Fig. 3), providing a rare example of 3d–4f open framework.

Fig. 2 (a) Chain 1: infinite 1D zigzag, with a η¹μ¹-η¹μ¹ mode between dinuclear unit and nds. (b) Chain 2: view of (Eu₂O₁₆)–nds–(Eu₂O₁₆) chains, nds bridging dinuclear unit exhibiting the η²μ²-η²μ² coordination mode. (c) The bridging Cu(ina)₂⁻ chain 1D with N–Cu–N mode. (d) Ln(nds)⁺ layers formed in compound 1. All hydrogen atoms are omitted for clarity.

Fig. 3 Diagram for the (3,6)-connected net of 1. Green: Eu; yellow: S; dark: C.

Luminescent properties

Due to the excellent photoluminescence properties of the lanthanide compounds,¹⁶ the luminescence of 1, 5 and 6 containing Eu(III), Sm(III) and Tb(III) ions, respectively, in the solid state were investigated. As shown in Fig. 4, the emission spectrum of 1 upon excitation at 395 nm exhibits the characteristic transition of Eu(III) ion. They are attributed to ⁵D₀ → ⁷F_J (J = 0 → 4) transitions, i.e. 579 nm (⁵D₀ → ⁷F₀), 592 nm (⁵D₀ → ⁷F₁), 613 and 619 nm (⁵D₀ → ⁷F₂), 654 nm (⁵D₀ → ⁷F₃), 704 nm (⁵D₀ → ⁷F₄). The ⁵D₀ → ⁷F₂ transition is stronger than that of the ⁵D₀ → ⁷F₁ transition, indicating that Eu(III) ions have a low symmetric coordination environment and without an inversion center. This is in agreement with the results of the single-crystal X-ray analysis.¹⁷ Compound 5 emits an orange light when excited at 362 nm (Fig. 5), it gives a typical Sm(III) emission spectrum. The emission at 561, 599, and 645 nm correspond to the characteristic emission of ⁴G_5/2 → ⁶H_J (J =5/2, 7/2, 9/2) transitions of the Sm(III) ion, where the peak at 599 nm is the strongest one. Compound 6 yields green light and exhibits the characteristic emission of ⁵D₄ → ⁷F_J (J = 3–6) of the Tb(III) ion (Fig. 6). Two intense emission bands at 489 and 544 nm is attributed to ⁵D₄ → ⁷F₆ and ⁵D₄ → ⁷F₅, while the weaker emission bands at 590 nm and 619 nm originate from ⁵D₄ → ⁷F₄ and ⁵D₄ → ⁷F₃.

Fig. 4 Solid-state emission spectrum for 1 at room temperature.

Fig. 5 Solid-state emission spectrum for 5 at room temperature.

Fig. 6 Solid-state emission spectrum for 6 at room temperature.

Thermal stability and PXRD analysis

Owing to the similarity of the structures for 1–7, compound 1 was selected for the TGA to examine the thermal stability of both compounds. The TG curve was performed in air atmosphere from 50 to 750 °C at a heating rate of 10 °C min⁻¹(Fig. S1).† It can be seen from the TG curve that there is no weight loss between 50 and 225 °C. Such a thermal stability of 1 may be attributed to the formation of the 2D layer of [Ln(nds)(H₂O)]⁺ and the 1D chain of Cu(ina)₂⁻. A Weight loss occurs between 225 and 335 °C, accompanied by an endothermic effect corresponding to the loss of the coordinated water molecule per formula unit (found, 2.8%; calcd, 2.4%). Above 335 °C, all of the organic components are removed and the framework is collapsed.

The as-isolated samples of the complexes were also characterized by powder X-ray diffraction at room temperature (Fig. 7 and S1).† When compared to the simulated patterns based on the single crystal data samples, the experimental patterns are in agreement with the calculated diffractograms, thus basically pointing toward the formation of only a single phase product under the reaction conditions employed for these complexes.

Fig. 7 The experimental PXRD pattern of complex 4 at room temperature (top). The simulated PXRD pattern from single crystal X-ray data of complex 4 (bottom).

Magnetic property

Solid-state dc magnetic susceptibility measurement for compound 4 was performed in the range of 2–300 K under a field of 1000 Oe, and the magnetic behaviour is shown in Fig. 8 as plots of χ_MTvs.T and χ_M⁻¹vs.T, where χ_M is the magnetic susceptibility per [Gd₂] unit. The room-temperature χ_MT value is 15.7 cm³ K mol⁻¹, closed to the spin-only value 15.75 cm³ K mol⁻¹ for two Gd(III) (S = 7/2). As the temperature lowered from 300 to 15 K, the χ_MT value remained the unchanged value 15.7 cm³ K mol⁻¹, and then decreased steadily to 14.5 cm³ K mol⁻¹ at 2 K, which reveals an overall antiferromagnetic behaviour in compound 4. The temperature dependent χ_M⁻¹ value obey the Curie–Weiss law with Curie constant C = 15.74 cm³ K mol⁻¹ and Weiss constant θ = −0.15 K. Because of the complicated three-dimensional framework of 4, no exact theoretical expression could be used to simulate the magnetic data. Since the organosulfonic ligands separated the Gd₂ units well, the magnetic bahaviour of 4 can be roughly represented by Gd₂ interaction expression, and the best fitting parameters can be given as g = 2.01, J = 0.008 cm⁻¹. Because the small positive J value can not explain the decrease of the χ_MT value at low temperature, the magnetic interaction expression of 4 should be further developed.

Fig. 8 χ _M T vs. T and χ_M⁻¹vs.T plots for compound 4. The dots represent the experimental data, and the solid lines represent the best fitting data which were calculated with the method as shown in the text.

Conclusions

In summary, seven novel 3D Ln–TM coordination compounds were successfully synthesized by applying hydrothermal strategy. All of the seven compounds were constructed by the linkages of 2D [Ln(nds)(H₂O)]⁺ layers and Cu(ina)₂⁻ chains. The 2D layers are the consequence of the naphthalenedisulfonic acid used as linkers with two different coordination mode. It is of interest that the novel (3,6)-connected net exhibited by the seven frameworks are the first examples, in the family of Ln–TM heterometallic coordination polymers with organodisulfonate ligand. The luminescence and magnetic properties have also been discussed. Moreover, the successful syntheses of the title compounds provide a good method for constructing high dimensional coordination polymers by organodisulfonate ligands.

Acknowledgements

This work was financially supported by Guangdong Provincial Science and Technology Bureau (grant 2008B010600009), and NSFC (grant no. 20971047 and U0734005).

References

1. (a) G. A. Lawrance, Chem. Rev., 1986, 86, 17; (b) A. P. Côté and G. K. H. Shimizu, Coord. Chem. Rev., 2003, 245, 49; (c) G. K. H. Shimizu, R. Vaidhyanathan and J. M. Taylor, Chem. Soc. Rev., 2009, 38, 1430.
2. (a) J. W. Cai, C. H. Chen, C. Z. Liao, J. H. Yao, X. P. Hu and X. M. Chen, J. Chem. Soc., Dalton Trans., 2001, 1137; (b) J. W. Cai, C. H. Chen, C. Z. Liao, X. L. Feng and X. M. Chen, J. Chem. Soc., Dalton Trans., 2001, 2370.
3. (a) P. Kanoo, K. L. Gurunatha and T. K. Maji, Cryst. Growth Des., 2009, 9, 4147; (b) B. D. Chandler, G. D. Enright, S. Pawsey, J. A. Ripmeester, D. T. Cramb and G. K. H. Shimizu, Nat. Mater., 2008, 7, 229; (c) S. A. Dalrymple and G. K. H. Shimizu, J. Am. Chem. Soc., 2007, 129, 12114; (d) B. D. Chandler, D. T. Cramb and G. K. H. Shimizu, J. Am. Chem. Soc., 2006, 128, 10403; (e) B. D. Chandler, J. O. Yu, D. T. Cramb and G. K. H. Shimizu, Chem. Mater., 2007, 19, 4467.
4. (a) F. Gándara, A. García-Cortés, C. Cascales, B. Gómez-Lor, E. Gutiérrez-Puebla, M. Iglesias, A. Monge and N. Snejko, Inorg. Chem., 2007, 46, 3475; (b) F. Gándara, C. Fortes-Revilla, N. Snejko, E. Gutiérrez-Puebla, M. Iglesias and A. Monge, Inorg. Chem., 2006, 45, 9680.
5. X. Ribas, D. Maspoch, K. Wurst, J. Veciana and C. Rovira, Inorg. Chem., 2006, 45, 5383.
6. (a) S. R. Miller, G. M. Pearce, P. A. Wright, F. Bonino, S. Chavan, S. Bordiga, I. Margiolaki, N. Guillou, G. Ferey, S. Bourrelly and P. L. Llewellyn, J. Am. Chem. Soc., 2008, 130, 15967; (b) S. K. Mäkinen, N. J. Melcer, M. Parvez and G. K. H. Shimizu, Chem.–Eur. J., 2001, 7, 5176; (c) J. O. Yu, A. P. Côté, G. D. Enright and G. K. H. Shimizu, Inorg. Chem., 2001, 40, 582; (d) A. P. Côté and G. K. H. Shimizu, Chem. Commun., 2001, 251; (e) P. Römbde, A. Schier and H. Schmidbaur, J. Chem. Soc., Dalton Trans., 2001, 2482; (f) G. K. H. Shimizu, G. D. Enright, C. I. Ratcliffe and J. A. Ripmeester, Chem. Commun., 1999, 461; (g) J. H. Teles, S. Brodes and M. Chabanas, Angew. Chem., Int. Ed., 1998, 37, 1415.
7. (a) H. Wu, X. W. Dong, H. Y. Liu, J. F. Ma, S. L. Li, J. Yang, Y. Y. Liu and Z. M. Su, J. Chem. Soc., Dalton Trans., 2008, 5331; (b) Z. X. Lian, J. W. Cai, C. H. Chen and H. B. Luo, CrystEngComm, 2007, 9, 319; (c) C. H. Chen and J. W. Cai, Inorg. Chem., 2002, 41, 4967; (d) A. P. Côté, M. J. Ferguson, K. A. Khan, G. D. Enright, A. D. Kulynych, S. A. Dalrymple and G. K. H. Shimizu, Inorg. Chem., 2002, 41, 287; (e) J. W. Cai, C. H. Chen, C. Z. Liao, X. L. Feng and X. M. Chen, Acta Crystallogr., Sect. B: Struct. Sci., 2001, 57, 520; (f) N. S. Hu1sgen, G. A. Luinstra, F. Schaper and K. Schmidt, Inorg. Chem., 1998, 37, 3471.
8. (a) A. P. Côté and G. K. H. Shimizu, Coord. Chem. Rev., 2003, 86, 17; (b) T. Z. Forbes and S. C. Sevov, Inorg. Chem., 2009, 48, 6873; (c) N. J. Burke, A. D. Burrows, M. F. Mahon and J. E. Warren, CrystEngComm, 2008, 10, 15.
9. J. W. Cai, Coord. Chem. Rev., 2004, 248, 1061.
10. (a) J. P. Zhao, B. W. Hu, F. C. Liu, X. Hu, Y. F. Zeng and X. H. Bu, CrystEngComm, 2007, 9, 902; (b) F. Gándara, J. Perles, N. Snejko, M. Iglesias, B. Gómez-Lor, E. Gutiérrez-Puebla and M. A. Monge, Angew. Chem., Int. Ed., 2006, 45, 7998; (c) J.-L. Song, C. Lei and J. G. Mao, Inorg. Chem., 2004, 43, 5631; (d) N. Snejko, C. Cascales, B. Gomez-Lor, E. Gutiérrez-Puebla, M. Iglesias, C. Ruiz-Valero and M. A. Monge, Chem. Commun., 2002, 1366; (e) R. G. Xiong, J. Zhang, Z. F. Chen, X. Z. You, C. M. Che and H. K. Fun, J. Chem. Soc., Dalton Trans., 2001, 780; (f) G. B. Deacon, A. Gitilits, G. Zelestny, D. Stellfeldt and G. Meyer, Z. Anorg. Allg. Chem., 1999, 625, 764.
11. R. G. Pearson, J. Am. Chem. Soc., 1963, 85, 3533.
12. (a) Z. Y. Li, N. Wang, J. W. Dai, S. T. Yue and Y. L. Liu, CrystEngComm, 2009, 11, 2003; (b) N. Wang, S. T. Yue, Y. L. Liu, H. Y. Yang and H. Y. Wu, Cryst. Growth Des., 2009, 9, 368; (c) Y. F. Zhou, F. L. Jiang, D. Q. Yuan, B. L. Wu, R. H. Wang, Z. Z. Lin and M. C. Hong, Angew. Chem., Int. Ed., 2004, 43, 5665; (d) Y. F. Zhou, M. C. Hong and X. T. Wu, Chem. Commun., 2006, 135; (e) C. M. Zaleski, E. C. Depperman, J. W. Kampf, M. L. Kirk and V. L. Pecoraro, Angew. Chem., Int. Ed., 2004, 43, 3912; (f) B. Zhao, X. Y. Chen, P. Cheng, D. Z. Liao, S. P. Yan and Z. H. Jiang, J. Am. Chem. Soc., 2004, 126, 15394; (g) A. D. Cutland-Van Noord, J. W. Kampf and V. L. Pecoraro, Angew. Chem., Int. Ed., 2002, 41, 4667; (h) F. C. Liu, Y. F. Zeng, J. Jiao, J. R. Li, X. H. Bu, J. Ribas and S. R. Batten, Inorg. Chem., 2006, 45, 6129; (i) X. Hu, Y. F. Zeng, Z. Chen, E. C. Sañudo, F. C. Liu, J. Ribas and X. H. Bu, Cryst. Growth Des., 2009, 9, 421.
13. V. V. Adrabinska, Coord. Chem. Rev., 2007, 251, 1987.
14. (a) G. M. Sheldrick, SHELXS–97, Program for Crystal Structure Solution, University of Göttingen: Göttingen, Germany, 1997; (b) G. M. Sheldrick, SHELXL–97, Program for Crystal Structure Refinement, University of Göttingen: Göttingen, Germany, 1997.
15. (a) A. J. Shubnell, E. J. Kosnic and P. J. Squattrito, Inorg. Chim. Acta, 1994, 216, 101; (b) B. J. Gunderman, I. D. Kabell, P. J. Squattrito and S. N. Dubey, Inorg. Chim. Acta, 1997, 258, 237; (c) E. J. Kosnic, E. L. McClymont, R. A. Hodder and P. J. Squattrito, Inorg. Chim. Acta, 1992, 201, 143; (d) C. H. Chen, J. W. Cai, X. L. Feng and X. M. Chen, J. Chem. Crystallogr., 2001, 31, 271; (e) J. W. Cai, C. H. Chen and J. S. Zhou, Chin. J. Inorg. Chem., 2003, 19, 81; (f) J. W. Cai, J. S. Zhou and M. L. Lin, J. Mater. Chem., 2003, 13, 1806.
16. Y. Li, F. Zheng, X. Liu, W. Zou, G. Guo, C. Lu and J. Huang, Inorg. Chem., 2006, 45, 6308 and references therein.
17. (a) A. de Bettencourt–Dias and S. Viswanathan, Chem. Commun., 2004, 1024; (b) Y. Q. Sun, J. Zhang and G. Y. Yang, Chem. Commun., 2006, 4700.

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Footnote

† Electronic supplementary information (ESI) available: Further characterisation data. CCDC reference numbers 768850, 768848, 772500, 768851, 768853, 768854, 768849. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c0ce00077a

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