A Series of Heteromultinuclear Zinc(II)âLanthanide(III) Complexes

Article pubs.acs.org/crystal

A Series of Heteromultinuclear Zinc(II)−Lanthanide(III) Complexes Based on 3‑MeOsalamo: Syntheses, Structural Characterizations, and Luminescent Properties Wen-Kui Dong,* Jian-Chun Ma, Li-Chun Zhu, Yin-Xia Sun, Sunday Folaranmi Akogun, and Yang Zhang School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P. R. China S Supporting Information *

ABSTRACT: Using 3-MeOsalamo H2L (H2L = 1,2-bis(3methoxysalicylideneaminooxy)ethane) with Zn(OAc)2·2H2O, Ln(NO3)3·6H2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, and Tb), and 4,4′-bipy (4,4′-bipyridine) or H2bdc (terephthalic acid), three new families of heteromultinuclear ZnII−LnIII complexes: [{Zn(L)Ln(NO3)3(CH3OH)}2(4,4′-bipy)] (Ln = La (1·2CH3OH) and Ce (2)), [{Zn(L)Ln(NO3)3}2(4,4′-bipy)] (Ln = Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), and Tb(8)), [{(ZnL)2Ln}2(bdc)2]·(NO3)2·2CHCl3 (Ln = Ce (9), Pr (10) and Sm (11· 2CH3CH2OH)), and 2∞[Zn(L)Ln(bdc)1.5] (Ln = Eu (12) and Gd (13·2CHCl3)) were obtained, respectively. Complexes 1−8 are heterotetranuclear dimers based on [Zn(L)Ln] moieties which are linked through the exo-dentate 4,4′-bipy having nitrogen-donor atoms. Heterohexanuclear complexes 9−11 constructed from almost linear trinuclear cationic [(ZnL)2Ln] moieties which are linked through the exodentate (bdc)2− bearing oxygen-donor atoms. Two 2D coordination polymers 12 and 13 are also assembled by [Zn(L)Ln] units with (bdc)2− linker. Furthermore, the luminescence properties of complexes 1−13 have been studied. An appropriate and selective linker could enhance the construction of a Salamo-type zinc(II)−lanthanide(III) complex possessing efficient luminescent properties.

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INTRODUCTION Self-assembling behavior of a metallohost complex with organic ligands is usually utilized in the building of metal−organic framework (MOF) materials.1−3 A lot of novel complexes have been synthesized through this method which makes use of bipyridine and carboxylates compounds.4 Many efforts have been given to 3d-4f heteronuclear complexes because these complexes possess excellent magnetic5−17 and luminescent properties.18−28 However, control over the stoichiometries and structures of 3d−4f heteromutinuclear complexes is synthetically difficult due to the challenge in manipulating the different coordination site of the metal cations. 3-Alkoxy Salen-type compounds could be utilized in obtaining the 3d−4f complexes owing to their inner coordination site having a N2O2 chelating moiety which is appropriate for the linkage to d-block cations, and an outer coordination site having O4 donor atoms. However, the outer coordination site is bigger than the inner coordination site and can thereby accommodate larger LnIII ions.29 An interesting feature of these complexes is that the axial sites of 3d metal ions are usually held by anions and/or solvent molecules that result in a distorted octahedral, trigonal bipyramidal, or square pyramidal coordination configuration.13 It is known that acetate ion frequently join both 3d and 4f metal ions.30,31 These features show that 3d-4f complexes could be studied through the combination of appropriate Salen-type compounds and selected di- or multidentate linkers which could hold these bridging/axial positions of each 3d or 3d−4f moiety.20 © XXXX American Chemical Society

Herein, we designed and synthesized eight 3d−4f heterotetranuclear complexes [{Zn(L)Ln(NO3)3(CH3OH)}2(4,4′bipy)] (Ln = La (1·2CH3OH) and Ce (2)) and [{Zn(L)Ln(NO3)3}2(4,4′-bipy)] (Ln = Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), and Tb(8)), three heterohexanuclear complexes [{(ZnL)2Ln}2(bdc)2]·(NO3)2·2CHCl3 (Ln = Ce (9), Pr (10), and Sm (11·2CH3CH2OH)), and two 2D coordination polymers 2∞[Zn(L)Ln(bdc)1.5] (Ln = Eu (12) and Gd (13· 2CHCl3)) by 3-MeOsalamo ligand H2L. The 4,4′-bipy was selected as a simple bidentate linker owing to its availability and application in the building of Salen-type ZnII−NdIII complex,21 and H2bdc as a tetradentate linker was utilized to gather Salentype hexanuclear ZnII−NdIII complex.20 Though many homo or heteronuclear complexes have been studied using Salentype32−41 or Salamo-type42−69 N2O2 compounds in the past years, few Salamo-type 3d−4f heteromultinuclear complexes have been reported, and most of them are Zn II −Ln III heteromultinuclear complexes bearing simple di- or multinuclear cores.56−69 As far as we know, this is the first time that Salamo-type ZnII−LnIII complexes 1−13 would be reported, and these complexes are gotten by binding 3d−4f Salamo units with (bdc)2− or 4,4′-bipy linkers. Synthetic routes to complexes 1−13 are drawn in Scheme 1. Received: July 19, 2016 Revised: October 14, 2016 Published: October 18, 2016 A

DOI: 10.1021/acs.cgd.6b01067 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

Scheme 1. Synthetic Routes to Complexes 1−13

Table 1. Crystallographic Data and Refinement Parameters for Complexes 1−6 complex

1

2

3

4

5

6

formula Mr T (K) system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) θ (deg) F(000) R1 (I > 2σ(I)) wR2 (I > 2σ(I)) S

C50H60La2N12O34Zn2 1781.66 173 triclinic P1̅ 9.3012(8) 11.6392(7) 17.8757(10) 103.542(5) 92.979(6) 103.361(6) 1818.9(2) 1 1.627 3.5, 26.0 890 0.0490 0.1329 1.075

C48H52Ce2N12O32Zn2 1719.99 293(2) triclinic P1̅ 10.9670(9) 11.5241(11) 16.0481(10) 92.925(6) 108.990(7) 117.451(9) 1652.3(3) 1 1.729 4.7, 69.9 856 0.0356 0.0994 1.098

C46H44Pr2N12O30Zn2 1657.49 293.33(10) monoclinic I2/c 21.6414(7) 8.8285(3) 34.7349(14) 90 102.886(4) 90 6469.4(4) 4 1.702 3.3, 26.0 3288 0.0426 0.0692 0.993

C46H44Nd2N12O30Zn2 1664.15 296(2) monoclinic C2/c 36.5198(14) 8.8760(4) 21.4741(9) 90 112.696(1) 90 6421.8(5) 4 1.721 2.5, 25.5 3296 0.0366 0.0900 1.073

C46H44Sm2N12O30Zn2 1676.37 293.64(10) monoclinic I2/c 21.4451(9) 8.8457(5) 34.388(2) 90 102.412(5) 90 6370.8(6) 4 1.748 3.4, 26.0 3312 0.0401 0.0703 0.957

C46H44Eu2N12O30Zn2 1679.59 173 monoclinic I2/c 21.5648(6) 8.8319(3) 34.7855(9) 90 102.895(3) 90 6458.1(3) 4 1.727 3.3, 26.0 3320 0.0426 0.0694 0.993

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infrared (NIR) spectra in solid state were determined through PTI QM4 spectrofluorometer with a PTI QM4 Nearinfrared InGaAs detector. Other measurements are the same as the methods reported earlier.55 X-ray Crystallography. Single crystal X-ray diffraction measurements were performed with a Bruker Smart 1000 CCD area detector. The diffraction data were collected by a graphite monochromated Mo Kα (1, 3−10, 12, and 13) and Cu Kα radiations (2 and 11), respectively. Data collection and reduction were carried out through

EXPERIMENTAL SECTION

General Details. All reagents and solvents employed were commercially available and used without further purification. Fluorescence spectra in solid state and solution were carried out on a PerkinElmer LS-55 luminescence spectrophotometer. Quantum yields in solid state were measured using an absolute method by integrating sphere on FLS920 of Edinburgh Instrument. The luminescence decays in solid state were made by a pumped dye laser (Lambda Physics model FL2002) as the excitation source. Near B


8 C46H44Tb2N12O30Zn2 1693.51 296(2) monoclinic C2/c 36.4508(17) 8.8934(4) 21.3694(10) 90 112.749(1) 90 6388.5(5) 4 1.761 2.1, 26.0 3336 0.0257 0.0584 1.033

7

C46H44Gd2N12O30Zn2 1690.17 173 monoclinic I2/c 21.3581(7) 8.8475(3) 34.1518(12) 90 102.124(3) 90 6309.6(4) 4 1.779 3.3, 26.0 3328 0.0306 0.0560 1.020

complex

formula Mr T (K) system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) θ (deg) F(000) R1 (I > 2σ (I)) wR2 (I > 2σ (I)) S

C90H82Cl6Ce2N10O38Zn4 2666.07 293.33(10) triclinic P1̅ 11.6545(5) 16.3873(10) 19.6884(9) 107.116(5) 104.458(4) 99.238(4) 3366.8(3) 1 1.315 3.3, 26.0 1334 0.0678 0.1315 0.891

9

Table 2. Crystallographic Data and Refinement Parameters for Complexes 7−13 10 C90H82Cl6Pr2N10O38Zn4 2667.65 293.33(10) triclinic P1̅ 11.6515(4) 16.2135(9) 19.6072(5) 106.518(4) 104.627(3) 98.718(4) 3335.0(3) 1 1.328 3.3, 26.0 1336 0.0414 0.0823 0.934

11 C94H94Cl6Sm2N10O40Zn4 2778.67 291.48(10) triclinic P1̅ 11.6472(6) 15.9784(9) 19.5622(10) 105.749(5) 104.874(4) 98.131(5) 3298.2(3) 1 1.399 4.0, 69.8 1394 0.0830 0.2246 1.110

12 C30H24EuN2O12Zn 821.84 291.73(10) triclinic P1̅ 12.5764(15) 12.6610(15) 13.9174(18) 76.328(3) 83.715(3) 84.497(2) 2134.7(5) 2 1.279 3.5, 27.0 814 0.0284 0.0637 0.960

13 C31H25Cl3GdN2O12Zn 946.50 173 triclinic P1̅ 12.5745(9) 12.6334(7) 13.9017(9) 76.229(5) 84.109(6) 84.429(5) 2127.6(2) 2 1.477 3.3, 26.0 932 0.0601 0.1313 0.987

Crystal Growth & Design Article

C



a

Distances (Å) and angles (deg). bFor τ values, see ref 73. cDihedral angle between ZnO(phenoxo)2 and LnO(phenoxo)2 planes. dDihedral angle between two pyridine rings of 4,4′-bipy.

2.039(2) 2.030(2) 2.121(3) 2.042(3) 2.063(3) 107.71(10) 106.70(10) 3.535(3) 0.159 5.99(8) 35.20(11) 2.042(3) 2.029(3) 2.125(4) 2.041(4) 2.065(3) 107.93(15) 106.85(15) 3.555(3) 0.177 5.12(11) 38.08(17) 2.032(3) 2.035(3) 2.122(5) 2.036(4) 2.063(4) 107.80(16) 106.37(15) 3.552(4) 0.175 4.90(12) 34.12(2) 2.028(3) 2.035(3) 2.042(4) 2.121(4) 2.063(4) 107.06(13) 108.32(14) 3.531(4) 0.171 5.02(11) 34.98(18) 2.039(3) 2.029(3) 2.131(4) 2.039(4) 2.065(4) 108.24(12) 106.90(11) 3.605(3) 0.179 4.43(10) 34.85(14)

7 6

2.616(3) 2.349(3) 2.390(3) 2.563(4) 2.464(3)−2.580(3) 2.590(4) 2.358(3) 2.394(3) 2.592(4) 2.466(4)−2.590(4)

5 4

2.558(4) 2.357(3) 2.316(3) 2.604(4) 2.432(4)−2.589(4)

3

2.648(3) 2.403(3) 2.621(3) 2.448(3) 2.519(3)−2.626(4)

2.678(3) 2.512(3) 2.402(3) 2.654(3) 2.540(4)−2.684(4) 2.582(4) 2.062(3) 1.994(3) 2.026(4) 2.141(4) 2.088(3) 104.47(11) 110.83(11) 3.6264(7) 0.207 10.71(9) 0

2 1

2.686(4) 2.507(3) 2.506(3) 2.784(4) 2.556(4)−2.697(4) 2.643(4) 2.032(3) 2.024(3) 2.063(4) 2.096(5) 2.085(4) 106.95(13) 107.27(13) 3.659(4) 0.126 9.88(11) 0

Table 3. Selected Structural Parametersa of Complexes 1−7 D

Ln1−O1 Ln1−O2 Ln1−O5 Ln1−O6 Ln1−O (nitrate) Ln1−O (methanol) Zn1−O2 Zn1−O5 Zn1−N1 Zn1−N2 Zn1−N3 Zn1−O2−Ln1 Zn1−O5−Ln1 Ln1···Zn1 τ (Zn)b δc δd

the SMART and SAINT softwares.70 The crystal structures were solved by a direct method and refined by full matrix least-squares refinement using the SHELXL-97.71,72 Anisotropic thermal parameters were used for the non-hydrogen atoms and isotropic parameters for the hydrogen atoms. Hydrogen atoms were added geometrically and refined via a riding model. Crystallographic data and refinement parameters are given in Tables 1 (1−6) and 2 (7−13). Selected structural parameters are summarized in Tables 3 (1−7) and 4 (8− 13). Synthesis of Ligand 1,2-Bis(3methoxysalicylideneaminooxy)ethane (H2L). H2L was synthesized in accordance with the earlier reported method.55,74 Yield: 83.0%. Mp: 132−134 °C. The characterization of H2L was same as the literature.55 Syntheses of Complexes [{Zn(L)Ln(NO3)3(CH3OH)}2(4,4′bipy)] (Ln = La (1·2CH3OH) and Ce (2)), [{Zn(L)Ln(NO3)3}2(4,4′bipy)] (Ln = Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), and Tb(8)). To a stirring solution of H2L (0.036 g, 0.1 mmol) in chloroform (1 mL) was added Zn(OAc)2·2H2O (0.022 g, 0.1 mmol) and Ln(NO3)3·6H2O (0.1 mmol) in methanol (2 mL). After the mixture was stirred for about 10 min at r.t., a solution of 4,4′-bipy (0.016 g, 0.1 mmol) in methanol and chloroform (1:1 V/V, 1 mL) was added and continued to stir for 10 min. The mixture was filtered, and the filtrate was obtained. Several single crystals suitable for X-ray crystallographic analysis were obtained by vapor diffusion of diethyl ether into the filtrate for almost a week at r.t. For complex 1, clear light yellow blocks. Yield: 0.073 g, 80%. Anal. Calcd for C50H60La2N12O34Zn2: C, 33.71; H, 3.39; N, 9.43%. Found: C, 33.69; H, 3.45; N, 9.38%. IR (cm−1, KBr): 3419 (w), 1612 (s), 1535 (m), 1456 (s), 1382 (s), 1313 (m), 1215 (m), 1072 (m), 1035 (w), 808 (s), 724 (w), 642 (m), 492 (w). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 230 (6.76 × 104), 276 (3.07 × 104), 350 (1.11 × 104). For complex 2, clear dark yellow blocks. Yield: 0.067 g, 78%. Anal. Calcd for C48H52Ce2N12O32Zn2: C, 33.52; H, 3.05; N, 9.77%. Found: C, 33.40; H, 3.17; N, 9.70%. IR (cm−1, KBr): 3068 (w), 1612 (s), 1537 (w), 1456 (s), 1382 (s), 1301 (w), 1257 (m), 1215 (m), 1072 (s), 1014 (w), 964 (m), 808 (s), 734 (m), 642 (s), 491 (w). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 230 (1.25 × 105), 273 (5.61 × 104), 349 (1.64 × 104). For complex 3, clear yellow-green blocks. Yield: 0.064 g, 77%. Anal. Calcd for C46H44Pr2N12O30Zn2: C, 33.33; H, 2.68; N, 10.14%. Found: C, 33.03; H, 2.59; N, 10.10%. IR (cm−1, KBr): 2939 (w), 1606 (s), 1556 (w), 1463 (s), 1385 (s), 1280 (s), 1242 (w), 1219 (s), 1099 (w), 1070 (s), 1039 (m), 970 (w), 941 (w), 918 (w), 848 (w), 810 (w), 741 (s), 642 (w), 617 (w), 559 (w), 518 (w). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 230 (9.53 × 104), 276 (5.23 × 104), 350 (1.53 × 104). For complex 4, clear light purple blocks. Yield: 0.065 g, 78%. Anal. Calcd for C46H44Nd2N12O30Zn2: C, 33.20; H, 2.66; N, 10.10%. Found: C, 33.11; H, 2.56; N, 10.01%. IR (cm−1, KBr): 2939 (w), 1606 (s), 1556 (m), 1465 (s), 1383 (s), 1282 (s), 1240 (w), 1219 (s), 1099 (w), 1070 (s), 1031 (m), 970 (w), 941 (w), 918 (w), 848 (w), 815 (w), 741 (s), 644 (w), 619 (w), 559 (w), 520 (w). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 230 (8.42 × 104), 276 (4.65 × 104), 349 (1.37 × 104). For complex 5, clear light colorless blocks. Yield: 0.060 g, 72%. Anal. Calcd for C46H44Sm2N12O30Zn2: C, 32.96; H, 2.65; N, 10.03%. Found: C, 32.79; H, 2.73; N, 9.97%. IR (cm−1, KBr): 2949 (w), 1606 (s), 1556 (w), 1465 (s), 1385 (s), 1282 (s), 1242 (w), 1219 (s), 1097 (w), 1070 (s), 1037 (s), 970 (w), 943 (m), 918 (w), 848 (w), 813 (w), 792 (w), 740 (s), 619 (w), 559 (w), 522 (w). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 229 (9.48 × 104), 276 (4.95 × 104), 349 (1.42 × 104). For complex 6, clear light colorless blocks. Yield: 0.059 g, 70%. Anal. Calcd for C46H44Eu2N12O30Zn2: C, 32.89; H, 2.64; N, 10.01%. Found: C, 32.80; H, 2.72; N, 10.11%. IR (cm−1, KBr): 2939 (w), 2848 (w), 1606 (s), 1556 (w), 1467 (s), 1384 (s), 1282 (s), 1240 (w), 1219 (s), 1099 (w), 1070 (s), 1039 (s), 970 (m), 941 (m), 918 (m), 848 (m), 815 (w), 792 (w), 740 (s), 619 (m), 559 (w), 522 (w). UV−Vis

2.583(2) 2.334(2) 2.370(2) 2.570(2) 2.447(2)−2.582(2)

Article



Article

Table 4. Selected Structural Parametersa of Complexes 8−13 8 Ln1−O11 Ln1−O12 Ln1−O13 Ln1−O14 Ln1−O (nitrate) Zn1−O13 Zn1−O14 Zn1−N1 Zn1−N2 Zn1−N6 Zn1−O13−Ln1 Zn1−O14−Ln1 Ln1···Zn1 τ (Zn)b δc δd

2.593(2) 2.563(2) 2.350(2) 2.3144(19) 2.431(2)−2.586(2) 2.0255(19) 2.0342(19) 2.042(2) 2.118(3) 2.062(2) 106.83(8) 107.84(9) 3.518(2) 0.177 5.28(11) 34.42(12)

Ln1−O1 Ln1−O2 Ln1−O5 Ln1−O6 Ln1−O7 Ln1−O8 Ln1−O11 Ln1−O12 Ln1−O13 Ln1−O15 Zn1−O2 Zn1−O5 Zn2−O8 Zn2−O11 Zn2−O14 Zn1−O16 Zn1−N1 Zn1−N2 Zn2−N3 Zn2−N4 Zn1−O2−Ln1 Zn1−O5−Ln1 Zn2−O8−Ln1 Zn2−O11−Ln1 Zn1···Ln1 Zn2···Ln1 τ (Zn1, Zn2)b

9

10

11

2.811(5) 2.464(5) 2.490(5) 2.719(5) 2.787(5) 2.499(5) 2.504(6) 2.695(5) 2.449(5) 2.493(6) 2.091(5) 1.981(5) 2.053(5) 1.998(5) 1.983(5) 1.982(5) 2.042(6) 2.080(7) 2.086(8) 2.076(7) 101.20(17) 103.6(2) 101.73(17) 103.2(2) 3.5281(11) 3.5419(11) 0.593, 0.587

2.692(2) 2.455(2) 2.470(2) 2.781(3) 2.806(2) 2.506(2) 2.467(2) 2.695(2) 2.449(2) 2.435(2) 1.989(2) 2.067(3) 2.063(3) 2.001(2) 1.973(2) 1.988(2) 2.109(3) 2.037(3) 2.063(3) 2.101(3) 103.92(9) 101.05(9) 100.36(9) 103.48(9) 3.5118(5) 3.5207(5) 0.591, 0.608

2.686(6) 2.425(5) 2.464(6) 2.828(6) 2.679(6) 2.415(5) 2.435(6) 2.777(6) 2.384(5) 2.403(6) 2.000(5) 2.056(6) 1.984(5) 2.062(6) 1.986(6) 1.988(6) 2.087(8) 2.075(7) 2.099(8) 2.037(7) 103.4(2) 100.4(2) 104.0(2) 101.0(3) 3.4819(11) 3.4769(11) 0.620, 0.580

Ln1−O1 Ln1−O2 Ln1−O5 Ln1−O6 Ln1−O8 Ln1−O9 Ln1−O10 Ln1−O11 Ln1−O12 Zn1−O2 Zn1−O5 Zn1−O7 Zn1−N1 Zn1−N2 Zn1−O2−Ln1 Zn1−O5−Ln1 Ln1···Zn1 τ (Zn)b δc

12

13

2.6186(18) 2.3603(18) 2.3803(17) 2.607(2) 2.4095(18) 2.4437(18) 2.4215(18) 2.4337(17) 2.4781(19) 2.0228(17) 2.0301(18) 1.9901(19) 2.086(2) 2.121(2) 102.60(8) 101.70(8) 3.4273(5) 0.331 28.28(2)

2.602(5) 2.357(5) 2.362(5) 2.599(5) 2.402(4) 2.412(4) 2.473(4) 2.428(5) 2.420(5) 2.023(5) 2.037(5) 1.985(4) 2.076(6) 2.116(6) 102.2(2) 101.6(2) 3.4148(8) 0.323 28.12(15)

Distances (Å) and angles (deg). bFor τ values, see ref 73. cDihedral angle between ZnO(phenoxo)2 and LnO(phenoxo)2 planes. dDihedral angle between two pyridine rings of 4,4′-bipy. a

(CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 229 (1.195 × 105), 275 (6.28 × 104), 348 (1.72 × 104). For complex 7, clear dark yellow blocks. Yield: 0.058 g, 69%. Anal. Calcd for C46H44Gd2N12O30Zn2: C, 32.69; H, 2.62; N, 9.94%. Found: C, 32.59; H, 2.73; N, 9.80%. IR (cm−1, KBr): 2939 (w), 1608 (s), 1554 (w), 1467 (s), 1383 (s), 1319 (s), 1282 (s), 1240 (w), 1219 (s), 1099 (w), 1070 (s), 1037 (s), 970 (m), 943 (m), 918 (m), 848 (m), 813 (w), 792 (w), 740 (s), 630 (m), 559 (w), 524 (w). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 227 (8.51 × 104), 275 (4.14 × 104), 347 (1.07 × 104). For complex 8, clear light yellow blocks. Yield: 0.051 g, 60%. Anal. Calcd for C46H44Tb2N12O30Zn2: C, 32.62; H, 2.62; N, 9.92%. Found: C, 32.55; H, 2.70; N, 9.85%. IR (cm−1, KBr): 2943 (w), 1610 (s), 1554 (w), 1467 (s), 1384 (s), 1319 (s), 1282 (s), 1242 (w), 1219 (s), 1099 (w), 1070 (s), 1037 (s), 972 (w), 943 (m), 918 (w), 850 (m), 813 (w), 792 (w), 740 (s), 642 (w), 559 (w), 524 (w). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 228 (8.65 × 104), 275 (4.33 × 104), 349 (1.15 × 104). Syntheses of Complexes [{(ZnL)2Ln}2(bdc)2]·(NO3)2·2CHCl3 (Ln = Ce (9), Pr (10) and Sm (11·2CH3CH2OH)), 2∞[Zn(L)Ln(bdc)1.5] (Ln = Eu (12) and Gd (13·2CHCl3)). Complexes 9, 10, 12, and 13 were prepared by a similar procedure as for complexes 1−8, using H2bdc instead of 4,4′-bipy. A mixture of 3-MeOsalamo ligand H2L (0.018 g, 0.05 mmol), Zn(OAc)2·2H2O (0.011 g, 0.05 mmol), and Ln(NO3)3·6H2O (0.05 mmol) in chloroform and methanol (1:2 V/V, 3 mL) (chloroform and ethanol for 11) was stirred for 10 min at room temperature. Then, a solution of H2bdc (0.008 g, 0.05 mmol) in DMF (1 mL) was added dropwisely, and the mixture was kept stirring for another 10 min at room temperature. Then the mixture was filtered, and the filtrate was obtained. The crystals suitable for X-ray diffraction studies were obtained by vapor diffusion of diethyl ether into the filtrate for 4 days at room temperature. For complex 9, clear dark yellow blocks. Yield: 0.020 g, 61%. Anal. Calcd for C90H82Cl6Ce2N10O38Zn4: C, 40.54; H, 3.10; N, 5.25%.

Found: C, 40.50; H, 3.17; N, 5.18%. IR (cm−1, KBr): 2937 (m), 2839 (w), 1606 (s), 1556 (s), 1469 (s), 1381 (s), 1290 (s), 1242 (s), 1215 (s), 1168 (w), 1074 (s), 1045 (m), 976 (w), 939 (m), 918 (w), 852 (m), 827 (w), 781 (w), 739 (s), 615 (m), 536 (m), 514 (m). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 233 (1.01 × 105), 276 (4.06 × 104), 350 (1.37 × 104). For complex 10, clear dark yellow blocks. Yield: 0.021 g, 63%. Anal. Calcd for C90H82Cl6Pr2N10O38Zn4: C, 40.52; H, 3.10; N, 5.25%. Found: C, 40.48; H, 3.21; N, 5.19%. IR (cm−1, KBr): 2937 (m), 2839 (w), 1606 (s), 1556 (s), 1468 (s), 1384 (s), 1290 (s), 1242 (s), 1215 (s), 1170 (w), 1074 (s), 1045 (m), 976 (w), 939 (m), 921 (w), 852 (m), 827 (w), 781 (w), 739 (s), 615 (m), 536 (m), 514 (m). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 233 (1.012 × 105), 276 (4.06 × 104), 351 (1.37 × 104). For complex 11, clear dark yellow blocks. Yield: 0.020 g, 57%. Anal. Calcd for C94H94Cl6Sm2N10O40Zn4: C, 40.63; H, 3.41; N, 5.04%. Found: C, 40.57; H, 3.52; N, 5.10%. IR (cm−1, KBr): 2937 (m), 2839 (w), 1606 (s), 1558 (s), 1471 (s), 1383 (s), 1290 (s), 1244 (s), 1215 (s), 1170 (w), 1074 (s), 1043 (m), 977 (w), 939 (m), 920 (w), 852 (m), 829 (w), 783 (w), 740 (s), 617 (m), 538 (w), 516 (m). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 231 (5.11 × 104), 278 (2.90 × 104), 351 (0.82 × 104). For complex 12, clear light yellow blocks. Yield: 0.022 g, 53%. Anal. Calcd for C30H24EuN2O12Zn: C, 43.84; H, 2.94; N, 3.41%. Found: C, 43.78; H, 2.99; N, 3.37%. IR (cm−1, KBr): 2939 (w), 2843 (w), 1608 (s), 1545 (s), 1506 (m), 1465 (m), 1384 (s), 1298 (s), 1242 (m), 1219 (s), 1172 (w), 1076 (m), 1045 (w), 979 (w), 939 (m), 837 (m), 752 (s), 619 (w), 524 (m). UV−Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 233 (1.01 × 105), 276 (4.35 × 104), 350 (1.53 × 104). For complex 13, clear dark yellow blocks. Yield: 0.024 g, 50%. Anal. Calcd for C31H25Cl3GdN2O12Zn: C, 39.34; H, 2.66; N, 2.96%. Found: C, 39.38; H, 2.56; N, 2.88%. IR (cm−1, KBr): 2935 (w), 2852 (w), 1651 (m), 1608 (m), 1548 (s), 1504 (m), 1465 (m), 1384 (s), 1296 (m), 1244 (w), 1217 (m), 1171 (w), 1076 (m), 1045 (w), 1022 (w), E



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Figure 1. (a) Molecule structure and atom numberings of 1 (hydrogen atoms and solvent molecules are omitted for clarity). (b) Coordination polyhedron for ZnII and LnIII atoms of 1.

Figure 2. View of the supramolecular structures of 1 (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).

and 2 crystallize in the triclinic system, space group P1.̅ As the crystal structures of complexes 1 and 2 are similar, only the crystal structure of complex 1 is discussed in full detail. The reaction of two binuclear [Zn(L)La(NO3)3(CH3OH)] units and one 4,4′-bipy linker give rise to a discrete tetranuclear complex [{Zn(L)Ln(NO3)3(CH3OH)}2(4,4′-bipy)]·2CH3OH (Figure 1a), similar to the Salen-type [Zn2(salen)2Nd2(4,4′bipy)(NO3)6] complex.21 Two crystallographically equivalent [Zn(L)La] units are located in the inversion center and are joined by one 4,4′-bipy linker. Each ZnII atom adopts a squarepyramid configuration (τ = 0.126)73 (Figure 1b), where the equatorial coordination positions are comprised of N2O2 donor atoms of the tetradentate Salamo-type (L)2− moiety with the distances of Zn1−O2 = 2.032(3), Zn1−O5 = 2.024(3), Zn1− N1 = 2.063(4), and Zn1−N2 = 2.096(5) Å, and the axial

976 (w), 941 (w), 885 (w), 840 (m), 752 (s), 617 (w), 526 (m). UV− Vis (CH3OH), λmax (nm) [εmax (dm3 mol−1 cm−1)]: 231 (1.38 × 105), 276 (5.84 × 104), 349 (2.07 × 104).

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RESULTS AND DISCUSSION Complexes 1−13 were synthesized in MeOH−CHCl3 solution of H2L, Ln(NO3)3·6H2O, and Zn(OAc)2·2H2O in a 1:1:1 molar ratio, respectively, then followed by the addition of equimolar amount of 4,4′-bipy (1−8) or H2bdc (9−13) by one-pot method, respectively. Crystal Structures of [{Zn(L)Ln(NO3)3(CH3OH)}2(4,4′bipy)] (Ln = La (1·2CH3OH) and Ce (2)). The structures of two heterotetranuclear complexes 1 and 2 are given in Figures 1 and S1 (Supporting Information), respectively, and selected bond lengths and angles for complexes 1 and 2 are summarized in Table 3. The crystallographic data reveal that complexes 1 F



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graphically equivalent [Zn(L)Sm] moieties lie within the inversion center, and one 4,4′-bipy linker bridges the two ZnII atoms. It is interesting that the two pyridine rings of the 4,4′-bipy linker are non-coplanar possessing a larger dihedral angle (34.12(2)°) which is not found in Salen-type [Zn2(salen)2Nd2(4,4′-bipy) (NO3)6] complex.21 Each ZnII atom is positioned in a penta-coordinated sphere and has a distorted square pyramid (τ = 0.175),73 coordinated by the inner N2O2 core (O2, O5, N1, and N2) from deprotonated (L)2− moiety, and one terminal nitrogen (N3) atom from the coordinated 4,4′-bipy linker at the apical position. The bond lengths of Zn1−O2, Zn1−O5, Zn1−N1, Zn1−N2, and Zn1− N3 are 2.032(3), 2.035(3), 2.122(5), 2.036(4), and 2.063(4) Å, respectively. Each of SmIII atom, it is deca-coordinated and composed of the outer O4 cavity (O1, O2, O5, and O6) from deprotonated (L)2− unit and six oxygen atoms from three bidentate nitrate groups. The 10 Sm−O bond lengths (2.358(3) and 2.394(3) Å) from the phenolic oxygen atoms (O2 and O5) are a little shorter than those (2.590(4) and 2.592(4) Å or 2.466(4)−2.590(4) Å) from −OMe or nitrate groups, respectively. The ZnII···SmIII distance of complex 5 is 3.552(4) Å, a little longer than those of heterobinuclear ZnII− LnIII 3-MeOsalamo complexes reported earlier,65 where the apical position of ZnII atom is held by oxygen atoms from anions (OAc−), instead of nitrogen atoms from the 4,4′-bipy linker in complex 5. The dihedral angle between the O2−Zn1− O5 and O2−Sm1−O5 planes is 4.90(12)° which is smaller than that of complex 1. Moreover, the π···π contacts (Table S1, Supporting Information) are found in the complexes 3−8. As shown in Figure S10 (Supporting Information), the 3D supramolecular structure is formed by π···π stacking and C− H···O hydrogen bonding interactions in complex 5. Crystal Structures of [{(ZnL)2Ln}2(bdc)2]·(NO3)2·2CHCl3 (Ln = Ce (9), Pr (10), and Sm (11·2CH3CH2OH)). The crystal structures of the heterohexanuclear complex 11 are shown in Figure 4, and complexes 9 and 10 are given in Figures S7 and S8 (Supporting Information), respectively, and selected bond lengths and angles are summarized in Table 4, respectively. The crystallographic data reveal that complexes 9−11 crystallize in the triclinic system, space group P1̅. As the structures of complexes 9−11 are similar, only the structure of complex 11 is described in detail. The replacement of 4,4′-bipy bridge from 4,4′-bipy to H2bdc leads to a significant change in complex 11. By the reaction of H2L with zinc(II) acetate, samarium(III) nitrate, and H2bdc in a 1:1: 1:1 molar ratio, a heterohexanuclear complex based on the trinuclear [(ZnL)2Sm] moiety (Figure 4b) is formed: [{(ZnL) 2 Ln} 2 (bdc) 2 ]·(NO 3 ) 2 ·2CHCl 3 · 2CH3CH2OH (11) (Figure 4a). The heterohexanuclear complex is positively charge with the cations being counterbalanced by two uncoordinated NO3− ions. Two [(ZnL)2Sm] units are joined via two (bdc)2− linkers. Each carboxylato group serves as a bridge between the ZnII and SmIII atoms (the classical syn−syn bridging mode). Similar heterohexanuclear cationic [Zn4Nd2L4(bdc)2]20 and [Cu4Sm2L4(fum)2]75 have been obtained by using the Salen−type ligand and H2bdc or fumaric acid as linker. Within each [(ZnL)2Sm] moiety the distances between the metallic centers are Zn1···Sm1 = 3.4819(11) and Zn2···Sm1 = 3.4769(11) Å. The ZnII atoms (Zn1 and Zn2) assume a distorted trigonal bipyramidal coordination geometry (τ1 = 0.620 and τ2 = 0.580),73 in which the equatorial coordination positions are made up N2O2 donor atoms from (L)2− units. And the carboxylato oxygen atoms are held in the apical sites (for the ZnII atoms, the apical

position is held via a nitrogen atom of 4,4′-bipy with the distance of Zn1−N3 = 2.085(4) Å. The ZnII atom is deviated by 0.430(3) Å from the equatorial N2O2 plane toward the nitrogen atom of 4,4′-bipy linker. The coordination number of LaIII atom is 10, consisting of four oxygen atoms of two bidentate nitrate groups, one oxygen atom of monodentate nitrate group, two phenolato and two methoxy oxygen atoms of deprotonated (L)2− unit, and one oxygen atom of coordinated methanol molecule. Thus, the LaIII atom is in a decacoordinated environment and adopts a distorted bicapped square antiprism coordination geometry (Figure 1b). The La− O distances of three nitrate groups and one coordinated methanol molecule are in the range of 2.556(4)−2.697(4) Å (Table 3). The two methoxy oxygen and two phenolic atoms of (L)2− moiety coordinate to a LaIII atom, having the distances of La1−O1 = 2.686(4), La1−O2 = 2.507(3), La1−O5 = 2.506(3), and La1−O6 = 2.784(4) Å. Although the La−O distances from the methoxy oxygen atoms are longer than those from the phenolic oxygens, the bridging mode from the phenolic oxygen atoms assists in forming the binuclear structure. Because the dihedral angle between the planes of O2−Zn1−O5 and O2− La1−O5 is approximately 9.88(11)°, the bridging network, Zn−O2−La is not planar. Thorough investigation of the structure reveals that three 1D structures are formed by C−H··· O (nitrate O) hydrogen bonding interactions in complex 1. It can be seen that three 1D chains are firmly held by a threedimensional (3D) supramolecular network through C−H···O hydrogen bond interactions (Figure 2). The hydrogen bond parameters are summarized in Table S1 (Supporting Information). Crystal Structures of [{Zn(L)Ln(NO3)3}2(4,4′-bipy)] (Ln = Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), and Tb(8)). The crystal structures of the heterotetranuclear complex 5 is shown in Figure 3 and those of complexes 3, 4, and 6−8 are given in

Figure 3. Molecule structure and atom numberings of 1 (hydrogen atoms are omitted for clarity).

Figures S2−S6 (Supporting Information), and selected bond lengths and angles are summarized in Tables 3 (3−7) and 4 (8), respectively. The crystallographic data reveal that complexes 3−8 crystallize in the monoclinic system, space groups I2/c (3 and 5−7) and C2/c (4 and 8). The structures of complexes 3−8 are similar to those of complexes 1 and 2; however, they are different in the sense that one monodentate nitrate group and coordinated methanol molecule of LnIII atoms in complexes 1 and 2 are replaced by one bidentate nitrate group in complexes 3−8. As the structures of complexes 3−8 are similar, only the crystal structure of complex 5 is discussed in full detail. As given in Figure 3, two crystalloG



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Figure 4. (a) Molecule structure and atom numberings of 11. (b) View of the trinuclear cationic [(ZnL)2Sm] unit of 11 (hydrogen atoms and solvent molecules are omitted for clarity).

Figure 5. View of the 2D supramolecular structure of 11 showing the π···π stacking and C−H···π hydrogen bonding interactions.

2CHCl3 (Ln = Ce (9), Pr (10) and Sm (11·2CH3CH2OH)) and 2∞[Zn(L)Ln(bdc)1.5] (Ln = Eu (12) and Gd (13· 2CHCl3)). Complexes 9−11 are heterohexanuclear complexes, but complexes 12 and 13 are 2D coordination polymers with a brick-wall architecture (Figure 6c).75 The 2D structure of coordination polyhedron for ZnII and GdIII atoms of polymer 13 is shown in Figure 6d. And the 2D network topology structure of polymer 13 is shown in Figure 6e. Each [Zn(L)Gd] unit is joined by (bdc)2− linkers to three other heterobinuclear [Zn(L)Gd] moieties. Two of the three (bdc)2− linkers join the GdIII atoms from three [Zn(L)Gd] moieties, where each carboxylato group serves as a chelating agent. The GdIII atoms have distances of 11.325(4) and 12.081(4) Å. For the last (bdc)2− linker, each carboxylato group joins the ZnII and GdIII atoms present in the [Zn(L)Gd] building block (syn−syn bridging mode).75 The intranode Zn··· Gd distance is 3.4148(8) Å. The ZnII atoms show a distorted square pyramid (τ = 0.323),73 and the carboxylato oxygen atom in the apical site (Zn1−O7 = 1.985(4) Å) (Figure 6a). The GdIII atom is nona-coordinated, and the coordination polyhedron is a distorted tricapped trigonal prism (Figure 6b), consisting of four oxygen atoms from the deprotonated (L)2− moiety and five from the carboxylato groups. The Gd−O distances are in the range of 2.357(5)−2.602(5) Å (Table 4).

distances for Zn1−O14 and Zn2−O16 are 1.988(6) and 1.986(6) Å, respectively). The SmIII atoms are also in a decacoordinate sphere and adopt a distorted bicapped square antiprism, with eight oxygen atoms from two outer O4 sets of two deprotonated (L)2− units and two oxygen atoms from two (bdc)2− linkers. The 10 Sm−O bond lengths (2.415(5)− 2.464(6) Å) from the phenoxo oxygen atoms (O2, O5, O8, and O11) are slightly shorter than those (2.679(6)−2.828(6) Å) of −OMe groups (O1, O6, O7, and O12) but slightly longer than (2.384(5) and 2.403(6) Å)) of (bdc)2− linkers (Table 4). Moreover, the π···π contacts are found in complexes 9−11 (Table S1, Supporting Information). As shown in Figure 5, a 2D structure is formed by π···π stacking and C−H···π hydrogen bonding interactions in complex 11. Crystal Structures of 2∞[Zn(L)Ln(bdc)1.5] (Ln = Eu (12) and Gd (13·2CHCl3)). The structures of the 2D coordination polymers 12 and 13 are drawn in Figure S9 (Supporting Information) and Figure 6, respectively, and selected bond lengths and angles are summarized in Table 4. The data reveal that complexes 12 and 13 crystallize in the triclinic system, space group P1̅. As the structures of complexes 12 and 13 are similar, only the structure of complex 13 is described in full detail. Two kind of complexes were gotten via terephthalic acid (H 2 bdc) auxiliary ligand: [{(ZnL)2 Ln} 2 (bdc)2 ]·(NO 3 ) 2 · H



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Figure 6. (a) Projection of a fragment showing the binding modes of the (bdc)2− linkers in 13 (hydrogen atoms and solvent molecules are omitted for clarity). (b) Coordination polyhedron for GdIII atoms of 13. (c) Projection of the 2D structure of 13. (d) Projection of the 2D structure of coordination polyhedron for ZnII and GdIII atoms. (e) View of 2D network with (6, 3) topology.

Figure 7. UV-Vis and visible luminescence spectra (excitation at 350 nm) of H2L, 3, 5, 10, and 11 in CH3OH (1 × 10−5 M).

The bridging mode, Zn−O2−Gd is nonplanar, and the dihedral angle between the O2−Zn1−O5 and O2−Gd1−O5 planes is 28.12(15)°. The remaining data for 13 are summed in Table 4. Spectroscopic Studies. The luminescence characteristics of LnIII complexes are uniquely important because they could be potentially applied in materials and life sciences.76−80 Various complexes of EuIII and TbIII, that exhibit intense photoluminescence, have been widely explored. A lot of ZnII−

LnIII heterometallic complexes of Salen-type ligands are known to show a NIR or visible luminescence.18−28,81−83 As a result, we have studied the luminescence characteristics of heteromultinuclear ZnII−LnIII complexes 1−13. The UV−Vis absorption spectra and luminescence spectra of the free ligand H2L and complexes 3, 5, 10, and 11 in MeOH solution (1 × 10−5 M) at r.t. are shown in Figure 7 and Figures S11 and S12 (Supporting Information) for complexes 1, 2, 4, I



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Figure 8. Visible luminescence spectra of 5, 11, and NIR luminescence spectrum of 4 in the solid state with excitation at 350 nm.

In the luminescence spectra of [{Zn(L)Ln(NO3)3}2(4,4′bipy)] (Ln = Eu (6) and Tb(8)) and 2∞[Zn(L)Eu(bdc)1.5] (12) (Figure S12, Supporting Information), only a broad emission band at about 400−470 nm owing to intraligand fluorescence is observed instead of the f−f emission expected for EuIII and TbIII. In complexes 6 and 12, the emission from EuIII are quenched, and the intraligand fluorescence are also weak which may be a result of thermal quenching of the 5D0 level of EuIII by an intramolecular ligand-to-metal chargetransfer (LMCT) process.86 In complex 8, energy transfer from the ligand to the metal is not effective, possibly because the energy levels of the excited states of TbIII ion lies higher than that of the excited state of the [Zn(L)] unit. Thus, the (L)2− unit could selectively and effectively sensitized SmIII ion from among SmIII, EuIII, and TbIII ions, though these complexes usually show f−f luminescence.65 Moreover, visible luminescence measurements of complexes 3, 5, 6, 8, and 10−12 in the solid state are also conducted. As given in Figure 8 and Figure S13 (Supporting Information), the visible luminescence spectra of complexes 5 and 11 upon excitation at 350 nm show three characteristic emission peaks at ca. 564, 596, and 644 nm for SmIII ions. A small difference in relative intensities of complexes 5 and 11 (in the solid state other than in solution) shows that the directional close stacking of crystal molecules has a small effect on their luminescence. The luminescence decay curves of the 4G5/2 emitting level of ZnII−SmIII complexes 5 and 11 are monitored in the 4G5/2 → 6 H7/2 (596 nm) transition. The two luminescence decay curves (Figures S14 and S15, Supporting Information) can be fitted monoexponentially with time constants of microseconds (27.31 μs for 5 and 42.94 μs for 11), and the intrinsic quantum yields ΦSm (0.10% for 5 and 0.32% for 11) of the SmIII emissions in the solid state. The luminescence decays and quantum yields of heterohexanuclear complex 11 are larger than those of heterotetranuclear complex 5, which also indicates that higher nuclearity species could efficiently increase the luminescence properties of their complexes. Because SmIII complexes usually exhibit relatively weak f−f emission with short decays and small quantum yields,87 these value of complexes 5 and 11 are much lower than those of the luminous EuIII and TbIII complexes reported earlier.23,80 The NIR luminescence spectrum of complex [{Zn(L)Nd(NO3)3}2(4,4′-bipy)] (4) in the solid state upon excitation at 350 nm shows the characteristic emitting peaks at 874, 903,

6−9, 12, and 13, respectively. The free ligand H2L shows absorption bands at 223, 271, and 317 nm, which exhibits bathochromic-shift upon coordination with the metal ions in complexes 1−13. The UV−Vis spectra of complexes 1−13 are alike, showing a π−π* absorption band at about 350 nm. The visible luminescence spectra of complexes [{Zn(L)Sm(NO3)3}2(4,4′-bipy)] (5) and [{(ZnL)2Sm}2(bdc)2]·(NO3)2· 2CHCl3·2CH3CH2OH (11) upon excitation at 350 nm show three characteristic maximum emissions at 563, 596, and 643 nm (Figure 7). These emission peaks could be given to the transitions of 4G5/2 state to 6HJ (J = 5/2, 7/2, 9/2) which is common to SmIII ions. The transition at 563 nm, 4G5/2→6H5/2, has a predominantly magnetic dipole character, whereas the transition at 643 nm, 4G5/2→6H9/2, is mainly a hypersensitive transition. In addition, the spectra show a broad peak at around 395−460 nm, which was assigned to the intraligand fluorescence emission of (L)2−. The emission of SmIII ions is due to the effective sensitization of the [Zn(L)] unit and not by direct metal excitation. The broad emission at 395−460 nm also approves the effective energy transfer from the ligand to SmIII ions.65,81 Complexes 5 and 11 are determined under the same experimental conditions, but the relative emission intensities of complex 11 is more intense than those of complex 5. The relative emitting intensity at 596 nm is calculated to be 4.3 fold for complex 11 in CH3OH, because each central SmIII ion of complex 11 is incorporated by two chromophoric ligands and protected from solvent interactions compared to complex 5. Thus, complex 11 has excellent luminescence properties compared to complex 5.20 This fact indicates that the higher nuclearity species could efficiently increase the luminescent properties of their complexes.21 It is noteworthy that the ZnII ions in ZnII−SmIII complexes 5 and 11 could enhance fluorescence properties due to ZnII chelation, which can increase light absorption capability of the fluorophore and decrease the energy loss caused by the vibration of aliphatic chain.84 In the emission spectrum of complex [{(ZnL)2Pr}2(bdc)2]· (NO3)2·2CHCl3 (10), a strong emission at about 400−470 nm owing to intraligand emission is observed (Figure 7). Its weak emission band at 599 nm has been assigned to the transition of 1 D2→3H4;85 however, it is stronger than the heterotetranuclear [{Zn(L)Pr(NO3)3}2(4,4′-bipy)] (3), because the central PrIII of complex 10 is incorporated by four chromophoric ligands and protected from solvent interactions. J



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1059, and 1339 nm (Figure 8). These emission peaks were assigned to the 4F3/2 state to the 4IJ (J = 9/2, 11/2, 13/2) transitions typical of NdIII ions. Emissions near 874 and 903 nm are assigned to 4F3/2→4I9/2, near 1059 nm to 4F3/2→4I11/2 and near 1339 nm to 4F3/2→4I13/2 transitions.88 The ligand (L)2− serves as sensitizing agent for NdIII luminescence in the NIR region. The process of sensitization that results in luminescence has been proven to proceeds by the excitation of the organic ligand to its singlet excited state. The energy is then transferred to its triplet state by intersystem crossing, and then followed by energy transfer to the excited state of the LnIII ions to produce the luminescence.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86-931-4938703. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This project was funded by the National Natural Science Foundation of China (21361015).

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REFERENCES

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CONCLUSION A series of ZnII−LnIII heteromultinuclear complexes have been assembled by the one-pot method of H2L with zinc(II) acetate, lanthanide(III) nitrate and 4,4′-bipyridine or terephthalic acid. The assembly of two binuclear units [Zn(L)Ln] and one 4,4′bipyridine linker results in heterotetranuclear dimers 1−8. Heterohexanuclear complexes 9−11 have been constructed from trinuclear [(ZnL)2Ln] cationic moieties which are connected by (bdc)2− linker and two 2D coordination polymers 12 and 13 are also assembled by [Zn(L)Ln] units with (bdc)2− linker. The 3-MeOsalamo ligand (L)2− can effectively sensitize visible luminescence of SmIII and NIR luminescence of NdIII ions. The corresponding complexes containing other lanthanide(III) ions only exhibit blue emission owing to the ligand unit. Moreover, the higher nuclearity species could efficiently increase the luminescence properties of their complexes. An appropriate and selective linkers like 4,4′bipy and H2bdc derivatives could enhance the construction of a Salamo-type zinc(II)−lanthanide(III) complex possessing efficient luminescent properties. An intensive research regarding the syntheses and properties of polymetallic Salamo-type 3d−4f complex using the described linkers is now in progress.

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Article

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01067. The parameters of hydrogen bond and π···π interactions (Å, deg) for complexes 1 and 3−11. ORTEP drawing of the structures of complexes 2−4, 6−10, and 12. The supramolecular structures of complex 5. Electronic spectra of complexes 1, 2, 4, 6−9, 12, and 13 in CH3OH (1 × 10‑5 M). Emission spectra of complexes 1, 2, 4, 6−9, 12, and 13 in CH3OH (1 × 10−5 M), excitation (350 nm). Luminescence spectra of complexes 3, 6, 8, 10, and 12 in solid state upon excitation at 350 nm. Luminescence decay curve of complexes 5 and 11 in the solid state (PDF) Accession Codes

CCDC 1434623, 1434627−1434628, 1434633−1434634, and 1447921−1447922 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. K



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A Series of Heteromultinuclear Zinc(II)âLanthanide(III) Complexes

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