Lanthanoid Heteroleptic Complexes with Cucurbit[5]uril and

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Lanthanoid Heteroleptic Complexes with Cucurbit[5]uril and Dicarboxylate Ligands: From Discrete Structures to OneDimensional and Two-Dimensional Polymers Yingjie Zhang,*,† Santosh Panjikar,‡ Kai Chen,§ Inna Karatchevtseva,† Zhu Tao,# and Gang Wei⊥

Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF WINNIPEG on 12/18/18. For personal use only.

†

Nuclear Fuel Cycle Research Theme, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia ‡ Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia § Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, P. R. China # Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang, Guizhou 550025, P. R. China ⊥ CSIRO Manufacturing, P.O. Box 218, Lindfield, New South Wales 2070, Australia S Supporting Information *

ABSTRACT: Lanthanoid heteroleptic complexes with cucurbit[5]uril {Q[5]} and two dicarboxylate ligands, e.g., diglycolic acid (H2DGC) and glutaric acid (H2GT), have been investigated with six new compounds featuring a tetrametallic and dimetallic discrete structures, a one-dimensional (1D) polymer, and three two-dimensional (2D) polymers with a unique honeycomb-type topology being synthesized and structurally characterized. [La4(Q[5])3(DGC)2(NO3)2(H2O)12][La(DGC)(H2O)6]·7NO3·nH2O (1) has a tetrametallic structure constructed with three bis-bidentate Q[5] ligands linking two [La(DGC)(H2O)2]+ species in the middle and two [La(H2O)4(NO3)]2+ species at both ends. [Ce2(Q[5])(DGC)(NO3)(H2O)10]·3NO3·4H2O (2) has a dimetallic structure built up with a bis-bidentate Q[5] ligand linking [Ce(DGC)(H2O)3(NO3)] and [Ce(H2O)7]3+ on each side of the Q[5] portals. [Ce3(Q[5])3(DGC)2(H2O)9][Ce(DGC)(H2O)6]2·7NO3· nH2O (3) has a 1D polymeric structure built up with bis-bidentate Q[5] ligands in-turn linking one [Ce(H2O)6]3+ and two [Ce(DGC)(H2O)6]1+ cationic species. [Ln2(Q[5])2(GT)(H2O)6]·4NO3·nH2O [Ln = La (4), Ce (5) and Nd (6)] have similar 2D polymeric structures built up with two types of 9-fold coordinated Ln polyhedra linked by Q[5] via bis-bidentate carbonyl groups on both sides forming 1D chains which are further connected by bridging GT2− ligands to form 2D polymers with a unique honeycomb-type topology. Their vibrational modes and electronic structures have also been investigated. well-established3 while Q[n] complexes with transition metal ions are also available.4 However, the most exciting parts of the coordination chemistry of Q[n] are their complexes with lanthanoid (Ln3+) ions5 and tetravalent actinide (An4+) ions,6 demonstrating great complexities and perhaps unpredictable structural architectures. In addition, Q[n] can form slightly

1. INTRODUCTION The cucurbit[n]urils {Q[n]s} are a group of organic molecules, each containing a rigid hydrophobic macrocyclic cavity accessible via the two identical opposite portals rimmed with carbonyl groups.1 The pumpkin-shaped molecules with relatively large cavities can incorporate suitable guest molecules via host−guest and noncovalent interactions for catalysis reactions and selective molecular recognitions.2 Q[n] complexes with alkali and alkaline earth metal ions have been © XXXX American Chemical Society

Received: September 25, 2018

A

DOI: 10.1021/acs.inorgchem.8b02732 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Elemental analysis (calc., found) for C102H138N69O90La5·11H2O: C (26.27, 26.56), H (3.46, 3.28), and N (20.73, 21.05). 2.1.2. [Ce2(Q[5])(DGC)(NO3)(H2O)10]·3NO3·4H2O (2) and [Ce3(Q[5])3(DGC)2(H2O)9][Ce-(DGC)(H2O)6]2·7NO3·nH2O (3). Q[5] (10 mg, 1.0 mmol) was dissolved in 3.0 mL of DI water. Cerium nitrate hexahydrate (Ce: 434.3 mg; 1.0 mmol) and diglycolic acid (134.1 mg, 1.0 mmol) were dissolved in 3.0 mL of DI water and added to the above Q[5] solution. Diluted triethylamine was used to neutralize the solution to pH 6 (±0.1). A fine crystalline mixture of compound 2 (trace amounts in fine needles) and compound 3 (major in blocks) was formed in a few days with an overall ∼60% yield based on Q[5], which were collected and dried in air. Elemental analysis (calc., found) for separated compound 3 (C106H140N67O92La5·15H2O): C (26.55, 26.36), H (3.57, 3.69) and N (19.57, 19.05). 2.1.3. [Ln2(Q[5])2(GT)(H2O)6]·4NO3·nH2O [Ln = La (4), Ce (5) and Nd (6)]. Q[5] (10 mg, 1.0 mmol) was dissolved in 3.0 mL of DI water. The Ln nitrate hexahydrate [La: 433.1 mg; Ce: 434.3 mg; Nd: 438.4 mg; 1.0 mmol] and glutaric acid (132.2 mg, 1.0 mmol) were dissolved in 3.0 mL of DI water and added to the Q[5] solution. Diluted triethylamine was used to neutralize the solution pH to 6 (±0.1). Needle type crystalline products of compounds 4−6 were formed in a week, with 50−60% yields based on Q[5], which were collected and dried in air. Elemental analysis (calc., found) for compound 4 (C65H78N44O42La2·16.5H2O): C (28.67, 28.95), H (4.11, 3.97), and N (22.64, 22.86); compound 5 (C65H78N44O42Ce2· 10H2O): C (29.93, 30.28), H (3.79, 3.64), and N (23.64, 23.88); compound 6 (C65H78N44O42Nd2·13H2O): C (29.24, 29.05), H (3.92, 4.02), and N (23.08, 22.98). 2.2. Single Crystal and Powder X-ray Diffraction Studies. Single crystal data for compounds 1−6 were collected at 100 K on the MX1 beamline8 at the Australian Synchrotron employing silicon double crystal monochromated synchrotron radiation (0.71080 Å) with Blu-Ice software.9 Data integration and reduction were undertaken with XDS.10 Empirical absorption corrections were applied to the data using the program SADABS.11 The structures were solved by direct methods12 and refined with SHELXL-2014,13 and subsequent computations were carried out using the Olex2 graphical user interface.14 In general, non-hydrogen atoms with occupancies greater than 0.5 were refined anisotropically. Carbonand nitrogen-bound hydrogen atoms in Q[5], DGC2−, and GT2− units were included in calculated positions and refined using a riding model. Oxygen-bound hydrogen atoms for disordered water molecules were not included in the final structure refinements as the potential hydrogen bonds could not be resolved. All structures have solvent accessible voids due to the disorders of both nitrate anions and water molecules in the crystal lattices. Consequently, SQUEEZE function of PLATON15 was used to remove their contributions in the final structure refinements. In general, the ineffective absorption corrections due to the nature of very thin needle type crystals resulted in some ripples around Ln3+ metal ions. In addition, the single crystals for compounds 3−5 suffered serious radiation damage leading to some unexpected large Q-peaks close to C−H of Q[5] ligands. Potential hydrogen bonds were calculated using PLATON.15 Powder X-ray diffraction (XRD) patterns were collected on a PANalytical X’Pert Pro machine with Cu Ka radiation, in the range 5° < 2θ < 60°, with a step size of 0.02° (2θ) and an acquisition time of 2 s per step. 2.3. Scanning Electron Microscopy (SEM)/Energy-Dispersive X-ray Spectroscopy (EDS). A Zeiss Ultra Plus SEM (Carl Zeiss NTS GmbH, Oberkochen, Germany) operating at 15 kV equipped with an Oxford Instruments X-Max 80 mm2 SDD X-ray microanalysis system was used to check the crystal morphologies and determine the presence of key elements. 2.4. Raman Spectroscopy. Raman spectra were recorded on a Renishaw inVia spectrometer equipped with a 514 nm excitation Ar laser in the range of 2000−100 cm−1 with a spectral resolution of ∼1.7 cm−1. 2.5. UV−vis Absorption Spectroscopy. Absorption spectra were collected on an Agilent Cary 5000 spectrophotometer equipped

different complexes with Ln3+/An4+ ions, suggesting the real potential of using Q[n] for separations of Ln3+ and An4+ ions.5a,6 Unlike larger Q[n]s with rich host−guest chemistries, Q[5] has a relatively smaller portal size which reduces the possibility of forming host−guest complexes. However, Q[5] offers two sets of five portal carbonyl oxygen atoms which can form metal complexes through metal cap coordination by one set of five portal oxygen atoms.5a This makes it an interesting linker ligand especially for Ln3+ ions in some molecular assemblies. Several structural types of Q[5] complexes with Ln3+ ions are available: (1) monometallic with one cap, Sm−Q[5];5b (2) homo-dimetallic with double caps, Ln−Q[5]−Ln (Ln = La, Ce, Pr, and Nd);5n,v (3) homo-dimetallic with one cap and one side bonded by two carbonyl O atoms, Ln−Q[5]−Ln (Ln = La, Pr, Nd, and Gd);5o−q (4) homo-trimetallic, Sm−Q[5]− Sm−Q[5]−Sm;5b (5) a homo-trimetallic, Pr−Q[5]−(Pr)2,5p (6) a hetero-trimetallic complex with both K+ and Nd3+ cap coordinated on each side of the portals with additional nitrate bridging between a [Nd(NO3)4(H2O)3]− anion and K+ ion,5s (7) heterometallic double caps, Ln−Q[5]−K (Ln = La, Ce, Nd);5u (8) a hetero-tetrametallic, two Pr−Q[5] units bridged by two Ca2+ ions;5s (8) one-dimensional (1D) polymers, {Ln− Q[5]}n (Ln = La,5c Ce,5l and Yb5r) with Q[5] molecules linking Ln3+ ions through two carbonyl O atoms from each side in a bis-bidentate coordination mode. It seems that both discrete polymetallic structures and 1D polymers are quite common for Q[5] complexes with Ln3+ ions. Despite the current advances in Ln3+ ion complexes with Q[5], the heteroleptic system of Ln3+ ions with both Q[5] and dicarboxylate ligands has not been established. This has become the prime motivation for undertaking the current investigation. In this paper, we report the synthesis and characterization of six new heteroleptic compounds of Ln3+ ions with Q[5] and two dicarboxylate ligands, e.g., diglycolic acid (H2DGC) and glutaric acid (H2GT) shown in Figure 1

Figure 1. Line drawing structures of diglycolic acid (H2DGC) and glutaric acid (H2GT).

below, featuring a tetrametallic and a dimetallic structures, a 1D polymer and three 2D polymers with a unique hexagonal honeycomb-type topology. In addition, their vibrational modes and electronic structures have also been investigated.

2. EXPERIMENTAL SECTION 2.1. Materials and Synthesis. Q[5] was prepared with the reported method.7 Other chemicals in A.R. grade were purchased from Sigma-Aldrich and used without further purification. 2.1.1. [La4(Q[5])3(DGC)2(NO3)2(H2O)12][La(DGC)(H2O)6]·7NO3· nH2O (1). Q[5] (10 mg, 1.0 mmol) was dissolved in 3.0 mL of deionized (DI) water. Lanthanum nitrate hexahydrate (433.1 mg; 1.0 mmol) and diglycolic acid (134.1 mg, 1.0 mmol) were dissolved in 3.0 mL of DI water and added to the above Q[5] solution. Diluted triethylamine was used to neutralize the solution to pH 6 (±0.1). Fine needle crystalline product of compound 1 was formed in a week, with 74% yield based on Q[5], which was collected and dried in air. B


Article

Inorganic Chemistry Table 1. Crystal Data and Refinement Details for Compounds 1−6 compounds

compound 1

compound 2

compound 3

formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z/dcalcd (g cm−3) μ (mm−1)/F(000) reflns/indep Rint/params S R1a/wR2b SAV (Å−3) electrons in SAV compounds

C53H72N30.5O38La2.5 2091.69 monoclinic C2 24.067(5) 14.673(3) 27.462(6) 90 111.13(3) 90 9046(4) 4/1.536 1.260/4199 57210/15894 0.0824/1146 1.043 0.0770/0.1964 1908 399 compound 4

C34H62.5N24 O41.5Ce2 1751.82 triclinic P1̅ 13.050(3) 13.760(3) 18.270(4) 89.42(3) 87.41(3) 65.57(3) 2983.8(13) 2/1.950 1.639/1765 55448/10429 0.0476/918 1.023 0.0528/0.1288

compound 5

C106H144N61O80Ce5 4253.41 triclinic P1 14.120(3) 14.150(3) 28.000(6) 84.84(3) 79.96(3) 61.91(3) 4860(2) 1/1.453 1.247/2137 69006/31513 0.0365/2176 1.041 0.0613/0.1602 1442 706 compound 6

C65H89N41O39Ce2 2349.01 triclinic P1̅ 14.680(3) 16.200(3) 24.530(5) 103.61(3 95.89(3) 105.89(3) 5365(2) 2/1.454 0.935/2388 143840/18911 0.0994/1325 1.166 0.1208/0.31114 1455 259

C65H90N41O39Nd2 2358.26 triclinic P1̅ 14.628(3) 16.134(3) 24.547(5) 103.54(3) 95.79(3) 106.03(3) 5328(2) 2/1.470 1.061/2398 30063/15526 0.0316/1311 1.139 0.0702/0.1640 1440 379

formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z/dcalcd (g cm−3) μ (mm−1)/F(000) reflns/indep Rint/params S R1a/wR2b SAV (Å−3) electrons in SAV

C65H104N42.5O58.5La2 2694.72 triclinic P1̅ 14.940(3) 16.550(3) 26.220(5) 76.06(3) 76.83(3) 72.90(3) 5927(2) 2/1.510 0.822/2747 156534/20865 0.0418/1577 1.090 0.0987/0.2497

R1 = Σ∥Fo| − |Fc∥/|Fo|. bwR2 = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]}1/2..

a

of Q[n] complexes with Ln3+ ions via cation−anion interactions. However, the synthesis of heteroleptic complexes involving dicarboxylic acids is quite different as the deprotonation of dicarboxylic acids is necessary. In the syntheses of compounds 1−6, the control of solution pHs is crucial, and the desired products form at solution pHs ≈ 6, where H2DGC and H2GT are primarily deprotonated and present as DGC2− and GT2− anions. Lower solution pHs (2− 5) lead to the formation of homoleptic Ln3+−Q[5] complexes with 1D polymeric structures, comparable to those reported earlier.5a Similarly, the Ln3+ ions from Nd3+ to Ho3+ under the similar synthesis conditions for compounds 1−3, and the synthesis conditions for compounds 4−6 also form the homoleptic Ln3+−Q[5] complexes with 1D structures. When solution pHs are over 7, no mature crystalline products were positively identified. SEM-EDS examinations of the crystalline products confirmed the crystal morphologies with most of them in needle shapes and the presence of C, N, O, and La in compounds 1

with a Labsphere Biconical Accessory. Spectra were referenced to that of a Labsphere certified standard (Spectralon) and transformed into Kubelka−Munk units, F(R) = (1 − R)2/2R.16

3. RESULTS AND DISCUSSION 3.1. Synthesis and General Characterizations. The choice of the two secondary linker ligands is based on the consideration that H2DGC (pK1 = 2.79 and pK2 = 3.93 at 20 °C) acts mainly as a nonbridging tridentate dicarboxylate ligand, while H2GT (pK1 = 4.13 and pK2 = 5.03 at 20 °C) is a typical bridging dicarboxylate ligand. They form a good pair of comparison to encourage structural diversities in the chosen heteroleptic systems. Note most of the Q[n] complexes with Ln3+ ions were synthesized by the direct reactions of Q[n] and Ln3+ ions in HCl solutions often with added transition metal chlorides as structure directing agents.5a There are two reasons for choosing such an approach. First, Q[n]s are very stable in acidic solutions. Second, HCl will aid the formation of various transition metal chloride species to facilitate the crystallization C


Article

Inorganic Chemistry Table 2. Ln−O Bond Lengths (Å) for Compounds 1−6 compound 1 La1−O1 La1−O26 La2−O6 La2−O12 La2−O25 La3−O35 La3−O39

2.68(3) 2.47(4) 2.493(11) 2.519(12) 2.495(12) 2.514(16) 2.623(14)

La1−O2 La1−O27 La2−O7 La2−O19 La3−O30 La3−O36 La3−O40

2.51(4) 2.63(3) 2.603(12) 2.551(11) 2.568(14) 2.58(2) 2.516(17) compound

Ce1−O1 Ce1−O10 Ce1−O29 Ce2−O21 Ce2−O25

2.524(5) 2.522(4) 2.499(6) 2.463(5) 2.490(5)


2.577(5) 2.506(4) 2.524(4) 2.578(5) 2.487(6) compound

3

Ce1−O1 Ce1−O7 Ce1−O38 Ce2−O6W Ce2−O16 Ce3−O23 Ce3−O29

2.494(9) 2.487(11) 2.525(9) 2.445(12) 2.458(11) 2.483(10) 2.526(11)

Ce1−O1W Ce1−O8 Ce2−O3W Ce2−O12 Ce2−O22W Ce3−O24 Ce3−O30

2.468(10) 2.568(9) 2.466(11) 2.507(11) 2.505(14) 2.483(9) 2.469(9) compound

La1−O1 La1−O3W La1−O19 La2−O9 La2−O20

2.513(6) 2.519(7) 2.554(6) 2.512(6) 2.570(6)

La1−O1W La1−O11 La2−O4W La2−O10 La2−O24

2.498(6) 2.561(7) 2.500(6) 2.521(6) 2.477(6) compound


2.555(12) 2.504(10) 2.506(12) 2.495(10) 2.506(12)


2.557(12) 2.457(10) 2.560(12) 2.489(10) 2.465(11) compound

Nd1−O1 Nd1−O16 Nd1−O30 Nd2−O13 Nd2−O26

2.460(6) 2.534(7) 2.432(6) 2.517(6) 2.421(6)

Nd1−O3 Nd1−O18 Nd2−O5 Nd2−O14 Nd2−O27

2.456(6) 2.549(6) 2.471(6) 2.511(7) 2.479(6)

La1−O4 La1−O28 La2−O8 La2−O21 La3−O31 La3−O37

2.559(19) 2.63(4) 2.556(12) 2.520(12) 2.446(16) 2.623(11)

La1−O5 La1−O29 La2−O10 La2−O24 La3−O33 La3−O38

2.44(2) 2.42(5) 2.549(11) 2.481(12) 2.486(15) 2.580(13)

2.537(5) 2.486(4) 2.521(4) 2.506(5)

Ce1−O8 Ce1−O28 Ce2−O20 Ce2−O24

2.435(5) 2.549(5) 2.489(5) 2.572(5)

Ce1−O2 Ce1−O9 Ce2−O4W Ce2−O13 Ce3−O7W Ce3−O25 Ce3−O31 4

2.509(10) 2.532(10) 2.522(15) 2.571(11) 2.451(9) 2.548(9) 2.501(8)

Ce1−O2W Ce1−O37 Ce2−O5W Ce2−O15 Ce3−O8W Ce3−O27

2.451(10) 2.541(9) 2.484(15) 2.684(13) 2.481(10) 2.558(10)

La1−O2 La1−O12 La2−O5W La2−O13

2.519(6) 2.588(7) 2.494(7) 2.617(7)

La1−O2W La1−O15 La2−O6W La2−O14

2.519(6) 2.476(6) 2.528(7) 2.567(6)

2.503(10) 2.508(11) 2.554(12) 2.586(10)

Ce1−O9 Ce1−O29 Ce2−O6 Ce2−O25

2.490(10) 2.459(12) 2.441(10) 2.467(12)

2.407(6) 2.434(6) 2.459(6) 2.420(6)

Nd1−O15 Nd1−O29 Nd2−O12 Nd2−O25

2.516(6) 2.464(6) 2.480(6) 2.462(6)

2 Ce1−O6 Ce1−O27 Ce2−O16 Ce2−O23

5 Ce1−O5 Ce1−O28 Ce2−O4 Ce2−O17 6 Nd1−O11 Nd1−O28 Nd2−O6 Nd2−O17

and 4; C, N, O, and Ce in compounds 3 and 5; and C, N, O and Nd in complex 6 (Figures S1−S5, Supporting Information). PXRD patterns of compounds 1 and 6 (Figure S6, Supporting Information) are consistent with the patterns calculated from their single crystal data, confirming the purity of the crystalline products obtained. The lack of XRDs at wide angles (2θ > 25°) is in agreement with the extensive solvent disorders in the large solvent accessible voids. 3.2. Structure Descriptions. The crystal data and structural refinement details for compounds 1−6 are summarized in Table 1, and the selected bond lengths are listed in Table 2. The structure of compound 1 contains a La heteroleptic tetramer (Figure 2) constructed by three bisbidentate Q[5] ligands linking four La3+ species, two hydrated DGC2− species {[La(DGC)(H2O)6]+} in the middle and two hydrated nitrate species {[La(NO3)(H2O)4]2+} at both ends, and an isolated {[La(DGC)(H2O)6]+} in the crystal lattice, charge balanced by nitrate anions. La1 has an 8-fold coordination environment with a bidentate Q[5] ligand

Figure 2. Structure of compound 1: a tetramer {La(NO3)(H2O)4Q[5]-La(DGC)(H 2 O) 2 -Q[5]-La(DGC)(H 2 O) 2 -Q[5]-La(NO 3 )(H2O)4}6+ and a [La(DGC)(H2O)6]+ cationic unit, charge balanced with nitrate anions (nitrate anions, lattice water molecules, and hydrogen atoms are omitted for clarity), La in bright green sphere, C in gray, N in blue, and O in red sticks.

[2.44(2)−2.559(19) Å for La−OQ[5]], four coordinated water molecules [2.42(5)−2.63(3) Å for La−OH2O] and a D


Article

Inorganic Chemistry

and Table S1, Supporting Information). Extensive intermolecular hydrogen bonds are among coordinated and lattice water molecules, carbonyl oxygen atoms from Q[5] and nitrate anions leading the monomeric structure into three dimensions (Figure S8b and Table S1, Supporting Information). Compound 3 has a 1D undulating heteroleptic polymeric structure (Figure 4) constructed by bis-bidentate Q[5] ligands in-turn linking one [Ce(H2O)5]3+ and two {[Ce(DGC)(H2O)2]+}, with separate [Ce(H2O)9]3+ in the crystal lattice, charge balanced by nitrate anions. The sub-building unit in the structure of compound 3 is quite similar to the asymmetric unit of compound 1 with one [Ce(H2O)5]3+ and two {[Ce(DGC)(H2O)2]+} which are connected with bis-bidentate Q[5] ligands forming 1D undulating polymers. Ce1 and Ce3 have similar 9-fold coordination environments, with two bidentate Q[5] ligands [2.483(10)−2.541(9) Å for Ce− OQ[5]], a tridentate DGC2− anion [2.487(11)−2.568(9) Å for Ce−ODGC] and two coordinated water molecules [2.451(10)− 2.481(10) Å for Ce−OH2O]. Ce2 is 9-fold coordinated with two bidentate Q[5] ligands [2.458(11)−2.684(13) Å for Ce− OQ[5]] from both sides and five coordinated water molecules [2.445(12)−2.522(15) Å for Ce−OH2O]. Both Ce4 and Ce5 are 8-fold coordinated [Ce(DGC)H2O)6]3+ species. The Ce− Ce distances in the 1D polymers are 10.842(15) Å for Ce1− Ce2, 10.325(15) Å for Ce2−Ce3, and 10.823(15) Å for Ce3− Ce1 with Ce−Ce−Ce angles of 115.77(15)° for Ce1−Ce2− Ce3, 142.13(15)° for Ce2−Ce3−Ce1, and 136.07(15)° for Ce3−Ce1−Ce2. Intramolecular hydrogen bonds are between coordinated water molecules and carbonyl oxygen atoms from Q5 (Figure S9a and Table S1, Supporting Information). The coordinated water molecules in [Ce(H2O)9]3+ species are hydrogen bonded to the nearby carbonyl O atoms of Q[5] and coordinated water molecules leading the 1D polymer into three dimensions (Figures S9b−c and Table S1, Supporting Information). Compounds 4−6 [4 (La), 5 (Ce), and 6 (Nd)] have similar 2D polymeric structures [Figures S10a (4) and S10c (5), Supporting Information and Figure 5a (6)] with a honeycombtype topology [Figures S10b (4) and S10d (5), Supporting Information and Figure 5b (6)]. Both Ln3+ ions in the asymmetric units are 9-fold coordinated by two bidentate Q[5] ligands from opposite directions, a bidentate carboxylate group from GT2− ligand and three coordinated water molecules forming 1D zigzag chains via Q[5] as linear ligands, further linked with bridging GT2− ligands to form the 2D polymers. Intramolecular hydrogen bonds are mainly between coordinated water molecules and carbonyl oxygen atoms from Q5 [Figure S11a (6) and Table S1, Supporting Information]. Both intra- and intermolecular hydrogen bonds are among coordinated and lattice water molecules, carbonyl oxygen

bidentate nitrate anion [2.51(4) and 2.68(3) Å for La−ONO3]. La2 is 9-fold coordinated with two bis-bidentate Q[5] ligands [2.493(11)−2.551(11) Å for La−OQ[5]] from each side, a chelating DGC2− anion [2.549(11)−2.603(12) Å for La− ODGC] and two coordinated water molecules [2.481(12) and 2.495(12) Å for La−OH2O]. La3 is a 9-fold coordinated La− DGC hydrate species with a tridentate DGC2− anion [2.446(16)−2.568(14) Å for La−ODGC] and six coordinated water molecules [2.514(16)−2.623(14) Å for La−OH2O]. The La−La distances within the tetramer are 10.831(15) Å for La1−La2 and 10.060(15) Å for La1−La1 with a La1−La2− La2 angle of 132.62(14)°. Some coordinated water molecules form intramolecular hydrogen bonds with carbonyl oxygen atoms from Q[5] ligands (Figure S7a and Table S1, Supporting Information). The intermolecular hydrogen bonds among coordinated water molecules from {[La(DGC)(H2O)6]+} species and carbonyl oxygen atoms from both Q[5] and DGC2− lead the tetramers into 2D layers on the a−b plane (Figures S7b−c and Table S1, Supporting Information). Compound 2 has a Ce heteroleptic dimetallic structure with a bis-bidentate Q[5] ligand linking [Ce(DGC)(NO3)(H2O)3] and [Ce(H2O)7]3+ species on the opposite portal sides (Figure 3). Ce1 is 9-fold coordinated with a bidentate Q[5] ligand

Figure 3. Structure of compound 2: a heteroleptic dimetallic cationic unit {Ce(DGC)(NO3)(H2O)3-Q[5]-Ce(H2O)7}3+ charge balanced with nitrate anions (nitrate anions, lattice water molecules and hydrogen atoms are omitted for clarity), Ce in turquoise sphere, C in gray, N in blue, and O in red sticks.

[2.506(4)−2.522(4) Å for Ce1−OQ[5]], a chelating DGC2− anion [2.435(5)−2.577(5) Å for Ce1−ODGC], three coordinated water molecules [2.486(4)−2.549(5) Å for Ce1−OH2O)] and a monodentate NO3− anion [2.524(5) Å for Ce1−ONO3] making it charge neutral. Ce2 also has a 9-fold coordination environment with a bidentate Q[5] ligand [2.521(4)− 2.524(4) Å for Ce2−OQ[5]] and seven coordinated water molecules [2.463(5)−2.578(5) Å for Ce2−OH2O]. Intramolecular hydrogen bonds are between coordinated water molecules and carbonyl oxygen atoms from Q5 (Figure S8a

Figure 4. Structure of compound 3: a 1D undulating cationic polymer {[Ce(H2O)5-Q[5]-Ce(DGC)(H2O)2-Q[5]-Ce(DGC)(H2O)2]5+-Q[5]}n and [Ce(DGC)H2O)6]3+ cationic units, charge balanced with nitrate anions ([Ce(DGC)H2O)6]3+, nitrate anions, lattice water molecules, and hydrogen atoms are omitted for clarity), Ce in turquoise sphere, C in gray, N in blue, and O in red sticks. E


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Figure 5. Structure of compound 6: Nd3+ ions are linked by bis-bidentate Q[5] ligands forming zigzag 1D polymers which are further connected by GT2− anions to form 2D sheets (a) and the honeycomb-type topology (b) with Nd3+ ions in green spheres, C in gray, N in blue, O in red sticks, Q[5] in pink, and GT2− in orange bars (b).

errors with the average bond length values, such a contraction trend is fairly weak. In addition, the Ln−Ln distances are also reduced from 9.709(7) Å for compound 4 to 9.574(12) for compound 5 and 9.532(6) for compound 6. The Ln−Ln−Ln angles are quite similar for compounds 4−6 ranging from 102.7(2)° to 134.0(2)° with the average angle of 119(±1)°, close to the ideal 120° for the hexagon. 3.3. Structural Discussion. It can be inferred from the solid structures of compounds 1−3 that several Ln3+ species exist in the reaction system with the presence of DGC2− anions, e.g., hydrated species [Ln(H2O)n]3+ (A), hydrated nitrate species [Ln(NO3)(H2O)6]2+ (B), hydrated DGC2− species [Ln(DGC)(H2O)6]+ (C) and hydrated DGC2− nitrate neutral species [Ln(DGC)(NO3)(H2O)3] (D). Q[5] acts as bis-bidentate ligand linking: (1) B and C to form the tetrametallic structure in compound 1; (2) A and D to form a dimetallic unit in compound 2; (3) A and C to form a 1D undulating polymer in compound 3. It seems that the nitrate coordinated species (B and D) have stopped Ln3+ ions further linking with Q[5] ligands in the cases of compounds 1 and 2, highlighting the complexity in the chosen heteroleptic system when nitrate anions are also present. It is anticipated that other potential nonbridging oxygen donor ligands may also involve in the formation of Ln3+ heteroleptic complexes with Q[5] to form polynuclear discrete complexes similar to compounds 1 and 2 or 1D polymers similar to compound 3. Several types of polymetallic discrete complexes of Q[5] with Ln3+ ions were previously reported including a homotrimetallic (Sm−Q[5]−Sm−Q[5]−Sm),5b a hetero-trimetallic with both K+ and Nd3+ cap coordinated on each side of the portals with additional nitrate bridging between a [Nd(NO3)4(H2O)3]− anion and K+ ion,5s a hetero-trimetallic (Pr−Q[5]− Pr2),5p and a hetero-tetrametallic (two Pr−Q[5] units bridged by two Ca2+ ions).5s However, compound 1 possesses a tetrametallic structure representing a different structure type with the additional coordinated nonbridging DGC as the secondary ligand. As for Ln3+ dimetallic discrete complexes with Q[5], homodimetallic Ln3+ complexes of Q[5] with one cap and one side bonded by two carbonyl O atoms {Ln− Q[5]−Ln (Ln = La, Pr, Gd, and Nd)}5o−q are common. With the additional coordinated nonbridging DGC, compound 2 displays a Ce heteroleptic dimetallic discrete structure with a bis-bidentate Q[5] ligand linking [Ce(DGC)(NO3)(H2O)3] and [Ce(H2O)7]3+ species on the opposite portal sides. Such a

atoms from Q[5] and nitrate anions [Figure S11b (6) and Table S1, Supporting Information]. The coordination environments of Ln3+ ions including Ln−O bond lengths, Ln−Ln distances, and Ln−Ln−Ln angles for compounds 4−6 are summarized in Table 3. The three sets of mean Ln−O (Ln− Table 3. Ln−O, Ln−Ln Distances (Å) and Ln−Ln−Ln Angles (deg) for Compounds 4−6 compounds (Ln) Ln−OQ[5] (Å) mean Ln−OQ[5] (Å) Ln−OGT (Å) mean Ln−OGT (Å) Ln−OH2O (Å) mean Ln−OH2O (Å) overall mean Ln−O (Å) Ln−Ln (Å) mean Ln−Ln (Å) Ln−Ln−Ln (deg) mean Ln−Ln−Ln (deg)

compound 4 (La)

compound 5 (Ce)

compound 6 (Nd)

2.476(6) −2.570(6) 2.518(6)

2.441(10) −2.586(10) 2.496(10)

2.407(6) −2.549(6) 2.463(6)

2.561(7) −2.617(7) 2.583(7)

2.554(12) −2.560(12) 2.556(12)

2.511(7) −2.534(7) 2.519(7)

2.494(7) −2.528(7) 2.510(7)

2.459(12) −2.508(11) 2.485(12)

2.421(6) −2.479(6) 2.448(6)

2.530(7)

2.506(12)

2.470(6)

8.770(7) −10.291(7) 9.709(7)

8.466(12) −10.271(12) 9.574(12)

8.478(6) −10.200(6) 9.532(6)

102.93(19) −134.23(19) 119.99(19)

102.73(17) −134.03(17) 119.79(17)

102.72(19) −134.38(19) 119.82(19)

OQ[5], Ln−OGT, and Ln−OH2O) bond lengths are reduced along the lanthanide series: (1) mean Ln−OQ[5] bond lengths from 2.518(6) Å for compound 4 to 2.496(10) for compound 5 and 2.463(6) for compound 6; (2) mean Ln−OGT bond lengths from 2.583(7) Å for compound 4 to 2.556(12) for compound 5 and 2.519(7) for compound 6; (3) mean Ln− OH2O bond lengths from 2.510(7) Å for compound 4 to 2.485(12) for compound 5 and 2.448(6) for compound 6. Consequently the overall mean Ln−O bond lengths are reduced from 2.530(7) Å for compound 4 to 2.506(12) for compound 5 and 2.470(6) for compound 6, reflecting the lanthanide contraction along the series. Considering systematic F


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Inorganic Chemistry

coordination mode of Q[5] has been observed in compounds 1−6 in the current study. This may result from the very similar synthesis conditions in near neutral aqueous solutions. 3.4. Vibrational Spectroscopy. Raman spectroscopy has been successfully used to investigate the systematic trend of vibration modes in Q[n]s.17 Raman spectra of compounds 1 and 3 (Figure 6) and compounds 4−6 (Figure 7) revealed the

new dimetallic discrete structure type has not been observed before. Earlier work5a has also demonstrated that Q[5] can react with Ln3+ ions in HCl solutions to form 1D polymers. It is of interest to compare the two types of 1D polymers, homoleptic Ln−Q[5] and heteroleptic {Ln−Q[5]−DGC}, to examine the effect of coordinated DGC on the formation of the 1D polymer in the heteroleptic system. The Ce coordination environments including Ce−O and Ce−Ce distances, and Ce−Ce−Ce angles in the two types of 1D polymer are summarized in Table 4. Both 1D polymers have Table 4. Comparison of 1D Polymers in Compound 3 and a Ce−Q[5]5l compounds

compound 3

Ce−Q[5]

Ce−OQ[5] (Å) mean Ce−OQ[5] (Å) Ce−ODGC (Å) mean Ce−ODGC (Å) Ce−OH2O (Å)

2.483(10)−2.684(13) 2.516(13) 2.487(11)−2.568(9) 2.536(11) 2.445(12)−2.522(15)

2.496(3)-2.607(4) 2.552(4)

mean Ce−OH2O (Å)

2.475(15)

2.502(4)

overall mean Ce−O (Å) Ce−Ce distance (Å) mean Ce−Ce distance (Å) Ce−Ce−Ce (deg) mean Ce−Ce−Ce (deg)

2.506(15) 10.325(15)−10.842(15) 10.663(15) 115.77(15)−142.13(15) 131.3(15)

2.524(4) 10.451(8)

2.450(3)−2.562(4)

135.71(8)

Figure 6. Raman spectra of compounds 1 (a) and 3 (b).

similar Ce−Ce distances and Ce−Ce−Ce angles suggesting quite similar 1D polymer shapes. However, the coordination of DGC instead of water molecules on Ce3+ ions makes the heteroleptic 1D polymer more stable with relatively shorter Ce−OQ[5] and Ce−OH2O bond lengths compared to the homoleptic Ln−Q[5] 1D polymer without coordinated DGC anions. It seems to imply that the coordination of nonbridging DGC on Ce3+ ions may have some effects on the local Ce coordination spheres. However, no obvious effect on the structure type has been observed. The coordination environments of Ln3+ ions involving DGC2− or GT2− in compounds 1−6 are summarized in Figure S12, Supporting Information File. As expected, DGC2− acts as a tridentate nonbridging ligand in compounds 1−3, while GT2− acts as a bridging dicarboxylate ligand in compounds 4− 6. It is apparent that the addition of H2GT does not encourage the formation of Ln3+ heteroleptic complexes unless H2GT is deprotonated and present as GT2− anions in the reaction system. In contrast to DGC2−, the incorporation of GT2− anions results in the formation of 2D polymers by linking Ln− Q[5] 1D polymers with GT2− anions in compounds 4−6. In fact, the current approach provides a new strategy to synthesize 2D polymers with Q[5] as a bridging ligand. By carefully selecting suitable dicarboxylic acids and reaction conditions, the formation of other types of 2D polymers in the heteroleptic systems involving Q[5] is perhaps possible. Further work with the incorporation of other dicarboxylate ligands, such as longer alkyl chains or phenyl groups, may encourage the formation of lanthanoid heteroleptic polymers with greater complexity. As a potential multidentate bridging ligand, several different Q[5] coordination modes have been identified in Q[5] complexes with Ln3+ ions:5a (1) one cap [η5 η0]]; (2) bicap [η5 η5]; (3) one cap and bidentate [η5 η2]; (4) bis-bidentate [η2 η2]; (5) one cap and two bidentate [η5 η4]; (6) one cap and tridentate [η5 η3]. However, only bis-bidentate [η2 η2]

Figure 7. Raman spectra of compounds 4 (a), 5 (b), and 6 (c).

three major signature vibrations of Q[5] due to R5 ring deformations, e.g., two strong Raman bands at 455−457 cm−1 and 829−831 cm−1, and a band of medium intensity at around 887−889 cm−1. Both strong vibrational modes have slightly shifted to higher wavenumbers upon coordination to Ln3+ ions, from 452 cm−1 {Q[5]} to 455−457 cm−1 for σ(N−C−N) and from 826 cm−1 {Q[5]} to 829−831 cm−1 for δ(C−N−C) band, respectively. Such minor shifts to higher wavenumbers indicate the formations of slightly more inelastic Q[5] upon coordinating to Ln3+ ions. However, the shifts are generally very subtle compared to those Q[5] complexes with tetravalent actinide ions (Th4+/U4+),6 reflecting the relatively lower charge densities of Ln3+ ions compared to their tetravalent actinide counterparts. In addition, strong νs (NO3) vibrations at ∼1040 cm−1 were also observed, consistent with the presence of G


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properties enabling further investigation into their potential applications.

nitrate anions in all compounds 1−6. The presence of DGC or GT is evident with νas (COO) vibrations observed in the region 1639−1697 cm−1. Furthermore, the Raman band of medium intensity located at 960−965 cm−1 has been assigned to the ester (C−O−C) group vibrations within DGC in compounds 1 and 3 (Figure 6). Detailed Raman band assignments for compounds 1−6 are available in Tables S2− S3, Supporting Information. 3.5. Electronic Structures. The electronic structures of compounds 1 and 3−6 have been investigated with optical absorption spectroscopy in the UV−vis region with their UV− vis absorption spectra shown in Figure S13 (compounds 1 and 3−6), Supporting Information. In general, ligand charge transfer (LC) of Q[5] and DGC/GT contributes to the strong absorption bands in the far UV region, e.g. bands at 224 and 228 nm for compounds 1 and 3, ∼232 nm for compounds 4−6. Metal-to-ligand charge-transfer (MLCT) bands at 268− 304 nm can be detected for all complexes. In addition, some weak absorption bands in the region of 400−900 nm are present for compound 6 corresponding to the intraconfiguration transitions of the Nd3+ ion. The initial state of these transitions is the ground 4I9/2 state and the most intensive bands are 4G9/2 + 4G7/2 + 2K13/2 at 523 nm, 4G5/2 + 2G7/2 at 578 nm, 4S3/2 + 4F7/2 at 735−744 nm and 2H9/2 + 4F5/2 at 795 nm, respectively, consistent with the values reported for Nd3+ ion in the literature.18

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02732. Additional information with SEM-EDS, PXRD, UV−vis, and Raman (PDF) Accession Codes

CCDC 1864439−1864444 (for 1−6) 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 [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Yingjie Zhang: 0000-0001-6321-4696 Santosh Panjikar: 0000-0001-7429-3879 Notes

The authors declare no competing financial interest.

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4. CONCLUSIONS Lanthanoid heteroleptic complexes with Q[5] and two dicarboxylic acids, e.g., diglycolic acid and glutaric acid, have been investigated with six new compounds featuring discrete tetrametallic and dimetallic structures, as well as a 1D polymer and three 2D polymers with a unique honeycomb-type topology being synthesized in near neutral aqueous solutions at room temperature. This accounts for the first systematic study on lanthanoid heteroleptic complexes involving Q[5] and dicarboxylate ligands. The 1D coordination polymers of Ln3+−Q[5] are well-documented with/without transition metal chlorides as the structure inducers. The introduction of DGC2− as the second organic ligand to some extent influences the formation of 1D polymers, although DGC2− tends to coordinate to Ln3+ ions in tridentate form without bridging between the metal centers. As such compound 1 contains two types of La3+ cationic units, a discrete tetrametallic and [La(DGC)(H2O)6]1+ species. Compound 2 has a dimetallic cationic structure with a Q[5] bis-bidentate ligand linking [Ce(DGC)(NO3)(H2O)3] and [Ce(H2O)7]3+ on the opposite portal sides, while compound 3 has a 1D cationic polymer built up with Q[5] bis-bidentate ligands in turn linking one hydrated [Ce(H2O)5]3+ and two [Ce(DGC)(H2O)2]1+ species. In contrast, 1D polymers can be further linked into 2D polymers by introducing dicarboxylate ligands with longer alkyl chains, e.g., GT2−. Consequently, compounds 4−6 with similar 2D sheets are built up by Q[5] linking two types of 9-fold coordinated Ln polyhedra via bis-bidentate carbonyl O atoms first forming 1D chains which are further connected by bridging GT2−. It is anticipated that other bridging carboxylate ligands with either alkyl chain or phenyl groups as spacers may also bridge the metal centers forming various polymeric structures. This perhaps may provide the opportunity to synthesize unique lanthanoid heteroleptic polymers involving other Q[n]s as well as a variety of polycarboxylate ligands to access their unique structures and

ACKNOWLEDGMENTS We would like to thank the Nuclear Materials Development and Characterization platform at ANSTO for facility access to synthesize and characterize the materials. The crystallographic data for compounds 1−6 were collected on the MX1 beamline at the Australian Synchrotron, a part of ANSTO.

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REFERENCES

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