Metal and Ligand Effects on the Construction of Divalent Coordination Polymers Based on bis-Pyridyl-bis-amide and Polycarboxylate Ligands

Abstract

Ten coordination polymers constructed from divalent metal salts, polycarboxylic acids, and bis-pyridyl-bis-amide ligands with different donor atom positions and flexibility are reported. They were structurally characterized by single-crystal X-ray diffraction. The ten coordination polymers are as follows: (1) {[Ni(L¹)(3,5-PDA)(H₂O)₃]·2H₂O}_n (L¹ = N,N′-di(3-pyridyl)suberoamide, 3,5-H₂PDA = 3,5-pyridinedicarboxylic acid); (2) {[Ni₂(L¹)₂(1,3,5-HBTC)₂(H₂O)₄]·H₂O}_n (1,3,5-H₃BTC = 1,3,5-benzenetricarboxylic acid); (3) {[Ni(L²)(5-tert-IPA)(H₂O)₂]·2H₂O}_n (L² = N,N′-di(3-pyridyl)adipoamide, 5-tert-H₂IPA = 5-tert-butylisophthalic acid); (4) [Ni(L³)_1.5(5-tert-IPA)]_n (L³ = N,N′-di(4-pyridyl)adipoamide); (5) [Co(L¹)(1,3,5-HBTC)(H₂O)]_n; (6) {[Co₃(L¹)₃(1,3,5-BTC)₂(H₂O)₂]·6H₂O}_n; (7) [Cu(L⁴)(AIPA)]_n (L⁴ = N,N′-bis(3-pyridinyl)terephthalamide, H₂AIPA = 5-acetamido isophthalic acid); (8) {[Cu(L²)_0.5(AIPA)]·MeOH}_n; (9) {[Zn(L⁴)(AIPA)]·2H₂O}_n; and (10) {[Zn(L²)(AIPA)]·2H₂O}_n. Complex 1 forms a 1D chain and 2 is a two-fold interpenetrated 2D layer with the sql topology, while 3 is a 2D layer with the hcp topology and 4 shows a self-catenated 3D framework with the rare (4²·6⁷·8)-hxg-d-5-C2/c topology. Different Co/1,3,5-H₃BTC ratios were used to prepare 5 and 6, affording a 2D layer with the sql topology and a 2D layer with the (4·8⁵)₂(4)₂(8³)₂(8) topology that can be further simplified to an hcp topology. While complex 7 is a 2D layer with the (4²·6⁷·8)(4²·6)-3,5L2 topology and 8 is a 2-fold interpenetrated 3D framework with the pcu topology, complexes 9 and 10 are self-catenated 3D frameworks with the (4²⁴·6⁴)-8T2 and the (4⁴·6¹⁰·8)-mab topologies, respectively. The effects of the identity of the metal center, the ligand isomerism, and the flexibility of the spacer ligands on the structural diversity of these divalent coordination polymers are discussed. The luminescent properties of 9 and 10 and their photocatalytic effects on the degradation of dyes are also investigated.

1. Introduction

Owing to the interesting structures of coordination polymers (CPs) and their potential applications in magnetism, luminescence, catalysis, gas storage, and sensing, CPs have been extensively studied and discussed by scientists during recent years [1,2,3,4]. Through the self-assembly process, the coordination of spacer ligands to the metal ions may lead to the formation of infinite one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D) CPs. Judicial choice of the metal-ion template and spacer ligands with diverse functionalities and flexibility may form well-defined frameworks.

The bis-pyridyl-bis-amide (bpba) ligands are intriguing ligands that can be tailored to prepare diverse CPs [5]. Most of the bpba ligands are flexible, although some are semi-rigid. While diverse bpba-based CPs have been reported, the control of structural dimensionality remains a challenge and the governing factors are less ascertained [5,6]. We have shown that reactions of the flexible N,N′-di(3-pyridyl)suberoamide (L¹) with Cu(II) salts in the presence of the isomeric phenylenediacetic acids under hydrothermal conditions afforded a 3D CP with the (4²·6⁵·8³)(4²·6)-3,5T1 topology, a 5-fold interpenetrated 3D CP with the (6⁵·8)-cds topology, and the first 1D self-catenated CP [7]. We have recently further shown that by manipulating the isomeric effect of the dicarboxylate ligands, self-catenated CPs incorporating the flexible bpba ligands can be expected [8].

To investigate the structure-directing roles of the spacer ligands on the construction of bpba-based CPs by changing their donor atom positions and flexibility, the flexible L¹, N,N′-di(3-pyridyl)adipoamide (L²), and N,N′-di(4-pyridyl)adipoamide (L³), and the semi-rigid N,N′-bis(3-pyridinyl)terephthalamide (L⁴) (Figure 1) were used to react with different divalent metal salts and auxiliary polycarboxylic acids (Figure 2). Various CPs with fascinating topology and interesting properties were prepared. Herein, we report the synthesis and crystal structures of the following: (1) {[Ni(L¹)(3,5-PDA)(H₂O)₃]·2H₂O}_n (L¹ = N,N′-di(3-pyridyl)suberoamide, 3,5-H₂PDA = 3,5-pyridinedicarboxylic acid); (2) {[Ni₂(L¹)₂(1,3,5-HBTC)₂(H₂O)₄]·H₂O}_n (1,3,5-H₃BTC = 1,3,5-benzenetricarboxylic acid); (3) {[Ni(L²)(5-tert-IPA)(H₂O)₂]·2H₂O}_n (L² = N,N′-di(3-pyridyl)adipoamide, 5-tert-H₂IPA = 5-tert-butylisophthalic acid); (4) [Ni(L³)_1.5(5-tert-IPA)]_n (L³ = N,N′-di(4-pyridyl)adipoamide); (5) [Co(L¹)(1,3,5-HBTC)(H₂O)]_n; (6) {[Co₃(L¹)₃(1,3,5-BTC)₂(H₂O)₂]·6H₂O}_n; (7) [Cu(L⁴)(AIPA)]_n (L⁴ = N,N′-bis(3-pyridinyl)terephthalamide, H₂AIPA = 5-acetamido isophthalic acid), (8) {[Cu(L²)_0.5(AIPA)]·MeOH}_n; (9) {[Zn(L⁴)(AIPA)]·2H₂O}_n; and (10) {[Zn(L²)(AIPA)]·2H₂O}_n. The luminescent and catalytic properties of some applicable complexes were also investigated.

2. Experimental Section

2.1. Materials

The reagent Ni(OAc)₂·4H₂O, 3,5-pyridinedicarboxylic acid, and 1,3,5-benzenetricarboxylic acid were purchased from Alfa Aesar Co. (Heysham, UK); Cu(OAc)₂·H₂O and Zn(OAc)₂·2H₂O from SHOWA Co. (Tokyo, Japan); Co(OAc)₂·4H₂O from J. T. Baker Co. (Phillipsburg, MO, USA); and 5-tert-butylisophthalic acid from ALDRICH Co. (St. Louis, MO, USA) N,N′-di(3-pyridyl)suberoamide (L¹), N,N′-di(3-pyridyl)adipoamide (L²), N,N′-di(4-pyridyl)adipoamide (L³), N,N′-bis(3-pyridinyl)terephthalamide (L⁴), and 5-acetamido isophthalic acid (H₂AIPA) were prepared according to published procedures [5,9].

2.2. Instruments

IR spectra (KBr disk) were performed on a JASCO FT/IR-460 plus spectrometer (JASCO, 28600 Mary’s Court City, USA). Elemental analyses were carried out on a PE 2400 series II CHNS/O analyzer (PerkinElmer, Boston, MA, USA) or an elementary VarioEL-III analyzer (Elementar Americas Inc., New Jersey, NJ, USA). Emission spectra were obtained using a Hitachi F-4500 spectrometer (Hitachi, Tokyo, Japan). Powder X-ray diffraction measurements were conducted on a Bruker D₂ PHASER diffractometer (Bruker, Billerica, MA, USA) with CuK_α (λ_α = 1.54 Å) radiation. The solution UV–Vis absorption spectra were recorded using an UV-2450 spectrophotometer (Shimadzu, Kyoto, Japan).

2.3. Preparations

2.3.1. General Procedure

A mixture of metal salts, bpba, and polycarboxylic acids in an appropriate volume of solvent was sealed in a 23 mL Teflon-lined stainless steel autoclave, which was heated under autogenous pressure to 100 °C for two days. The reaction system was then cooled to room temperature at a rate of 2 °C per hour. Crystals suitable for single-crystal X-ray diffraction were collected and washed with methanol and water.

2.3.2. {[Ni(L¹)(3,5-PDA)(H₂O)₃]·2H₂O}_n, c1

A mixture of Ni(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L¹ (0.033 g, 0.10 mmol), and 3,5-H₂PDA (0.017 g, 0.10 mmol) in 10 mL of NaOH (0.01 M) solution was used. Yield: 0.028 g (44%). Anal. Calcd for C₂₅H₃₅NiN₅O₁₁ (M_W = 640.29): C, 46.93; H, 5.51; N, 10.95%. Found: C, 46.42; H, 5.24; N, 10.73%. FT–IR (cm⁻¹): 3414(s), 3253(s), 3084(m), 2905(m), 2360(w), 1672(m), 1608(s), 1550(s), 1479(w), 1428(s), 1376(s), 1340(w), 1320(w), 1274(m), 1236(w), 1175(w), 1057(w), 967(w), 812(m), 700(m), 641(w), 579(w).

2.3.3. {[Ni₂(L¹)₂(1,3,5-HBTC)₂(H₂O)₄]·H₂O}_n, c2

A mixture of Ni(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L¹ (0.033 g, 0.10 mmol), and 1,3,5-H₃BTC (0.021 g, 0.10 mmol) in 5 mL of NaOH (0.01 M) solution was used. Yield: 0.046 g (36%). Anal. C₅₄H₆₄Ni₂N₈O₂₂ (M_W = 1294.54) (2 + 1 H₂O): C, 50.10; H, 4.98; N, 8.66%. Found: C, 49.78; H, 5.02; N, 8.65%. FT–IR (cm⁻¹): 3414(s), 3253(s), 3084(m), 2905(m), 2360(w), 1672(m), 1608(s), 1550(s), 1479(w), 1428(s), 1376(s), 1340(w), 1320(w), 1274(m), 1236(w), 1175(w), 1057(w), 967(w), 812(m), 700(m), 641(w), 579(w).

2.3.4. {[Ni(L²)(5-tert-IPA)(H₂O)₂]·2H₂O}_n, c3

A mixture of Ni(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L² (0.030 g, 0.10 mmol) and 5-tert-H₂IPA (0.022 g, 0.10 mmol) in 10 mL H₂O was used. Yield: 0.0423 g (65.28%). Anal. Calcd for C₂₈H₃₈NiN₄O₁₀ (M_W = 649.31): C, 51.84; H, 5.90; N, 8.64%. Found: C, 51.56; H, 5.92; N, 8.59%. FT–IR (cm⁻¹): 3251(w), 3069(w), 2960(w), 1686(m), 1614(m), 1553(s), 1489(s), 1434(m), 1408(m), 1372(s), 1294(m), 1123(w), 1060(w), 1030(w).

2.3.5. [Ni(L³)_1.5(5-tert-IPA)]_n, c4

A mixture of Ni(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L³ (0.030 g, 0.10 mmol), and 5-tert-H₂IPA (0.022 g, 0.10 mmol) in 10 mL of NaOH (0.01 M) solution was used. Yield: 0.0389 g (53.58%). Anal. Calcd for C₃₆H41NiN₆O₈ (M_W = 744.44) (4 + 1 H₂O): C, 58.08; H, 5.55; N, 11.29%. Found: C, 58.00; H, 5.47; N, 11.16%. FT–IR (cm⁻¹): 3614(w), 3521(w), 3443(w), 3267(w), 3077(w), 2959(w), 1712(m), 1600(s), 1567(m), 1514(s), 1424(m), 1354(m), 1331(m), 1299(m), 1204(m), 1152(w), 1133(m), 1063(w), 1021(w).

2.3.6. [Co(L¹)(1,3,5-HBTC)(H₂O)]_n, c5

A mixture of Co(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L¹ (0.033 g, 0.10 mmol), and 1,3,5-H₃BTC (0.021 g, 0.10 mmol) in 10 mL of NaOH (0.01 M) solution was used. Yield: 0.046 g (36%). Anal. Calcd for C₂₇H₂₈CoN₄O₉ (M_W = 611.46): C, 53.02; H, 4.62; N, 9.16%. Found: C, 52.60; H, 4.73; N, 9.18%. FT–IR (cm⁻¹): 3850(w), 3835(w), 3289(m), 2934(m), 2864(m), 1868(w), 1679(s), 1613(s), 1552(s), 1487(s), 1427(m), 1371(s), 1323(m), 1294(m), 1234(s), 1188(s), 1103(m), 1052(w), 995(w), 937(w), 913(w), 804(m), 679(m), 642(m), 557(w), 518(w), 490(w), 446(w), 423(w), 116(w).

2.3.7. {[Co₃(L¹)₃(1,3,5-BTC)₂(H₂O)₂]·6H₂O}_n, c6

A mixture of Co(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L¹ (0.033 g, 0.10 mmol), and 1,3,5-H₃BTC (0.015 g, 0.05 mmol) in 10 mL of NaOH (0.01 M) solution was used. Yield: 0.046 g (36%). Anal. Calcd for C₇₂H₈₈Co₃N₁₂O₂₆ (M_W = 1714.33): C, 50.43; H, 5.18; N, 9.81%. C₇₂H₈₄Co₃N₁₂O₂₄ (M_W = 1677.37) (6 − 2 H₂O): C, 51.50; H, 5.04; N, 10.01%. Found: C, 51.18; H, 4.97; N, 9.84%. FT–IR (cm⁻¹): 3073(w), 2914(w), 2854(w), 1682(w), 1614(m), 1587(m), 1542(s), 1477(w), 1428(s), 1363(s), 1280(m), 1193(w), 1133(w), 1101(w), 1052(w), 961(w), 807(w), 771(w), 730(m), 693(m), 567(w), 509(w), 475(w), 459(w), 448(m), 436(m), 423(w), 409(s).

2.3.8. [Cu(L⁴)(AIPA)]_n, c7

A mixture of Cu(OAc)₂·H₂O (0.020 g, 0.10 mmol), L⁴ (0.032 g, 0.10 mmol), and H₂AIPA (0.022 g, 0.10 mmol) in 5 mL of MeOH/H₂O (1:1, v/v) solution was used. Yield: 0.049 g (79%). Anal. Calcd for C₂₈H₂₁CuN₅O₇ (M_W = 603.04): C, 55.81; H, 3.52; N, 11.63%. Found: C, 55.31 ; H, 3.89; N, 11.31%. FT–IR (cm⁻¹): 3043(w), 2283(w), 1673(s), 1627(m), 1551(s), 1488(s), 1411(m), 1352(s), 1329(s), 1293(m), 1199(m), 1116(m), 1030(w), 937(w), 887(w), 861(w), 590(w), 538(w), 496(w), 454(w), 427(w), 416(m).

2.3.9. {[Cu(L²)_0.5(AIPA)]·MeOH}_n, c8

A mixture of Cu(OAc)₂·H₂O (0.020 g, 0.10 mmol), L² (0.030 g, 0.10 mmol), and H₂AIPA (0.022 g, 0.10 mmol) in 5 mL of MeOH/H₂O (1:1, v/v) solution was used. Yield: 0.029 g (47%). Anal. Calcd for C₁₉H₂₂CuN₃O₈ (M_W = 483.94) (8 + 1 H₂O): C, 47.16; H, 4.58; N, 8.68%. Found: C, 47.02; H, 4.17; N, 8.91%. FT–IR (cm⁻¹): 3841(w), 3736(w), 3677(w), 3053(w), 1714(m), 1653(m), 1595(m), 1541(s), 1485(m), 1418(s), 1374(s), 1324(m), 1288(m), 1197(m), 1174(m), 1134(m), 1621(m), 903(m), 779(m), 727(s), 706(m), 644(w), 540(w), 418(w), 481(m), 460(m), 442(m), 428(m), 414(m).

2.3.10. {[Zn(L⁴)(AIPA)]·2H₂O}_n, c9

A mixture of Zn(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L⁴ (0.032 g, 0.10 mmol), and H₂AIPA (0.022 g, 0.10 mmol) in 5 mL of MeOH/H₂O (1:1, v/v) solution was used. Yield: 0.049 g (79%). Anal. Calcd for C₂₈H₂₅ZnN₅O₉ (M_W = 640.90): C, 52.47; H, 3.93; N, 10.93%. Found: C, 52.36; H, 3.78; N, 10.94%. FT–IR (cm⁻¹): 3504(w), 3070(m), 2284(w), 1671(s), 1637(m), 1545(s), 1485(s), 1420(s), 1368(s), 1329(s), 1276(m), 1234(m), 1197(m), 1105(w), 1055(w), 1028(w), 940(w), 910(w), 886(w), 863(w), 810(m), 781(m), 719(m), 643(w), 602(w), 514(w), 452(w), 144(w).

2.3.11. {[Zn(L²)(AIPA)]·2H₂O}_n, c10

A mixture of Zn(OAc)₂·4H₂O (0.025 g, 0.10 mmol), L² (0.030 g, 0.10 mmol), and H₂AIPA (0.022 g, 0.10 mmol) in 5 mL of MeOH/H₂O (1:1, v/v) solution was used. Yield: 0.029 g (47%). Anal. Calcd for C₂₆H₂₉ZnN₅O₉ (M_W = 620.91): C, 50.39; H, 4.72; N, 11.31%. Found: C, 50.18; H, 4.70; N, 11.06%. FT–IR (cm⁻¹): 3484(m), 3243(m), 3119(m), 3039(m), 2945(m), 1662(s), 1630(m), 1576(s), 1553(s), 1488(s), 1420(s), 1365(s), 1330(m), 1287(s), 1221(m), 1140(m), 1100(w), 1064(w), 1031(w), 949(w), 909(w), 780(m), 700(m), 647(w), 542(m), 500(w), 457(w), 420(m).

2.4. Photodegradation Experiment

Tube 1 (blank), tube 2 (0.1 mL 30% H₂O₂), tube 3 (5 mg complex), and tube 4 (5 mg complex + 0.1 mL 30% H₂O₂) were prepared. To each tube was added 10 mL of a 50 ppm methyl blue (MB, C₃₇H₂₇N₃Na₂O₉S₃, Scheme S1 in Supplementary Materials) solution, which was prepared by diluting 50 mg MB with deionized water in a 1000 mL quantitative bottle. Each tube was then irradiated with the 365 nm UV light for 15, 30, 45, and 60 min, respectively; the absorption spectra were then measured. Tube 3 and tube 4 were first stirred in the dark for 15 min to determine the physical adsorption of the complex.

2.5. Single-Crystal X-ray Analysis

Single crystals of complexes 1 to 10 suitable for X-ray analysis were obtained from the hydrothermal reactions and their diffraction data were measured at 296 K using a Bruker AXS SMART APEX II CCD diffractometer, which was equipped with graphite monochromated MoK_α (λ_α = 0.71073 Å) radiation [10]. Data reductions were performed using the standard methods with well-established computational procedures and the empirical absorption corrections were carried out based on “multi-scan”. The atomic positions of some of the heavier atoms were located by the direct or Patterson method, followed by a series of alternating difference Fourier maps and least-square refinements to find the remaining atoms. Except those of the water molecules, the hydrogen atoms coordinated to the other atoms were added by using the HADD command in SHELXTL 6.1012 [11]. Basic information pertaining to the crystal parameters and structure refinement is summarized in

Table 1. Crystal data for complexes 1 to 10.

Complex	1	2	3	4	5
Formula	C25H35NiN5O11	C54H62Ni2N8O21	C28H38NiN4O10	C36H39NiN6O7	C27H28CoN4O9
Formula weight	640.29	1276.53	649.33	726.44	611.46
Crystal system	Triclinic	Triclinic	Triclinic	Monoclinic	Triclinic
Space group	Pī	Pī	Pī	C2/c	Pī
a, Å	10.2217(2)	9.2151(1)	11.7614(2)	12.9109(14)	9.6229(1)
b, Å	12.1140(2)	15.2396(2)	12.0360(2)	16.2298(17)	10.2784(1)
c, Å	13.1648(3)	20.1781(2)	12.2961(2)	33.736(4)	14.7068(2)
α, °	67.612(1)	105.765(1)	78.548(1)	90	87.707(1)
β, °	76.879(1)	96.500(1)	67.752(1)	95.395(7)	89.509(1)
γ, °	70.475(1)	90.244(1)	86.067(1)	90	73.917(1)
V, Å3	1411.27(5)	2707.76(6)	1578.94(5)	7037.8(13)	1396.56(3)
Z	2	2	2	8	2
dcalc, mg/m3	1.507	1.566	1.366	1.371	1.454
F(000)	672	1332	684	3048	634
µ(Mo Kα), mm−1	0.756	0.786	0.674	0.609	0.674
Range (2θ) for data collection	3.36 to 56.68	3.92 to 56.72	3.46 to 56.59	4.14 to 56.92	4.12 to 56.56
Independent reflections	7003	13388	7815	8791	6910
	[R(int) = 0.0355]	[R(int) = 0.0253]	[R(int) = 0.0245]	[R(int) = 0.0337]	[R(int) = 0.0185]
Data/restraints/parameters	7003/0/412	13388/1369/819	7815/0/395	8791/808/484	6910/0/382
Quality-of-fit indicator c	1.076	1.062	1.037	1.067	1.053
Final R indices [I > 2σ(I)] a,b	R1 = 0.0329	R1 = 0.0472	R1 = 0.0401	R1 = 0.0666	R1 = 0.0353
	wR2 = 0.0731	wR2 = 0.1282	wR2 = 0.1018	wR2 = 0.1864	wR2 = 0.0925
R indices (all data)	R1 = 0.0473	R1 = 0.0756	R1 = 0.0533	R1 = 0.0955	R1 = 0.0426
	wR2 = 0.0793	wR2 = 0.1460	wR2 = 0.1096	wR2 = 0.2044	wR2 = 0.0962
Complex	6	7	8	9	10
Formula	C72H88Co3N12O26	C28H21CuN5O7	C19H20CuN3O7	C28H25ZnN5O9	C26H29ZnN5O9
Formula weight	1714.33	603.04	465.92	640.90	620.91
Crystal system	Triclinic	Triclinic	Orthorhombic	Monoclinic	Monoclinic
Space group	Pī	Pī	Pbca	C2/c	P21/c
a, Å	10.0136(2)	9.7425(2)	12.8022(2)	26.4979(10)	12.5193(1)
b, Å	11.9834(3)	9.9983(2)	14.5368(2)	12.7299(5)	12.8079(2)
c, Å	17.2930(4)	15.1361(2)	20.5531(2)	17.1560(6)	16.8353(2)
α, °	98.375(2)	81.021(1)	90	90	90
β, °	90.027(1)	84.597(1)	90	108.868(2)	91.488(1)
γ, °	95.361(1)	61.683(1)	90	90	90
V, Å3	2043.79(8)	1281.71(4)	3824.99(9)	5476.0(4)	2698.56(6)
Z	1	2	8	8	4
dcalc, mg/m3	1.393	1.563	1.618	1.555	1.528
F(000)	893	618	1920	2640	1288
µ(Mo Kα), mm−1	0.685	0.911	1.192	0.962	0.973
Range(2θ) for data collection	3.89 to 52.00	4.66 to 56.64	4.68 to 56.64	3.25 to 56.66	3.26 to 56.58
Independent reflections	8041	6365	4760	6783	6539
	[R(int) = 0.0411]	[R(int) = 0.0551]	[R(int) = 0.0486]	[R(int) = 0.0609]	[R(int) = 0.0193]
Data/restraints/parameters	8041/0/568	6265/0/374	4760/0/283	6783/0/397	6539/0/370
Quality-of-fit indicator c	1.053	1.056	1.021	1.024	1.023
Final R indices [I > 2σ(I)] a,b	R1 = 0.0660,	R1 = 0.0453,	R1 = 0.0438,	R1 = 0.0521,	R1 = 0.0399,
	wR2 = 0.1807	wR2 = 0.1040	wR2 = 0.0997	wR2 = 0.0930	wR2 = 0.1144
R indices (all data)	R1 = 0.0907,	R1 = 0.0714,	R1 = 0.0724,	R1 = 0.1033,	R1 = 0.0510,
	wR2 = 0.1980	wR2 = 0.1150	wR2 = 0.1129	wR2 = 0.1090	wR2 = 0.1219

^a R₁ = Σ||F_o| − |F_c||/Σ|F_o|; ^b wR₂ = [Σw(F_o² − F_c²)²/Σw(F_o²)²]^1/2. w = 1/[σ²(F_o²) + (ap)² + (bp)], p = [max(F_o² or 0) + 2(F_c²)]/3. a = 0.0318, b = 0.4608, 1; a = 0.0655, b = 2.0327, 2; a = 0.0533, b = 0.9980, 3; a = 0.1035, b = 14.0450, 4; a = 0.0473, b = 0.7901, 5; a = 0.1153, b = 2.1116, 6; a = 0.0495, b = 0.6944, 7; a = 0.0421, b = 6.0326, 8; a = 0.0401, b = 3.4024, 9; a = 0.0705, b = 1.4721, 10; ^c quality-of-fit = [Σw(|F_o²| − |F_c²|)²/N_observed − N_parameters )]^1/2.

.

3. Results and Discussion

3.1. Structural Descriptions

3.1.1. Structure of {[Ni(L¹)(3,5-PDA)(H₂O)₃]·2H₂O}_n, 1

X-ray structural analysis reveals that complex 1 forms a 1D CP and crystallizes in the triclinic space group Pī with two independent halves of Ni(II) ions that occupy the inversion centers, one 3,5-PDA²⁻ ligand, three coordinated water molecules, and two lattice water molecules in the asymmetric unit. Figure 3a depicts a drawing showing the coordination environments about the Ni(II) ions, both of which adopt the distorted octahedral geometries. While the Ni(1) atom is coordinated by two pyridyl nitrogen atoms from two L¹ ligands [Ni(1)—N = 2.1214(15) Å] and four oxygen atoms from two 3,5-PDA²⁻ ligands and two water molecules [Ni(1)—O = 2.0338(11)–2.0788(11) Å], the Ni(2) atom is coordinated by two nitrogen atoms from two L¹ ligands [Ni(2)—N = 2.1189(15) Å] and four oxygen atoms from four water molecules [Ni(2)–O = 2.0342(11)–2.0890(12) Å]. Noticeably, the 3,5-PDA²⁻ ligands are coordinated to the metal ions in a monodentate fashion through one of the carboxylate oxygen atoms. The Ni(II) ions are bridged by the L¹ ligands to afford 1D chains (Figure 3b) that are supported by N–H---O (N---H = 2.01 and 2.05 Å; ∠N–H---O = 175.3 and 168.8°) hydrogen bonds originating from the amine hydrogen atoms to the oxygen atoms of the uncoordinated water molecules and 3,5-PDA²⁻ ligands, and O–H---O (O---H = 1.74–2.04 Å; ∠O–H---O = 153.2–175.5°) hydrogen bonds resulting from the interactions among coordinated water molecules, uncoordinated water molecules, 3,5-PDA²⁻ ligands, and L¹ ligands (see Table S1 and Figure S1). To our best knowledge, this type of μ₁-κ¹,κ⁰,κ⁰,κ⁰ bonding mode for the 3,5-PDA²⁻ ligands in CPs is unique.

3.1.2. Structure of {[Ni₂(L¹)₂(1,3,5-HBTC)₂(H₂O)₄]·H₂O}_n, 2

X-ray structural analysis reveals that complex 2 forms a 2D CP and crystallizes in the triclinic space group Pī. The asymmetric unit consists of one independent Ni(II) ion at the general position, two halves of an independent Ni(II) ion that occupy the inversion centers, two L¹ ligands, two 1,3,5-HBTC²⁻ ligands, four coordinated water molecules, and one lattice water molecule. Figure 4a depicts a drawing showing the coordination environments about the Ni(II) ions. All of the metal centers are six-coordinated by two pyridyl nitrogen atoms from two L¹ ligands [Ni–N = 2.091(2)–2.152(2) Å] and four oxygen atoms from two 1,3,5-HBTC²⁻ ligands [Ni–O = 2.0297(15)–2.1112(18) Å] and two coordinated water molecules [Ni–O = 2.0491(16)–2.0993(17) Å], resulting in distorted octahedral geometries. The Ni(II) ions are linked together by L¹ and 1,3,5-HBTC²⁻ ligands to form 2D layers, which stack along the a axis (see Figure S2 and Figure 4b). If the Ni(II) ions are defined as 4-connected nodes, the structure of 2 can be regarded as a two-fold interpenetrated and 4-connected net with the sql topology, determined using ToposPro [12] (see Figure 4c). The 2D layers are sustained by N–H---O (N---H = 2.22–2.35 Å; ∠N–H---O = 155.4–168.1°) hydrogen bonds to the oxygen atoms of the carboxylate and carbonyl oxygen atoms and O–H---O (O---H = 1.83–2.45 Å; ∠O–H---O = 125.3–174.8°) hydrogen bonds resulting from the interactions among coordinated water molecules, uncoordinated water molecules, 1,3,5-HBTC²⁻ ligands, and L¹ ligands (see Table S2 in Supplementary Materials).

3.1.3. Structure of {[Ni(L²)(5-tert-IPA)(H₂O)₂]·2H₂O}_n, 3

X-ray structural analysis reveals that complex 3 forms a 2D CP and crystallizes in the triclinic space group Pī with one Ni(II) ion, one L² ligand, one 5-tert-IPA²⁻ ligand, two coordinated water molecules, and two lattice water molecules in the asymmetric unit. Figure 5a depicts a drawing showing the coordination environment about the Ni(II) ion, which is six-coordinated by two pyridyl nitrogen atoms from two L² ligands [Ni–N = 2.0910(18) and 2.0949(17) Å] and four oxygen atoms from two 5-tert-IPA²⁻ ligands [Ni–O = 2.0661(13) and 2.0878(12) Å] and two coordinated water molecules [Ni–O = 2.0641(16) and 2.1060(18) Å], resulting in a distorted octahedral geometry. Moreover, the Ni(II) ions are linked by the 5-tert-IPA²⁻ ligands and one independent L² ligand to afford 1D looped chains (see Figure 5b), which are further connected by the other independent L² ligands to form 2D layers (see Figure 5c), which stack along the a axis (see Figure S3 in Supplementary Materials). If the Ni(II) ions are defined as 3-connected nodes, the structure of 3 can be simplified as a 3-connected net with the hcp topology (Figure 5d). The 2D layers are supported by N–H---O (N---H = 1.97 and 2.07 Å; ∠N–H---O = 173.1 and 178.2°) hydrogen bonds to the uncoordinated water molecules and O–H---O (O---H = 1.86–2.35 Å; ∠O–H---O = 132.2–174.6°) hydrogen bonds resulting from the interactions among the coordinated water molecules, uncoordinated water molecules, 5-tert-IPA²⁻ ligands, and L² ligands (see Table S3 in Supplementary Materials).

3.1.4. Structure of [Ni(L³)_1.5(5-tert-IPA)]_n, 4

X-ray structural analysis reveals that complex 4 forms a 3D CP and crystallizes in the monoclinic space group C2/c. The asymmetric unit consists of one Ni(II) ion, one half of an L³ ligand, and one 5-tert-IPA²⁻ ligand. Figure 6a depicts a drawing showing the coordination environment about the Ni(II) ion, which is six-coordinated by three oxygen atoms from two 5-tert-IPA²⁻ ligands [Ni–O = 2.064(2)–2.263(2) Å] and three pyridyl nitrogen atoms from three L³ ligands [Ni–N = 2.037(3)–2.092(3) Å], resulting in a distorted octahedral geometry. The Ni(II) ions are further linked by L³ and 5-tert-IPA²⁻ ligands to form a 3D framework. Treating the Ni(II) cations as 5-connected nodes and the spacer ligands as linkers reveal a 3D net with the rare (4²·6⁷·8)-hxg-d-5-C2/c topology (see Figure 6b), which can be regarded as polycatenated nets cross-linked by the linkers. The (4²·6⁷·8)-hxg-d-5-C2/c net has been observed in two isostructural complexes {[Cu₂(L4-4)X]₂·CuX}_n (X = Cl and Br; HL4-4 is 3,5-bis(4-pyridyl)-1H-pyrazole) that were obtained by reacting HL4-4 with corresponding copper salts (CuBr₂/CuCl₂), where the Cu(II) ions were reduced to monovalent Cu(I) in solvothermal conditions [13]. The 3D framework is supported by the N–H---O (N---H = 1.92 and 2.14 Å; ∠N–H---O = 174.4 and 157.8°) hydrogen bonds to the carboxylate oxygen atoms of the 5-tert-IPA²⁻ ligands (see Table S4 in Supplementary Materials).

3.1.5. Structure of [Co(L¹)(1,3,5-HBTC)(H₂O)]_n, 5

X-ray structural analysis reveals that complex 5 forms a 2D CP and crystallizes in the triclinic space group Pī with one Co(II) ion, one L¹ ligand, one 1,3,5-HBTC²⁻ ligand, and one coordinated water molecule in the asymmetric unit. Figure 7a depicts a drawing showing the coordination environment about the Co(II) ion, which is six-coordinated by two pyridyl nitrogen atoms from two L¹ ligands [Co–N = 2.1561(15) and 2.1589(15) Å] and four oxygen atoms from two 1,3,5-HBTC²⁻ ligands [Co–O = 2.0141(13)–2.1804(13) Å] and one coordinated water molecule [Co–O = 2.0350(13) Å], resulting in a distorted octahedral geometry. Moreover, the Co(II) ions are linked together by the L¹ and 1,3,5-HBTC²⁻ ligands to afford 2D layers (Figure 7b), which stack along the a axis (see Figure S4). If the Co(II) ions are defined as 4-connected nodes, the structure of 5 can be regarded as a 4-connected net with the sql topology (Figure 7c). The 2D layers are sustained by N–H---O (N---H = 1.99 and 2.16 Å; ∠N–H---O = 179.3 and 174.7°) hydrogen bonds to the carbonyl and carboxylate oxygen atoms and O–H---O (O---H = 1.84–1.91 Å; ∠O–H---O = 155.9–174.4°) hydrogen bonds resulting from the interactions between coordinated water molecules and 1,3,5-HBTC²⁻ ligands (see Table S5 in Supplementary Materials).

3.1.6. Structure of {[Co₃(L¹)₃(1,3,5-BTC)₂(H₂O)₂]·6H₂O}_n, 6

X-ray structural analysis reveals that complex 6 forms a 2D CP and crystallizes in the triclinic space group Pī. The asymmetric unit consists of one independent Co(II) ion at the general position and a half of a Co(II) ion at the inversion center, one and a half L¹ ligands, one 1,3,5-BTC³⁻ ligand, one coordinated water molecule, and three co-crystallized water molecules. Figure 8a depicts a drawing showing the coordination environment about the Co(II) ions. The Co(1) atom adopts the distorted trigonal bipyramidal geometry (τ = 0.65) [14], which is coordinated by three oxygen atoms from two different 1,3,5-BTC³⁻ ligands [Co(1)–O = 1.957(3)–2.346(3) Å] and two pyridyl nitrogen atoms from two L¹ ligands [Co(1)–N = 2.055(3) and 2.061(3) Å], while the Co(2) atom adopts the distorted octahedral geometry, which is coordinated by two pyridyl nitrogen atoms from two L¹ ligands [Co(2)–N = 2.181(3) Å] and four oxygen atoms from two 1,3,5-BTC³⁻ ligands and two coordinated water molecules [Co(2)–O = 2.054(3)–2.112(3) Å]. The Co(II) ions are linked by L¹ ligands and 1,3,5-BTC³⁻ ligands to form 2D layers with loops (see Figure 8b), which stack along the b axis (see Figure S5 in Supplementary Materials). If the L¹ ligands are considered as 2-connected nodes, the structure of 6 can be simplified as a 2,2,3,4-connected (4·8⁵)₂(4)₂(8³)₂(8) topology (as shown in Figure 8c), which can be further reduced to the hcp topology (as shown in Figure 8d) if the L¹ ligands are considered as linkers. Moreover, the 2D layers are supported by N–H---O (N---H = 2.00–2.26 Å; ∠N–H---O = 162.6–177.5°) hydrogen bonds to the carbonyl and carboxylate oxygen atoms and O–H---O (O---H = 1.69–2.28 Å; ∠O–H---O = 113.8–178.5°) hydrogen bonds resulting from the interactions among coordinated water molecules, uncoordinated water molecules, 1,3,5-BTC³⁻ ligands, and L¹ ligands (see Table S6).

3.1.7. Structure of [Cu(L⁴)(AIPA)]_n, 7

X-ray structural analysis reveals that complex 7 forms a 2D CP and crystallizes in the triclinic space group Pī with one Cu(II) ion, one L⁴ ligand, and one AIPA²⁻ ligand in the asymmetric unit. Figure 9a depicts a drawing showing the coordination environment about the Cu(II) ions, which are five-coordinated by three oxygen atoms from three AIPA²⁻ ligands [Cu–O = 1.9220(17)–2.2115(18) Å] and two pyridyl nitrogen atoms from two L⁴ ligands [Cu–N = 2.0410(2)–2.0610(2) Å], resulting in a distorted square pyramidal geometry (τ = 0.27). Moreover, the Cu(II) ions are linked by the AIPA²⁻ ligands to form dinuclear units [Cu---Cu = 4.202(2) Å], which are further linked by AIPA²⁻ and L⁴ ligands to form 2D layers (Figure 9b), which stack along the a axis (see Figure S6). If the Cu(II) ions are considered as 5-connected nodes and the AIPA²⁻ ligands as 3-connected nodes, the structure of 7 can be simplified as a 3,5-connected net with the (4²·6⁷·8)(4²·6)-3,5L2 topology (Figure 9c). The 2D layers are supported by the N–H---O (N---H = 2.14–2.31 Å; ∠N–H---O = 150.7–166.7°) hydrogen bonds to the carbonyl and carboxylate oxygen atoms of AIPA²⁻ and L⁴ ligands (see Table S7 in Supplementary Materials).

3.1.8. Structure of {[Cu(L²)_0.5(AIPA)]·MeOH}_n, 8

X-ray structural analysis reveals that complex 8 forms a 3D CP and crystallizes in the orthorhombic space group Pbca. The asymmetric unit consists of one Cu(II) ion, a half of L² ligand, one AIPA²⁻ ligand, and one lattice methanol molecule. Figure 10a depicts a drawing showing the coordination environments about the Cu(II) ions, which are five-coordinated by four oxygen atoms from four AIPA²⁻ ligands [Cu–O = 1.9600(2)–1.9780(2) Å] and one pyridyl nitrogen atom from one L² ligand [Cu–N = 2.1660(2) Å], resulting in a distorted square pyramidal geometry (τ = 0.01). The metal atoms are linked by the AIPA²⁻ ligands to form dinuclear units [Cu---Cu = 2.6431(6) Å], which are further connected by AIPA²⁻ and L² ligands to form a 3D framework. If the Cu(II) ions are considered as 6-connected nodes and the AIPA²⁻ ligands as 4-connected nodes and the L² ligands as linkers, the structure of 8 can be simplified as a 4,6-connected, 2-fold interpenetrated net with the (3²·6²·7²)(3⁴·4⁶·6⁴·7)-sqc493 topology (Figure 10b). Furthermore, treating the dinuclear Cu(II) units as 6-connected nodes affords a 2-fold interpenetrated net with pcu topology (Figure 10c). N–H---O (N–--H = 2.01 and 2.18 Å; ∠N–H---O = 171.8–173.7°) hydrogen bonds to the carbonyl oxygen atoms of AIPA²⁻ ligands and the methanol oxygen atoms and O–H---O (O---H = 2.00 Å; ∠O–H---O = 161.2°) hydrogen bonds originating from methanol to the carbonyl oxygen atoms of AIPA²⁻ ligands are found in the 3D framework (see Table S8 in Supplementary Materials).

3.1.9. Structure of {[Zn(L⁴)(AIPA)]·2H₂O}_n, 9

X-ray structural analysis reveals that complex 9 forms a 3D CP and crystallizes in the monoclinic space group C2/c with one Zn(II) ion, one L⁴ ligand, one AIPA²⁻ ligand, and two lattice water molecules in the asymmetric unit. Figure 11a depicts a drawing showing the coordination environments about the Zn(II) ions. Each of the symmetry-related Zn(II) ions is five-coordinated by three oxygen atoms from three AIPA²⁻ ligands [Zn–O = 1.9840(2)–2.0720(2) Å] and two pyridyl nitrogen atoms from two L⁴ ligands [Zn–N = 2.1700(2)–2.1890(2) Å], resulting in a distorted trigonal bipyramidal geometry (τ = 0.61). The metal ions are linked by two AIPA²⁻ ligands to form dinuclear units [Zn---Zn = 3.979(2) Å], which are further linked by L⁴ and AIPA²⁻ ligands to form a 3D framework. Treating the dinuclear Zn(II) units as 8-connected nodes and the spacer ligands as linkers reveal the presence of a self-catenated 3D net with the (4²⁴·6⁴)-8T2 topology (Figure 11b). A closer investigation reveals that the topological structure can be viewed as a two-fold interpenetration of pcu-type nets cross-linked by the linkers, as shown in Figure 11c. Moreover, the 3D framework is supported by N–H---O (N---H = 2.13–2.52 Å; ∠N–H---O = 127.7–156.6°) hydrogen bonds to the carbonyl oxygen atoms of AIPA²⁻ ligands and the water oxygen atoms and O–H---O (O---H = 1.83–2.18 Å; ∠O–H---O = 125.3–165.0°) hydrogen bonds originating from water molecules to the carbonyl oxygen atoms of AIPA²⁻ ligands, carbonyl oxygen atoms of L⁴ ligands, and the water oxygen atoms (see Table S9 in Supplementary Materials).

3.1.10. Structure of {[Zn(L²)(AIPA)]·2H₂O}_n 10

X-ray structural analysis reveals that complex 10 forms a 3D CP and crystallizes in the monoclinic space group P2₁/c. The asymmetric unit consists one Zn(II) ion, one L² ligand, one AIPA²⁻ ligand, and two lattice water molecules. Figure 12a depicts a drawing showing the coordination environment about the Zn(II) ion, which is five-coordinated by three oxygen atoms from three AIPA²⁻ ligands [Zn–O = 1.9693(6)–2.0206(6) Å] and two pyridyl nitrogen atoms from two L² ligands [Zn–N = 2.1918(21) and 2.1615(23) Å], resulting in a distorted trigonal bipyramidal geometry (τ = 0.67). The metal atoms are linked by two AIPA²⁻ ligands to form dinuclear units [Zn---Zn = 3.8970(5) Å], which are further linked by L² and AIPA²⁻ ligands to form a 3D framework. If the dinuclear Zn(II) units are defined as 6-connected nodes and the spacer ligands as linkers, the structure of 10 can be regarded as an underlying self-catenated net with the (4⁴·6¹⁰·8)-mab topology (Figure 12b). It is noted that the mab net is closely related to the self-catenated net roa. Both of the nets have the same Schläfli symbol (4⁴·6¹⁰·8) but differ in the vertex symbols, which are 4·4·4·4·6₄·6₄·6₅·6₅·6₅·6₅·6₁₁·6₁₁·6₁₁·6₁₁* and 4·4·4·4·6₂·6₂·6₅·6₅·6₅·6₅·6₅·6₅·6₅·6₅*, respectively. The 3D framework is sustained by N–H---O (N---H = 2.01–2.12 Å; ∠N–H---O = 149.3–178.0°) hydrogen bonds to the carbonyl and carboxylate oxygen atoms of AIPA²⁻ ligands and the water oxygen atoms and O–H---O (O---H = 2.18–2.48 Å; ∠O–H---O = 116.8–170.6°) hydrogen bonds originating from water molecules to the carboxylate oxygen atoms of AIPA²⁻ ligands and carbonyl oxygen atoms of L² ligands (see Table S10).

The solvent-accessible volumes of complexes 1 to 10 have been calculated using PLATON [15], which are 1.1, 0.6, 6.7, 0, 0, 14.9, 0, 6.6, 7.9, and 10.1% of each of their corresponding unit cell volumes, respectively, indicating small or no porosity.

3.2. Ligand Conformations and Bonding Modes

The descriptor that has been proposed to establish the ligand conformations of the bpba ligands is applicable for L¹–L⁴ [5]: (a) If the C–C–C–C torsion angle (θ) of the backbone carbon atoms is 180 ≥ θ > 90° and 0 ≤ θ ≤ 90°, L¹–L³ adopt the A and G conformations, respectively. (b) On the basis of the relative orientation of the C=O (or N–H) groups, each of the L¹–L⁴ ligands adopt the cis or trans arrangement. (c) Due to the different orientations of the pyridyl nitrogen atom positions, three more orientations—anti-anti, syn-anti, and syn-syn—can also be imposed on L¹, L², and L⁴. Accordingly, the ligand conformations of complexes 1 to 10 are assigned and listed in

Table 2. Ligand conformation of L¹ to L⁴ and bonding modes of the polycarboxylate ligands in 1–10.

Complex	Ligand conformation	Bonding mode
{[Ni(L1)(3,5-PDA)(H2O)3]·2H2O}n, 1	AAAAA trans syn-syn	μ1-κ1,κ0,κ0,κ0
{[Ni2(L1)2(1,3,5-HBTC)2(H2O)4]·H2O}n, 2	AAAAA trans anti-syn AGAGA trans syn-anti	μ2-κ1,κ0,κ1,κ0,κ0,κ0
{[Ni(L2)(5-tert-IPA)(H2O)2]·2H2O}n, 3	AAA trans anti-anti GAG trans syn-anti	μ2-κ1,κ0,κ1,κ0
[Ni(L3)1.5(5-tert-IPA)]n, 4	AAA trans GAG trans	μ2-κ1,κ0,κ1,κ0
[Co(L1)(1,3,5-HBTC)(H2O)]n, 5	GAAAA cis anti-syn	μ2-κ1,κ0,κ1,κ1,κ0,κ0
{[Co3(L1)3(1,3,5-BTC)2(H2O)2]·6H2O}n, 6	AAGGA cis syn-syn	μ3-κ1,κ0,κ1,κ0,κ1,κ1
	AGAGA trans syn-syn
[Cu(L4)(AIPA)]n, 7	trans syn-syn	μ3-κ0,κ1,κ1,κ1
{[Cu(L2)0.5(AIPA)]·MeOH}n, 8	GAG trans anti-anti	μ4-κ1,κ1,κ1,κ1
{[Zn(L4)(AIPA)]·2H2O}n, 9	trans anti-anti	μ3-κ0,κ1,κ1,κ1
{[Zn(L2)(AIPA)]·2H2O}n, 10	GAG trans anti-anti	μ3-κ0,κ1,κ1,κ1

, which also shows the various bonding modes for the polycarboxylate ligands. The diverse ligand conformations and bonding modes shown in Table 2 indicate that L¹–L⁴ and the polycarboxylate ligands are flexible and can be adjusted to fit the stereochemical requirements for forming the structures of complexes 1 to 10, which presumably result from the maximization of their intra and intermolecular forces.

3.3. Structural Comparisons

The structural difference between 1 and 2 is presumably due to the different identities of the dicarboxylate ligands. Structural comparisons of complexes 3 and 4 reveal that ligand isomerism (the donor atom position of the bpba ligand) is important in determining the structural diversity, resulting in a 2D layer with the hcp topology and a 3D framework with the (4²·6⁷·8)-hxg-d-5-C2/c topology, respectively. The different metal/ligand ratios used for complexes 5 and 6 are also important in determining the structural type, giving a 2D layer with the sql topology and a 2D layer with the hcp topology, respectively. Moreover, a comparison of the structures of complexes 7–10 shows that the metal centers and flexibility of the ligands significantly affect the structural diversity. The metal centers are Cu(II) in 7 and Zn(II) in 9, affording a 2D layer with the sql topology and a self-catenated 3D framework with the (4²⁴·6⁴)-8T2 topology, respectively. Similarly, complexes 8 and 10 display a 2-fold interpenetrated 3D framework with the pcu topology and a self-catenated 3D framework with the (4⁴·6¹⁰·8)-mab topology, respectively. It is also shown that with the same bpba and AIPA²⁻ ligands, the CPs with Zn(II) ions prefer to form 3D self-catenated frameworks (7 vs. 9 and 8 vs. 10), which can be ascribed to the formation of the distorted trigonal bipyramidal geometries in complexes 9 and 10, rather than the distorted square pyramidal geometries in complexes 7 and 8. Structural differences in the pairs of 7 and 8, and 9 and 10 are presumably due to the different flexibility between L⁴ and L² ligands. Structural comparisons of 1–10 indicate that the identity of the dicarboxylate ligands, the ligand isomerism and flexibility of the bpba ligands, the metal/ligand ratio, and the nature of the metal centers play important roles in determining the structural diversity of the divalent coordination polymers.

3.4. Luminescent Properties

Luminescent d¹⁰ metal complexes have the ability to enhance, shift, and quench emissions of organic ligands, which are of great interest due to the potential applications of these complexes in areas such as sensors and displays. The luminescent properties of 9 and 10 were thus investigated.

Table 3. The absorption, excitation, and emission wavelengths (nm) of L², L⁴, H₂AIPA, and complexes 9 and 10 in the solid state.

Complex	λabs (nm)	λex (nm)	λem (nm)
L2	300	370	415
L4	341	330/365	420
H2AIPA	323	336	425
9	340	340/400	460
10	322	325/350	415

summarizes the UV–VIS and luminescent properties of complexes 9 and 10 and the free organic ligands L², L⁴, and H₂AIPA. Figures S7–S11 depict the corresponding excitation/emission spectra, which were measured in solid state at room temperature. The spectra of L², L⁴, and H₂AIPA show emissions in the range of 415–425 nm, which may be ascribed to the intraligand (IL) n → π* or π → π* transitions. The red shifts of 9 with respect to the free organic ligands can be ascribed to the different ligand conformations and coordination modes adopted by the organic ligands and the formation of different structural types. It is well known that the Zn(II) ion is hardly susceptible to oxidation or reduction and it is thus not possible that the emissions of 9 and 10 are due to ligand-to-metal charge transfer (LMCT) or metal-to-ligand charge transfer (MLCT). Therefore, these emissions may be attributed to intraligand or ligand-to-ligand charge transfer (LLCT) [16].

3.5. Photocatalytic Properties

The photocatalytic role of CPs in the detoxification of water from organic pollutants is a subject of current interest [17,18]. However, only a few bpba-based CPs have exhibited plausible photocatalytic properties [6,19]. It was proposed that in photocatalysis, the hydroxyl radical (OH·) is the major oxidant in charge of the heterogeneous oxidation process, which decomposes the organic dye with good efficiency. Due to the easy preparation and applicable stability in water, the photocatalytic effects of complexes 9 and 10 with the degradation of a dye were investigated. Methyl blue (MB) was selected as a model of dye contaminant and the experiments were carried out in 30 wt % H₂O₂ under 365 nm UV light.

The changes in A/A₀ of MB solutions versus irradiation time for complexes 9 and 10 are shown in Figure 13a,b, respectively, wherein A₀ is the initial absorption of the MB solution and A is the absorption at the reaction time t (min). Time-dependent absorption spectra of the MB solution under 365 nm UV light are provided as supplementary material in Figures S12–S29. The percentage of MB (pmb) remaining in solution was evaluated according to pmb = (A₀ − A_t)/A₀ × 100%, while the degradation efficiency (de) was calculated as de = pmb (t = 0)–pmb (t = 60) (see Table S11 in Supplementary Materials). Accordingly, the enhanced de due to the complexes with the participation of H₂O₂ is 8(1) and 12(2)% for 9 and 10, respectively. It is clearly shown that both complexes exhibit a photocatalytic effect toward MB degradation. Moreover, the PXRD patterns of complexes 9 and 10 after the photocatalytic reactions have been measured. As shown in Figure S30, no obvious changes are observed, indicating their structural integrity and suitability for being used as catalysts in the photocatalytic reaction system. For comparison, it is noted that the 3-fold interpenetrating coordination polymer Zn(bdc)(L’)·solvents (L’ = N⁴,N⁴′-di(pyridin-4-yl)biphenyl-4,4′-dicarboxamide, H₂bdc = terephthalic acid), which adopts a self-catenated net with the hxg-d-4-Fddd topology, shows photocatalytic activity under visible light with the degradation of rhodamine B (RhB) [17].

4. Conclusions

The synthesis and structural characterization of ten divalent CPs based on bpba and polycarboxylate ligands have been successfully accomplished, which show 1D, 2D, and 3D structures. Complex 1 is a 1D chain and 2 and 5 are 2D layers with the sql topology, while 3 and 6 are 2D layers with the hcp topology and 4 displays a 3D self-catenated framework with the rare (4²·6⁷·8)-hxg-d-5-C2/c topology. Complex 7 forms a 2D layer with the (4²·6⁷·8)(4²·6)-3,5L2 topology and 8 is a 2-fold interpenetrated 3D framework with the pcu topology, while 9 and 10 display 3D self-catenated frameworks with the (4²⁴·6⁴)-8T2 and the (4⁴·6¹⁰·8)-mab topologies, respectively. In addition to the nature of the dicarboxylate ligands, we have shown that the identity of the metal ions, the isomerism and flexibility of the bpba ligands, and the metal to ligand ratio play important roles in determining the structural diversity of these divalent CPs. With the same bpba and AIPA²⁻ ligands, the CPs with Zn(II) ions prefer to form the 3D self-catenated frameworks. We have also shown that both complexes 9 and 10 display luminescent properties and can be used as catalysts to accelerate the photodegradation of organic dyes.