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Article Cite This: Cryst. Growth Des. XXXX, XXX, XXX−XXX

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[Zn(tp)(RdmB)(H2O)] and [Cd(tp)(RdmB)]: Two Unusual OneDimensional Rhodamine B Coordination Polymeric Ribbons as Luminescent Sensors for Small Molecules and Metal Cations Published as part of a Crystal Growth and Design virtual special issue on Crystalline Functional Materials in Honor of Professor Xin-Tao Wu Li Liu and Jing-Cao Dai* Downloaded via UNIV OF SUSSEX on June 27, 2018 at 00:10:31 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Institute of Materials Physical Chemistry, Huaqiao University, Xiamen, Fujian 361021, China S Supporting Information *

ABSTRACT: Two new complexes, [Zn(tp)(RdmB)(H2O)] (I) and [Cd(tp)(RdmB)] (II) (tp = terephthalate, RdmB = rhodamine B), are obtained by similar hydrothermal synthesis reactions. X-ray crystallography reveals that both compounds are one-dimensional (1D) polymeric solids, in which I (C36H36N2O8Zn) ascribes to monoclinic C2/m space group, Z = 4 (a = 18.834(5) Å, b = 16.859(5) Å, c = 10.111(3) Å, β = 97.638(4)°), while II (C108H102N6O21Cd3) crystallizes in monoclinic P21/n, 4 (a = 12.2309(1) Å, b = 61.5661(7) Å, c = 12.5852(1) Å, β = 93.951(1)°). Owing to the difference in the coordination sphere around the metal center, four-coordinated zinc centers for I bridged by linear tp molecules associated with RdmB ligands result in an interesting 1D infinite zigzag tape-like structure, whereas six-/seven-coordinated cadmium centers for II bridged by the same ligands generate a novel 1D infinite biserrated edge ribbon structure with a 2,3,3-linked {62.10}{63}{6} network or a simplified 2,4-linked {43.62.8}{4} topological network. The former exhibits excellent luminescent selective sensing behaviors for Cu2+ cation, pyridine, dimethylformamide, and ammonia vapor molecules, while the latter also displays selectivity for sensing Cu2+ cation, pyridine, and methanol molecules.

1. INTRODUCTION Explorations of multifunctional molecule-based materials have been a prominent topic in recent decades since their promising prospects are expected to find applications in the areas of information storage, optoelectronic devices, chemosensors, solar cells, and drug delivery.1−5 The popular promising avenue for the construction of multifunctional materials is frequently based on the self-assembled reactions of functional organic and inorganic components via the principles of crystal engineering to avail the advantages of their versatile and tunable physical properties.6−12 Luminescent complexes are among of the attractive multifunctional molecule-based materials, in which either their structures or functionalities are closely tied to the intrinsic geometry and characteristic properties of their fluorescent molecular moieties because the integrity for both geometries and physical properties of these molecular components can be imparted to target solid-state © XXXX American Chemical Society

materials during the spontaneous reactions. Thus, these molecular components play a vital role in design and fabrication of luminescent multifunctional materials with intriguing structures and novel functionalities.13,14 Numerous interesting examples have been reported in the literature, exhibiting fascinating structural diversities associated with the desired luminescent properties, as to one-dimensional (1D) polymeric chains,15−18 two-dimensional (2D) layer frameworks,19−26 and three-dimensional (3D) porous polymeric solids.27−35 We are continuing efforts in the exploratory design and synthesis of porous luminescent frameworks mimicking important mineral architectures so as to reveal and understand the fluorescent ligands’ role better. In attempts to prepare new Received: March 27, 2018 Revised: June 3, 2018 Published: June 18, 2018 A

DOI: 10.1021/acs.cgd.8b00455 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Table 1. Some Crystal Data Collection and Structure Refinement Parameters for I and II identification code

I (CCDC978512)

II (CCDC1479265)

empirical formula formula weight T (K) λ (Å) crystal system, space group, Z unit cell dimensions (Å, °, Å3) a b c β V ρcalcd (g·cm3) μ (mm−1) F(000) crystal size (mm) θ range (deg) collected reflections unique reflections observed reflections Rint data/restraints/parameters GOF R indices (for obs.): R1a, wR2b R indices (for all): R1, wR2 largest diff. peak/hole (e·Å−3)

C36H36N2O8Zn 690.04 296(2) 0.71073 (MoKα) monoclinic, C2/m, 4 18.834(5) 16.859(5) 10.111(3) 97.638(4) 3182(2) 1.440 0.829 1440 0.20 × 0.15 × 0.12 1.6−25.5 8870 2961 2233 0.0519 2961/0/228 1.055

C108H102N6O21Cd3 2157.15 293(2) 1.54184 (CuKα) monoclinic, P21/n, 4 12.2309(1) 61.5661(7) 12.5852(1) 93.951(1) 9454.2(2) 1.516 5.995 4416 0.23 × 0.18 × 0.10 3.8−66.5 38252 16586 13972 0.0404 16586/2660/1234 1.066

0.0644, 0.1773

0.0493, 0.1201

0.0834, 0.1938 1.68/-0.94

0.0642, 0.1270 0.90/-1.25

R1 = ∑(||Fo| − |Fc||)/∑|Fo|, wR2 = {∑w[(Fo2 − Fc2)2]/∑w[(Fo2)2]}1/2. bw = 1/[σ2(Fo2) + (aP)2 + bP], where P = (Fo2 + 2Fc2)/3].

a

between 4000 and 400 cm−1 using KBr plates. Powder X-ray diffractions (PXRD) investigations were performed on polycrystalline samples using a Rigaku SmartLab diffractometer at 40 kV and 30 mA equipped with Cu Kα radiation (λ = 1.5406 Å) with a scan speed of 5°·min−1 and a step size of 0.02° in 2θ. Thermogravimetric analysis (TGA) were carried out with a TA DSC2910/SDT2960 system at a heating rate of 5 °C·min−1 under Ar atmosphere. Fluorescent data were recorded on an Edinburgh FL-FS920 TCSPC spectrometer or an Edinburgh FS5 fluorescence spectrophotometer, and the solid state absorption spectra were conducted on a Shimadzu UV2550 spectrometer with an ISR-2200 integral sphere using a plate of barium sulfate as a reflectance standard at ambient temperature. Synthesis of [Zn(tp)(RdmB)(H2O)] (I) and [Cd(tp)(RdmB)] (II). The hydrothermal reaction of 0.5 mmol of zinc acetate dihydrate (110 mg) or cadmium acetate dihydrate (133 mg), 0.7 mmol of H2tp (120 mg), 0.5 mmol of RdmB (240 mg), and 227.8 mmol of water (5 mL) in a 2:3:2:911 molar ratio in a 25 mL Parr Teflon lined stainless steel vial was performed under autogenous pressure heated at 185 °C in a resistance furnace for 1 day, followed by cooling at ca. 6 °C·h−1 to ambient temperature. The resultant red block-shaped crystals were isolated by hand and washed with water and absolute alcohol to give a yield (based on RdmB used) of about 24.6% (85 mg) for Zn phase (I) or 27.3% (98 mg) for Cd phase (II). Their phase purities were supported by PXRD patterns (Figure S1, see Supporting Information). Anal. Calcd (found) for C36H36N2O8Zn (I): C 62.66(62.62), H 5.26(5.35), N 4.06(4.03), and for C108H102N6O21Cd3 (II): C 60.13(60.21), H 4.77(4.91), N 3.90(3.75), respectively. IR (KBr pellet, cm−1) for I: 3435 (s), 2982 (m), 2936 (w), 1591 (s), 1527 (w), 1492 (w), 1464 (m), 1431 (w), 1412 (m), 1391 (w), 1354 (s), 1296 (w), 1273 (s), 1248 (m), 1198 (w), 1182 (s), 1157 (w), 1132 (m), 1076 (m), 1013 (w), 978 (w), 921 (w), 886 (w), 876 (w), 831 (w), 795 (w), 769 (w), 752 (m), 712 (w), 683 (w), 664 (w), 563 (w), 521 (w), 461 (w), and for II: 3435 (s), 2976 (m), 2935 (w), 1752 (w), 1645 (m), 1591 (s), 1527 (w), 1481 (w), 1464 (m), 1411 (m), 1381 (s), 1348 (s), 1274 (s), 1251 (m), 1182 (s), 1160 (w), 1132 (s),

luminescent multifunctional materials, the rhodamine B dye (RdmB) has caught our attention. RdmB is a well-known diaminoxanthene dye, which exists in two forms either zwitterion or lactone; the former has intense fluorescence over the visible spectral region, while the latter has not optically activity and is transparent in the visible.36−39 The chromophoric properties, originated from its diaminoxanthene skeleton, can be easily influenced by the local environment of the RdmB dye dependent on the interchange between zwitterionic and lactone forms. This unique spectral feature is quite suitable as an ideal chromophoric linker to bind the metal centers for the development of new luminescent multifunctional materials. Our design strategy for preparing new luminescent materials is the choice of RdmB as a fluorescent organic ligand associated with small rigid polycarboxylate ligand molecules, such as terephthalate, aminoterephthalate, trimesate, etc., as a bridging spacer as well as metal centers to construct the luminescent functional frameworks. Accordingly, two new 1D polymeric solids, [Zn(tp)(RdmB)(H2O)] (I) and [Cd(tp)(RdmB)] (II) (tp = terephthalate, RdmB = rhodamine B), based on the fluorescent ligand RdmB, bridging ligand tp molecule, and the d10 transition metal centers, have been now prepared, of which we herein present their synthesis, structural characterization, and luminescent sensitivity.

2. EXPERIMENTAL SECTION General Remarks. All the reagents and solvents for synthesis were commercially available and used as supplied without further purification. The microanalyses of the C, H, and N elements were conducted on a Vario EL III elemental analyzer. IR spectra were collected on a Shimadzu FTIR-8400S spectrometer within the scope B



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Table 2. Selected Bond Lengths [Å] and Angles [°] for I and II Ia Zn−O(1) Zn−O(2) O(1)−Zn−O(2) O(1)−Zn−O(4) O(1)−Zn−O(2a)

2.061(5) 1.969(3) 100.4(1) 97.1(2) 100.4(1)

Zn−O(2a) Zn−O(4) O(2)−Zn−O(2a) O(2)−Zn−O(4) O(4)−Zn−O(2a)

1.969(3) 1.929(5) 107.0(2) 122.7(1) 122.7(1)

IIb Cd(1)−O(1) Cd(1)−O(4) Cd(1)−O(10) Cd(1)−O(11) Cd(1)−O(12a) Cd(1)−O(13a) Cd(2)−O(1) Cd(2)−O(4) Cd(2)−O(5) Cd(2)−O(14) O(1)−Cd(1)−O(4) O(1)−Cd(1)−O(10) O(1)−Cd(1)−O(11) O(1)−Cd(1)−O(12a) O(1)−Cd(1)−O(13a) O(4)−Cd(1)−O(10) O(4)−Cd(1)−O(11) O(4)−Cd(1)−O(12a) O(4)−Cd(1)−O(13a) O(10)−Cd(1)−O(11) O(10)−Cd(1)−O(12a) O(10)−Cd(1)−O(13a) O(11)−Cd(1)−O(12a) O(11)−Cd(1)−O(13a) O(12a)−Cd(1)−O(13a) O(1)−Cd(2)−O(4) O(1)−Cd(2)−O(5) O(1)−Cd(2)−O(14) O(1)−Cd(2)−O(15) O(1)−Cd(2)−O(20b) O(1)−Cd(2)−O(21b) O(4)−Cd(2)−O(5) O(4)−Cd(2)−O(14) O(4)−Cd(2)−O(15) O(4)−Cd(2)−O(20b) O(4)−Cd(2)−O(21b)

2.279(3) 2.434(3) 2.432(3) 2.293(3) 2.305(4) 2.443(4) 2.451(3) 2.279(3) 2.584(3) 2.306(3) 70.6(1) 132.3(1) 118.8(1) 98.5(1) 132.7(1) 144.1(1) 90.5(1) 114.9(1) 85.9(1) 55.3(1) 91.0(1) 90.3(1) 140.6(1) 101.2(1) 54.7(2) 70.3(1) 120.1(1) 91.0(1) 143.4(1) 85.7(1) 118.2(1) 52.8(1) 122.2(1) 136.5(1) 128.1(1) 96.8(1)

Cd(2)−O(15) Cd(2)−O(20b) Cd(2)−O(21b) Cd(3)−O(7) Cd(3)−O(8) Cd(3)−O(16) Cd(3)−O(17) Cd(3)−O(18) Cd(3)−O(19) O(5)−Cd(2)−O(14) O(5)−Cd(2)−O(15) O(5)−Cd(2)−O(20b) O(5)−Cd(2)−O(21b) O(14)−Cd(2)−O(15) O(14)−Cd(2)−O(20b) O(14)−Cd(2)−O(21b) O(15)−Cd(2)−O(20b) O(15)−Cd(2)−O(21b) O(20b)−Cd(2)−O(21b) O(7)−Cd(3)−O(8) O(7)−Cd(3)−O(16) O(7)−Cd(3)−O(17) O(7)−Cd(3)−O(18) O(7)−Cd(3)−O(19) O(8)−Cd(3)−O(16) O(8)−Cd(3)−O(17) O(8)−Cd(3)−O(18) O(8)−Cd(3)−O(19) O(16)−Cd(3)−O(17) O(16)−Cd(3)−O(18) O(16)−Cd(3)−O(19) O(17)−Cd(3)−O(18) O(17)−Cd(3)−O(19) O(18)−Cd(3)−O(19)

2.441(3) 2.354(4) 2.381(4) 2.407(3) 2.270(3) 2.313(4) 2.363(4) 2.307(4) 2.358(4) 103.1(1) 84.2(1) 142.8(2) 88.1(2) 55.0(1) 102.8(1) 138.2(1) 89.2(1) 87.1(1) 54.9(1) 55.3(1) 108.2(2) 107.2(1) 105.2(1) 145.7(1) 97.1(2) 144.4(2) 113.7(2) 102.9(1) 56.0(1) 143.6(2) 100.1(2) 100.4(2) 104.5(2) 55.9(1)

a = x, −y + 1, z. ba = x + 1/2, −y + 1/2, z − 1/2; b = x − 1, y, z + 1.

a

1078 (m), 1016 (m), 979 (w), 925 (m), 887 (w), 839 (m), 748 (s), 712 (w), 685 (m), 563 (w), 522 (w) (Figure S2). Structure Determinations. Single crystals of title compounds with appropriate dimensions of 0.20 × 0.15 × 0.12 mm for I and 0.23 × 0.18 × 0.10 mm for II were selected with the aid of an optical microscope, then quickly coated with high vacuum grease, and subsequently mounted on a glass fiber for single crystal X-ray data collection. Diffraction data were collected at 296 K with the aid of a Bruker Smart APEX II CCD diffractometer equipped with monochromated Mo Kα radiation (λ = 0.71073 Å) for I and at 293 K on a Agilent Gemini/Xcalibur X-ray diffractometer with monochromated Cu Kα radiation (λ = 1.54178 Å) for II, respectively. The reflection intensities were reducted with the Saint subprogram in the Smart software package for I and CryAlisPro software (Version 1.171.36.32) for II, respectively. The SADABS program and the MUTI-SCAN program were applied on all of the data sets for I and II, respectively, for empirical absorption corrections. The XPREP program in the SHELXL-2014 software package was applied for the

space group determination, in which systematic absences suggested the highest possible space group for I and II were C2/m (No. 12) and P21/n (No. 14), respectively. The structural solutions were obtained by direct methods and refined by full-matrix least-squares techniques of F2 using the SHELXTL-2014 software package. Several carbon atoms (C25, C26, C49, C50, C53, C54, C77, C79, and C80) of RdmB’s ethyl amine groups in II were observed to be disordered over two positions, and their refined occupancies were 0.5 each. All nonhydrogen atoms were treated anisotropically unless those disordered atoms were treated by the SIMU model. The organic hydrogen atoms were located in the riding model and treated isotropically. The Addsym subroutine PLATON was used for checking both structures to ensure that either structural model had no additional symmetry. Final refinements were converged at R1 = 0.064 for I and 0.049 for II, respectively. Some crystallographic data are given in Table 1. The important bond lengths and bond angles of both compounds are presented in Table 2. The supplementary crystallographic information has been deposited in the CIF files as CCDC-978512 for I and C



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-1479265 for II, which are available free of charge from the Cambridge Crystallographic Data Centre.

1.98 Å; all are comparable to those observations of several related species.19,24,25,29 Although most tetrahedral coordinated metal centers linked by linear bridging tectonic molecules will generally lead to a diamondoid network, this Zn center is only given as a two-connected node rather than a four-connected node in the structure due to the presence of two terminal ligands. On the other hand, as a μ2-spacer, every rigid linear tp molecule is bridged to two Zn centers through its bis-unidentate carboxylate groups to form a 1D infinite zigzag tape (Figure 1a (bottom)). The distance between two zinc neighbors in the tape is ∼11.2 Å, and the angle of (Zn··· Zn···Zn) is 97.6°. RdmB molecules only served as the hanging terminal ligands staggered parse on two sides of the tape through coordination to zinc centers by their aromatic carboxylate groups that are found to be almost perpendicular to their diaminoxanthene skeletons; as discussed later, this configuration of the vertical aromatic carboxylate group may be connected to the spectroscopic properties of RdmB molecule and, therefore, is important for luminescent sensitivity of I. The adjacent zigzag tapes are arrayed into the parallel rows appearing in somewhat close resemblance to a “zipped fastener” to give a 2D supramolecular sheet along the ∼[011] lattice plane, which is further stacked into a 3D supramolecular architecture in a slipped parallel alignment rather than a perfect eclipse packing of the neighboring sheets (Figure 1b). For II, although coordinated to the same ligands of tp and RdmB, the coordination sphere of cadmium centers is completely different from that of above zinc center. Figure 2a gives the local coordination geometry around the Cd centers of II. There are three crystallographically distinct cadmium centers in the building unit, where two Cd centers (Cd1, Cd2) are each seven-coordinated in a highly distorted pentagonal bipyramidal environment by two groups of seven oxygen molecules (O1, O2, O4, O10, O11, O12a, and O13a for Cd1; O1, O4, O5, O14, O15, O20b, and O21b for Cd2) to give a binuclear {Cd2O12} cluster (Figure 2a, upper left), the separation between two Cd centers is 3.86 Å. These oxygen molecules all come from the carboxylate groups in either bridging tp spacers or terminal RdmB ligands, of which both (O1, O2) and (O4, O5) pairs are from two separated chelating/bridging bidentate carboxylate groups of two different ((κ2-μ2)-μt) RdmB molecules, while the pairs of (O10, O11), (O12a, O13a), (O14, O15), and (O20b, O21b) attribute four separated chelating bis-bidentate carboxylate groups of bridging ((κ2)-(κ2)-μ2) tp molecules. Thus, every {Cd2O12} cluster is actually as a four-linked node with four different bridging tp spacers and two hanging terminal RdmB ligands in the structure. The rest of Cd center (Cd3) is sixcoordinated in a distorted octahedral environment by three pairs of oxygen molecules ((O7, O8), (O16, O17), and (O18, O19)) that ascribe to three separated chelating bidentate carboxylate groups of either two different bridging ((κ2)-(κ2)μ2) tp spacers or a terminal ((κ2)-μt) RdmB ligand, giving rise to each Cd3 center only serving as a two-linked node with a hanging terminal RdmB molecule in the structure. The separations between cadmium centers and surrounding oxygen donors are spread quite broad, ranging from 2.279(3) to 2.584(3) Å. The 2.584(3) Å of the longer bond length for Cd2−O5 is already near a semicoordinated bonding (∼2.7 Å),40 reflecting the highly degree of asymmetry chelating catboxylate visage. These bond lengths are all comparable to those observed elsewhere.20,23,27,28,31 On the other hand, each four-linked binuclear {Cd2O12} cluster is connected to two

3. RESULTS AND DISCUSSION Structure. Both compounds are the 1D polymeric solids that crystallized in monoclinic C2/m space group for I and monoclinic P21/n for II, respectively. For I, as presented in Figure 1a (top), the building block contains a four-coordinated

Figure 1. (a) A view of the 1D infinite zigzag tape in I depicting the local coordination environment around the Zn center; symmetry code: (a) x, 1 − y, z; (b) 2.5 − x, 1.5 − y, 3 − z; (c) 2.5 − x, −0.5 + y, 3 − z. (b) Crystal packing of I showing 2D supramolecular arrangements fabricated by the parallel rows of zigzag tape along the ∼[011] lattice plane; the lighter colored arrangements of the same zigzag tapes showing a stagger offset packing of the neighboring sheet stacks. The hydrogen atoms are omitted for clarity.

Zn center that lies in a little distorted tetrahedral coordination sphere (tetrahedral angle fall within 97.1(2)−122.7(1)°), bonding to a terminal aqua O1 donor and three oxygen molecules (O2, O2a, O4) of three unidentate carboxylate groups that come from a hanging terminal RdmB ligand (O4) and two different bridging ((κ1)-(κ1)-μ2) tp molecules (O2 and O2a), respectively. The Zn−O bond distances lie within the range of 1.929(5)−2.061(5) Å with an average length of D



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Figure 2. (a) A view of the building unit depicting the local coordination environment around the Cd center (upper left) in the 1D infinite biserrated edge ribbon structure (upper right); a topology can be recognized as a 2,3,3-linked {62.10}{63}{6} network (bottom right) or a simplified 2,4-linked {43.62.8}{4} network (bottom left), observed in II. (b) Crystal packing of II showing smart tongue-and-groove stacking of neighboring 1D infinite biserrated edge ribbons along the ∼ [010] direction. (c) Schematic diagrams showing the alternate or stagger offset stacking of neighboring of 1D infinite biserrated edge ribbons along the ∼ [101] lattice plane observed in II (left) and their topological model of 2fold alternate 2,4-linked {43.62.8}{4} networks based on II (right). The hydrogen atoms and all carbon atoms of the ethyl amine groups are omitted for clarity. Symmetry code: (a) 0.5 + x, 0.5 − y, −0.5 + z; (b) −1 + x, y, 1 + z.

or 2,4-linked {43.62.8}{4} network is very scarce so far in the coordination polymeric chemistry. Interestingly, all the aromatic carboxylate groups for RdmB molecules coordinated to cadmium centers are also observed to be perpendicular to their diaminoxanthene skeletons as that in I. These 1D infinite biserrated edge ribbons are parallel stacked in a smart tongueand-groove fashion along the ∼[010] direction to extend to a 2D supramolecular lamella (Figure 2b). The neighboring lamellae are further alternated or staggered offset stacking to generate a 3D supramolecular architecture along the ∼[101] lattice plane (Figure 2c). Characterization and Properties. The elemental microanalysis data for both polymers are very consistent with the

two-linked Cd3 centers as well as other two four-linked binuclear {Cd2O12} neighbors by four bridging tp spacers, while each two-linked Cd3 center only bridged to two fourlinked binuclear {Cd2O12} neighbors by two tp spacers (Figure 2a, upper right). Thus, connection of these four-linked binuclear {Cd2O12} clusters associated with two-linked Cd3 centers in the building block will result in a remarkable 1D infinite biserrated edge ribbon structure with a fishnet-like mesh size of ∼11.2 × 11.2 Å, a topology that can be described as a 2,3,3-linked {62.10}{63}{6} network (Figure 2a, bottom right) or further simplified as a 2,4-linked {43.62.8}{4} network (Figure 2a, bottom left) by TOPOS analysis.41 To our best knowledge, this topology of either 2,3,3-linked {62.10}{63}{6} E



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formulas as [Zn(tp)(RdmB)(H2O)] (I) and [Cd(tp)(RdmB)] (II). Either is very stable in air at room temperature and is almost insoluble in alcohol, acetonitrile, acetone, and toluene. The IR spectra of both complexes show the characteristic bands of carboxylate groups of ligands at 1354−1381 cm−1 for the symmetric stretching vibration and 1591 cm−1 for the asymmetric stretching vibration, all are in the general region.42,43 The bands at 1273, 1248, 1182, 2982, and 2936 cm−1 for I as well as the bands at 1274, 1251, 1182, 2976, and 2935 cm−1 for II verify that the presence of diaminoxanthene skeleton in the either. In additional, the vanished bands at 1690−1730 cm−1 for the protonated carboxylate groups of both compounds implicate the fully deprotonation of H2tp and RdmB on the reactions with metal ions, also reflect that the RdmB molecules in both are in a zwitterion rather than in a lactone fashion.44 All these match well with the structures of both compounds. TGA suggests that there are two distinct weight losses occurring in I; the first weight loss started at approximately 140 °C up to 160 °C to lead a total weight loss of about 2.4% (also see Figure S3, blue line), corresponding to loss of a H2O molecule per formula unit (calcd 2.6%). This implicates the presence of the strongly coordinated aqua molecule, which is agreement with the structure of I. The second weight loss occurs at approximately 270 °C, reflecting that the framework integrity for I can be held over 250 °C that has been also supported by the PXRD pattern (Figure S4). Different from I, the TGA trace for II only gives a clear weight loss started at approximately 350 °C up to ca. 400 °C giving a weight loss of about 60%, corresponding to loss of a RdmB ligand (calcd 61.5%), following a large incline stage up to 600 °C to result in a total approximately 23% weight loss, corresponding to loss of a tp molecule per formula unit (calcd 22.8%). The final thermal decomposition product should be CdO (found ∼18%, calcd 17.9%, Figure S3, red line). This is in agreement with the structure of II and indicates that the framework thermal stability for II is better than that for I, which should clearly arise from their structural difference in the coordinated fashion: the chelating bisbidentate carboxylate in the former versus the unidentate carboxylate in the latter. Some spectroscopic properties for both polymers are investigated since the RdmB ligand is a chromophoric linker and usually presents rather outstanding optical properties. As given in Figure 3, the solid state UV−vis absorption spectra for both compounds and free RdmB ligand are similar at ambient temperature. The free ligand molecule (black line, Figure 3) shows a high intensity and spin-allowed broad band closer ca. 562 nm with a small shoulder around 613 nm, which should be generally originated from the zwitterionic RdmB rather than its lactone type because the latter is almost transparent in the visible region.36−39 The main absorption can be ascribed to the π → π* transition45,46 within the S0 → S1 state of the RdmB molecule,47 and the red-shifted shoulder phenomenon should arise from the presence of dimer species.48 This main absorption band also appears for both polymers but has been blueshifted to about 556 nm for I (red line, Figure 3) and 553 nm for II (blue line, Figure 3). The vanished shoulder peak and the blueshift phenomenon can be recognized as the results from the coordination between the carboxylate group of RdmB ligand and the metal center, the former rising from the absence of dimer species while the latter from the breach of a conjugated system of RdmB molecule since the aromatic carboxylate group is almost oriented perpendicular to the

Figure 3. UV−vis spectra of RdmB (black), I (red), and II (blue) in the solid state at ambient temperature.

diaminoxanthene skeleton. Under the illumination of a UV lamp light, both polymers exhibit intense fluorescent behaviors. Figure 4 gives the solid state fluorescent spectra for both

Figure 4. Solid-state fluorescent emission spectra of RdmB (gray), I (red), and II (blue) at ambient temperature.

compounds and free RdmB ligand. The emission spectra exhibit an intense fluorescent emission at about 695 nm for free RdmB ligand (gray line, Figure 4), corresponding to the π* → π transition. After complexation with metal centers, this ligand-centered emission band has been blueshifted to the maximum at 663 nm for I (red line, Figure 4) and 674 nm for II (blue line, Figure 4), respectively. However, these are clearly red-shifted compared to those emissions of RdmB elsewhere in the gas phase at 542 nm36 and in the solution phase either methanol solution at 577 nm49 or aqueous solution at 580 nm.50 This presumably reflects the RdmB ligand having a smaller S0 → S1 energy level gap in the solid state,51−53 consistent with its zwitterionic form being better stabilized and preventing the formation of lactone type due to the coordination of metal centers.54 Luminescent Sensitivities. As is well-known, many porous polymeric solids exhibit attractive chemical selectivity in molecular sensing applications since their flexible porosity can offer selective adsorption for some chemical species.55 F



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from ruby to pink (Figure 6) or at 610 nm by dimethylformamide (dmf) solvent. This blueshifted effect is

Although I and II are 1D coordination polymeric ribbons that are not typical porous frameworks, the resemblance of chemical sensing may occur in both because they have the same chromophoric components. In order to study the luminescent sensing behavior, the polycrystalline samples (10 mg) for either I or II are dispersed into various organic solvents (10 mL) or immersed in the alcohol solutions (10−2 M, 10 mL) of six different metal acetates (Na+, Mg2+, Mn2+, Co2+, Ni2+, and Cu2+) for 10 h in ambient temperature. The suspensions are subsequently separated by filtration and are air-dried for solid-state spectroscopic data collection. As shown in Figure 5, the intensity of luminescent spectra for either I or

Figure 6. Crystal photographs showing the discernible color conversions occurring in I after treatment by either soaking in both alcohol solution of copper acetate and pyridine solvent or fumigating in the atmosphere of ammonia evaporation.

also observed to occur in II (Figure 5b), because the emission band has been drastically moved to 578 nm but with a remarkable enhancement effect by pyridine or to 594 nm with a similar quenching effect by methanol molecules. These indicate that I could be a promising fluorescent probe for either pyridine or dmf molecules, while II should also be as a selective turn-on sensor for pyridine and methanol molecules. As is well-known, the luminescent behaviors of RdmB molecule and its derivatives are easily perturbed by various metal ions and exhibit selective sensitivity for some metal cations.38,39,56−59 Similarly, the fluorescent emissions for both I and II are also found to be influenced by some metal ions. As shown in Figure 7, the emission intensities for either I at 663 nm or II at 674 nm exhibit different reductions under the perturbation of six different metal ions, of which the perturbation of Cu2+ ion is very sharp. Especially, the Cu2+ ion dramatically decays the luminescence of I to reach only a 17% of original emission intensity at 663 nm, close to decay ∼6 times as much as that from the blank parent (Figure 7a). In stark contrast, the quenching effect of other five metal cations (Na+, Mg2+, Mn2+, Co2+, and Ni2+) is not exhibited so remarkably; the luminescent intensities only decay ∼15% to 30% on I (Figure 7a). This quenching effect of the Cu2+ ion also obviously occurred in II, the emission intensity at 674 nm being decayed 2 times more than that of blank (Figure 7b). Moreover, the sensitivity for this luminescence quenching effect of Cu2+ ion on I is still retained under the perturbation of other five metal ions (Figure S5, see Supporting Information), implicating that I will be an excellent sensing material used in the detection of the Cu2+ ion through the luminescent quenching effect. On the other hand, the emission for I is

Figure 5. Solid-state emission spectra of (a) I and (b) II after treatment by soaking in different organic solvents.

II is closely dependnent on the organic solvent molecules. The solid state emissions are still present at ∼663 nm (Figure 5a) for I and ∼674 nm (Figure 5b) for II with an intensity change, ranging from +27% to −21% for the former and at most −10% for the latter more than that of their blank parents, under the perturbation of most organic solvents including dioxane, acetone, toluene, dichloromethane, acetidin, alcohol, ether, and so on. However, the emission band for I (Figure 5a) is obviously decayed and blueshifted to a maximum either at 598 nm by pyridine molecule accompanying the color conversion G



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luminescence of I presents a dramatic reduction with an emission intensity at 663 nm of ∼7 times less than that of pure blank in the atmosphere of ammonia evaporation. For the sake of understanding the sensing of I for the ammonia molecule better, the powder samples of I were placed inside a desiccator filled with the ammonia vapor for different times. As presented in Figure 8b, the luminescence quenching effect is still clearly observed once I the samples touched the ammonia vapor only for 5 s, suggesting that the response for I as an ammonia vapor probe is quite sensitive. Interestingly, PXRD patterns for either I (Figure S6) or II (Figure S7) show that the overall frameworks remain almost intact after being soaked in various 10−2 M alcohol solution of five metal cations, while their structural collapse has obviously occurred by introduction into the Cu2+ cation. This breach phenomenon of the framework is also observed in I for sensing pyridine, dmf (Figure S8) and even ammonia vapor molecules (Figure S9). These indicate that the luminescent sensing behavior for metal cations and small molecules on either I or II may presumably result from their crystalline phase transitions.

4. CONCLUSION In summary, two new rhodamine-based complexes, [Zn(tp)(RdmB)(H2O)] (I) and [Cd(tp)(RdmB)] (II), were successfully prepared and characterized. They crystallize in two interesting 1D ribbon structures with a 1D infinite zigzag tape in I and a remarkable 1D 2,4-linked {43.62.8}{4} topological network in II and are rather stable in ambient environment. The experimental observations reveal either polymeric solid is an optically active material, exhibiting interesting luminescent sensitivities that I has excellent selectivity for Cu2+ cation, pyridine, dmf, and ammonia vapor molecules sensing behavior, while II also displays selective sensitivity for Cu2+ cation, pyridine, and methanol molecules. These will be of great significance for expanding our chemical insights into the construction of functional materials associated with their optoelectronic applications.

Figure 7. Solid-state emission spectra showing the different luminescence quenching effects of metal ions on (a) I and (b) II after treatment by soaking in various alcohol solutions of different metal acetates.

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ASSOCIATED CONTENT

S Supporting Information *

also observed to be completely quenched by the fumigation of ammonia vapor accompanying the discernible color changes by the naked eye (Figure 6). As shown in Figure 8a, the

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.8b00455.

Figure 8. (a, b) Solid-state emission spectra showing the luminescence quenching effects of NH3 on I after treatment by absorbed the ammonia vapor. H



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Figures S1−S9 providing the PXRD patterns, the FT-IR spectra and the TGA traces of both I and II, as well as the luminescence quenching of I (PDF) Accession Codes

CCDC 1479265 (II) and 978512 (I) 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]. Phone/Fax: +86-595-22690569. ORCID

Jing-Cao Dai: 0000-0002-0659-1329 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to the NSF of Fujian Province (Grant No. 2015J01202) and the Package Funding for the Distinguished Professorship of the Tong-Jiang Scholars for financially support.

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DEDICATION Dedicated to Professor Xin-Tao Wu on the occasion of his 80th birthday. REFERENCES

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