A New Strategy of Designing New Crystal Structures Based on

Apr 19, 2013 - A New Strategy of Designing New Crystal Structures Based on Topological Structure: Syntheses and Crystal Structures of Five Coordinatio...
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A New Strategy of Designing New Crystal Structures Based on Topological Structure: Syntheses and Crystal Structures of Five Coordination Polymers with (4,4) Topology Jin-Shuang Guo, Gang Xu, Guo-Cong Guo,* and Jin-Shun Huang State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, People’s Republic of China S Supporting Information *

ABSTRACT: Five coordination polymers 1−5 with four types of (4,4) layers have been synthesized through a new strategy of designing their crystal structures based on (4,4) topology. Compound [Co(adc)(bpp)(H2 O)]n (1) presents a 2-D structure with 2-fold homointerpenetration of layer A, while the 2-D compound {[Ni(adc)(bpp) 2 (H 2 O)] 2 ·bpp} n (2) presents 2-fold heterointerpenetration of layer B and layer C. Compound [Zn(adc)(bpp)·DMF]n (3) displays a typical 2-D → 3-D parallel interpenetrating structure of layer D. Compounds [Ni(Cladc)(bpp)(H2O)]n (4) and [Co(Cladc)(bpp)(H2O)]n (5) are isomorphous and display similar structures to 1. (H2adc = 4,4′-azodibenzoic acid, ClH2adc = 3,3′-dichloro-4,4′azodibenzoic acid, bpp = 1,3-di(4-pyridyl)propane, DMF = N,N-dimethylformamide). Luminescence properties and thermal stabilities of 1−5 have been explored.

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INTRODUCTION The ongoing research on polymeric coordination networks has been rapidly expanding, which results in large numbers of novel and fascinating coordination polymers with potential properties as functional materials, such as gas adsorption, separation, catalytic activities, luminescence, etc.1 The topological approach is widely employed to help understanding the complex crystal structures through abstracting inorganic building blocks (such as metal ions, secondary building units, small metal clusters, etc.) as nodes, and organic building blocks as spacers, then constructing the nodes and spacers to a topological structure with higher symmetry in comparison with its crystal structure. Conversely, it is also possible to diversify structures from a topological structure to crystal structures, which is a process of reducing structural symmetry by rationally preparing and controlling nodes and/or spacers of the target topology. Nodes can be diversified by controlling the coordination number and coordination sphere of metal ions, while organic spacers can be judiciously predesigned to rigid or flexible/long or short/bi- or polydentate ligands, single- or multifunctional ligands, and even ligands as single or double bridges.2 This structural diversification conception providing us an infinite space to create different crystal structures is of substantial significance in crystal engineering. However, only a few examples were reported scatteredly until now, and the systematic study is highly desired. To tentatively and systematically study the diversity of a topological structure, the simple (4,4) topology is picked out as the subject of research because of a great growth on the number © XXXX American Chemical Society

of 2-D mixed-ligand coordination polymers with (4,4) topology.2h,i,3 On the premise that rigid and flexible ligands are abstracted as lines and arcs, respectively, (4,4) topology in these reported compounds can be diversified to five types of structures, which are named here types a, b, c, and d that have a single arched bridge and type e that has double arched bridges (Figure 1). The discrepancy in these diversified structures is embodied by their different locating rules of flexible arched bridging ligands. Theoretically, if each of the flexible arched bridging ligands can rotate 360°, an infinite number of 2-D polymeric layers with (4,4) topology could be constructed, from which we got enlightenment to study (4,4) topology. In this paper, five novel 2-D coordination polymers, [Co(adc)(bpp)(H2O)]n (1), {[Ni(adc)(bpp)2(H2O)]2·bpp}n (2), [Zn(adc)(bpp)·DMF]n (3), [Ni(Cladc)(bpp)(H2O)]n (4), and [Co(Cladc)(bpp)(H2O)]n (5), with four types of edge-transitive 4,4 square lattices (sql)4 were obtained. The (4,4) topological structure is diversified via this scheme: Co(II)/Ni(II)/Zn(II) were chosen as nodes and coordinated by ligating O atoms of rigid ligands μ2-adc2−/μ2-Cladc2− to form 1-D chains [−M-adc2−−]n/[−M-Cladc2−−]n (M = Co, Ni, Zn); these chains were bridging by flexible bpp ligands to construct different crystal structures based on (4,4) topology. Herein, we report the syntheses and structures of 1−5, and the first systematic study on structural diversification of (4,4) Received: March 17, 2013 Revised: April 17, 2013

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II powder diffractometer with Cu-Kα radiation and 5 ≤ 2θ ≤ 75°. Single-crystal X-ray diffraction was carried out by a Rigaku Mercury CCD diffractometer. Syntheses of 1−5. [Co(adc)(bpp)(H2O)]n (1). The required amount of triethylamine was put into a mixture of CoCl2·6H2O (59 mg, 0.25 mmol), H2adc (67 mg, 0.25 mmol), and bpp (99 mg, 0.5 mmol) in 4 mL of H2O to adjust the pH of the solution to be 8. The whole reactants were then sealed into a 25 mL poly(tetrafluoroethylene)-lined stainless steel container under autogenous pressure and then heated at 100 °C for 5 days and cooled naturally to room temperature. Red block crystals of 1 were produced, and then selected by hand and washed with H2O. Yield: 22% based on Co. IR (KBr pellet)/cm−1: 3412vs, 3064m, 2924s, 2863m, 1946w, 1606vs, 1545vs, 1505m, 1418s, 1384vs, 1298m, 1217s, 1150w, 1124w, 1097m, 1070m, 1010s, 883m, 864s, 789vs, 749w, 702s, 642w, 615m, 582w, 508m, 482w. Anal. Calcd for C27H24CoN4O5: C, 59.68; H, 4.45; N, 10.31. Found: C, 59.38; H, 4.53; N, 10.14%. {[Ni(adc)(bpp)2(H2O)]2·bpp}n (2). The required amount of triethylamine was put into a mixture of Ni(CH3COO)2·4H2O (62 mg, 0.25 mmol), H2adc (67 mg, 0.25 mmol), and bpp (198 mg, 1 mmol) in 4 mL of H2O to adjust the pH of the solution to be 8. The whole reactants were then sealed into a 25 mL poly(tetrafluoroethylene)lined stainless steel container under autogenous pressure and then heated at 100 °C for 5 days and cooled naturally to room temperature. Red block crystals of 2 were synthesized, and then selected by hand and washed with H2O. Yield: 14% based on Ni. IR (KBr pellet)/cm−1: 3412vs, 3064m, 2924s, 2863m, 1946w, 1606vs, 1545vs, 1505m, 1418s, 1384vs, 1298m, 1217s, 1150w, 1124w, 1097m, 1070m, 1010s, 883m, 864s, 789vs, 749w, 702s, 642w, 615m, 582w, 508m, 482w. Anal. Calcd for C93H90N14Ni2O10: C, 66.44; H, 5.40; N, 11.66. Found: C, 64.30; H, 5.65; N, 11.45%. [Zn(adc)(bpp)·DMF]n (3). A mixture of Zn(NO3)2·6H2O (74 mg, 0.25 mmol), H2adc (67 mg, 0.25 mmol), and bpp (99 mg, 0.5 mmol) in 4 mL of DMF was sealed into a 25 mL poly(tetrafluoroethylene)lined stainless steel container under autogenous pressure and then heated for 3 days at 100 °C and cooled naturally to room temperature, yielding red block crystals of 3. Yield: 38% based on Zn. IR (KBr pellet)/cm−1: 3439s, 3055w, 3038w, 2952w, 2858w, 1951w, 1619vs, 1593vs, 1549vs, 1508w, 1455w, 1432s, 1400vs, 1306m, 1221m, 1101w, 1069m, 1028s, 1008w, 873m, 856m, 823s, 794vs, 730w, 698s, 622m,

Figure 1. Five types of reported 2-D layers constructed of mixed flexible and rigid ligands with (4,4) topology, which are named as types a, b, c, d, and e.

topology based on mixed-ligand layers. In addition, luminescence properties and thermal stabilities of these compounds have also been explored.

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EXPERIMENTAL SECTION

Materials and Instruments. All chemicals were obtained from commercial sources and used as received without further purification. 4,4′-Azodibenzoic acid and 3,3′-dichloro-4,4′-azodibenzoic acid were prepared according to the literature method.5 The elemental analyses were measured on an Elementar Vario EL III microanalyzer. The FTIR spectra were obtained on a PerkinElmer Spectrum using KBr disks in the range of 4000−450 cm−1. Photoluminescent analyses were performed on an EI920 fluorescence spectrometer. Thermal analyses were made on a Netzsch STA 449C Jupiter under a N2 atmosphere with the sample heated in an Al2O3 crucible at a heating rate of 10 K·min−1. Powder X-ray diffraction data were collected using a Miniflex

Table 1. Crystal and Structure Refinement Data for 1−5 formula Mr (g mol−1) cryst syst space group Dcalcd (g cm−3) a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z abs coeff (mm−1) reflns collcd/unique Rint data/params/restraints R1a [I > 2σ(I)] wR2b [I > 2σ(I)] goodness of fit Δρmax, Δρmin (e Å−3) a

1

2

3

4

5

C27H24CoN4O5 543.43 triclinic P1̅ 1.440 10.63410(10) 10.76710(10) 12.37710(10) 67.066(8) 83.639(12) 73.758(10) 1253.047(99) 2 0.730 9566/4497 0.0300 3721/340/3 0.0471 0.1196 1.055 0.597, −0.622

C93H90N14Ni2O10 1681.21 orthorhombic Pbca 1.289 19.708(2) 24.955(3) 35.224(4) 90 90 90 17324(3) 8 0.502 113496/15996 0.0527 10851/1084/6 0.0722 0.1833 0.992 1.003, −0.439

C30H29N5O5Zn 604.95 monoclinic P21/c 1.385 8.5216(6) 30.4113(15) 11.6223(9) 90 105.554(3) 90 2901.6(3) 4 0.894 22961/5356 0.0789 2989/370/0 0.0698 0.1966 1.011 0.446, −0.465

C27H22Cl2N4NiO5 612.08 triclinic P1̅ 1.604 9.479(4) 11.835(5) 12.798(5) 67.543(11) 76.936(15) 74.777(15) 1267.5(9) 2 1.024 9727/4568 0.0446 3241/359/3 0.0451 0.0892 0.971 0.977, −0.325

C27H22Cl2CoN4O5 612.32 triclinic P1̅ 1.591 9.503(3) 11.880(3) 12.818(3) 67.556(9) 76.977(9) 74.837(8) 1278.1(5) 2 0.928 9632/4552 0.0272 3107/363/0 0.0401 0.0783 0.926 1.321, −0.395

R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = {∑w[(Fo)2 − (Fc)2]2/∑w[(Fo)2]2. B

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516s, 493w. Anal. Calcd for C30H29N5O5Zn: C, 59.56; H, 4.83; N, 11.58. Found: C, 59.12; H, 4.72; N, 11.24%. [Ni(Cladc)(bpp)(H2O)]n (4). A mixture of Ni(CH3COO)2·4H2O (62 mg, 0.25 mmol), ClH2adc (83 mg, 0.25 mmol), and bpp (99 mg, 0.5 mmol) in 4 mL of H2O was sealed into a 25 mL poly(tetrafluoroethylene)-lined stainless steel container under autogenous pressure and then heated for 3 days at 160 °C and cooled naturally to room temperature, yielding green block crystals of 4. Yield: 52% based on Ni. IR (KBr pellet)/cm−1: 3502s, 3243m, 3107w, 3078w, 2940m, 2860w, 1938w, 1667m, 1614vs, 1567s, 1550s, 1506m, 1482m, 1463m, 1415vs, 1392vs, 1290w, 1223m, 1193s, 1129w, 1072m, 1037m, 1021m, 898s, 854s, 822s, 795s, 733m, 694m, 642m, 619s, 517m, 492m. Anal. Calcd for C27H22Cl2N4NiO5: C, 52.98; H, 3.62; N, 9.15. Found: C, 52.76; H, 3.77; N, 9.23%. [Co(Cladc)(bpp)(H2O)]n (5). A mixture of CoCl2·6H2O (59 mg, 0.25 mmol), ClH2adc (83 mg, 0.25 mmol), and bpp (99 mg, 0.5 mmol) in 4 mL of EtOH−H2O (V/V = 1:1) was sealed into a 25 mL poly(tetrafluoroethylene)-lined stainless steel container under autogenous pressure and then heated for 3 days at 100 °C and cooled naturally to room temperature, yielding brown tabular crystals of 5. Yield: 78% based on Co. IR (KBr pellet)/cm−1: 3507s, 3234m, 3105w, 3072w, 2939m, 2860w, 1932w, 1668m, 1613vs, 1550m, 1505m, 1481w, 1461w, 1412vs, 1392vs, 1375vs, 1287w, 1224m, 1192s, 1149w, 1128w, 1072w, 1037m, 1019m, 909m, 897s, 820s, 804m, 793s, 730m, 695m, 670w, 641m, 615s, 581w, 551w, 514m, 492m. Anal. Calcd for C27H22Cl2CoN4O5: C, 52.96; H, 3.62; N, 9.15. Found: C, 52.76; H, 3.77; N, 9.23%. Single-Crystal Structures Determination. The crystal structures of 1−5 were studied by single-crystal X-ray diffraction analysis. Data collections were performed at 293 K on a Rigaku Mercury CCD diffractometer with a graphite-monochromatic Mo-Kα radiation source (λ = 0.71073 Å). There was no evidence of crystal decay during data collection. The intensity data sets were collected with an ω scan technique and reduced using the CrystalClear software.6 The structures were solved by direct methods, which revealed the positions of metal atoms using the Siemens SHELXTL Version 5.0 package of crystallographic software.7 The structures were refined using fullmatrix least-squares refinement on F2. Non-hydrogen atoms for 1−5 were located by difference Fourier maps and subjected to anisotropic refinement. All hydrogen atoms of coordinated water molecules were calculated in idealized positions and refined with O−H distances restrained to a target value of 0.85 Å and Uiso(H) = 1.5 * Ueq(O). The remaining hydrogen atoms were calculated in idealized positions and allowed to ride on their parent atoms. Pertinent crystal data and structural refinement results as well as selected bond distances and angles for 1−5 are listed in Table 1 and Table S1 (Supporting Information), respectively. CCDC 919084−919088 contain the crystallographic data for 1−5. These data can be obtained free of charge from The Cambridge Crystallographic Data Center (CCDC) via www.ccdc.cam.ac.uk/data_request/cif.

Scheme 1. Solvo(Hydro)Thermal Synthetic Route of 1−5

H2O, triethylamine is needed to adjust the pH value of the reaction mixture to be weakly alkaline in order to obtain compound 1. Compared with 1, the relatively good solubility of ClH2adc in H2O makes compounds 4 and 5 able to be obtained simply without triethylamine. Besides the solvent and pH value, an increase in the ratio of bpp to Ni(II):H2adc:bpp = 0.25:0.25:1 yields compound 2, which contains more bpp to be monodentate bpp ligands and lattice bpp molecules (Figure 4). Structural Descriptions. [Co(adc)(bpp)(H2O)]n (1). Singlecrystal X-ray diffraction analysis reveals that compound 1 crystallizes in the triclinic system with space group P1̅ and features 2-D undulated layers named layer A. The asymmetric unit of 1 contains one Co(II) atom, one adc2− ligand, one bpp ligand, and one coordinated water molecule (Figure 3a). Each Co(II) atom is five-coordinated by two carboxylate O atoms (Co1−O1 2.058(2) Å, Co1−O3(x + 1, y + 1, z) 2.026(2) Å), two pyridine N atoms (Co1−N3 2.127(2) Å, Co1−N4(x + 1, y − 1, z) 2.135(3) Å), and one O atom of a water molecule (Co1−O1W 2.082(2) Å), producing a distorted tetragonal pyramid coordination sphere. In this arrangement, three O atoms, O1, O1W, and O3(x + 1, y + 1, z), together with one N4(x + 1, y − 1, z) atom, reside in four vertexes of the bottom quadrangle (∠O1−Co1−O1W 87.78(9)°, ∠O1W−Co1−O3(x + 1, y + 1, z) 87.62(9)°, ∠O3(x + 1, y + 1, z)−Co1−N4(x + 1, y − 1, z) 90.78(9)°, ∠N4(x + 1, y − 1, z)−Co1−O1 93.01(9)°) and one N3 atom occupies the apex of the tetragonal pyramid (Figure 3a; Table S1 (Supporting Information)). Two N atoms of bpp coordinate to one Co(II) center nearly along the vertical direction (∠N3−Co1−N4(x + 1, y − 1, z) 98.99(10)°). Moreover, these distorted tetragonal pyramids all slant in the same direction with the dihedral angle of 48.075(46)° between the bottom quadrangle and the plane where Co(II) atoms are. In 1, the cis-adc2− ligands, with a μ2-κ2O1:O3 binding mode, link Co(II) atoms into 1-D [−Coadc2−−]n chains with a Co(II)···Co(II) distance of 17.1191(13) Å. Parallel [−Co-adc2−−]n chains are pillared into a (4,4) rhomboid grid [Co(adc)(bpp)(H2O)]n motif, named layer A, by flexible μ2-bpp ligands that span a Co(II)···Co(II) distance of 12.8439(16) Å (Figure 2, Layer A). The most protruding feature of the resulting (4,4) layer A is all arched bpp ligands that display a TT conformation8 (N3−to−N4 9.6169(35) Å) bent in one direction, showing the type a of wave mode. Two identical A layers further interpenetrate each other to block the free spaces in the squares (Figure 3b). Two resulting entangled sheets (AA) exist in face-to-face pairs (A1A1)(A2A2), and then these complex 2-D arrays stack in the sequence of −(A1A1)(A2A2)(A1A1)(A2A2)− to form the crystal structure of 1 (Figure 3c).

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RESULTS AND DISCUSSION Syntheses. Aiming at obtaining a variety of crystal structures based on (4,4) topology by the above designed scheme, our first choice is solvo(hydro)thermal reactions to realize the process of coordination and polymerization with mixed ligands in one step. The synthetic route is shown in Scheme 1. There are many influencing factors in these solvo(hydro)thermal reactions that give compounds 1−5, such as reactant ratio, solvent, pH value, and reaction temperature. The reason for their different effective synthetic conditions is found to be mainly in the different solubility between H2adc and ClH2adc. H2adc is hardly soluble in H2O or EtOH, and it tends to coordinate to metal atoms more easily in DMF. Therefore, with the same M(II) (M = Co(II), Zn(II)), H2adc, and bpp molar ratio of 0.25:0.25:0.5 in equal volumes of solvent and the same temperature, compound 3 is formed when the solvent is DMF, whereas when the solvent is changed to C

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Figure 2. 2-D layers A, B, C, and D in 1, 2, and 3.

Figure 3. (a) Coordination environment around the Co(II) atom of 1. Symmetry codes: #1 x + 1, y + 1, z; #2 x + 1, y − 1, z. (b) 2-Fold homointerpenetration in a parallel fashion of 1 (shown with green and blue for each single layer A). (c) Stacking of the 2-fold interpenetrated layers with a sequence of −(A1A1)(A2A2)(A1A1)(A2A2)−.

{[Ni(adc)(bpp)2(H2O)]2·bpp}n (2). Different from 1, compound 2 crystallizes in the orthorhombic system with space group Pbca and features 2-D undulated layers B and C that are heterointerpenetrated. There are two crystallographically independent Ni(II) centers and one lattice bpp molecule in an asymmetric unit of 2 (Figure 4a; Figure S1a (Supporting Information)). The Ni1(II) and Ni2(II) atoms are both sixcoordinated by two carboxylate O atoms, three pyridine N

atoms, and one O atom of a water molecule to form a distorted octahedral coordination geometry. The Ni−O bond distances are in the normal range of 2.041(2)−2.092(2) Å, as well as Ni− N bond distances of 2.109(3)−2.201(3) Å. Three pyridine N atoms and one O atom from a water molecule reside in the equatorial positions, and the apical positions are occupied by the two carboxylate O atoms with the axial angle of O1−Ni1− O3(−x + 1/2, −y + 1, z − 1/2) of 178.31(10)° and O5−Ni2− D

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Figure 4. (a) Coordination environment around the Ni(II) atoms of 2. Lattice bpp molecule and hydrogen atoms have been omitted for clarity. Two independent fragments containing Ni(II) are shown by blue and pink colors. (b) Left: heterointerpenetration of 2 with monodentate bpp omitted. Right: stacking of the entangled layers (BC) with a sequence of −(BC)(BC)− along the a direction (blue, layer B; pink, layer C; green, free bpp molecule).

Figure 5. (a) Coordination environment around the Zn(II) atom of 3. Lattice DMF molecule and hydrogen atoms have been omitted for clarity. Symmetry codes: #1 −x + 1, y − 1/2, −z + 3/2; #2 x − 1, y, z − 1. (b) 2-D (4,4) layer D of 3 with the hydrogen atoms omitted for clarity. (c) The 2-D → 3-D parallel interpenetration of layers D in 3.

O8(x, −y + 1/2, z + 1/2) of 176.83(10)°, as opposed to the ideal angle of 180°. The Ni(II) centers are linking by transadc2− ligands with O atoms of monodentate carboxylate groups, resulting in 1-D [−Ni-adc2−−]n chains that are bridged by μ2bpp, giving rise to two types of undulated 2-D (4,4) networks named layer B, containing Ni1(II), and layer C, containing Ni2(II), based on square grids with dimensions of [Ni4(adc2−)2(bpp)2)] squares being 21.2959(19) Å × 21.880(2) Å and 21.3617(19) Å × 21.8229(19) Å (diagonal distances), respectively. Octahedra for Ni(II) centers lean at certain angles between the equatorial plane and the undulated surface of Ni(II) atoms, and array edge-transitively in two orientations

shown in Figure 2 (layers B and C). In layer B, octahedra lie with alternating orientations along μ2-bpp ligands, and at the same time, μ2-bpp are protruding at both sides of the Ni1(II) layer regularly like a sinusoidal wave, whereas along adc2− ligands, octahedra lie with the same orientation, leading to a parallel array of those sinusoidal waves, which shows a standard lumpy layer B. Unlike layer B, octahedra in layer C display alternating orientations along both adc2− and μ2-bpp ligands, forming the layer C, in which sinusoidal bpp waves are alternately parallelly arranged. Furthermore, besides μ2-bpp ligands that adopt a TT conformation with distances of N3− to−N4 being 9.4304(40) Å in layer B and N9−to−N10 being E

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to be investigated thoroughly. Take layer A (belonging to type a) and layer D (belonging to type d), for example, all coordination geometries are arrayed in the same orientation along bpp ligands, resulting in a certain conformation of the winding [−M-adc2−−]n (M = Co, Zn) chain. Along adc2− ligands, however, [−Co-adc2−−]n chains are parallelly arranged in layer A owing to the coordination geometries arrayed in one orientation, while [−Zn-adc2−−]n chains are alternately parallelly arranged in layer D that resulted from the arrangement of coordination geometries along adc2− ligands being in two different orientations by turns. In other words, it is the different arrangements of coordination geometries along adc2− ligands that lead to different structures between layer A and layer D. The distinction between layer B and layer C is same argument. That is how we design different crystal structures based on the (4,4) topological structure. Obviously, many similar compounds with (4,4) topology have been reported in chemical journals. For now, however, researchers often synthesize new compounds and determine their crystal structures first and then study topological structures, which is the conventional method that uses a topological approach to help in understanding complex crystal structures in the field of crystal engineering. In contrast, our work focuses on the design of crystal structures based on a certain topological structure, and it is the first systematic study on (4,4) topology whose diversification is embodied by different mixed-ligand layers designed from the topological structure to crystal structures. So far, this design strategy that designs crystal structures based on the topological structure has rarely been put into practice. However, exactly, our work demonstrates the feasibility and value of this design strategy. Luminescence Properties. As the hybrids of organic ligands and metal ions, coordination polymers that show special photoluminescence have been reported.1f Although a variety of transition-metal ions have been used to construct photoluminescent coordination polymers, d10 transition-metal complexes exhibiting high luminescence are the most commonly reported. However, the reported luminescent examples of paramagnetic metal atoms with a single electron occupying the d orbital, such as Co(II) and Ni(II), are relatively rare,9 because, commonly, the emission of these compounds beomes drastically quenched, probably owing to d−d electron transitions and vibrations of single electrons. In the present work, we have examined the photoluminescent properties of 1−5 and free ligands H2adc, ClH2adc, as well as bpp in the solid state at room temperature. Excited at 310 nm, the free bpp, H2adc, and ClH2adc ligands have emission peaks at 417, 418, and 432 nm, respectively, as indicated in Figure 6. Compounds 1 and 2 have very similar emission spectra to the H2adc ligand with peaks at 416 and 404 nm, but the emission profile of 3 with a maximum at 406 nm is more like that of the free bpp ligand. Therefore, we temporarily assign the photoluminescence of 1−3 mainly to the emission of their ligands with perturbation of their metal ions. The emission peaks at 440 and 432 nm were observed for 4 and 5, respectively; however, their emission profiles display appreciable distinction with their ligands. The luminescence properties of mixed-ligand coordination polymers have been investigated and found to be relatively complicated to assign their fluorescent emission served by several factors.10 For instance, the different conformations of each ligand and their coordination fashions to mental centers could affect their contributions to luminescence of the whole compound, and

9.3741(40) Å in layer C, monodentate bpp ligands coordinated to Ni1(II)/Ni2(II) atoms display GG′ (N5−to−N6 7.8282(65) Å)/TT (N11−to−N12 9.6076(49) Å) conformations. Compared to the homointerpenetration of 1, the most interesting structural feature of 2 is that two distinct layers B and C heterointerpenetrate each other, and the resulting entangled sheets (BC) stack in the a direction with a sequence of −(BC)(BC)−. In addition, the interlayer voids are partly occupied by the free bpp molecules (TG, N13−to−N14 8.9713(56) Å) (Figure 4b). Calculation by PLATON reveals the free volume accounting for 6.4% (1116.0 Å3 per unit cell volume) in 2 (Figure S1e, Supporting Information). [Zn(adc)(bpp)·DMF]n (3). As shown in Figure 5a, the asymmetric unit of 3 comprises one Zn(II) ion, one adc2− ligand, one bpp ligand, and one lattice DMF molecule. Each Zn(II) ion is surrounded by two O atoms from two μ2-κ2O1:O3 adc2− ligands with the trans-configuration and two N atoms from two μ2-bpp ligands, giving a distorted tetrahedral geometry. The Zn−O/Zn−N bond distances are in the range of 1.937(3)−2.084(3) Å, and the bond angle of N3−Zn−N4(x − 1, y, z − 1) is 104.18(12)°. In 3, the Zn(II) centers are connected by adc2− ligands to afford 1-D zigzag [−Zn-adc2−−]n chains with the Zn···Zn distance being 17.2150(9) Å. These 1D zigzag chains are interlinked by arched bpp (TT 9.2657(42) Å) ligands constituting a step-shaped 2-D (4,4) network (Figure 5b). Compared with layer A, a unique feature of this layer named layer D is that orientations of tetrahedral Zn(II) centers alternately change along adc2− ligands, following which bpp ligands protrude from both sides of the layer. The structure of 3 represents a typical 2-D → 3-D parallel interpenetration, in which each D layer is entangled with two adjacent identical layers (Figure 5c). As reported, the stepshaped 2-D (4,4) networks that are highly undulating favor much more dimension-increasing parallel interpenetration than those flat layers and slightly undulated ones.2j [Ni(Cladc)(bpp)(H2O)]n (4) and [Co(Cladc)(bpp)(H2O)]n (5). When ClH2adc was used instead of H2adc and reaction solvent as well as temperature were changed accordingly, isomorphous compounds 4 and 5 were obtained. Single-crystal X-ray diffraction analysis reveals that compounds 4 and 5 feature the same type of structures as 1 with differences in several bond lengths and angles (Figure S2, Table S1, Supporting Information). It is most worthy to note that, although the ClH2adc ligands adopt a μ2-κ2-O1:O4 binding mode in 4, the O3 of carboxylate is close to the Ni(II) center with the distance of 2.337(3) Å. Similarly, this phenomenon also exists in 5. Design Philosophy. Our greatest interest of 1−5 is in their simple layers A, B, C, and D, which are four types of 2-D polymeric layers with (4,4) topology, but distinct wrinkles (Figure 2). They represent four typical (4,4) grids constructed of mixed flexible/rigid linear ligands as a single bridge. All differences in this series of (4,4) wavy layers result from arched ligands that link metal centers with different coordination angles and coordination orientations. In the reported compounds with (4,4) topology, the most common topological configurations are types a and d, in which the metal center (M) is coordinated by two ligating atoms (LA) of arched bridging ligands with the coordination angle (∠LA−M−LA) being close to 90°.3j,l−o In contrast, those coordination angles in types b and c are much near 180°.3r,w For further analysis of the distinctions between types a and d, and types b and c, the arrangement of their coordination geometry in each type needs F

dx.doi.org/10.1021/cg400394d | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Article

ASSOCIATED CONTENT

S Supporting Information *

Additional structural plots, PXRD patterns, FT-IR spectra, selected bond lengths and angles, and X-ray crystallographic files in CIF format of 1−5. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Telephone: +86 591 83705882. Fax: +86 591 83714946. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the financial support by the NSF of China (21003126, 21101152, 21221001), the National Key Technology R&D Program (2012BAE06B08), the Key Project from the CAS (KJCX2.YW.M10), and the NSF of Fujian Province (2011J06006).

Figure 6. Solid-state emission spectra (excitation wavelength at 310 nm) for 1−5 and free ligands H2adc, ClH2adc, and bpp.

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introduction of the second ligand, leading to more intricate molecular orbitals of luminescent compounds, perplexes us to clearly confirm each origin of luminescence in one compound, such as charge-transfer luminescence, including intraligand charge transfer, ligand-to-ligand charge transfer, metal-to-ligand charge transfer, ligand-to-metal charge transfer, etc. Thermogravimetric Analyses. To investigate thermal stability of 1−5, thermogravimetric analysis (TGA) experiments were performed from room temperature to 1200 °C, and the TGA curves are provided in Figure S5 (Supporting Information). For 1, the TGA curve displays a weight loss of 3.35% from 60 to 155 °C, corresponding to the removal of coordinated water molecules (calculated: 3.32%). The desolvated compound of 1 is stable up to 200 °C, and then begins to decompose upon further heating. For 2, its weight loss begins at 65 °C, and a small gradual weight loss occurs from 260 to 335 °C during the whole process of decomposition. The TGA measurement for 3 exhibits two distinct weight loss steps. The first step (115−250 °C) shows loss of lattice DMF molecules and partial decomposition of the organic ligands. After the small gradual weight loss in the temperature range of 250−350 °C, the second sharp continual weight loss occurs. Although compounds 4 and 5 are isostructural, their thermal stabilities are quite different. Compound 4 is stable up to 225 °C, and then the rapid pyrolysis of the framework takes place. For 5, however, it begins to lose weight when the temperature is raised to only 96 °C.

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REFERENCES

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CONCLUSION

In summary, five compounds with new crystal structures designed from the (4,4) topological structure have been successfully obtained by adjusting the coordination geometry of the center atoms and the nodes of the (4,4) topology and taking full advantage of flexible ligands. Our experimental results indicate the feasibility and value of the new strategy that designs new crystal structures based on the topological structure, which indicates that this strategy will be a much more usual method with immense potential in the field of crystal engineering. G

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