Zinc Tricarballylate Coordination Polymers with a Threaded-Loop Self

Feb 25, 2010 - ... Layer and Triply Interpenetrated 3,4-Connected Binodal Network ... an unprecedented self-penetrated two-dimensional (2-D) layered ...
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DOI: 10.1021/cg100006a

Zinc Tricarballylate Coordination Polymers with a Threaded-Loop Self-Penetrated Layer and Triply Interpenetrated 3,4-Connected Binodal Network Structures: Topological Control through Anion Inclusion

2010, Vol. 10 1897–1903

Gregory A. Farnum and Robert L. LaDuca* Lyman Briggs College and Department of Chemistry, Michigan State University, East Lansing, Michigan 48825 Received January 2, 2010

ABSTRACT: Hydrothermal reaction of zinc perchlorate, tricarballylic acid (H3tca), and bis(4-pyridylmethyl)piperazine (bpmp) resulted in generation of {[Zn3(tca)2(bpmp)(Hbpmp)2](ClO4)2 3 5H2O}n (1), which possesses an unprecedented selfpenetrated two-dimensional (2-D) layered topology with threaded-loop type linkages. A similar reaction using zinc sulfate as precursor afforded the oxoanion-free phase {[Zn3(H2O)4(tca)2(bpmp)2] 3 8H2O}n (2), which manifests a new yet simple 3-fold interpenetrated (63)(658) 3,4-connected three-dimensional (3-D) binodal network. Both materials undergo blue-violet luminescence upon exposure to UV radiation.

Introduction Crystalline coordination polymer solids have become an important materials synthesis focus in recent years, as these materials show impressive capabilities in gas storage,1 molecular separations,2 ion exchange,3 catalysis,4 and nonlinear optics.5 Another impetus for basic research in this field is certainly provided by the aesthetic beauty of these phases’ underlying networks,6 many of which have not yet been predicted by theoretical investigations of possible topologies.7 In comparison to the numerous non-interpenetrated and mutually interpenetrated covalent coordination polymer structural topologies that have been discovered, self-penetrated topologies are much more rarely observed. This type of network possesses tethering ligands that penetrate through the shortest possible circuits between metal atom nodes. Selfpenetrated three-dimensional (3-D) networks are often observed in cases of high nodal connectivity,8-15 for example, in the 6-connected 48668 lattice (rob) in {[Cu2(glutarate)2(4,40 bipyridine)] 3 3H2O}n9 and the 8-connected 4245.63 topology (ilc) based on pentanuclear cluster nodes in [Zn5(μ3-OH)2(terephthalate)4(1,10-phenanthroline)2]n.10 Rarer still are selfpenetrated two-dimensional (2-D) layer coordination polymer networks. The few examples in the literature are dualligand phases with embedded self-catenated helical motifs.16-18 {[Cd(succinate)(L)] 3 H2O}n (L = N,N0 -bispyridin-4-yl-methylsuccinamide) manifests [Cd(L)]n triple helices,16 joined into a 2-D self-penetrated layer by short dicarboxylate ligands; {[Ni(oxybisbenzoate)(4,40 -dipyridylamine)] 3 H2O}n has a 2-D nondiamondoid 66 topology formed by the linkage of [Ni(oxybisbenzoate)]n double helices through the kinked dipyridyl tethers.17 A (4,4) rhomboid grid selfpenetrated layer was observed in {[Cu(N,N0 -bis(4-pyridyl)suberamide)2 (H2O)2](SO4) 3 H2O 3 2EtOH}n, whose very long tethering ligands intertwine each other within the grid apertures.18 An alternative method for the generation of self-penetrated coordination polymer layers, eschewing helical motifs, may

involve the incorporation of pseudo-rotaxane threaded-loop type linkages. Recently, Yaghi and co-workers were successful in incorporating crown-ether derivatized rigid diacetylenedicarboxylates, with threaded box-shaped polypyridinium cations, into 3-D divalent zinc coordination polymer systems.19 In this contribution, we report the synthesis and structural characterization of {[Zn3(tca)2(bpmp)(Hbpmp)2](ClO4)2 3 5H2O}n (1, tca = tricarballylate, 1,2,3-propanetricarboxylate; bpmp = bis(4-pyridylmethyl)piperazine), which manifests a unique selfpenetrated layer topology with threaded-loop pseudo-rotaxane motifs. The oxoanion-free analogue of 1, {[Zn3(H2O)4(tca)2 (bpmp)2] 3 8H2O}n (2), adopts a novel interpenetrated binodal 3-D topology despite common structural elements in both complexes. Luminescent properties of these materials are also discussed herein. Experimental Section

*To whom correspondence should be addressed. Address: Lyman Briggs College, E-30 Holmes Hall, Michigan State University, East Lansing, MI 48825 USA. E-mail: [email protected].

General Considerations. Zinc salts and tricarballylic acid were purchased from Aldrich. Bis(4-pyridylmethyl)piperazine was prepared using a published procedure.20 Water was deionized above 3 MΩ-cm in-house. IR spectra were recorded on powdered samples using a Perkin-Elmer Spectrum One instrument. The luminescence spectra were obtained with a Hitachi F-4500 fluorescence spectrometer on solid crystalline samples anchored to quartz microscope slides with Rexon Corporation RX-22P ultraviolet-transparent epoxy adhesive. Preparation of {[Zn3(tca)2(bpmp)(Hbpmp)2](ClO4)2 3 5H2O}n (1). Zn(ClO4)2 3 6H2O (68 mg, 0.18 mmol), bpmp (99 mg, 0.37 mmol), and tricarballylic acid (33 mg, 0.19 mmol) were placed into 5 mL of distilled H2O in a 15 mL screw-cap glass vial. The vial was sealed and heated in an oil bath at 80 C for 72 h, whereupon it was cooled slowly to 25 C. Colorless blocks of 1 (52 mg, 0.032 mmol, 52% yield based on Zn) were isolated after washing with distilled water and acetone, and drying in air. Anal. Calc. for C60H82Cl2N12O25Zn3 1: C, 43.98; H, 5.04; N, 10.26% Found: C, 43.71; H, 4.86; N, 10.13%. IR (cm-1): 2832 w, 1620 m, 1594 s, 1652 m, 1449 w, 1430 m, 1384 m, 1317 w, 1284 w, 1227 w, 1193 w, 1156 w, 1082 s, 1030 m, 1001 w, 975 w, 923 w, 883 w, 836 w, 809 m, 771 w, 730 w. Preparation of {[Zn3(H2O)4(tca)2(bpmp)2] 3 8H2O}n (2). ZnSO4 3 7H2O (53 mg, 0.18 mmol), bpmp (99 mg, 0.37 mmol), and tricarballylic acid (33 mg, 0.19 mmol) were placed into 5 mL of distilled H2O in a 15 mL screw-cap glass vial. The vial was sealed and heated

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in an oil bath at 80 C for 72 h, whereupon it was cooled slowly to 25 C. Colorless blocks of 2 (33 mg, 0.024 mmol, 39% yield based on Zn) were isolated after washing with distilled water and acetone, and drying in air. Anal. Calc. for C44H74N8O24Zn3 2: C, 40.80; H, 5.76; N, 8.65% Found: C, 41.12; H, 5.43; N, 8.32%. IR (cm-1): 3266 w br, 1620 m, 1600 m, 1557 s, 1410 m, 1394 s, 1360 m, 1323 m, 1304 m, 1180 m, 1274 m, 1124 m, 1064 s, 1030 s, 1013 s, 980 m, 838 s, 804 s, 675 s. X-ray Crystallography. Single crystal X-ray diffraction was performed on single crystals of 1 and 2 with a Bruker-AXS ApexII CCD instrument at 173 K. Reflection data were acquired using graphite-monochromated Mo-KR radiation (λ = 0.71073 A˚). The data was integrated via SAINT.21 Lorentz and polarization effect and empirical absorption corrections were applied with SADABS.22 The structures were solved using direct methods and refined on F2 using SHELXTL.23 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms bound to carbon atoms were placed in calculated positions and refined isotropically with a riding model. The hydrogen atoms bound to the piperazinyl nitrogen atom of the Hbpmp ligand in 1 was found via Fourier difference maps, then restrained at fixed positions and refined isotropically. Relevant crystallographic data for 1 and 2 are listed in Table 1.

Table 1. Crystal and Structure Refinement Data for 1 and 2 data empirical formula formula weight crystal system space group a (A˚) b (A˚) c (A˚) R () β () γ () V (A˚3) Z Dcalc (g cm-3) μ (mm-1) min/max trans hkl ranges total reflections unique reflections R (int) parameters/restraints R1 (all data) R1 (I > 2σ(I)) wR2 (all data) wR2 (I > 2σ(I)) max/min residual (e-/ A˚3) GOF

1

2

C60H82Cl2N12O25Zn3 1638.47 triclinic P1 9.545(3) 13.783(4) 14.087(4) 69.967(3) 86.315(4) 88.713(4) 1737.7(9) 1 1.566 1.193 0.789/0.875 -11 e h e 11, -16 e k e 16, -16 e l e 16 25 417 6358 0.0574 481/1 0.0677 0.0513 0.1463 0.1361 1.410/-0.840 1.028

C44H74N8O24Zn3 1295.22 triclinic P1 8.3207(6) 13.1120(10) 13.4253(10) 71.716(1) 79.758(1) 88.055(1) 1368.23(18) 1 1.572 1.394 0.626/0.652 -10 e h e 10, -15 e k e 15, -16 e l e 16 20 127 4972 0.0401 391/18 0.0282 0.0266 0.0704 0.0697 0.924/-0.537 1.067

Crystallographic data (excluding structure factors) for 1 and 2 have been deposited with the Cambridge Crystallographic Data Centre with Nos. 754534 and 754535, respectively. Copies of the data can be obtained free of charge via the Internet at http://www. ccdc.cam.ac.uk/conts/retrieving.html or by post at CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (Fax: 44-1223336033; e-mail: [email protected]).

Results and Discussion Synthesis and Spectral Characterization. The compounds in this study were prepared cleanly as crystalline products by hydrothermal reaction of bpmp and tricarballylic acid with either zinc perchlorate (for 1) or zinc sulfate (for 2). The infrared spectra of 1 and 2 were consistent with their structural characteristics as determined by single-crystal X-ray diffraction. Medium intensity bands in the range of ∼1600 cm-1 to ∼1200 cm-1 can be ascribed to stretching modes of the pyridyl rings of the bpmp or Hbpmp ligands. Puckering modes of the pyridyl rings are evident in the region between 820 and 600 cm-1. Asymmetric and symmetric C-O stretching modes of the fully deprotonated tca ligands correspond to the intense, broadened features at 1594 cm-1 and 1430/1384 cm-1 (for 1) or 1557 cm-1 and ∼1394 cm-1 (for 2). Broad yet weak bands in the region of ∼3400 cm-1 to ∼3200 cm-1 in the spectrum of 2 arise from the O-H bonds within the water molecules of crystallization. The broadness of these higher energy spectral features is caused by hydrogen-bonding (see below). The spectrum of 1 shows a very intense feature at 1082 cm-1, indicative of Cl-O vibrational modes within the perchlorate ions. Structural Description of {[Zn3(tca)2(bpmp)(Hbpmp)2](ClO4)2 3 5H2O}n (1). The asymmetric unit of compound 1 contains two divalent zinc atoms, one of which (Zn1) lies on a crystallographic inversion center, along with a triply deprotonated tca trianion, a complete cationic Hbpmpþ ligand that is protonated at one of its piperazinyl nitrogen atoms, half of a bpmp ligand situated across another crystallographic inversion center, an unligated disordered perchlorate ion, and two and one-half water molecules of crystallization (Figure 1). The coordination environment at Zn1 is a distorted {ZnO4N2} octahedron, with trans pyridyl nitrogen donor atoms belonging to two different unprotonated bpmp ligands. Chelating carboxylate groups from two tca ligands occupy the remaining coordination sites. In contrast, Zn2 is tetrahedrally coordinated in a {ZnO2N2} environment, with pyridyl nitrogen donor

Figure 1. Coordination environment of 1, with thermal ellipsoids at 50% probability and partial atom numbering scheme. A complete bpmp ligand is shown. The symmetry codes are as in Table 2. Most hydrogen atoms have been omitted.

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Figure 2. A single neutral [Zn3(tca)2]n ribbon motif in 1.

Figure 3. (a) The self-penetrated [Zn3(tca)2(Hbpmp)2(bpmp)]n2nþ cationic coordination polymer layer in 1. [Zn3(tca)2]n ribbon motifs are drawn in green. The Hbpmpþ and bpmp tethering ligands are shown in red and blue, respectively. (b) A close-up view of the penetration of bpmp ligands through loops formed by Hbpmpþ ligands. Table 2. Selected Bond Distance (A˚) and Angle () Data for 1a Zn1-O6#1 Zn1-N3#1 Zn1-O5#1 Zn2-O1#2 Zn2-O2 Zn2-N2#3 Zn2-N1 O6-Zn1-O6#1 O6-Zn1-N3 O6-Zn1-N3#1 N3-Zn1-N3#1

2.067(3) 2.241(3) 2.266(3) 1.940(3) 1.970(3) 2.040(3) 2.044(3) 180 88.57(11) 91.43(11) 180

O6-Zn1-O5#1 N3-Zn1-O5#1 O6-Zn1-O5 N3-Zn1-O5 O5#1-Zn1-O5 O1#2-Zn2-O2 O1#2-Zn2-N2#3 O2-Zn2-N2#3 O1#2-Zn2-N1 O2-Zn2-N1 N2#3-Zn2-N1

119.08(10) 91.51(11) 60.92(10) 88.49(11) 180 108.24(12) 115.73(12) 106.04(12) 124.45(13) 96.80(13) 102.85(13)

Symmetry transformation to generate equivalent atoms: #1 -x þ 1, -y þ 2, -z; #2 x - 1, y, z; #3 -x, -y þ 1, -z. a

atoms from two different Hbpmpþ ligands and oxygen atom donors from monodentate carboxylate groups belonging to two different tca ligands. Relevant bond lengths and angles within the respective coordination spheres are given in Table 1.

Figure 4. Framework perspectives of the self-penetrated cationic coordination polymer layer in 1. The color scheme for the ligands is the same as in Figure 3. (a) Edge-crossed 3,6-connected binodal network. (b) 2,4,6-connected trinodal network showing penetration of bpmp ligands (blue rods) through Hbpmpþ loops (red rods with green spheres denoting ligand centroids).

Each tca ligand is exotridentate, with two of its longer carboxylate arms connecting to Zn2 atoms in a monodentate fashion, and its shorter carboxylate arm binding to Zn1 in a chelating manner. The Zn2 3 3 3 Zn2 through-ligand distance matches the a lattice parameter of 9.545 A˚; neighboring Zn2 atoms within the resulting [Zn2(tca)]nn- chain motifs are spanned by the full length of the anti-anti conformation tca backbone (four C-atom torsion angles = 168.3 and 174.8). Pairs of [Zn2(tca)]nn- chains, oriented parallel to the (1 0 0)

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Figure 5. Coordination environment of 2, with thermal ellipsoids at 50% probability and partial atom numbering scheme. Complete bpmp ligands are shown; each is sited across a crystallographic inversion center. The symmetry codes are as in Table 4. Most hydrogen atoms have been omitted.

crystal direction, are connected by the Zn1 atoms via chelation by pendant tca short-arm carboxylate groups. Thus, neutral [Zn3(tca)2]n ribbon motifs are formed (Figure 2). The Zn1 3 3 3 Zn2 through-ligand distances from the exterior to the interior of the ribbon patterns measure 6.132 and 6.438 A˚. Neighboring [Zn3(tca)2]n ribbon motifs (shown in green in Figure 3a) are linked by tethering bpmp and Hbpmpþ ligands into a 2-D coordination polymer layer. Pairs of cationic Hbpmpþ ligands (red in Figure 3a) connect Zn2 atoms in neighboring [Zn3(tca)2]n ribbons with a Zn2 3 3 3 Zn2 distance of 13.009 A˚. Two Zn2 atoms and two curled Hbpmpþ ligands thus construct a {Zn2(Hbpmp)2} loop motif; these link [Zn3(tca)2]n ribbons into a 2-D layer pattern. Threading through these {Zn2(Hbpmp)2} loops are unprotonated bpmp ligands in a straight-rod conformation (blue in Figure 3a), that bridge Zn1 atoms in neighboring [Zn3(tca)2]n ribbons with a Zn1 3 3 3 Zn1 distance of 16.588 A˚. Therefore, the overall [Zn3(tca)2(Hbpmp)2(bpmp)]n2nþ cationic coordination polymer motif in 1 possesses a very rare self-penetrated layer topology. A close-up view of the loop penetration is shown in Figure 3b. Covalent connectivity within the layer is supplemented by hydrogen bonding between the protonated piperazinyl nitrogen atoms of the Hbpmpþ ligands and unligated tca long-arm carboxylate oxygen atoms (Table 2). Topological analyses using TOPOS software24 were undertaken to examine the self-penetrated layer topology of 1. The Zn1 atoms can be considered 6-connected nodes, connecting to two other Zn1 atoms in other [Zn3(tca)2]n ribbons via bpmp tethers, and connecting to four Zn2 atoms within the same [Zn3(tca)2]n ribbon through the carboxylate arms of the tca ligands. In turn, the Zn2 atoms can be considered 3-connected nodes, connecting to one other Zn2 atom in a neighboring [Zn3(tca)2]n ribbon through a pair of loopdefining Hbpmpþ ligands, and connecting to two Zn1 atoms within its own [Zn3(tca)2]n ribbon. Using this connectivity pattern, the coordination polymer topology in 1 can be construed as a 3,6-connected binodal lattice with {(426)2(446982)} topology (Figure 4a). However, this is an edge-crossed network that cannot exist in a real chemical system, an artifact of treating the looped pairs of Hbpmpþ

ligands as individual connecting rods. Instead, it is better to view the self-penetrated network employing the notation of Batten et al.,25 treating the centroids of the piperazine rings of the curled Hbpmpþ ligands as 2-connected nodes. Doing so causes the Zn2 atoms to become 4-connected nodes that link to two Zn1 atoms within a single [Zn3(tca)2]n ribbon and to two Hbpmpþ centroids, while leaving the connectedness of the Zn1 atoms the same. The resulting 2,4,6-connected self-penetrated trinodal network, shown in Figure 4b, has a Schafli symbol of {(4)2(425272)2(42526673.8.9)}. The topology of 1 has not previously been reported and is a new entry in the very rare class of self-penetrated coordination polymer layered networks. Compound 1 appears to possess the first self-penetrated layered topology not constructed from helical submotifs, to the best of our knowledge. Unligated perchlorate anions and water molecules of crystallization lie in the regions between adjacent self-penetrated [Zn3(tca)2(Hbpmp)2(bpmp)]n2nþ layers, anchored by hydrogen bonding mechanisms mediated by tca carboxylate oxygen atoms and unprotonated piperazinyl nitrogen atoms within the bpmp and Hbpmpþ ligands (Figure S1, Supporting Information). The unbound water molecules form a R(4)A(2) hexameric aggregation26 featuring a cyclic fourmolecule unit with two additional attached water molecules (Figure S2, Supporting Information). The unligated species occupy 20.7% of the unit cell volume, according to a calculation performed with PLATON.27 Structural Description of {[Zn3(H2O)4(tca)2(bpmp)2] 3 8H2O}n (2). The asymmetric unit of compound 2 contains two divalent zinc atoms, one of which (Zn2) is located on a crystallographic inversion center, one triply deprotonated tca trianion, crystallographically independent halves of two bpmp ligands (bpmp-A, N1-N2; bpmp-B, N3-N4), along with two ligated and four unligated water molecules. The crystallographically distinct zinc atoms display either a distorted{ZnO2N2} tetrahedral environment (for Zn1) or a {ZnO6} octahedral coordination sphere (for Zn2) (Figure 5). Nitrogen donor atoms from a bpmp-A ligand and a bpmp-B ligand, and oxygen donor atoms from long-arm carboxylate groups of two different tca ligands define the coordination

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Figure 6. A single neutral [Zn3(tca)2(H2O)4]n ribbon motif in 2.

sphere at Zn1. In turn, the coordination environment at Zn2 is defined by four aqua ligands and two trans carboxylate oxygen donor atoms belonging to short-arm carboxylate groups of two different tca ligands. Bond lengths and angles about the crystallographically independent zinc atoms are consistent with their respective coordination spheres (Table 4). As in 1, each tca ligand adopts an exotridentate bridging mode, linking together two Zn1 atoms and one special position Zn2 atom. However, the specific binding mode is different, with all three carboxylate arms of the tca moiety ligating in a monodentate fashion. Additionally, no nitrogen donor atoms are bound to Zn2, replaced by aqua ligands to complete the {ZnO6} coordination environment. Through the tris(monodentate) tca ligands, a [Zn3(tca)2(H2O)4]n neutral ribbon motif is constructed in 2 (Figure 6). While this ribbon motif is superficially similar to the [Zn3(tca)2]n ribbons in 1, the presence of the aqua ligands at Zn2 and concomitant alteration of the carboxylate binding mode results in a noticeable twisting of the tca backbone. In 1, the five C-atom backbone of the tca ligand adopts an antianti conformation, while in 2 it possesses a gauche-anti conformation (four C-atom torsion angles = 66.5, 177.9). As a result, the Zn1 3 3 3 Zn1 distance (8.321 A˚) spanned by the full extent of the tca ligand is ∼1.2 A˚ shorter than the related distance in 1. The Zn1 3 3 3 Zn2 distances within a single [Zn3(tca)2(H2O)4]n ribbon (5.705 and 9.066 A˚) vary to a much greater extent than in 1, reflecting the monodentate binding mode of the short-arm carboxylate of the tca ligands. The bpmp ligands on the periphery of the [Zn3(tca)2(H2O)4]n ribbons in 2 link Zn1 atoms in neighboring ribbons, creating a [Zn3(tca)2(H2O)4(bpmp)2]n 3-D coordination polymer lattice in contrast to the 2-D self-penetrated layer seen in 1. The Zn1-Zn1 distances through bpmp-A and bpmp-B ligands measure 16.391 and 16.213 A˚, respectively. As all of the bpmp ligands in 2 adopt a splayed-open conformation, there is substantial incipient void space within a single [Zn3(tca)2(H2O)4(bpmp)2]n 3-D coordination polymer lattice, permitting mutual 3-fold interpenetration. A view of the triply interpenetrated 3-D network of 2, with the bpmp ligands shown as rods, is given in Figure 7. It is plausible that the lack of any piperazinyl nitrogen protonation in 2, which obviates the necessity of counteranion occlusion, promotes the formation of a 3-D coordination polymer network at the expense of a self-penetrated layered topology. Topological analysis of the 3-D coordination polymer network of 2 was carried out using the Zn1 atoms as 4-connected nodes and the central carbon atoms of the tricarballylate anions as 3-connected nodes. In this binodal perspective, the Zn1 atoms connect to two other Zn1

Figure 7. The 3-fold interpenetrated 3-D coordination polymer network in 2. The bpmp ligands are represented as long rods. The [Zn3(tca)2(H2O)4]n ribbon motifs are oriented into the plane of the page.

Figure 8. The underlying triply interpenetrated 3,4-connected binodal {(63)(658)} lattice in 2.

atoms via bpmp ligands, and to two tricarballylate anions. In turn, each tricarballylate anion connects to two Zn1 atoms along the periphery of a [Zn3(tca)2(H2O)4]n ribbon, and another tricarballylate anion through a [Zn2(H2O)4]2þ moiety, which is treated here simply as a linker. The resulting 3-fold interpenetrated 3,4-connected binodal topology has a very simple (63)(658) topology

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Table 3. Hydrogen Bonding Distance (A˚) and Angle () Data for 1 and 2 D-H 3 3 3 A 1 N4-H4N 3 3 3 O7 2 O1W-H1WA 3 3 3 N2 O1W-H1WB 3 3 3 O1W O2W-H2WA 3 3 3 O6 O2W-H2WB 3 3 3 O1W O3W-H3WA 3 3 3 N4 O3W-H3WB 3 3 3 O3W O4W-H4WA 3 3 3 O2W O4W-H4WB 3 3 3 O8 O7-H7C 3 3 3 O2W O7-H7D 3 3 3 O4 O8-H8C 3 3 3 O1 O8-H8D 3 3 3 O6

d(H 3 3 3 A)

— DHA

1.79(2)

158(4)

2.629(4)

x, y - 1, z

2.12(2) 1.975(17) 1.940(18) 1.983(17) 2.066(18) 2.055(18) 2.06 1.986(18) 2.031(17) 1.906(17) 1.907(17) 1.840(17)

158(3) 174(3) 168(3) 175(3) 171(3) 166(3) 179.5 174(3) 168(2) 168(2) 179(3) 163(2)

2.913(3) 2.766(4) 2.765(2) 2.821(3) 2.908(3) 2.836(4) 2.909(3) 2.837(3) 2.847(2) 2.748(2) 2.748(2) 2.656(2)

-x þ 1, -y þ 2, -z -x þ 1, -y þ 2, -z - 1 x, y þ 1, z - 1

d(D 3 3 3 A)

symmetry transformation for A

-x, -y þ 1, -z x - 1, y þ 1, z - 1 -x þ 1, -y þ 1, -z þ 1 -x þ 2, -y, -z þ 2 -x þ 1, -y, -z þ 2

Table 4. Selected Bond Distance (A˚) and Angle () Data for 2a Zn1-O3#1 Zn1-O2 Zn1-N3 Zn1-N1 Zn2-O5#2 Zn2-O7#2 Zn2-O8#2 O3#1-Zn1-O2 O3#1-Zn1-N3 O2-Zn1-N3 O3#1-Zn1-N1

1.9449(14) 1.9884(14) 2.0457(17) 2.0698(17) 2.0273(13) 2.1197(15) 2.1473(15) 137.44(6) 105.88(6) 97.17(6) 91.80(6)

O2-Zn1-N1 N3-Zn1-N1 O5#2-Zn2-O5 O5-Zn2-O7#2 O5-Zn2-O7 O7#2-Zn2-O7 O5-Zn2-O8 O7-Zn2-O8 O5-Zn2-O8#2 O7-Zn2-O8#2 O8-Zn2-O8#2

114.17(7) 108.77(7) 180 87.34(6) 92.66(6) 180 91.52(6) 93.02(6) 88.48(6) 86.98(6) 180

a Symmetry transformation to generate equivalent atoms: #1 x -1, y, z; #2 -x þ 2, -y, -z þ 2.

Conclusions Figure 9. Emission spectra of 1 and 2, along with that of free bpmp.

(Figure 8). The extended point symbols for the 3- and 4-connected nodes, respectively, are (6.6.62) and (6.6.6.6.6.82). To the best of our knowledge, this simple 3,4-connected binodal lattice has not yet been reported in coordination polymer chemistry; it is also not included in the EPINET database7 of theorized network topologies. The extra-framework spaces between the interpenetrated [Zn3(tca)2(H2O)4(bpmp)2]n lattices, which occupy 14.9% of the unit cell volume, contain hydrogen-bonded C8 classification26 “infinite” water chains (Figure S3, Supporting Information). The unligated water molecules are connected to the coordination polymer backbone by hydrogen-bonding with the aqua ligands bound to Zn2, piperazinyl nitrogen atoms within the bpmp ligands, and the tca carboxylate groups. Metrical parameters regarding these supramolecular interactions are given above in Table 3. Luminescence Spectra Irradiation of complexes 1 and 2 with ultraviolet light (λex = 300 nm) in the solid state resulted in modest blue-violet visible light emission with λmax values of ∼470 nm and ∼450 nm, respectively (Figure 9). The emission profiles are quite similar to that of free, unligated bpmp. Thus, the emissive behavior property is ascribed to ligand-centered electronic transitions between π-π* or π-n molecular orbital manifolds within the aromatic pyridyl rings of the bpmp or Hbpmpþ tethers.28 The difference in intensity between the emission of solid 1 and 2 is attributed to crystallite size effects as opposed to any molecular structure-based effects.

Zinc tricarballylate coordination polymers containing ditopic bis(4-pyridylmethyl)piperazine ligands manifest new 2-D (1) and 3-D (2) topologies, with a marked structural dependence on piperazinyl protonation and anion inclusion.29 It is plausible that the piperazinyl protonation in 1, resulting in hydrogen-bonding donation to an unligated tca carboxylate oxygen atom, enforces a curled conformation of the Hbpmpþ ligands and the generation of {Zn2(Hbpmp)2} loops. In turn, the straight-rod conformation bpmp ligands can then thread through these loops, affording the unique self-penetrated 2-D layer topology of 1. The lack of piperazinyl protonation in 2 appears to preclude both curling of the bpmp ligands and anion inclusion during self-assembly. Despite the presence of related zinc tricarballylate ribbons in both compounds, the anion-free material 2 adopts an unprecedented, yet simple, triply interpenetrated low-connected binodal lattice. The topologies of both 1 and 2 differ substantially from the standard (4,4) grid motifs seen in both {[Zn(Htca)(4,40 bipyridine)] 3 3H2O}n and {[Zn(Htca)(1,2-bis(4-pyridyl)ethane)] 3 4H2O}n, the only previously reported zinc-organic phases containing the tricarballylate ligand.30 Therefore, this study also demonstrates the continued utility of the conformationally flexible, potentially basic, and hydrogen-bonding capable bis(4-pyridylmethyl)piperazinyl tethers in developing the scope of accessible coordination polymer topologies. Acknowledgment. We acknowledge the donors of the American Chemical Society Petroleum Research Fund for funding this work. Supporting Information Available: Stacking pattern of selfpenetrated layers in 1; R(4)A(2) hexameric aggregation of water

Article

Crystal Growth & Design, Vol. 10, No. 4, 2010

molecules in 1; C8 “infinite” water chain in 2. Crystallographic information files. This material is available free of charge via the Internet at http://pubs.acs.org.

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