Structural Diversity in Luminescent Three-Dimensional Cadmium

Structural Diversity in Luminescent Three-Dimensional Cadmium Aliphatic Dicarboxylate Coordination Polymers Incorporating 4,4′-Dipyridylamine: Interpenetrated, Non-Interpenetrated, and Self-Penetrated Networks

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 5 2481–2491

Eric Shyu,† Ronald M. Supkowski,‡ and Robert L. LaDuca*,§ Lyman Briggs College and Department of Chemistry, Michigan State UniVersity, East Lansing, Michigan 48825, Department of Chemistry and Physics, King’s College, Wilkes-Barre, PennsylVania 18711, Illinois Mathematics and Science Academy, Aurora, Illinois 60506 ReceiVed December 22, 2008; ReVised Manuscript ReceiVed February 3, 2009

ABSTRACT: Three cadmium coordination polymers incorporating both a flexible aliphatic R,ω-dicarboxylate and the hydrogenbonding capable diimine 4,4′-dipyridylamine (dpa) have been prepared and structurally characterized. {[Cd(adp)(dpa)]}n (1, adp ) adipate) adopts a doubly interpenetrated decorated primitive cubic three-dimensional (3D) coordination polymer network. {[Cd7(pim)6(dpa)6(H2O)2](ClO4)2 · 6H2O}n (2, pim ) pimelate) exhibits a complex (8,10)-connected binodal self-penetrated cationic 3D network with (384145462)(31041851463) topology constructed from the linkage of oligomeric {Cd7(dpa)6(H2O)2}14+ secondary building units through pimelate ligands with different conformations. To the best of our knowledge, this is the highest-connected binodal self-penetrated lattice reported to date. Extending the length of the R,ω-dicarboxylate resulted in a CdSO4-type (658 topology) 4-connected 3D network in {[Cd(sub)(dpa)] · 2H2O}n (3, sub ) suberate). The length of the polymethylene unit within the dicarboxylate ligand, the coordination preferences at cadmium and anion inclusion, together with dpa-mediated hydrogen bonding, exert a cooperative structure directing effect in this system. All three coordination polymers undergo blue-violet luminescence under ultraviolet irradiation. Introduction Synthetic and structural studies of divalent metal dicarboxylate coordination polymers are a continued focus of present research, driven by the aesthetic appeal of their extended structures and their potential utility in gas storage,1 molecular separation technology,2 ion exchange,3 catalysis,4 nonlinear optical behavior,5 and luminescence.6 The structural diversity apparent in this family of materials is influenced by donor group disposition within the dicarboxylate dianions, their particular binding and bridging modes, and the coordination geometry preferences of the metal ions. Much of the exploratory synthesis of divalent metal coordination polymers has involved aromatic dicarboxylates. While less commonly employed, aliphatic R,ωdicarboxylate ligands have permitted the generation of kinetically metastable coordination polymer networks in the presence or absence of nitrogen-base coligands.7 During coordination polymer self-assembly the methylene groups within the longspanning R,ω-dicarboxylate ligands can adopt different conformations, responding to the requirements of specific coordination environments, carboxylate metal binding modes, and unligated counterions. For instance, the glutarate ligands adopt an anti-gauche conformation in [Cu2(glutarate)2(4,4′-bpy)]n,7i whereas in {[Cu4(4,4′-bipyridine)4(glutarate)2(H2O)4](ClO4)4}n, they possess a more splayed-open anti-anti conformation.7j In {[Cd(glutarate)(bpmp)(H2O)] · 6H2O}n [bpmp ) bis(4-methylpyridyl)piperazine],7k the glutarate ligands lie in a very twisted gauche-gauche conformation. Over the past two years, we have exploited the kinked nitrogen donor orientation and the hydrogen-bonding facility of 4,4′-dipyridylamine [dpa] to prepare several flexible aliphatic R,ω-dicarboxylate divalent metal coordination polymers, some * Corresponding author. Address: Lyman Briggs College, E-30 Holmes Hall, Michigan State University, East Lansing, MI 48825. E-mail: [email protected]. † Illinois Mathematics and Science Academy. ‡ King’s College. § Michigan State University.

with unique topologies including the uniform 5-connected selfcatenated 610-rld-z topology in {[Ni(succinate)(dpa)]Cl}8 and the first-ever triply interpenetrated PtS lattice in [Ni(adp)(dpa)(H2O)2]n [adp ) adipate].9 {[Co(sub)(dpa)(H2O)]n [sub ) suberate] and its nickel analogue possess crystallographic disorder among the central six atoms of the suberate ligands, creating two idealized layer motifs that form a 3D primitive cubic lattice with randomly distributed “ligand vacancies”.10 In these materials and other dpa-containing coordination polymer solids,11–16 the orientation of this diimine’s nitrogen donor atoms and the hydrogen-bonding patterns promoted by its central N-H group act synergistically as important structure-directing agents during self-assembly. Herein we report the extension of this prior work, into dpabased cadmium coordination polymers incorporating even longer aliphatic R,ω-dicarboxylate ligands. All three of the new materials reported in this study, {[Cd(adp)(dpa)]}n (1), {[Cd7(pim)6(dpa)6(H2O)2](ClO4)2 · 6H2O}n (2), and {[Cd(sub)(dpa)] · 2H2O}n (3) [adp ) adipate, pim ) pimelate, sub ) suberate) display 3D coordination polymer networks. However, the overall structural topologies vary with the length of the R,ωdicarboxylate tether. The doubly interpenetrated network of 1 and the noninterpenetrated network of 3 possess different, known 3D structure types. Compound 2 manifests a complex (8,10)connected self-penetrated topology, representing the highestconnected binodal self-penetrated lattice to the best of our knowledge. Luminescence properties are also reported for all three new materials. Experimental Section General Considerations. Cadmium perchlorate hexahydrate and all dicarboxylic acids were purchased from Aldrich. 4,4′-Dipyridylamine (dpa) was prepared via a published procedure.16 Water was deionized above 3 MΩ in-house. Elemental Analysis was carried out using a Perkin-Elmer 2400 Series II CHNS/O Analyzer. IR spectra were recorded on powdered samples using a Perkin-Elmer Spectrum One instrument. Luminescence spectra were obtained with a Hitachi F-4500

10.1021/cg801396k CCC: $40.75  2009 American Chemical Society Published on Web 03/23/2009

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Table 1. Crystal and Structure Refinement Data for 1-3 data empirical formula fw collection T (K) λ (Å) cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm-3) µ (mm-1) min/max trans. hkl ranges total reflns unique reflns R(int) params/restraints R1 (all data) R1 (I > 2σ(I)) wR2 (all data) wR2 (I > 2σ(I)) max/min residual (e- Å-3) GOF.

1

2

3

C16H17CdN3O4 427.73 173(2) 0.71073 monoclinic C2/c 17.145(4) 10.151(2) 18.750(4) 90 94.875(2) 90 3251.1(12) 8 1.748 1.369 0.633/0.746 -22 e h e 22, -13 e k e 13, -24 e l e 24 16 697 3 725 0.0237 241/1 0.0431 0.0342 0.0784 0.0752 1.307/-1.038 1.056

C102H130Cd7N18O40 3105.96 173(2) 0.71073 monoclinic P21/n 12.0398(14) 23.199(3) 21.517(3) 90 93.483(1) 90 5998.9(12) 2 1.715 1.351 0.652/0.746 -15 e h e 15, -29 e k e 30, -28 e l e 28 66 081 13 832 0.0243 802/9 0.0252 0.0211 0.0515 0.0498 1.169/-1.090 1.029

C36H50Cd2N6O12 983.64 173(2) 0.71073 triclinic P1j 10.2938(16) 10.5884(16) 18.556(3) 90.444(2) 95.115(2) 93.133(2) 2011.3(5) 2 1.624 1.125 0.665/0.746 -13 e h e 13, -13 e k e 13, -24 e l e 24 22 522 8 956 0.0246 508/14 0.0323 0.0245 0.0630 0.0591 1.160/-0.454 1.021

Fluorescence Spectrometer on solid crystalline samples anchored to quartz microscope slides with Rexon Corporation RX-22P ultraviolettransparent epoxy adhesive. Caution! Perchlorate compounds can be explosiVe. Although no issues occurred during this work, minimum quantities were used and any materials containing perchlorate were not subject to heating aboVe the temperature of their synthesis. Preparation of [Cd(adp)(dpa)]n (1). Cd(ClO4)2 · 6H2O (150 mg, 0.35 mmol), dpa (165 mg, 0.96 mmol), and adipic acid (70.5 mg, 0.46 mmol)

were mixed with 10 mL of distilled H2O in a 23 mL Teflon-lined Parr acid digestion bomb. The bomb was sealed and heated at 120 °C for 48 h, whereupon it was cooled slowly to 25 °C. Colorless blocks of 1 (57 mg, 38% yield based on Cd) were isolated after washing with distilled water and ethanol and drying in air. Anal. Calcd for C16H17CdN3O4 1: C, 44.93; H, 4.01; N, 9.82%. Found: C, 43.90; H, 3.84; N, 9.67%. IR (cm-1): 2932 w, 1653 w, 1577 s, 1562 s, 1525 s, 1500 m, 1438 m, 1407 s, 1358 s, 1316 m, 1296 m, 1257 w, 1208 s,

Figure 1. Coordination environment in 1, with thermal ellipsoids at the 50% probability level and with the atom numbering scheme. Most hydrogen atoms have been omitted for clarity. Atoms labeled with an “A” indicate disordered positions; those labeled with “i” denote symmetry equivalents. The water molecules of crystallization are not shown.

3D Cd R-Dicarboxylate Coordination Polymers with dpa Table 2. Selected Bond Distance (Å) and Angle (deg) Data for 1; Atoms Labeled “A” Indicate Disordered Componentsa

Crystal Growth & Design, Vol. 9, No. 5, 2009 2483 Table 3. Hydrogen Bonding Distance (Å) and Angle (deg) Data for 1-3

D-H · · · A

symmetry transformation for A

d(H · · A) ∠DHA d(D · · · A) 1

N2-H2N · · · O1

1.881(19) 174(4)

O1W-H1WA · · · O5 O1W-H1WB · · · O10 O1W-H1WB · · · O12 O13-H13A · · · O4 O13-H13B · · · O8

1.877(17) 2.495(19) 2.51(2) 1.862(17) 1.843(17)

171(3) 154(3) 152(2) 158(2) 164(2)

2.697(2) 3.253(5) 3.256(5) 2.658(2) 2.636(2)

N2-H2N · · · O1W

1.972(16) 176(2)

2.816(2)

N5-H5N · · · O14

1.944(16) 176(2)

2.815(2)

N8-H8N · · · O10

2.069(17) 170(2)

2.934(3)

2.750(4)

-x + 3/2, y + 1/2, -z + 3/2

2

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

1146 w, 1097 w, 1053 w, 1012 s, 921 w, 907 m, 858 w, 839 m, 811 s, 779 m, 727 m, 677 w, 661 w, 640 m. Preparation of {[Cd7(pim)6(dpa)6(H2O)2](ClO4)2 · 6H2O}n (2). Cd(ClO4)2 · 6H2O (150 mg, 0.35 mmol), dpa (165 mg, 0.96 mmol), and pimelic acid (77 mg, 0.46 mmol) were mixed with 10 mL of distilled H2O in a 23 mL Teflon-lined Parr acid digestion bomb. The bomb was sealed and heated at 150 °C for 48 h, whereupon it was cooled slowly to 25 °C. Colorless blocks of 2 (54 mg, 35% yield based on Cd) were isolated after washing with distilled water and ethanol and drying in air. No single-crystalline materials could be prepared at lower temperatures. Anal. Calcd for C102H130Cd7N18O40 (with loss of cocrystallized water) 2: C, 41.47; H, 3.62; N, 8.53%. Found: C, 41.86; H, 4.06; N, 8.61%. IR (cm-1): 3268 w, 3174 w, 2938 w, 2858 w, 1589 s, 1561 s, 1547 s, 1515 s, 1439 m, 1409 s, 1346 s, 1255 w, 1210 s, 1139 w, 1089 m, 1058 w, 1012 s, 948 w, 903 w, 837 w, 808 s, 765 w, 727 w, 675 w, 662 m, 636 m. Preparation of {[Cd(sub)(dpa)] · 2H2O}n (3). Cd(ClO4)2 · 6H2O (100 mg, 0.233 mmol), dpa (110 mg, 0.64 mmol), and suberic acid (56.0 mg, 0.303 mmol) were mixed with 10 mL of distilled H2O in a 23 mL Teflon-lined Parr acid digestion bomb. The bomb was sealed and heated at 120 °C for 48 h, whereupon it was cooled slowly to 25 °C. Colorless blocks of 3 (52 mg, 45% yield based on Cd) were isolated after washing with distilled water and ethanol and drying in air. Anal. Calcd for C18H25CdN3O6 3: C, 43.96; H, 5.12; N, 8.54%. Found: C, 44.23; H, 5.15; N, 8.44%. IR (cm-1): 3283 w, 2929 w, 2855 w, 1672 w, 1631 w, 1594 m, 1561 m, 1525 s, 1443 m, 1419 s, 1353 s, 1313 m, 1254 w, 1234 m, 1171 w, 1134 w, 1095 w, 1073 w, 1050 w, 1015 s, 958 w, 907 w, 8803 m, 8510 m, 815 s, 746 m, 728 m, 664 m, 620 s. X-ray Crystallography. A colorless plate of 1 (with dimensions 0.25 mm × 0.20 mm × 0.15 mm), a colorless block of 2 (0.60 mm × 0.40 mm × 0.15 mm), and a colorless block of 3 (0.70 mm × 0.30 mm × 0.20 mm) were subjected to single-crystal X-ray diffraction using a Bruker-AXS SMART 1k CCD instrument. Reflection data were acquired using graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). The data was integrated via SAINT.17 Lorentz and polarization effect and empirical absorption corrections were applied with SADABS.18 The structures were solved using direct methods and refined on F2 using SHELXTL.19 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 nitrogen atoms of the dpa moieties and any water molecules were found via Fourier difference maps, then restrained at fixed positions and refined isotropically. Relevant crystallographic data for 1-3 is listed in Table 1.

Results and Discussion Synthesis and Spectral Characterization. Compounds 1-3 were prepared as single-phase crystalline products by hydrothermal reaction of cadmium perchlorate hydrate, 4,4′-dipyridylamine, and the requisite aliphatic dicarboxylic acid. The infrared spectra of 1-3 were consistent with the structural

- 1, y, z - 1, y, z + 1, y, z + 1/2, -y + 1/2, z - 1/2 -x + 1, -y + 1, -z -x + 1, -y + 1, -z

x x x x

3 N3-H3N · · · O2W N6-H6N · · · O1

1.960(17) 170(2) 2.105(18) 154(2)

2.774(2) 2.889(2)

O1W-H1WA · · · O3W 2.01(2) 157(3) O1W-H1WB · · · O4W 1.98(2) 165(3) O2W-H2WA · · · O7 1.888(17) 178(3)

2.849(3) 2.842(2) 2.752(2)

O2W-H2WB · · · O4 O3W-H3WA · · · O3

2.013(17) 174(3) 1.97 164.4

2.860(2) 2.807(3)

O4W-H4WA · · · O8 O4W-H4WB · · · O6 O4W-H4WB · · · O6

1.98 2.59 2.64

2.795 3.070 3.196(1)

155.0 117.0 124.0

-x, -y + 1, -z -x + 1, -y + 1, -z x, y + 2, z - 1 x, y + 2, z - 1 x + 1, y + 1, z-1 x - 1, y - 1, z+2 x, y - 1, z -x, -y - 1, -z + 1

elements within their single crystal structures (vide infra). Sharp, medium intensity bands in the range of ∼1600-1200 cm-1 match with stretching modes of the aromatic rings of the dpa ligands.20 Features corresponding to the puckering of these aromatic rings are observed in the region between 820 and 600 cm-1. Asymmetric and symmetric C-O stretching modes of the fully deprotonated dicarboxylate anions give rise to the strong bands at 1577 and 1358 cm-1, 1589 and 1346 cm-1, and 1525 and 1353 cm-1 for 1-3, respectively. The absence of any spectral features near 1700 cm-1 is indicative of the deprotonation of the original dicarboxylic acids. Broadened bands between ∼3400 and 3200 cm-1 in the spectra of 2 and 3 represent O-H stretching modes present within the hydrogenbonded water molecules. A band at ∼1090 cm-1 in 2 is ascribed to the Cl-O stretching frequencies within the perchlorate anions. Structural Description of [Cd(adp)(dpa)]n (1). Compound 1 possesses an asymmetric unit (Figure 1) consisting of one cadmium atom, one dpa molecule, and two halves of two adipate dianions (adp-A, O1-O2/C11-C13; adp-B, O3-O4/C21-C23). Three atoms within the adp-B ligand (C22, O3, O4) are disordered equally over two positions. The cadmium ion manifests a slightly distorted octahedral [CdO4N2] coordination environment, with two trans nitrogen donor atoms from dpa ligands, two carboxylate oxygen donors from two different adp-B ligands, and two oxygen donors from a chelating terminus of a adp-A ligand. Bond lengths and angles are standard for chelated octahedral coordination at cadmium (Table 2). Neighboring cadmium atoms are joined into a {Cd2} binuclear unit with a six-membered {CdOCdOCO} ring by the bridging carboxylate terminus of one adp-B ligand, and a µ2-oxygen atom belonging to a second adp-B ligand. The Cd · · · Cd distance across the binuclear unit measures 3.872 Å. Through the µ2carboxylato/µ2-oxygen exotetradentate bridging mode of the gauche-gauche conformation adp-B ligands (88.3 and 74.8° 4-C atom torsion angles), adjacent {Cd2} binuclear units are

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Figure 2. Single [Cd(adp)]n layer motif within 1.

Figure 3. Interpenetration of decorated primitive cubic coordination polymer networks in 1.

linked into [Cd2(adp-B)]n chains oriented along the b crystal direction. In turn, these chains are connected by bis(chelating)

gauche-gauche adp-A ligands (56.6 and 56.6° 4-C atom torsion angles) along the c crystal axis, to construct a [Cd(adp)]n layer

3D Cd R-Dicarboxylate Coordination Polymers with dpa

Crystal Growth & Design, Vol. 9, No. 5, 2009 2485

Figure 4. Coordination environment of 2 with thermal ellipsoids at a 50% probability level and with a partial atom numbering scheme. Hydrogen atoms have been omitted for clarity. The water molecules of crystallization are not shown.

Figure 5. Single [Cd7(dpa)6(H2O)2]14+ oligomeric building unit in 2.

Figure 6. Undulating layer structure formed from the linkage of [Cd7(dpa)6(H2O)2]14+ oligomers in 2 through bridging pimelate carboxylate termini. Perchlorate anion positions are shown as green spheres.

motif that sits normal to the (101) crystal direction (Figure 2). The Cd · · · Cd distance through adp-A ligands is 9.497 Å. The [Cd(adp)]n layers in 1 are similar to those seen in {[Cd(adp)(1,10phenanthroline)] · 3H2O}.7a Parallel [Cd(adp)]n layers are connected by the tethering dpa ligands to form a 3D [Cd(adp)(dpa)]n coordination polymer network, with a through-imine Cd · · · Cd approach distance of 12.185 Å. The rectangular channels within a single network, with ∼16.4 × 14.4 Å apertures as defined by through-space Cd · · · Cd distances neglecting van der Waals radii, allow interpenetration of an identical net (Figure 3) assisted by hydrogen bonding between the central amines of the dpa ligands in one network and carboxylate oxygen atoms of the adp-A dianions in the other (Table 3). These supramolecular interactions are optimized by the 32.7° inter-ring twist between the pyridyl rings of the dpa ligands. Considering the centroids of the {Cd2} binuclear units as 6-connected nodes, a doubly interpenetrated R-Po primitive cubic lattice with 41263 topology can be invoked. The structure of 1 is similar in nature to those of [Cd(succinate)(dpa)]n8 and [Cd(glutarate)(dpa)]n,21 indicating

that the flexibility of the aliphatic dicarboxylates can permit generation of similar coordination polymer networks during selfassembly in this system. Structural Description of {[Cd7(pim)6(dpa)6(H2O)2](ClO4)2 · 6H2O}n (2). The large asymmetric unit of 2 contains four crystallographically distinct cadmium atoms, one of which (Cd2) rests on a crystallographic inversion center. Three pimelate dianions (pim-A, C31-C37/O1-O4; pim-B, C41-C47/O5-O8; pim-C, C51-C57/O14-O17), three dpa ligands (dpa-A, N1-N3; dpa-B, N4-N6; dpa-C, N7-N9), one aqua ligand, one unligated perchlorate anion, and three water molecules of crystallization comprise the rest of the asymmetric unit (Figure 4). Operation of the inversion center at Cd2 generates a cationic [Cd7(dpa)6(H2O)2]14+ oligomer (Figure 5), wherein the connectivity string of the cadmium atoms is Cd3 · · · Cd1 · · · Cd4 · · · Cd2 · · · Cd4 · · · Cd1 · · · Cd3. The oligomer-terminating Cd3 atoms possess a distorted {CdNO5} octahedral coordination environment, with the nitrogen donor provided by a dpa-B ligand. Oxygen donor atoms at Cd3 are provided by pim-B, pim-C, an aqua ligand, and a

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Figure 7. Face-on view of the layer motif formed by [Cd7(dpa)6(H2O)2]14+ oligomers in 2.

Figure 8. 3D covalent network of compound 2.

chelating pim-A carboxylate group. Cd2 manifests a more regular {CdN2O4} octahedral environment, with trans nitrogen donors from two different yet crystallographically identical dpa-A ligands, and oxygen donor atoms from pim-A and pimC. Atoms Cd1 and Cd4 are both pentagonal bipyramidally coordinated in a {CdN2O5} arrangement. The trans nitrogen donors at Cd1 belong to dpa-B and dpa-C; those at Cd4 belong to dpa-C and dpa-A. Cd1 is bound in the equatorial plane of its coordination sphere by a single oxygen atom from pim-C and chelating carboxylates from different termini of two different

pim-A ligands. Similarly, the coordination sphere at Cd4 is rounded out by a single oxygen atom from one pim-B and chelating carboxylates from pim-C and a different pim-B ligand. Within the [Cd7(dpa)6(H2O)2]14+ oligomer, the terminal Cd3 atoms connect inward to Cd1 atoms through dpa-B ligands with an inter-ring torsion angle of 31.8°. In turn, Cd1 atoms connect to Cd4 atoms through dpa-C tethers, which have a much narrower inter-ring torsion measuring 17.4°. Both Cd4 atoms conjoin to the central Cd2 atom through dpa-A, whose pyridyl


Crystal Growth & Design, Vol. 9, No. 5, 2009 2487 Table 4. Selected Bond distance (Å) and angle (°) data for 2a

Figure 9. Schematic view of the (8,10)-connected self-penetrated 3D coordination polymer network in 2. The blue and magenta spheres represent the Cd2 atoms and Cd4-based{Cd2O2} ring centroids, respectively.

rings are twisted by 19.9° with respect to each other. The Cd · · · Cd distances through dpa-A, dpa-B, and dpa-C within the oligomer measure 12.073, 12.229, and 12.170 Å, respectively. The [Cd7(dpa)6(H2O)2]14+ oligomers are joined together by pimelate oxygen atoms to produce an undulating layered motif (Figure 6), where the “wavelength” of 23.199 Å gives the b lattice parameter. Unligated perchlorate anions are situated near the layer pattern, held in place by hydrogen bonding mediated by the central amine groups of dpa-C ligands. The peaks and troughs of the undulating layer are marked by Cd3 atoms, the terminal cadmium positions within the oligomers. These are connected to Cd4 atoms through pim-C bis(bridging) carboxylates, and to Cd1 atoms through carboxylate oxygen atoms belonging to pim-A. The Cd3 · · · Cd4 and Cd3 · · · Cd1 distances are 4.393 and 4.470 Å, respectively. Cd4 atoms in adjacent oligomers are bound to each other through oxygen atoms of two different pim-B ligands, forming a small {Cd2O2} parallelogram with a Cd · · · Cd distance of 3.791 Å. Cd1 atoms connect to Cd2 atoms in neighboring oligomers through pim-A oxygen atoms and through a bis(bridging) pim-C carboxylate, with a Cd · · · Cd distance equaling 4.225 Å. The interactions between cadmium atoms in adjacent oligomers are shown in a face-on view of the layer motif, seen in Figure 7. The oligomer-based layers are connected through the full length of all three types of pimelate ligand to generate the cationic 3D {[Cd7(pim)6(dpa)6(H2O)2]n2n+ coordination polymer network within 2 (Figure 8). The closest Cd · · · Cd distance between layers, 12.040 Å, determines the a lattice parameter. The exotetradentate pim-A ligands, which adopt an anti-antigauche-anti conformation (torsion angles 178.1, 178.4, 66.9 and 175.2°), bridge Cd3 and Cd1 atoms in one layer and Cd2 and Cd1 atoms in another. In contrast, the pim-B ligands are exotridentate, connecting Cd3 atoms with two Cd4 atoms in another layer. These also have an anti-anti conformation (torsion angles 173.0, 174.6, 74.2, and 164.2°). The pim-C ligands are exotetradentate, connecting Cd1 and Cd3 atoms in one layer with Cd2 and Cd4 atoms in the next; these rest in an anti-anti-anti-gauche conformation (torsion angles 174.1, 178.7, 179.8, and 64.4°).

Cd1-O17#1 Cd1-N9#2 Cd1-N6#3 Cd1-O4#4 Cd1-O2 Cd1-O3#4 Cd1-O1 Cd2-N3#5 Cd2-N3 Cd2-O16#6 Cd2-O16#7 Cd2-O3#8 Cd2-O3#9 Cd3-O13 Cd3-O1 Cd3-O6 Cd3-N4 Cd3-O15 Cd3-O5 Cd4-N1 Cd4-N7 Cd4-O7#10 Cd4-O14 Cd4-O8#8 Cd4-O7#8 Cd4-O15

2.2767(14) 2.2790(16) 2.3021(16) 2.4092(13) 2.4295(15) 2.5323(13) 2.5448(14) 2.2939(16) 2.2940(16) 2.2953(15) 2.2954(15) 2.3225(13) 2.3225(13) 2.2540(14) 2.2716(14) 2.3121(15) 2.3176(16) 2.3244(14) 2.3808(14) 2.2812(16) 2.2914(15) 2.3437(14) 2.3824(13) 2.4030(13) 2.4948(14) 2.5014(14)

O17#1-Cd1-O1 N9#2-Cd1-O1 N6#3-Cd1-O1 O17#1-Cd1-N9#2 O17#1-Cd1-N6#3 N9#2-Cd1-N6#3 O17#1-Cd1-O4#4 N9#2-Cd1-O4#4 N6-Cd1-O4#4 O17#1-Cd1-O2 N9#2-Cd1-O2 O4#4-Cd1-O1 O2-Cd1-O1 O3#4-Cd1-O1 N6#3-Cd1-O2 O4#4-Cd1-O2 O17#1-Cd1-O3#4 N9#2-Cd1-O3#4 N6#3-Cd1-O3#4 O4#4-Cd1-O3#4 O2-Cd1-O3#4 Cd3-O1-Cd1 Cd2#9-O3-Cd1#11 Cd4#1-O7-Cd4#12

135.09(5) 81.78(5) 94.49(5) 98.53(6) 87.51(6) 173.91(6) 145.71(5) 86.86(5) 87.71(5) 83.08(5) 87.68(6) 79.15(4) 52.00(5) 130.87(4) 93.82(6) 131.12(5) 93.76(5) 86.70(5) 92.18(5) 52.54(4) 173.09(5) 136.22(6) 120.93(5) 103.13(5)

N3#5-Cd2-N3 N3#5-Cd2-O16#6 N3-Cd2-O16#6 N3#5-Cd2-O16#7 N3-Cd2-O16#7 O16#6-Cd2-O16#7 N3#5-Cd2-O3#8 N3-Cd2-O3#8 O16#6-Cd2-O3#8 O16#7-Cd2-O3#8 N3#5-Cd2-O3#9 N3-Cd2-O3#9 O16#6-Cd2-O3#9 O16#7-Cd2-O3#9 O3#8-Cd2-O3#9 O13-Cd3-O1 O13-Cd3-O6 O1-Cd3-O6 O13-Cd3-N4 O1-Cd3-N4 O6-Cd3-N4 O13-Cd3-O15 O1-Cd3-O15 O6-Cd3-O15 N4-Cd3-O15 O13-Cd3-O5 O1-Cd3-O5 O6-Cd3-O5 N4-Cd3-O5 O15-Cd3-O5 N1-Cd4-N7 N1-Cd4-O7#10 N7-Cd4-O7#10 N1-Cd4-O14 N7-Cd4-O14 O7#10-Cd4-O14 N1-Cd4-O8#8 N7-Cd4-O8#8 O7#10-Cd4-O8#8 O14-Cd4-O8#8 N1-Cd4-O7#8 N7-Cd4-O7#8 O7#10-Cd4-O7#8 O14-Cd4-O7#8 O8#8-Cd4-O7#8 N1-Cd4-O15 N7-Cd4-O15 O7#10-Cd4-O15 O14-Cd4-O15 O8#8-Cd4-O15 O7#8-Cd4-O15

180.00(8) 92.99(6) 87.01(6) 87.01(6) 92.99(6) 180.0 92.99(5) 87.01(5) 88.81(5) 91.20(5) 87.01(5) 92.99(5) 91.20(5) 88.80(5) 180.0 81.19(5) 95.91(5) 91.39(5) 92.91(6) 94.90(6) 169.86(6) 93.29(5) 172.80(5) 93.79(5) 80.69(5) 149.57(5) 87.86(5) 55.85(5) 116.38(6) 99.19(5) 178.43(6) 92.23(6) 86.90(5) 93.22(5) 88.05(5) 87.67(5) 89.25(5) 90.30(5) 129.67(5) 142.48(5) 87.21(5) 91.32(5) 76.87(5) 164.54(5) 52.95(4) 103.83(5) 77.67(5) 137.90(5) 53.30(4) 89.78(4) 141.39(4)

a Symmetry transformations to generate equivalent atoms: #1 -x + 3/2, y - 1/2, -z + 1/2; #2 x - 1/2, -y + 1/2, z - 1/2; #3 x + 1/2, -y + 1/2, z + 1/2; #4 x + 1, y, z; #5 -x + 1, -y + 1, -z - 1; #6 x + 1, -y + 1, -z; #7 x, y, z - 1; #8 x + 1/2, -y + 1/2, z - 1/2; #9 -x + 1/ 2, y + 1/2, -z - 1/2; #10 -x + 3/2, y + 1/2, -z + 1/2, #11 x - 1, y, z; #12 x - 1/2, -y + 1/2, z + 1/2.

If the special position Cd2 atoms and the centroids of the {Cd2O2} parallelograms formed by Cd4 atoms are considered as connecting nodes, the cationic framework of 2 can be considered to be a (8,10)-connected 3D network (Figure 9). The Scha¨fli symbol for this highly complex topology is (384145462)(31041851463) as determined by TOPOS software,22 with the Cd2 atoms serving as 8-connected nodes. Moreover, 2 represents another entry in the small but growing family of selfpenetrated networks, with its connecting ligands penetrating through the smallest circuits elsewhere in the network. Several modes of self-penetration/ring-crossing were found by TOPOS (see the Supporting Information for topological analysis); the simplest involves the self-penetration of four-membered circuits formed from {Cd2O2} centroids by six-membered circuits formed by the connection of four Cd2 atoms with two {Cd2O2}

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Figure 10. Self-penetration of four-membered and six-membered circuits in 2. The blue and magenta spheres represent the Cd2 atoms and Cd4based{Cd2O2} ring centroids, respectively.

Figure 11. Coordination environment of 3 with thermal ellipsoids at the 50% probability level and partial atom numbering scheme. Most hydrogen atoms have been omitted for clarity. The water molecules of crystallization are not shown.

centroids (Figure 10). To the best of our knowledge, the (8,10)connectivity of 2 represents the highest connected binodal selfpenetrated lattice reported to date.23 In addition to perchlorate ions, isolated water molecules and water molecule dimers exist in the incipient void space within the 3D self-penetrated cationic network of 2. These unligated species are held in place to the coordination polymer matrix by hydrogen bonding patterns (Table 3) provided by the dpa ligands and carboxylate oxygen atoms. The extra-framework space filled by all of the unligated species occupies 13.7% of the unit cell volume of 2, as calculated by PLATON.24 Structural Description of {[Cd(sub)(dpa)] · 2H2O}n (3). The asymmetric unit of compound 3 consists of two cadmium atoms, two suberate dianions (sub-A, O1-O4; sub-B, O5-O8) and two dpa molecules (dpa-A, N1-N3; dpa-B, N4-N6) along with four water molecules of crystallization (Figure 11). Each cadmium atom is seven-coordinate with a {CdN2O5} pentagonal bipyramidal geometry, with trans nitrogen donor atoms in the axial positions belonging to dpa-A and dpa-B ligands. The equatorial coordination sites at Cd1 are taken up by two chelating termini of sub-A dianions, along with a single oxygen

donor atom from a third sub-A ligand. The coordination environment about Cd2 is very similar, with oxygen donor atoms provided by three different sub-B ligands. Bond lengths and angles about cadmium are consistent with distorted pentagonal bipyramidal coordination (Table 5). Cd1 atoms are joined into pinched binuclear {Cd2O2} parallelograms by µ2-oxygen atoms from sub-A carboxylates. The Cd · · · Cd through space distance is 3.824 Å, with Cd · · · Cd · · · Cd angles of 76.4 and 103.6°. Cd2 atoms are connected in very similar binuclear units by oxygen atoms from sub-B carboxylates, but with a shorter Cd · · · Cd distance of 3.788 Å. The {Cd2O2} parallelograms based on Cd2 are even more distorted from rectangular than those built from Cd1, with Cd · · · Cd · · · Cd angles of 75.0 and 105.0°. The binuclear {Cd2O2} units based on Cd1 and Cd2 atoms are linked into 1-D [Cd(sub)]n chains through bis(chelating) sub-A and sub-B carboxylates, respectively (Figure 12). In both sub-A and sub-B, the pimelate conformation is gaucheanti-anti-anti-gauche, but with subtly altered torsion angles (sub-A: 68.9, 168.8, 174.7, 176.0, 69.8°; sub-B: 57.0, 170.0, 166.5, 165.5, 68.4°). The [Cd(sub)]n chains based on Cd1 and



Figure 12. Two crystallographically distinct [Cd(sub)]n chains in 3.

Figure 13. View of the noninterpenetrated 3D 658 topology network in 3. Orange spheres represent the water molecules of crystallization.

sub-A are oriented along the a crystal direction; those based on Cd2 and sub-B are arranged along b. Individual [Cd(sub)]n chains are connected into the 3D covalent lattice of 3 through bridging dpa ligands (Figure 13). The Cd · · · Cd distances through dpa-A and dpa-B are 12.014 and 12.227 Å, respectively. The different metal-metal contact lengths are caused by slight variances in the inter-ring torsion angles of the dpa ligands (29.2° in dpa-A, 31.2° in dpa-B). If

the centroids of the {Cd2O2} parallelograms are taken as connecting nodes, the topology of 3 is a 4-connected 658 (CdSO4 structure type25) noninterpenetrated net. The stability of the structure is enhanced by hydrogen bonding between the dpa-B amine and an oxygen atom from sub-A. Acyclic water molecule trimers and isolated water molecules lie in the extra-framework spaces within the 3D network of 3 (10.0% of the unit-cell volume). The cocrystallized species are anchored to the

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Figure 14. Emission spectra of 1-3, with excitation at λ ) 300 nm. Table 5. Selected Bond Distance (Å) and Angle (deg) data for 3 Cd1-N2 Cd1-N4 Cd1-O2#1 Cd1-O3#2 Cd1-O1 Cd1-O4#2 Cd1-O2 Cd2-N5#3 Cd2-N1 Cd2-O5#4 Cd2-O7#5 Cd2-O8#5 Cd2-O5 Cd2-O6

2.2867(16) 2.3066(16) 2.3659(14) 2.4031(15) 2.4165(14) 2.4206(15) 2.4996(15) 2.2885(16) 2.2958(16) 2.3543(16) 2.4074(16) 2.4103(16) 2.4191(16) 2.4589(16)

N2-Cd1-N4 N2-Cd1-O2#1 N4-Cd1-O2#1 N2-Cd1-O3#2 N4-Cd1-O3#2 O2#1-Cd1-O3#2 N2-Cd1-O1 N4-Cd1-O1 O2#1-Cd1-O1 O3#2-Cd1-O1 N2-Cd1-O4#2 N4-Cd1-O4 O2#1-Cd1-O4#2 O3#2-Cd1-O4#2 O1-Cd1-O4#2

171.69(6) 84.08(6) 87.63(5) 92.99(6) 86.90(5) 92.07(5) 91.32(5) 94.24(5) 129.21(5) 138.71(5) 100.93(5) 85.76(4) 146.15(4) 54.46(4) 84.42(4)

N2-Cd1-O2 N4-Cd1-O2 O2#1-Cd1-O2 O3#2-Cd1-O2 O1-Cd1-O2 O4#2-Cd1-O2 N5#3-Cd2-N1 N5#3-Cd2-O5#4 N1-Cd2-O5#4 N5#3-Cd2-O7#5 N1-Cd2-O7#5 O5#4-Cd2-O7#5 N5#3-Cd2-O8#5 N1-Cd2-O8#5 O5#4-Cd2-O8#5 O7#5-Cd2-O8#5 N5#3-Cd2-O5 N1-Cd2-O5 O5#4-Cd2-O5 O7#5-Cd2-O5 O8#5-Cd2-O5 N5#3-Cd2-O6 N1-Cd2-O6 O5#4-Cd2-O6 O7#5-Cd2-O6 O8#5-Cd2-O6 O5-Cd2-O6

86.40(5) 92.05(5) 76.40(5) 168.47(5) 52.81(5) 136.95(4) 176.00(6) 89.68(5) 88.68(5) 93.17(5) 83.26(5) 92.2(5) 89.64(5) 89.72(5) 146.4(5) 54.3(5) 93.11(5) 89.99(5) 75.0(5) 165.7(5) 138.6(5) 94.68(5) 89.21(5) 127.8(5) 139.2(5) 85.7(5) 52.9(5)

Symmetry transformation to generate equivalent atoms: #1 -x, -y + 1, -z, #2 -x + 1, -y + 1, -z, #3 x - 1, y - 1, z + 1, #4 -x - 1, -y, -z + 1, #5 x, y + 1, z.

coordination polymer network via hydrogen bonding involving dpa-A and both suberate ligands, supplemented by some weak C-H · · · O interactions originating from the dpa motifs. Infor-

mation regarding these supramolecular interactions is given in Table 3 above. Luminescence Behavior of 1-3. In the solid state at room temperature, 1-3 exhibited blue-violet luminescence upon ultraviolet excitation (λ ) 300 nm) (Figure 14). The luminescent behavior in these materials is most likely ascribed to ligandcentered π f π* or π f n orbital transitions within the aromatic rings of the dpa ligands, by comparison with other luminescent d10 coordination polymers containing dipyridyl-type neutral linkers.26 The emission maxima are red-shifted in the order of 3 (λmax ) 360 nm), 2 (λmax ) 375 nm) and 1 (λmax ) 390 nm), though this trend is difficult to rationalize at this time. It is possible that the stronger intensity observed for 3 is related to a diminishing of nonemissive energy-loss mechanisms, perhaps induced by some rigidity imparted by the tethering of the orthogonally arranged [Cd(sub)]n chain motifs. Thermogravimetric Analysis of 1 and 3. Although compound 2 was not subjected to heating because of the explosive tendencies of perchlorate-containing compounds, polycrystalline samples of 1 and 3 were subjected to thermogravimetric analysis to test their dehydration and/or decomposition behavior. The mass of 1 was stable to ∼275 °C, whereupon a significant mass loss occurred, indicating likely destruction of the doubly interpenetrated 3D coordination polymer framework. The mass remnant of 17.2% at ∼650 °C marks the deposition of Cd metal, some of which had evaporated (bp Cd ) 765 °C). Compound 3 had lost 1 equiv. of cocrystallized water on standing at room temperature, with the second equivalent removed by heating to 50 °C (3.5% mass loss observed, 7.0% calc’d for two molar equivalents of H2O). At ∼250 °C, a precipitous mass loss was observed, indicating ejection of the organic components. The 26.0% mass remnant at 650 °C is consistent with a deposition



of CdO (25.9% calcd). TGA traces of 1 and 3 are given in Figures S1 and S2 (see the Supporting Information). Conclusions Use of long-spanning, flexible R,ω-dicarboxylate ligands in conjunction with dpa, a kinked-donor disposition diimine, resulted in a series of luminescent cadmium coordination polymers with 3D structures. Compound 1, containing adipate moieties, presented a doubly interpenetrated primitive cubic lattice, very similar to its succinate and glutarate congeners. Thus, the presence of two, three, or four methylene units in the R,ω-dicarboxylate chain does not appreciably alter the overall coordination polymer topology. However, members of this series based on longer R,ω-dicarboxylates manifest significant structural differences, showing synergistic effects between the coordination geometry at the d10 configuration divalent cadmium ion and aliphatic group conformation. The suberate-containing material 3 displays a 4-connected noninterpenetrated 658 topology lattice, in contrast to the “ligand-vacancy” primitive cubic net of its cobalt and nickel analogues. Use of the seven-carbon pimelate ligand resulted in the coordination polymer 2 featuring a complicated cationic self-penetrated (8,10)-connected lattice; representing the highest connectedness for a self-penetrated topology reported to date to the best of our knowledge. Acknowledgment. Funding for this work was provided by the donors of the American Chemical Society Petroleum Research Fund. E.S. thanks the MSU High School Honors Science Program and Dr. Gail Richmond for his participation in the research. We thank Dr. Rui Huang for performing the elemental analyses and Dr. Kathryn Severin for use of the fluorimeter. Supporting Information Available: TGA traces for 1 and 3 (PDF); topological analysis of 2 (TXT); and CIF files for 1-3. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data (excluding structure factors) for 1-3 have also been deposited with the Cambridge Crystallographic Data Centre with Nos. 698204-698206, 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]).

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CG801396K

Structural Diversity in Luminescent Three-Dimensional Cadmium

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