Cadmium Glutarate Coordination Polymers Containing Hydrogen-Bonding Capable Tethering Organodiimines: From Double Interpenetration to Supramolecular Cavities Containing an Unprecedented Water Tape Morphology
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 8 3091–3097
David P. Martin,† Matthew R. Montney,† Ronald M. Supkowski,‡ and Robert L. LaDuca*,† Lyman Briggs College and Department of Chemistry, Michigan State UniVersity, East Lansing, Michigan 48825, and Department of Chemistry and Physics, King’s College, Wilkes-Barre, PennsylVania 18711 ReceiVed March 24, 2008; ReVised Manuscript ReceiVed May 5, 2008
ABSTRACT: Two cadmium glutarate coordination polymers incorporating the hydrogen-bonding capable tethering organodiimines 4,4′-dipyridylamine (dpa) or bis(4-pyridylmethyl)piperazine (bpmp) have been prepared and structurally characterized. [Cd(glutarate)(dpa)]n (1) manifests a doubly interpenetrated decorated R-Po (pcu, 41263 topology) lattice, with octahedral coordination at cadmium. Compound 1 undergoes blue-violet luminescence upon UV irradiation. Use of the longer tethering organodiimine resulted in the formation of {[Cd(glutarate)(bpmp)(H2O)] · 6H2O}n (2), which displays non-interpenetrated (4,4)-rhomboid grid coordination polymer layers. In contrast to 1, the cadmium ions in 2 adopt a pentagonal bipyramidal coordination geometry, with aqua ligands allowing construction of a hexagonal boron nitride (bnn, 4466 topology) supramolecular framework through interlayer hydrogen bonding. Unprecedented one-dimensional water molecule tapes with 2T5(2)7(2) classification occupy large ellipsoid channels coursing through the structure of 2, stabilizing the coordination polymer framework through hydrogen bonding. Upon partial dehydration the structure of 2 degrades irreversibly. Introduction Coordination polymers constructed from divalent d10 configuration ions and dicarboxylate ligands have attracted high levels of interest because of their potential to serve in hydrogen storage,1 gas absorption,2 photoluminescence,3 and nonlinear optical4 applications. Other coordination polymers incorporating divalent zinc or cadmium ions have been observed to stabilize co-crystallized water molecule clusters and tapes.5 The molecular-level structures of these materials are synergistically imposed during self-assembly by the binding modes of the carboxylate moieties and the varying coordination geometries possible at d10 configuration ions because of their lack of any preferences from crystal field stabilization, along with numerous more subtle supramolecular interactions. A successful approach toward the structural elaboration of these materials has been the inclusion of neutral tethering organodiimines, such as 4,4′bipyridine (4,4′-bpy), that can link together metal dicarboxylate subunits into higher dimensionalities.6–8 Compared to rigid tethering ligands such as 4,4′-bpy and 4,4′dipyridylethylene, the use of organodiimines with a kinked disposition of nitrogen donor atoms in the construction of coordination polymers is much less common. Hanton and colleagues9 and our group10 have shown that 4,4′-dipyridylamine (dpa) acts as both a covalent linking agent and a supramolecular structure director through its hydrogen-bonding capable central amine in oxoanion coordination polymer systems. Recently, we have been able to isolate multifunctional coordination polymers with intriguing structural motifs by the self-assembly of zinc ions with aliphatic dicarboxylates and dpa.11,12 The threedimensional (3-D) coordination polymer {[Zn(succinate)(dpa)] · H2O}n manifested an uncommon 4-fold interpenetrated SrAl2-type framework,11 while the mutually inclined interpen* To whom correspondence should be addressed. E-mail:
[email protected]. † Michigan State University. ‡ King’s College.
etrated 2d + 2d f 3-D phase{[Zn(adipate)(dpa)] · H2O}n displayed blue light emission upon ultraviolet irradiation along with a reversible structural reorganization upon desolvation/ resolvation.12 The longer tethering ligand bis(4-pyridylmethyl)piperazine (bpmp), which also possesses hydrogen bonding points of contact within its central core, has also proven advantageous in the construction of luminescent d10 ion coordination polymers with diverse morphologies. Very recently we were able to obtain the first dicarboxylate coordination polymers to incorporate bpmp tethers.13 [Cd(isophthalate)(bpmp)]n possesses a decorated (4,4) rhomboid grid layered structure, while its zinc congener [Zn(isophthalate)(bpmp)]n forms a 5-fold interpenetrated diamondoid lattice. In this contribution, we present the successful extension of our previous work with dpa and bpmp ligands to a flexible R,ωdicarboxylate system, with the synthesis and structural characterization of [Cd(glutarate)(dpa)]n (1) and {[Cd(glutarate)(bpmp)(H2O)] · 6H2O}n (2). The materials display substantially different structural morphologies and interpenetration levels depending on the binding modes of the glutarate dianions, the coordination environment about the cadmium ions, and the length and hydrogen bonding facility of the organodiimine tethering ligands. Compound 2 manifests unprecedented flat onedimensional water molecule tapes with 2T5(2)7(2) classification trapped within large incipient oblate void spaces; 1 displays blue-violet luminescence. Experimental Section General Considerations. Cadmium salts (Fisher) and glutaric acid (Aldrich) were obtained commercially. The organodiimines 4,4′dipyridylamine (dpa)10a and bis(4-pyridylmethyl)piperazine (bpmp)14 were prepared by published procedures. Water was deionized above 3 MΩ in-house. Thermogravimetric analysis was performed on a TA Instruments TGA 2050 Thermogravimetric analyzer with a heating rate of 10 °C/min up to 900 °C. Elemental analysis was carried out using a Perkin-Elmer 2400 Series II CHNS/O analyzer. IR spectra were recorded on powdered samples on a Perkin-Elmer Spectrum One
10.1021/cg8003118 CCC: $40.75 2008 American Chemical Society Published on Web 06/28/2008
3092 Crystal Growth & Design, Vol. 8, No. 8, 2008 instrument. 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 ultraviolettransparent epoxy adhesive. Preparation of [Cd(glutarate)(dpa)]n (1). Cd(NO3)2 · 6H2O (127 mg, 0.37 mmol), glutaric acid (49 mg, 0.37 mmol), dpa (127 mg, 0.74 mmol), and 10 mL of distilled H2O were placed into a 23 mL Teflonlined Parr acid digestion bomb. The bomb was sealed and heated to 120 °C for 72 h after which it was gradually cooled to 25 °C. Colorless blocks of 1 (61 mg, 54% based on Cd) were obtained after washing with distilled H2O and acetone and drying in air. Anal. Calc. for C30H30N6O8Cd2 (1): C, 43.54; H, 3.66; N, 10.16%; Found: C, 43.30; H, 3.47; N, 10.15%. IR (cm-1): 2873(w), 1601(w), 1532(s), 1498(m), 1407(s), 1365(m), 1320(m), 1264(w), 1197(m), 1098(s), 1049(m), 1008(s), 910(w), 811(m), 795(m), 755(m), 704(s). Preparation of {[Cd(glutarate)(bpmp)(H2O)] · 6H2O}n (2). CdCl2 · 2.5H2O (0.042 g, 0.19 mmol) and glutaric acid (0.024 g, 0.19 mmol) were added to 4 mL of distilled H2O in a borosilicate glass tube that had been sealed at one end. A solution of bpmp (0.050 g, 0.19 mmol) in 3 mL of methanol was then carefully layered on top of the aqueous solution. Colorless blocks of 2 (0.036 g, 0.057 mmol, 30% yield based on Cd) deposited after ∼1 week. The crystals of 2 grew opaque shortly after removal from the mother liquor, indicative of dehydration. Anal. Calc. for C21H40N4O11Cd (2) with loss of 5 equiv of water: C, 46.12; H, 5.53; N, 10.24%; Found: C, 45.53; H, 5.23; N, 9.77%. IR of partially dehydrated 2 (cm-1): 3224(w, br), 2946(w), 2815(w), 1610(m), 1544 s, 1440(w), 1411(s), 1352(w), 1333(w), 1310(w), 1297(w), 1249(w), 1235(w), 1156(m), 1124(w), 1063(w), 1010(s), 920(w), 909(w), 842(m), 802(m), 728(m). X-ray Crystallography. A colorless block of 1 (with dimensions 0.36 × 0.12 × 0.12 mm) and a colorless block of 2 (0.65 × 0.40 × 0.25 mm) were subjected to single-crystal X-ray diffraction using either a Bruker-AXS SMART 1k CCD instrument (1) or a Bruker-AXS Apex II CCD instrument (2). Reflection data were acquired using graphitemonochromated Mo KR radiation (λ ) 0.71073 Å). The data were integrated via SAINT.15 Lorentz and polarization effect and multiscan absorption corrections were applied with SADABS.16 The structures were solved using direct methods and refined on F2 using SHELXTL.17 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 central nitrogens of the dpa moieties and any water molecules were found via Fourier difference maps, then restrained at fixed positions and refined isotropically. A large residual electron density peak for 2 (2.699 e-/Å3) was located 0.12 Å from the cadmium atom. This peak is considered an artifact because it does not show a reasonable bond length to cadmium; it could not be eliminated even through application of alternative absorption correction routines. Relevant crystallographic data for 1 and 2 are listed in Table 1.
Martin et al. Table 1. Crystal and Structure Refinement Data for 1 and 2 data empirical formula formula weight collection T λ (Å) crystal system space group a (Å) b (Å) c (Å) β (°) V (Å3) Z Dcalc (g cm-3) µ (mm-1) min/max T hkl ranges total reflections unique reflections R(int) parameters/restraints R1 (all data)a R1 (I > 2σ(I)) wR2 (all data)b wR2 (I > 2σ(I)) max/min residual (e-/Å3) GOF a
1
2
C30H30Cd2N6O8 827.40 173(2) 0.71073 monoclinic P21/n 16.701(2) 9.8114(12) 19.272(2) 94.242(2) 3132.9(7) 4 1.754 1.417 0.874 -22 e h e 22 -12 e k e 12 -25 e l e 25 37283 7617 0.0565 421/2 0.0685 0.0455 0.0709 0.0662 1.128/-1.023 1.133
C21H40CdN4O11 636.97 173(2) 0.71073 monoclinic P21/n 8.7296(11) 14.4136(19) 22.956(3) 95.295(2) 2876.2(6) 4 1.471 0.818 0.753 -11 e h e 11 -18 e k e 18 -29 e l e 30 31151 6590 0.0365 376/21 0.0535 0.0404 0.1115 0.1031 2.699/-0.664 1.069
R1 ) Σ||Fo| - |Fc||/Σ|Fo|. b wR2 ) {Σ[w(Fo2 - Fc2)2]/Σ[wFo2]2}1/2.
Results and Discussion Synthesis and Spectral Characterization. Compound 1 was obtained cleanly as a uniform phase crystalline product (as judged by elemental analysis and powder XRD) under hydrothermal conditions through the combination of cadmium nitrate, glutaric acid, and dpa. Hydrothermal attempts to prepare compound 2 failed, but layering an aqueous solution of cadmium chloride and glutaric acid with a methanolic solution of bpmp yielded the desired mixed ligand phase 2 in high yield. The infrared spectra of 1 and 2 were consistent with their formulations. Medium intensity bands in the range of ∼1600 to ∼1200 cm-1 were ascribed to stretching modes of the pyridyl rings of the dpa or bpmp ligands.18 Features corresponding to pyridyl ring puckering exist in the region between ∼820 and ∼600 cm-1. Asymmetric and symmetric C-O stretching modes of the fully deprotonated glutarate dianions were substantiated by strong, broadened bands at ∼1530 and ∼1400 cm-1. The lack of any bands in the region of ∼1710 cm-1 is indicative of complete deprotonation of glutaric acid during the synthesis of 1 and 2. Broad bands in the area of ∼3400 to ∼3200 cm-1 represent N-H stretching modes within the dpa ligands in 1,
Figure 1. Coordination environment of 1 with thermal ellipsoids at 50% probability. Most hydrogen atoms have been removed for clarity.
and O-H stretching modes within ligated and unligated water molecules in 2. The broadness of the latter features is attributed to significant hydrogen bonding pathways. Structural Description of [Cd(glutarate)(dpa)]n (1). Compound 1 possesses an asymmetric unit (Figure 1) consisting of two crystallographically distinct cadmium atoms, two glutarate dianions (glu-A, O1-O4; glu-B, O5-O8), and two dpa molecules (dpa-A, N1-N3; dpa-B, N4-N6). Each unique Cd ion possesses a slightly distorted octahedral [CdO4N2] coordination
Cadmium Glutarate Coordination Polymers
Crystal Growth & Design, Vol. 8, No. 8, 2008 3093
Table 2. Selected Bond Distance (Å) and Angle (°) Data for 1a Cd1-O1 Cd1-O3#1 Cd1-N6#2 Cd1-N4 Cd1-O5 Cd1-O6 Cd2-O2 Cd2-N3#2 Cd2-N1 Cd2-O3#1 Cd2-O7#3 Cd2-O8#3 O1-Cd1-O3#1 O1-Cd1-N6#2 O3#1-Cd1-N6#2 O1-Cd1-N4 O3#1-Cd1-N4 N6#2-Cd1-N4 O1-Cd1-O5 O3#1-Cd1-O5 N6#2-Cd1-O5
2.236(3) 2.243(2) 2.339(3) 2.365(3) 2.386(3) 2.425(3) 2.260(3) 2.292(3) 2.297(3) 2.333(2) 2.377(3) 2.427(3) 104.87(9) 85.56(10) 99.20(10) 89.86(10) 87.86(10) 172.37(11) 154.77(9) 100.19(9) 93.34(10)
N4-Cd1-O5 O1-Cd1-O6 O3#1-Cd1-O6 N6#2-Cd1-O6 N4-Cd1-O6 O5-Cd1-O6 O2-Cd2-N3#2 O2-Cd2-N1 N3#2-Cd2-N1 O2-Cd2-O3#1 N3#2-Cd2-O3#1 N1-Cd2-O3#1 O2-Cd2-O7#3 N3#2-Cd2-O7#3 N1-Cd2-O7#3 O3#1-Cd2-O7#3 O2-Cd2-O8#3 N3#2-Cd2-O8#3 N1-Cd2-O8#3 O3#1-Cd2-O8#3 O7#3-Cd2-O8#3 Cd1#4-O3-Cd2#4
88.21(10) 100.32(9) 153.90(9) 89.36(10) 85.46(10) 54.45(8) 95.79(11) 90.26(11) 172.96(11) 101.33(9) 85.80(10) 89.49(10) 135.39(9) 93.60(10) 84.56(10) 122.82(9) 81.31(10) 96.35(10) 88.11(10) 176.44(9) 54.31(9) 111.88(10)
a Symmetry transformations to generate equivalent atoms: (#1) x, y + 1, z. (#2) x + 1/2, -y + 1/2, z + 1/2. (#3) x + 1/2, -y + 1/2, z - 1/2 (#4) x, y - 1, z.
environment, with bond lengths and angles given in Table 2. Cd1 is coordinated by trans nitrogen donors belonging to two different dpa-B ligands, along with cis oxygen atoms belonging to a chelating carboxylate terminus of a glu-B ligand. The remaining two coordination sites are occupied by oxygen donors provided by two different glu-A ligands. The environment about Cd2 is largely similar, except that its trans nitrogen donor atoms are part of two different dpa-A ligands. Adjacent Cd1 and Cd2 atoms are joined into a binuclear kernel consisting of a six-membered {CdOCdOCO} ring by the bridging carboxylate group of a glu-A ligand, and a µ2-oxygen atom (O3) belonging to a second glu-A ligand. The Cd · · · Cd distance across the binuclear unit measures 3.791(1) Å. The glu-A dianions adopt an exotetradentate µ2-carboxylate/µ2-oxo binding mode, thereby linking the binuclear kernels into onedimensional (1-D) chain motifs propagating along the b crystal direction. Four-atom torsion angles within the aliphatic chain of glu-A (170.7 and 166.9°) indicate a splayed-open “anti-anti” conformation; the centroid-to-centroid distance between {CdOCdOCO} rings connected through glu-A is 9.811 Å. Binuclear units are conjoined in an orthogonal direction through bisbridging/bis-chelating exobidentate glu-B ligands, which rest in a twisted “gauche-anti” conformation (torsion angles ) 63.5
Figure 2. A single [Cd(glutarate)]n layer in 1.
Figure 3. 2-fold interpenetration of [Cd(glutarate)(dpa)]n networks in 1. Each network is shown in a different color for clarity.
and 166.5°). Thus, [Cd(glutarate)]n (4,4) rhomboid grid coordination polymer layers, coplanar with the [101] crystal planes, are formed by junction of binuclear kernels through both glu-A and glu-B (Figure 2). This motif contrasts with other cadmium glutarate coordination polymers, such as [Cd(glutarate)(1,10phenantroline)]19 and {[Cd(glutarate)(H2O)3] · H2O}20 in which the [Cd(glutarate)]n subunits are simple 1-D chains with bisbridging/bischelating glutarate tethers. Neighboring [Cd(glutarate)]n layers are strutted by dpa ligands to create a 3-D [Cd(glutarate)(dpa)]n coordination polymer network (Figure 3). Cd1 atoms in adjacent [Cd(glutarate)]n layers are connected through dpa-B ligands with Cd · · · Cd distances of 12.250(2) Å; the corresponding Cd2 · · · Cd2 distance through dpa-A ligands is 12.261(2) Å. The incipient void space within the [Cd(glutarate)(dpa)]n network is occupied by an identical interpenetrated network (Figure 4), held in place by hydrogen bonding between the central amine subunits of the dpa ligands and carboxylate oxygen atoms of the glu-B anions in the other network (Table 3). These supramolecular interactions are maximized by inter-ring torsions within the dpa ligands (24.7° for dpa-A, 36.5° for dpa-B). Treating the centroids of the {CdOCdOCO} rings as a 6-connected node reveals a doubly interpenetrated R-Po primi-
3094 Crystal Growth & Design, Vol. 8, No. 8, 2008
Martin et al. Table 4. Selected Bond Distance (Å) and Angle (°) Data for 2a Cd1-O5 Cd1-N1 Cd1-N4#1 Cd1-O4#2 Cd1-O2 Cd1-O1 Cd1-O3#2 O5-Cd1-N1 O5-Cd1-N4#1 N1-Cd1-N4#1 O5-Cd1-O4#2 N1-Cd1-O4#2 N4#1-Cd1-O4#2 O5-Cd1-O2
2.274(2) 2.327(2) 2.330(2) 2.398(2) 2.4391(19) 2.470(2) 2.487(2) 90.05(8) 90.96(8) 178.98(8) 138.28(8) 86.07(8) 93.22(8) 139.42(7)
N1-Cd1-O2 N4#1-Cd1-O2 O4#2-Cd1-O2 O5-Cd1-O1 N1-Cd1-O1 N4#1-Cd1-O1 O4#2-Cd1-O1 O2-Cd1-O1 O5-Cd1-O3#2 N1-Cd1-O3#2 N4#1-Cd1-O3#2 O4#2-Cd1-O3#2 O2-Cd1-O3#2 O1-Cd1-O3#2
92.36(8) 86.82(7) 82.28(7) 86.51(7) 98.56(8) 81.43(8) 135.15(6) 53.08(6) 85.03(7) 81.89(8) 98.27(8) 53.29(6) 135.39(6) 171.53(7)
a Symmetry transformation to generate equivalent atoms: (#1) x - 3/ 2, -y + 3/2, z - 1/2 (#2) x + 1, y, z.
Figure 4. Schematic representation of the 2-fold interpenetrated R-Po networks in 1. Centroids of the {CdOCdOCO} six-membered rings are shown as spheres. Table 3. Hydrogen-bonding Distance (Å) and Angle (°) Data for 1 and 2 D-H · · · A
symmetry d(H · · · A)
