Structure and Physical Properties of Two- and Three-Dimensional

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Structure and Physical Properties of Two- and Three-Dimensional Divalent Metal Adipate Coordination Polymers with Bis(4-pyridylmethyl)piperazine Tethers Arash Banisafar, David P. Martin, Jacqueline S. Lucas, and Robert L. LaDuca* Lyman Briggs College and Department of Chemistry, Michigan State University, E-30 Holmes Hall, East Lansing, Michigan 48825, United States

bS Supporting Information ABSTRACT: Hydrothermal reaction of divalent metal salts, adipic acid and bis(4-pyridylmethyl)piperazine (bpmp), resulted in the generation of a series of coordination polymers whose twodimensional and three-dimensional topologies depend on coordination environment, adipate conformation and carboxylate binding mode, and piperazinyl ring protonation. {[Cd(adipate)(H2bpmp)(H2O)]SO4 3 4H2O}n (1) manifests simple (4,4) grid cationic layers, while its oxoanion-free congener [Cd(adipate)(bpmp)]n (2) has a 5-fold interpenetrated diamondoid lattice. {[Cu(adipate)(Hbpmp)(H2O)]ClO4 3 3H2O}n (3) displays {Cu2O2} dimerbased (4,4) grid cationic layers. The isostructural complexes [M(adipate)(bpmp)(H2O)]n (M = Co, 4; M = Ni, 5) possess antisyn bridged one-dimensional [M(OCO)]n chains and rare 3,5-connected binodal nets with (4.62)(4.6683) topology. The cadmium derivatives 1 and 2 undergo blue-violet light emission on excitation with ultraviolet. Antiferromagnetic coupling is observed in 3, while ferromagnetic superexchange occurs in 4 and 5.

’ INTRODUCTION Recent years have seen an explosion of interest in coordination polymer solids, as this class of crystalline materials has potentially important industrial uses such as gas storage,1 molecular separations,2 ion exchange,3 catalysis,4 and nonlinear optics.5 Basic research in this field is stimulated by the discovery of aesthetic molecular networks,6 many of which have not yet been predicted by theoretical investigations of connectivity and topology.7 Aromatic dicarboxylates have been to date the most popular choice of connecting ligands for the construction of divalent metal coordination polymers,810 wherein the geometric disposition of the carboxylate ligands and their numerous possible binding modes play a crucial role in structure direction, in tandem with coordination geometry preferences. In comparison to ligands such as terephthalate,8 isophthalate,9 and benzene tricarboxylates,10 aliphatic dicarboxylates have received less attention,1113 perhaps because less a priori structure/function design is possible. Conformational flexibility via energetically facile σ-bond rotation within the polymethylene chains can permit a variety of metalmetal contact distances in response to specific supramolecular environments during self-assembly. As a result, dicarboxylate ligands such as succinate,11 glutarate,12 and adipate13 have promoted the generation of diverse and novel topologies in coordination polymers containing neutral dipodal tethering ligands. For instance, {[Cd(succinate)(N,N0 -bispyridin-4-yl-methylsuccinamide)] 3 H2O}n manifests [Cd(N,N0 -bispyridin-4-yl-methylsuccinamide)]n triple helices,11a joined into a two-dimensional (2D) r 2011 American Chemical Society

self-penetrated layer with four-connected 66 topology by gauche conformation succinate ligands. {[Ni(succinate)0.5(4,40 -dipyridylamine)2]Cl}n displays a unique regular self-penetrated three-dimensional (3D) 610 rld-z topology cationic network formed from the bridging of 4-fold interpenetrated [Ni(4,40 -dipyridylamine)2]n diamondoid lattices by gauche conformation succinate ligands.11b A self-penetrated six-connected 48668 rob lattice is seen in {[Cu2(glutarate)2(4,40 -bipyridine)] 3 3H2O}n,12a while use of the longer bis(4-pyridylmethyl)piperazine (bpmp) tethering ligand afforded a rarer self-penetrated 446108 topology mab lattice in {[Cu2(glutarate)2(bpmp)] 3 4H2O}n.12b In both of these materials, the glutarate ligands adopt a gaucheanti conformation. [Co(adipate)(1,2-bis(4pyridyl)ethane)]n13a and [Co(adipate)(4,40 -dipyridylamine)]n13b have 2-fold interpenetrated pcu 41263 lattices based on {Co2(OCO)2} dinuclear units, while [Ni(adipate)(4,40 -dipyridylamine)(H2O)]n contained the first example of a 3-fold interpenetrated 4284 pts binodal net.13b We thus aimed to explore the structural effects imposed by conformationally flexible adipate and bis(4-pyridylmethyl)piperazine ligands in crystalline divalent metal coordination polymers. This dipyridyl ligand can provide structure-directing hydrogen-bonding points of contact or protonation sites at its Received: November 30, 2010 Revised: March 21, 2011 Published: April 06, 2011 1651

dx.doi.org/10.1021/cg101596y | Cryst. Growth Des. 2011, 11, 1651–1661

Crystal Growth & Design piperazinyl nitrogen atoms and has proven useful in accessing novel and diverse topologies.14 Herein, we report the synthesis and structural characterization of {[Cd(adipate)(H2bpmp)(H2O)] SO4 3 4H2O}n (1), [Cd(adipate)(bpmp)]n (2), {[Cu(adipate)(Hbpmp)(H2O)]ClO4 3 3H2O}n (3), [Co(adipate)(bpmp)(H2O)]n (4), and [Ni(adipate)(bpmp)(H2O)]n (5). These materials manifest diversiform 2D and 3D network topologies depending on coordination geometry preference, adipate conformation, and bpmp piperazinyl ring protonation. The variable temperature behavior of magnetically active subunits in the paramagnetic derivatives 35 has been probed, along with the luminescent properties of the d10 derivatives 1 and 2.

’ EXPERIMENTAL SECTION General Considerations. Metal salts and adipic acid were purchased commercially. Bis(4-pyridylmethyl)piperazine was prepared using a published procedure.15 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 ultraviolettransparent epoxy adhesive. Variable temperature magnetic susceptibility data (2300 K) for 2 were collected on a Quantum Design MPMS SQUID magnetometer at an applied field of 0.1 T. After each temperature change, the sample was kept at the new temperature for 5 min before magnetization measurement to ensure thermal equilibrium. The susceptibility data were corrected for diamagnetism using Pascal's constants.16 Preparation of {[Cd(adipate)(H2bpmp)(H2O)]SO4 3 4H2O}n (1).

CdSO4 (62 mg, 0.30 mmol), adipic acid (43 mg, 0.29 mmol), bpmp (120 mg, 0.45 mmol), and 8 mL of deionized water were placed into a 23 mL Teflonlined acid digestion bomb. The bomb was sealed and heated in an oven at 120 C for 96 h and then cooled slowly to 25 C. Straw-colored blocks of 1 (94 mg, 44% yield based on Cd) were isolated after washing with distilled water and acetone and drying in air. Anal. calcd for C22H40CdN4O13S after loss of 1 molar equiv of water (1): C, 38.02; H, 5.51; N, 8.06%. Found: C, 38.69; H, 5.11; N, 8.14%. IR (cm1): 3378 (w), 3053 (w), 2945 (w), 2855 (w), 2602 (w), 2162 (w), 1982 (w), 1868 (w), 1614 (w), 1562 (s), 1548 (s), 1504 (w), 1451 (s), 1417 (s), 1358 (w), 1317 (w), 1302 (w), 1228 (w), 1193 (w), 1153 (w), 1100 (s), 1068 (s), 1046 (s), 1017 (s), 1003, 977 (w), 928 (w), 885 (w), 852 (w), 837 (w), 801 (s), 723 (w), 655 (s). Preparation of [Cd(adipate)(bpmp)]n (2). CdCl2 3 2H2O (85 mg, 0.37 mmol), adipic acid (70 mg, 0.48 mmol), and 4-bpmp (99 mg, 0.37 mmol) were placed into 10 mL of distilled H2O in a Teflon-lined 23 mL Parr acid digestion bomb. The bomb was sealed and heated at 120 C for 120 h, whereupon it was cooled slowly in air to 25 C. Colorless blocks of 2 (58 mg, 30% yield based on Cd) were isolated after washing with distilled water and acetone and drying in air. Anal. calcd for C22H28CdN4O4 (2): C, 50.34; H, 5.38; N, 10.67%. Found: C, 50.11; H, 4.99; N, 10.40%. IR (cm1): 2946 (w), 2835 (w), 1612 (m), 1565 (m), 1547 (s), 1500 (w), 1456 (m), 1410 (s), 1358 (w), 1310 (m), 1296 (m), 1269 (w), 1224 (w), 1188 (w), 1145 (w), 1122 (m), 1069 (w), 1011 (m), 999 (w), 939 (w), 925 (w), 848 (m), 837 (m), 802 (s), 741 (w), 695 (w), 675 (w).

Preparation of {[Cu(adipate)(Hbpmp)(H2O)]ClO4 3 3H2O}n.

Cu(ClO4)2 3 6H2O (160 mg, 0.43 mmol), adipic acid (65 mg, 0.44 mmol), and 4-bpmp (180 mg, 0.67 mmol) were placed into 8 mL of distilled H2O in a Teflon-lined 23 mL Parr acid digestion bomb. The bomb was sealed and heated at 90 C for 96 h, whereupon it was cooled slowly in air to 25 C. Blue blocks of 3 (151 mg, 0.24 mmol, 58% yield) were isolated after washing with distilled water and acetone and drying in air. Anal. calcd for C22H35ClCuN4O11 with loss of one water molecule (3): C, 43.14; H, 5.43; N, 9.15%. Found: C, 42.91; H, 5.11; N, 8.98%. IR (cm1): 3456 (w), 3053 (w), 2949 (w), 2683 (w), 2496 (w), 2445 (w), 1979 (w), 1619 (s), 1580 (s), 1568 (s), 1550 (s), 1505 (w), 1431 (s), 1381 (s), 1322 (w), 1310 (w), 1292 (w),

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1283 (w), 1266 (w), 1222 (w), 1191 (w), 1146 (w), 1077 (s), 1067 (s), 1034 (s), 1003 (s), 973 (s), 929 (w), 880 (w), 840 (s), 826 (w), 806 (s), 723 (w), 695 (w). Preparation of [Co(adipate)(bpmp)(H2O)]n (4). Co(NO3)2 3 6H2O (130 mg, 0.45 mmol), adipic acid (65 mg, 0.44 mmol), and 4-bpmp (183 mg, 0.68 mmol) were placed into 8 mL of distilled H2O in a Teflon-lined 23 mL Parr acid digestion bomb, followed by 0.8 mL of a 1.0 M NaOH solution. The bomb was sealed and heated at 120 C for 96 h, whereupon it was cooled slowly in air to 25 C. Pink blocks of 4 (64 mg, 30% yield) were isolated after washing with distilled water and acetone and drying in air. Anal. calcd for C44H60Co2N8O10 (4): C, 53.98; H, 6.18; N, 11.45%. Found: C, 53.85; H, 5.93; N, 11.36%. IR (cm1): 3375 (w), 3063 (w), 2940 (w), 2830 (w), 2683 (w), 2318 (w), 2167 (w), 1979 (w), 1608 (s), 1567 (s), 1550 (s), 1512 (w), 1456 (w), 1422 (s), 1391 (s), 1327 (w), 1283 (w), 1265 (w), 1223 (w), 1148 (w), 1099 (s), 1067 (s), 1035 (s), 1006 (s), 974 (w), 930 (w), 910 (w), 839 (s), 806 (w), 753 (w), 722 (s), 695 (s), 662 (s). Preparation of [Ni(adipate)(bpmp)(H2O)]n (5). The preparation of 4 was followed with the substitution of Ni(NO3)2 3 6H2O (131 mg, 0.450 mmol). Green blocks of 5 (111 mg, 0.113 mmol, 50.2% yield) were isolated after washing with distilled water and acetone and drying in air. Anal. calcd for C44H60N8Ni2O10 (5): C, 54.02; H, 6.18; N, 11.45%. Found: C, 53.78; H, 6.25; N, 11.41%. IR (cm1): 3382 (w), 2805 (w), 1608 (w), 1560 (s), 1497 (w), 1419 (w), 1399 (s), 1353 (w), 1325 (w), 1158 (m), 1126 (s), 1062 (m), 1011 (s), 905 (w), 834 (s), 796 (s), 708 (m), 670 (w). X-ray Crystallography. Single-crystal X-ray diffraction was performed on crystals of 15 with a Bruker-AXS ApexII CCD instrument at 173 K. Reflection data were acquired using graphite-monochromated Mo KR radiation (λ = 0.71073 Å). The data were integrated via SAINT.17 Empirical absorption corrections were applied with SADABS.18 The structures were solved using direct methods and refined on F2 using SHELXTL.19 The crystal of 5 was nonmerohedrally twinned, with its twin law determined using CELLNOW.20 All nonhydrogen 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(s) of the bpmp ligands in 1 and 3 were found via Fourier difference maps, then restrained at fixed positions, and refined isotropically. Where possible, hydrogen atoms for aqua ligands and water molecules of crystallization were found via Fourier difference maps, then restrained at fixed positions, and refined isotropically. A disordered model was successfully implemented for some of the water molecules of crystallization in the crystal structures of 1 and 3. Relevant crystallographic data for 15 are listed in Table 1. Crystallographic data (excluding structure factors) for 15 have been deposited with the Cambridge Crystallographic Data Centre with Nos. 799956, 799960, 799958, 799957, and 799959, 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 as crystalline products by hydrothermal reaction of the requisite divalent metal salt, adipic acid, and bpmp, with optimized yields as reported in the preparations above. The infrared spectra for 15 were consistent with their structural characteristics as determined by single-crystal X-ray diffraction. Medium intensity bands in the range of ∼1600 to ∼1200 cm1 can be ascribed to stretching modes of the pyridyl rings of the 4-bpmp ligands. Puckering modes of the pyridyl rings are evident in the region between 820 and 600 cm1. Asymmetric and symmetric CO stretching modes of the fully deprotonated adipate ligands correspond to the intense, broadened features at 1548 and 1417 cm1 1652

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Crystal Growth & Design

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Table 1. Crystal and Structure Refinement Data for 15 data empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) R () β () γ () V (Å3) Z Dcalcd (g cm3) μ (mm1) 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/Å3) GOF

1

2

3

4

5

C22H40CdN4O13S 713.04 monoclinic P21/n 11.4029(8) 18.3206(13) 14.0987(10) 90 98.841(1) 90 2910.3(4) 4 1.627 0.892 13 e h e 12, 21 e k e 22, 17 e l e 16 17 772 5 209 0.0202 395/5 0.0321 0.0297 0.0797 0.0781 0.721/0.644 1.036

C22H28CdN4O4 524.89 monoclinic C2/c 19.610(5) 6.5390(17) 16.914(5) 90 93.675(3) 90 2164.4(10) 4 1.611 1.046 25 e h e 25, 8 e k e 8, 21 e l e 21 13 000 2 490 0.0300 141/0 0.0193 0.0173 0.0456 0.0447 0.383/0.265 1.055

C22H35ClCuN4O11 630.53 triclinic P1 9.602(3) 11.394(3) 14.200(4) 79.385(3) 83.276(3) 65.372(3) 1386.6(6) 2 1.510 0.947 11 e h e 11, 13 e k e 13, 17 e l e 17 19 799 5 074 0.0839 392/7 0.0989 0.0820 0.2365 0.2247 1.368/1.036 1.059

C44H60Co2N8O10 978.86 triclinic P1 8.5547(7) 15.8060(12) 16.6219(13) 99.459(1) 92.049(1) 90.575(1) 2215.3(3) 2 1.467 0.817 10 e h e 10, 19 e k e 19, 20 e l e 20 33 215 8 410 0.0738 589/6 0.0638 0.0506 0.1395 0.1288 1.309/0.656 1.049

C44H60N8Ni2O10 978.42 triclinic P1 8.580(2) 15.886(4) 16.534(4) 99.558(3) 92.066(3) 90.370(3) 2220.8(9) 2 1.463 0.915 11 e h e 11, 20 e k e 20, 0 e l e 22 41 562 16 415 0.0856 597/6 0.1276 0.0668 0.1574 0.1351 1.015/0.738 1.016

(for 1), 1547 and 1410 cm1 (for 2), 1580 and 1431 cm1 (for 3), 1567 and 1422 cm1 (for 4), and 1560 and 1399 cm1 (for 5). Broad yet weak bands in the region of ∼3400 to ∼3200 cm1 in the spectrum of all materials except 2 arise from the OH bonds within the water molecules of crystallization or aqua ligands. The broadness of these higher energy spectral features is caused by hydrogen bonding (see below). The SO stretching frequencies for the sulfate ions in 1 are marked by intense, broad bands at 1100 and 1068 cm1, while the perchlorate ion in 3 manifests a broad, intense ClO stretching band at ∼1070 cm1. Structural Description of {[Cd(adipate)(H2bpmp)(H2O)]SO4 3 4H2O}n (1). The asymmetric unit of compound 1 consists of a divalent Cd atom, a fully deprotonated adipate ligand, a doubly protonated bpmp molecule, an aqua ligand, four total water molecules of crystallization, and an unligated sulfate ion. The cadmium atom possesses a distorted {CdN2O5} pentagonal bipyramidal coordination sphere, with the axial positions occupied by pyridyl nitrogen donor atoms from bpmp ligands. Within the equatorial plane are two chelating adipate carboxylate groups and the aqua ligand. Bond lengths and angles within the coordination sphere are listed in Table 2. Cadmium ions are linked by bis-chelating adipate ligands (Scheme 1) with a distorted gaucheantigauche conformation (torsion angles = 59.7, 132.5, and 67.8) into [Cd(adipate)(H2O)]n 1D chains aligned along the b crystal direction. The Cd 3 3 3 Cd contact distance through the adipate ligands measures 9.437 Å. The chain patterns are strutted into (4,4) grid [Cd(adipate)(H2O)(H2bpmp)]n2nþ cationic coordination polymer layers (Figure 1a) by H2bpmp2þ tethers, which span a Cd 3 3 3 Cd distance of 17.511 Å. The NN 3 3 3 NN torsion angle within the open conformation bpmp ligands is 178.1. Apertures within the grid motif measure 17.34 Å 22.15 Å, as determined by through-space Cd 3 3 3 Cd distances. The [Cd(adipate)(H2O)(H2bpmp)]n2nþ layers are oriented parallel to the (103) crystal planes. They stack into the pseudo

Table 2. Selected Bond Distance (Å) and Angle () Data for 1 and 2a 1 Cd1N2 Cd1O1 Cd1N1#1 Cd1O10 Cd1O3#2 Cd1O2 Cd1O4#2 N2Cd1O1 N2Cd1N1#1 O1Cd1N1#1 N2Cd1O10 O1Cd1O10 N1#1Cd1O10 N2Cd1O3#2

2.338(4) 2.340(3) 2.342(4) 2.348(3) 2.387(3) 2.419(3) 2.492(3) 95.49(12) 167.66(13) 96.76(13) 85.84(12) 137.87(11) 86.11(12) 89.74(11)

Cd1O1 Cd1O1#3 Cd1N1 Cd1N1#3 Cd1O2 Cd1O2#3 O1Cd1O1#3 O1Cd1N1 O1#3Cd1N1 O1Cd1N1#3 O1#3Cd1N1#3

2.2830(12) 2.2830(12) 2.3239(12) 2.3239(12) 2.4565(12) 2.4565(12) 142.77(6) 119.84(4) 86.02(4) 86.02(4) 119.84(4)

O1Cd1O3#2 N1#1Cd1O3#2 O10Cd1O3#2 N2Cd1O2 O1Cd1O2 N1#1Cd1O2 O10Cd1O2 O3#2Cd1O2 N2Cd1O4#2 O1Cd1O4#2 N1#1Cd1O4#2 O10Cd1O4#2 O3#2Cd1O4#2 O2Cd1O4#2

82.02(10) 90.44(11) 140.1(1) 98.86(12) 54.45(12) 89.52(12) 83.66(11) 136.11(10) 83.54(11) 135.18(11) 86.70(11) 86.89(10) 53.22(9) 170.04(10)

N1Cd1N1#1 O1Cd1O2 O1#1Cd1O2 N1Cd1O2 N1#1Cd1O2 O1Cd1O2#1 O1#1Cd1O2#1 N1Cd1O2#1 N1#1Cd1O2#1 O2Cd1O2#1

95.78(6) 105.24(4) 54.94(4) 134.92(4) 87.04(4) 54.94(4) 105.24(4) 87.04(4) 134.92(4) 121.58(6)

2

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

a

3D crystal structure (Figure S1 in the Supporting Information) via hydrogen-bonding donation from protonated piperazinyl groups of the H2bpmp2þ tethers to adipate carboxylate groups and aqua ligands in neighboring layers (Table 3). Unligated 1653



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Scheme 1. Conformations and Binding Modes of Adipate Ligands in 15

Table 3. Hydrogen Bonding Distance (Å) and Angle () Ddata for 1, 3, 4, and 5

DH 3 3 3 A

Figure 1. (a) [Cd(adipate)(H2O)(H2bpmp)]n2nþ cationic (4,4) grid layer in 1. (b) Hydrogen-bonded water molecule tape in 1.

charge-balancing sulfate ions and water molecules of crystallization occupy incipient 1D channels coursing through the supramolecular structure, which comprise 26.7% of the unit cell volume according to Platon.21 The unligated water molecules form a 1D water tape constructed from hydrogen-bonded R(4) classification22 cyclic tetramers (Figure 1b); these are anchored to the coordination polymer layers by hydrogen bonding acceptance from the aqua ligands. The (4,4) grid topology of 1 is comparable to that of its glutarate analog, {[Cd(glutarate)(bpmp)(H2O)] 3 6H2O}n, which also exhibited 1D water tapes but with 2T5(2)7(2) classification.14a However, the longer polymethylene tethers in 1 and {[Cd(glutarate)(bpmp)(H2O)] 3 6H2O}n appear to prevent formation of the rare 2D 658 layer topology seen in the shorter dicarboxylate succinate derivative {[Cd(succinate)(bpmp)(CH3OH)] 3 2H2O}n.14b Structural Description of [Cd(adipate)(bpmp)]n (2). The asymmetric unit of compound 2 contains a divalent Cd atom on the crystallographic 2-fold rotation axis, one-half of an adipate ligand, and one-half of a bpmp molecule. In contrast to 1, cadmium is six-coordinated, adopting a distorted {CdN2O4}

d(H 3 3 3 A)

d(D 3 3 3 A)

— DHA

O10H10AO2 O10H10BO4W

2.33 2.01(2)

1 3.180(4) 2.811(7)

179.8 170(5)

N4H4NO3

1.89(2)

2.778(4)

177(5)

N3H3NO10

2.02(3)

2.839(5)

152(4)

N3H3NO4

1.79(3)

3 2.667(6)

164(6)

O9H9CO2 O9H9DO8 O10H10CO6

1.784(19) 2.06(2) 1.735(19)

4 2.613(3) 2.881(3) 2.576(3)

162(3) 162(3) 165(3)

O10H10DO4

2.045(19)

2.868(3)

169(3)

O3H3CO9 O3H3DO8 O10H10CO1 O10H10DO6

2.11(2) 1.76(2) 2.14(3) 1.73(2)

5 2.900(3) 2.619(3) 2.887(3) 2.584(4)

150(3) 162(3) 144(3) 158(3)

symmetry transformation for A

x þ 1/2, y 1/2, z þ 3/2 x þ 3/2, y 1/2, z þ 3/2 x þ 1/2, y þ 1/2, z þ 1/2 x þ 1, y þ 1, z þ 1

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

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

Table 4. Selected Bond Distance (Å) and Angle () Data for 3a Cu1O3 Cu1O1#1 Cu1N1 Cu1N4#2 Cu1O1#3 O3Cu1O1#1 O3Cu1N1 O1#1Cu1N1

1.946(4) 1.972(4) 2.006(5) 2.018(5) 2.374(4) 173.02(16) 90.59(18) 91.30(17)

O3Cu1N4#2 O1#1Cu1N4#2 N1Cu1N4#2 O3Cu1O1#3 O1#1Cu1O1#3 N1Cu1O1#3 N4#2Cu1O1#3

86.78(18) 92.73(17) 167.89(19) 94.54(15) 78.55(15) 97.61(17) 94.38(17)

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

a

octahedral coordination geometry because of the absence of an aqua ligand. The nitrogen donor atoms from two bpmp ligands are disposed in a cis orientation; the remaining four coordination 1654



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Figure 2. (a) [Cd(adipate)]n chain motif in 2. (b) A single [Cd(adipate)(4-bpmp)]n 66 diamondoid network in 2. (c) Network perspective of the 5-fold interpenetration in 2.

sites are taken up by oxygen atoms from two chelating carboxylate groups belonging to adipate ligands. Bond lengths and angles within the coordination sphere are listed in Table 4. Extension of the structure through the bis-chelating adipate ligands (Scheme 1) produces [Cd(adipate)]n chain motifs that are arranged parallel to the c crystal direction (Figure 2a). The gaucheantigauche conformation (torsion angles = 68.3, 180.0, and 68.3) of the adipate ligands is more splayed open than that in 1, increasing the Cd 3 3 3 Cd contact distance by about 1.5 Å, to 10.607 Å. These chains are in turn linked by bpmp ligands, with a through-ligand Cd 3 3 3 Cd distance of 16.649 Å, producing a four-connected diamondoid 66 topology 3D coordination polymer lattice (Figure 2b). The NN 3 3 3 NN torsion angle within the open conformation bpmp ligands is a perfect 180, imposed by the crystallographic

symmetry. The substantial apertures (∼28 Å ∼19 Å) within a single neutral [Cd(adipate)(bpmp)]n network permit the interpenetration of four other identical nets, resulting in an overall 5-fold interpenetrated network in 2 (Figure 2c). Despite the presence of an odd-numbered level of interpenetration,23 the crystal structure of 2 is achiral because of the crystallographic symmetry elements present within the adipate and bpmp ligands. The structural topology of 2 stands in direct contrast to its 4,40 -bpy analog, [Cd(adipate)(4,40 -bpy)]n, which adopts a 2-fold interpenetrated primitive cubic pcu network based on {Cd2O2} dimeric clusters.13c Lack of anion inclusion in 2 obviates the need for charge-balancing protonation of bpmp piperazinyl rings. In turn, the carboxylate groups of the adipate ligands in 2 do not serve as hydrogen-bonding acceptors, which plausibly alters their 1655



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Table 5. Selected Bond Distance (Å) and Angle () Data for 4 and 5a 4

Co1O8#1 Co1O3 Co1O5#2 Co1O10 Co1N5#3 Co1N6 Co2O4 Co2O1 Co2O7#4 Co2O9 Co2N4#3 Co2N1 O8#1Co1O3 O8#1Co1O5#2 O3Co1O5#2 O8#1Co1O10 O3Co1O10 O5#2Co1O10 O8#1Co1N5#3 O3Co1N5#3 O5#2Co1N5#3

2.076(2) 2.082(2) 2.093(2) 2.108(2) 2.150(3) 2.172(3) 2.076(2) 2.079(2) 2.084(2) 2.115(2) 2.170(3) 2.188(3) 81.80(8) 176.52(8) 99.03(8) 91.28(8) 172.42(9) 87.69(9) 91.49(9) 90.35(9) 91.88(9)

Ni1O9 Ni1O10 Ni1O2 Ni1O5#2 Ni1N4#5 Ni1N1 Ni2O1 Ni2O7#1 Ni2O3 Ni2O11#6 Ni2N8#5 Ni2N5 O9Ni1O10 O9Ni1O2 O10Ni1O2 O9Ni1O5#2 O10Ni1O5#2 O2Ni1O5#2 O9Ni1N4#5 O10Ni1N4#5 O2Ni1N4#5

2.059(2) 2.080(3) 2.089(2) 2.090(2) 2.098(3) 2.116(3) 2.060(2) 2.072(2) 2.078(3) 2.096(2) 2.117(3) 2.127(3) 91.80(9) 80.87(9) 171.96(10) 176.40(9) 89.42(9) 97.70(9) 91.61(10) 93.26(10) 90.26(10)

5

O10Co1N5#3 O8#1Co1N6 O3Co1N6 O5#2Co1N6 O10Co1N6 N5#3Co1N6 O4Co2O1 O4Co2O7#4 O1Co2O7#4 O4Co2O9 O1Co2O9 O7#4Co2O9 O4Co2N4#3 O1Co2N4#3 O7#4Co2N4#3 O9Co2N4#3 O4Co2N1 O1Co2N1 O7#4Co2N1 O9Co2N1 N4#3Co2N1

92.94(9) 88.23(9) 88.54(9) 88.42(9) 88.15(9) 178.88(10) 177.05(8) 83.09(8) 96.08(8) 93.81(8) 86.87(9) 175.85(8) 88.94(9) 88.21(9) 88.56(9) 88.62(10) 92.53(9) 90.31(9) 90.57(9) 92.33(9) 178.19(10)

O5#2Ni1N4#5 O9Ni1N1 O10Ni1N1 O2Ni1N1 O5#2Ni1N1 N4#5Ni1N1 O1Ni2O7#1 O1Ni2O3 O7#1Ni2O3 O1Ni2O11#6 O7#1Ni2O11#6 O3Ni2O11#6 O1Ni2N8#5 O7#1Ni2N8#5 O3Ni2N8#5 O11#6Ni2N8#5 O1Ni2N5 O7#1Ni2N5 O3Ni2N5 O11#6Ni2N5 N8#5Ni2N5

91.7(1) 88.61(10) 88.21(10) 88.31(10) 88.05(10) 178.50(11) 176.04(9) 94.26(9) 88.63(9) 81.69(9) 95.27(9) 174.81(9) 89.33(10) 88.05(10) 88.22(11) 88.49(10) 92.29(10) 90.25(10) 93.06(10) 90.35(10) 177.85(11)

Symmetry transformation to generate equivalent atoms: #1: x þ 2, y, z; #2: x þ 2, y þ 1, z þ 1; #3: x, y, z þ 1; #4: x þ 3, y, z; #5: x, y, z þ 1; and #6: x þ 1, y, z. a

conformation. The cis disposition of the bpmp nitrogen donors at each cadmium ion assists in fostering formation of the 3D network of 2, while the trans orientation of the pyridyl donors in 1 appears to promote a layered structure. Structural Description of {[Cu(adipate)(Hbpmp)(H2O)]ClO4 3 3H2O}n (3). The asymmetric unit of compound 3 comprises a divalent copper ion, an adipate ligand, a singly protonated bpmp molecule, an aqua ligand, three water molecules of crystallization, and an unligated perchlorate ion. Copper is coordinated in a slightly distorted {CuN2O3} square pyramidal environment (τ = 0.09),24 in which the basal plane contains two trans Hbpmp pyridyl donors and two trans oxygen atom donors from different adipate ligands. The “long” apical coordination site is occupied by an oxygen atom donor from a third adipate ligand. Bond lengths and angles are consistent with the JahnTeller active d9 electronic configuration (Table 4).

In contrast with the bis-chelating exobidentate binding mode seen in 1 and 2, the carboxylate groups of the adipate ligands in 3 bridge three copper ions in a κ1-μ1, κ1-μ2 fashion (Scheme 1). A pair of κ1-μ2 adipate carboxylate groups forms equatorialapical bridged {Cu2O2} dimeric rhomboid clusters, which have Cu 3 3 3 Cu and O 3 3 3 O through-space distances of 3.376 and 2.769 Å, respectively, and a CuOCu angle of 101.49. Individual {Cu2O2} clusters are connected into a [Cu(adipate)]n ribbon (Figure 3a) by gaucheantigauche conformation adipate ligands (torsion angles = 65.0, 179.6, and 65.0). Through-ligand Cu 3 3 3 Cu distances are 8.524 and 9.602 Å within the ribbon motif. [Cu(adipate)]n ribbons are pillared into [Cu(adipate)(Hbpmp)]nnþ cationic coordination polymer slabs (Figure 3b) by Hbpmp tethers, which provide a through-ligand Cu 3 3 3 Cu contact distance of 16.488 Å. The NN 3 3 3 NN torsion angle within the bpmp ligands is 161.7, reflecting a greater tendency toward a curled conformation than in 1 or 2. A side view of the slab motif is shown in Figure 3c. If the {Cu2O2} clusters are considered as connecting nodes, joining to four others through pairs of adipate and Hbpmpþ ligands; the underlying topology of 3 is actually that of a simple (4,4) rectangular grid. [Cu(adipate)(Hbpmp)]nnþ cationic coordination polymer slabs stack in an AAA pattern along the b crystal direction (Figure S2 in the Supporting Information) by means of hydrogen-bonding donation from the protonated piperazinyl groups of the Hbpmpþ ligands to unligated adipate carboxylate oxygen atoms (Table 3). Unligated perchlorate ions and disordered water molecules of crystallization lie within the slab apertures and interslab regions. Incipient extra-framework space containing the unligated species occupies 26.9% of the unit cell volume. Structural Description of [Co(adipate)(bpmp)(H2O)]n (4) and [Ni(adipate)(bpmp)(H2O)]n (5). As both 4 and 5 are essentially isostructural, only the cobalt derivative 4 will be discussed in detail here. Its asymmetric unit consists of two crystallographically distinct cobalt atoms, two adipate ligands, two unprotonated bpmp molecules, and two aqua ligands. The coordination environment about each cobalt atom is a {CoN2O4} octahedron with trans bpmp pyridyl nitrogen donors. Three sites are occupied by adipate carboxylate oxygen atom donors in a mer arrangement, with an aqua ligand rounding out the coordination sphere. Bond lengths and angles within the crystallographically distinct coordination environments in 4 and 5 are given in Table 5. The bond lengths in 5 are slightly shorter in accordance with ionic radius trends.25 The adipate ligands adopt different conformations in 4, with one type resting in an antiantianti conformation (torsion angles = 163.3, 179.0, and 176.7) and the other type resting in a gaucheantigauche conformation (torsion angles = 56.8, 178.6, and 72.9). Both types of adipate ligands exhibit an exotridentate binding mode (Scheme 1), with three of their oxygen atoms serving as monodentate donors. Carboxylate termini in which both oxygen atoms are ligated bridge cobalt atoms in an antisyn disposition to construct [Co(OCO)]n chains that are aligned parallel to the [100] crystal direction. Alternating Co 3 3 3 Co contact distances along these chains measure 5.223 and 5.237 Å. The full span of the adipate ligands connects the [Co(OCO)]n chain subunits into [Co(adipate)(H2O)]n coordination polymer layer motifs (Figure 4a). In 5, the alternating Ni 3 3 3 Ni contact distances along the [Ni(OCO)]n chains within its [Ni(adipate)(H2O)]n layers are 5.219 and 5.235 Å. If both the metal atoms and the adipate ligands in 4 and 5 are considered three-connected nodes, their respective metal dicarboxylate layer motifs can be construed as 4.82 Archimedean nets of rhomboid and octagonal circuits (Figure 4b). 1656



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Figure 3. (a) [Cu(adipate)]n ribbon motif in 3, highlighting equatorialaxial bridged {Cu2O2} dimeric units. (b) Face-on view of the dimer-based [Cu(adipate)(Hbpmp)]nnþ cationic coordination polymer slab in 3. (c) Side-on view.

Figure 4. (a) [Co(adipate)(H2O)]n coordination polymer layer in 4. (b) Network perspective of the Archimedean 4.82 layer in 4, with Co atom and adipate ligand nodes drawn as blue and brown spheres, respectively.

The [Co(adipate)(H2O)]n layers in 4 are pillared into a noninterpenetrated 3D [Co(adipate)(bpmp)(H2O)]n coordination

polymer network (Figure 5a) by open-conformation bpmp tethers, which span Co 3 3 3 Co distances of 16.622 Å. Corresponding 1657



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Figure 5. (a) [Co(adipate)(bpmp)(H2O)]n 3D coordination polymer network in 4. (b) Network perspective of the rare 3,5-connected binodal (4.62)(4.6683) net in 4 and 5.

intermetallic contact distances in 5 are 16.534 Å. The Co atoms can be considered five-connected nodes, joining to three adipate ligand nodes within the [Co(adipate)(H2O)]n layer motifs and to two Co atom nodes in adjacent layers. Thus, the topology of 4 (and 5) can be simplified as a 3,5-connected binodal net with a Schl€afli symbol of (4.62)(4.6683), formed by the pillaring of Archimedean 4.82 layers at every other node (Figure 5b). This rarely seen network has been previously observed in {[Cd(SO4)(4-bpfp)(H2O)] 3 H2O}n26 and {[Mn(succinate)(4,40 -bpy)(H2O)] 3 0.5(4,40 -bpy)}n,11c although it was not identified in the latter. The binodal, noninterpenetrated nets in 4 and 5, with embedded 1D [M(OCO)]n chains, differ dramatically from the dimer-based 2-fold interpenetrated six-connected pcu net seen in [Mn(adipate)(4,40 -bipyridine)]n13 and [Co(adipate)(4,40 -dipyridylamine)]n.13b

’ MAGNETIC PROPERTIES OF 35 Variable temperature magnetic susceptibility experiments were carried out on the paramagnetic materials in this study to investigate spin communication within the equatorialapical bridged {Cu2O2} dimeric clusters in 3 and along the antisyn bridged {Co(OCO)}n and {Ni(OCO)}n chains in 4 and 5, respectively. The χmT product at 300 K for 3 was 0.39 cm3 K mol1, consistent with that expected for an uncoupled S = 1/2 d9 configuration ion. The value decreases very slowly from 300 to 50 K, whereupon it drops more rapidly, reaching 0.26 cm3 K mol1 at 2 K. This behavior is

indicative of weak antiferromagnetic coupling in 3. The data were fit to the well-known BleaneyBowers equation27 (eq 1) for an isotropically interacting pair of S = 1/2 ions, giving g = 2.041(2) and J = 1.72(3) cm1 with R = {Σ[(χmT)obs (χmT)calcd]2/ Σ[(χmT)obs]2}1/2 = 2.68 105 (Figure 6). Weak antiferromagnetic coupling within the {Cu2O2} dimeric clusters in 3 is fostered by the small overlap of magnetic dx2y2 orbitals on neighboring copper ions, provided by the deviations from idealized square pyramidal coordination geometry. ! 1 Ng 2 β2 1 ð1Þ χm T ¼ 1 þ expðJ=kTÞ 3 3k The χmT product at 300 K for 4 was 3.71 cm3 K mol1, higher than expected for an uncoupled S = 3/2 d7 configuration ion neglecting spinorbit coupling. This value decreased upon cooling, slowly at first (3.43 cm3 K mol1 at 140 K), and then more precipitously, reaching a minimum of 2.45 cm3 K mol1 at 9.3 K. Below this temperature, the χmT increased, reaching 2.91 cm3 K mol1 at 2 K. This behavior is ascribed to a cooperative effect of ferromagnetic superexchange along the antisyn carboxylate bridged 1D [Co(OCO)]n chains in 4 and zero-field splitting, which tends to reduce the χmT value upon cooling in Co2þ ions with distorted octahedral environments via the formation of pseudo S = 1/2 Kramers doublets.16 Both of 1658



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Figure 6. Variable temperature magnetic susceptibility data for 3. The best fit to eq 1 is shown as a dashed line.


Figure 9. Solid state luminescence spectra for 1, 2, and free bpmp.

ð2Þ

in χmT was more rapid, attaining values of 1.74 cm3 K mol1 at 5.5 K and 2.47 cm3 K mol1 at 2 K. This behavior corresponds to weak ferromagnetic coupling along the antisyn carboxylate bridged 1D [Ni(OCO)]n chains in 5. To quantify this behavior, the magnetic data were fit over the entire temperature range to Fisher's model for an “infinite” chain of classical spins (eq 3).29 The best fit values (Figure 8) for S = 1 were g = 2.211(9) and J = 0.83(2) cm1, with R = 3.1 103; the positive but small value of J is indicative of weak ferromagnetic superexchange involving the eg-like magnetic orbitals on divalent nickel. ! Ng 2 β2 SðS þ 1Þ 1þu χm T ¼ 3k 1u ð3Þ JSðS þ 1Þ kT u ¼ coth kT JSðS þ 1Þ

The χmT product at 300 K for 5 was 1.17 cm3 K mol1, slightly higher than expected for an uncoupled S = 1 d8 ion. This value increased upon cooling, to 1.27 cm3 K mol1 at 50 K and to 1.51 cm3 K mol1 at 9.3 K. Below this temperature, the increase

’ LUMINESCENCE SPECTRA OF 1 AND 2 Irradiation of complexes 1 and 2 with ultraviolet light (λex = 300 nm) in the solid state resulted in blue-violet visible light


these effects can be suitably estimated by a phenomenological equation proposed by Rueff (eq 2).28 The best fit values (Figure 7) were A = 1.62(1) cm3 K mol1, B = 2.369(9) cm3 K mol1 (giving g = 2.92), D = 42.5(8) cm1, and J = 0.27(1) cm1, with R = 3.47 104. High values of the gyromagnetic ratio g are not uncommon for the d7 configuration Co2þ because of spinorbit coupling.16 No field-dependent hysteresis was observed at 2 K for 4. χm T ¼ A expð D=kTÞ þ B expðJ=kTÞ where A þ B ¼ C ¼ ð5Ng 2 β2 =4kÞ

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Crystal Growth & Design emission with λmax values of ∼450 and ∼420 nm, respectively (Figure 9). A crystalline sample of free bis(4-pyridylmethyl)piperazine was subjected to the same excitation, resulting in a weaker, broad emission profile centered at ∼455 nm. The emissive behavior of 1 and 2 is thus ascribed to ligand-centered electronic transitions between ππ* or πn molecular orbital manifolds within the aromatic pyridyl rings of the bpmp or Hbpmpþ tethers.30 The difference in maximum emission wavelength could result from coordination environment variances between pentagonal bipyramidal in 1 and octahedral in 2. A greater intensity for the emission in 1 and 2 as opposed to the free ligand can be rationalized by a decrease in nonradiative vibronic energy-loss mechanisms, because of pyridyl ring coordination to cadmium and resulting conformational locking.30

’ CONCLUSIONS Divalent metal coordination polymers containing the conformationally flexible adipate ligand and a long-spanning dipyridyl ligand with capacity for hydrogen-bonding or protonation exhibit a variety of 2D and 3D topologies, including a very rarely seen 3,5-connected simple binodal topology formed from the partial pillaring of Archimedean nets. A confluence of factors appears to determine the underlying polymer topology during crystal selfassembly, including coordination geometry preference, adipate binding mode, and the protonation level of the piperazinyl rings of the bpmp ligands with concomitant anion inclusion. In all cases, a gaucheantigauche conformation of the adipate ligand is observed, indicating that polymethylene conformation is of secondary importance in this system. Magnetic orbital overlap between distorted square pyramidally coordinated d9 ions in the copper derivative affords weak antiferromagnetic superexchange, while antisyn bridges along metal-carboxylate chain submotifs in the cobalt and nickel congeners promote ferromagnetic interactions. In the case of the cobalt derivative, single-ion effects provide a counterbalancing effect on the temperature-dependent magnetic behavior. The cadmium derivatives display slightly different emission maxima depending on coordination preference and the presence or absence of nonligating anionic species. ’ ASSOCIATED CONTENT

bS

Supporting Information. Additional molecular graphics. This material is available free of charge via the Internet at http:// pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT We acknowledge the donors of the American Chemical Society Petroleum Research Fund for funding this work. We thank Chaun Gandolfo and Amy Pochodylo for acquiring the variable temperature magnetic susceptibility data. R.L.L. thanks Aldo Tagliapietra for assistance in manuscript preparation. ’ REFERENCES (1) For example:(a) Roswell, J. L. C.; Yaghi, O. M. Angew. Chem., Int. Ed. Engl. 2005, 44, 4670–4679. (b) Kondo, M.; Okubo, T.; Asami, A.;

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