Copper glutarate coordination polymers with dipyridylamide ligands: Effect of donor disposition and steric bulk on structure

Inorganica Chimica Acta 405 (2013) 31–42

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Copper glutarate coordination polymers with dipyridylamide ligands: Effect of donor disposition and steric bulk on structure Jacob W. Uebler, Amy L. Pochodylo, Robert L. LaDuca ⇑ Department of Chemistry and Lyman Briggs College, Michigan State University, East Lansing, MI 48825, USA

a r t i c l e

i n f o

Article history: Received 19 March 2013 Accepted 12 May 2013 Available online 21 May 2013 Keywords: Copper Glutarate Dipyridylamide Coordination polymer

a b s t r a c t A structurally diverse series of divalent copper glutarate coordination polymers incorporating dipyridylamide ligands has been prepared and structurally characterized. {[Cu2(glu)2(3-pina)]3.5H2O}n (1, glu = glutarate, 3-pina = 3-pyridylisonicotinamide) manifests a 3D pcu network constructed from [Cu(glu)]n layers containing {Cu2(OCO)4} paddlewheel dimers. Increasing the steric bulk of the glutarate ligand afforded [Cu2(dmg)2(3-pina)]n (2, dmg = 3,3-dimethylglutarate), which shows a (4,4) grid structure based on linked [Cu(dmg)]n chains containing similar {Cu2(OCO)4} paddlewheel dimers. {[Cu(glu)(3-pna)(H2O)]H2O}n (3, 3-pna = 3-pyridylnicotinamide) has a simple (4,4) grid-like layer structure with isolated copper atoms, while {[Cu(glu)(4-pna)(H2O)]H2O}n (4, 4-pna = 4-pyridylnicotinamide) possesses a 2-fold parallel interpenetrated (6,3) herringbone lattice. Increased steric bulk and counterion inclusion in [Cu3(Hmg)2(4-pna)4(SO4)2(H2O)4]n (5, meg = 2-methylglutarate) results in a 1D ribbon structure. Thermal properties are also investigated. Ó 2013 Elsevier B.V. All rights reserved.

1. Introduction The preparation, structural characterization, and physical property measurements of crystalline coordination polymer solids remains an active field of research after almost two decades of consistent study. Recent efforts have been frequently geared towards materials designed towards diverse useful applications in hydrogen storage [1], molecular separations [2], ion exchange [3], catalysis [4], and luminescence [5]. Most coordination polymer solids are constructed from divalent metal atoms and dicarboxylate ligands, which impart both the charge balance and structural framework of the resulting crystalline lattice [6]. Varied coordination geometry preferences, along with the wide scope of possible dicarboxylate ligands and their accessible binding or bridging modes, can thus afford a myriad of possible coordination polymer structural topologies [7]. In contrast to coordination polymers built using rigid aromatic ligands such as terephthalate [8] and isophthalate [6a,9], those based on more flexible aliphatic dicarboxylates have received less attention [10–13]. The polymethylene chain conformational flexibility of these ligands allows them to respond to specific supramolecular environments, to coordination geometric or steric requirements, to carboxylate binding and bridging modes, or to the presence of any included neutral coligands.

⇑ Corresponding author at: Lyman Briggs College, E-30 Holmes Hall, Michigan State University, East Lansing, MI 48825, USA. E-mail address: [email protected] (R.L. LaDuca). 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2013.05.009

The straight chain aliphatic dicarboxylate ligands such as succinate (suc) [11], glutarate (glu) [12], and adipate (adp) [13] have promoted the generation of diverse and novel topologies in coordination polymers containing neutral dipodal tethering ligands. For example, {[Cd(suc)(L)]H2O}n (L = N,N0 -bispyridin-4-yl-methylsuccinamide) exhibits [Cd(L)]n triple helices [11a], connected into an intriguing and rare 2D self-penetrated layer with a 4-connected 66 topology by gauche conformation suc ligands. {[Ni(suc)0.5 (dpa)2]Cl}n (dpa = 4,40 -dipyridylamine) possesses a regular selfpenetrated 3D 610 rld-z topology formed from the bridging of 4fold interpenetrated [Ni(dpa)2]n diamondoid lattices by gauche conformation succinate ligands [11b]. Inclusion of sterically bulky methyl groups on the succinate-type ligand results in a reduction in dimensionality in that system, to a regular (4,4) grid in [Ni(dms)(dpa)]n (dms = 2,2-dimethylsuccinate) [14]. A self-penetrated 6-connected 48668 rob lattice occurs in {[Cu2(glu)2 (bpy)]3H2O}n (bpy = 4,40 -bipyridine) [12a], in which the glu ligands rest in a gauche-anti conformation. [Co(adp)(1,2-bis(4-pyridyl)ethane)]n [13a] and [Co(adp)(dpa)]n [13b] exhibit simple and common 2-fold interpenetrated primitive cubic nets. In comparison to the more widely used rigid-rod bpy ligand and even the kinked, hydrogen-bonding capable dpa ligand, coordination polymers containing the isomeric dipyridylamide ligands (Scheme 1) 3-pyridylnicotinamide (3-pna), 3-pyridylisonicotinamide (3-pina), 4-pyridylnicotinamide (4-pna), and 4-pyridylisonicotinamide (4-pina) are far less common [15]. These dipyridylamide ligands can all provide hydrogen bonding donor and acceptor groups at their internal amide functional groups, which would

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2.2. Preparation of {[Cu2(glu)2(3-pina)]3.5H2O}n (1) Cu(NO3)22.5H2O (43 mg, 0.185 mmol), glutaric acid (49 mg, 0.185 mmol) and 3-pina (37 mg, 0.185 mmol) were placed into 5 mL distilled H2O in a 15 mL screw-cap vial. The vial was sealed and heated in an oil bath at 90 °C for 24 h, and then cooled slowly to 25 °C. Green blocks of 1 (38 mg, 63% yield based on Cu) were isolated after washing with distilled water and acetone, and drying in air. Anal. Calc. for C21H28Cu2N3O12.5 1: C, 38.83; H, 4.35; N, 6.47. Found: C, 38.97; H, 3.83; N, 6.43%. IR (cm1): 3411 (br, w), 2947 (w), 2833 (w), 1687 (m), 1615 (s), 1599 (m), 1482 (w), 1463 (w), 1426 (s), 1407 (m), 1375 (w), 1351 (w), 1325 (w), 1301 (m), 1268 (w), 1214 (w), 1181 (m), 1145 (m), 1114 (m), 1053 (w), 1034 (w), 999 (m), 973 (w), 945 (w), 935 (w), 880 (w), 848 (w), 803 (m), 725 (m), 709 (m), 692 (m).

Scheme 1. Ligands used in this study.

impose similar supramolecular structure directing effects during coordination polymer self-assembly. Nevertheless it would be expected that significant coordination polymer structural diversity could be obtained by using different dipyridylamide ligands while employing the same divalent metal ion and dicarboxylate ligand set, thereby revealing the importance of nitrogen donor disposition on structural trends. In a zinc succinate system [15a], donor disposition played an extremely important role, with [Zn(suc)(4-pina)]n displaying an uncommon 6-connected self-penetrated 446108 mab topology, while [Zn(suc)(4-pna)]n possessed simple corrugated (4,4) layer motifs. Even greater structural diversity was seen in related conformationally rigid zinc fumarate (fum) coordination polymers [15a]. {[Zn(fum)(3-pina)]1.5H2O}n has a 4-fold interpenetrated 43628 sra topology, [Zn(fum)(4-pna)]n possesses a 4-fold interpenetrated 66 dia topology, and [Zn(fum)(4-pina)]n has a 2fold interpenetrated 41263 pcu topology based on dimeric cluster nodes. We therefore intended to extend this work into paramagnetic divalent metal coordination polymers by attempting to prepare a series of copper glutarate and substituted glutarate crystalline solids containing the isomeric 3-pna, 3-pina, 4-pna, or 4-pina dipyridylamide coligands. While 4-pina failed to yield any isolable coordination polymers in this system, use of the other three isomeric forms resulted in the successful preparation of five new crystalline coordination polymer solids: {[Cu2(glu)2(3-pina)]3.5H2O}n (1), [Cu2(dmg)2(3-pina)]n (2, dmg = 3,3-dimethylglutarate), {[Cu (glu)(3-pna)(H2O)]H2O}n (3), {[Cu(glu)(4-pna)(H2O)]H2O}n (4), and [Cu3(Hmg)2(4-pna)4(SO4)2(H2O)4]n (5, meg = 2-methylglutarate). In this contribution we report the single-crystal structural determinations and thermal degradation properties of these materials.

2.3. Preparation of [Cu2(dmg)2(3-pina)]n (2) Cu(NO3)22.5H2O (50 mg, 0.21 mmol), 3,3-dimethylglutaric acid (33 mg, 0.21 mmol) and 3-pina (45 mg, 0.23 mmol) were placed into 10 mL distilled H2O in a 23 mL Teflon-lined Parr acid digestion bomb, followed by 0.5 mL of 1.0 M NaOH solution. The bomb was sealed and heated in an oven at 120 °C for 24 h, whereupon it was cooled slowly to 25 °C. Green blocks of 2 (44 mg, 42% yield based on Cu) were isolated after washing with distilled water and acetone, and drying in air. Anal. Calc. for C25H29Cu2N3O9 2: C, 46.73; H, 4.55; N, 6.54. Found: C, 46.81; H, 4.40; N, 6.59%. IR (cm1): 3258 (w), 3135 (w), 3079 (w), 3048 (w), 2947 (w), 2905 (w), 2866 (w), 1980 (w), 1684 (m), 1607 (s), 1540 (s), 1483 (m), 1470 (m), 1419 (s), 1401 (s), 1378 (m), 1360 (m), 1326 (m), 1302 (m), 1242 (m), 1220 (m), 1196 (m), 1131 (m), 1162 (m), 110 (m), 1074 (m), 1051(m), 1029 (m), 1010 (m), 989 (m), 937 (w), 910 (w), 892 (m), 883 (m), 858 (m), 836 (m), 797 (m), 733 (m), 722 (m), 699 (m), 662 (m).

2.4. Preparation of {[Cu(glu)(3-pna)(H2O)]H2O}n (3) Cu(NO3)22.5H2O (43 mg, 0.185 mmol), glutaric acid (49 mg, 0.185 mmol) and 3-pna (37 mg, 0.185 mmol) were placed into 5 mL distilled H2O in a 15 mL screw-cap vial. The vial was sealed and heated in an oil bath at 90 °C for 24 h, and then cooled slowly to 25 °C. Blue blocks of 3 (31 mg, 39% yield based on Cu) were isolated after washing with distilled water and acetone, and drying in air. Anal. Calc. for C16H19CuN3O7 3: C, 44.81; H, 4.47; N, 9.80. Found: C, 44.87; H, 4.05; N, 9.62%. IR (cm1): 3298 (m, br), 1689 (m), 1617 (m), 1555 (s), 1488 (m), 1458 (m), 1400 (s), 1333 (s), 1310 (s), 1289 (m), 1191 (w), 1164 (w), 1110 (m), 1057 (m), 929 (w), 903 (w), 843 (m), 810 (m), 723 (s), 692 (s).

2.5. Preparation of {[Cu(glu)(4-pna)(H2O)]H2O}n (4) 2. Experimental 2.1. General considerations Copper salts and unsubstituted or substituted glutaric acids were purchased commercially. The isomeric dipyridylamide ligands were prepared using a published procedure [16]. Water was deionized above 3 MX-cm in-house. IR spectra were recorded on powdered samples using a Perkin Elmer Spectrum One instrument. Elemental Analysis was carried out using a Perkin Elmer 2400 Series II CHNS/O Analyzer. Thermogravimetric analysis was performed on a TA Instruments high-resolution Q500 thermal analyzer under flowing N2.

CuSO45H2O (45 mg, 0.18 mmol), glutaric acid (28 mg, 0.21 mmol) and 4-pna (50 mg, 0.25 mmol) were placed into 5 mL distilled H2O in a 15 mL glass vial. The vial was sealed and heated in an oil bath at 85 °C for 24 h, whereupon it was cooled slowly to 25 °C. Blue blocks of 4 (13 mg, 16% yield based on Cu) were isolated after washing with distilled water and acetone, and drying in air. Anal. Calc. for C16H19CuN3O7 4: C, 44.81; H, 4.47; N, 9.80. Found: C, 44.75; H, 4.29; N, 10.14%. IR (cm1): 3073 (w, br), 2954 (m), 1684 (m), 1602 (s), 1556 (s), 1518 (s), 1457 (m), 1422 (s), 1393 (s), 1333 (s), 1248 (m), 1211 (s), 1195 (m), 1154 (m), 1123 (m), 1051 (m), 1049 (m), 1031 (m), 948 (m), 894 (m), 841 (m), 824 (s), 814 (s), 738 (m), 728 (m).

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2.6. Preparation of [Cu3(Hmg)2(4-pna)4(SO4)2(H2O)4]n (5) CuSO45H2O (45 mg, 0.18 mmol), 3-methylglutaric acid (31 mg, 0.21 mmol) and 4-pna (52 mg, 0.26 mmol) were placed into were placed into 5 mL distilled H2O in a 15 mL glass vial. The vial was sealed and heated in an oil bath at 85 °C for 24 h, whereupon it was cooled slowly to 25 °C. Blue blocks of 5 (31 mg, 31% yield based on 4-pna) were isolated after washing with distilled water and acetone, and drying in air. Anal. Calc. for C56H62Cu3N12O24S2 5: C, 43.62; H, 4.05; N, 10.90. Found: C, 43.75; H, 4.29; N, 10.14%. IR (cm1): 3200 (m, br), 1704 (m), 1611 (m), 1511 (m), 1431 (w), 1329 (m), 1304 (m), 1282 (m), 1201 (m), 1093 (s), 1060 (s), 947 (s), 857 (s), 835 (s). 3. X-ray crystallography Single crystal X-ray diffraction was performed on single crystals of 1–5 with a Bruker-AXS ApexII CCD instrument at 173 K. Reflection data were acquired using graphite-monochromated Mo Ka radiation (k = 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 amide nitrogen atoms, and water molecules where possible, were found via Fourier difference maps. These were then restrained at fixed positions and refined isotropically. The crystal of 1 was non-merohedrally twinned; its twin law was found using CELL NOW [20]. Only the reflections from the major twin component were used in the solution and refinement. Some unresolvable disorder within one of the 3-pina ligands in 1 was evidenced by

distended thermal ellipsoids. Some significant crystallographic disorder was present in 5. The sulfate ions were disordered over two positions in an 85/15 ratio. Within the Hmg ligand, disorder amongst the aliphatic carbons could be modeled with a 67/33 ratio of two sets of positions, while the unligated carboxylate terminus was disordered over three sets of positions in a 60/20/20 ratio. Relevant crystallographic data for 1–5 is listed in Table 1.

4. Results and discussion 4.1. Synthesis and infrared spectra Compounds 1–5 were prepared by hydrothermal reaction of divalent copper salts with the requisite aliphatic dicarboxylic acid and dipyridyl ligand. Their infrared spectra were consistent with structural components determined by single-crystal X-ray diffraction. Intense, slightly broadened asymmetric and symmetric C–O stretching bands were observed at 1615 and 1426 cm1 in 1, 1607 and 1419 cm1 in 2, 1555 and 1400 cm1 in 3, 1602 and 1392 cm1 in 4, and 1611 and 1329 cm1 in 5. Sharper bands in the range of 1610 to 1300 cm1 were attributed to stretching modes of pyridyl rings of nitrogen base ligands [21]. Features corresponding to C–H bending and arene puckering within the pyridyl rings exist in the region between 900 and 650 cm1. The C@O stretching bands within the dipyridylamide ligands were observed at 1687 cm1 in 1, 1684 cm1 in 2, 1689 cm1 in 3, 1686 cm1 in 4, and 1704 cm1 in 5. Broad, weak spectral bands in the vicinity of 3000–3200 cm1 indicate the presence of any dipyridylamide N–H bonds, bound and unbound water molecules where present, and protonated carboxylate groups in 5. A pair of intense bands at 1093 and 1060 cm1 in the spectrum of 5 is indicative of S–O stretches within the bound sulfate ions.

Table 1 Crystal and structure refinement data for 1–5. Data

1

2

3

4

5

Empirical formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm3) l (mm1) Min./max. trans. hkl ranges

C21H28Cu2N3O12.5

C25H29Cu2N3O9

C16H19CuN3O7

C16H19CuN3O7

C56H62Cu3N12O24S2

649.54 triclinic  P1 8.531(2) 12.570(4) 13.252(4) 105.078(3) 90.123(3) 107.139(3) 1306.4(6) 2 1.640 1.696 0.7625/0.9200 10 6 h 6 10, 15 6 k 6 14, 0 6 l 6 15 22928 4762

642.59 triclinic  P1 6.570(3) 13.987(6) 14.694(6) 77.243(7) 89.427(7) 85.409(10) 1312.6(9) 2 1.626 1.679 0.8595/0.9031 7 6 h 6 7, 16 6 k 6 16, 17 6 l 6 17 21788 4789

428.88 monoclinic P21/n 8.6901(14) 15.562(3) 13.569(2) 90 105.630(2) 90 1767.1(5) 4 1.612 1.282 0.5057/0.6815 10 6 h 6 10, 18 6 k 6 15, 10 6 l 6 16 7782 3211

428.88 monoclinic C2/c 23.476(3) 8.8641(10) 17.5434(19) 90 110.884(1) 90 3410.8(6) 8 1.670 1.328 0.7018/0.8943 28 6 h 6 28, 10 6 k 6 10, 20 6 l 6 21 13480 3121

1541.92 triclinic  P1 10.2538(7) 11.2279(8) 15.3232(11) 110.251(1) 97.209(1) 105.779(1) 1544.88(19) 1 1.657 1.185 0.7731/0.8689 12 6 h 6 12, 13 6 k 6 13, 18 6 l 6 18 25383 5646

0.1399 320/2

0.0937 355/0

0.0461 259/7

0.0352 259/7

0.0312 522/9

0.1878 0.0896 0.2621 0.2182 1.417/1.092

0.1021 0.0550 0.1508 0.1278 0.534/0.874

0.0475 0.0355 0.0836 0.0796 0.539/0.522

0.0395 0.0321 0.0899 0.0853 0.572/0.505

0.0423 0.0353 0.0952 0.0902 0.931/0.456

0.989

1.037

0.964

1.055

1.034

Total reflections Unique reflections Rint Parameters/ restraints R1 (all data)a R1 (I > 2r(I))a wR2 (all data)b wR2 (I > 2r(I))b Max/min residual (e/ Å3) Goodness-of-fit a b

P P R1 = ||Fo|  |Fc||/ |Fo|. P P 2 wR2 = { [w(Fo  Fc2)2]/ [wFo2]2}1/2.

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4.2. Structural description of {[Cu2(glu)2(3-pina)]3.5H2O}n (1) The asymmetric unit of compound 1 contains two divalent copper atoms, two glutarate anions (glu-A, glu-B), a 3-pina ligand, and three-and-one-half total water molecules of crystallization. At Cu1, a Jahn–Teller distorted {CuNO4} square pyramidal coordination environment is observed (s = 0.007) [22], with single oxygen donor atoms from glu-A ligands in trans basal positions, and single oxygen donor atoms from glu-B ligands in trans basal positions. The apical site is taken up by a 3-pyridyl nitrogen donor atom from the N-side of a 3-pina ligand. A very similar coordination environment is seen at Cu2 (s = 0.017), but with a 4-pyridyl nitrogen donor atom from the O-side of a 3-pina ligand and a slightly greater deviation from ideal square pyramidal geometry. The coordination

environments are shown in Fig. 1a, with relevant bond lengths and angles listed in Table 2. Both the glu-A and glu-B ligands in 1 adopt an exotetradentate l4-j4O:O0 :O00 :O000 binding mode, which produce {Cu2(OCO)4} paddlewheel dimers. Each dimer contains either only Cu1 atoms or only Cu2 atoms, with respective Cu  Cu distances of 2.648(2) and 2.627(2) Å. Both glu-A ligands (torsion angles = 62.9, 173.6°) and glu-B ligands (torsion angles = 60.4, 175.0°) share the same gauche-anti conformation. These link the {Cu2(OCO)4} paddlewheel dimers into [Cu2(glu)2]n layers that are oriented parallel to the ac crystal planes (Fig. 1b). Each dimer connects to four others through the full span of two glu-A and two glu-B ligands, revealing a (4,4) type rectangular grid. This particular paddlewheel-bearing [Cu2 (glu)2]n layer motif appears to be a relatively common feature in

Fig. 1. (a) Coordination environments in 1. (b) [Cu2(glu)2]n layer in 1 with embedded {Cu2(OCO)4} paddlewheel dimers.

J.W. Uebler et al. / Inorganica Chimica Acta 405 (2013) 31–42

copper glutarate coordination polymers, having been observed in the self-penetrated 6-connected phases [Cu2(glu)2(bpy)]n [12a] and [Cu2(glu)2(bpmp)]n [12b]. Table 2 Selected bond distance (Å) and angle (°) data for 1. Cu1–O5#1 Cu1–O7#1 Cu1–O6 Cu1–O3 Cu1–N1 O5#1–Cu1–O7#1 O5#1–Cu1–O6 O7#1–Cu1–O6 O5#1–Cu1–O3 O7#1–Cu1–O3 O6–Cu1–O3 O5#1–Cu1–N1 O7#1–Cu1–N1 O6–Cu1–N1 O3–Cu1–N1

1.950(8) 1.966(7) 1.969(7) 1.978(7) 2.168(8) 90.2(3) 167.3(3) 87.5(3) 90.0(3) 168.1(3) 89.7(3) 88.6(3) 96.1(3) 104.1(3) 95.8(3)

Cu2–O8#2 Cu2–O2#3 Cu2–O4#4 Cu2–O1 Cu2–N3#5 O8#2–Cu2–O2#3 O8#2–Cu2–O4#4 O2#3–Cu2–O4#4 O8#2–Cu2–O1 O2#3–Cu2–O1 O4#4–Cu2–O1 O8#2–Cu2–N3#5 O2#3–Cu2–N3#5 O4#4–Cu2–N3#5 O1–Cu2–N3#5

1.959(7) 1.964(7) 1.971(6) 1.983(7) 2.155(10) 168.7(3) 86.5(3) 92.0(3) 89.8(3) 89.2(3) 167.3(3) 95.1(4) 96.2(4) 102.5(3) 89.9(3)

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

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In turn parallel into [Cu2(glu)2]n layers are connected into a 3D [Cu2(glu)2(3-pina)]n coordination polymer network by the dipodal 3-pina ligands (Fig. 2), which span a Cu1  Cu2 interlayer distance of 12.227 Å. The centroids of the embedded {Cu2(OCO)4} paddlewheels can now be considered 6-connected nodes, connecting to four others within a [Cu2(glu)2]n layer through glutarate linkages, and to two others in neighboring [Cu2(glu)2]n layers via 3-pina linkages. Simplifying the connectivity in this manner reveals a 6-connected 41263 pcu topology (Fig. 3a). The length of the dipyridyl ligand appears to play a predominant role in the topology of related 6-connected paddlewheel-based copper glutarate coordination polymers. Shorter tethers such as bpy can instill a self-penetrated 48668 rob topology in [Cu2(glu)2(bpy)]n [12a] (Fig. 3b), while longer tethers such as bpmp can afford a rarer self-penetrated 446108 mab topology (Fig. 3c), seen in [Cu2(glu)2 (bpmp)]n [12b]. Here the 3-pina ligand spans just the correct distance between the layer motifs to generate a standard pcu primitive cubic-type topology in [Cu2(glu)2(3-pina)]n. Entrained within the 1D apertures within the 3D [Cu2(glu)2 (3-pina)]n pcu net are chains of disordered water molecules of crystallization, with some anchored to the coordination

Fig. 2. [Cu2(glu)2(3-pina)]n coordination polymer network in 1. Water molecules of crystallization are located in 1D apertures within the net.

Fig. 3. Related 6-connected copper glutarate coordination polymer topologies. (a) pcu net of 1. (b) self-penetrated rob net in [Cu2(glu)2(bpy)]n. (c) Self-penetrated mab net in [Cu2(glu)2(bpmp)]n.

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polymer backbone by accepting hydrogen bonds from 3-pina N–H groups, and donating hydrogen bonds to ligated glu carboxylate oxygen atoms. The water molecule chains are shown in orange in Fig. 2b in the online version of this article. They occupy incipient solvent-accessible void spaces comprising 19.5% of the unit cell volume, according to a calculation performed with PLATON [23]. Hydrogen bonding parameters for 1 are listed in Table 3.

4.3. Structural description of [Cu2(dmg)2(3-pina)]n (2) The asymmetric unit of compound 2 contains two divalent copper atoms, two 3,3-dimethylglutarate anions (dmg-A, dmg-B), and a 3-pina ligand. Dissimilar to its unsubstituted congener 1, there are no co-crystallized water molecules. Yet the two {CuNO4} square pyramidal coordination environments in 2 are remarkably similar to those in 1. The respective s values for Cu1 and Cu2 in

Table 3 Hydrogen bonding distance (Å) and angle (°) data for 1–5. D–H  A

d(H  A)

d(D  A)

\DHA

Symmetry transformation for A

1 N2–H2  O1W

2.06

2.903(17)

161.5

x + 1, y, z

2 N3–H3N  O1

1.95(6)

2.940(7)

164(5)

x + 1, y, z

3 O1W–H1WA  O1 O1W–H1WB  O4 O6–H6A  O4 O6–H6B  O2 N2–H2N  O1W

1.939(18) 1.836(17) 1.906(18) 1.941(18) 1.959(19)

2.763(3) 2.697(3) 2.734(3) 2.799(3) 2.835(3)

170(3) 175(3) 166(3) 171(3) 163(3)

4 O1W–H1WA  O1 O1W–H1WB  O6 O6–H6C  O3 O6–H6D  O4 N3–H3N  O5

2.11(2) 2.22(3) 1.800(19) 1.842(18) 1.992(18)

3.016(5) 3.085(4) 2.618(3) 2.683(3) 2.862(3)

172(5) 155(5) 166(3) 177(3) 175(3)

5 O9–H9A  O11 O9–H9B  O6 O10–H10A  O5 O10–H10B  O12 N4–H4N  O3 N5–H5N  O3 O14–H14A  O13

1.868(18) 1.855(18) 1.813(19) 1.822(18) 2.10(2) 2.14(2) 1.62(5)

2.708(3) 2.689(4) 2.630(3) 2.659(3) 2.954(3) 2.952(3) 2.240(8)

170(3) 178(3) 171(3) 175(3) 165(3) 154(3) 129(6)

Fig. 4. (a) Coordination environments in 2. (b) [Cu2(dmg)2]n chain motif in 2.

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

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

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2 are 0.018 and 0.007. The Cu1 atoms have single oxygen donor atoms from four different dmg-A ligands in the basal positions, while the Cu2 atoms have single oxygen donor atoms from four different dmg-B ligands in their basal coordination sites. The apical site at Cu1 is taken up by a 3-pyridyl nitrogen donor atom from the N-side of the 3-pina ligand, while that at Cu2 is filled by a 4-pyridyl nitrogen donor atom from the O-side of another 3-pina ligand. The coordination environments are shown in Fig. 4a, with relevant bond lengths and angles listed in Table 4. The dmg-A and dmg-B ligands in 2 adopt the same exotetradentate l4-j4O:O0 :O00 :O000 binding mode seen in the glutarate derivative 1, again producing {Cu2(OCO)4} paddlewheel dimers. The Cu1  Cu1 and Cu2  Cu2 through-space distances across the crystallographically distinct dimeric units are identical within experimental error, at 2.622(3) and 2.623(3) Å respectively. Pairs of dmg ligands link each {Cu2(OCO)4} paddlewheel dimer to two others, resulting in [Cu2(dmg)2]n chains (Fig. 4b), in stark contrast with the [Cu2(glu)2]n layers seen in the unsubstituted analog 1. The backbones of the dmg ligands in 2 rest in a gauche–gauche conformation, with four-C torsion angles of 47.8 and 51.1° in dmg-A and 51.8° and 52.2° in dmg-B. The methyl groups of the Table 4 Selected bond distance (Å) and angle (°) data for 2. Cu1–O3#1 Cu1–O4#2 Cu1–O1 Cu1–O2#3 Cu1–N2 O3#1–Cu1–O4#2 O3#1–Cu1–O1 O4#2–Cu1–O1 O3#1–Cu1–O2#3 O4#2–Cu1–O2#3 O1–Cu1–O2#3 O3#1–Cu1–N2 O4#2–Cu1–N2 O1–Cu1–N2 O2#3–Cu1–N2

1.950(4) 1.976(4) 1.977(4) 1.979(4) 2.167(5) 168.19(16) 88.33(18) 89.02(18) 87.95(19) 92.29(19) 167.88(17) 95.15(17) 96.66(17) 105.06(17) 86.77(17)

Cu2–O7#2 Cu2–O6#4 Cu2–O8#5 Cu2–O5 Cu2–N1 O7#2–Cu2–O6#4 O7#2–Cu2–O8#5 O6#4–Cu2–O8#5 O7#2–Cu2–O5 O6#4–Cu2–O5 O8#5–Cu2–O5 O7#2–Cu2–N1 O6#4–Cu2–N1 O8#5–Cu2–N1 O5–Cu2–N1

1.952(5) 1.968(5) 1.972(5) 1.978(5) 2.213(5) 91.2(2) 168.32(19) 88.1(2) 87.8(2) 168.32(19) 90.6(2) 94.59(19) 104.02(19) 96.90(19) 87.67(19)

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

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dmg ligands project away from the central regions of the [Cu2 (dmg)2]n chains in order to relieve steric hindrance. This possibly enforces the gauche–gauche conformation of the dmg ligands, and resultant avoidance of a [Cu2(dmg)2]n layer motif in lieu of the observed chains. Neighboring [Cu2(dmg)2]n chains are connected into [Cu2 (dmg)2(3-pina)]n coordination polymer layers by dipodal 3-pina ligands (Fig. 5), which span a Cu  Cu distance of 11.736 Å. Hydrogen bonding donation from 3-pina N–H groups to ligated dmg carboxylate oxygen atoms serves an ancillary role in stabilizing the layer structural motif (Table 3). Weak C–H  O interactions (C  O distance = 3.46 Å) between 3-pyridyl rings and C@O groups of 3-pina ligands in neighboring [Cu2(dmg)2(3-pina)]n coordination polymer layers provide the impetus for supramolecular stacking in the crystal of 2 (Fig. S1). Consistent with literature precedent [24], sterically bulky ligands afforded a reduction of coordination polymer dimensionality when compared to their unsubstituted congeners [24]. 4.4. Structural description of {[Cu(glu)(3-pna)(H2O)]H2O}n (3) The asymmetric unit of compound 3 contains a divalent copper atom, a complete glu ligand, a 3-pna ligand, an aqua ligand, and a water molecule of crystallization. The coordination environment at copper is best described as a distorted {CuN2O4} octahedron (Fig. 6a), with a chelating glu carboxylate group, a single oxygen donor from another glu ligand, trans pyridyl nitrogen donors belonging to two 3-pna ligands, and an aqua ligand. The long Jahn–Teller distorted apical positions are delineated by one of the donors within the chelating carboxylate group and the aqua ligand. Pertinent bond lengths and angles within the coordination sphere are listed in Table 5. Conformationally flexible glu ligands in a gauche–gauche conformation (four-C atom torsion angles = 67.9°/78.3°) connect copper atoms in a chelating/monodentate l2-j3O,O0 :O00 binding mode (Scheme 2) to construct [Cu(glu)(H2O)]n chain motifs. The Cu  Cu distance through the glu ligands is 8.682 Å, which denotes the a lattice parameter. In turn the [Cu(glu)(H2O)]n chain are connected by cis-conformation 3-pna ligands to establish [Cu(glu)(3-pna)(H2O)]n

Fig. 5. [Cu2(dmg)2(3-pina)]n coordination polymer layer in 2. (a) Face view. (b) Edge view.

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Fig. 6. (a) Coordination environment of 3. (b) Face view of [Cu(glu)(3-pna)(H2O)]n (4,4) grid coordination polymer in 3. (c) Edge view.

Table 5 Selected bond distance (Å) and angle (°) data for 3. Cu1–O3#1 Cu1–N3#2 Cu1–O1 Cu1–N1 Cu1–O6 Cu1–O2 O3#1–Cu1–N3#2 O3#1–Cu1–O1 N3#2–Cu1–O1 N1–Cu1–O2 O6–Cu1–O2

1.9465(18) 2.011(2) 2.0139(17) 2.026(2) 2.424(2) 2.4768(18) 93.33(9) 155.75(8) 90.17(8) 93.13(7) 158.82(7)

O3#1–Cu1–N1 N3#2–Cu1–N1 O1–Cu1–N1 O3#1–Cu1–O6 N3#2–Cu1–O6 O1–Cu1–O6 N1–Cu1–O6 O3#1–Cu1–O2 N3#2–Cu1–O2 O1–Cu1–O2

92.08(9) 169.69(9) 88.49(8) 102.99(7) 87.28(9) 101.14(7) 82.95(8) 97.94(7) 94.81(8) 57.84(7)

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

(4,4) grids (Fig. 6b), with the Cu  Cu distance through the 3-pna ligands measuring 9.159 Å. Hydrogen bonding between the aqua ligands and bound and unbound glu carboxylate oxygen atoms provides an ancillary stabilization effect (Table 3). The water molecules of crystallization are anchored within the coordination polymer layers by accepting hydrogen bonds from the 3-pna N–H moieties, and by donating hydrogen bonds to ligated and unligated glu carboxylate oxygen atoms. The unligated water molecules rest directly within the grid apertures and therefore occupy only a

negligible fraction of the unit cell volume. The 3-pna ligands alternate above and below the coordination polymer planes, providing a ruffled aspect to the [Cu(glu)(3-pna)(H2O)]n layers (Fig. 6c). These aggregate via weak C–H  O interactions to afford the necessary supramolecular stacking (Fig. S2). 4.5. Structural description of {[Cu(glu)(4-pna)(H2O)]H2O}n (4) The asymmetric unit of compound 4 contains a divalent copper atom, a fully deprotonated glu ligand, a 4-pna ligand, an aqua ligand, and a water molecule of crystallization. Different from 3, the coordination environment at Cu in 4 is a Jahn–Teller distorted {CuN2O3} square pyramid (s = 0.413) with an aqua ligand in the apical position. Here the deviation from ideal square pyramidal geometry is far more significant than those seen in 1 and 2. The basal plane has cis nitrogen donor atoms from the 4-pyridyl N-side of one 3-pina ligand and the 3-pyridyl O-side of another 3-pina ligand, along with cis oxygen donor atoms from two different glu ligands. The coordination environment is depicted in Fig. 7a, with pertinent bond lengths and angles listed in Table 6. The gauche–anti conformation glu ligands (torsion angles = 58.1°, 179.1°) in 4 lie in a bis(monodentate) l2-j2O:O00 binding mode. Pairs of these bridging adjacent copper atoms, forming [Cu2(glu)2] dimeric units (Fig. 7b) with a Cu  Cu distance of 7.838 Å. Each of these [Cu2(glu)2] units conjoins to four others

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Scheme 2. Binding modes and conformations of the dicarboxylate ligands in 1–5.

Fig. 7. (a) Coordination environment of 4. (b) [Cu2(glu)2] dimeric unit in 4.

Table 6 Selected bond distance (Å) and angle (°) data for 4. Cu1–O2 Cu1–O4#1 Cu1–N1 Cu1–N2#2 Cu1–O6 O2–Cu1–O4#1 O2–Cu1–N1 N2#2–Cu1–O6

1.9472(18) 1.9867(19) 2.002(2) 2.075(2) 2.257(2) 86.18(8) 173.97(8) 90.67(8)

O4#1–Cu1–N1 O2–Cu1–N2#2 O4#1–Cu1–N2#2 N1–Cu1–N2#2 O2–Cu1–O6 O4#1–Cu1–O6 N1–Cu1–O6

88.38(8) 89.83(8) 149.21(8) 93.53(9) 96.50(7) 120.11(7) 88.48(8)

Symmetry transformation to generate equivalent atoms: #1 x + 1/2, y + 5/2, z; #2 x + 1, y + 1, z + 1/2.

via 4-pna tethers, which span a Cu  Cu internuclear distance of 11.785 Å, over 2.6 Å longer than the comparable 3-pna linkage in 3. Through the 4-pna linkages, [Cu(glu)(4-pna)(H2O)]n coordination polymer layers are formed (Fig. 8a). Hydrogen bonding donation from the aqua ligands to unligated glu carboxylate oxygen atoms serves a supporting structure directing role (Table 3). Treating the pairs of glu ligands as single linkers, and the copper atoms as 3-connected nodes, allows the [Cu(glu)(4-pna)(H2O)]n layers to be simplified as (6,3) herringbone nets. The significant rectangular apertures within the layer motifs (11.9  18.8 Å) permit parallel interpenetration of an identical layer (Fig. 8b), anchored in place by hydrogen bonding donation from 4-pna N–H groups to unligated glu carboxylate oxygen atoms (Table 3). Parallel sets of 2-fold interpenetrated [Cu(glu)(4-pna)(H2O)]n layers

stack along the c crystal axis (Fig. S3), facilitated by hydrogen bonding mechanisms involving the water molecules of crystallization. The small solvent-accessible interlamellar regions contain 4.7% of the unit cell volume. 4.6. Structural description of [Cu3(Hmg)2(4-pna)4(SO4)2(H2O)4]n (5) The asymmetric unit of compound 5 contains two copper atoms (Cu1, Cu2), one of which (Cu1) sits on a crystallographic inversion center, along with a disordered singly protonated Hmg ligand, a disordered sulfate ion, a 4-pna ligand, and two aqua ligands. Two different coordination environments are observed. Cu1 displays a Jahn–Teller distorted {CuN4O2} octahedron with oxygen atom donors from two sulfate ligands in the elongated axial positions, and 3-pyridyl donors from the O-sides of four different 3-pina ligands in the equatorial position. Cu2 possesses a Jahn–Teller distorted {CuN2O3} square pyramidal geometry (s = 0.351) with 4-pyridyl nitrogen donors from the N-sides of two 4-pna ligands in trans basal positions. An aqua ligand and a single oxygen donor from a pendant Hmg ligand fill the remaining trans basal positions, with a second aqua ligand in the apical site. The coordination environments in 5 are shown in Fig. 9, with relevant bond lengths and angles listed in Table 7. Dissimilar to the carboxylate ligands in 1–4, which bridge either two or four copper atoms, the gauche–anti conformation Hmg ligands (torsion angles = 63.9°, 156.6°) in 5 act as simple, pendant monodentate ligands and are thus not involved in coordination

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Fig. 8. A single [Cu(glu)(4-pna)(H2O)]n (6,3) herringbone layer in 4.

Fig. 9. Parallel interpenetration of herringbone layers in 4.

polymer connectivity. Instead the dipodal 4-pna ligands serve this role by themselves in 5, as the sulfate ligands also serve only as monodentate donors. Each Cu1 atom connects to four Cu2 atoms, and each Cu2 atom connects to two Cu1 atoms through 4-pna

tethers, with a Cu1  Cu2 distance of 11.345 Å. In contrast to the 3D net of 1 and the 2D structures of 2–4, 1D [Cu3(Hmg)2(4-pna)4 (SO4)2(H2O)4]n chain-like coordination polymers are seen in 5 (Fig. 10). Within the interior of the chain motifs, which are oriented

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 1], multiple hydrogen bonding mechanisms are parallel to [0 1 operative (Table 3). The 4-pna N–H groups donate hydrogen bonds to unligated sulfate oxygen atoms, while aqua ligands on Cu2 donate hydrogen bonds to unligated oxygen atoms of the monodentate Hmg carboxylate groups. Hydrogen bonding between aqua ligands and sulfate ions ligated in separate chains serves to aggregate the chains into the supramolecular crystal structure of 5. 4.7. Thermogravimetric analysis To probe the decomposition behavior of the 2D and 3D coordination polymers prepared in this study, thermogravimetric analysis was undertaken on polycrystalline samples of compounds 1–4. Compound 1 underwent loss of its water molecules of crystallization between 40 and 70 °C, as evidenced by 4.7% mass loss. As the full 3.5 equivalents of unligated water would have accounted for a 9.7% mass loss, it is apparent that some dehydration occurred on storage at room temperature for over a month. The 3D coordination

Table 7 Selected bond distance (Å) and angle (°) data for 5. Cu1–N3 Cu1–N1 Cu1–O4 Cu2–O11 Cu2–O10 Cu2–N2 Cu2–N6#1 Cu2–O9 N3–Cu1–N3#2 N3–Cu1–N1#2 N3–Cu1–N1 N1#2–Cu1–N1 N3–Cu1–O4 N1–Cu1–O4

2.060(2) 2.061(2) 2.4044(19) 2.001(2) 2.004(2) 2.017(2) 2.017(2) 2.1844(19) 180.0 88.84(9) 91.16(9) 180.0 86.60(8) 89.37(8)

N1–Cu1–O4#2 O4–Cu1–O4#2 N3–Cu1–O4#2 O11–Cu2–O10 O11–Cu2–N2 O10–Cu2–N2 O11–Cu2–N6#1 O10–Cu2–N6#1 N2–Cu2–N6#1 O11–Cu2–O9 O10–Cu2–O9 N2–Cu2–O9 N6#1–Cu2–O9

90.63(8) 180.0 93.40(8) 156.64(8) 89.53(9) 88.25(9) 88.47(8) 93.12(9) 177.67(9) 107.62(8) 95.63(8) 90.04(8) 91.70(8)

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

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polymer framework of 1 likely stayed intact until 260 °C, at which point rapid ligand ejection ensued. The 30.3% mass remnant at the analysis ending temperature of 475 °C is consistent with a mixture of CuCO3 (38.0% calc’d) and CuO (24.5% calc’d). The very small amount of residue precluded any XRD analysis. The mass of the 2D coordination polymer 2 remained largely stable until 270 °C, whereupon the organic ligands began to combust. The final mass remnant of 38.6% matches extremely well with a putative deposition of CuCO3 (38.4% calc’d). The aqua ligands and unligated water molecules in the grid-like layered coordination polymer 3 were removed between 140 and 212 °C, as marked by mass loss of 5.8%. This is lower than expected (8.3% calc’d), indicative of partial loss of cocrystallized water upon long-term storage. Above 215 °C, ligand ejection occurred. The final mass remnant of 27.2% is reasonably consistent with deposition of CuCO3 (28.8% calc’d). The thermal behavior of 4 was rather similar to that of 3, despite its different 2D topology and the presence of parallel interpenetration. Bound and unbound water molecules in 4 were ejected between 145 and 200 °C, as marked by mass loss of 5.8%. This is once again lower than expected (8.3% calc’d), again signifying some partial loss of co-crystallized water upon long-term storage. Ligand ejection occurred above 205 °C. The final mass remnant of 27.8% matches well with a deposition of CuCO3 (28.8% calc’d). It is plausible that the {Cu2 (OCO)4} paddlewheel dimers in 1 and 2 serve to enhance the thermal stability of these materials. Thermograms for 1–4 are shown in Figs. S4–S7 in the Supplementary information. 5. Conclusions Unsubstituted and substituted glutarate ligands were used to construct divalent copper coordination polymers containing one of four possible isomeric dipyridylamide coligands. The specific glutarate and dipyridylamide ligand used played a crucial role in dictating the dimensionality and topology of the resulting solid crystalline coordination polymer. In the case of 3-pyridylisonicotinamide, used in 1 and 2, {Cu2(OCO)4} paddlewheel dimers are

Fig. 10. (a) Coordination environment of 5. Only the major components of the disordered ligands are shown. (b) 1D [Cu3(Hmg)2(4-pna)4(SO4)2(H2O)4]n chain-like coordination polymer in 5.

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observed. Adjustment of nitrogen donor disposition from 3-pyridylnicotinamide to 4-pyridylnicotinamide resulted in a change from a standard non-interpenetrated (4,4) grid topology to a twofold parallel interpenetrated (6,3) topology. It is likely that the longer metal–metal contact distance provided by 4-pna promotes the formation of larger grid apertures, which in turn permit interpenetration of an identical net. Consistent with previously observed trends, increase in steric bulk within the aliphatic dicarboxylate component results in a decrease in coordination polymer dimensionality, when paired with the same dipyridylamide isomer. Divalent metal aliphatic dicarboxylate coordination polymers with the four isomeric dipyridylamide coligands 3-pina, 3-pna, 4-pna, and 4-pina have proven to be an exceptionally structurally diverse class of materials. Acknowledgments We acknowledge the donors of the American Chemical Society Petroleum Research Fund and Michigan State University for funding this work. We thank Mr. Rui Huang and Ms Lestella Bell for experimental assistance. Appendix A. Supplementary material CCDC 923511, 923509, 923512, 923513, and 923510 contains the supplementary crystallographic data for 1–5. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2013.05.009. References [1] L.J. Murray, M. Dinca, J.R. Long, Chem. Soc. Rev. 38 (2009) 1294 (and references therein). [2] J.R. Li, R.J. Kuppler, H.C. Zhou, Chem. Soc. Rev. 38 (2009) 1477 (and references therein). [3] (a) M. Plabst, L.B. McCusker, T. Bein, J. Am. Chem. Soc. 131 (2009) 18112; (b) Y. Liu, V.C. Kravtsov, M. Eddaoudi, Angew. Chem., Int. Ed. 47 (2008) 8446; (c) F. Nouar, J. Eckert, J.F. Eubank, P. Forster, M. Eddaoudi, J. Am. Chem. Soc. 131 (2009) 18112. [4] (a) J. Lee, O.K. Farha, J. Roberts, K.A. Scheidt, S.T. Nguyen, J.T. Hupp, Chem. Soc. Rev. 38 (2009) 1450 (and references therein); (b) L. Ma, C. Abney, W. Lin, Chem. Soc. Rev. 38 (2009) 1248 (and references therein).

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