Syntheses, Structural Characterization, and ... - ACS Publications

DOI: 10.1021/cg1013208

Syntheses, Structural Characterization, and Properties of {[Cu(bpp)2(H2O)2](tp) 3 7H2O} and {[Cu(bpp)2(H2O)](ip) 3 7H2O} Complexes. New Examples of the Organic Anionic Template Effect on Induced Assembly of Water Clusters (bpp = 1,3-Bis(4-pyridyl)propane, tp = Terephthalate, ip = Isophthalate)†

2011, Vol. 11 507–515

Geng-Geng Luo,* Hong-Bo Xiong, and Jing-Cao Dai* Institute of Materials Physical Chemistry, Huaqiao University, Xiamen, Fujian 361021, China Received October 8, 2010; Revised Manuscript Received December 3, 2010

ABSTRACT: A unique zero-dimensional (0D) discrete (H2O)14 cluster containing a rare hanging-ladder-like water octamer and an infinite one-dimensional (1D) loose-string-like water chain, respectively, was observed in the coordination polymeric solids {[Cu(bpp)2(H2O)2](tp) 3 7H2O} (1) and {[Cu(bpp)2(H2O)](ip) 3 7H2O} (2) (bpp = 1,3-bis(4-pyridyl)propane, tp = terephthalate, and ip = isophthalate), obtained by similar solution phase ultrasonic synthesis techniques, in which 1 (C34H50CuN4O13) crystallized in the monoclinic P21/n space group, Z = 4 (a = 12.824(3) A˚, b = 16.867(3) A˚, c = 17.660(4) A˚; β = 94.50(3)°; V = 3808(1) A˚3) and 2 (C34H48CuN4O12) was attributed to the monoclinic P21 chiral space group, Z = 2 (a = 10.439(2) A˚, b = 16.863(3) A˚, c = 11.302(2) A˚; β = 107.84(3)°; V = 1893.9(6) A˚3), respectively. Of particular interest, the shapes of water clusters have been obviously well-tuned by modulating different relative orientations of carboxylate groups based on the tp2- and ip2dianions, demonstrating that water aggregates with different morphologies can be controlled by employing adequate organic anionic species as templates. Both complexes are apparently reducible/oxidizable, which has been confirmed through the electrochemical investigation, and 1 exhibits appreciable electrocatalytic activity for the reduction reaction of nitrite.

Introduction The present upsurge in studying water clusters is aimed not only at understanding the “anomalous” behavior of bulk water but also at probing its possible roles in the stabilization and functionlization of biomolecules1 and in designing new materials.2 Hydrogen-bonding interactions and their fluctuations determine the properties of water in bulk, as well as in molecular confinements, although they still remain as illunderstood phenomena.3 The key to understanding the behavior of water is the precise structural data of various hydrogen-bonded water networks in diverse environments.4 This realization has promoted extensive investigations of water structures in recent years. A variety of discrete water clusters (H2O)n (where n = 2-10, 11-12, 14-18, 20, 32, 45)5,6 have been structurally characterized, as to one-dimensional (1D) water chains or tapes,7,8 two-dimensional (2D) water layers,9 and three-dimensional (3D) water structures,10 revealing various configurations in the crystal hosts in the solid state. Obviously, these observations have significantly promoted the elucidation of the interactions between water molecules, as well as between water molecules and hosts, and enriched the water chemistry. However, the aspects of water behavior are complex and so far have not been still wellunderstood for researchers from all branches of natural sciences. In fact, the tunable construction of water aggregates is remaining a challenging scientific endeavor.11 A simple and useful strategy to tune the shape of the water clusters with new topologies or architectures is to use so-called † Dedicated to both the Fujian Institute of Research on the Structure of MatterCAS and the Huaqiao University on the occasions of their 50th anniversaries. *Corresponding author. E-mail: [email protected] (G.-G.L.); djc@hqu. edu.cn (J.C.D.). Phone/Fax: þ86-595-22690569.

r 2010 American Chemical Society

anionic templates that are capable of inducing water aggregates. The hydration phenomena of inorganic anions such as halides, sulfate, phosphate, and nitrate have been widely studied,12 whereas organic anionic species have been largely unexplored.13 On the other hand, in recent years, the structural study of anion water clusters of X- 3 (H2O)n (X = F-, Cl-, Br-, I-, OH-, n = 1-6) has been an important topic in either solution chemistry or biochemistry14 and has been extensively investigated both experimentally and theoretically due to their suitable simplified model systems for the aerosol as well as molecular recognition studies to design X receptors.15 By comparison, organic dicarboxylic anion water clusters structurally have received less attention to date. Dicarboxylic acids in atmospheric particles play an important role as cloud condensation nuclei,16 and thus, understanding the microsolvation of dicarboxylic acids and their behavior at the water/ vapor interface is very important for atmospheric chemistry.17 Moreover, the reactivity of organic dicarboxylate anions is strongly affected by hydration.18 Enlightened by some hydrated molecules such as C6H6 3 (H2O)819 and phenol 3 (H2O)8,20 we will focus on aromatic polycarboxylate species because they can form strong and directional hydrogen bonds, and the numbers and the different relative orientations of the carboxylate groups on the aromatic ring may be helpful for inducing the formation of different water aggregations. Recognizing the potential of this approach, we have embarked on a program aimed at getting some insights into the templet effect of these polycarboxylate species on induced assembly of water clusters. In this contribution, we present both a novel discrete (H2O)14 cluster containing a rare hanging-ladder-like water octamer and one 1D loose-string-like water cluster observed in the complexes {[Cu(bpp)2(H2O)2](tp) 3 7H2O} (1) Published on Web 12/27/2010

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and {[Cu(bpp)2(H2O)](ip) 3 7H2O} (2) (bpp = 1,3-bis(4-pyridyl)propane, tp = terephthalate, ip = isophthalate), respectively. Of particular interest, herein, the formation of water clusters with different morphologies is well-controlled by using tp2and ip2- dianions as anionic templates. Meanwhile, these complexes are also two typical crystal examples of the anion clusters tp2- 3 (H2O)8 and ip2- 3 (H2O)8, which are essential for understanding the solvation of benzenedicarboxylate dianions in water clusters and further studying the molecular recognition phenomena of organic carboxylic anionic systems.18 Experimental Section Materials and General Methods. All chemicals and solvents employed in the syntheses were of analytical grade, obtained commerically, and used as received without further purification. The pH value was measured with a Delta 320 meter. The C, H, and N microanalyses were carried out with a CE instruments EA 1110 analyzer. The FT-IR spectra were recorded from KBr pellets in the range 4000-400 cm-1 on a Nicolet AVATAT FT-IR360 spectrometer. TG curves were performed from 25 to 800 °C on a NETZSCH TG 209 F1 instrument at a heating rate of 10 °C 3 min-1 under a nitrogen atmosphere. Powder X-ray diffraction (PXRD) data were collected on a Philips X’Pert Pro MPD X-ray diffractometer with Cu KR radiation equipped with an X’Celerator detector. The electrochemical experiments were carried out using a PARSTAT 2273 Electrochemical Workstation. A conventional three-electrode cell was used at room temperature (25 ( 3 °C). The modified electrode was used as working electrode. A saturated calomel electrode (SCE) and a platinum wire were used as reference and auxiliary electrodes, respectively. All potentials were measured and reported versus the SCE. Synthesis of {[Cu(bpp)2(H2O)2](tp) 3 7H2O} (1). A mixture of in situ synthesized Cu(OH)2 by CuCl2 3 2H2O (0.34 g, 1 mmol), NaOH (0.08 g, 2 mmol), H2tp (0.166 g, 1 mmol), and bpp (0.410 g, 2 mmol) was stirred in CH3OH-H2O mixed solvent (10 mL, v/v, 1:4) under ultrasonic treatment (160 W, 40 kHz, 40 °C) for 10 min. Then, an aqueous NH3 solution (25%) was dropped into the mixture to give a clear solution. The resultant blue filtrate (pH = 9.3) was allowed to evaporate slowly at ambient temperature. After one day, blue rod crystals were obtained in 42.1% yield (based on Cu). Anal. Calcd (%) for C34H50CuN4O13: C 51.93, H 6.41, N 7.12. Found: C 50.88, H 6.35, N 7.20. FT-IR (KBr, cm-1): v=3440(s), 3240(br), 2955(w), 2846(w), 1617(s), 1571(s), 1503(w), 1434(m), 1388(s), 1228(m), 1067(m), 822(m), 748(m), 622(m), 571(w), 530(m) (also see Figure S1a, Supporting Information). Synthesis of {[Cu(bpp)2(H2O)](ip) 3 7H2O} (2). The reaction was carried out by a method similar to that for 1, using H2ip (0.166 g, 1 mmol) instead of H2tp. The resultant blue filtrate (pH = 9.2) was allowed to evaporate slowly at room temperature. Blue block crystals were collected in 39.5% yield (based on Cu) two days later. Anal. Calcd (%) for C34H48CuN4O12: C 53.15, H 6.30, N 7.29. Found: C 53.78, H 6.17, N 7.35. FT-IR (KBr, cm-1): v = 3428(s), 3265(br), 2940(w), 2865(w), 1623(s), 1553(s), 1437(m), 1390(m), 1361(s), 1234(m), 1076(m), 1036(m), 821(w), 757(m), 711(w), 624(m), 583(w), 525(w) (see Figure S1b of the Supporting Information). Preparation of the Modified Carbon Paste Electrodes 1-CPE and 2-CPE. The electrode 1-CPE (or 2-CPE) was fabricated by the following procedure: about 0.015 g of complex 1 (or 2) was first dispersed in 0.25 g of graphite powder by grinding with the aid of an agate mortar and pestle to achieve an even and dry mixture, and about 0.08 mL of paraffin oil was then added into the above mixture under manual stirring with a glass rod to produce a homogenized electroconducting poultice that was subsequently filled into a 5 cm length of Pyrex tube with a 2 mm inner diameter. The electrical contact for the electrode was established with the copper stick in the conducting poultice, and the surface of the electrode was wiped with weighing paper for freshness. The same procedure was used for preparation of the bare CPE electrode without 1 or 2. X-ray Crystallography. Single crystals of complexes 1 and 2 with appropriate dimensions were chosen under an optical microscope and quickly coated with high vacuum grease (Dow Corning Corporation) before being mounted on a glass fiber for data collection.

Luo et al. Table 1. Crystal Data and Structure Refinement for 1 and 2 complex empirical formula formula weight crystal system space group a (A˚) b (A˚) c (A˚) β (deg) Z, Dcalc (Mg/m3) V (A˚3) μ (mm-1) F(000) total no. of reflns no. of unique reflns no. of variables parameters final R indices [I > 2σ(I)]

1 (CCDC 790590) C34H50 CuN4O13 786.32 monoclinic P21/n 12.824(3) 16.867(3) 17.660(4) 94.50(3) 4, 1.371 3808(1) 0.64 1660 31729 7462 (Rint = 0.044) 6266 470 R1 = 0.0351a

2 (CCDC 790591) C34H48 CuN4O12 768.31 monoclinic P21 (flack parameter 0.01 (1)) 10.439(2) 16.863(3) 11.302(2) 107.84(3) 2, 1.347 1893.9(6) 0.64 810 15346 7357 (Rint = 0.048) 5092 460 R1 = 0.0373

wR2 = 0.0708 wR2 = 0.0869b R1 = 0.0957 R1 = 0.0442 wR2 = 0.1092 wR2 = 0.0914 GOF 1.06 1.13 P P P P a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ w(Fo2 - Fc2)2]/ w(Fo2)2]1/2. R indices (all data)

Data were collected on a Rigaku R-AXIS RAPID Image Plate single-crystal diffractometer with a graphite-monochromated Mo KR radiation source (λ = 0.71073 A˚) operating at 50 kV and 90 mA in ω scan mode for 1 and 2. A total of 44  5.00° oscillation images was collected, each being exposed for 5.0 min. Absorption correction was applied by correction of symmetry-equivalent reflections using the ABSCOR program.21 In all cases, the highest possible space group was chosen. All structures were solved by direct methods using SHELXS-9722 and refined on F2 by full-matrix least-squares procedures with SHELXL-97.23 Atoms were located from iterative examination of difference Fourier maps following least-squares refinements of the earlier models. The organic hydrogen atoms were generated geometrically and refined with isotropic temperature factors. Hydrogen atoms attached to oxygen in 1 and 2 were located by difference Fourier maps and then refined subject to the constraint O-H = 0.85 A˚ and Uiso(H) = 1.5Ueq(O). All structures were examined using the Addsym subroutine PLATON24 to ensure that no additional symmetry could be applied to the models. Crystal structure views were obtained using Diamond v3.1.25 Some crystallographic data for 1 and 2 are summarized in Table 1. Selected bond lengths and angles for 1 and 2 are listed in Table 2. The hydrogen bond geometries for 1 and 2 are shown in Table 3. More details on crystallographic information are in the Supporting Information.

Results and Discussion Comments on the Synthesis. Two novel complexes {[Cu(bpp)2(H2O)2](tp) 3 7H2O} (1) and {[Cu(bpp)2(H2O)](ip) 3 7H2O} (2) were prepared in similar solution phase ultrasonic reactions of Cu(OH)2 (in situ synthesized from CuCl2 3 2H2O and NaOH), bpp ligand, and tp2- or ip2- species in H2O/CH3OH/NH3 media. It is well-known that the mixing of metal salts and polycarboxylates solution will usually result in microcrystals or precipitation in traditional aqueous reactions, presumably due to the fast coordination of the carboxylate groups to metal centers to form polymers,26 making it difficult to grow good crystals of complexes. Hence, properly slowing-down the reaction rate or enhancing solubility, such as using solvothermal methods, layerseparation diffusion treatment, gel permeation, or even a microwave assisted hydrothermal method, may favor the formation of

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Table 2. Selected Bond Distances (A˚) and Angles (deg) for 1 and 2a

Cu1-N1 Cu1-O1w N3-Cu1-N4 N4-Cu1-N2 N1-Cu1-O1w N1-Cu1-O2w

2.039(2) 2.387(1) 177.76(6) 93.29(7) 97.77(6) 88.79(5)

Cu1-N2 Cu1-O2w N3-Cu1-N1 N1-Cu1-N2 N2-Cu1-O1w N2-Cu1-O2w

Complex 1 2.040(2) Cu1-N3 2.495(1) 90.08(7) N4-Cu1-N1 175.38(6) N3-Cu1-O1w 86.73(5) N3-Cu1-O2w 86.72(5) O1w-Cu1-O2w

Cu1-N1i Cu1-O1w N4-Cu1-N1i N1i-Cu1-N3i N2-Cu1-O1w

2.021(4) 2.171(3) 167.3(2) 87.3(1) 94.3(1)

Cu1-N4 N3-Cu1ii N4-Cu1-N2 N2-Cu1-N3i N3i-Cu1-O1w

Complex 2 2.019(3) Cu1-N2 2.039(3) 87.7(1) N1i-Cu1-N2 169.7(2) N4-Cu1-O1w 96.0(2)

a

2.026(2) 87.73(7) 89.62(5) 91.25(5) 173.38(5)

2.030(4) 91.7(1) 95.9(2)

Cu1-N4 N3-Cu1-N2 N4-Cu1-O1w N4-Cu1-O2w

Cu1-N3i N4-Cu1-N3i N1i-Cu1-O1w

2.035(2) 88.92(7) 90.20(5) 89.18(5)

2.039(3) 91.0(1) 96.8(1)

Symmetry codes: (i) x, y, z þ 1; (ii) x þ 1, y, z - 1 for 2.

crystalline products.27 However, running of the reaction and crystallization processes by using the above traditional methods will usually take a long time (e.g. several days for solvothermal methods or several weeks for the diffusion method) and need to be performed at higher reaction temperature (usually 373523 K) and pressure (1-10 MPa) in many cases. Our solution strategy for the problem of precipitates is dropping ammonia solution into the reaction mixture under ultrasonic treatment until all reactants are almost completely dissolved and then filtering to get a clear resultant solution to evaporate in air. In this system, ultrasound technique28 can realize the rapid (∼10 min) and high efficient preparation of complexes (max. 30 different experiments in one batch). Meanwhile, by employing the ultrasonic synthesis method under the ammoniacal conditions, good crystals of 1 and 2 for structural data collection can be obtained within two days. The formation of 1 and 2 is not so significantly influenced by changes of the molar ratio of organic ligands to metal ions, and the resultant crystals are air-stable and insoluble in water and other common organic solvents. The compositions of 1 and 2 were first documented from single-crystal X-ray crystallography at low temperature and further confirmed from elemental analysis, IR spectra, and thermogravimetric analysis (TGA). The phase purity of either 1 or 2 has been sustained by PXRD patterns (Figure S2, see Supporting Information) Crystal Structures. Single-crystal X-ray analysis reveals that 1 crystallizes in the monoclinic space group P21/n and consists of a well-separated Cu-bpp cationic polymeric host, guest tp2- dianions, and lattice water molecules (Figure S3). In the host, each six-coordinated copper(II) center is equatorially coordinated to four independent bpp ligands via their pyridyl groups and axially to two water molecules, giving an axially elongated [4 þ 1 þ 1] octahedral geometry. The elongations of these Cu-O bonds [Cu1-O1w = 2.387(1) and Cu1-O2w = 2.495(1) A˚] may be ascribed to the JohnTeller effect. Also, the flexible bpp ligands can assume different conformations defined by quite different N-to-N distances (TT 9.1-10.1 A˚, TG 8.6-9.2 A˚, GG0 6.7-8.6 A˚, and GG 3.9 A˚; where T = Trans, G = Gauge).29 Thus, in complex 1, each bpp ligand adopts a TG conformation with a N 3 3 3 N separation of 8.475 A˚ and bridges two different metal centers, yielding a 1D cationic polymeric arrangement of metallaloop tape by repeating looplike units of {Cu2(bpp)2} in which each copper center is shared by two neighboring loops (Figure S4). Moreover, adjacent 1D cationic tapes are further interacted through the weak C-H 3 3 3 π interactions [C8-H8A 3 3 3 Cg1=108.07°, dH 3 3 3 Cg1 =3.54 A˚; C16H16B 3 3 3 Cg2 = 109.03°, dH 3 3 3 Cg2 = 3.52 A˚; where Cg1 and Cg2 are centroids of rings C9-C13 and C19-C23,

Table 3. Hydrogen-Bond Distances (A˚) and Angles (deg) Associated with Water Molecules in 1 and 2a D-H 3 3 3 A

D-H

H3 3 3A

D3 3 3A

D-H 3 3 3 A

O1w-H1wA 3 3 3 O3 O1w-H1wB 3 3 3 O2 O2w-H2wA 3 3 3 O1v O2w-H2wB 3 3 3 O3v O3w-H3wA 3 3 3 O2v O3w-H3wB 3 3 3 O4v O4w-H4wA 3 3 3 O6w O4w-H4wB 3 3 3 O5w O5w-H5wA 3 3 3 O7w O5w-H5wB 3 3 3 O2vi O6w-H6wA 3 3 3 O3 O6w-H6wB 3 3 3 O9w O7w-H7wA 3 3 3 O4iv O7w-H7wB 3 3 3 O3wvii O8w-H8wA 3 3 3 O9wviii O8w-H8wB 3 3 3 O4wviii O9w-H9wA 3 3 3 O8wi O9w-H9wB 3 3 3 O1

Complex 1 0.85 1.97 0.85 1.93 0.85 1.85 0.85 1.96 0.85 2.22 0.85 2.00 0.85 1.99 0.85 1.92 0.85 1.96 0.85 1.99 0.85 2.02 0.85 2.12 0.85 2.03 0.85 1.95 0.85 2.01 0.85 1.93 0.85 1.94 0.85 1.90

2.814(2) 2.773(2) 2.685(2) 2.811(2) 3.053(2) 2.823(2) 2.796(2) 2.753(3) 2.809(2) 2.840(2) 2.870(2) 2.916(2) 2.867(2) 2.786(2) 2.823(2) 2.772(2) 2.791(2) 2.750(2)

172 174 168 174 168 162 158 166 176 176 174 156 170 166 159 169 179 174

O1w-H1wA 3 3 3 O5w O1w-H1wB 3 3 3 O3iii O2w-H2wA 3 3 3 O1iv O2w-H2wB 3 3 3 O4iii O3w-H3wA 3 3 3 O1iv O3w-H3wB 3 3 3 O6w O4w-H4wA 3 3 3 O2w O4w-H4wB 3 3 3 O3w O5w-H5wA 3 3 3 O4w O5w-H5wB 3 3 3 O2 O6w-H6wA 3 3 3 O3iv O6w-H6wB 3 3 3 O8w O7w-H7wA 3 3 3 O4 O7w-H7wB 3 3 3 O2ii O8w-H8wA 3 3 3 O7w O8w-H8wB 3 3 3 O5wii

Complex 2 0.85 2.01 0.85 1.81 0.85 1.97 0.85 2.00 0.85 1.98 0.85 1.87 0.85 1.87 0.85 2.18 0.85 1.88 0.85 1.95 0.85 1.94 0.85 1.91 0.85 1.93 0.85 1.89 0.85 1.91 0.85 2.00

2.724(4) 2.626(4) 2.819(4) 2.845(4) 2.827(5) 2.715(5) 2.719(5) 2.785(5) 2.707(5) 2.733(5) 2.750(5) 2.731(5) 2.778(5) 2.733(4) 2.709(5) 2.821(5)

141 160 172 172 173 173 178 128 164 153 158 162 173 174 157 161

a Symmetry codes: (i) x þ 1/2, -y þ 3/2, z - 1/2; (iv) -x þ 1, -y þ 2, -z þ 2; (v) -x þ 3/2, y - 1/2, -z þ 3/2; (vi) x - 1, y, z; (vii) -x þ 1/2, y þ 1/2, -z þ 3/2; (viii) -x þ 1/2, y - 1/2, -z þ 3/2; for 1. (ii) x, y, z - 1; (iii) x þ 1, y, z þ 1; (iv) x þ 1, y, z for 2.

respectively] to generate a 2D cationic layer of {[Cu(bpp)2(H2O)2]2þ}n (also see Figure S5). The bond distances and bond angles involving the metal ion are closely similar to those observed in several related species.30 Interestingly, the linear-type H2tp guest completely deprotonates to balance the polymeric host charge whereas it does not participate in coordinating to any Cu2þ cation. Thus, around the tp2- anion, the lattice water molecules are aggregated to form a novel ordered 2D hydrogen-bonded-driven

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Figure 1. View showing the novel {[(tp) 3 7H2O]2-}n layer (middle) assembly by the hydrogen-bonded network of the lattice water molecules and template tp2- dianions fabricated through forming the “Θ” fashion (top) of tp2- 3 (H2O)8 anion clusters associated with the interesting (H2O)14 cluster (bottom) composed of two acyclic bent D3 trimeric aggregates as well as a hanging-ladder-like octameric water aggregate in 1. Atoms marked with the superscripts i and viii are at the symmetry positions (x þ 1/2, -y þ 3/2, z - 1/2) and (-x þ 1/2, y - 1/2, -z þ 3/2), respectively. Hydrogen bond lengths and angles are provided in Table 3.

water-tp anionic layer {[(tp) 3 7H2O]2-}n that is observed parallel to the above host {[Cu(bpp)2(H2O)2]2þ}n sheet along the ∼[010] direction (Figure 1, middle; also see Figure S5b). An interesting question arises as to how this novel {[(tp) 3 7H2O]2-}n layer assembles. Although the real mechanism route is not clear yet, a reasonable speculation can be made. Herein, the self-assembly of this 2D water-tp anion layer is therefore assumed to occur via the following two steps: The H2tp molecules in aqueous ammonia are first deprotonated and then hydrated into tp2- 3 (H2O)8 anionic clusters; subsequently, the tp2- 3 (H2O)8 anion clusters are further interacted through hydrogen bonding to form the 2D water-tp anionic sheet. Within this anion tp2- 3 (H2O)8 cluster, each tp2- anion is surrounded by double four water molecules (four are crystallographically independent, and the other four are their symmetry-related molecules) to produce two equivalent solvation shells almost distributed uniformly in two rows along the dicarboxylate dividing line, displaying a beautiful shape of a “Θ” motif, where the deprotonated carboxylate groups of tp2- act as hydrogen bond acceptors while the lattice

Luo et al.

water molecules serve as hydrogen donors. And two such “Θ” tp2- 3 (H2O)8 clusters are further fused together to generate an interesting twin (Figure 1, top). According to graphset analysis nomenclature,31 the hydrogen motifs within the tp2- 3 (H2O)8 anion clusters can be assigned to be R55(17). As shown in Figure 1 (bottom), a closer look at the connectivity of lattice water molecules reveals the presence of a new type of discrete tetradecameric water cluster (H2O)14 in the 2D water-tp dianion layer. The (H2O)14 cluster consists of three fused cyclic tetramers in a hanging-ladder-like conformation and two acyclic bent D3 water trimers. It should be noted that there are only a few cases of discrete (H2O)14 clusters32 that are captured in the void of the metal coordination complex, but the present novel configuration of the (H2O)14 cluster has been neither predicted theoretically nor previously reported experimentally. The fascinating feature is that four lattice water molecules (O4w, O5w, O8w, and O9w) and their symmetry-related ones link to each other to form a novel tricyclic (H2O)8 cluster through hydrogen bonds (see Table 3). This tricyclic water octamer assumes a rare hanging-ladder-like conformation, in which three tetramers fuse each other through edge-sharing, and its structure can be represented by the graph set notation R44(8)R44(8)R44(8).31 The four oxygen atoms within the left (I) and equivalent right tetramer (III) are noncoplanar, with a dihedral angle of ca. 26.05° (O6w/O9w/O8w plane vs O6w/ O4w/O8w plane), in which one water molecule (O8w) acts as double donor and another one (O9w) as double acceptor, with the remaining two waters (O4w and O6w) each acting as both single donor and single acceptor. Within the middle one (II), the four water molecules (O8w, O9w, O8wi, and O9wviii; symmetry codes: i = -x, 1 - y, 1 - z; viii = -x þ 1/2, y - 1/2, -z þ 3/2) are fully coplanar, and each water monomer acts as both single hydrogen bond donor and acceptor. The remaining hydrogen atoms of O8w and O9w are 0.74 and 0.60(2) A˚ above the ring, compared to the hydrogen atoms of O8wi and O9wviii, which are 0.74 and 0.60 A˚ below the ring. Such an arrangement results in a S4 symmetry with an up-updown-down (uudd) conformation. It is noteworthy that structural data of this uudd cyclic water tetramer are very scarce so far,5f,33 although some reports of successful characterization of hydrogen-bonded water tetramers in different hosts have been published. The formation of a less stable uudd water tetramer in 1 indicates the cooperative association of the water clusters. The O 3 3 3 O distance within the octamer ranges from 2.771 to 2.916 A˚, with an average value of 2.819 A˚, which is longer than the value of 2.759 A˚ in ice Ih at -90 °C3e but slightly shorter than those observed in liquid water (2.854 A˚)34 and comparable to those in the ice II phase (2.77-2.84 A˚).35 The intracyclic O 3 3 3 O 3 3 3 O angles are in the range 82.22-94.24°, with an average of 88.92°, considerably deviating from the preferred ideal tetrahedral geometry of water. Earlier extensive theoretical calculations and experiments suggested that the higher stability for the (H2O)8 cluster structure should be the cubic array rather than the cyclic motif, owing to the former having a possibility for the formation of a maximum number of hydrogen bonds.5k,36 However, because of a template effect, the shape and size of the void space as well as the role of tp2- template dianions prevent the (H2O)8 cluster in 1 from forming a cubic arrangement of the water octamer. As a result, the octameric water cluster adopts a tricyclic fused ladder conformation and its stability is obviously derived from the strong hydrogen-bonding interactions with the available carboxylate

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O atoms and water trimers. Furthermore, the (H2O)8 cluster is also bonded to two equivalent adjacent D3 water trimers via hydrogen bonding between the O5w and O4w waterbridged molecules, giving rise to an interesting tetradecameric water cluster. The O5w 3 3 3 O4w separation of 2.753 A˚ observed in 1 is substantially the same as the distance of 2.759 A˚ in ice Ih at -90 °C.3e,f To the best of our knowledge, complex 1 is the first example of the novel (H2O)14 cluster being composed of two different types of odd (D3 trimer) and even ((H2O)8 octamer) numbers of water aggregates and of the stable water cluster phase coexisting in their host lattice. Complex 2 crystallizes in chiral space group P21 with Flack’s parameter x = 0.01(1), whose building unit contains one crystallographically unique Cu2þ cation, one water, as well as two bpp ligands, one ip2- dianion, and an additional seven lattice water molecules (Figure S6). Similar to those in 1, the host consists of 1D double-stranded polymeric metallaloop tapes formed by interconnecting looplike subunits made from two bpp ligands, two Cu2þ ions, and one water molecule (Figure S7). Compared with the former complex, each Cu2þ ion exhibits as five-coordinate rather than sixcoordinate, as in 1, and therefore has a square pyramidal geometry with a parameter τ = 0.04,37 where basal coordination comes from four N donors of four different bpp ligands with an average Cu-N distance of 2.027 A˚ while the apical site is occupied by a water oxygen [Cu1-O1w = 2.171(3) A˚]. Obviously, the Cu1-O1w distance is indicative of John-Teller distortion due to the d9 configuration. Similarly, the neighboring 1D double-stranded cationic metallaloop tapes are further interacted through weak C-H 3 3 3 π interactions to generate a 2D cationic layer {[Cu(bpp)2(H2O)]2þ}n. Similar to the case of complex 1, the lattice water molecules around the ip2- anion are also aggregated to generate an ordered 2D hydrogen-bonded-driven water-ip anionic layer {[(ip) 3 7H2O]2-}n parallel to the host polymeric sheet along the ∼[010] direction (Figure 2, middle). In this {[(ip) 3 7H2O]2-}n water-ip anionic layer, the angular-type H2ip molecule is also fully deprotonated into ip2- dianion that is hydrated into an ip2- 3 (H2O)8 anion cluster. However, different from the case of those water arrays observed in complex 1, the eight lattice water molecules are distributed pockety between two sides of the dicarboxyl groups of an ip2- anion to yield a boxing-glove-like ip2- 3 (H2O)8 anion cluster with two unequivalent solvation shells (Figure 2, top). According to graph-set analysis nomenclature,31 the hydrogen motifs in this anion water cluster of ip2- 3 (H2O)8 can be assigned to be R33(11) and R77(22). Compared with the discrete (H2O)14 cluster observed in 1, the angular-type ip2- dianionic template induces lattice water molecules into a position favorable for the formation of hydrogen-bonded-driven 1D loose-string-like rather than above hanging-ladder-like water clusters. As well-known, in fact, it appears to be quite important for water chainlike clusters in the control of proton fluxes in a variety of biomolecules,38 as well as facilitating selective permeation of water across membranes. Figure 2 (bottom) presents the view of the 1D loose-string-like water chain, primarily consisting of (H2O)7 subunits, which contain one acyclic water (H2O)5 cluster (O8w, O6w, O3w, O4w, and O5w) and two dangling water molecule lateral arms (O7w, O2w). The [(H2O)5]n chain can be represented by a C5 unit according to the water cluster notation39 when two dangling water

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Figure 2. View showing how a {[(ip) 3 7H2O]2-}n layer (middle) assembles by the hydrogen-bonded network of the lattice water molecules and ip2- dianions fabricated through forming the interesting boxing-glove-like ip2- 3 (H2O)8 anion cluster (top) and the 1D loose-string-like water aggregates (botton) in 2. Hydrogen bond lengths and angles are listed in Table 3.

molecules are temporarily unconsidered. Within this water chain, all water molecules are found to act as single hydrogen bond donor as well as acceptor. The O 3 3 3 O distance in the chain ranges from 2.706 to 2.821 A˚, with an average value of 2.751 A˚, which is apparently shorter than those observed in liquid water (2.854 A˚)34 but is close to the corresponding value in ice Ic (2.75 A˚) and Ih (2.759 A˚), determined at -130 and -90 °C.3e,f The average O 3 3 3 O 3 3 3 O angle is 128.84°, which is larger than the corresponding value of 109.3° in ice Ih. Several 1D zigzag water chains in the solid state have recently been reported.7b,l,11c The average O 3 3 3 O distances in these cases are analogous to that in 2, implying the present 1D loose-string-like water chain has similarly strong interior interactions. In addition, two dangling water molecules (O2w and O7w) as hydrogen bond acceptors are, respectively, bonded to the unshared water molecules O4w and O8w (average dO 3 3 3 O = 2.714 A˚) within the chains in an alternate up-and-down fashion. The whole water chain further connects to carboxylate groups of ip2- dianions through Ow-H 3 3 3 O hydrogen bonds, exhibiting an important role in the stabilization of both the organic species and

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Chart 1. Some Substantial and Imaged Hydration Models for Different Benzenedicarboxylates

the water chain. Thus, a 2D negative charged network {[(ip) 3 7H2O]2-}n is formed by the 1D water chains and the ip2hydrated dianions based on hydrogen bonding interactions (Figure 2, middle). The 2D cationic and anionic layers in 1 and 2 are stacked along the ∼[001] direction, following the alternating -ABABsequence (where A and B represent, for 1, the {[Cu(bpp)2(H2O)2]2þ}n cationic layer and the {[(tp) 3 7H2O]2-}n anionic layer and, for 2, the {[Cu(bpp)2(H2O)]2þ}n cationic layer and the {[(ip) 3 7H2O]2-}n anionic layer, respectively). In other words, those water-anion layered species are occupied in the interlayer spacing between two metallo-organic lamellar networks. Consequently, the overall structure of either 1 or 2 could also be considered as a 2D metallo-supramolecular sandwich lamellar network (Figure S5 and Figure S8). Each anionic layer counterbalances the positive charges of the cationic sheet via extensive hydrogen bonds involving some of the carboxylate oxygen atoms and both the coordination and lattice water molecules. Significant O-H 3 3 3 O hydrogen bonds are observed between each coordinated water molecule and anionic layer, with the former providing hydrogenbond donors and the latter serving as hydrogen-bond acceptors (Table 3). Influence of Dianionic Templates on Arrays of Water Aggregates. The present two complexes give us an impression that the structural diversities of water aggregates seem to be arisen from the different relative orientations of carboxylate groups situated in the aromatic ring. In 1, tp2anion, with an angle θ40 between the two carboxylate groups of 180°, is hydrated by eight water molecules into a tp2- 3 (H2O)8 anion cluster with two equivalent solvation shells (both solvation shells are surrounded by four water molecules on each side of a dicarboxylate group; also see Chart 1, left), which induces other lattice water molecules to aggregate and form the discrete (H2O)14 cluster. However, when the linear-type tp2- groups are replaced by an angular-type ip2- anion, in which the angle θ40 between the two carboxylate groups is turned from 180 to ∼120°, the anionic hydration ip2- 3 (H2O)8, with two unequivalent solvation shells (one big solvation shell surrounded by six water molecules and another small shell encompassed by two waters; Chart 1, middle), is generated, which further makes lattice water molecules aggregate into the 1D water chain. In addition, the arrays of solvation shells seem to be influenced by those numbers and the site of lipo-hydrogen C-H in the aromatic ring besides dicarboxylate groups. Assuming these two factors, either lipo-hydrogen or dicarboxylate group, are certainly responsible for the template effect of benzenedicarboxylate, a similar anionic hydration, op2- 3 (H2O)8 (op2- = ophthalate), in which the angle θ40 between two carboxylate groups

is now greatly reduced to ∼60°, with one bigger solvation shell (Chart 1, right) completely occupied by eight water molecules, should be, therefore, expected. Unfortunately, this anionic hydration, op2- 3 (H2O)8, has not been isolated so far, probably due to the instability for so many as eight water molecules simultaneously aggregated, and we are always dealing with those thermodynamically most stable phases. IR Characterization. The IR spectra of 1 and 2 in the region 4000-400 cm-1, showing the characteristic bands for tp2-, ip2-, and bpp ligands, are given in Figure S1. The IR spectrum of 1 shows a broad band centered at about 3440 cm-1 (3428 cm-1 for 2), indicating the presence of water molecules in the complex. Generally, the IR spectrum of ice shows the O-H stretching at 3220 cm-1, while this stretching vibration in liquid water appears at 3490 cm-1.3e This suggests that the O-H stretching frequency of the water aggregates in 1 (or 2) is similar to that of liquid water, and the slight shift can be attributed to the water environment differences between the cluster and the bulk phase.7h,41 The wellresolved peaks spanning over the region 1617-1571 cm-1 for 1 and 1623-1553 cm-1 for 2 may be assigned to the asymmetric stretching mode of the carboxylate groups, while those in the region 1434-1388 cm-1 for 1 and 1437-1390 cm-1 for 2 are attributed to the symmetric stretching mode of the carboxylate groups.13 The absence of characteristic bands at 1730-1690 cm-1 for the two title complexes indicates the complete deprotonation of the H2tp or H2ip molecules.42 Additionally, the IR spectra also show the bands corresponding to Fr(H2O) (748 and 757 cm-1) and Fw(H2O) (571 and 583 cm-1) for 1 and 2, respectively, indicating the presence of coordinated water molecules.43 These show good agreement with the structures of the title complexes based on the X-ray single crystal analysis. Thermal Stability. To understand the thermal stability of the two title complexes, thermal gravimetric analyses (TGA) are carried out for 1 and 2 between 30 and 800 °C under a nitrogen atmosphere (Figure S9). Probably due to the existence of multiple hydrogen bonds associated with the lattice water molecules in 1 and 2, the initial loss temperature of lattice water molecules is somewhat higher than those without any hydrogen-bonding interactions (generally starts from ca. 50 °C).44 The TGA profile of 1 indicates that the release of all water molecules including coordinated and lattice water molecules at the first step of weight loss occurs in the temperature range 80-110 °C (found, 20.1%; anal. calcd, 20.6%), resulting in the dehydrated form of [Cu(bpp)2(tp)], which is stable up to ∼190 °C, and then from 190 to 300 °C, the structure gradually decomposes, due to the loss of tp2molecules and bpp ligands (found, 68.4%; anal. calcd, 69.2%). Finally, over 300 °C, a CuO is obtained representing the

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remaining mass, 10.9% (calcd, 10.2%). The TGA trace of 2 is rather similar to that of 1 and also shows two steps of weight loss. The first step occurs in the range 70-100 °C, corresponding to the loss of all eight water molecules (found, 18.0%; anal. calcd 18.7%), resulting in the dehydrated forms of [Cu(bpp)2(ip)], which are stable up to ∼195 °C. The second weight loss, 69.8%, is observed in the range 195300 °C, which may be ascribed to the loss of ip2- molecules and bpp ligands (calcd, 70.9%). Upon heating over 300 °C, the final decomposition residue is assumed to the predicted CuO (10.7% vs calcd 10.4%). Electrochemical Properties. In order to get some insight into the redox properties of the two title complexes, the voltammetric behaviors are measured on a PARSTAT 2273 Electrochemical Workstation. For this purpose, 1-CPE and 2-CPE (also see the Experimental Section) are, respectively, fabricated as the working electrode. Figures S10 and S11 give the cyclic voltammetric plots for 1-CPE and 2-CPE, which were carried out in 0.1 M phosphates buffer aqueous solution (pH = 2.5) at a scan rate of 50 mV 3 s-1, respectively, suggesting a quasi-reversible behavior for each in the potential range of (400 mV, which can be attributed to the redox of Cu(II)/Cu(I),45 which is further confirmed by measurement of the scan rate effect on the electrochemical behaviors of 1 and 2 (Figure S12). In addition, the electrocatalytic reduction of nitrite in the same phosphates buffer aqueous solution is also investigated based on 1-CPE (Figure S13). Usually, the electroreduction reaction of nitrite ion almost does not work directly unless employing a large overpotential on the surface of most electrodes, so neither response can be observed at any bare electrode under the normal potential condition.46 The same theme is found for nitrite electroreduction on a bare CPE electrode, as shown in Figure S13. However, comparable to no response on the bare CPE in the range from 400 to -400 mV (Figure S13a), the obvious electroreduction peak of nitrite occurs on on a 1-CPE electrode in the same potential region, with the reduction peak intensifying dramatically vs the corresponding oxidation peak weakening with the addition and increasing concentration of nitrite solution (Figure S13c, d). These suggest that the 1-CPE electrode has a good electrocatalytic activity for the reduction reaction of nitrite. Conclusions In summary, we have successfully constructed two different water morphologies by simply employing tp2- or ip2- species as templates. The present route demonstrates novel examples of the formation of tunable water aggregates, which is very important for providing insight into hydrogen-bonding motifs and understanding better the properties of water clusters of different sizes and shapes in diverse environments. Meanwhile, it should be a robust strategy to control the formation of water clusters in different crystal hosts by using such templates. Moreover, current work exhibits the structural cases of the anion clusters tp2- 3 (H2O)8 and ip2- 3 (H2O)8, which are essential for further understanding the aqueous salvation and molecular recognition phenomena of organic carboxylic anionic systems. Acknowledgment. This work was financially supported by the National Natural Science Foundation of China (Grant No. 50971063), the Natural Science Foundation of Fujian Province (Grant No. 2003F006, 2010J01042), and the Scientific

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Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry of China. The authors are grateful to Mr. Yi Zhang for the assistance with the electrochemical data collection; and G.-G.L. also acknowledges the Startup Package Funding of Huaqiao University (No. 10BS210) for support. Supporting Information Available: Figures S1-S13, including the FT-IR spectra, comparison of observed and calculated PXRD patterns, and views of the building units and the host polymers, as well as the 2D metallo-supramolecular sandwich lamellar networks, TGA traces, and cyclic voltammetric data for 1 and 2; and additional crystallographic data in CIF files (that has also been deposited as CCDC-790590 for 1 and CCDC-790591 for 2 in the Cambridge Crystallographic Data Centre). These materials are available free of charge via the Internet at http://pubs.acs.org.

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