Growth of Copper Pyrazole Complex Templated Phosphomolybdates

Growth of Copper Pyrazole Complex Templated Phosphomolybdates: Supramolecular Interactions Dictate Nucleation of a Crystal Jency Thomas and Arunachalam Ramanan*

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 9 3390–3400

Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India ReceiVed April 4, 2008; ReVised Manuscript ReceiVed June 6, 2008

ABSTRACT: Five copper pyrazole complex based phosphomolybdates are self assembled at room temperature from an aqueous solution containing sodium molybdate, cupric chloride, and pyrazole acidified with phosphoric acid: one-dimensional (1D) chains in [{Cu(pz)(H2O)}{Cu(pz)3(H2O)}{Cu(pz)4}{P2Mo5O23}], 1, copper pyrazole complex intercalated two-dimensional (2D) sheets in {Cu(pz)2(H2O)4}[{Cu(pz)2(H2O)}2{Cu(pz)4}2{HP2Mo5O23}2] · 6H2O, 2, hexadecameric water clusters incorporated between 1D chains in [{Cu(pz)4}3{Cu(pz)3(H2O)}2{HP2Mo5O23}2] · 9H2O, 3, a water-mediated interpenetrated three-dimensional (3D) network in [{Cu(pz)4}2{H2P2Mo5O23}] · H2O, 4, and copper pyrazole complex pillared 2D phosphomolybdate sheets in [{Cu(pz)2}P2Mo2O12(H2O)2], 5. Detailed structural characterization of these solids was established by single crystal and powder X-ray diffraction techniques, FTIR, and thermal analysis. This paper proposes intuitive mechanisms to provide molecular insights into the role of in situ copper pyrazole complexes generated in solution in dictating a particular supramolecular assembly which eventually influences the nucleation of a crystal through a concerted condensation process. The role of the complexes as intercalant, pillaring unit, etc. has been demonstrated by these examples. Introduction Understanding nucleation of a crystal from its reacting molecular units in solution is crucial for engineering materials with desirable properties and function.1 However, rational design of solids is still far fetched. Although nucleation is considered as a self-assembly process, no hypothesis or postulates are being proposed in terms of chemical events that precede the organization of a structure. Factors such as low solubility of heterogeneous reactants in a solvent medium, inability to control pH during the reaction due to hydrolysis of metal and organic amines, redox coupling and complexation between metal and organic moieties complicate the chemistry of formation. Recently, Davey et al.2 have highlighted the necessity to understand the link between molecular assemblies (crystal growth units) found in the liquid phase and their solid state counterparts, the supramolecular synthons3 to understand the nucleation of solids. In this context, the mechanistic approach by Ramanan and Whittingham is significant as it provides chemical insights into self-assembly of solids in terms of supramolecular interactions.4 Phosphomolybdates (PMOs) provide an excellent opportunity to explore these issues as one can tune the architectures from simple cluster based solids to nanostructured materials by a suitable choice of organic amine(s).5–12 A careful analysis of the PMOs synthesized from solution routes suggested the following structural features: (i) Extended PMOs having -Mo-O-P-O-Mo-O- connectivity are invariably obtained under hydrothermal conditions in acidic medium.13 (ii) Occurrence of solids based on well-known PMO cluster anions like fully oxidized {P2MoVI5O23}6-, fully reduced {P4MoV6O31}12-, Keggin cluster {PMoVI12O40}3- and Wells-Dawson cluster {P2MoVI18O68}18- is more facile as compared to extended PMOs * To whom correspondence should be addressed. Fax: 91 11 2658 2277; tel: 91 11 2659 1507; e-mail: [email protected].

Scheme 1. Occurrence of Various Phosphomolybdate Cluster Anions As a Function of pH

under ambient or hydrothermal conditions.5–12,14–20 However, the pH is crucial in dictating the formation of a particular cluster anion (refer to Scheme 1). The cluster anion {P2MoVI5O23}6(henceforth referred as {P2Mo5}) is quite stable over a wide pH range (1-7). Higher pH (4-7) favors {P4MoV6O31} under reducing conditions; Keggin or Wells-Dawson are stable over a narrow pH range but also depend on selected organic cations.14–20 In contrast, long chain amines like dodecylpyridinium chloride favor nanostructural features.12 In our earlier work, we have rationalized the structural features of PMOs crystallized in the presence of several organic

10.1021/cg800344h CCC: $40.75  2008 American Chemical Society Published on Web 07/26/2008

Cu Pyrazole Complex Templated Phosphomolybdates

Crystal Growth & Design, Vol. 8, No. 9, 2008 3391

Scheme 2. Scheme Showing the Experimental Conditions for the Formation of Solids 1-5 with Varying Pyrazole/Copper Ratio and pH

Table 1. Crystal and Refinement Data for Compounds 1-5 1 formula C24H32Cu3Mo5N16O25P2 formula weight, g 1676.95 T (K) 273(2) space group P21/n (no. 14) a, Å 14.751(2) b, Å 21.635(3) c, Å 16.489(2) R, ° β, ° 110.343(3) γ, ° V, Å3 4934.1(11) Z 4 dcalc, g · cm-3 2.257 µMoKR, cm-1 2.658 λ (Å) 0.71073 R1 (I > 2σI), WR2 (all) 0.0576, 0.1015 GOF 1.020 CCDC no. 649358

2

3

4

5

C21H30Cu2.5Mo5N14O29P2 643.105 273(2) P1j (no. 2) 9.187(5) 12.409(7) 22.099(12) 90.640(10) 94.513(10) 95.490(10) 2500(2) 2 2.183 2.420 0.71073 0.0565, 0.1193 1.054 675674

C27H37Cu2.5Mo5N18O32P2 1826.265 298(2) P1j (no. 2) 12.5446(9) 15.4392(12) 15.9536(12) 94.7020(10) 95.5840(10) 100.2570(20) 3010.5(4) 2 2.015 2.026 0.71073 0.0588, 0.1135 1.162 646304

C22H32Cu2Mo5N18O24P2 1595.36 273(2) Pcca (no. 54) 16.1420(10) 13.9222(8) 23.3927(14)

C6H10CuMo2N4O14P2 679.55 273(2) P21/c (no. 14) 6.2556(19) 17.599(5) 7.889(2)

amines.21–23 It was observed that supramolecular synthons between organic and water along with {P2Mo5} resulted in various topologies.23The non-bonding interactions dictated the self-assembly of molecules and in selected cases facilitated the aggregation of water clusters resulting in crystal hydrates.24,25 On the other hand, incorporation of transition metal complexes formed in situ can invariably result in structurally diverse metal complex linked {P2Mo5} cluster based solids of varying dimentionality.26 However, selfassembly of metal complex based PMOs in terms of supramolecular interactions between their molecular units has rarely been investigated. Therefore, our objective was two fold: (i) To understand the nucleation of PMO based solids in terms of interactions between metal amine complexes and molybdenum as well as phosphate precursors in aqueous solution. (ii) To manipulate structures systematically to vary its dimensionality. To achieve our goal of structure-synthesis correlation, the reactivity of cupric ions, pyrazole and

98.994(6) 5257.1(5) 4 2.016 2.099 0.71073 0.0671, 0.1550 1.309 675675

857.8(4) 2 2.631 2.940 0.71073 0.0845, 0.1475 1.384 646192

molybdate species in aqueous solution was investigated under ambient conditions. Since unambiguous ab initio structural characterization of hybrid PMOs in powder form is difficult, invariably the reaction conditions were tuned to obtain suitable single crystals for X-ray diffraction analysis. In all the cases, single phasic nature of the solids was established by powder and single crystal XRD, TGA and FTIR. During the course of our investigation it was observed that pH of the reaction medium and the concentration of reactants were the major structural determinants influencing the self assembly. Five new copper pyrazole complex based PMO solids were isolated Viz. [{Cu(pz)(H2O)}{Cu(pz)3(H2O)}{Cu(pz)4}{P2Mo5O23}], 1, {Cu(pz)2(H2O)4}[{Cu(pz)2(H2O)}2{Cu(pz)4}2{HP 2 Mo 5 O 23 } 2 ] · 6H 2 O, 2, [{Cu(pz) 4 } 3 {Cu(pz) 3 (H 2 O)} 2 {HP2Mo5O23}2] · 7H2O, 3, [{Cu(pz)2(H2O)2}{Cu(pz)4}{H2´ P2Mo5O23}] · H2O, 4 and [{Cu(pz)2}P2Mo2O12(H2O)2], 5. A posteriori analysis of the crystal structures of 1-5 has been interpreted in terms of postulates recently proposed by

3392 Crystal Growth & Design, Vol. 8, No. 9, 2008

Thomas and Ramanan

Figure 1. (a) {P2Mo5} clusters are linked covalently by Cu1 and Cu2 to form 1D chain in 1. (b) View along [101]. (Hydrogens are omitted for clarity in (a) and (b)). (c) H-bonding interactions between the chains result in corrugated sheets. One of the corrugated sheets is shown here. (d) The sheets are stacked parallel to each other through CH · · · π interactions. Supramolecular assembly of such three adjacent sheets is depicted in red, green, and cyan (also refer to Figure S1 in the Supporting Information).

Ramanan and Whittingham.4 Our recent analysis on the growth of copper chloride based organic frameworks suggested that supramolecular aggregation between molecular units is influenced by non-bonding interactions during the initial stages of the reaction.27 Therefore, the growth and nucleation of copper pyrazole based PMOs has been discussed herein by inducing supramolecular interactions prior to crystallization. Experimental Section Synthesis. Initially two different aqueous solutions were prepared for precipitating copper pyrazole based phosphomolybdates. Solution A was prepared from cupric chloride (CuCl2 · 2H2O, 0.2349 g, 1.37 mmol, Merck, 99%) and pyrazole (Acros, 98%) while solution B was 50 mL of aqueous sodium molybdate solution (Na2MoO4 · 2H2O, 1.0 g, 4.13 mmol, Merck, 99%). In all the cases solution B was slowly added

to A with constant stirring for 5-10 min. Immediate precipitation occurred in most of the cases and hence the solution was acidified using 1 M orthophosphoric acid (H3PO4, Merck, 85%) until clear solutions were obtained. In all the cases the same strategy was employed; however, pH > 3 resulted in precipitation of inhomogeneous products. In few cases, pH ∼ 1 was necessary to obtain clear solution as higher pH led to amorphous powder. The resulting blue solutions were left undisturbed for crystallization at room temperature (25°C). It was observed that the formation of the solids was dependent on the pyrazole to copper molar ratio as well as pH of the reaction medium as summarized in Scheme 2. X-ray Structure Determination. X-ray diffraction studies of crystal mounted on a capillary were carried out on a BRUKER AXS SMARTAPEX diffractometer with a CCD area detector (KR ) 0.71073 Å, monochromator: graphite).28 Frames were collected at T ) 293 K by ω, φ and 2θ-rotation at 10 s per frame with SAINT.29 The measured intensities were reduced to F2 and corrected for absorption with SADABS.29 Structure solution, refinement, and data output were carried



Figure 2. (a) The 2D sheets in 2 are stacked parallel to each other and the interlamellar space is occupied by {Cu(pz)2(H2O)4}2+ complexes and water molecules (view along b axis). (b) Two water (O4W and O5W) belonging to copper coordination and three lattice water aggregate into a pentameric water cluster in the hydrophilic pockets of 2.

Figure 3. (a) Packing diagram of 3 showing double chains of {P2Mo5} clusters with water clusters in hydrophilic voids. (b) Figure showing the double chains. (c) Hexadecameric water cluster that occurs in the crystal lattice. out with the SHELXTL program.30 Non-hydrogen atoms were refined anisotropically. C-H hydrogen atoms were placed in geometrically calculated positions by using a riding model. O-H hydrogen atoms were localized by difference Fourier maps and refined in subsequent

refinement cycles. Images were created with the Diamond program.31 Hydrogen bonding interactions in the crystal lattice were calculated with SHELXTL and Diamond.30,31 Crystal and refinement data are summarized in Table 1.


Thomas and Ramanan

Figure 4. Each {P2Mo5} cluster is linked to octahedral {Cu(pz)4O2} complex units that result in 3D framework solid in 4. (a) Two adjacent zig-zag chains in 4 linked by Cu1 (water molecule and hydrogen are omitted for clarity). (b) View along c axis showing the 3D network in 4. (c) Interpenetration of framework (green color) into a second one (cyan color) mediated by water molecule (red color). The pyrazole rings are omitted for clarity.

Figure 5. (a) 2D sheets in 5 (view along b axis) with extended {-Cu-O-Mo-O-} (b) View along a axis showing the packing of sheets through C-H · · · O interactions (shown as blue dashed lines). Other Physical Measurements. FTIR spectra were recorded on KBr pellets using Nicolet 5DX spectrophotometer. TG analysis was carried out using Perkin-Elmer TGA7 system on well ground samples in flowing nitrogen atmosphere with a heating rate of 10 °C/min.

Results and Discussion Crystal Structures of 1-5. The solids 1-4 are based on {P2Mo5} cluster anion while 5 is an extended solid. The cluster anion {P2Mo5} consists of edge and corner sharing MoO6 octahedra forming a Mo5O15 ring capped by two PO4 tetrahedra; the anion is identical to the one found in many solids.32,33 In [{Cu(pz)(H2O)}{Cu(pz)3(H2O)}{Cu(pz)4}{P2Mo5O23}], 1, three sets of copper complexes (represented by three asymmetric copper, Cu1, Cu2 and Cu3) are involved in the structure building. The distorted octahedral {Cu1II(pz)3(H2O)O2} and trigonal bipyramidal {Cu2II(pz)(H2O)O3} complex units covalently link adjacent {P2Mo5} clusters into linear chains along [101]; each cluster is also capped by {Cu3II(pz)4O} square pyramids as shown in Figure 1. The pyrazole groups attached to Cu1 and Cu2 further participate in intra-chain H-bonding interactions with cluster oxygens. The pyrazole

groups linked to Cu3 lead to inter-chain supramolecular interactions (H-bonding between NH and cluster oxygens) leading to corrugated 2D sheets about the ac-plane. This feature in addition to the absence of protonation of the phosphate groups of the {P2Mo5} cluster accounts for the absence of lattice water molecules. The corrugated sheets are stacked parallel to each other through CH · · · π interactions between pyrazole (pz) groups of Cu3 and Cu1 (refer to Figure S1 in the Supporting Information). {Cu(pz)2(H2O)4}[{Cu(pz)2(H2O)}2{Cu(pz)4}2{HP2Mo5O23}2] · 6H2O, 2, is also made of three different copper(II) pyrazole complexes. However, in this structure the octahedral {Cu(pz)4O2} and the trigonal bipyramidal {Cu(pz)2(H2O)O2} link the {P2Mo5} clusters into a 2D sheet. Since the sheet is anionic, a third complex unit, {CuII(pz)2(H2O)4} occurs in between the sheets as counter cation. Intercalation of these complex cations in between the sheets is further stabilized by three lattice water molecules. This arrangement favors a pentameric water cluster between the three lattice water and two belonging to the counter cation {CuII(pz)2(H2O)4} as shown in Figure 2. Unlike 1, one of the two phosphate groups is



Figure 6. Self-assembly in 1 is dictated by various forces operating between molecules reacting in a supramolecular reaction. Aggregation of soluble molybdenum and phosphate anionic/neutral species is driven by the stabilization of the {P2Mo5} cluster (pink). Anionic charge distribution around the cluster anions is neutralized by the presence of appropriate copper pyrazole complex units (blue). While Cu1 and Cu2 link a pair of {P2Mo5} clusters to form 1D chain; Cu3 units functionalize the {P2Mo5} cluster. H-bonding interactions (black dashed lines) facilitate aggregation of the molecular units to form corrugated sheets. The self assembly of adjacent corrugated sheets is further stabilized by CH · · · π interactions as shown above. Two 1D chains involved in CH · · · π interactions between the neighboring corrugated sheets are shown above in red and green. (Also refer to Figure S1 in the Supporting Information.)

protonated.34 Protonation of phosphate groups do favor the occurrence of lattice water molecules.24,25 The 2D sheets in 2 are linked by H-bonding interactions through the {Cu(pz)2(H2O)4} complex. Extensive intrasheet CH · · · π and Hbonding interactions further stabilize the structure (refer to Figure S2 in the Supporting Information). The structure of [{Cu(pz)4}3{Cu(pz)3(H2O)}2{HP2Mo5O23}2] · 7H2O, 3, is built of two types of copper complex units of which one is octahedral {CuII(pz)4O2} and the other is square pyramidal {Cu(pz)3(H2O)O}. The octahedral units {CuII(pz)4O2} covalently link neighboring {P2Mo5} clusters to form 1D chain; two such chains are brought together by a second octahedral {CuII(pz)4O2} unit to form a double chain. Square pyramidal {Cu(pz)3(H2O)O} caps the double chains through oxygen of the phosphate group (Cu(3)-O(PO4) ) 1.934(3) Å). The chains do not extend into 2D sheets as the coordinated water molecules are involved in the formation of a novel hexadecameric water cluster. The O-O distances in the water cluster lie in the range ∼2.6-2.8 Å as shown in Figure 3. Earlier we have observed the role of nonbonding interactions between isomeric phenylenediamines and water are influenced by {P2Mo5} cluster anion resulting in water clusters.24 The occurrence of water clusters does not seem to be accidental as in previous case.24,25 CH · · · π interactions mediated by pyrazole groups of Cu3 results in 2D sheet (refer to Figure S3 in the Supporting Information). [{Cu(pz)4}2(HPO4)2Mo5O15] · H2O, 4, is the first example of a 3D framework consisting of octahedral copper pyrazole

complex based {P2Mo5} containing solid. In 4, {P2Mo5} cluster is linked to four octahedral copper units, {CuII(pz)4O2} of which two asymmetric Cu1 lie at the inversion center and two asymmetric Cu2 fall at the two fold axis. Cu2 covalently connects {P2Mo5} clusters to form zig-zag chains which are further covalently linked by Cu1 (Figure 4). One of the pyrazole rings attached to Cu2 is distorted. Since each {P2Mo5} cluster is linked to two Cu1, the Cu-O-Mo connectivity results in a 3D network (Figure 4). Interestingly two such networks (represented in green and cyan colors) interpenetrate each other mediated by the water molecule. A strong H-bonding occurs between water and OH group of phosphates belonging to two different {P2Mo5} clusters (also refer to Figure S4 in the Supporting Information). Solvent mediated interpenetration is already known in the literature,35 but to the best of our knowledge it has been observed for the first time in a PMO cluster based solid. [{Cu(pz)2}P2Mo2O12(H2O)2], 5, is the first example wherein transition metal amine complex is pillaring a layered phosphomolybdate. MoO5(H2O) units share corners with PO4 tetrahedra to form chains consisting of eight-membered rings. These chains on further corner sharing with {Cu(pz)2O4} octahedra form 2D sheets in the ac plane (Figure 5). Under our experimental conditions we could obtain 5 only in polycrystalline form. However, good crystals of 5 were readily grown under hydrothermal conditions using the same molar ratio of reactants acidified to pH ∼ 1 and heated between 120-180 °C.


Thomas and Ramanan

Figure 7. The self-assembly in 2 is mainly influenced by the strong H-bonding interactions between the {P2Mo5} cluster and copper complexes to form 2D sheets which are stacked parallel one above the other (the molecules shown in red and green represent two sheets perpendicular to the plane of the paper; the copper complex present on the plane of the paper links the sheets mediated by the pentameric water cluster as shown here). The sheets are linked by H-bonding interactions (black dashed lines) through the {Cu(pz)2(H2O)4} complex. (Also refer to Figure S2 in the Supporting Information.)

Chemistry of Formation. Crystal structures of all the solids 1-5 reported here clearly suggest that supramolecular interactions considerably influence their assembly and hence the crystal packing. Rationalization of such network structures involving covalent bonds is difficult to interpret. However, we have made a systematic a´ posteriori analysis in terms of reacting synthons (chemically reasonable molecules) participating in the supramolecular reaction. Under our reaction conditions, the molar ratio of P/Mo apparently does not influence the nature of polyoxo cluster anion, and hence {P2Mo5} dominates in the formation of solids 1-4. In all the reactions, one or more copper pz complex (formed in situ) gets incorporated into the solid suggesting that as soon as pz is the added to the solution, copper pz complex is formed. However, the nature of the complex (ligand to metal ratio) varies depending on the concentration of the reactants (Scheme 2). We have adopted a synthetic protocol to ensure that crystallization from homogenous solution leads to unambiguous analysis of the crystallized solids. In all the reactions, pH control was achieved by acidification with required amounts of H3PO4. It should be remembered that a part of the acid is consumed by the organic base, pz through acid-base reaction resulting in protonated pyrazolium cation. Formation of copper pz complex occurs in a stepwise manner

and at equilibrium the solution may contain more than one type of copper pz complex:

[Cu(H2O)6]2+ T [Cu(H2O)5(pz)]2+ T [Cu(H2O)4(pz)2]2+ T [Cu(H2O)3(pz)3]2+ T [Cu(H2O)2(pz)4]2+ At a controlled pH (for e.g., pH ∼ 3), increasing ligand/metal ratio favor the growth of three different crystals 1-3, respectively. While 4 is exclusively made of the tetra-ligated unit, {Cu(pz)4}, 1 and 2 are made of a combination of mono-, di- or triligated units; 3 contains only a set of tri- and tetra-ligated units. Interestingly, the growth of 4 could be achieved from the filtrate of the reaction which yielded 3. All these results suggest that nucleation of a particular crystal is driven by the aggregation of a limited number of reacting molecules in the supramolecular reaction. The reaction condition with low ligand to metal ratio favors clustering of {P2Mo5} anions which further influences aggregation of copper complex cations, {Cu(pz)m(H2O)n} around it. Hydrolysis of {Cu(pz)m(H2O)n} facilitates the formation of -Mo-O-Cu-O-Mo- and -P-O-Cu-O-Mo- thereby signaling the extended interaction (long range cooperative effect) and hence the crystal packing. Occurrence of the solids 1-4 is therefore obvious.



Figure 8. Self-assembly in 3 is mainly influenced by the strong H-bonding interactions between the double chains mediated by the water cluster. H-bonding interactions between such chains (red and green represent two separate double chains) result in 2D sheet. (Also refer to Figure S3 in Supporting Information.)

Another important feature of the structure building is water aggregation in these solids. Molar ratio of the complex to cluster is the highest in 1 and hence the phosphate groups are not protonated. Here the solid occurs in anhydrous form. In 2 and 3 the clusters are monoprotonated and hence favor water aggregation as observed in previous cases.23,24 2 is a 2D anionic sheet incorporated with copper complex cation and hence the aggregation of water molecules are restricted to pentameric cluster. In 3, the linkage of complex and {P2Mo5} clusters lead to double chains. The availability of interlamellar space between two double chains has possibly led to aggregation of sixteen water molecules. In 4, both phosphate groups of the cluster are protonated. This should favor the incorporation of larger water clusters in the structure. However, interpenetration in 4 mediated by water molecule prevents further inclusion of solvent in the structure. The structure of 5 is unusual. Two factors appear to drive the stability of an extended -Mo-O-P- solid in 5. Increasing amount of P/Mo (more acid neutralizes higher amount of ligand) and the larger amount of organic prevent aggregation of molybdate units. This restricts the condensation between molybdate and phosphate units in a plane with the counter cations (copper complex) pillaring the sheets. The mechanistic approach proposed here in the light of Ramanan and Whittingham’s model4 clearly highlights the role of supramolecular interactions influencing the assembly of these solids

(Figures 6–10). The rationale provided here shows how composition and structure of each solid becomes obvious in terms of chemically reasonable molecular bricks (soluble molecular species such as {P2Mo5}, {Cu(pz)m(H2O)n}, etc). Analyzing the growth and crystal structures in terms of supramolecular synthons and how non-bonding interactions facilitate the supramolecular assembly in the reaction preceding nucleation will provide better insights towards achieving “designed materials”. Vibrational and Thermal Analysis. FTIR spectra of 1-5 showed bands at 650-690, 750-830 and 900-930 cm-1 which can be assigned due to molybdenum oxygen stretching. Bands at 1000-1100, 1400-1420, 1620-1640, and 3100-3400 cm-1 can be attributed to P-O stretching, N-H bending, C-H bending and O-H stretching vibrations respectively. Thermal analysis of 1-5 (Figure 11) indicates thermal stability of the different frameworks. In the case of 1, the first two steps correspond to the loss of pz and water molecules. The third step corresponds to degradation of the phosphomolybdate framework. In 2, the first weight loss ∼5% corresponds to the loss of 10 water molecules and the subsequent weight loss can be accounted for the loss of remaining water and pz molecules. In 3, the water loss occurs significantly at higher temperature (∼200 °C), as water molecules form a hexadecameric water cluster. The first weight loss corresponds to the loss of water and eight pz


Thomas and Ramanan

Figure 9. Self-assembly in 4 is mainly influenced by the strong H-bonding interactions between the {P2Mo5} cluster and copper complexes to form a 3D framework. Interpenetration of framework (green color) into a second one (red color) mediated by water molecule is also shown above (Also refer to Figure S4 in Supporting Information.)

Figure 10. Self-assembly in 5 is mainly influenced by the strong H-bonding interactions. The packing of sheets (two such sheets are shown in red and green) is facilitated by weak CH · · · O interactions.

molecules and the second weight loss corresponds to the loss of remaining pz molecules and degradation of the framework.

The solid 4 shows weight loss in two steps; the water and pz molecules are lost in the first step followed by degradation



Figure 11. TGA curves of 1-5.

of the phosphomolybdate framework. In 5, weight loss occurs in two steps corresponding to the loss of water and pz molecules.

Supporting Information Available: Crystallographic information files (CIF) for 1-5; figures showing weak interactions for 1-4; comparison of simulated and experimental PXRD patterns. This material is available free of charge via the Internet at http://pubs.acs.org.

Conclusions A systematic investigation of structure-synthesis correlation enabled the growth of five copper pyrazole complex based phosphomolybdates of varying dimensionality under self ´ posteriori analysis assembly condition at room temperature. A of the solids reported in this paper is advantageous to rationalize the influence of synthetic variables such as pH, concentration, templating effect of organic molecule, temperature, etc. Molecular aggregation in solution is initially dominated by electrostatic interactions between cations (copper pyrazole complex) and anions (PMO cluster). However, supramolecular interactions dictate the organization of ions such that favorable bonding takes place considering crystal packing effects as well. The occurrence of intercalation, interpenetration, pillaring, and aggregation of water clusters therefore becomes self evident. Crystal engineering will be more meaningful if we consider “chemically reasonable molecules” as building blocks and correctly address the weak interactions. Five copper pyrazole complex based phosphomolybdates are self assembled at room temperature from an aqueous solution containing sodium molybdate, cupric ions and pyrazole acidified with phosphoric acid by varying the pyrazole to copper ratio. Our results suggest that supramolecular interactions between in situ copper pyrazole complexes generated in solution and phosphomolybdate clusters dictate the nucleation of a particular crystal. Acknowledgment. J.T. thanks Honeywell International India Private Limited for a research fellowship and A.R. acknowledges DST, Government of India, for financial support as well as for powder X-ray diffractometer under IRHPA and a single crystal diffractometer under FIST to the Department of Chemistry, IIT Delhi, India. Dr. Shailesh Upreti, Binghamton University, is acknowledged for structure solution of 4.

References (1) (a) Braga, D.; Grepioni, F. Chem. Commun. 1996, 571–598. (b) Braga, D.; Brammer, L.; Champness, N. R. CrystEngComm 2005, 7, 1–19. (2) Davey, R. J.; Allen, K.; Blagden, N.; Cross, W. I.; Lieberman, H. F.; Qualye, M. J.; Righini, S.; Seton, L.; Tiddy, G. J. T. CrystEngComm 2002, 4, 257–264. (3) Desiraju, G. R. Angew. Chem. Int. Ed. 1995, 34, 2311–2327. (4) Ramanan, A.; Whittingham, M. S. Cryst. Growth Des. 2006, 6, 2419– 2421. (5) Yue, S. M.; Yan, L. K.; Su, Z. M.; Li, G. H.; Chen, Y. G.; Ma, J. F.; Xu, H. B.; Zhang, H. J. J. Coord. Chem. 2004, 57, 123–132. (6) Vitoria, P.; Ugalde, M.; Gutierrez-Zorrilla, J. M.; Roman, P.; Luque, A.; San Felices, L.; Garcia-Tojal, J. New J. Chem. 2003, 27, 399– 408. (7) You, W.; Wang, E.; Xu, Y.; Li, Y.; Xu, L.; Hu, C. Inorg. Chem. 2001, 40, 5468–5471. (8) Kurmoo, M.; Bonamico, M.; Bellitto, C.; Fares, V.; Federici, F.; Guionneau, P.; Ducasse, L.; Kitagawa, H.; Day, P. AdV. Mater. 1998, 10, 545–550. (9) Gamelas, J. A. F.; Santos, F. M.; Felix, V.; Cavaleiro, A. M. V.; De Matos Gomes, E.; Belsley, M.; Drew, M. G. B. Dalton Trans. 2006, 1197–1203. (10) (a) Li, Y.; Hao, N.; Wang, E.; Yuan, M.; Hu, C.; Hu, N.; Jia, H. Inorg. Chem. 2003, 42, 2729–2735. (b) Wang, S.; Wang, E.; Hou, Y.; Li, Y.; Wang, L.; Yuan, M.; Hu, C. Trans. Metal Chem. 2003, 28, 616– 620. (11) Kortz, U. Inorg. Chem. 2000, 39, 625–626. (12) Thomas, J.; Kannan, K. R.; Ramanan, A. Submitted to J. Chem. Sci. (13) (a) Mundi, L. A.; Haushalter, R. C. Inorg. Chem. 1990, 29, 2879– 2881. (b) Mundi, L. A.; Strohmaier, K. G.; Haushalter, R. C. Inorg. Chem. 1991, 30, 153–154. (c) Mundi, L. A.; Haushalter, R. C. J. Am. Chem. Soc. 1991, 113, 6340–6341. (d) Lu, J.; Xu, Y.; Goh, N. K.; Chia, L. S. Chem. Commun. 1998, 1709–1710. (e) du Peloux, C.; Mialane, P.; Dolbecq, A.; Marrot, J.; Rivie`re, E.; Se´cheresse, F. J. Mater. Chem. 2001, 11, 3392–3396. (14) Lu, J.; Xu, Y.; Goh, N. K.; Chia, L. S. Chem. Commun. 1998, 2733– 2734. (15) (a) Burkholder, E.; Zubieta, J. Chem. Commun. 2001, 2056–2057. (b) Burkholder, E.; Golub, V.; O’Connor, C. J.; Zubieta, J. Inorg. Chem. 2003, 42, 6729–6740.

3400 Crystal Growth & Design, Vol. 8, No. 9, 2008 (16) Weng, J.; Hong, M.; Liang, Y.; Shi, Q.; Cao, R. Dalton Trans. 2002, 289–290. (17) Knaust, J. M.; Inman, C.; Keller, S. W. Chem. Commun. 2004, 492– 493. (18) (a) Lu, Y.; Li, Y.; Wang, E.; Lu¨, J.; Xu, L.; Cle´rac, R. Eur. J. Inorg. Chem. 2005, 1239–1244. (b) Lu, Y.; Xu, Y.; Wang, E.; Lu¨, J.; Hu, C.; Xu, L. Cryst. Growth Des. 2005, 5, 257–260. (19) (a) Kong, X.-J.; Ren, Y.-P.; Zheng, P.-Q.; Long, Y.-X.; Long, L.-S.; Huang, R.-B.; Zheng, L.-S. Inorg. Chem. 2006, 45, 4016–4023. (b) Ren, Y.-P.; Kong, X.-J.; Hu, X.-Y.; Sun, M.; Long, L.-S.; Huang, R.-B.; Zheng, L.-S. Inorg. Chem. 2006, 45, 10702–10711. (20) (a) Mundi, L. A.; Haushalter, R. C. Inorg. Chem. 1992, 31, 3050– 3053. (b) Haushalter, R. C.; Mundi, L. A. Chem. Mater. 1992, 4, 31– 48. (c) Mundi, L. A.; Haushalter, R. C. Inorg. Chem. 1993, 32, 1579– 1586. (d) Lightfoot, Ph.; Masson, D. Acta Crystallogr. 1996, C52, 1077–1080. (e) Guesdon, A.; Borel, M. M.; Leclaire, A.; Raveau, B. Chem. Eur. J. 1997, 11, 1797–1800. (f) Leclaire, A.; Guesdon, A.; Berrah, F.; Borel, M. M.; Raveau, B. J. Solid State Chem. 1999, 145, 291–301. (21) (a) Duraisamy, T. Ph.D Thesis, Indian Institute of Technology, Delhi, India, 1999. (b) Asnani, M. Ph.D Thesis, Indian Institute of Technology, Delhi, India, 2006. (c) Upreti, S. Ph.D Thesis, Indian Institute of Technology, Delhi, India, 2008. (22) Upreti, S.; Ramanan, A. Acta Crystallogr. 2005, E61, m414–m416. (23) Upreti, S.; Ramanan, A. Cryst. Growth Des. 2006, 6, 2066–2071.

Thomas and Ramanan (24) Upreti, S.; Ramanan, A. Cryst. Growth Des. 2007, 7, 966–971. (25) Upreti, S.; Ramanan, A. Syn. React. Inorg., Metal-Org., Nano-Metal Chem. 2008, 38, 69–75. (26) (a) Lu, Y.; Wang, E.; Xu, X.; Ma, Y. J. Coord. Chem. 2007, 60, 53– 60. (b) Bo, Q. B.; Sun, Z. X.; Sun, G. X.; Zhang, Z. W.; Chen, C. L.; Li, Y. X. J. Coord. Chem. 2007, 60, 275–283. (27) Thomas, J.; Ramanan, A. Curr. Sci. 2007, 93, 1664–1667. (28) Bruker Analytical X-ray Systems, SMART: Bruker Molecular Analysis Research Tool, Version 5.618; Bruker AXS: Madison, WI2000. (29) Bruker Analytical X-ray Systems, SAINT-NT, Version 6.04, Bruker AXS: Madison, WI2001. (30) Bruker Analytical X-ray Systems, SHELXTL-NT, Version 6.10; Bruker AXS: Madison, WI2000. (31) Klaus, B. DIAMOND, Version 1.2c; University of Bonn: Germany, 1999. (32) Lowe, M. P.; Lockhart, J. C.; Clegg, W.; Fraser, K. A. Angew. Chem., Int. Ed. 1994, 33, 451–454. (33) Zhang, X. M.; Fang, R. Q.; Wu, H. S.; Ng, S. W. Acta Crystallogr. 2004, E60, m171–m173. (34) Brown, I. D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244–247. (35) (a) Batten, S. R. CrystEngComm 2001, 18, 1–17. (b) Manna, S. C.; Okamoto, K.; Zangrando, E.; Chaudhuri, N. R. CrystEngComm 2007, 9, 199–202.

CG800344H

Growth of Copper Pyrazole Complex Templated Phosphomolybdates

Recommend Documents