Coordination Polymers Formed by the Mono- and Dinuclear Cu(II

Article pubs.acs.org/crystal

Coordination Polymers Formed by the Mono- and Dinuclear Cu(II) Complexes of 1,1′-Methylene/thio-bis(2-naphthoxy) Acetic Acid Garima Singh Baghel,† Jugun Prakash Chinta,† Abdellah Kaiba,‡ Phillippe Guionneau,‡ and Chebrolu P. Rao*,† †

Bioinorganic Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai − 400 076, India CNRS, Université de Bordeaux, ICMCB, 87 Av. Doc. A. Schweitzer, F-33608 Pessac, France

‡

S Supporting Information *

ABSTRACT: A series of five new Cu2+ coordination polymers, namely, {[CuL C H 2 (DMF)](DMF)} n (1), {[CuLCH2(DMF)(2,2′-bipy)](CH3OH)}n (2), {[CuLCH2(2,2′bipy)](2H2O)}n (3), {[CuLCH2(H2O)(2,2′-bipy)](2H2O)}n (5), {[Cu2(LS)2(DMF)2](DMF)(CH3OH)(2H2O)}n (6), and three discrete coordination complexes {[Cu2LCH2(2,2′bipy)2(CH3O)](ClO4)(CH3OH)} (4), {[CuLS(2,2′bipy)](CH3OH)} (7), and {[CuLS(1,10-phen)](DMF)} (8) have been prepared by the reaction of Cu(ClO4)2·6H2O and 1,1′methylene-bis(2-naphthoxy acetic acid) (LCH2) or 1,1′-thiobis(2-naphthoxy acetic acid) (LS), with or without the presence of 2,2′-bipyridine, under varying reaction conditions or methods of crystallization or both. All the compounds were characterized by elemental analysis, IR, thermogravimetric analysis, and single crystal X-ray diffraction (XRD). The structures of LCH2 and LS obtained by single crystal XRD indicated antiorientation of the pendant arms which upon metal complexation may turn into cis- orientation leading to discrete metal ion complexes or may remain in antiorientation leading to extended multidimensional co-ordination polymers. The complexation with Cu2+ led to five different coordination spheres which in turn resulted in five different lattice structures. Thus, the present paper demonstrates the design of coordination polymers that are rich with mononuclear as well as dinuclear Cu2+ centers wherein LCH2 or LS coordinates in a monodentate as well as a bridging fashion leading to the formation of one-dimensional curving, helical, and two-dimensional networks.

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INTRODUCTION Coordination polymers are of current interest not only because of their coordination behavior but also because of their potential application as functional solid materials, viz., as ion exchangers,1−3 as catalysts,4−6 and as important materials of use in opto-electonics7,8 and magnetic devices.9−21 In some cases, the property has been dictated not only by the metal ion present in it but also by the dimensionality of the polymer formed. Therefore, the design of coordination polymers indeed demands organic molecular frameworks possessing chemical functionalities that would terminally chelate as well as bridge the metal ions. The choice of metal ions is of utmost importance in designing the directionality of the resulting polymer, because this depends upon the coordination preference of the corresponding metal ion.22,23 Further, with the use of spacer molecules, it is possible to control the distance between the repetitive units.24−36 Molecules possessing −COOH moieties as well as those possessing other groups (such as phenolic-OH, -SH, etc.) in conjunction with −COOH have proven to be potential systems to result in a variety of coordination polymers. Di- (1,4-), tri (1,3,5-), and tetra (1,2,4,5-) carboxylic derivatives of benzene have been studied © 2012 American Chemical Society

extensively to demonstrate the high dimensional structures formed with Cu(II), Zn (II), Mn(II), Ni(II), Cd(II), La (III), Pr (III), and Nd(III).37−46 Therefore, the present paper demonstrates the design of interesting coordination polymers that are rich with dinuclear Cu(II) centers wherein Cu···Cu distances vary widely, using 1,1′-methylene-bis(2-naphthoxy acetic acid) (LCH2) and 1,1′-thio-bis(2-naphthoxy acetic acid) (LS) that possess -COOH moieties on the pendants of naphthalene units.

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RESULTS AND DISCUSSION Organic Multidentate Ligands (LCH2 and LS). The dicarboxylic derivatives, viz., 1,1′-methylene-bis(2-naphthoxy acetic acid) (LCH2) and 1,1′-thio-bis(2-naphthoxy acetic acid) (LS), have been synthesized starting from the corresponding precursor molecules 1,1′-methylene-bis(2-naphthol) (mbn) and 1,1′-thio-bis(2-naphthol) (tbn) as reported by us earlier.47 The crystallographic parameters for both the ligands and their Received: October 14, 2011 Revised: January 2, 2012 Published: January 3, 2012 914

dx.doi.org/10.1021/cg2013683 | Cryst. Growth Des. 2012, 12, 914−926

Crystal Growth & Design

Article

Table 1. Crystal and Experimental Data for (LCH2) and Cu(II) Complexes from 1 to 5 T (K) molecular formula mol wt crystal system space group Z-formula a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 ρcalcd, g cm−3 μ, mm−1 total reflections unique reflections Rint refined parameters goodness of fit (F2) wR2obs Robs

LCH2

1

2

3

4

5

150 C29 H26 O8 S2 566.62 triclinic P1̅ 2 9.4892(2) 12.7294(3) 12.9882(5) 70.593(12) 75.330(13) 83.063(12) 1430.3(3) 1.316 0.234 11931 9728 0.0229 381 1.002 0.108 0.041

150 C31H31CuN2O8 623.12 monoclinic P21/n 4 10.372(2) 12.019(1) 23.490(3)

150 C39H37CuN3O8 739.26 orthorhombic Pbca 8 19.401(5) 18.677(5) 19.423(5)

150 C35H28CuN2O8 668.16 orthorhombic Pbca 8 18.363(3) 17.628(2) 19.958(3)

150 C35H28CuN2O7 2(H2O) 688.18 orthorhombic Pbca 8 11.359(2) 18.258(2) 29.443(5)

7034.2(3) 1.396 0.679 51481 7116 0.030 462 1.11 0.1387 0.0497

6460.5(2) 1.357 0.728 52832 7381 0.057 430 1.14 0.1309 0.0433

150 C47H37ClCu2N4O12 1012.34 triclinic P1̅ 2 11.601(1) 13.791(1) 14.645(1) 95.539(2) 111.645(4) 93.578(2) 2155.6(1) 1.560 1.120 17718 7543 0.039 596 1.03 0.170 0.062

100.44(1) 2879.8(6) 1.437 0.831 20587 5817 0.108 392 1.02 0.133 0.057

6106.3(16) 1.497 0.777 47046 6984 0.067 451 1.02 0.0888 0.0348

Table 2. Crystal and Experimental Data for (LS) and Cu(II) Complexes from 6 to 8 T (K) molecular formula mol wt crystal system space group Z-formula a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 ρcalcd, g cm−3 μ, mm−1 total reflections unique reflections Rint refined parameters goodness of fit (F2) wR2obs Robs

LS

6

7

8

150 C24H18O6S 434.44 triclinic P1̅ 2 4.7783(3) 10.1163(8) 22.1832(6) 78.920(8) 83.82 76.34 1020.36(11) 1.414 0.199 6918 3578 0.0239 288 0.838 0.0771 0.0349

150 C31H31CuN2O8S 668.16 monoclinic P21 2 12.996(1) 13.425(1) 18.890(1)

150 C35H26CuN2O7S 682.18 triclinic P1̅ 2 11.106(3) 11.440(6) 12.139(5) 97.86(4) 91.17(3) 105.16(3) 1472.0(10) 1.437 0.869 11358 5125 0.2073 423 0.906 0.2519 0.1050

150 C72H50Cu2N4O12S2,2(C3H7NO) 1500.59 triclinic P1̅ 2 11.392(1) 12.780(2) 12.779(2) 63.890(10) 83.853(2) 79.596(2) 1642.4(4) 1.517 0.787 10434 6650 0.043 460 1.02 0.1288 0.0485

95.79(1) 3279.0(4) 1.260 0.776 27940 14931 0.047 722 1.14 0.1271 0.0508

copper complexes are given in Tables 1 and 2. Both LCH2 and LS crystallize in the triclinic system with space group P1̅, and the structures clearly show that the two pendant arms are oriented away from each other and these are given as their ORTEP diagrams in Figure 1. The distances (in Å) observed between the corresponding atoms of the two pendants, viz., O1···O4/O3···O4 = 5.490/4.503, C2···C24/C2···C23 = 8.273/ 6.464, C1···C25/C1···C24 = 9.795/9.169, O3···O6/O1···O6 = 8.974/9.764, and O2···O5/O2···O5 = 12.373/10.960 in the case of L CH2/LS, are all indicative of “staggered-like” conformation of the two pendants with respect to the naphthyl moieties, though the atom-to-atom interarm distances differ in

both cases. On the other hand, if the two pendants were on the same side, the O1···O4/O3···O4 distance is expected to be around 3 Å. Thus, the overall molecule is folded into a bowl shape wherein the two pendant arms are disposed anti- to each other as can be seen from the stereoviews given in Figure 1. In the crystal lattice of LCH2 (Figure 2a), each unit is connected through intermolecular H bonds between the neighbor −COOH moieties resulting in a linear supramolecular network. These linear chains are further extended into complicated three-dimensional (3-D) lattice structures through the involvement of two DMSO solvent molecules present in the lattice, whereas in the lattice of LS (Figure 2b), each 915



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Figure 1. Stereoview of the molecular structure showing 50% ellipsoids: (a) LCH2 and (b) LS. Hydrogens are not shown for clarity.

Figure 2. Lattice structures: (a) LCH2 viewed along the perpendicular to the b-axis and (b) LS viewed along a slightly rotated a-axis.

−COOH moiety is involved in an intermolecular hydrogen bond with the adjacent carboxylic group and thus leads to the formation of a one-dimensional (1-D) chain which is further extended into two dimensions through −C−H···O hydrogen bonds, wherein the −C−H is drawn from the naphthyl moiety and the ‘O’ is drawn from the carboxylate moiety. Synthesis and Characterization of the Copper Complexes. A number of Cu(II) complexes, dominant with the dinuclear centers, have been synthesized both from LCH2 as well as from LS simply by varying the reaction conditions (Scheme 1). The reaction of LCH2 with 1 equiv of copper perchlorate gives product 1. When such a reaction is being carried out along with 1 equiv of 2,2′-bipyridine in DMF, it yielded 2. The same occurred when carried out in wet DMF: it resulted in 5. Compounds 2 and 5 were also obtained directly from 1. The reaction of 1 with 2,2′-bipyridine gives product 3. When the solution of 2 was layered with 2,2′-bipyridine for a longer period, 3 was obtained. The reaction of LCH2 with 2 equiv each of copper perchlorate and 2 equiv of 2,2′-bipyridine in DMF-MeOH resulted in crystals of 4 directly. Crystals of 4 were obtained when the reaction mixture of 3 was diffused with CH3OH and was left in the refrigerator; complexes 6−8 were synthesized through the reaction of LS with copper perchlorate followed by the addition of amines (2,2′-bipyridine or 1,10phenonthroline) in a 1:1:1 mol ratio (Scheme 1). While compounds 1−5 possess LCH2 (the methylene bridged one), those of 6−8 possess LS (-S- bridged). The spectral and analytical characterizations as well as the structural details of all these complexes were discussed in this paper. FTIR. IR spectra of the complexes showed both the asymmetric (1620−1670 cm−1) and symmetric (∼1590, ∼1470, and ∼1460, ∼1430, and 1400 cm−1) stretching bands

of carboxylate moieties. The difference in the {υasym(COO) − υsym(COO)} clearly indicate the presence of bridging (160−180 cm−1) and monodentate coordination modes (240−260 cm−1) of the −CO2− groups. This is consistent with the structures established and reported in this paper. The absence of the expected vibration at 1690−1730 cm−1 for the protonated carboxylate groups indicates the complete deprotonation of all the carboxylate groups of LCH2/LS in 1−8. Absorption and Emission Spectra. The absorption spectra of the complexes showed characteristic differences from that of the corresponding ligand by exhibiting ligand to metal charge transfer (LMCT) in the range 300−500 nm and d → d transition bands around 500−800 nm (Figure 3). Only minor variations were observed in the appearance of the absorption bands among the different complexes as can be seen from Figure 3. Both LCH2 and LS showed good fluorescence in their unbound states with λmax ∼ 360 and 382 nm, respectively, upon exciting the samples at 280 nm. However, the fluorescence was quenched in their Cu(II) complexes suggesting the presence of paramagnetic species bound to the organic molecular framework (Supporting Information SI 01). Thermogravimetry. The thermogravimetric analyses were performed in the temperature range 30−1000 °C under N2 atmosphere (Supporting Information SI 02). The weight loss behavior of LCH2 can be broken into three parts, viz., 80−270 °C (∼12%), 270−430 °C (∼41%), and 430−900 °C (∼11%), and above 1000 °C no residual mass was found to be left out. In the case of LS, about 80% weight loss was observed within 400 °C. However, the copper complexes exhibited a different nature of weight loss pattern, and the temperatures at which the corresponding loss occurs is high in these complexes. The first weight loss observed in the temperature range 30−160 °C 916



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Scheme 1. Reaction Schemea

(a) 1:1 equiv LCH2/LS and Cu(ClO4)2·6H2O, DMF, rt, 6 h; (b) 1:1:1 equiv LCH2, Cu(ClO4)2·6H2O and 2,2′ bipy (shown as N∪N) DMF, rt, 6 h; (c) 1:1:1 equiv LCH2, Cu(ClO4)2·6H2O and 2,2′ bipy, DMF, 70 °C, 24 h; (d) 1:2:2 equiv LCH2, Cu(ClO4)2·6H2O and 2,2′ bipy, DMF-methanol, 70 °C, 24 h; (e) 1:1 equiv Cu(ClO4)2·6H2O and 2,2′ bipy, DMF (wet), rt, 6 h; (f) solution of 1 was layered with 2,2′ bipy in DMF; (g) solution of 2 was left in refrigerator for long period, (h) 3 was diffused with CH3OH and kept in refrigerator for long period; (i) for 1 → 5, solution of 1 was layered with 2,2′ bipy in wet DMF; (j) for 7, 1:1:1 equiv LS, Cu(ClO4)2.6H2O and 2,2′-bipyridine, DMF, rt, 24 h; (k) for 8, 1:1:1 equiv LS, Cu(ClO4)2·6H2O and 1,10-phenanthroline, DMF, rt, 24 h. a

Figure 3. Diffuse reflectance UV−Visible spectra (DRUV): (a) (i) LCH2, (ii) 1, (iii) 2, (iv) 3, (v) 4 and (vi) 5. (b) (i) LS, (ii) 6, (iii) 7, and (iv) 8.

corresponds to the loss of lattice, uncoordinated and coordinated solvent molecules. The decomposition of the coordinated ligands seems to take place in the temperature range 160−1000 °C leading to the formation of the inorganic residue. The corresponding data for the ligands and the complexes are being given in Table 3. All the complexes

exhibited high residual mass as compared to the ligand as expected owing to the formation of the corresponding inorganic residues indicating a higher temperature is needed for their decomposition. Crystal Structures of Copper Complexes. Structures of 1, {[CuLCH2(DMF)](DMF)}n and 6, {[Cu2(LS)2(DMF)2](DMF)917



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Table 3. Thermogravimetric Data for LCH2 and LS and Their Copper Complexes compound

temperature in °C (% wt loss)

LCH2 LS 1 2 3 4 5 6 7 8

80−270(12); 270−430(41); 430−900(11); >1000 (no residual mass) 30−400(84); 400−1000(6); >1000(10) 30−145(10); 145−250(20); 250−400(32); 400−1000(14); >1000(24) 30−145(10); 145−250(20); 250−400(32); 400−1000(10); >1000(28) 30−165(07); 165−400(62); 400−1000(08); >1000(23) 30−165(02); 165−270(16); 270−490(26); 490−1000(12); >1000(44) 30−90(08); 90−200(14); 200−400(38); 400−550(05); 550−1000(10); 1000(25) 30−160(12); 160−210(10); 210−300(53); 300−1000(20); >1000(05) 30−90(14); 90−400(52);400−1000(10); >1000(24) 30−217(12); 217−400(55); 490−1000(08); >1000(25)

Figure 4. (a) Single crystal XRD structure of 1 showing thermal ellipsoid plot using ORTEP. Hydrogens are not shown for clarity except for DMF. (b) Crystal packing in 1 along a slightly rotated a-axis.

Figure 5. (a) Single crystal XRD structure of 6 showing a thermal ellipsoid plot using ORTEP. Hydrogens are not shown for clarity except for DMF. (b) Crystal packing in 6.

(CH3OH)(2H2O)}n. Complex 1 crystallizes in monoclinic with space group P21/n and exhibits asymmetric unit formula of {[CuLCH2(DMF)](DMF)}, resulting in the formation of dinuclear Cu(II) complex centers as can be seen from Figure 4a wherein the two coppers are related through the center of symmetry with a Cu···Cu distance of 2.64 Ǻ. The di-Cu(II) center is bridged through four carboxylate moieties coming from four different LCH2’s. The second carboxylate moiety of each of these LCH2’s is involved in further bridging another neighbor di-Cu(II) center, thus extending the connectivity between the dinuclear-Cu(II) complex units via LCH2’s into the

lattice in a two-dimensional (2-D) manner (Figure 4b), wherein the effective Cu(II) to LCH2 ratio is 1:1. Thus in 1, each Cu(II) center is coordinated through four carboxylate-oxygens arising from four different LCH2’s and a DMF oxygen, resulting in a five-coordinated species that extends to an octahedral when Cu···Cu interaction is being considered. Thus, in the octahedral geometry at each of the Cu(II) centers the trans angles are in the range of 168.2− 175.3° with equatorial Cu−O distances being in the range 1.956−1.995 and axial Cu−O being 2.116 Å and Cu···Cu being 2.647 Å, suggesting a tetragonal distortion at the Cu(II) 918



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Figure 6. (a) Single crystal XRD structure of 2 showing thermal ellipsoid plot using ORTEP. Hydrogens are not shown for clarity except for DMF. (b) Crystal packing for 2 viewed along the b-axis.

Figure 7. (a) Single crystal XRD structure of 5 showing thermal ellipsoid plot using ORTEP. Hydrogens are not shown for clarity except for water. (b) Crystal packing for 5.

methanol, and water, are present in the lattice in the spaces formed from the aggregation of chains (Figure 5b). The data for the hydrogen bonds present in the lattice are given in Supporting Information SI 03. Structure of 2, {[CuLCH2(DMF)(2,2′ bipy)](CH3OH)}n and {[CuLCH2(H2O)(2,2′bipy)](2H2O)}n, 5. Complex 2 crystallizes in orthorhombic with space group Pbca and exhibits asymmetric unit formula of {[CuLCH2(DMF)(2,2′bipy)](CH3OH). The molecular structure of 2 (Figure 6a) exhibited a five coordinated N2O3 binding core about Cu(II) leading to a square pyramidal geometry wherein the oxygen of DMF is bound in the apical position. The Cu(II) center is surrounded by two LCH2 units, wherein each LCH2 extends a coordination through one of its carboxylate moieties as monodentate in addition to the bidentate binding of 2,2′-bipy, and the fifth coordination is through DMF oxygen. The carboxylate moiety of the second arm of each LCH2 is bonded to a neighbor Cu(II) thus extending a 1-D linear chain owing to the transoidal orientation of the two arms of LCH2 (Figure 6b). The metric data corresponding to the coordination sphere are given in Supporting Information SI 17 and 18. Though the observed bond lengths and bond angles are normal with the organic moiety, the coordination sphere exhibited distorted square pyramidal geometry. Further the geometry can also be

centers. In 1, each LCH2 is tetradentate and dinegative resulting in a neutral complex species. The polymeric formation of the dinuclear centers has been facilitated by the transoidal orientation of LCH2 wherein the two carboxylate moieties are oriented in opposite directions with a Ccarboxy···Ccarboxy distance of 9.8 Å, a distance that has also been noticed in simple LCH2. Metric data corresponding to the coordination sphere are given in Supporting Information SI 17 and 18. The bond lengths and bond angles observed for the organic moiety were found to be normal. In the lattice of 1, each dinuclear Cu(II) center is surrounded by six other dinuclear centers as primary shell, wherein four of these are at a distance of 12 Å and two are at a distance of 13.4 Å with respect to the central one, forming a hexagon, indicating the 2-D sheet structure that is extended through the lattice (Figure 4b). When the layers were added along the a-axis, other neighbors were found to be at a distance of 7.9 Å as can be seen from Figure 4b. The DMF molecules are included as a solvent in the structure and are positioned between the sheets and form short C−H···O contacts with oxygen atoms of the coordination sphere (3.453 Å and 141°). Even the 6 that was formed from S-bridged LS ligands exhibited the same structure (Figure 5a) as that observed for 1, except that in the case of 6, the solvent molecules, viz., DMF, 919



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Figure 8. (a) Single crystal XRD structure of 3 showing a thermal ellipsoid plot using ORTEP. Hydrogens are not shown for clarity. (b) Crystal packing for 3.

Figure 9. (a) Single crystal XRD structure of 4 showing a thermal ellipsoid plot using ORTEP. Hydrogen atoms except for methanol and perchlorate anion are not shown for clarity. (b) Crystal packing for 4 viewed along the a-axis. The perchlorate moieties are found in the channel.

an asymmetric unit formula of [CuLCH2(2,2′ bipy)] (2H2O). The Cu(II) center is five coordinated with N2O3 core like that observed for 2, where the apical position is filled by CO of a carboxylate moiety rather than DMF, with a Cu···O distance of 2.308 Å (Figure 8a). Certainly this distance is much longer than a covalent bond but within the van der Waal radii. In each LCH2, one of the carboxylate moieties acts as bidentate bridged between two Cu(II) centers and the other one is bonded to only one Cu(II) as monodentate. The Cu(II)···Cu(II) distance is 4.4 Å, which is too far to exhibit any inter metal ion interaction. Thus in 3, the Cu(II) dinuclear centers are noninteracting and hence are different from that observed in 1. The corresponding Cu(II) dinuclear centers are further connected to result in a 2-D lattice. In 3, unlike complex 1, LCH2 bridges simultaneously with three Cu(II) centers. The carboxylato-group exhibits its classical syn−syn bridging mode forming pairs of copper centers connected through two ligands of LCH2. These pairs are further interconnected through LCH2, each of which is coordinated to the apical and two of the basal positions of the copper ion from an adjacent pair. This particular coordination type of the LCH2 leads to a 2-D polymer running along the crystallographic bc-plane (Figure 8b). The polymer exhibits the shortest intrasheet Cu···Cu distance of 4.4 Å and a long intersheet Cu···Cu distance of 11.3 Å. The solvent

considered as distorted octahedral with one vacancy. In the lattice of 2, each Cu(II) is surrounded by six other Cu(II) centers in the form of a hexagon in the distance range of 9.9− 11.6 Å as a primary shell as also observed in case of 1 and 6. However, there are 12 other Cu(II) centers with respect to the central one in its second shell in a distance range of 16.7−21.8 Å. The sheet type polymers formed in the lattice are found parallel to each other with the shortest intrasheet Cu···Cu distance being 10.4 Å, and the distance between Cu centers of neighboring sheets is relatively short. The solvent methanol molecules are positioned in the lattice in between the sheets and form short C−H···O contacts with oxygen atoms present in the co-ordination sphere. The structure of 5 is similar to that of 2; however, the apical DMF present in 2 is replaced by a water molecule in 5 with a Cu(1)−O(1)water distance of 2.274 Å (Figure 7a). Similar to 2, the LCH2 bridges simultaneously with two copper(II) centers leading to a 1-D polymer even in 5 (Figure 7b). In 5, the shortest intrasheet Cu···Cu distances are 9.3 and 9.7 Å, and the shortest distances between Cu centers of the neighboring sheets are 7.7 and 15.6 Å. The water molecules present in the lattice interacts with the chain through hydrogen bonding. Structure of {[CuLCH2(2,2′ bipy)] (2H2O)}n, 3. Complex 3 crystallizes in orthorhombic with space group Pbca and exhibits 920



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Figure 10. (a) Single crystal XRD structure of 7 showing a thermal ellipsoid plot using ORTEP. Hydrogens are not shown for clarity. (b) Crystal packing in 7.

Figure 11. (a) Single crystal XRD structure of 8 showing a thermal ellipsoid plot using ORTEP. Hydrogens are not shown for clarity. (b) Crystal packing in 8.

perpendicular. Every other macrocycle in the crystal lattice lie essentially in parallel to the bc-plane to afford open channels that are occupied by perchlorate and methoxide guest species (Figure 9b). In each pair, two of the bipy moieties are oriented toward the interior and the other two are toward the exterior. Structures of 7, {[CuL S (2,2′bipy)](CH 3 OH)} and 8, {[CuLS(1,10-Phen)](DMF)}. Complex 7 crystallizes in triclinic with space group P1̅ and exhibits an asymmetric unit formula of {[CuLS(2,2′-bipy)](CH3OH)}, resulting in the formation of discrete dinuclear Cu2+ complex centers as can be seen from Figure 10 wherein the two coppers are related by a center of symmetry with a Cu···Cu distance of 4.711 Å. The two Cu(II) centers of the dinuclear units are bridged through two carboxylate moieties coming from two different LS’s. The structure exhibited a N2O3 binding core where LS acts as a tridentate ligand using one of its carboxylate moiety as bridging and one as monodentate co-ordination site and two bipyridyl nitrogens arranged in a distorted square pyramidal environment around the Cu2+ center, wherein the effective Cu2+ to LS ratio is 1:1. In 7, each LS is tridentate and dinegative resulting in a

molecules, viz., one CH3OH and three H2O, are present in the lattice and extend hydrogen bond interactions. Structure of {[Cu2LCH2(2,2′bipy)2(CH3O)](ClO4)(CH3OH)}, 4. Compound 4 crystallizes in the triclinic system with P1̅ space group and exhibits an asymmetric unit formula of {[Cu2LCH2(2,2′bipy)2(CH3O)](ClO4)(CH3OH)} and the molecular formula is twice this. The molecules exhibit discrete double binuclear units. Each binuclear center in such discrete units is the same wherein the Cu(II)···Cu(II) distance is 3.211 Å and is bridged through the methoxide ion. The geometry of the Cu(II) is square pyramidal. The basal plane is formed by two nitrogen atoms arising from the bipy ligand and two oxygen atoms from the carboxylato-bridges. The apical position is occupied by an oxygen atom from the dibridged carboxylate moiety. Unlike the other complexes, in 4, LCH2 bridges simultaneously to four Cu(II) centers resulting in a discrete tetranuclear unit. The other coordination features of LCH2 are similar to that observed in the case of 3 (Figure 9a). Two adjacent Cu centers and two LCH2 ligands form a 28-membered macrocycle, and the adjacent macrocycles are almost mutually 921



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Figure 12. Co-ordination modes of LCH2 and LS in complexes 1−8.

The Cu−O distances were found to be in the range of 1.929−1.995 Å, and C−O distances in the carboxylic groups were in the range of 1.202−1.3 Å, suggesting that these groups bind in the form of carboxylates. In some cases (3, 4, 7, and 8), the Cu−O distances in the apical position were found to be higher than that observed for covalent bond but within the van der Waal radii. The mononuclear Cu2+ centers, where LCH2 is coordinating in monodentate fashion and are oriented in trans-like fashion as in the free ligand leading to the formation of 1-D curving (2) and helical networks (5). When the LCH2 coordinates in a bridging fashion by binding to dinuclear Cu2+ centers, transorientation of LCH2 leads to the formation of 2-D network (1), and cis- orientation of LCH2 leads to the formation of discrete dimers of these dinuclear centers (4). When LCH2 binds to both mononuclear as well as dinculear Cu2+ centers and coordinating in monodentate as well as bridging fashion, the transorientation of LCH2 leads to the formation of a 2-D network as observed in 3. All this resulted in the formation of distorted geometries of square pyramidal (2−5, 7, and 8) and octahedral complexes (1 and 6, when the Cu···Cu bond is being considered). As we go from six-coordinated to five-coordinated species, the coordination environment changes from O6 to N2O3 as derived from the crystal structures of 6, 7, and 8, respectively. The primary coordination spheres of these complexes are shown in Figure 13 for comparison. Thus, the present paper demonstrates a variety of coordination polymers as well as discrete coordination complexes that are rich with mononuclear as well as dinuclear Cu2+ centers wherein Cu···Cu distances (in Å) vary from 2.65 Å (dinuclear, 1 and 6) to 3.21 (dinuclear, 4) to 4.38 (dinuclear, 3) to 4.71 (dinuclear, 7 and 8) to 9.33 (mononuclear, 5) to 10.25 (mononuclear, 2) using LCH2 and Ls that possesses −COOH moieties on the pendants of naphthalene units connected by either a −CH2− or S- bridge (Scheme 2). This demonstration also led to the formation of dimers of these dinuclear centers in 4. Thus, by changing the reaction conditions, the composition of the components, and the method of crystallization, eight different copper complexes could be obtained using LCH2 and LS. These results indicate that as a promising new type of multifunctional ligand, LCH2 has great potential in the field of coordination polymers, and further endeavors for exploration of complexes of LCH2 are underway.

neutral complex species. The formation of the dinuclear centers has been facilitated by the cis-orientation of LS wherein the two carboxylate moieties are oriented in the same direction with a Ccarboxy···Ccarboxy distance of 4.230 Å. Metric data corresponding to the coordination sphere are given in Supporting Information SI 17 and 18. The bond lengths and bond angles observed for the organic moiety were found to be normal. In the lattice structure of 7, each dinuclear Cu2+ center is surrounded by eight other dinuclear centers as the primary shell, wherein Cu···Cu distances were found to be 11.4, 12.1, 15.5, and 17.8 Å with respect to the central one, forming an octagon (Figure 10b). The lattice is filled with one methanol molecule that interacts through C−H···O and O−H···O hydrogen bonds. A list of hydrogen bond interactions including those of the weak type are given in Supporting Information SI 03. The structure of 8 is similar to that of 7, wherein the bipy is replaced by 1,10-Phen and the methanol is replaced by the DMF (Figure 11).

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CONCLUSIONS A dicarboxy derivative containing two arms linked through a bridged naphthyledene, viz., LCH2 and LS were synthesized and characterized. The structures of these were established by single crystal XRD and it was found that the two arms in each ligand were disposed in space resulting in a trans-like fashion and they exhibit bowl shape structures. The synthesis of copper complexes with diverse coordination as well as lattice structures is controlled by the ratio of the components taken and the nature and ratio of the supporting ligands, both for coordination as well as for crystallization. Thus a series of five new Cu2+ coordination polymers, namely, {[CuLCH2(DMF)](DMF)}n (1), {[CuLCH2(DMF)(2,2′-bipy)](CH 3 OH)} n (2), {[CuL CH2 (2,2′-bipy)](2H 2 O)} n (3), {[CuLCH2(H2O)(2,2′-bipy)](2H2O)}n (5), {[Cu2 (L S) 2(DMF) 2](DMF)(CH3 OH)(2H 2 O)}n (6), and three discrete coordination complexes {[Cu 2 L CH2(2,2′bipy)2(CH3O)](ClO4)(CH3OH)} (4), {[CuLS(2,2′bipy)](CH3OH)} (7), and {[CuLS(1,10-phen)](DMF)} (8) have been demonstrated. The binding nature of the carboxylate moieties present in LCH2 and LS can be grossly classified into three categories as can be seen from Figure 12. One of these is where both the carboxylates bind as monodentate and to a different copper center by maintaining the trans-like structure of the ligand as noticed in the case of 2 and 5. The second category is that where the ligand binds through one of the carboxylates as monodentate and the other carboxylate as bridged bidentate to result in a dinuclear center as noticed in the structures of 3, 7, and 8. In the third category, both the carboxylates form bridges to result in two dinuclear centers found in both trans- as well as syn-like conformation as noticed in the structures of 1, 4, and 6.

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EXPERIMENTAL SECTION

All the solvents were purified and dried before use by standard procedures. FTIR spectra were recorded on an Impact 400 Nicolet machine in KBr matrix. C, H, and N analysis were performed on a Carlo Erba 1106 elemental analyzer. The 1H and 13C NMR spectra were recorded on a Varian 400S spectrometer in CDCl3 or DMSO-d6. 922



Article

130.0, 133.7, 153.1 (Nap-C) 169.3 (CO). ESI MS: m/z (%), 248 (100, M+ − 224), 472 (48, M+). La/S. This was synthesized as per the reported procedure with some modifications.50 Yield 6.23 g, 41%. Mp 209−210 °C dec Anal. Calcd for La/S (C20H14O2S): C, 75.45; H, 4.43. Found: C, 75.59; H, 4.41. FTIR (KBr, cm−1): 3356, 3345, 1619, 1595, 1570, 1462, 1243 cm−1. 1H NMR (400 MHz, CDCl3, δ ppm) 7.01 (s, 2 H, aryl), 7.41 (d, 2 H, aryl, J = 9.02 Hz), 7.35 (t, 2 H, aryl, J = 7.5 Hz), 7.52 (t, 2 H, aryl, J = 7.5 Hz), 7.76 (d, 4 H, aryl, J = 8.5 Hz), 8.63 (d, 2 H, aryl, J = 8.5 Hz). 10.24 (s, 2H, −OH). 13C NMR (100 MHz, CDCl3, δ ppm): 156.8, 135.4, 130.5, 128.5, 127.1, 124.7, 123.8, 118.2, 112.5 (Nap-C). ESI MS: m/z (%), 319 (100, M+); 175 (95). Lb/S: This was synthesized by using a procedure similar to that reported for Lb/CH2 except that the isolated solid product was dissolved in dichloromethane, washed with 10% sodium hydroxide and organic phase was evaporated. Recrystallization from methanol afforded pure Lb/S. Yield 85%. Mp 125−127 °C. Anal. Calcd for Lb/S (C26H22O6S): C, 67.52; H, 4.79. Found: C, 67.42; H, 4.61. FTIR (KBr, cm−1): 3040, 3000, 2970, 1750, 1595, 1500, 1450, 1300, 1250, 1200, 1090, 1040, 810, 750 cm−1. 1H NMR (400 MHz, CDCl3, δ ppm) 1.15 (t, −COO-CH2−, 2H, J = 7.17 Hz), 4.18 (q, 4H), 4.45 (s, 4H), 7.08−7.11 (ddd, 2H), 7.25−7.28 (dd, 2H), 7.32−7.38 (ddd, 2H), 7.60−7.62 (d, 2H), 7.72−7.75 (d, 2H), 8.72 (d, 2H, J = 8.12 Hz) . 13C NMR (100 MHz, CDCl3, δ ppm): 168.8, 156.4, 135.5, 128.5, 127.1, 124.7, 123.8, 119.2, 115.5 (Nap-C); 66.9, 61.1 (−CH2−CH3); 14.1 (−CH3). ESI MS: m/z (%), 491 (80, M+); 261 (100). LCH2. This was synthesized by reported procedure with little modifications. The solid product formed was filtered and dried under a vacuum. Single crystals of LCH2 of X-ray quality were grown from a DMSO-MeOH layering method. Yield: 0.578 g (85%). Mp 222 (decomp.). Anal. Calcd. for C25H20O6·H2O (434.17): C 69.12, H 5.10; found: C 69.41, H 4.89%. FTIR (KBr, cm−1): 1716 (νCO), 3432 (νOH). 1H NMR (400 MHz, DMSO-d6, δ ppm): 13.159 (br, 2H, −COOH), 8.178 (m, 2H, Nap-H), 7.778 (d, 2H, Nap-H), 7.745 (m, 2H, Nap-H), 7.378 (d, 2H, Nap-H), 7.203 (m, 4H, Nap-H), 5.045 (s, 4H, −O−CH2−COOH), 4.953 (s, 2H, Nap-CH2−Nap). 13C NMR (100 MHz, DMSO-d6, δ ppm): 20.8 (Nap-CH2−Nap), 65.9 (−CH2− CO2H), 114.2, 122.7, 123.2, 124.4, 125.9, 127.8, 127.9, 129.1, 133.0, 152.4 (Nap-C), 170.5 (CO). ESI MS: m/z (%), 416 (56, M+). LS. This was synthesized by adapting the procedure given for LCH2. Pure LS was obtained after recrystallization from ethanol. Single crystals of X-ray quality were grown from CH3CN-Benzene layering method. Yield 95%. Mp 255−261 °C . Anal. Calcd for C24H18O6S: C, 66.35; H, 4.18. Found: C, 66.28; H, 4.08. FTIR (KBr, cm−1): 3210− 2420 (broad), 1720, 1710, 1620, 1580, 1500, 1460, 1430, 1350, 1290, 1275, 1250, 1215, 1150, 1100, 1020, 950, 910, 800, 775, 740. 1H NMR (400 MHz, DMSO-d6) 4.83 (s, 4H), 7.23 (d, 2H, J = 7.75 Hz), 7.31− 7.S13C NMR (100 MHz, DMSO-d6, δ ppm) 170.77, 156.55, 135.28, 130.12, 129.61, 128.30, 127.10, 125.86, 124.28, 119.06, 115.14, 66.61. ESI MS: m/z (%), 457 (67, M+ + Na+); 435 (46, M+); 232 (100). Synthesis and Characterization of Cu(II) Complexes. All the copper complexes synthesized using LCH2 and LS as shown in Scheme 2. {[CuLCH2(DMF)](DMF)}n, 1. LCH2 (0.416 g, 1.0 mmol) was dissolved in 5 mL of dry DMF (N,N-dimethylformamide). To this a clear solution of Cu(ClO4)2·6H2O (0.365 g, 1.0 mmol) in 10 mL of DMF was slowly added. The colorless solution turned to green and the reaction mixture was stirred at 70 °C for 6 h. This was cooled and filtered and the filtrate was kept at room temperature. After 30−40 days, green colored crystals started separating out from the solution. Yield: 300 mg (48%). Mp > 300 °C. Anal. Calcd for C31H31CuN2O8: C, 59.75; H, 5.01; N, 4.50. Found: C, 58.60; H, 5.21; N, 4.25. Selected IR bands (KBr, cm−1): 3415(s), 2924(s), 1634(s), 1509(w), 1420(s), 1112(s), 794(w), 721(w), 632(w). {[CuLCH2(DMF)(2,2′bipy)](CH3OH)}n, 2. This was synthesized by adapting procedure given for 1 except using 1.0 mmol of 2,2′bipyridine along with the copper perchlorate. In order to obtain the crystalline product, the final filtrate was diffused with methanol in a closed system. After 40−50 days, blue colored crystals started separating out from the solution. Yield: 320 mg (23%). Mp >300

Figure 13. Primary co-ordination environment for Cu2+ complexes 1− 8. UV−visible spectra were obtained on a Shimadzu UV-260 or UV2101PC spectrophotometer. The fluorescence emission spectra were recorded on a Perkin-Elmer LS 55 spectrofluorimeter. Synthesis and Characterization of the Ligands. All the ligands used in the present study are synthesized as per that given in Scheme 3. Both La/CH2 and Lb/CH2 have been synthesized by the same procedures as reported by us and others.47−49 La/CH2: Yield: 109.38 g (70%). Mp 195−200 °C (decomp.). Anal. Calcd. for La/CH2 (C21H16O2, 300.35): C 83.98, H 5.37; found C 83.95, H 5.87%. FTIR (KBr, cm−1): 3331 (υOH). 1H NMR (400 MHz, CDCl3, δ ppm): 8.213 (d, 2H, naph-H), 7.668 (d, 2H, naph-H), 7.456 (t, 2H, naph-H), 7.336 (t, 2H, naph-H), 7.051 (d, 2H, naph-H), 6.578 (s, 2H, OH), 4.823 (s, 2H, Ar−CH2−Ar). 13C NMR (100 MHz, CDCl3, δ ppm): 21.91 (Ar−CH2−Ar), 118.1, 118.5, 120.6, 123.1, 123.3, 126.9, 128.91, 129.8, 133.5, 151.9 (Nap-C). ESI MS: m/z (%), 281 (100, M+-19), 300 (56, M+). Lb/CH2: Yield: 1.74 g (46%) M.P. 90−95 °C. Anal. Calcd. for Lb/CH2 (C29H28O6, 472.19): C 73.73, H 5.93; found C 73.95, H 5.87%. FTIR (KBr, cm−1): 1751 (νCO). 1H NMR (CDCl3, δ ppm): 8.249 (d, 2H, Nap-H), 7.699 (t, 4H, Nap-H), 7.368−7.246 (m, 4H, Nap-H), 7.147 (d, 2H, Nap-H), 5.059 (s, 2H, Nap−CH2−Nap), 4.596 (s, 4H, −CH2−CO−), 4.239 (q, 4H, −CO−CH2−CH3), 1.266 (t, 6H, −CO−CH2−CH3). 13C NMR (100 MHz, CDCl3, δ ppm): 14.1 (−CH3), 22.2 (Ar−CH2−Ar), 61.2 (−COCH2−CH3), 67.2 (−O−CH2-CO−), 114.8, 123.7, 124.7, 124.8, 126.1, 128.0, 128.2, 923



Article

Scheme 2. A Generalized View at the Coordination Spheres and Their Lattice Structures

3.64; N, 5.36. Selected IR bands (KBr, cm−1): 3056(s), 1665(s), 1645(s), 1565(s), 1452(s), 1104(s), 805(w), 768(w), 634(w). {[CuLCH2(2,2′bipy)(H2O)](2H2O)}n, 5. This was synthesized by following the same procedure as that given for 2 except that the DMF was not dried. The resulting reaction mixture was kept at room temperature. After 30−40 days, blue-colored crystals started separating out from the solution. Yield: 360 mg (53%). Mp 290−300 °C (decomp.). Anal. Calcd for C35H27CuN2O9 C, 61.54; H, 3.98; N, 4.10; Found: C, 61.14; H, 3.78; N, 4.04. Selected IR bands (KBr, cm−1): 3589(s), 2919(s), 1650(s), 1601(s), 1508(w), 1447(s), 1112(s), 794(w), 721(w), 632(w). {[Cu2(LS)2(DMF)2](DMF)(CH3OH)(2H2O)}n,6. Similar procedure as that of 1 was adapted for the synthesis. In this case the reaction mixture was kept at room temperature. After 30−40 days, greencolored crystals started separating out from the reaction mixture. Yield: 300 mg (46%). Mp > 300 °C. Anal. Calcd for C58H63N3O17S2 (1137.36): C, 61.20; H, 5.58; N, 3.69. Found: C, 60.98; H, 5.58; N, 3.54. Selected IR bands (KBr, cm−1): 3448(s), 2926(s), 1671(s), 1640(s), 1589(s), 1503(w), 1460(s), 1416(s), 1386(s), 1317(s), 1284(s), 1112(s), 794(w), 721(w), 631(w). {[CuLS(2,2′bipy)](CH3OH)},7. This was synthesized by adapting the procedure given for 2 using LS, copper perchlorate, and 2,2′-bipyridine in a 1:1:1 molar ratio. Yield: 320 mg (21%). Mp 280−290 °C. Anal. Calcd for C35H26CuS2N2O7: C, 61.62; H, 3.84; N, 4.11. Found: C, 61.02; H, 3.11; N, 3.98. Selected IR bands (KBr, cm−1): 3589(s), 3431(s), 2919(s), 1650(s), 1601(s), 1508(w), 1467(s), 1447(s), 1393(s), 1212(s), 794(w), 721(w), 632(w). {[CuLS(1,10-phen)](DMF)}, 8. This was synthesized by following a similar procedure as that given for 7 except using 1,10-phenanthroline in place of 2,2′-bipyridine. Yield: 280 mg (35%). Mp > 290−300 °C (decomp.). Anal. Calcd for C39H32CuN3O7S (749.13): C, 62.43; H, 4.30; N, 5.60. Found: C, 61.89; H, 4.21; N, 5.56. Selected IR bands (KBr, cm−1): 3651(w), 3441(w), 2924(w), 1630(s), 1615(s), 1548(s), 1516(s), 1460 (w), 1281(s), 1103(s), 804(w), 769(w), 633(w). Crystal Structure Determination by Single Crystal XRD. Single crystals suitable for X-ray diffraction were obtained for LCH2, LS, and all complexes 1−8. Experimental and crystal data are given in Tables 1 and 2. For LCH2, LS, and copper complexes 4 and 7, single crystal X-ray diffraction data were collected on an OXFORD DIFFRACTION XCALIBUR-S CCD system with graphite-monochromated Mo-Kα radiation by ω − 2θ scan mode and the absorption corrections were applied by using multiscan. For the complexes 1−3, 5, 6, and 8, data

Scheme 3. (i) Two equivalents of BrCH2CO2C2H5, K2CO3, CH3CN, reflux, 12 h; (ii) 3 equiv of KOH, C2H5OH, reflux, 24 h

°C. Anal. Calcd for C78H74Cu2N6O16: C, 63.36; H, 5.04; N, 5.68;. Found: C, 62.60; H, 4.92; N, 5.05. Selected IR bands (KBr, cm−1): 3459(s), 2919(s), 1645(s), 1611(s), 1508(w), 1420(s), 1112(s), 794(w), 721(w), 631(w). {[CuLCH2(2,2′bipy)](CH3OH)(3H2O)}n, 3. This was also synthesized by following a procedure given for 2 except that the reaction mixture was heated and stirred for longer time, that is, 24 h. In order to obtain the crystalline product, the final filtrate was diffused with methanol in a closed system. In order to get single crystals of diffraction quality, the reaction mixture was diffused with methanol. After 40−50 days, blue colored crystals started separating out from the solution. Yield: 280 mg (40%). Mp 290−300 °C (decomp.). Anal. Calcd for C36H26CuN2O10: C, 60.89; H, 3.69; N, 3.94. Found: C, 60.89; H, 3.85; N, 3.27. Selected IR bands (KBr, cm−1): 3544(s), 1630(s), 1546(s), 1103(s), 804(w), 769(w), 633(w). {[Cu2LCH2(2,2′bipy)2(CH3O)](ClO4)(CH3OH)}, 4. Here, again a similar procedure was followed only the molar ratio of Cu(ClO4)2.6H2O and 2,2′ bipyridine used was doubled with respect to LCH2. The color of the reaction mixture changed from colorless to green and then blue and was heated at 70−75 °C and stirred for 44−48 h. The filtered solution was diffused with methanol and kept in the refrigerator wherein a nice blue-colored crystalline compound was separated out about 9−10 months and the crystals were found to be suitable for X-ray diffraction. Yield: 240 mg (24%). Mp 290−300 °C (decomp.). Anal. Calcd for C47H37ClCu2N4O12 C, 55.76; H, 3.68; N, 5.53. Found: C, 55.89; H, 924



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collections were carried out on a NONIUS KAPPA CCD diffractometer with graphite-monochromated Mo-Kα radiation using mixed Φ and Ω scans. The structural determinations by direct methods, and the refinements of atomic parameters based on fullmatrix least-squares on F2 were performed using the SHELX-97 programs.51 All hydrogen atoms were geometrically fixed and allowed to refine using a riding model except for complex 5 where the high resolution of the crystal structures allowed locating hydrogen atoms of water molecules on Fourier maps.

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ASSOCIATED CONTENT

S Supporting Information *

Solid state emission spectral studies (SI 01), TGA curves for LCH2/LS and Cu(II) complexes (SI 02), hydrogen bond data observed in all the crystal structures (SI 03), C−O distances (Å) in LCH2/S, 1−8 (SI 04), selected dihedral angles of both the arms based on the crystal structure (SI 05), selected nonbonded distances (ND) between both the arms (SI 06), single crystal XRD structure of LCH2 (SI 07), single crystal XRD structure of LS (SI 08), single crystal XRD structure of 1 (SI 09), single crystal XRD structure of 2 (SI 10), single crystal XRD structure of 3 (SI 11), single crystal XRD structure of 4 (SI 12), single crystal XRD structure of 5 (SI 13), single crystal XRD structure of 6 (SI 14), single crystal XRD structure of 7 (SI 15), single crystal XRD structure of 8 (SI 16), selected bond lengths (Å) in the coordination sphere of the complexes (SI 17), selected bond angles (°) in the coordination sphere of the complexes (SI 18). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +91-22-2576-7162; fax: +91-22-2572 3480; e-mail: [email protected].

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ACKNOWLEDGMENTS C.P.R. acknowledges the financial support from DST, DAEBRNS, and CSIR. G.S.B. and J.P.C. are thankful to CSIR for their SRF fellowships.

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REFERENCES

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Coordination Polymers Formed by the Mono- and Dinuclear Cu(II

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