Carbophosphazene-Based Multisite Coordination Ligands: Metalation

ARTICLE pubs.acs.org/crystal

Carbophosphazene-Based Multisite Coordination Ligands: Metalation Studies on the Pyridyloxy Carbophosphazene, [NC(NMe2)]2[NP(p-OC5H4N)2] Published as part of a virtual special issue on Structural Chemistry in India: Emerging Themes. Vadapalli Chandrasekhar,* Tapas Senapati, Atanu Dey, Sakiat Hossain, and Kandasamy Gopal Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India

bS Supporting Information ABSTRACT: The pyridyloxycarbophosphazene, [NC(NMe2)]2[NP(p-OC5H4N)2] (L), reacted with Cd(OAc)2 3 4H2O to afford a rail-road-like double-strand coordination polymer, [{Cd(CH3COO)2(L)}(CH3OH)(H2O)2]n (1). The crystal structure of 1 reveals that L functions as a bridging ligand to link successive cadmium atoms. Two such parallel-running strands are further interconnected by actetate bridging ligands forming Cd2O2 four-membered connections. The double-stranded coordination polymer is taken into the second dimension by intermolecular hydrogen bonding between the oxygen atoms of the acetate bridge and a tetrameric water cluster. Interaction of L with Cd(NO3)2 3 4H2O leads to the formation of [Cd(NO3)2(L)(MeOH)]n (2). In the presence of pyridine (Py), this reaction affords [Cd(NO3)2 (L)(Py)2]n (3). In contrast to 1, compounds 2 and 3 are single-strand one-dimensional (1-D) coordination polymers. In 13, the cadmium atoms are seven-coordinate in a pentagonalbipyramidal geometry. The reaction of L with ZnCl2, MnCl2, or CoCl2 leads to the formation of [{Zn(Cl)2(L)}(MeOH)]n (4), [Mn(Cl)2(L)2]n (5), and [Co(Cl)2(L)2]n (6). Structure 4 is a simple 1-D coordination polymer containing tetrahedral zinc atoms, while 5 and 6 are macrocycle-linked coordination polymers. In the latter, successive metal atoms are linked by a pair of carbophosphazene ligands to generate 24-membered macrocyclic rings which are interconnected to each other at the metal center to afford the coordination polymer chain.

’ INTRODUCTION Cyclocarbophosphazenes are hybrid inorganicorganic heterocyclic rings.1 These can be considered as the hybrids of the organic heterocyclic rings triazines and the inorganic heterocyclic rings cyclophosphazenes (Chart 1). Recently, there has been considerable interest in the use of cyclophosphazenes as scaffolds for the preparation of a large variety of multisite coordination ligands (Chart 2).2 This interest has spurred us to explore whether cyclocarbophosphazenes can also be similarly used. Previous work from our laboratory has indicated that some pyrazolylcyclophosphazenes and more commonly acyclic phosphorus pyrazolides such as MeP(S)(3,5-Me2Pz)2, PhP(O)(3,5-Me2Pz)2, and (O)P(3,5-Me2Pz)3 undergo PN bond cleavage upon interaction with metal salts.3 Utilizing this principle, we effected a regiospecific metal-assisted hydrolysis on the pyrazolyl carbophosphazene [{NP(3,5-Me2Pz)2}{NC(3,5-Me2Pz)}2] to generate novel tetrameric copper assemblies, [{(O)PN3C2(3,5Me2Pz)2CuCl}2O]2 and [{N3C2(3,5-Me2Pz)2P(O) 3 CuBr2}2{N3C2(3,5-Me2Pz)2P(O) 3 Cu(3,5-Me2PzH)}2O]2.3 r 2011 American Chemical Society

In contrast to phosphorus-supported ligands containing pyrazolyl substituents, those containing pyridyloxy substituents were found to be relatively more stable to hydrolysis upon metalation.1f,b Also, these ligands were found to be more flexible because of the presence of the oxygen spacer that separates the pyridyl group from the inorganic heterocyclic ring. In view of this, we wished to build carbophosphazene ligands that contained pyridyloxy substituents. In a preliminary communication we reported the formation of three-dimensional (3-D) coordination polymers [L2{CdCl2}3 3 H2O]n and [L2{CdCl2}2] 3 4H2O 3 CHCl3 upon the interaction of [NC(NMe2)]2[NP(p-OC5H4N)2] (L) with CdCl2. We report the full investigations of L with other Cd(II) salts as well as with Zn(II), Mn(II), and Co(II) salts. The formation of various coordination polymers [{Cd(CH3COO)2(L)}n(CH3OH) (H2O)2n] (1), [Cd(NO3)2(L)(MeOH)]n (2), [Cd(NO3)2 Received: October 23, 2010 Revised: February 26, 2011 Published: April 11, 2011 1512

dx.doi.org/10.1021/cg1014169 | Cryst. Growth Des. 2011, 11, 1512–1519

Crystal Growth & Design Chart 1

Chart 2

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X-ray Crystallography. Crystals suitable for single crystal X-ray analyses were obtained by slow evaporation from their mother liquor of the reaction mixture. The crystal data have been collected on a Bruker SMART CCD diffractometer (MoKR radiation, λ = 0.71073 Å). The program SMART9a was used for collecting the frames, indexing reflections and determining lattice parameters, SAINT9a for integration and scaling, SADABS9b for absorption correction, and SHELXTL9c,d for structure determination. All the structures were solved by direct methods and refined by full-matrix least-squares methods against F2. All the non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were fixed at calculated positions and their positions were refined by a riding model. Details of the data collection and refinement parameters for compounds 16 are given in Table 1. The asymmetric units of 14 contain one ligand (L) and one metal atom (Cd1 or Zn1) along with solvent molecules: two water molecules and one methanol molecule in 1; one chloroform and one methanol molecule in 2; one chloroform molecule in 3; and one methanol molecule in 4. The asymmetric units of 5 and 6 contain two ligands (L) and one metal atom (Mn1 or Co1). In these cases their solvent molecules were absent in the crystal lattice. CCDC 814294814299 (16) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/ retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: þ441223/336033; E-mail: [email protected]]. Figures 19 and their bonding parameters were obtained using Diamond 3.1e software.9e

’ SYNTHESIS

(L)(Py)2]n (3), [{Zn(Cl)2(L)}(MeOH)]n (4), [Mn(Cl)2(L)2]n (5), and [Co(Cl)2(L)2]n (6) and the role of the multisite coordination ligand L in their assembly are discussed in this manuscript.

’ EXPERIMENTAL SECTION Reagents and General Procedures. Solvents and other general reagents used in this work were purified according to standard procedures.4 NaN(CN)2, 4-hydroxy pyridine (Aldrich, U.S.A.), MnCl2, ZnCl2, CoCl2, Cd(OAc)2 3 4H2O, Cd(NO3)2 3 4H2O, PCl5, and pyridine (Py) (s. d. Fine Chemicals, India) were used as purchased. [NCCl]2[NPCl2],5 N,N,N0 ,N0 -tetramethylmethylenediamine,6 [NC(NMe2)]2[NPCl2],7 and [NC(NMe2)]2[NP(p-OC5H4N)2] (L)8 were prepared according to literature procedures. Instrumentation. Melting points were measured using a JSGW melting point apparatus and are uncorrected. IR spectrum was recorded as KBr pellets on a Bruker Vector 22 FT IR spectrophotometer operating at 4004000 cm1. Electrospray ionization mass spectrometry (ESIMS) analyses were performed on a Waters Micromass Quattro Micro triple quadrupole mass spectrometer. Capillary voltage was maintained at 3 kV and cone voltage was kept at 30 V. The ionization mechanism used was electrospray in positive ion full scan mode using methanol as solvent and nitrogen gas for desolvation. The temperature maintained for ion source was 100 °C and for desolvation was 250 °C. Elemental analyses of the compounds were obtained on a Thermoquest CE instrument CHNS-O EA/110 model.

General Procedure for the Synthesis of Metal Complexes. A 1:1 mixture of metal salt and ligand (L) was taken in a solvent and stirred for 16 h at room temperature to afford a clear solution. This was filtered, concentrated to 50%, and kept for slow evaporation. After 37 days, pure crystalline products were isolated in 6275% yield. Specific details of each reaction and the characterization data of the products obtained are given below. [{Cd(CH3COO)2(L)}(CH3OH)(H2O)2]n (1). Cd(OAc)2 3 2H2O (0.09 g, 0.32 mmol), L (0.12 g, 0.32 mmol), and methanol (20 mL). Yield: 0.15 g (66.7%, based on Cd). Mp.: 270 °C (d). FT-IR (ν/cm1): 3475(b), 3102(w), 2929(m), 2867(w), 1598(s), 1566(s), 1530(m), 1407(m), 1381(s) 1252(s), 1200(s), 1090(s), 1058(s), 1019(s), 989(m), 936(s), 774 (m), 732 (m), 671 (m), 573 (m), 502 (m). Anal. Calcd. for C21H34CdN7O9P: C 37.54, H 5.10, N 14.59; found: C 37.57, H 5.15, N 14.47. [Cd(NO3)2(L)(MeOH)]n (2). Cd(NO3)2 3 4H2O (0.1 g, 0.32 mmol), L (0.12 g, 0.32 mmol), and methanol (20 mL). Yield: 0.17 g (64.2%, based on Cd). Mp.: 145 °C (d). FT-IR (ν/cm1): 3240(b), 3103(m), 29275(s), 2856(m), 2427(m), 1602(s), 1572(m), 1535(m), 1501(m) 1381(s), 1248(s), 1201(s), 1088(s), 1059(s), 920(s), 834(m), 781(s), 660(s), 603(s), 575(s). Anal. Calcd. for C19H28CdCl3N9O10P: C 28.81, H 3.56, N 15.91; found: C 28.93, H 3.62, N 15.88. [Cd(NO3)2(L)(Py)2]n (3). Cd(NO3)2 3 4H2O (0.15 g, 0.48 mmol), L (0.18 g, 0.48 mmol), Py (1 mL) and methanol (10 mL). Yield: 0.27 g (62.6%, based on Cd). Mp.: 185 °C (d). FT-IR (ν/cm1): 3445(b), 3105(m), 3070(m), 2934(s), 2477(m), 2293(m), 1756(m), 1467(b), 1378(m), 1194(s), 1020(s), 923(s), 844(s), 772(s), 700(s), 629(s), 605(s) 578(s). Anal. Calcd. for C27H30CdCl3N11O8P: C 36.59, H 3.41, N 17.38; found: C 36.63, H 3.46, N 17.29. [{Zn(Cl)2(L)}(MeOH)]n (4). ZnCl2 (0.05 g, 0.36 mmol), L (0.14 g, 0.36 mmol), and 1:1 methanolchloroform (20 mL). Yield: 0.13 g (68.8%, based on Zn). Mp.: 130 °C (d). FT-IR 1513

dx.doi.org/10.1021/cg1014169 |Cryst. Growth Des. 2011, 11, 1512–1519

Crystal Growth & Design

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Table 1. Details of the Data Collection and Refinement Parameters for Compounds 16 compound

1

2

3

4

5

6

formula

C21H34CdN7O9P

C19H29CdCl3N9O10P C27H31CdCl3N11O8P C17H24Cl2N7O3PZn C32H40MnCl2N14O4P2 C32H40Cl2CoN14O4P2

formula weight

671.93

793.23

887.36

541.67

872.56

temp (K)

100(2)

273(2)

273(2)

273(2)

153(2)

273(2)

crystal system space group

monoclinic C2/c

triclinic P1

triclinic P1

triclinic P1

monoclinic P21/c

monoclinic P21/c

a (Å)

26.154(5)

8.661(5)

9.413(5)

9.507(3)

17.251(5)

17.462(7)

b (Å)

15.106(5)

14.334(5)

14.990(5)

11.992(4)

20.112(5)

20.228(9)

c (Å)

16.753(5)

15.004(5)

15.112(5)

12.418(4)

11.419(5)

11.371(5)

R (°)

90

61.64(5)

116.84(5)

66.83(5)

90

90

876.55

unit cell dimensions

β (°) γ (°) volume (Å3); Z

118.63(5)

78.65(5)

97.93(5)

68.15(5)

97.79(5)

96.94(8)

90 5809(3); 8

78.35(5) 1594.3(12); 2

94.08(5) 1862.8(13); 2

88.92(6) 1194.6(7); 2

90 3925(2); 4

90 3987(3); 4

density (mg m3)

1.537

1.652

1.582

1.506

1.477

1.460

abs coef (mm1)

0.865

1.049

0.905

1.351

0.611

0.701

F (000)

2752

800

896

556

1804

1812

crystal size (mm)

0.09 0.07 0.06 0.10 0.08 0.07

0.08 0.07 0.06

0.09 0.08 0.05

0.12 0.10 0.08

0.12 0.09 0.07

θ range (°)

2.39 to 26.00

2.42 to 26.00

4.12 to 25.03

2.37 to 25.50

2.03 to 26.00

2.33 to 26.50

limiting indices

32 e h e 26

8 e h e 10

10 e h e 11

11 e h e 11

13 e h e 21

21 e h e 18

18 e k e 18 17 e l e 20

14 e k e 17 18 e l e 18

17 e k e 13 17 e l e 17

8 e k e 14 12 e l e 15

24 e k e 23 13 e l e 14

25 e k e 22 14 e l e 11

8958

9588

6392

21401

22559

6137 [0.0272]

6427 [0.0327]

4348 [0.0217]

7675 [ 0.0544]

8179 [0.0707]

reflections collected 15708 unique reflections

5674 [0.0327]

[Rint] completeness to θ

99.1% (26.00°)

97.8% (26.00°)

97.9% (25.03°)

97.6% (25.5°)

99.5% (26.00°)

98.8% (26.50°)

data/restraints/

5674/4/376

6137/1/399

6427/0/464

4348/0/286

7675/0/504

8179/0/504

1.049 R1 = 0.0373,

1.019 R1 = 0.0668,

1.016 R1 = 0.0772,

1.053 R1 = 0.0501,

0.986 R1 = 0.0533,

0.907 R1 = 0.0549,

parameters GOF on F2 final R indices [I > 2σ (I)]

wR2 = 0.0956

wR2 = 0.1820 R1 = 0.0839,

wR2 = 0.2091

wR2 = 0.1344

R1 = 0.0937,

R1 = 0.0621,

wR2 = 0.1194 R1 = 0.0853,

wR2 = 0.1132 R1 = 0.1391,

R indices (all data)

R1 = 0.0434, wR2 = 0.0997

wR2 = 0.2014

wR2 = 0.2309

wR2 = 0.1446

wR2 = 0.1365

wR2 = 0.1449

largest residual

1.486 and 0.545

1.318 and 1.182

2.958 and 1.160

0.936 and 0.443

0.779 and 0.362

0.467 and 0.301

peaks (e Å3)

Figure 1. 1-D coordination polymer of 1.

(ν/cm1): 3063(b), 2925(s), 2855(m), 2483(m), 1593(s), 1475(s), 1389(s), 1201(s), 1091(s), 1058(s), 995(s), 925(s), 877(s),

845(s), 601(s) 536(s) . Anal. Calcd. for C17H24Cl2N7O3PZn: C 37.69, H 4.47, N 18.10; found: C 37.83, H 4.76, N 17.98. 1514



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Scheme 1. Synthesis of Metal Complexes from 16

[Mn(Cl)2(L)2]n (5). MnCl2 3 4H2O (0.07 g, 0.35 mmol), L (0.13 g, 0.35 mmol), and methanol (20 mL). Yield: 0.12 g (74.6%, based on Mn). Mp.: 130 °C (d). FT-IR (ν/cm1): 3412(b), 3264(m), 2939(m), 1959(w), 1600(s), 1562(s), 1497(s), 1404(s), 1363(m), 1296(m), 1241(s), 1203(s), 1086(s), 1015(m), 953(m), 922(s), 847(m), 758(m), 618(m), 598(m), 526(s). Anal. Calcd. for C32H40MnCl2N14O4P2: C 44.05, H 4.62, N 22.47; found: C 43.09, H 4.58, N 22.38. [Co(Cl)2(L)2]n (6). CoCl2 (0.05 g, 0.38 mmol), L (0.14 g, 0.38 mmol), and 1:1 methanolchloroform (20 mL). Yield: 0.13 g (65.8%, based on Co). Mp.: 110 °C (d). FT-IR (ν/cm1): 3426(b), 3068(m), 2928(m), 2479(m), 1635(s), 1603(s), 1531(s), 1448(s), 1405(s), 1238(s), 1202(s), 1089(s), 1066(m), 956(s), 925(s), 850(m), 758(s), 695(s), 570(s). Anal. Calcd. for C32H40Cl2CoN14O4P2: C 38.19, H 4.01, N 19.49; found: C 38.45, H 4.56, N 19.32.

’ RESULTS AND DISCUSSION Synthetic Aspects. The tetrachlorocyclocarbophosphazene, [NCCl]2[NPCl2], having four reactive chlorine atoms in the periphery, is an ideal starting material for the construction of multisite coordination ligands through the substitution of the chlorine atoms by suitable coordinating groups. It is possible to vary the number of the coordinating groups by protection of carbon centers and replacement of the other chlorine atoms on phosphorus by suitable coordinating groups. Accordingly, utilizing known protocols, the [NC(NMe2)2[NPCl2] was prepared.7 In this compound, the carbon centers were blocked from further reactions, leaving the phosphorus center containing two reactive chlorine atoms for further elaboration. The reaction of [NC(NMe2)]2[NPCl2] with 4-hydroxypyridine afforded the bis-pyridyloxycarbophosphazense, [NC(NMe2)]2 [NP(p-OC5H4N)2] (L).8 A two-component reaction involving the metal salt [Cd(OAc)2 3 2H2O, Cd(NO3)2 3 4H2O, ZnCl2, MnCl2 3 4H2O or CoCl2] and L afforded various types of metal complexes, 16 (Scheme 1). Molecular and Crystal Structures of the Pyridyloxycarbophosphazene Ligand L and Its Metal Complexes (16). The molecular structure of L has been previously reported by us in a preliminary communication.8 In view of the relevance of the

molecular structure of L vis-a-vis its complexes (16), its salient features are briefly described here. The average value of the two PN bonds in L is 1.575(3) Å, which is comparable to that found in [NC(NMe2)]2[NPCl2]7 and [NC(Cl)]2[NPCl2].5 This distance is shorter than that found for an ideal PN single bond distance which is 1.771(6) Å.10 The average NPN bond angle is 114.43(13)°, which is slightly wider than the ideal tetrahedral angle. The average exocyclic PO distance is 1.589(4) Å. The OPO angle is 92.05(11)°, which is considerably acute in comparison to the ideal tetrahedral angle. The average ring CN distance (1.351(4) Å) is not too different from the exocyclic CN distance (1.343(4) Å). In contrast to the approximate tetrahedral geometry around phosphorus, the ring carbon atom is planar. Finally, the N3C2P six-membered ring of L is nearly planar. Thus, the coordinating units of L are positioned on an approximate tetrahedral phosphorus center and are directed away from each other. In contrast to 2-pyridyloxy cyclophosphazenes where the orientaion of the pyridyloxy substituents favors a concerted coordination response to the same metal ion,1 the orientation of the coordinating groups in L predisposes this ligand to favor coordination polymers. The reaction of L with different kinds of metal salts afforded a variety of complexes whose solid-state structures are described below. An important structural aspect of these complexes is that in all the cases the carbophosphazene ring retains its planarity. This suggests that the coordination interaction of the pyridyloxycarbophosphazene ligand with metal ions is quite facile and does not impose any steric strain on the inorganic heterocyclic ring. This is clearly a consequence of the oxygen atom, which acts like a hinge and separates the carbophosphazene ring from the coordinating motif. Cadmium Complexes, [{Cd(CH 3 COO)2 (L)}(CH 3 OH) (H2O)2]n (1), [Cd(NO3)2(L)(MeOH)]n (2), and [Cd(NO3)2(L) (Py)2]n (3). The reaction of L with CdCl2 leading to the formation of 3-D coordination polymers [L2{CdCl2}3 3 H2O]n and [L2{CdCl2}2] 3 4H2O 3 CHCl3 has been reported by us recently.8 These coordination polymers consisted of CdCl2 layers that were interconnected by the multisite coordination action of L. It was of interest to investigate the structures of products formed in the reactions involving other cadmium salts. Accordingly, the reaction of L with Cd(OAc)2 3 2H2O or Cd(NO3)2 3 4H2O afforded the 1515


Crystal Growth & Design neutral coordination polymers 13. The solid-state structure of 1 reveals that it is also a coordination polymer (Figure 1). Dimeric Cd2 units are linked to each other by the bridging coordination action of L (in pairs) to generate a rail-road like polymer that contains two parallel interconnected one-dimensional (1-D) polymeric strands. Because of the 2-fold symmetry of the crystal structure (monoclinic, C2/c), the parallel strands of the rail-road

Figure 2. (a) Dimeric Cd2-motif and (b) coordination environment around cadmium in 1.

Figure 3. 2-D layer structure of 1 as a result of OH---O hydrogen bonding interaction with a [(H2O)4] cluster. The other lattice solvent methanol molecules have been omitted for clarity.

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polymer do not slip away from each other, since, at regular intervals, pairs of cadmium atoms present on either strand are clamped by the residual coordination action of the acetate ligands. Two chelating acetates are present on each cadmium atom; the oxygen atom of one of these acetate moieties is involved in coordination to the second cadmium atom. This generates a Cd2O2 four-membered ring (Figure 2a). The remaining coordination environment around each cadmium atom is comprised of the two pyridyloxy nitrogen atoms derived from two different carbophosphazene molecules. Overall, therefore, each cadmium atom has a 5O, 2N coordination environment in a pentagonal bipyramid geometry where the basal plane is comprised of five oxygen atoms and the two apical positions are taken up by the pyridyloxy nitrogen atoms belonging to two different carbophosphazene ligands (Figure 2b). The bond parameters of 1 are summarized in Table S1, Supporting Information.11 The CdO distances involving the chelating acetate ligands reveal their near isobidentate nature of coordination [Cd1O4 2.354(2) Å and Cd1O3 2.442(2) Å, Cd1O5 2.367(3) and Cd1O6 2.378(2) Å]. These distances are only slightly shorter than the CdO distances involved in Cd2O2 ring (Cd1O5* 2.507(3) Å). The two CdN bond distances [Cd1N6 2.304(2) and Cd2N7 2.308(2) Å] are quite similar indicating the symmetrical nature of coordination from the two pyridyloxy units. Another point of interest is the near linear NCdN angle [N6Cd1N7 173.57(7)°]. A comparison of bond angles at cadmium reveals that the OCdO angles involving the chelating rings are about 53° (average value), while those involving the four-membered ring are about 75° (average value). The rail-road polymer of 1 undergoes a further interesting supramolecular organization as a result of the interaction with water clusters formed in the crystal lattice. Thus, the 1-D chains of 1 as described above are interconnected to each other by stepup-step-down links resulting from intermolecular hydrogen bonding (average OH---O 1.901(5) Å) between tetrameric water clusters [(H2O)4] and the oxygen atoms of the chelating acetate ligand (Figure 3). The reaction of Cd(NO3)2 3 4H2O with L afforded [Cd(NO3)2 (L)(MeOH)]n (2) as a coordination polymer (Figure 4). However, unlike 1, in 2 only one strand is present. Each cadmium atom is present in pentagonal bipyramidal geometry. The basal plane comprises of two isobidentate, chelating nitrate ligands [Cd1O6 2.429(5), Cd1O7 2.434(5), Cd1O3 2.419(5) and Cd1O4 2.448(5) Å]. Such pentacoordinate cadmium atoms are linked to each other by the carbophosphazene ligands through their pyridyloxy arms; the two coordinating nitrogen atoms are present in

Figure 4. Solid-state structure of 2. 1516



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Figure 5. Solid-state structure of 3.

Figure 6. 1-D coordination polymeric structure of 4.

Figure 7. 2-D layer structure of 4 as a result of the CH---Cl bonding interaction.

the axial position [Cd1N6 2.298(5) and Cd1N7 2.303(4) Å]. As in 1, the NCdN angle in 2 also is almost linear (Table S2, Supporting Information).11 The lattice solvent chloroform and methanol molecules are present in between the 1-D [Cd-L] polymeric networks. The reaction of L with Cd(NO3)2 3 4H2O in the presence of pyridine afforded [Cd(NO3)2(L)(Py)2]n (3). The molecular structure of 3 is slightly different from that of 2 (Figure 5). The additional pyridine ligands occupy two coordination sites around cadmium; consequently, one of the two nitrate ligands present around cadmium is monodentate while the other is chelating. As a result, in 3, the coordination environment around cadmium is 3O, 4N. As in 1 and 2, the axial positions in 3 are also occupied by the nitrogen donor atoms of the pyridyloxy units of two different carbophosphazene ligands. The bond parameters involved in 3 are summarized in Table S3, Supporting Information.11 Similar to 2, 3 also contains the lattice solvent chloroform molecules present between the 1-D [Cd-L] polymeric networks.

The reaction of L with ZnCl2 afforded the neutral 1-D coordination polymer [{Zn(Cl)2(L)}(MeOH)]n (4). The solid-state structure of 4 reveals that Zn atoms are tetracoordinate (2N, 2Cl) and the geometry around the Zn atom is distorted tetrahedral (Figure 6). Such tetra coordinated zinc atoms are linked to each other through the pyridyloxy arms of carbophosphazene ligands (L). The flexibility of the pyridyloxy carbophosphazene ligand allows it to adjust to the coordination needs of zinc; consequently, the NZnN angles in this compound (103.41(12)°) do not cause any strain in the ligand which retains its planarity. The average ZnN and ZnCl bond distances are 2.052(3) and 2.220(1) Å respectively. Other bond parameters involved are summarized in Table S4, Supporting Information.11 The 1-D chains of 4 are interconnected to each other by a weak CH---Cl (2.852(6) Å) interaction, which converts a 1-D chain to a two-dimensional (2-D) layer structure (Figure 7). The lattice solvent methanol molecules are found to be present between these 2-D layered networks. 1517



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The remarkable flexibility of L and its capability to adjust to the needs of the coordination requirements of the metal ion come fully into play in the complexes 5 and 6. Unlike Zn(II) in the complex 4, Mn(II) and Co(II) in complexes 5 and 6 prefer octahedral geometries particularly if the ligands are not sterically encumbered. Consequently, the reactions of MnCl2 and CoCl2 with L lead to 1:2 complexes [Mn(Cl)2(L)2]n (5) and [Co(Cl)2(L)2]n (6). The crystal structure of 5 and 6 are isomorphic (monoclinic, P21/c) and contains different metal ions. Both of these are coordination polymers where successive manganese or cobalt ions are bridged by a pair of pyridyloxy carbophosphazene ligands (Figures 8 and 9). This leads to the formation of 24-membered macrocycles that are connected to each other at the metal centers. The ligand readily adapts itself to

the needs of this requirement and the OPO hinge that connects the two parts of the bipyridyloxy ligand is sufficiently flexible to allow the macrocycle formation. Such macrocyclelinked coordination polymers are of interest and we have recently described such systems, although these were built in the reactions involving pyrazole dicarboxylic acid with diorganotin dihalides.12 Both Mn(II) and Co(II) are hexacoordinate (4N, 2Cl) in an octahedral geometry with the axial positions being occupied by the two chloride ligands and the equatorial plane consisting of the four pyridyloxy nitrogen atoms derived from four different pyridyloxy carbophosphazene ligands. The bond parameters of 5 and 6 are summarized in Tables S5 and S6, respectively.11 Remarkably, the trans as well as the cis NMN bond angles are quite close to the ideal bond angles. 1518



’ CONCLUSION In conclusion, the pyridyloxycarbophosphazene [NC(NMe2)]2[NP(p-OC5H4N)2] (L) has been shown to be an efficient multisite coordination ligand toward various metal ions. The flexible architecture of the ligand, resulting from the presence of the spacer oxygen atoms that separate the coordinating pyridyloxy substituents from the cyclocarbophosphazenes ring, allows a strain-free coordination response from the ligand in its interactions with metal ions. This means that the ligand can readily adjust to the coordination requirements of the metal ion. As a proof of this principle, we have demonstrated the capability of L to interact with a variety of metal salts to afford a large variety of coordination polymers. In view of this success, it would be of interest to examine if such inorganic-heterocyclic ring-supported ligands can be used for preparing porous metalorganic frameworks. We are currently investigating this possibility. ’ ASSOCIATED CONTENT

bS

Supporting Information. Selected bond parameters and CIF files of crystals 16. This materials are available free of charge via the Internet at http://pubs.acs.org.

ARTICLE

39, 3238. (c) Kingsley, S.; Vij, A.; Chandrasekhar, V. Inorg. Chem. 2001, 40, 6057. (4) Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; Longman: London, 1989. (5) Becke-Goehring, M.; Jung, D. Z. Anorg. Allg. Chem. 1970, 372, 233. (6) Baumgarten, H. E. Organic Synthesis Coll. Vol. 5; John Wiley: New York, 1973; p 434. (7) Dastagiri Reddy, N.; Elias, A. J.; Vij, A. J. Organomet. Chem. 1999, 580, 41. (8) Chandrasekhar, V.; Senapati, T. CrystEngComm 2010, 12, 682. (9) (a) SMART & SAINT Software Reference Manuals, Version 6.45; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2003. (b) Sheldrick, G. M. SADABS: A Software for Empirical Absorption Correction, Ver. 2.05; University of G€ oettingen: G€oettingen, Germany, 2002. (c) SHELXTL Reference Manual, Ver. 6.1; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2000. (d) Sheldrick, G. M. SHELXTL, Ver. 6.12; Bruker AXS Inc.: Madison, WI, 2001. (e) Bradenburg, K. Diamond, Ver. 3.1eM; Crystal Impact GbR: Bonn, Germany, 2005. (10) (a) Rademacher, P. In Strukturen Organischer Molec€ule; VCH: Weinhelm, 1987. (b) Wingerter, S.; Pfeiffer, M.; Murso, A.; Lustig, C.; Stey, T.; Chandrasekhar, V.; Stalke, D. J. Am. Chem. Soc. 2001, 123, 1381. (11) See Supporting Information. (12) Chandrasekhar, V.; Thirumoorthi, R. Organometallics 2009, 28, 2096.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; tel.: þ91-512-256-7259.

’ ACKNOWLEDGMENT We thank the Department of Science and Technology (DST), India, and Council of Scientific and Industrial Research (CSIR), India, for financial support. V.C. is thankful to the Department of Science and Technology for a J. C. Bose fellowship. T.S., A.D. and S.H. thank CSIR, India, for a Senior Research Fellowship. ’ REFERENCES (1) (a) Carriedo, G. A.; Elipe, P. G.; Alonso, F. J. G.; FernandezCatuxo, L.; Díaz, M. R.; Granda, S. G. J. Organomet. Chem. 1995, 498, 207. (b) Ainscough, E. W.; Brodie, A. M.; Depree, C. V. J. Chem. Soc., Dalton Trans. 1999, 4123. (c) Ainscough, E. W.; Brodie, A. M.; Moubaraki, B.; Murray, K. S.; Otter, C. A. Dalton Trans 2005, 20, 3337. (d) Ainscough, E. W.; Brodie, A. M.; Depree, C. V.; Jameson, G. B.; Otter, C. A. Inorg. Chem. 2005, 44, 7325. (e) Ainscough, E. W.; Brodie, A. M.; Depree, C. V.; Jameson, G. B.; Otter, C. A. Polyhedron 2006, 25, 2341. (f) Chandrasekhar, V.; Pandian, B. M.; Azhakar, R. Inorg. Chem. 2006, 45, 3510. (2) (a) Allcock, H. R. Phosphorus-Nitrogen Compounds; Academic Press: New York, 1972. (b) Allcock, H. R. Chem. Rev. 1972, 72, 315. (c) Keat, R.; Shaw, R. A. In Organic Phosphorus Chemistry; Kosalopoff, G. M.; Maier, L., Eds.; Wiley: New York, 1973; Vol. 6. (d) Krishnamurthy, S. S.; Sau, A. C.; Woods, M. Adv. Inorg. Chem. Radiochem. 1978, 21, 41. (e) Heal, H. G. In The Inorganic Heterocyclic Chemistry of Sulfur, Nitrogen and Phosphorus; Academic Press: New York, 1980. (f) Allen, C. W. In The Chemistry of Inorganic Homo and Heterocycles; Haiduc, I., Sowerby, D. B., Eds.; Academic Press: New York, 1987; Vol. 2. (g) Shaw, R. A. Phosphorus Sulfur Silicon 1989, 45, 103. (h) Chandrasekhar, V.; Muralidhara, M. G.; Selvaraj, I. I. Heterocycles 1990, 31, 2231. (i) Allen, C. W. Chem. Rev. 1991, 91, 119. (j) Roesky, H. W. In The Chemistry of Inorganic Ring Systems; Steudel, R., Ed.; Elsevier: Amsterdam, 1992. (k) Chandrasekhar, V.; Krishnan, V. Adv. Inorg. Chem. 2002, 53, 159. (3) (a) Chandrasekhar, V.; Azhakar, R.; Krishnan, V.; Athimoolam, A.; Pandian, B. M. J. Am. Chem. Soc. 2006, 128, 6802. (b) Chandrasekhar, V.; Kingsley, S.; Vij, A.; Lam, K. C.; Rheingold, A. L. Inorg. Chem. 2000, 1519


Carbophosphazene-Based Multisite Coordination Ligands: Metalation

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