ARTICLE pubs.acs.org/crystal
Thiocyanate and Dicyanamide Anion Controlled Nuclearity in Mn, Co, Ni, Cu, and Zn Metal Complexes with Hemilabile Ligand 2-Benzoylpyridine Totan Ghosh,† Tanmay Chattopadhyay,‡ Sudhanshu Das,† Sandip Mondal,† Eringathodi Suresh,# Ennio Zangrando,*,^ and Debasis Das*,† †
Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata - 700 009, India Department of Chemistry, Panchakot Mahavidyalya, Sarbari, Neturia, Purulia, 723121, India # Analytical Science Discipline, Central Salt and Marine Chemicals Research Institute, G.B. Marg, Bhavnagar 364 002, India ^ Dipartimento di Scienze Chimiche e Farmaceutiche, University of Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy ‡
bS Supporting Information ABSTRACT: Two pseudohalides thiocyanate and dicyanamide have been employed to synthesize complexes of MnII, CoII, NiII, CuII, and ZnII in the presence of a hemilabile ligand 2-benzoylpyridine (Phpyk). With thiocyanate all the aforesaid metal ions (except for CoII, of which suitable single crystals for X-ray analysis were not obtained) produce mononuclear complexes having general composition of [MII(NCS)2(Phpyk)2]. The structure determination reveals that Mn and Zn complexes (1, 4) are isomorphous and isostructural (crystallizing in space group C2/c), while Ni and Cu complexes (2, 3) crystallize in space groups P1 and P21/n, respectively. Interestingly, no complex has been obtained with a configuration having the N of one Phpyk trans to the O of the other chelating ligand and among the four complexes only in complex 3 the two thiocyanato ligands are in trans-configuration. On the other hand, complexes 58 are isomorphous and crystallize in orthorhombic chiral space group P212121. The bridging mode of dicyanamide anions helps to generate a three-dimensional covalently bonded polymeric network of 66 topology for all the polynuclear complexes. By using 8 as sole precursor, we have pyrolytically synthesized triangular shaped ZnO nanoparticles.
’ INTRODUCTION Design and synthesis of transition metal complexes with structural diversities as far as dimensionality and topology of the species are concerned have become a fascinating area of contemporary research. The interest lies in the possible applications of the crystal engineering in various fields such as heterogeneous catalysis,1 nonlinear optical activity,2 molecular sensors,3 magnetic switches,4 and in the production of microporous materials.5 Pseudohalides, especially thiocyanate and dicyanamide anions, have attracted much attention because of their versatile coordination binding modes (Scheme 1), in making complexes with various dimensionalities.6 It is observed that the coordination modes of thiocyanate and dicyanamide are largely influenced by the nature of the coligands, and a variety of these have been exploited in this respect, although reports with the hemilabile 2-benzoylpyridine ligand are scanty.7 In this paper, we have explored the role of thiocyanate and dicyanamide in controlling the nuclearity and structural diversity of metal complexes with first row transition metal ions MII (M = Mn, Co, Ni, Cu, and Zn) and 2-benzoylpyridine (Phpyk). All thiocyanate mediated complexes r 2011 American Chemical Society
are mononuclear with cis configuration of SCN anions, except for the copper complex in which the thiocyanate moieties are in mutual trans position. On the other hand, all dicyanamide mediated complexes are polymeric forming a three-dimensional (3D) network arrangement having 66 topology. In addition to the importance as coordination polymers, these complexes can also be used as sole precursors in making nano sized metal oxides/sulphides.8 Among these, the different metal oxide materials, zinc oxide is one of the attractive inorganic crystalline materials with many applications due to its unique combination of interesting properties such as nontoxicity, good electrical, optical and piezoelectric behavior, stability in a hydrogen plasma atmosphere, and low price. So, we finally devoted special attention on our synthesized zinc polymer for preparation of ZnO nanoparticles.
Received: April 11, 2011 Revised: May 23, 2011 Published: May 25, 2011 3198
dx.doi.org/10.1021/cg2004485 | Cryst. Growth Des. 2011, 11, 3198–3205
Crystal Growth & Design Scheme 1. Possible Coordination Modes of (a) Thiocyanate and (b) Dicyanamide
’ EXPERIMENTAL SECTION Materials and Methods. All chemicals were obtained from commercial sources and used as received. Solvents were dried according to standard procedure and distilled prior to use. 2-Benzoyl pyridine was purchased from Aldrich Chemical Co. and used as received. All other chemicals used were of AR grade. Elemental analyses (carbon, hydrogen, and nitrogen) were performed using a Perkin-Elmer 240C elemental analyzer. Infrared spectra (4000400 cm1) were recorded at 25 C using a PERKIN-ELMER SPECTRUM RXIFT-IR SYSTEM and KBr as medium. Electronic spectra (2001200 nm) were obtained at 25 C using a U-3501 HITACHI JAPAN, where dry methanol was used as medium as well as reference. Thermal analyses (TGDTA) were carried out on a TGA/SDTA851e METTLER - TOLEDO thermal analyzer in flowing dinitrogen (flow rate: 40 cm3 min1). The morphology and size of ZnO particles were characterized by Hitachi S-3400N scanning electron microscopy (SEM). Preparation of Mononuclear Complexes (14). [Mn(Phpyk)2(SCN)2] (1). A methanolic solution (5 mL) of 2-benzoylpyridine (Phpyk) (0.366 g; 2 mmol) was added dropwise with constant stirring to 10 mL methanolic solution of manganese(II) perchlorate hexahydrate (1 mmol; 0.362 g). The stirring was continued for further 1 h, and then an aqueous solution (5 mL) of sodium thiocyanate (0.162 g; 2 momol) was added dropwise. After 2 h stirring the resulting mixture was filtered and the filtrate was kept in a CaCl2 desiccator. Single crystals suitable for X-ray data collection were obtained from the filtrate after a few days. Yield: 90%. Anal. Calcd for C26O2N4S2H18Mn: C, 58.05; H,3.35; N,10.42 (%). Found: C, 58.13; H, 3.28; N, 10.37 (%). IR: ν(SCN) = 2076 cm1, ν (CdO) = 1625 cm1, ν (skeletal vibration) = 1579 cm1. [Ni(Phpyk)2(SCN)2] (2). The synthetic procedure was the same as that adopted for 1 only differing in using nickel(II) perchlorate hexahydrate
ARTICLE
(0.366 g, 1 mmol), instead of manganese perchlorate hexahydrate. Single crystals suitable for X-ray analysis were obtained from the filtrate after a few days. Yield: 85%. Anal. Calcd for C26O2N4S2H18Ni: C, 52.50; H, 3.02; N,9.42 (%). Found: C, 52.79; H, 3.21; N, 9.63 (%). IR: ν(SCN) = 2087 cm1, ν (CdO) = 1621 cm1, ν (skeletal vibration) = 1584 cm1. [Cu(Phpyk)2(SCN)2] (3). This was synthesized by adopting a similar procedure followed for 1 using copper(II) perchlorate hexahydrate (0.370 g, 1 mmol), instead of manganese perchlorate hexahydrate. Single crystals suitable for X-ray analysis were obtained from the filtrate after a few days. Yield: 69%. Anal. Calcd for C26O2N4S2H18Cu: C, 57.13; H, 3.30; N, 10.25 (%). Found: C, 57.36; H, 3.53; N, 10.41 (%). IR: ν(SCN) = 2080 cm1, ν (CdO) = 1645 cm1, ν (skeletal vibration) = 1587 cm1. [Zn(Phpyk)2(SCN)2] (4). This was synthesized by following a similar procedure adopted for 1 using zinc(II) perchlorate hexahydrate (0.372 g, 1 mmol), in place of manganese perchlorate hexahydrate. Single crystals suitable for X-ray analysis were obtained from the filtrate after a few days. Yield: 72%. Anal. Calcd for C26O2N4S2H18Zn: C, 56.94; H, 3.30; N, 10.22 (%). Found: C, 57.23; H, 3.48; N, 10.42 (%). IR: ν(SCN) = 2094 cm1, ν (CdO) = 1629 cm1, ν (skeletal vibration) = 1580 cm1. Preparation of Polynuclear Complexes (58). [Mn(dca)2(Phpyk)]n (5). A methanolic solution (5 mL) of 2-benzoyl pyridine (0.366 g; 2 mmol) was added dropwise with constant stirring to a methanolic solution (10 mL) of manganese(II) perchlorate hexahydrate (1 mmol; 0.362 g). The stirring was continued for further 1 h, and then an aqueous solution (5 mL) of sodium dicyanamide (0.178 g; 2 momol) was added dropwise. After 2 h stirring the resulting mixture was filtered and the filtrate was kept in a CaCl2 desiccator. Single crystals suitable for X-ray data collection were obtained from the filtrate after a few days. Yield: 87%. Anal. Calcd for C16N7H9MnO: C, 51.86; H,2.43; N,26.47 (%). Found: C, 52.13; H, 2.61; N, 26.70 (%). IR: νs(CN) = 2317 cm1, νas(CN) = 2175 cm1, ν(CdO) = 1639 cm1, ν(skeletal vibration) = 1584 cm1. [Co(dca)2(Phpyk)]n (6). This was synthesized by following a similar procedure adopted for 1 using cobalt(II) perchlorate hexahydrate (0.366 g, 1 mmol), instead of manganese perchlorate hexahydrate. Single crystals suitable for X-ray analysis were obtained from the filtrate after a few days. Yield: 91%. Anal. Calcd for C16N7H9CoO: C, 51.30; H, 2.40; N, 26.19 (%). Found: C, 51.13; H, 2.59; N, 26.40 (%). IR: νs(CN) = 2313 cm1, νas(CN) = 2179 cm1, ν(CdO) = 1630 cm1, ν(skeletal vibration) = 1586 cm1. [Cu(dca)2(Phpyk)]n (7). This was synthesized by following a similar procedure adopted for 1 using copper(II) perchlorate hexahydrate (0.370 g, 1 mmol), instead of manganese perchlorate hexahydrate. Single crystals suitable for X-ray analysis were obtained from the filtrate after a few days. Yield: 78%. Anal. Calcd for C16N7H9CuO: C, 50.68; H, 2.38; N, 25.87 (%). Found: C, 50.93; H, 2.67; N, 26.10 (%). IR νs(CN) = 2324 cm1, νas(CN) = 2184 cm1, ν(CdO) = 1655 cm1, ν(skeletal vibration) = 1586 cm1. [Zn(dca)2(Phpyk)]n (8). This was synthesized by following a similar procedure adopted for 1 using zinc(II) perchlorate hexahydrate (0.372 g, 1 mmol), instead of manganese perchlorate hexahydrate. Single crystals suitable for X-ray analysis were obtained from the filtrate after a few days. Yield: 63%. Anal. Calcd for C16N7H9ZnO: C, 50.44; H, 2.36; N, 25.74 (%). Found: C, 50.23; H, 2.68; N, 26.98 (%). IR νs(CN) = 2383 cm1, νas(CN) = 2287 cm1, νas(CN) = 2174 cm1, ν(CdO) = 1661 cm1, ν(skeletal vibration) = 1587 cm1. Crystallographic Data Collection and Refinement. Diffraction data for all the structures reported were collected at room temperature on a BRUKER SMART APEX diffractometer (MoKR radiation, λ = 0.71073 Å) equipped with CCD. Cell refinement, indexing and scaling of the data set were carried out using packages Bruker SMART APEX and Bruker SAINT package.9 All the structures were solved by 3199
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Table 1. Crystal Data and Details of Structure Refinements for Compounds 14 1
2 3 0.5H2O
3
4
empirical formula
C26H18MnN4O2S2
C26H19NiN4O2.50S2
C26H18CuN4O2S2
C26H18ZnN4O2S2
formula weight
537.50
550.28
546.10
541.49
crystal system
monoclinic
triclinic
monoclinic
monoclinic C2/c
space group
C2/c
P1
P21/n
a (Å)
13.7528(11)
8.148(6)
8.999(2)
13.914(3)
b (Å)
10.7643(9)
13.341(9)
10.750(3)
10.605(3)
c (Å)
18.0328(14)
13.685(9)
13.169(3)
17.861(6)
109.0340(10)
62.342(11) 87.107(13)
90.178(4)
108.927(7)
R () β () γ ()
a
82.933(13)
volume (Å3)
2523.6(4)
1307.6(16)
1273.9(6)
2493.1(13)
Z
4
2
2
4
Dcalcd (g cm3)
1.415
1.398
1.424
1.460
μ MoKR, (mm1)
0.719
0.934
1.052
1.184
F(000)
1100
566
558
1120
θmax () reflns collected
28.28 7281
25.00 9445
27.75 10818
28.25 10217
unique reflections
2923
4573
3051
2939
Rint
0.0179
0.0507
0.0346
0.0232
observed I > 2σ(I)
2677
3364
2299
2657
parameters
195
322
160
195
goodness of fit (F2)
1.013
1.222
0.774
0.556
R1 (I > 2σ(I))a
0.0312
0.1098
0.0376
0.0285
wR2a ΔF (e/Å3)
0.0831 0.296, 0.153
0.2355 0.854, 0.771
0.1034 0.501, 0.332
0.0919 0.343, 0.259
R1 = Σ ||Fo||Fc||/Σ|Fo|, wR2 = [Σw(Fo2 Fc2)2/Σw(Fo2)2 ]1/2.
direct methods and subsequent Fourier analyses10 and refined by the full-matrix least-squares method based on F2 with all observed reflections. The contribution of H atoms at calculated position was introduced in the final cycles of refinement. A residual in the ΔF map of compound 3 was interpreted as lattice water oxygen (situated on a symmetry center, H atoms not located). Crystallographic data and details of refinement are reported in Table 1 (for complexes 14) and Table 2 (for complexes 58). All the calculations were performed using the WinGX System, Ver 1.80.05.11
’ RESULTS AND DISCUSSION Structural Description of Complexes 14. The X-ray structure determinations of compounds 14 of formulation [MII(NCS)2(Phpyk)2] show octahedral metal complexes with SCN ligands monocoordinated through the nitrogen donor and the Phpyk acting, as expected, as bidentate chelating ligand. However, the complexes are diastereoisomers and exhibit different configuration. Complexes of type [M(A-A)2X2 ] with two bidentate and two monodentate ligands may have a C2 (of stereochemistry Δ or Λ) or a C2v symmetry.12 Since here the chelating Phpyk ligand is heterotopic (A-B), six additional stereoisomers are feasible in the former case. These are complexes having both X species trans located to oxygen or nitrogen atoms of the two chelating ligands (Scheme 2a,b) or two X are positioned trans to the oxygen of one Phpyk and to the nitrogen of the second Phpyk (Scheme 2c), plus the correspondent optical enantiomer. In case of trans located monodentate X ligands, two stereoisomers are possible (Scheme 2d,e) depending on the orientation assumed by the chelating ligand.
Crystal structures of complexes 1 and 4 (M = Mn, and Zn) are isomorphous and isostructural. The ORTEP drawing of 1 is illustrated in Figure 1, and a selection of bond lengths and angles for the two compounds is reported in Table 3. The octahedral metal ion is located on a crystallographic 2-fold axis bisecting the SCNMNCS and (py)NMN(py) angles, leading oxygen donors of the 2-pyridyl-phenylketone to be trans located. The MnO and MnN bond lengths follow the expected values according to the metal ion radius and metal coordination properties. In particular, the ZnN bond lengths appear 0.1 Å shorter than the corresponding ones of Mn. The molecular structure of nickel complex (2) appears to have a pseudo 2-fold axis, although no crystal symmetry is present, but the stereoisomer presents a reversed coordination for the chelating ligands (with respect to that observed in 1 and 4), being the Phpyk nitrogen atoms trans located. The coordination distances for the two ligands are close comparable (Table 4). Finally, in complex 3 the copper ion is located on a center of symmetry so that all the same donor atoms are trans to each other. In this case, the CuO distances (Table 3) undergo to the JahnTeller effect being considerably longer (2.4346(19) Å) with respect to the CuN bond lengths measured in the equatorial plane (CuN(1) = 2.016(2), CuN(2) = 1.958(2) Å). The values are comparable to those observed in the complex where trans located azido replace dicyanamide anions.13 It is worth noting the values observed in the byte angle of the phpyk ligand, which is of 70.69(4) for Mn (1) complex, of 73.97(7) and 73.27(5) for Cu (3) and Zn (4), respectively, and even larger in the Ni complex 2 [77.4(2) and 76.8(2) for the two independent 3200
dx.doi.org/10.1021/cg2004485 |Cryst. Growth Des. 2011, 11, 3198–3205
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Table 2. Crystal Data and Details of Structure Refinements for Compounds 58 5
6
7
8
empirical formula
C16H9MnN7O
C16H9CoN7O
C16H9N7CuO
C16H9N7OZn
formula weight
370.24
374.23
374.01
380.67
8.4574(11)
crystal system
orthorhombic P212121
space group a (Å)
8.6476(2)
8.4837(2)
8.3767(12)
b (Å)
12.7504(3)
12.7231(2)
12.9906(18)
12.7306(17)
c (Å)
15.8872(4)
15.5816(3)
15.469(2)
15.689(2)
volume (Å3) Z
1751.73(7)
1681.86(6)
1683.3(4)
1689.2(4)
4
Dcalcd (g cm3)
1.404
1.478
1.495
1.497
μ MoKR, (mm1)
0.772
1.039
1.316
1.473
F(000)
748
756
764
768
θmax ()
32.92
27.46
28.33
28.22
reflns collected
12564
20398
10040
10168
unique reflections
5584
3830
3907
3911
Rint observed I > 2σ(I)
0.0305 4403
0.0417 3516
0.0229 3671
0.0258 3605
goodness of fit (F2)
0.992
1.048
1.035
1.054
R1 (I > 2σ(I))a
0.0353
0.0258
0.0277
0.0288
wR2a
0.0807
0.0582
0.0672
0.0721
ΔF (e/Å3)
0.306, 0.278
0.353, 0.191
0.502, 0.231
0.292, 0.224
parameters
a
226
R1 = Σ ||Fo||Fc||/Σ|Fo|, wR2 = [Σw(Fo2 Fc2)2/Σw(Fo2)2]1/2.
Scheme 2. Possible Isomers for Complex [M(A-B)2X2] with Indication of Point Symmetry
ligands). All the complexes crystallize in centrosymmetric space groups, so that the Δ and Λ isomers are both present, but no complex was isolated with a configuration having the N of one Phpyk trans to the O of the other chelating ligand. We do not have a clear explanation for the formation of the different isomers obtained; however the configuration having trans located 2-benzoylpyridine ligands seems the preferred one, and complexes [Co(H2O)2(Phpyk)2](ClO4)2,13 [Zn(CH3OH)2(Phpyk)2](BF4)27a and [Zn(Phpyk)2(OTf)2]7a [Cu(H2O)2(Phpyk)2 ](NO 3 )2 , 14 [Cu(Phpyk)2 (N 3 )2 ], 15 and [Cu(Phpyk)2 (Br)2],15 with same donor atoms in trans position, have been reported. Structural Description of Complexes 58. All the compounds 58 of formulation [M(dca)2(Phpyk)]n are isomorphous
and crystallize in orthorhombic chiral space group P212121. Each metal displays a distorted octahedral coordination environment having a N5O chromophore; the ORTEP drawing of the coordination sphere of complex 5 with atom labeling scheme is depicted in Figure 2. The coordination bond lengths (reported in Table 4) show typical values as expected for these transition divalent metal ions. In the case of copper an elongation of the CuO(1) bond distance and of the CuN(dca) one in trans position is indicative of the JahnTeller effect in this derivative (2.5207(17), 2.219(2) Å, respectively (Table 5)). In Mn and Zn complexes, the chelating MO distances relative to the 2-benzoylpyridine are longer by ca. 0.1 Å, while the MN appear slightly shorter (0.05, 0.09 Å) with respect to those measured in the mononuclear species 1 and 4. This feature can be due to crystal packing effects, although the chelating O1MN1 angles do not differ from those measured in the above-reported complexes. The bridging behavior of dicyanamide anions gives origin to a 3D covalently bonded polymeric network of 66 topology. In fact, each metal center represents a four-connecting node, which links to equivalent four-connecting centers through μ1,5bridging dicyanamide ligands (Figures 3 and 4). Figure 5 sketches the coordination network where zigzag arrays of M(dca)M running parallel to plane ab are further connected along axis c by the other crystallographic independent dicyanamide anion. The end-on connections of the former dicyanamide anion (N5 3 3 3 N7) span the metal ions at longer distance (range 8.3158.458 Å) with respect to the N2 3 3 3 N4 dicyanamide linkers along axis c, which are averagely 0.15 Å shorter. On the other hand, Figure 6 shows a view of the 3D arrangement with indication of the Phpyk phenyl rings inside rhomboidal channels running parallel to axis a. 3201
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Figure 1. ORTEP drawing (40% probability ellipsoids) of complex 1 (primed atoms at x, y, z þ 1/2). The same label scheme is applied to the isomorphous structure of complex 4 (Zn) (given in Supporting Information).
Table 3. Selected Bond Lengths (Å) and Angles (ο) for Complexes 1, 3, and 4a 1, Mn
3, Cu
Table 4. Selected Bond Lengths (Å) and (ο) Angles for Complex 2
4, Zn
NiO(1)
2.154(5)
NiO(2)
2.159(6)
NiN(1)
2.083(6)
NiN(3)
2.070(6)
NiN(2)
1.987(8)
NiN(4)
2.014(8) 168.8(3)
MO(1)
2.2243(10)
2.4346(19)
2.1838(13)
MN(1)
2.3159(12)
2.016(2)
2.2161(15)
MN(2)
2.1160(14)
1.958(2)
2.0218(16)
O(1)NiO(2)
89.1(2)
N(4)NiO(2)
177.53(6)
N(1)NiO(1)
77.4(2)
N(2)NiN(1)
95.5(3)
172.0(3)
N(3)NiN(1)
164.7(2)
0
O(1 )MO(1)
178.23(5)
180.0
O(1)MN(1)
70.69(4)
106.03(7)
73.27(5)
N(2)NiO(1)
O(1)MN(10 )
107.88(4)
73.97(7)
104.78(5)
N(3)NiO(1)
89.3(2)
N(4)NiN(1)
92.6(3)
89.09(6) 92.49(6)
N(4)NiO(1)
84.8(3)
N(2)NiN(3)
97.3(3)
95.3(2) 88.0(3)
N(2)NiN(4) N(4)NiN(3)
99.3(3) 93.7(3)
76.8(2)
C(13)N(2)Ni
172.9(8)
C(26)N(4)Ni
168.5(8)
N(2)MO(1) N(2)MO(10 )
89.51(5) 91.60(5)
85.20(9) 94.80(9)
N(1)MN(1 )
80.07(6)
180.0
80.55(8)
N(1)NiO(2) N(2)NiO(2)
N(2)MN(10 )
92.93(5)
87.93(9)
92.59(6)
N(3)NiO(2)
0
N(2)MN(1)
155.42(5)
92.07(9)
158.51(6)
N(2 )MN(2)
102.32(8)
180.0
100.50(10)
C(13)N(2)M
172.75(14)
162.7(2)
175.57(15)
0
Symmetry codes for primed atoms: complex (1) x, y, z þ 1/2; (3) x, y, z þ 2; (4) x, y, z þ 1/2.
a
It is worth noting that the 66 topology usually refers to a diamantoid network; here the structure is built up by octahedral metal ions to form a 4 connected net being two coordination sites occupied by the chelating 2-benzoylpyridine ligand, which acts as a template for the construction of the coordination network having such a topology. IR-Spectral Study. The monomeric thiocyanato complexes 14 exhibit very strong sharp single band in the range of 20652095 cm1 correspond to the stretching frequency of SCN moiety. On the other hand, the IR spectral analyses of polymeric dicyanamido complexes (58) indicate the presence of dicyanamide moiety in them with different mode of coordination as is evidenced from splitted band in each case in the range 21202400 cm1. All the complexes exhibit IR stretching frequencies corresponding to the carbonyl group of the
hemilabile ligand, Phpyk at around 1640 cm1 and skeletal vibrations at ∼1430 and ∼1580 cm1 (spectra are in Supporting Information). Solid State Thermal Studies of complexes 18. Solid state thermal analyses have been performed in order to (i) understand the thermal decomposition patterns of the complexes, (ii) to verify the molecular composition of the complexes, and (iii) to synthesize the thermally stable end products. Critical analyses suggest that monomeric thiocyanato complexes yield corresponding metal sulphides as the end products, whereas corresponding metal oxides are the final results of the pyrrolytic reactions of the polymeric dicyanamido complexes. The thermograms as well as the calculated and experimental weight losses, temperature range of decomposition are reported as Supporting Information. Characterization and Photoluminescence Property of Synthesized ZnO Nanoparticale. Thermal analysis of [Zn(dca)2(Phpyk)]n indicates the formation of ZnO as the thermally stable end product obtained at 540 C. The SEM analysis reveals that pyrolytically synthesized ZnO nanoparticles 3202
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Figure 3. ORTEP drawing (40% probability ellipsoids) of complex 3 (primed atoms at x, y, z þ 2).
Figure 2. ORTEP drawing (40% probability ellipsoids) of complex 2.
Table 5. Selected Bond Lengths and Angles for Complexes 58 5, Mn
6, Co
7, Cu
8, Zn
MO(1)
2.3182(15)
2.2065(14)
2.5207(17)
2.3317(18)
MN(1)
2.2646(15)
2.1282(16)
2.0320(18)
2.1255(19)
MN(2)
2.177(2)
2.1377(17)
2.0230(19)
2.214(2)
MN(4) MN(5)
2.2310(18) 2.165(2)
2.0789(18) 2.0808(18)
1.9976(19) 1.972(2)
2.096(2) 2.055(2)
MN(7)
2.1419(19)
2.0595(18)
2.219(2)
2.045(2)
Mdca(567)M
8.458
8.339
8.398
8.315
Mdca(234)M
8.288
8.124
8.048
8.210
N(1)MO(1) N(1)MN(2)
70.86(5) 90.57(7)
74.80(6) 90.04(7)
72.70(6) 89.22(8)
73.04(7) 87.51(9)
N(1)MN(4)
88.99(7)
90.71(7)
90.22(8)
91.42(9)
N(1)MN(5)
165.00(7)
167.71(7)
166.89(8)
161.96(8)
N(1)MN(7)
92.96(7)
94.84(7)
94.90(7)
96.09(9) 169.94(10)
N(2)MN(4)
170.16(9)
171.68(8)
171.43(10)
N(2)MN(5)
91.20(8)
87.00(8)
88.33(9)
86.26(10)
N(2)MN(7)
95.35(9)
93.19(8)
93.30(9)
93.83(10)
N(2)MO(1) N(4)MN(5)
88.53(8) 86.73(8)
83.00(7) 90.53(7)
85.36(8) 90.29(9)
81.70(8) 91.77(10)
N(4)MN(7)
94.48(8)
95.00(8)
95.27(9)
96.23(10)
N(4)MO(1)
82.05(7)
89.21(7)
86.30(8)
88.42(9)
N(5)MN(7)
101.70(8)
97.23(8)
98.10(9)
101.21(10)
N(5)MO(1)
94.30(7)
93.00(6)
94.26(7)
89.31(8)
N(7)MO(1)
163.43(7)
168.89(7)
167.53(7)
168.33(8)
(∼20 nm) have a triangular morphology (Figure 7). In addition, with the purpose to confirm further the fine-quality ZnO nanoparticles, IR and UVvis spectral studies have been performed. The IR spectrum (Supporting Information) of the
Figure 4. ORTEP drawing (40% probability ellipsoids) of the coordination sphere of manganese(II) ion in complex 5. (symmetry codes: (i) x þ 5/2, y, z 1/2; (ii) x þ 3, y 1/2, z þ 3/2; (iii) x þ 5/2, y, z þ 1/2; (iv) x þ 3, y þ 1/2, z þ 3/2). The same labeling scheme is applied to the isomorphous structures of complexes 68 (Co, Cu, and Zn).
synthesized ZnO nanoparticles is very similar as is reported by other groups.16 The band at ∼438 cm1 can be attributed to the ZnO stretching mode and the weak bands in the range of 13803480 cm1 are possibly due to the presence of water in the KBr matrix.16 The UVvis spectrum of synthesized ZnO nanoparticles exhibits maximum absorption peak at 360 nm similar to reported value for ZnO nanoparticles (Supporting Information).17 The shape of the absorption edge is only due to the electronic transition from the top of the valence band to bottom of the conduction band. The optical band gap of the prepared ZnO nanoparticales 3203
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Crystal Growth & Design
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Figure 7. SEM image of ZnO nanoparticle.
Figure 5. 2D coordination network of complexes 58; the spheres represent the metal ions and the connections the dca bridging anions.
Figure 8. Room temperature photoluminescence spectra of ZnO nanoparticle excited at λexc = 360 nm.
20 nm. Finally, we investigated the photoluminescence (PL) emissions from the prepared ZnO nanoparticles at three different excitation wavelengths of 320, 360, and 516 nm. The maximum PL emission takes place in the 400600 nm wavelength range, covering nearly the whole visible region of the electromagnetic spectrum, from the prepared ZnO nanoparticles at 360 nm excitation (Figure 8).20
Figure 6. Perspective view down axis a of the coordination network of complexes 58.
is determined by applying the Tauc model.18 Rhν ¼ Dðhν EgÞn where hν is the photon energy, Eg is the optical band gap, and D is a constant. The band gap estimated for our sample is 3.1 eV, which is slightly lower than that of bulk ZnO (3.2 eV) (Supporting Information). The observed absorption edge led to a rough assessment that, according to the formula proposed by Brus,19 the mean diameter of ZnO particles should be less than
’ CONCLUSION The versatile coordination binding modes of two pseudohalides thiocyanate and dicyanamide have been exploited to synthesize complexes of some 3d-metal ions, namely, MnII, CoII, NiII, CuII, and ZnII, in the presence of the hemilabile ligand 2-benzoylpyridine. Mononuclear complexes are invariably obtained when the pseudo halide is thiocyanate with four (complexes 14) of the aforesaid five metal ions (to date we failed to obtain single crystals suitable for data collection of the Co-SCN-Phpyk system), whereas polynuclear species are generated with four (complexes 58) out of five metal ions (attempts to prepare single crystals of the Ni-dva-Phpyk species were unsuccessful up to now). All the mononuclear complexes crystallize in 3204
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Crystal Growth & Design centrosymmetric space groups, and therefore the expected Δ and Λ isomers for them are both present in the crystal. Interestingly, no complex has been obtained with a configuration having the N of one Phpyk trans to the O of the other chelating ligand and only in the Cu-complex (complex 3) the two thiocyanato ligands are in trans-configuration. On the other hand, polymeric dicyanamido complexes 58 are isomorphous and crystallize in orthorhombic chiral space group P 212121. The bridging mode of dicyanamide anions helps to generate a 3Dl covalently bonded polymeric network of 66 topology for all the polynuclear complexes. In addition, the coordination polymers demonstrated to be suitable precursors for the preparation of nanoscale materials and triangular shaped ZnO nanoparticles showing PL emission have pyrolytically been synthesized. The synthesis of nanoparticles from coordination polymers and their applications especially in the field of catalysis are underway in our laboratory.
’ ASSOCIATED CONTENT
bS Supporting Information. CIF files of compounds 18; FTIR spectra, thermograms, UVvis spectra. This information is available free of charge via the Internet at http://pubs.acs.org. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected] (D.D.);
[email protected] (E.Z.).
’ ACKNOWLEDGMENT The authors wish to thank the University Grants Commission, New Delhi [UGC Major Research Project, F. No. 34-308\2008 (SR) Dated: 31.12.2008 (DD) and Center for Nano Science and Nano Technology, University of Calcutta, for financial support. We also thank Department of Science and Technology (DST), New Delhi, for providing single crystal diffractometer facility at the Department of Chemistry, University of Calcutta, through DSTFIST program. ’ REFERENCES (1) (a) Ma, L.; Abney, C.; Lin, W. Chem. Soc. Rev. 2009, 38, 1248–1256. (b) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450–1459. (c) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim., K. Nature 2000, 404, 982. (d) Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura, K. J. Am. Chem. Soc. 1994, 116, 1151. (2) (a) Evans, O. R.; Lin, W. Acc. Chem. Res. 2002, 35, 511–522. (b) Evans, O. R.; Lin, W. Chem. Mater. 2001, 13, 2705–2712. (c) Evans, O. R.; Lin, W. Chem. Mater. 2001, 13, 3009–3017. (3) (a) Lan, A.; Li, K.; Wu, H.; Olson, D. H.; Emge, T. J.; Ki, W.; Hong, M.; Li, J. Angew. Chem.Int. Ed. 2009, 48, 2334–2338. (b) Chen, B.; Wang, L.; Xiao, Y.; Fronczek, F. R.; Xue, M.; Cui, Y.; Qian, G. Angew. Chem., Int. Ed. 2009, 48, 500–503. (c) Chen, B.; Wang, L.; Zapata, F.; Qian, G.; Lobkovsky, E. B. J. Am. Chem. Soc. 2008, 130, 6718–6719. (d) Gong, X.; Ostrowski, J. C.; Bazan, G. C.; Moses, D.; Heeger, A. J.; Liu, M. S.; Jen, A. K. Y. Adv. Mater. 2003, 15, 258. (e) Thompson, M. E. MRS Bull. 2007, 32, 694–701. (f) Mak, C. S. K.; Pentlehner, D.; Stich, M.; Wolfbeis, O. S.; Chan, W. K.; Yersin, H. Chem. Mater. 2009, 21, 2173–2175. (g) De Rosa, M. C.; Hodgson, D. J.; Enright, G. D.; Dawson, B.; Evans, C. E. B.; Crutchley, R. J. Am. Chem. Soc. 2004, 126, 7619–7626. (4) (a) Kurmoo, M. Chem. Soc. Rev. 2009, 38, 1353–1379. (b) Real, J. A.; Gaspar, A. B.; Niel, V.; Munoz, M. C. Coord. Chem. Rev. 2003,
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