Synthesis, single crystal structures, spectral and thermal characteristics of two cadmium coordination polymers, viz., [Cd(NO3)2(N2H4)2] (1) [Cd(C3H2O4)(N2H4)] (where C3H2O4 is malonate) (2) are reported. The μ2-bridging bidentate binding mode of the crystallographically unique hydrazine ligands in  (1) leads to a one-dimensional polymeric structure extending along c axis. The central Cd(II) in (2) exhibits hepta-coordination and is bonded to a unique malonate anion which exhibits a μ3-bridging pentadentate coordination, extending the structure along the a axis. The bridging bidentate binding of the crystallographically independent hydrazine ligand extends along b axis resulting in a 2-D structure

B. N., SIVASANKAR 

D, SANTHOSH SHANTHAKUMAR 

R, PRADEEP 

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Indian Journal of Chemistry Vol. 57A, July 2018, pp. 905-909    Notes   Synthesis and structure characterization of two cadmium coordination polymers based on μ2-bridging bidentate hydrazine ligand D Santhosh Shanthakumara, R Pradeepb, B Subramanic &  B N Sivasankarb, * aDepartment of Chemistry, Sri Krishna College of Technology, Kovaipudur, Coimbatore 641 042, Tamilnadu, India bDepartment of Chemistry, Government Arts College, Udhagamandalam, The Nilgiris 643 002, Tamilnadu, India cDepartment of Chemistry, Crescent School, Vandalur, Chennai 600 048, Tamil Nadu, India Email: sivabickol@yahoo.com Received 25 March 2017; re-revised and accepted 22 June 2018 Synthesis, single crystal structures, spectral and thermal characteristics of two cadmium coordination polymers, viz., [Cd(NO3)2(N2H4)2] (1) [Cd(C3H2O4)(N2H4)] (where C3H2O4 is malonate) (2) are reported. The μ2-bridging bidentate binding mode of the crystallographically unique hydrazine ligands in  (1) leads to a one-dimensional polymeric structure extending along c axis. The central Cd(II) in (2) exhibits hepta-coordination and is bonded to a unique malonate anion which exhibits a μ3-bridging pentadentate coordination, extending the structure along the  a axis. The bridging bidentate binding of the crystallographically independent hydrazine ligand extends along b axis resulting in a 2-D structure.  Keywords: Coordination polymers, Cadmium coordination polymers, Crystal structures, Hydrazines, Malonates, μ2-Bridging bidentate, μ3-Bridging pentadentate The synthesis, structure and physical and chemical properties of various hydrazinium salts have been reported in literature1. Basically, hydrazine in an aqueous solution exists in different forms like N2H4, N2H5+ and N2H62+. Several process methods have been developed for the synthesis of these salts, but typically, the method of preparation varies with the type of salt made2. Plenty of bis-hydrazine metal complexes have been prepared in basic medium (pH > 8) and well characterized by their spectral and thermal studies3-7. During the last two decades, a large number of metal carboxylates containing neutral hydrazine have been reported8-12.  In contrast, though bridged hydrazine metal complexes including carboxylates can be easily precipitated from aqueous solution at higher pH, they are mostly obtained only as polycrystalline material. Due to the difficulty in obtaining the single crystals, only a few crystal structures of bis-hydrazine complexes have been reported in the literature13-17. Furthermore, mono-hydrazine complexes are rare and only a few articles have been published so far18, 19. Herein, we report the synthesis, spectral and thermal characterization and X-ray structure determination  of two cadmium coordination polymers based on  μ2-bridging bidentate hydrazine ligand.  Experimental All reagents and chemicals used for synthesis and analyses were obtained commercially and used without further purification. Doubly distilled water was used in all the experiments. All glassware used were washed with acetone, followed by rinsing with distilled water and dried in an oven before use. The compositions of the complexes were determined by hydrazine and metal analyses. The metal  content of the complexes were determined by EDTA complexometric titrations after decomposing a known amount of the complex with concentrated nitric acid. The hydrazine content in the complexes was determined volumetrically by titrating against 0.025 M potassium iodate solution under Andrew’s condition20. Chemical analyses for carbon, hydrogen and nitrogen were performed using a Perkin-Elmer (model 1240 CHN) analyzer. Infrared spectra of the complexes were recorded on a Shimadzu spectrophotometer using KBr pellets in the range 4000–400 cm-1. The simultaneous TG-DTA of the complexes in air was carried out using SWI TG/DTA 6200 thermal analyser. The thermal experiments were performed in air at a heating rate of 10 oC min-1 using platinum cups as sample holders.  X-ray data collection was performed with Bruker AXS Kappa Apex II CCD diffractometer equipped with graphite monochromated Mo-K ( = 0.71073 Å) radiation at IIT Madras, Chennai, India. The automatic cell determination routine, with 36 frames at three different orientations of the detector, was employed to collect reflections for unit cell determination. Further, intensity data for structure determination were collected through an optimized strategy which gave an average  4-fold redundancy. The program APEX2-SAINT21 was used for integrating the frames. Four-fold redundancy per reflection was utilized for achieving good  multi-scan  absorption  correction  using  the  program  INDIAN J CHEM, SEC A, JULY 2018   906SADABS21. Besides absorption, Lorentz, polarization and decay corrections were applied to intensity during data reduction. The structures were solved by direct methods using SIR9222 and refined by full-matrix least squares techniques using SHELXL-9723, computer program. Molecular graphics were drawn using ORTEP324. Hydrogens on all carbon atoms were fixed at calculated positions and refined as riding model with C—H = 0.97 Å, Uiso(H) = 1.2 Ueq(C), whereas hydrogens on nitrogen were fixed from the difference electron density peaks and allowed to refine freely. Compound (1) was prepared as follows: An aqueous solution (50 mL) containing a mixture of propionic acid (1.48 mL, 0.02 mol) and 99% hydrazine hydrate (2 mL, 0.04 mol) was added slowly to the aqueous solution (50 mL) of cadmium nitrate hexahydrate (3.0847 g, 0.01 mol). The precipitate which formed immediately was filtered and then the resulting solution was concentrated to half of its volume and allowed to crystallize. The needle-like crystals formed after 2-3 days were filtered, washed with water and then dried. These crystals were soluble in water and insoluble in alcohol and other organic solvents. Yield: 74%. Anal. (%): Calc.: H, 2.68;  N, 27.97; N2H4, 21.30; Cd, 37.41. Found: H, 2.50;  N, 27.80; N2H4, 21.20; Cd, 38.00.  Compound (2) was prepared with malonic acid. An aqueous solution (50 mL) containing a mixture of malonic acid (1.04 g, 0.01 mol) and 99% hydrazine hydrate (2 mL, 0.04 mol) was added slowly with constant stirring to an aqueous solution (100 mL) containing cadmium nitrate hexahydrate (3.0847 g, 0.01 mol). The precipitate, formed immediately after adding the ligand solution to the metal solution, was separated by filtration and the clear solution was concentrated to half of its volume. The resultant  clear solution was filtered and kept aside at room temperature. The crystals were collected the next day, washed with water and then dried in air. Yield: 61% Anal. (%): Calc.: C, 14.62; H, 2.45; N, 11.37; N2H4, 12.98; Cd, 45.60. Found: C, 14.10; H, 2.50; N, 11.80; N2H4, 13.10; Cd, 46.20.  Results and discussion Compounds (1) and (2) were prepared by the aqueous reaction of cadmium nitrate hexahydrate with an aqueous solution containing hydrazine hydrate in the presence of propionic acid or malonic acid. It is observed that in the case of propionic acid, the carboxylic acid is not incorporated in the product, while use of the dicarboxylic malonic acid affords a nitrate free product containing malonate ion as the charge balancing anion. The infrared spectra of both the complexes  show two sharp bands in the region 3200–3400 cm-1, which is assigned to the N-H stretching of hydrazine molecule (Supplementary data, Figs S1 and S2). Generally, the coordinate (terminal) M-N-N stretching for hydrazinium cation is observed in the range  1000–1010 cm-1, but in the present complexes, a strong band at 965–975 cm-1 was observed in both  the compounds, which supports the N-N stretching  of bridged mode of hydrazine. Thermal degradation studies of (1) and (2) were carried out. Complex (1) exhibited a single step decomposition in the temperature range 250–280 oC and the corresponding DTA showed an exotherm at 256 oC (Supplementary data, Fig. S3). The final product obtained was CdO as expected. The malonatohydrazine cadmium(II) (2) shows a sharp exotherm at 227 oC indicating the loss of one hydrazine molecule in the temperature range 220–250 oC in the first stage.  The intermediate further undergoes ligand pyrolysis in the temperature range 380–420 oC to give CdO as a final residue. The DTA corresponding to this stage shows an exotherm at 405 oC (Supplementary data, Fig. S4).  The crystal data for the complexes are summarized in Table 1 and selected bond lengths are given in Table 2. The bond angles and hydrogen bonds  for the complexes are given in Table S1 and S2 (Supplementry data) respectively. Compound 1 crystallizes in the triclinic space group P-1. Its structure consists of an unique Cd(II) ion, two crystallographically independent nitrate anions and two unique hydrazine ligands, all of which are situated in the general positions (Fig. 1). The central Cd(II) is bonded to four N atoms from four different hydrazine ligands and to two O atoms  (O1, O6) of the nitrate anions which function as terminal ligand, and has a distorted octahedral geometry. The nitro groups are disposed trans to each other in the octahedron. One of the nitrate anions  is disordered over two positions (N2, O6, O7, O8 and N2', O6', O7', O8') with the occupancy ratio of 0.78:0.22. The disorder was resolved by successive Fourier electron density maps and least squares refinements. Sum of the occupancies of the disordered components were restrained as 1 during refinement. The corresponding bond distances of disordered groups were restrained to equal within an allowed standard deviation of 0.01 Å.  Anisotropic  displacement   Table 1  (1) CCDC No. 976540Empirical formula Cd HFormula weight 300.52Temperature 293(2) KWavelength 0.71073 ÅCrystal system, space group Triclinic, PUnit cell dimensions a = 6.91600(10) Å α = 80.5700(10) b = 7.01500(10) Å β = 80.6400(10) c = 8.6420(2) Å γ = 68.9500(10)Volume 383.546(12) ÅZ, Calculated density 2, 2.602 Absorption coefficient 2.867 mmF(000) 292 Crystal size 0.25×Theta range for data collection 2.40–Limiting indices -9 ≤ hReflections collected / unique 8603/ 1850 [R(int)Completeness to theta 27.99 Absorption correction SemiMax. and min. transmission 0.6856 and 0.5236Refinement method Full-Data / restraints / parameters 1850/ 7/ 188Goodness-of-fit on F2 1.162Final R indices [I>2sigma(I)] R1 = 0.0137, wR2 = 0.0337R indices (all data) R1 = 0.0139, wR2 = 0.0338Extinction coefficient 0.120(2)Largest diff. peak and hole 0.488 and  Table 2 — Selected bond lengths (Å) for [Cd(NOand Cd(C3H2O4)(N2H4) (2) (1)  Cd1-O6 2.413(6)  Cd1-O1 Cd1-N3 2.3509(13)  Cd1-O2 Cd1-O1 2.4550(12)  Cd1-O3 Cd1-N6 2.3480(13)  Cd1-O3#1 Cd1-N5 2.3445(13)  Cd1-O4 Cd1-N4 #1 2.3251(13)  Cd1-N1    Cd1-N2#2 Symmetry transformations used to generate equivalent atoms: #1 -x,-y,-z; #2 -x,-y,-z+1.  NOTES     Fig. 1 — Crystal structure of [Cd(NO3atom labelling scheme and the coordination sphere of Cd(II) in (1). Displacement ellipsoids are drawn at 30% probability level excepting for H atoms, which are shown as spheres of arbitrary radius. The nitrate anion (N2) is disordered. For clarity the disordered atoms are not displayed. [Symmetry code: i)  — Crystal data and structure refinement for 1 and 2 (2)  1055303 8N6O6 C3H6 Cd N2O4  246.5  293(2) K  0.71073 Å -1 Monoclinic, P21/c  a = 7.2908(3) Å ° α = 90°  b = 12.2477(5) Å ° β = 98.199(2)°  c = 6.8703(3) Å ° γ = 90° 3 607.22(4) Å3 mg/m3 2, 2.696 mg/m3 -1 3.549 mm-1 472 0.20×0.15 mm 0.20×0.20×0.15 mm 27.99o 2.82–24.99o  ≤ 9, -9 ≤ k ≤ 9, -11≤ l ≤ 11 -8 ≤ h ≤ 8, -14 ≤ k ≤ 14,   = 0.0234] 5088/ 1063  [R(int) = 0.0258] (99.8%) 24.99 (99.8%) -empirical from equivalents Semi-empirical from equivalents 0.6365 and 0.5236 matrix least-squares on F2 Full-matrix least-squares on F 1063/ 6/ 108  1.231  R1 = 0.0148, wR2 = 0.0364 R1 = 0.0154, wR2 = 0.0366 0.0326(9) 0.801 e Å-3 0.301 and –0.241 e Å3)2(N2H4)2] (1)(2) 2.5200(19) 2.3164(18) 2.3271(19) 2.3628(19) 2.627(2) 2.295(2) 2.331(2) 907 )2(N2H4)2] (1), showing the -x, -y, -z]. -6 ≤ l ≤ 8  2   -3 908 parameters (Uij) of atoms in the disordewere restrained to be equal within the limits of allowed standard deviation. The thermal parameters of the atoms of the disordered moieties were restrained to show approximate isotropic behaviour within an effective standard deviation of 0.02 ÅBoth the unique hydrazine ligands function as μ2-bridging bidentate ligands (Supplementary data, Fig. S5(a & b)) resulting in slightly different Cd···Cd separations. The binding of a pair of unique hydrazine ligands leads to the formation of a six membe{Cd2N4} ring. Analysis of the crystal structure reveals that the Cd(II) ions are linked into a one(1-D) chain, (Fig. 2) with alternating Cd···Cd separations of 4.328 and 4.335 Å respectively. In the 1-D chain, each Cd(II) is hexaand is bonded to two O atoms of the terminal nitrate ligands. Compound (2) crystallizes in monoclinic crystal system with P21/c space group. The asymmetric unit contains a unique malonate and one hydrazine in Fig. 2 — Alternating pairs of unique hydrazine ligands link the Cd(II) ions in (with alternating Cd···Cd separations of 4.328 and 4.335 Å respectively. For clarity only a portion of the infinite chain is shown.   Fig. 3 — Crystal structure of [Cd(C3H2O4)(N2Hhepta-coordination around Cd(II) and the atom labelling scheme. Displacement ellipsoids are drawn at 30% probability level excepting for H atoms, which are shown as spheres of arbitrary radius. [Symmetry code: i) -x, -y, -z; ii) -x, -y, 1-z INDIAN J CHEM, SEC A, JULY 2018   red groups 2.  red -dimensional  -coordinated  addition to Cd(II). The central metal Cd(II) is heptacoordinated to two nitrogen atoms of two different hydrazine ligands and five oxygen atoms of three different malonate ligands forminprism geometry (Fig. 3 and Supplementary data, Fig. S6). The μ2-bridging bidentate binding mode of the unique hydrazine ligand in (separation of 4.234 Å. (Supplementary data, Fig. S7) Note that a pair of unique (N1N2) of Cd(II) ions forming a Cd2Nmotif. The crystallographically unique malonate ligand exhibits a μ3-bridging pentadentate binding forming five Cd-O bonds. Each malonate is linked to three Cd(II). Alternatively, each Cd(II) is linked to three different malonate ligands (Supplementary data, Fig. S8) The μ3-bridging pentadentate binding mode, leads to three different Cd···Cd separations of 3.755, 6.939 and 7.291 Å (Supplementary data, Fig. S9). The bridging binding mode of the malonate ligand results in the formation of a 1-D chain extending along the whereas the bridging binding mode of the hydrazine ligands serves to link the Cd-malonate chains along c axis resulting in a 2-D layer structure (Fig. 4). 1) into a one-dimensional chain extending along  4)] (2) showing the ].  Fig. 4 — A view of the packing in the crystallographic showing the 2-D structure of (2).  -g a distorted trigonal  2) results in a Cd···Cd ligands links a pair 4 six membered ring mode a axis,    c axis   ac plane NOTES 909In both the complexes (1) and (2) the bidentate bridging mode of unique hydrazine ligand forms Cd2N4 six membered ring motifs. The Cd···Cd separation in Cd2N4 ring motif in (1) is found to be 4.328 Å and 4.335 Å, whereas in (2) it is 4.234 Å Supplementary data Crystallographic data for the structures reported in this article have been deposited with the Cambridge Crystallographic Data Centre under depository numbers CCDC 976540 and 1055303 for (1) and (2) respectively. These data may be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Other supplementary data associated with this article are available in the electronic form at http://www.niscair.res.in/jinfo/ijca/IJCA_57A(07)905-909_SupplData.pdf. Acknowledgement The authors thank Dr. Sudhadevi and Dr. Babu Varghese, SAIF, IIT Madras, Chennai, India for the structure refinement. The authors also thank the reviewer for useful discussion and help with the structural representations. 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Synthesis and structure characterization of two cadmium coordination polymers based on μ2-bridging bidentate hydrazine ligand

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Synthesis and structure characterization of two cadmium coordination polymers based on μ2-bridging bidentate hydrazine ligand

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