A three-dimensional network of H-bonding nickel (II) hexamethylenetetramine complex has been synthesized and characterised and its structure determined by single crystal X-ray diffraction studies which show that [Ni(H2O)6](HMTA)2Cl32.4H2O crystallizes in the triclinic crystal system with space group PĪ, a = 9.2955(4), b = 9.3187(2), c = 9.3996 Ǻ, α = 119.4160(10), β = 94.4940(10), ɣ = 100.8680(10)º, V =682.47(4) Å3 and z = 1. The nickel atoms are each bonded to six aquo ligands giving an octahedral geometry. The ligand hexamethylenetetramine (HMTA) and chloride ions are bonded to water molecules through hydrogen bonding. Thermal studies show a decomposition pattern corresponding to the loss of the coordinated and uncoordinated water molecules, chloride ions and HMTA ligand in the form of a mixture of gases

Agwara, Moise O.

Atamba, Moses A.

Awawou, Paboudam G.

Galindo del Pozo, Agustín

Ndifon, Peter T.

Tendo, Josepha N. Foba

Yufanyi, Mbom D.

Álvarez González, Eleuterio

idUS. Depósito de Investigación Universidad de Sevilla

 http://www.rasayanjournal.com  Vol.3, No.2 (2010), 207-213 ISSN: 0974-1496 CODEN: RJCABP  SYNTHESIS, CHARACTERISATION AND CRYSTAL STRUCTURE OF A THREE–DIMENSIONAL NETWORK OF AN H-BONDED Ni (II) HEXAMETYLENETETRAMINE COMPLEX  Moise O. Agwara1*, Peter T. Ndifon1, Mbom D. Yufanyi2, Josepha N. Foba Tendo2, Moses A. Atamba2,  Paboudam G. Awawou 1,Agustin Galindo3 and Eteuterio Álvarez41Co-ordination Chemistry Laboratory, Department of Inorganic Chemistry, Faculty of Science, University of Yaounde 1, P.O. Box 812 Yaounde, Cameroon. 2Department of Chemistry, University of Buea, P.O. Box 63 Buea, Cameroon 3Departemento de Quimica Inorganica, Universidad de Sevilla, Spain 4Insituto de Investigaciones Quimicas - CSIC - Universidad de Sevilla, Spain *E-mail: agwara29@yahoo.com  ABSTRACT A three-dimensional network of H-bonding nickel (II)-hexamethylenetetramine complex has been synthesized and characterised and its structure determined by single crystal X-ray diffraction studies which show that [Ni(H2O)6](HMTA)2Cl32.4H2O crystallizes in the triclinic crystal system with space group PĪ, a = 9.2955(4), b = 9.3187(2), c = 9.3996 Ǻ, α = 119.4160(10), β = 94.4940(10), ɣ = 100.8680(10)º, V =682.47(4) Å3 and z = 1. The nickel atoms are each bonded to six aquo ligands giving an octahedral geometry. The ligand hexamethylenetetramine (HMTA) and chloride ions are bonded to water molecules through hydrogen bonding. Thermal studies show a decomposition pattern corresponding to the loss of the coordinated and uncoordinated water molecules, chloride ions and HMTA ligand in the form of a mixture of gases. Key words: Nickel, hexamethylenetetramine, chloride, complexes, X-ray, structure, thermal, spectroscopy studies.   INTRODUCTION  There has been some considerable and renewed interest in the synthesis and characterisation of metal complexes of hexamethylenetetramine, a heterocyclic ligand having three fused rings in the chair configuration with four nitrogen atoms that can each donate a pair of electrons1-5. This is as a result of the varied coordination patterns which this ligand displays ranging from monodentate6, bridging7-10 non-chelating and the hydrogen-bonded frameworks5,11-14. Chain polymers for example,[Co (NO3)2(H2O)2(HMTA)2] has also been reported15 in which HMTA is covalently bonded to cobalt. The combination of covalent and hydrogen bonding in some of these metal-organic species gives rise to the observed three dimensional framework structures which easily decompose on thermal treatment to give thin films of the metal oxide. These complexes could therefore serve as precursors for metal oxide dispersions16-17.  In our recent paper18, we reported on the synthesis of some metal(II)-HMTA-aquo complexes and showed by infrared studies that water molecules in these compounds are both coordinating and non-coordinating. Molar conductance studies of Ni (H2O)6-HMTA-Cl2.4H2O revealed a 1:2 electrolyte type with the chloride acting as counter ions, thus non-coordinating.  In this paper, we report on the synthesis, characterisation, thermal analysis and the crystal structure of a three-dimensional network of H-bonded nickel (II)-hexamethylenetetramine complex.   H-BONDED Ni (II) HEXAMETYLENETETRAMINE COMPLEX                                                                                        Moise O. Aguara et al.  Vol.3, No.2 (2010), 207-213 EXPERIMENTAL All chemicals were used as supplied without further purification. The solvents were purified by standard methods. Elemental analyses for C, H, N were carried out on a Fisons Instrument 1108 CHNS-O, while quantitative estimation of Nickel (II) was done by complexometric titrations. Infrared spectra were recorded between pressed KBr discs on a Perkin – Elmer model IR-457 spectrometer and a Spectrum 100 FT-IR Perkin- Elmer Spectrometer, while electronic spectra were recorded on a Hitachi U-2000 spectrophotometer. Conductivity measurements were carried out in methanol using the Tacussel conductimeter, model CD810 at room temperature. Room temperature magnetic susceptibility measurements were determined using the Gouy method with mercury tetrathiocyanocobaltate (II) as calibrant. Thermogravimetric analyses were performed on a TGA Perkin – Elmer STA 6000 simultaneous Thermal Analyser Instrument under nitrogen atmosphere. Synthesis of [Ni(H2O)6](HMTA)2Cl2.4H2O  A solution of hexamethylenetetramine (2.80 g; 2.0 mmol) in 20 mL methanol was added dropwise to an aqueous solution of NiCl2.6H2O (4.75; 2.0 mmol) in 15 mL water with stirring. The mixture was further stirred for two hours and stored for four days during which crystallisation occurred giving green crystals. They were filtered, washed with diethylether and dried over silica gel in a dessicator, Mpt 215– 217ºC.  Analyses: Calc. for C12H44N8O10Cl2Ni (590.262): C: 24.42; H: 7.51; N: 19.02; Ni: 9.95%. Found C: 24.58; H: 7.74; N:  18.87; Ni: 10.15. Characteristic IR absorptions (KBr): 1 666, 1 623, 1 240, 813, 752 cm-1. Electronic: 24 938, 14 903 – 13 569 cm-1. Room temperature magnetic moment, µ = 3.32 B.M. molar conductance, 197Ω-1cm-1mol-1.  X-ray Crystal Structure Determination Suitable single crystals (green prism) of [Ni(H2O)6](HMTA)2Cl2.4H2O (0.70 x 0.60 x 0.55 mm3) coated with dry perfluoropolyether were mounted on glass fibres and fixed to the goniometer head in cold nitrogen stream (T =173 K). Data collection was performed on a Bruker-Nonius X8APEX-II CCD diffractometer using monochromatic radiation, λ(Mo-Kα1 ) = 0.71073Ǻ.  Out of the 33648 measured reflections, the final cell parameters were obtained by full matrix least squares techniques19 on 4140 observed unique reflections (Rint=0.0233) and 181 refined parameters with final R1=0.0229 for reflections with I > 2α(I) and ωR2 = 0.0644 for all data for the compound. All non-hydrogen atoms were refined with anisotropic displacement parameters. The data were reduced and corrected for Lorentz polarisation effects and absorption by multiscan method20. The structure was solved by direct methods21.  The hydrogen atoms were included from calculated positions and refined riding on their respective carbon atoms with isotropic displacement parameters.  Supplementary crystallographic data have been deposited at the Cambridge crystallographic data centre with deposition number CCDC 719425   RESULTS AND DISCUSSIONS The nickel (II)-Hexmethylenetetramine complex melted sharply at 215-217ºC.It has a molar conductance values of 197 Ω-1cm-1mol-1, suggesting that it is a 1:2 electrolyte type22. The counter ion, Cl- is therefore not coordinated to the nickel ion in the compound. The IR absorption bands observed at 1240 cm-1 and assigned to N-C stretch and the bands observed at 813 cm-1 and assigned to CH2 rock are in the range of 1240 and 813 cm-1 observed for the free hexamethylenetetramine ligand23. This observation suggests that hexamethylenetetramine is not strongly coordinated to the nickel ion. The IR bands at 1666, 1623 cm-1assigned to νH2O, are an indication of two types of crystallographically non-equivalent water molecules, (coordinated and non-coordinated water molecules) 24. The coordinate bond between water molecules and nickel ions results in the IR vibrational band observed at 752 cm-1. Hexamethylenetetramine is most probably bonded to the water molecules and the chloride anions by hydrogen bonds24.  The compound has a room temperature magnetic moment of 3.32 B.M. which is slightly higher than the spin-only value of 2.87 B.M. though within the 2.9 – 3.4 B.M. range for octahedral nickel (II) complexes25. The visible absorption spectrum of the compound reveals a band at 24950 cm-1 and another H-BONDED Ni (II) HEXAMETYLENETETRAMINE COMPLEX                                                                                Moise O. Aguara et al 208 Vol.3, No.2 (2010), 207-213 broad and split band at 14800-13570 cm-1. These bands have been assigned to 3A2g  → 3T1g (P) and 3A2g  → 3T1g (F) transitions respectively25. The splitting of the second band is probably due to spin-orbit coupling which mixes the 3T1g (F) and 1Eg states. The ratio of 1.84 of the height of the first to that of the second band is indicative of an octahedral geometry about the nickel ion26.  Thermal studies  Thermogravimetric, analysis (TGA) performed on powdered samples of the compound shows that it undergoes gradual mass loss from about 35oC to 246oC (Fig. 1). The TGA curve shows  a decomposition pattern which corresponds to the loss of ca. 12%, 18% and 42% mass consistent with the departure of four uncoordinated water molecules at 35 – 65oC, six coordinated water molecules at  85-110oC and the chloride ion and HMTA in the form of a mixture of various gases at 130-246oC.  The differential thermal analysis curves revealed endothermic peaks at ca. 50-190oC corresponding to the loss of water molecules and exothermic peaks at 205-246oC corresponding to the loss of the anions and HMTA molecules and the formation of nickel oxide.  X-ray Crystal Structures of compounds 1 and 2 The ORTEP view of the crystal structure of the compound is shown in Fig. 2, together with the atom numbering scheme used in the corresponding tables. The crystallographic and refinement data for this compound are shown on Table 1 while selected bond parameters are shown in Tables 2-4. The complex was found to crystallise in the triclinic crystal system, with space group Pī and Z=1.  Our results of elemental analysis, infrared, visible spectra, conductance and magnetic susceptibility measurements suggest that the nickel (II) ion in hexaaqua nickel (II)bis(hexamethylenetetramine) chloride tetrahydrate assumes an octahedral geometry with six water molecules covalently bonded to it. These results have been confirmed by X-ray structural analysis (Fig. 2) and TGA studies (Fig. 1). The Ni-O bond length of 2.0223(8) Å is consistent for nickel-oxygen covalently bonded species in an   octahedral geometry27.The chloride ions, hexamethylenetetramine ligands and the four uncoordinated water molecules are linked to each other through hydrogen bonding in which the chloride ions are hydrogen-bonded to free water molecules, which in turn form H-bonds with each other and with N-atoms of hexamethylenetetramine ligands, thus forming an overall three dimensional network structure.  ACKNOWLEDGMENTS The authors thank the government of Cameroon for financial assistance through the Fonds d’appui à la recherche (AMO and PTN) and we thank Pr Aminou Mohamadou of Institut de Chimie Moléculaire de Reims CNRS UMR 6229, Groupe de Chimie de Coordination, Faculté des Sciences, Université de Reims Champagne-Ardenne for assisting with some of the analyses.  Table-1: Summary of crystallographic and structure refinement data for [Ni(H2O)6](HMTA)2(NO3)2.4H2O  Formula C12H44Cl2N8NiO10[2(C6H12N4), H12NiO6, 4(H2O), 2(Cl)] Formula mass, g mol–1 590.16 Collection T, K 173(2)  λ (Mo Kα), Å 0.71073 crystal system triclinic space group  P1 a, Å 9.2955(4) b, Å 9.3187(2) c, Å 9.3996(2) α, deg 119.4160(10) β, deg  94.4940(10) γ, deg 100.8680(10) H-BONDED Ni (II) HEXAMETYLENETETRAMINE COMPLEX                                                                                Moise O. Aguara et al 209 Vol.3, No.2 (2010), 207-213 V, Å3 682.47(4) Z 1 ρ(calcd), Mg m–3 1.436 F(000) 314 µ, mm-1 0.963 Crystal dimensions,  0.70 x 0.60 x 0.55mm θ range, deg 2.53–30.50 No. of collected reflections 33648 No. of independent reflections/parameters 4140 / 181 Rint 0.0233 R1(F) [F 2>2σ(F 2)][a] 0.0229 wR2(F2)[b] (all data) 0.0658 S[c] (all data) 1.065 max./min. residual electron density, e Å–3+0.527 / –0.286   [a] R1(F) = ∑( Fo - Fc )/∑ Fo  for  the observed reflections [F 2>2σ(F 2)]. [b] wR2(F2) = {∑ [w(Fo2 Fc2)2]/ ∑ w(Fo2)2}1/2. [c] S = {∑ [w(Fo2- Fc2)2]/(n-p)}1/2;  (n = number of reflections, p =  number of parameters).  Table-2: Selected Bond lengths [Å] and Bond angles [°] for [Ni(H2O)6](HMTA)2(NO3)2.4H2O  Ni(1)-O(2) 2.0223(8) Ni(1)-O(1) 2.0434(7) Ni(1)-O(3) 2.0562(8) O(1)-H(1AO) 0.860(13) O(1)-H(1BO) 0.849(13) O(3)-H(3BO) 0.842(13) O(4)-H(4AO) 0.840(14) O(4)-H(4BO) 0.869(13) O(5)-H(5AO) 0.875(15) O(5)-H(5BO) 0.858(15) N(1)-C(3) 1.4731(13) N(1)-C(1) 1.4751(13) N(1)-C(2) 1.4753(14) N(2)-C(5) 1.4706(14) O(2)-Ni(1)-O(2) 180.0 O(2)-Ni(1)-O(1) 86.94(3) O(2)-Ni(1)-O(1) 93.06(3) O(2)-Ni(1)-O(3) 90.01(4) O(1)-Ni(1)-O(3) 86.30(3) O(3) -Ni(1)-O(3) 180.0 Ni(1)-O(1)-H(1AO) 118.7(10) Ni(1)-O(1)-H(1BO) 127.0(11) H(1AO)-O(1)-H(1BO) 106.4(15) Ni(1)-O(2)-H(2AO) 126.7(12) Ni(1)-O(2)-H(2BO) 126.2(12) H(2AO)-O(2)-H(2BO) 106.6(16) Ni(1)-O(3)-H(3AO) 118.7(11) Ni(1)-O(3)-H(3BO) 125.9(12) C(3)-N(1)-C(2) 108.44(8) C(1)-N(1)-C(2) 108.54(8) Symmetry transformations used to generate equivalent atoms: #1 -x+1,- y,y,-z+2 H-BONDED Ni (II) HEXAMETYLENETETRAMINE COMPLEX                                                                                Moise O. Aguara et al 210 Vol.3, No.2 (2010), 207-213   Table-3: Hydrogen bonds for [Ni(H2O)6](HMTA)2(NO3)2.4H2O  [Å and °].  D-H...A d(D-H) d(H...A) d(D...A) <(DHA) O(1)-H(1AO)...N(1)#2 0.860(13) 1.954(13) 2.8069(11) 171.3(14) O(1)-H(1BO)...O(5)#3 0.849(13) 1.891(13) 2.7268(12) 167.8(15) O(2)-H(2AO)...O(4)#2 0.846(14) 1.867(14) 2.6997(12) 167.6(17) O(2)-H(2BO)...N(4)#4 0.840(14) 1.955(14) 2.7818(12) 167.8(16) O(3)-H(3AO)...N(2)#3   0.846(13) 1.971(14) 2.7999(11) 166.0(16) O(3)-H(3BO)...Cl(1)#5 0.842(13) 2.412(14) 3.1897(9) 153.8(15) O(4)-H(4AO)...Cl(1) 0.840(14) 2.325(14) 3.1603(9) 173.2(15) O(4)-H(4BO)...N(3)#6 0.869(13) 1.952(14) 2.8154(13) 172.6(15) O(5)-H(5AO)...Cl(1)   0.875(15) 2.354(15) 3.2290(12) 178.6(6) O(5)-H(5BO)...Cl(1)#7 0.858(15) 2.341(16) 3.1896(11) 170(2) Symmetry transformations used to generate equivalent atoms:  #1 -x+1,-y,-z+2    #2 x,y,z+1    #3 -x+1,-y+1,-z+1       #4 -x+1,-y+1,-z+2    #5 x,y-1,z    #6 x+1,y,z    #7 -x+2,-y+2,-z+1  Table-4: Atomic coordinates (x 104) and equivalent isotropic displacement parameters (Å2x 103) for [Ni(H2O)6](HMTA)2(NO3)2.4H2O.  U(eq) is defined as one third of  the trace of the orthogonalized Uij tensor.   x y z U(eq) Ni(1) 5000 0 10000 16(1) O(1) 3866(1) 1353(1) 9375(1) 25(1) O(2) 6169(1) 2265(1) 12002(1) 31(1) O(3) 6473(1) 295(1) 8583(1) 30(1) Cl(1) 8093(1) 8230(1) 5630(1) 34(1) O(4) 8054(1) 4966(1) 2190(1) 30(1) O(5) 8522(1) 9526(2) 3036(2) 48(1) N(1) 3441(1) 4516(1) 1708(1) 22(1) N(2) 3358(1) 7429(1) 2565(1) 23(1) N(3) 1162(1) 5408(1) 2424(1) 23(1) N(4) 3385(1) 6526(1) 4597(1) 23(1) C(1) 3941(1) 5975(1) 1479(1) 24(1) C(2) 1792(1) 4000(1) 1342(1) 25(1) C(3) 3970(1) 5092(1) 3469(1) 23(1) C(4) 1708(1) 6848(1) 2180(1) 25(1) C(5) 3883(1) 7943(1) 4307(1) 24(1) C(6) 1740(1) 5963(1) 4171(1) 25(1)  REFERENCES 1. K.S.  Patel and M.O. Agwara, Nig. J. Sc., 24, 57 (1990) 2. M.O. Agwara, P.T. Ndifon and M.K.Ndikontar, Bull. Chem. Soc. Ethiop., 18(2), 143(2000) 3. O.S. Polezhaeva, N.V. Yaroshinskaya and V.K. Ivanov, Inorg. Mater., 44(1), 51(2008) 4. X. J. Yao, Y.W. Xuan and W. Wu, Acta. Cryst., E64, m1132 (2008) 5. 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Aguara et al 212 Vol.3, No.2 (2010), 207-213   Fig.-2: Ortep Drawing and Numbering scheme used for [Ni(H2O)6](HMTA)2Cl2.4H2O  (Received: 17 April 2010   Accepted: 12 June 2010                         RJC-556)  Highlights of RASĀYAN • It is a full text open access international journal of Chemical Sciences. Covers all fields related to Chemistry. •  Research papers will be published on the website and also in the printed version simultaneously. • Manuscript is reviewed and published very quickly. • Full text of the article is available on the site http://www.rasayanjournal.com all over the world. Reprints may be downloaded directly from the website. • Papers can be submitted through e-mail to rasayanjournal@gmail.com.  Adopt GREEN CHEMISTRY Save Our Planet. We publish papers of Green Chemistry on priority.   If you think that you may be a potential reviewer in field of your interest, write us at rasayanjournal@gmail.com with your detailed resume and recent color photograph.     H-BONDED Ni (II) HEXAMETYLENETETRAMINE COMPLEX                                                                                Moise O. Aguara et al 213

Synthesis, characterisation and crystal structure of a three-dimensional network of an h-bonded Ni (II) Hexametylenetetramine complex

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Synthesis, characterisation and crystal structure of a three-dimensional network of an h-bonded Ni (II) Hexametylenetetramine complex

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