The title compound was synthesized mechanochemically by grinding MnCl2.4H2O and the protonated organic ligand [H2Me4bpz] resulting in the formation of [H2Me4bpz][MnCl4]. Suitable single crystal of this compound was analysed through X-ray diffraction technique to ascertain its composition and internal structure. Single crystal structure determination at 100 K revealed needle-like crystals in an orthorhombic crystal system. The asymmetric unit of the cell consists of an isolated chloride ion, one half of a tetrahedral [MnCl4]2- anion, a [H2Me4bpz]2+ dication and one half of a molecule of water.Keywords: Crystal Engineering, Hydrogen Bond, X-ray Crystallograph

Kurawa, MA

Orpen, AG

English

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CSJ 6(1): June, 2015 ISSN: 2276 – 707X  Kurawa and Orpen   68        Synthesis and Single Crystal X-Ray Structure Determination of 3,3',5,5'-tetramethyl-4,4'-bipyrazolium tetrachloromanganate(II) monohydrate ([H2Me4bpz]2[MnCl4]Cl2·H2O)  1 Kurawa, M. A. and 2 Orpen, A. G. 1 Department of Pure and Industrial Chemistry, Bayero University Kano, P. M. B. 3011, Kano, Nigeria. 2 School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK. Email: makurawa.chm@buk.edu.ng   ABSTRACT The title compound was synthesized mechanochemically by grinding MnCl2.4H2O and the protonated organic ligand [H2Me4bpz] resulting in the formation of [H2Me4bpz][MnCl4]. Suitable single crystal of this compound was analysed through X-ray diffraction technique to ascertain its composition and internal structure. Single crystal structure determination at 100 K revealed needle-like crystals in an orthorhombic crystal system. The asymmetric unit of the cell consists of an isolated chloride ion, one half of a tetrahedral [MnCl4]2- anion, a [H2Me4bpz]2+ dication and one half of a molecule of water.   Keywords: Crystal Engineering, Hydrogen Bond, X-ray Crystallography  INTRODUCTION X-ray crystallography is one of the most important and most powerful tools for investigation of the structures of chemical compounds. It plays a vital role in modern chemistry, organic as well as inorganic, and probably ranks alongside NMR and mass spectrometry as the three most important structural techniques, being less widely applicable than these other two in its requirement for a crystalline solid sample, but far more powerful in the richness of its detailed results when successful. (Clegg, 2005). X-ray single crystal structure determination is undoubtedly the most important technique to characterize new compounds. No other analytical technique currently available can provide such complete and unambiguous information about internal structure, i.e. types of atoms, their spatial arrangement and interactions. Single crystal structure determination yields the internal symmetry of crystals, coordinates and population of atoms (occupancies) and anisotropic thermal parameters. The results obtained by single crystal structure determination are vital for the study of compounds by various other techniques including molecular modelling, and for giving information about crystal packing, polymorphism, absolute structure configuration, intra- and inter-molecular contacts, hydrogen bonding, crystal phase transition. (Harris et al., 2001; Evans and Evans 2004). It has recently been established by a number of researchers that a range of hydrogen bonded complex metal salts and coordination compounds can be prepared without recourse to solution methods through the exploitation of crystal engineering. (James et al., 2012; Fernandez-Bertran, 1999; Fernandez-Bertran et al., 1999; Kaupp et al., 2001; Shan et al., 2002; Braga and Grepioni, 2004; Sheldon, 2005; Kidwai, 2001; Garay et al., 2007; Kurawa, 2012). This has provided access to new synthetic routes via solid state grinding of protonated ligands [H2L]Cl (L = imidazole, pyrazole and 2,2'-biimidazole) with metal dichlorides MCl2 (M = Co, Cu, Zn) which results in the formation of hydrogen bonded metal salts [H2L]2[MCl4]. These salts ([H2L]2[MCl4]) are designed to offer thermal reactivity towards dehydrochlorination to yield coordination compounds ([MCl2(HL)2]) with novel properties. (Adams et al., 2008; Christopher et al., 2010; Kurawa, 2010).  Having established that protonated pyrazole can be used as a building block in crystal engineering as it is capable of forming hydrogen bonds to tetrachlorometallate dianions and hence forming ([MCl2(HL)2] coordination compounds and ([ML2] MOFs after dehydrochlorination, we attempted to use its derivative 3,3',5,5'-tetramethyl-4,4'-bipyrazole (Me4bpz) in a similar fashion. It was expected that this tecton (building block in crystal engineering) could form a hydrogen-ChemSearch Journal 6(1): 68 – 73, June, 2015 Publication of Chemical Society of Nigeria, Kano Chapter  Received: 15/06/2015   Accepted: 25/06/2015 http://dx.doi.org/10.4314/csj.v6i1.11  C.S.NCHEMICAL SOCIETY OF NIGERIACSJ 6(1): June, 2015 ISSN: 2276 – 707X  Kurawa and Orpen   69  bonding synthon as in Fig.  1 where the two NH donors bridge an Cl-M-Cl pocket with a view of dehydrochlorination of 4 HCl molecules to generate a metal-organic framework.                                               Fig. 1: N—H···Cl hydrogen-bonding synthon   This paper reports the exploitation of the state of the art techniques in crystal engineering and solid state methods to synthesize  [H2Me4bpz][MnCl4]  by reacting 3,3',5,5'-tetramethyl-4,4'-bipyrazolium dichloride ([H2Me4bpz]Cl2) and manganese (II) chloride and the analysis of synthesized compound using X-ray single crystal structure determination.   MATERIALS AND METHODS Analar grade reagents were purchased from Aldrich and Strem and used without further purification except where otherwise stated.  Preparation of the Ligand: [H2Me4bpz]Cl2 3,3',5,5'-tetramethyl-4,4'-bipyrazolium chloride [H2Me4bpz]Cl2 was prepared by dissolving neutral 3,3',5,5'-tetramethyl-4,4'-bipyrazole (synthesized according to the literature) (Boldog et al., 2001) in 15 ml of concentrated aqueous hydrochloric acid and 40 ml and deionised water. The solution was reduced to 25 ml by boiling and 50 ml of ethanol was added. The resulting mixture was put in the fridge to crystallize and white crystals were filtered out after five days. Microanalytical data (%), Calculated for [C10H16N4]Cl2: C, 45.64; H, 6.13; N, 21.29. Found C, 45.21; H, 6.54; N, 21.56.  Preparation of the Complex: [H2Me4bpz][MnCl4]·H2O: [H2Me4bpz]Cl2 (263 mg, 1 mmol) and 198 mg (1 mmol) of MnCl2∙H2O were ground in agate mortar resulting in the formation of a colourless polycrystalline compound.    Crystal Growth:  Suitable single crystals of the title compound were obtained by dissolving 5 mg amount of the synthesized compound in a 5 ml of concentrated hydrochloric acid solution. This was allowed to evaporate slowly at room temperature and after two weeks suitable single crystals were obtained.  X-ray Single Crystal Analysis Crystal suitable for X-ray structural analysis was mounted on a glass fibre and X-ray data was collected at 100 K on a Bruker APEX diffractometer using Mo-Kα X-radiation. Data were corrected for absorption using empirical methods (SADABS) (Sheldrick, 1995) based upon symmetry-equivalent reflections combined with measurements at different azimuthal angles. Crystal structures were solved and refined against all F2 values using the SHELXTL suite of programs (Sheldrick, 2008). Non-hydrogen atoms were refined anisotropically and hydrogen atoms were placed in calculated positions refined using idealized geometries (riding model) and assigned fixed isotropic displacement parameters.   RESULTS AND DISCUSSION Mechanochemical grinding of the reactants resulted in the formation white solid which dissolved in concentrated HCl solution yielding a colourless solution. Slow evaporation of this solution led to the re-crystallization of the title compound as colourless needle-like crystals. The compound was dissolved in concentrated hydrochloric acid in order to enforce the protonation of the pyrazole nitrogen atoms. Single crystal structure determination at 100 K revealed an  CSJ 6(1): June, 2015 ISSN: 2276 – 707X  Kurawa and Orpen   70   orthorhombic crystal in the Pnma space group. The asymmetric unit of the cell consists of an isolated chloride ion, one half of a tetrahedral [MnCl4]2- anion, a [H2Me4bpz]2+ dication and one half of a molecule of water indicating both molecules are sitting on a crystallographic inversion centres. In the crystal structure, the water molecule contributes to the three-dimensional hydrogen-bonding, forming two O—H····Cl hydrogen-bonds with tetrahedral [MnCl4]2- anions, making a two-dimensional chain of hydrogen bond bridges along the crystallographic c-axis through {O—H····Cl—Mn—Cl····H—O} interactions (Fig. 2). It also   makes two N—H····O hydrogen bonds with [H2Me4bpz]2+ dications. The [H2Me4bpz]2+ dication has two different pyrazolium hydrogen-bonding environments as shown in Figure 3, one pyrazolium hydrogen-bonding to two [MnCl4]2- anions and a water through N—H····Cl and N—H····O bonds respectively, whilst the other forms NH····Cl contacts with two isolated chlorine atoms.  Detailed hydrogen bond geometry is presented in table 1. The presence of the water of crystallization in the molecule rendered it unsuitable for designed synthetic route of synthesizing MOFs from hydrogen bonded complex [H2Me4bpz][MnCl4].                            Fig. 2: Two dimensional MnCl4-H2O hydrogen-bonded chains in [H2Me4bpz][MnCl4] viewed along the c-axis.                     Fig.  3: The cation environment seen in the structure of [H2Me4bpz][MnCl4].  CSJ 6(1): June, 2015 ISSN: 2276 – 707X  Kurawa and Orpen   71   The overall packing in the crystal structure consists of a central layer of the [MnCl4]2--H2O chain sandwiched between two layers of the   [H2Me4bpz]2+ dications, which in turn are packed between layers of the isolated chloride ions (Fig. 4).                         Fig. 4: Crystal packing of [H2Me4bpz][MnCl4].    Table 1 shows the hydrogen-bond geometry of the [H2Me4bpz][MnCl4] molecule, while table 2 presents its detailed crystal and structure refinement data.   Table 1:  Hydrogen bond geometry for [H2Me4bpz][MnCl4] [Å and °]. ____________________________________________________________________________  D-H...A d(D-H) d(H...A) d(D...A) <(DHA) ____________________________________________________________________________   N(1)-H(1A)...O(1) A 0.88 1.86 2.713(3) 162.4  N(2)-H(2A)...Cl(3) B 0.88 2.57 3.221(2) 131.0  N(4)-H(4A)...Cl(4) A 0.88 2.19 3.022(2) 157.2  O(1)-H(1)...Cl(2) C 0.833(19) 2.734(15) 3.342(2) 131.2(8)  O(1)-H(1)...Cl(2) D 0.833(19) 2.734(15) 3.342(2) 131.2(8)  O(1)-H(2)...Cl(1) E 0.834(19) 2.38(2) 3.166(3) 158(4) ____________________________________________________________________________  Symmetry transformations used to generate equivalent atoms: A x+1/2,y,-z+3/2 B x+1/2,y,-z+1/2  C x-1,-y+1/2,z+1 D x-1,y,z+1 E x-1/2,y,-z+1/2.   CSJ 6(1): June, 2015 ISSN: 2276 – 707X  Kurawa and Orpen   72   Table 2.  Crystal data and structure refinement for [H2Me4bpz][MnCl4]                                                                   Identification code  mak058a  Empirical formula  C10 H17 Cl3 Mn0.50 N4 O0.50  Formula weight  335.10  Temperature  100(2) K  Wavelength  0.71073 Å  Crystal system  Orthorhombic  Space group  Pnma  Unit cell dimensions a = 8.5855(17) Å = 90°.  b = 34.715(7) Å = 90°.  c = 9.997(2) Å  = 90°. Volume 2979.6(10) Å3  Z 8  Density (calculated) 1.494 Mg/m3  Absorption coefficient 1.011 mm-1  F(000) 1380  Crystal size 0.25 x 0.15 x 0.10 mm3  Theta range for data collection 1.17 to 27.48°.  Index ranges -10<=h<=11, -45<=k<=45, -12<=l<=12  Reflections collected 32148  Independent reflections 3465 [R(int) = 0.0784]  Completeness to theta = 27.48° 100.0 %   Absorption correction Semi-empirical from equivalents  Max. and min. transmission 1 and 0.885950  Refinement method Full-matrix least-squares on F2  Data / restraints / parameters 3465 / 0 / 177  Goodness-of-fit on F2 1.106  Final R indices [I>2sigma(I)] R1 = 0.0390, wR2 = 0.1015  R indices (all data) R1 = 0.0593, wR2 = 0.1199  Largest diff. peak and hole 0.535 and -0.484 e.Å-3   CONCLUSION: In conclusion, it has been shown X-ray single crystal structure determination revealed that despite the presence of water molecules in their lattice, the crystal structure of title compound displayed great potential as NH donors that could be used to synthesize crystalline solids which are explicitly planned to have thermal or other reactivity, and to yield coordination compounds with novel properties. The structures display robust hydrogen-bonded networks which give rise to well-defined arrangements with the tetrachlorometallate anions [MCl4]2- and the [H2Me4bpz]2+ cations stacked into sheets and layers. Furthermore, it has been shown that mechanochemistry can be exploited in the synthesis of hydrogen bonded metal complex which can serve as a precursor for the synthesis of coordination compounds.   ACKNOWLEDGEMENTS The Authors greatly acknowledge the contributions of Dr C. J. Adams of the School of Chemistry, University of Bristol, UK.  REFERENCES Adams, C. J., Kurawa, M. A., Lusi, M. and Orpen, A. G. (2008) "Solid state synthesis of coordination compounds from basic metal salts" CrystEngComm, 10, 1790-1795.    CSJ 6(1): June, 2015 ISSN: 2276 – 707X  Kurawa and Orpen   73   Boldog I., Rusanov E. B., Chernega A. N., Sieler J. and Domasevitch K. 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Synthesis and Single Crystal X-Ray Structure Determination of 3,3',5,5'- tetramethyl-4,4'-bipyrazolium tetrachloromanganate(II) monohydrate ([H2Me4bpz]2[MnCl4]Cl2·H2O)

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Synthesis and Single Crystal X-Ray Structure Determination of 3,3',5,5'- tetramethyl-4,4'-bipyrazolium tetrachloromanganate(II) monohydrate ([H2Me4bpz]2[MnCl4]Cl2·H2O)

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