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International Journal of Scientific and Research Publications, Volume 3, Issue 2, February 2013 551 ISSN 2250-3153 Metallophilicity in [CdBr] - : A Case Study of Hybrid Materials Mukesh Kumar *, S. Dalela*, Dinesh ** * School of Physical Sciences, Banasthali University, Banasthali, Rajasthan -304022, INDIA ** Department of Physics, Govt. G.M. Science College, Jammu -180006, INDIA, E-mail: phy.dinesh.ap@gmail.com Abstract- A series of inorganic―organic hybrid compounds were analyzed by using X-ray crystallographic techniques to study the secondary interactions in cadmium bromide based hybrid materials. The phenomenon of metallophilic interactions with minimum Cd…Cd distance [3.962(1), 3.389(3) and 3.924(1) Å] has been observed in Cd2, Cd7 and Cd11 compounds whereas the metallophilicity is missing in other compounds of the selected series. The novel entanglements of Cd motifs illustrate 1D and 2D chain pattern of metallophilic and Br…Br interactions. The Cd―Br bond distances experiential in the range of 2.505(1) to 2.924(1)Å and Br―Cd―Br bond angles in the range of 83.45(3) to 180⁰. The minimum value of Torsion angle is -3.647(3)⁰ for the compound Cd10, when Cd atoms are taken in the centre while its minimum value is calculated as 28.211(1)⁰ for the compound Cd1, when Br atoms are taken in the centre. Index Terms- Metallophilic interactions, inorganic-organic hybrid materials, Br...Br interactions, Cd motifs, 1D and 2D chain pattern. S I. INTRODUCTION tudents beginning their studies of structural science today are typically introduced to bonding partitioned between covalent and ionic extremes, supplemented by weaker intermolecular forces. Subsequently, they will learn about metallic bonding, the “sea of electrons” present in delocalized systems and perhaps read a little about cluster bonding. Yet to be incorporated into standard textbooks is the phenomenon of metallophilicity, a name that indicates the affinity of two metal centers for one another. The metallophilic attraction is an almost new form of chemical bonding and consists of dispersion. First described in detail based on the close Au…Au contacts in several Au(I) derivatives,[1] the phenomenon of two closed shell metal centers approaching closer than the sum of their van der Waals radii was termed aurophilicity,[2] and now the word metallophilicity is used in a general sense for many metals. These interactions are understood to be a type of dispersion interaction between electron densities on larger and relatively reduced metal centers [3, 4]. The energy of such bonding is on the order of hydrogenbonding and can therefore exert a significant influence on solidstate structures [3]. One of the most interesting aspects of metallophilic bonding is that it can overcome electrostatic repulsion between cations or anions and bring together groups of like charge. In recent years, the design and synthesis of metal-organic frameworks (MOF) based on the assembly of suitable and rigid building blocks have attracted great attention [5-10]. The design of polymeric coinage d 10 metal complexes with fascinating structures has also received much attention [11-15], indicating in some studies that direct metal-metal interactions are among the most important factors for the manifestation of such structures. Between closed-shell species, no strong attractions are expected and, in fact, two closed-shell metal cations will normally repel each other. However, in the case of some coordination compounds, metal-metal attractions are present. Metallophilic interactions can lead to the generation of dimeric or polymeric structures, such as coinage metals with short M-M distances [16- 20]. The most promising criteria in defining metallophilic interactions are bond length between two metal centres. This criteria must be modeled free of method error and remain systematic independent of system size to show strength is from metallophilic interactions. As a part of our research on secondary interactions in inorganic-organic hybrid materials [21-23], a series of eighteen compounds (Cd1 to Cd18) whose crystal structures were reported [24-41] have been selected based on [CdBr] - anion for study of metallophilic interactions through crystallography data. II. EXPERIMENTAL DATA The experimental data for Cadmium Bromide based compounds [Cd1-Cd18] have been collected from Cambridge Structural Data Centre, U.K. and recycled by using WINGX software [42] for different types of secondary interactions. The recycled crystal structure data for all the compounds is presented in Table 1. The Cd1 crystal structure was refined upto 0.0420 for 1934 observed reflections. The value of R- factor for Cd2 and Cd3 has been observed to be 0.036 and 0.058 with 887 and 1401 reflections respectively. The reliability index of 0.034 has been achieved with 2673 reflections in Cd4 whereas its value is 0.0177 for 1127 reflections in Cd5. The value of R- index is 0.0610 for 2427 reflections in Cd6 and in Cd7 it is 0.0389 for 1137 observed reflections. The well refined crystal structure of Cd8 with refined parameter of 0.0290 and 0.0199 for Cd9 shows the structure solution results with 1494 and 1535 reflections, respectively. Cd10 and Cd11 derivatives of the selected series were refined upto 0.0407 and 0.0168 values for 3769 and 330 reflections. The cell measurements reflection value of 961 and 3328 has been used to obtain the refine parameter of 0.0286 and 0.0353 for the compounds of Cd12 and Cd13, respectively. The MoKα type of radiations having wavelength 0.71073 have been used to obtain the refine parameter for all the compounds of the selected series (Cd1-Cd18). By the use of such radiations the www.ijsrp.org
International Journal of Scientific and Research Publications, Volume 3, Issue 2, February 2013 552 ISSN 2250-3153 value of R-index is 0.0212 for 2114 reflections in Cd14 and in Cd15 it is 0.0488 for 2877 independent reflections. Similarly Cd16 crystal structure has been refined upto 0.0235 with 2098 reflections and Cd17 has the R-factor of 0.0333 for 2348 independent reflections. The cell measurement reflections of 25 are used to refine the crystal structure of Cd18 upto 0.0628 with 2986 reflections. The crystallographic data for Cd―Centered bond distances and range of bond angles is given in Table 2. TABLE-1: Crystal Structure Data for [CdBr] - based inorganic-organic hybrid compounds. Molecul ar Code Cd1 Cd2 Cd3 Cd4 Cd5 Cd6 Cd7 Cd8 Cd9 Cd10 Cd11 IUPAC Name Chemical Formula Cell Parameters Space Group Catena-[Cd{m- S(CH2)3NHMe2}Br2] Catena-Poly[Bis(3-methyl- 4-nitropyridine N-oxide-O) cadmium-µ-bromo] Bis(tetraethylammonium) tetrabromocadmate Tetrabromocadmate(II)Daf one (4,5-Diazafluoren-9- one) Bis(thiourea)cadmium bromide Bis-(4-amino-2(1H)- pyridinone)dibromocadmiu m(II) Diethylammonium heptabromidedicadmium(II ) Strontium hexabromodicadmate(II)oc tahydrate Dibromobis(pyridinium-2- thiolato-kS)cadmium(II) Bis(tetra-nbutylammonium) tetrabromocadmate(II) toluene disolvate Poly[di-m2-bromido-m2- 4,4'-bipyridinecadmium(II)] C5H13Br2CdNS C12H12Br2Cd N4O6 C16H40Br4CdN2 C22H18Br4CdN4O 4 C2H8CdBr2N4S2 C8H10Br2CdN6O2 C12H36Br7Cd2N3 SrCd2Br6 8H2O [CdBr2(C5 H5NS)2] (C16H36N)2[CdBr4 ]2C7H8 [CdBr2(C10H8N2)] a = 9.993(2)Å b = 6.824(1)Å c = 16.398(2)Å β = 96.0(1)⁰ a = 15.743(5)Å b = 57.010(3)Å c = 3.962(1)Å a = 13.453(1)Å b = 13.453(1)Å c = 14.395(1)Å α = β = γ = 90.0⁰ a = 9.776(2)Å b = 10.740(2)Å c = 15.135(3)Å α = 71.69(2)⁰ β = 87.93(2)⁰ γ = 63.48(2)⁰ a = 13.052(2)Å b = 5.989(2)Å c = 13.542(3)Å α = β = γ = 90.0⁰ a = 7.874(2)Å b = 12.624(3)Å c = 7.117(3)Å α = 105.87(4)⁰ β = 92.67(3)⁰ γ = 87.93(3)⁰ a = 15.567(1)Å b = 15.567(1)Å c = 6.778(1)Å γ = 120.0⁰ a = 25.247(2)Å b = 4.083(1)Å c = 8.764(2)Å α = β = γ = 90.0⁰ a = 13.050(3)Å b = 28.521(1)Å c = 8.065(2)Å α = β = γ = 90.0⁰ a = 15.154(1)Å b = 15.154(1)Å c = 23.382(2)Å α = β = γ = 90.0⁰ a = 11.787(3)Å b = 12.554(3)Å c = 3.924(1)Å Crystal System Ref. P2 1 /n Monoclinic [24] Fdd Orthorhombic [25] P-42 1 m Tetragonal [26] P-1 Triclinic [27] Pnam Orthorhombic [28] P-1 Triclinic [29] P-3 Trigonal [30] P2 1 2 1 2 Orthorhombic [31] Fdd2 Orthorhombic [32] I-4 2 d Tetragonal [33] Cmmm Orthorhombic [34] www.ijsrp.org
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