Synthesis and Crystal Structure of a Cyano-Bridged Bimetallic Nickel(II)–Silver(I) Complex, [Ni(dmen) 2 {Ag(CN) 2 } 2 ] · 0.5H 2 O

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  A cyano-bridged heteronuclear bimetallic complex [Ni(dmen)2{Ag(CN)2}2] · 0.5H2O (dmen = N,N′-dimethylethylenediamine) has been prepared and characterized by IR spectroscopy and X-ray Crystallography. The compound crystallizes in the monoclinic space
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  ORIGINAL PAPER Synthesis and Crystal Structure of a Cyano-Bridged BimetallicNickel(II)–Silver(I) Complex, [Ni(dmen) 2 {Ag(CN) 2 } 2 ]    0.5H 2 O Saeed Ahmad   Muhammad Monim-ul-Mehboob   Muhammad Altaf    Helen Stoeckli Evans   Rashid Mehmood Received: 19 January 2007/Accepted: 18 July 2007/Published online: 4 August 2007   Springer Science+Business Media, LLC 2007 Abstract  A cyano-bridged heteronuclear bimetalliccomplex [Ni(dmen) 2 {Ag(CN) 2 } 2 ]    0.5H 2 O (dmen =N,N 0 -dimethylethylenediamine) has been prepared andcharacterized by IR spectroscopy and X-ray Crystallogra-phy. The compound crystallizes in the monoclinic spacegroup P2 1  /c. The crystal structure of the complex consistsof two independent centrosymmetric trinuclear moleculesmade up of a [Ni(dmen) 2 ] +2 unit linked to two [Ag(CN) 2 ]  anions in a  trans  configuration. The trinuclear units are joined by hydrogen bonding to form irregular chains. Keywords  Coordination polymer    Crystal structure   Nickel(II)    Silver cyanide Introduction Recently, a considerable research effort has been put intothe crystal engineering of supramolecular structures,which have potential applications in catalysis, host-guestchemistry, electrical conductivity and molecule-basedmagnets [1–6]. Covalent bonding, hydrogen bonding or other intermolecular interactions of strength equivalentto hydrogen bonds such as aurophilic/argentophilicinteractions are widely used tools for the design of varioussupramolecular structures [7–15]. Most bimetallic poly- meric compounds, which exhibit unique structures, prop-erties and reactivities are assembled from cyanometalatesas building blocks by means of coordination bonds [7–12]. Metal cyanides, like hexacyanoferrate(III), [Fe(CN) 6 ]  3 [16, 17], tetracyanonickelate(II), [Ni(CN) 4 ]  2 [5, 6] and dicyanoargenate(I), [Ag(CN) 2 ]  [7, 18] are used as build- ing blocks for the preparation of bimetallic coordinationpolymers. Although coordination polymers incorporatingoctahedral [M(CN) 6 ]  n and square planar [M(CN) 4 ]  2 units have been studied extensively in the last decade[1, 13–15, 19–21], the use of linear two-coordinate [Au(CN) 2 ]  and [Ag(CN) 2 ]  as building blocks has beenexplored recently [7–12, 18]. Consequently, the crystal structures of several M-diamine systems containing[Au(CN) 2 ]   and [Ag(CN) 2 ]  have been reported [7–12, 18]. A unique feature of these structures is that the centralgold or silver atom is capable of forming M–M bonds,which are useful tools in the crystal engineering of poly-meric structures [7–12, 18]. To investigate further about such structures, we report here the synthesis and crystalstructure of [Ni(dmen) 2 {Ag(CN) 2 } 2 ]    0.5H 2 O (dmen =N,N 0 -dimethylethylenediamine). Experimental MaterialsNiCl 2    6H 2 O was obtained from BDH Chemical Co.,England. AgNO 3  was purchased from Panreac, Spain.N,N 0 -dimethylethylenediamine (dmen) is a product of Acros Organics. K[Ag(CN) 2 ] was prepared by reactingAgNO 3  with KCN in a 1:2 mole ratio. S. Ahmad ( & )    M. Monim-ul-MehboobDepartment of Chemistry, University of Engineeringand Technology, Lahore 54890, Pakistane-mail: saeed_a786@hotmail.comM. Altaf     H. Stoeckli EvansInstitute of Microtechnology, University of Neuchaˆtel,Neuchatel, SwitzerlandR. MehmoodDepartment of Chemistry, Quaid-i-Azam University,Islamabad, Pakistan  1 3 J Chem Crystallogr (2007) 37:685–689DOI 10.1007/s10870-007-9232-7  SynthesisTo a solution of 0.120 g NiCl 2    6H 2 O (0.5 mmoles) in10 mL methanol was added a 15 mL methanolic solutionof 0.060 g (1.0 mmol) N,N 0 -dimethylethylenediamine.While stirring, 0.20 g K[Ag(CN) 2 ] (1.0 mmole) in waterwas added to this blue colored solution. The resultingpurple-colored mixture was stirred for 15 min. After sep-arating the purple residue by filtration, the filtrate was keptfor crystallization at room temperature. As a result purplecrystals were obtained in 5–6 % yield.IR MeasurementsThe IR spectrum of the complex was recorded on a Perkin-Elmer FTIR 1000 spectrophotometer using KBr pellets inthe 4000–400 cm  1 range.X-ray Structure DeterminationSingle crystal data collection was performed at 173 K (  100   C) on a Stoe Mark II-Image Plate DiffractionSystem [22] equipped with a two-circle goniometer andusing MoK  a  graphite monochromated radiation. Image platedistance 100 mm,  x  rotation scans 0–180   at  /  0  , and0–79   at  /  90  , step  D x  = 1.0  , exposures of 4 min perimage, 2 h  range 2.29–59.53  , d min  d max  = 17.779–0.716 A˚ . The structure was solved by Direct methods using the pro-gramme SHELXS  97 [23]. The refinement and all furthercalculations were carried out using SHELXL-97 [23].The water molecule is only partially occupied (0.5). Thewater H-atoms were located from a difference Fourier map.They were refined isotropically with the O–H distancesrestrained to 0.90 ± 0.02 A˚, and H  H restrained to1.45 ± 0.02 A˚. The remainder of the H-atoms were inclu-ded in calculated positions and treated as riding atoms:N–H = 0.93 A˚, C–H = 0.98–0.99 A˚and U * iso * (H) =1.2U * eq * (parent N or C-atom). The non-H-atoms wererefined anisotropically, using weighted full-matrix least-squares on F 2 . An empirical absorption correction wasapplied using the MULscanABS routine in PLATON [24].Crystal data and details of the data collection are summa-rized in Table 1. Selected atomic distances and bondangles are given in Table 2 and details of the hydrogenbonding in Table 3. Table 1  Crystal data anddetails of the structuredeterminationCrystal dataFormula C 12 H 24 Ag 2 N 8 Ni, 0.5H 2 OFormula weight 563.85Crystal system MonoclinicSpace group P2 1  /c (No. 14) a, b, c  (A) 12.3087(6), 14.0595(9), 11.5830(5) a ,  b ,  c  (deg) 90, 96.334(4),90 V   (A 3 ) 1992.25(18)  Z   4 q calc  (g/cm 3 ) 1.880 l  (MoK  a ) (mm  1 ) 2.895F(000) 1116Crystal size (mm) 0.30  ·  0.20  ·  0.10Data collectionTemperature (K) 173 k  MoK  a  (A) 0.71073 h  Min–Max (deg) 1.7–29.2h, k, l limits   16:16,   19:19,   15:15Reflns: Total, Uniq. Data, R int  27150, 5374, 0.036Observed data [  I   > 2 r  (  I  )] 4498Absorption: T min  /T max  0.450/0.689RefinementNref, Npar 5374, 226R,  w R2, S 0.0311, 0.0607, 1.08 w  = [ r 2 (F o2 ) + (0.0188P) 2 + 2.1532P]  1 where P = (F o2 + 2F c2 )/3Max. and Av. Shift/Error <0.001, < 0.001Min. and Max. Resd. Dens. [e/A 3 ]   0.59, 0.35686 J Chem Crystallogr (2007) 37:685–689  1 3  Results and Discussion In the IR spectrum of cyanide complexes, the very infor-mative parameter is the cyanide stretching frequency. Thetitle compound exhibits two sharp  m (CN) bands of mediumintensity at 2162 and 2136 cm  1 , which for K[Ag(CN) 2 ]appears at 2140 cm  1 . The appearance of two bands showsthat the structure contains both the bridging and terminalcyanides. Generally, the stretching frequencies of terminalcyanides are lower relative to those of bridging cyanides[7, 25, 26]. The appearance of a  m (N–H) band of mediumintensity at 3281 cm  1 indicates the presence of the dia-mine ligand. Weak signals at 2985, 2962 and 2923 cm  1 due to C–H strechings of CH 3  and CH 2  groups of diamine(dmen) are also observed. A broad peak at 3456 cm  1 dueto  m (O–H) vibration suggests that the complex containswater molecules.The molecular structure and crystallographic numberingscheme are illustrated in the PLATON drawing, Fig. 1. Thecrystal structure of the complex consists of two indepen-dent centrosymmetric trinuclear molecules and a moleculeof water of crystallization. Each molecule is made up of two [Ag(CN) 2 ]  anions linked to a [Ni(dmen) 2 ] +2 unitthrough cyanide in a  trans  configuration, with the formulaof [Ni(dmen) 2 {Ag(CN) 2 } 2 ]    0.5H 2 O. The Ni(II) ions,which are located on centers of inversion, assume slightlydistorted octahedral geometry with four nitrogen atoms of the diamines and two CN nitrogens completing the coor-dination sphere (Table 2). The  cis  N–Ni1–N angles varyfrom 83.23(12)   to 97.77(12)  ,while the  cis  N–Ni2–Nangles vary from 84.13(9)   to 95.87(9)  . The Ni1–N : Cunit is bent with a bond angle of 167.0(2)   in one of the twomolecules, while the Ni1–N : C angle is 175.0(2)  , whichis close to linear geometry. The coordination environment Table 3  Hydrogen bonds in thetitle complex (A˚,   )Symmetry operations:  a  x,  0.5 + y, 0.5  z;  b 1  x,  0.5 + y, 0.5  z;  c  1 + x, y,z ;  d 1 + x, 0.5  y, 0.5 + z ; e  1 + x, 0.5  y,   0.5 + zDonor-H  Acceptor D–H H  A D  A  \ D–H  AO1w–H1w  N8 a 0.92(5) 1.88(7) 2.784(7) 166(10)O1w–H2w  N8 b 0.91(7) 2.11(6) 3.022(7) 172(10)N1–H1N  N8 c 0.93 2.58 3.284(4) 133N2–H2N  N4 d 0.93 2.46 3.233(4) 140N5–H5N  N8 b 0.93 2.59 3.459(59) 156C4–H4C  O1W e 0.98 2.55 3.292(7) 132 Table 2  Selected bonddistances (A˚) and bond angles(  )Symmetry operations:  a x,0.5  y,   0.5 + z;  b  x,   y,   z; c 1  x,   y, 1  zBond distancesAg1–C5 2.054(3) Ni2–N6 2.132(2)Ag1–C6 2.058(3) Ni2–N7 2.058(2)Ag2–C11 2.046(3) N1–C1 1.481(5)Ag2–C12 2.048(3) N1–C3 1.476(4)Ni1–N1 2.115(2) N2–C2 1.472(6)Ni1–N2 2.126(3) N2–C4 1.468(6)Ni1–N1 a 2.115(2) N3–C5 1.143(4)Ni1–N3 2.083(2) N4–C6 1.129(4)Ni1–N3 a 2.083(2) C1–C2 1.503(6)Ni2–N5 2.127(2) Ag1–Ag2 a 3.6196(4)Bond anglesC5–Ag1–C6 176.08(12) C11–Ag2–C12 174.77(13)Ag1–C5–N3 173.9(3) Ag2–C11–N7 176.0(3)Ag1–C6–N4 177.0(3) Ag2–C12–N8 175.8(3)N1–Ni1–N2 83.23(12) N5–Ni2–N6 84.13(9)N1–Ni1–N2 b 96.77(12) N5–Ni2–N6 c 95.87(9)N1–Ni1–N3 93.05(9) N5–Ni2–N7 90.34(9)N1–Ni1–N3 b 86.95(9) N5–Ni2–N7 c 89.66(9)N2–Ni1–N3 91.17(10) N6–Ni2–N7 93.23(9)N2–Ni1–N3 b 88.83(10) N6–Ni2–N7 c 86.74(9)Ni1–N3–C5 167.0(2) Ni2–N7–C11 175.0(2)J Chem Crystallogr (2007) 37:685–689 687  1 3  of the [Ag(CN) 2 ]  units is also close to linear. TheNi–N(dmen) bond lengths are similar in both complexes,varying from 2.115(2) to 2.132(2) A˚. They can be com-pared with the same values in the known structures,[Ni(dmen) 2 (ONO) 2 ] (2.077 & 2.216 A˚) [27], [Ni(en) 2 Ag(CN) 2 ]{Ag(CN) 2 } (2.093 A˚) [28] and [Ni(en) 2 Ag 3 (CN) 5 ] n (2.114 A˚) [18]. The Ni–N(CN) bond lengths of 2.083 and 2.058 A˚indicate that the CN nitrogens are strongly boundto the Ni(II) center. The shorter Ni–N(CN) bond lengthcompared to Ni–N(dmen) indicates that there is a shift of  p -electron density from Ni to CN nitrogen, which confers adouble bond character in the Ni–CN bond.In an isostructural complex of 1,3-diaminopropane (tn),[Ni(tn) 2 {Ag(CN) 2 } 2 ] [29], the analogous trinuclear units are connected to each other by argentophilic (Ag  Ag)interactions forming a chain like arrangement within thestructure, while such kind of interactions are not observedin the present compound. The shortest Ag1  Ag2 distancebetween two trinuclear units is 3.6196(4) A˚, which is justbeyond the threshold of argentophilic interactions. TheAg  Ag distances are rather longer than the sum of the vander Waals radii of two Ag(I) centers (3.44 A˚), which isconsidered to be the upper limit of the distance for a viableargentophilic interactions [26, 28–30]. The corresponding Ag  Ag distances in some similar reported complexes are:3.289 A˚for [Ni(en) 2 Ag(CN) 2 ]{Ag(CN) 2 } [28], 3.3180 A ˚for [Ni(en) 2 {Ag 3 (CN) 5 ] n  [18], 3.2627 A˚for [Ni(tn) 2 {Ag(CN) 2 } 2 ] [29], 3.1580 A ˚for [Cu(en) 2 Ag(CN) 2 ]{Ag(CN) 2 }[26] and 3.1750 A˚for [Cd(en) 2 Ag(CN) 2 ]{Ag(CN) 2 } [7]. Although aurophilicility/argentophilicty plays a significantrole in increasing the dimensionality of such complexes, Fig. 2  Crystal packing of structure [Ni(dmen) 2 {Ag(CN) 2 } 2 ]    0.5H 2 O, viewed along the  a  axis showing the formation of the polymerchain formed by hydrogen bonding involving the water molecule of crystallization (O1w) and the second independent molecule involvingatom Ni2 (see Table 3 for details). The majority of the H-atoms havebeen omitted for clarity Fig. 1  A view of the molecular structure of the two independentmolecules in structure [Ni(dmen) 2 {Ag(CN) 2 } 2 ]    0.5H 2 O, showingthe crystallographic numbering scheme and thermal ellipsoids drawnat the 50% probability level. Hydrogen atoms have been omitted forclarity. [Symmetry operations: a) =   x,   y,   z; b) = 1  x,   y, 1  z]688 J Chem Crystallogr (2007) 37:685–689  1 3  there are some gold complexes, where no such interactionshave been found, for example, [Cu(tren)Au(CN) 2 ][Au(CN) 2 ] [9] and [Cu(tren)Au(CN) 2 ][Au(CN) 2 ] [31]. However, this is the first report showing the absence of argentophilic interactions in such type of silver complexes.In the crystal structure of the title complex the mole-cules involving Ni2 are hydrogen bonded via the watermolecule of crystallization to form polymer chains. Themolecules involving atom Ni1 stack along the  a  directionin channels formed the polymer chains. A view of thecrystal packing of the complex showing O–H  N hydrogenbonds is given in Fig. 2. Apart from these relatively stronghydrogen bonds there exist also some weak N–H  N andC–H  O bonds linking the two independent molecules.Further details of the hydrogen bonding distances are givenin Table 3. The order of their strength on the bais of thelengths and polarities is OH  N > NH  N    CH  O.The present study suggests that [Ag(CN) 2 ]  is a usefulstarting material for the preparation of various heterome-tallic M–Ag(I) complexes. Although a wide range of polymeric structures as a consequence of covalent bondingof bridging cyanide groups and argentophilic interactionsare expected, the present complex is a unique examplelacking these interactions. Supplementary Material Crystallographic data for the structure reported in thispaper have been deposited with the Cambridge Crystallo-graphic Center, CCDC No. 622551. Copies of the data canbe obtained free of charge on application to The Director,CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, e-mail:deposit@ccdc.cam.ac.uk or www.ccdc.cam.ac.uk. Acknowledgements  Financial support from Pakistan Council forScience and Technology, Islamabad is gratefully acknowledged. Prof.M. Javed Iqbal of QAU is thanked for extending cooperation in theanalysis. References 1. Dunbar KR, Heintz RA (1997) Prog Inorg Chem 45:2832. Verdaguer M, Bleuzen A, Marvaud V, Vaissermann J, SeuleimanM, Desplanches C, Scuiller A, Train C, Garde R, Gelly G,Lomenech C, Rosenman I, Veillet P, Cartier C, Villain F (1999)Coord Chem Rev 190:10233. Ohba M, Okawa K (2000) Coord Chem Rev 198:3134. Rogez M, Parsons MS, Villar V, Mallah T (2001) Inorg Chem.40:38365. Ghoshal D, Ghosh AK, Maji TK, Ribas J, Mostafa G, ZangrandoE, Chaudhuri NR (2006) Inorg Chim Acta 359:5936. Maji TK, Mukherjee PS, Mostafa G, Zangrando E, Chaudhuri NR(2001) Chem Commun 13687. Zhang H-X, Kang BS, Deng LR, Ren C, Su CY, Chen ZN (2001)Inorg Chem Commun 4:418. Colacio E, Lloret F, Kivekas R, Varela JS, Sundberg MR, UgglaR (2003) Inorg Chem 42:5609. Leznoff DB, Xue BY, Batchelor RJ, Einstein FWB, Patrick BO(2001) Inorg Chem 40:602610. 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