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Polyhedron 26 (2007) 1531–1540

Synthesis, structure, network and thermal analysis of four5-(pyrazinyl)tetrazolato copper(II) and cobalt(II) complexes

Morsy A.M. Abu-Youssef a,*, Franz A. Mautner b, Alshima’a A. Massoud a, Lars Ohrstrom c

a Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426 Ibrahimia, 21321 Alexandria, Egyptb Institut fur Physikalische und Theoretische Chemie, Technische Universitat Graz, A-8010 Graz, Austria

c Department of Chemical and Biological Engineering, Chalmers Tekniska Hogskola, SE-412 96 Goteborg, Sweden

Received 29 September 2006; accepted 25 November 2006Available online 3 December 2006

Abstract

Three new copper complexes and one cobalt complex with 5-(pyrazinyl)tetrazolate anion, (pyztz)�, as chelating bidentate ligand, wereobtained by the reaction of pyrazinecarbonitrile with sodium azide in the presence of copper(II) nitrate or cobalt(II)chloride. Complexesof composition [Cu(pyztz)2(H2O)] (1) deep blue crystals, [Cu(pyztz)2(H2O)2] (2a) green crystals, [Co(pyztz)2(H2O)2] (2b) orange crystals,[Cu(pyztz)2(H2O)2] Æ (H2O) (3) blue crystals were obtained. The single crystal X-ray diffraction revealed that complex 1 has square pyra-midal structure with one water molecule at apical and two pyrazine-tetrazolato ligands at basal sites, while structures of 2a, 2b and 3

consist of octahedrally coordinated metal ions, where two pyztz anions act as bidentate ligands via one of the pyrazine-N atoms andone of the tetrazole-N atoms in trans-positions and two trans water molecules. Complex 3 contains one extra lattice water molecule.Hydrogen bonds of the types O–H� � �O and O–H� � �N connect the mononuclear units to a three-dimensional network structure in 2

(a and b are isostructural) and 3. Although the H-bond patterns look complex it is shown that they can be related to the well-knownthree- and six-connected rutile net (rtl) in 2 and the four- and six-connected fsh-net in 3.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Copper(II); Cobalt(II); Crystal structures; Synthesis; Tetrazolate complexes; Vibrational spectroscopy; Network analysis; 3D-nets

1. Introduction

Tetrazole as functional group plays an increasinglyimportant role in coordination chemistry as ligand, inmedicinal chemistry as a metabolically stable surrogatefor a carboxylic acid group, and in various materials sci-ence applications, including special explosives [1–9].Although it has been known for some time that substitutedtetrazoles can be prepared by the 1,3-dipolar reaction of anitrile with azide ion, the synthesis were difficult, typicallyinvolving hydrothermal conditions with reaction times ofseveral days at 100–125 �C [10–13]. It has been shown sometime ago that performing the reaction on a metal site facil-itated the 1,3-dipolar addition [14]. More recently, Sharp-

0277-5387/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.poly.2006.11.044

* Corresponding author. Tel.: +2012 7866390; fax: +203 3911794.E-mail address: morsy5@link.net (M.A.M. Abu-Youssef).

less et al reported an environmentally friendly synthesisof a variety of 5-substituted-1H-tetrazoles using Zn(II)salts as catalysts [15]. In the presence of Zn(II) the tetraz-oles can be prepared in high yield in times from 6 to 48 hat 100 �C. The study of complexes containing substitutedtetrazole ligands is of interest to delineate the ways inwhich tetrazoles bind to metal centres. Recently, a seriesof 5-(pyridyl)tetrazole complexes as ‘‘metal organic frame-works’’ with Zn(II) and Cd(II) have been prepared underhydrothermal conditions in which a range of coordinationmodes for the tetrazoles were observed and extended 2Dand 3D structures were identified indicating hydrogenstorage properties [9]. In the course of our systematic inves-tigations of molecular magnets based on metal azido com-plexes containing pyridine derivative ligands [16–20] weobserved that the intermediate reaction of 4-cyanopyridinewith the azido ion takes place at even milder experimental

1532 M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540

conditions and we separated complexes of Ca(II), Cd(II)and Mn(II) with the 5-(4-pyridyl)tetrazolato (4-PTZ) anionas ligand [21]. Newly, other Mn(II)-5-pyridyl-tetrazolato(PTZ) complexes were obtained under similar experimentalconditions [22].

We now report four new M(II) (M = Cu, Co) complexesobtained by the 1,3-dipolar addition reaction of cyano pyr-azine with azide in aqueous solution and analyse their solidstate structures using the concept of three-dimensional nets[23].

2. Experimental

2.1. Materials and instrumentation

Infrared spectra were recorded on a Bruker IFS-125model FT-IR spectrophotometer as KBr pellets [24]. C,H, N analyses were carried out using a Perkin–Elmeranalyzer [25], Cu were analysed by a Perkin–Elmer Ana-lyst 300, AAS atomic absorption spectrometer. Ramanspectra were recorded on a Bruker IFS 6/s FT-Ramanspectrometer with Nd:CYAG laser wavelength(1064 nm) as the light source [26]. Thermogravimetry,TG and differential thermogravimetry, DTG were carriedout on a shimadzu DT-50. The measurements were per-formed by using a dynamic nitrogen atmosphere with aflow rate of 20 ml/min. The heating rate was kept at10 �C min�1 and the sample sizes ranged in mass from1.45 to 1.66 mg contained in a platinum crucible. Al2O3

was used as a reference material. Pyrazine carbonitrilehas been purchased from Aldrich Company and otherchemicals were of analytical grade quality and used with-out further purification.

Caution: Metal azide and metal tetrazolate complexesare potentially explosive. Only a small amount of materialshould be prepared and should be handled with caution.

2.2. Synthesis of copper complexes 1, 2a, and 3

To an ethanolic solution of Cu(NO3)2 Æ 3H2O (0.48 g,2 mmol) in 15 cm3, a (0.42 gm, 4 mmol) of pyrazinecarbo-nitrile, in 10 cm3 ethanol were added. Further, (0.65 g,10 mmol) NaN3 aqueous solution was added dropwise withcontinuous stirring. The clear blue solution was allowed tostand at room temperature for a couple of days. Deep bluecrystals of (1) [Cu(pyztz)2(H2O)], green crystals of (2a),[Cu(pyztz)2(H2O)2] and blue crystals of (3) [Cu(pyztz)2-(H2O)2](H2O) were formed. The three complexes were sep-arated under microscope after filtration, dried in air. Theproduct yielding about �10% of complex 1, 20% of com-plex 2, and 60% of complex 3. Anal. Calc. for 1: C,31.95; H, 2.14; N, 44.72; Cu, 16.91. Found: C, 32.21; H,2.52; N, 44.85; Cu, 17.23%. Anal. Calc. for 2: C, 30.49;H, 2.55; N, 42.68; Cu, 16.13. Found: C, 30.34; H, 2.34;N, 42.19; Cu, 16.37%. Anal. Calc. for 3: C, 29.16; H,2.93; N, 40.80; Cu, 15.43. Found: C, 29.06; H, 2.21; N,40.63; Cu, 15.69%.

2.3. Synthesis of cobalt complex 2b

To a methanolic solution of CoCl2 Æ 6H2O (0.476 g,2 mmol) in 15 cm3, (0.42 gm, 4 mmol) of pyrazinecarbonit-rile, in 10 cm3 methanol was added. Further, (0.65 g,10 mmol) NaN3 aqueous solution were added dropwisewith continuous stirring. The clear yellow solution wasallowed to stand in a refrigerator at around +4 �C for acouple of days. Orange crystals of (2b) [Co(pyztz)2(H2O)2]suitable for X-ray measurements were collected by filtra-tion, dried in air. The product yields about �50%. Anal.

Calc. for 2b: C, 30.86; H, 2.59; N, 43.19; Co, 22.08. Found:C, 30.95; H, 2.53; N, 43.35; Co, 22.13%.

2.4. X-ray crystallography

Single crystal X-ray data of 1, 2a, and 3 were measuredat 100(2) K on a modified STOE four circle diffractometer,of 2b were collected on a Bruker-AXS SMART APEXCCD diffractometer, using graphite crystal-monochroma-tized Mo Ka radiation (k = 0.7107 A). The intensities werecorrected for Lorentz-polarisation effects and for absorp-tion. Crystallographic data and processing parameters aregiven in Table 1. The structures were solved by direct meth-ods and subsequent Fourier analyses. The programsDIFABS [27a], SADABS [27b] and SHELXTL/PC program pack-age [28] were used for computations. Analytical expres-sions of neutral-atom scattering factors were employed,and anomalous dispersion corrections were incorporated.Anisotropic displacement parameters were applied tonon-hydrogen atoms in full-matrix least-squares refine-ments based on F2. All hydrogen atoms were located fromdifference Fourier maps assigned with isotropic displace-ment factors and included in the final refinement cyclesas follows: (a) pyrazine hydrogen atoms bonded to carbonby geometrical restraints using the HFIX utility ofSHELXTL/PC package; (b) water hydrogen atoms by use ofO–H distance restraints. Split occupancy of 0.5 was appliedto the disordered lattice water molecule O(2) of 3. Selectedbond distances and bond angles are given in Tables 2–5, forcomplexes 1, 2a, 2b and 3, respectively.

2.5. Network analysis

Abbreviations for 3D nets have been taken fromM. O’Keeffe and O.M. Yaghi, Reticular Chemistry Struc-ture Resource, 2005, Arizona State University, Tempe,http://okeeffe-ws1.la.asu.edu/rcsr/home.htm where crystal-lographic coordinates and other useful details for 3D-netscan be obtained. Another source is the EPINET project(http://epinet.anu.edu.au).

3. Results and discussion

In the attempt to prepare [M(pyrazinecarbonitrile)2-(N3)2]n, the [2+3] cycloaddition reaction of pyrazinecarbo-nitrile and sodium azide occurred in the presence of M2+ as

Table 1Crystallographic data and processing parameters

Compound 1 2a 2b 3

Empirical formula C10H8CuN12O C10H10CuN12O2 C10H10CoN12O2 C10H12CuN12O3

Formula mass 375.83 393.85 389.23 411.87System triclinic monoclinic monoclinic monoclinicSpace group P�1 P21/n P21/n C2/ca (A) 6.861(3) 6.294(2) 6.0806(12) 12.947(3)b (A) 9.397(3) 11.777(3) 11.396(2) 7.334(2)c (A) 11.169(4) 10.017(3) 10.533(2) 16.622(5)a (�) 72.94(3) 90 90 90b (�) 79.97(3) 106.24(2) 105.63(3) 101.07(2)c (�) 87.75(3) 90 90 90V (A3) 677.8(4) 712.9(3) 702.9(2) 1548.9(7)Z 2 2 2 4l (Mo Ka) (mm�1) 1.643 1.571 1.261 1.455Dcalc (Mg/m3) 1.842 1.835 1.839 1.766Crystal size (mm) 0.24 · 0.14 · 0.08 0.25 · 0.16 · 0.10 0.20 · 0.16 · 0.10 0.24 · 0.20 · 0.12h Range (�) 3.29–26.00 3.44–27.99 2.69–25.80 3.21–26.00Reflections collected 3035 2152 5198 1927Independent reflections/Rint 2616/0.0963 1724/0.0298 1347/0.0452 1518/0.0365Parameters 224 122 122 138Goodness-of-fit on F2 1.132 1.083 1.328 1.191R1/wR2 (all data) 0.0833/0.2106 0.0400/0.0881 0.0648/0.1330 0.0423/0.1152Residual extrema (e/A3) 0.983/�0.928 0.356/�0.395 0.734/�0.501 0.560/�0.402

Table 2Selected bond lengths (A) and angles (�) for (1)

Cu(1)–N(13) 1.967(3) Cu(1)–N(3) 1.975(4)Cu(1)–N(11) 2.048(4) Cu(1)–N(1) 2.052(4)Cu(1)–O(1) 2.219(4) N(1)–C(1) 1.340(6)N(1)–C(4) 1.351(5) C(1)–C(2) 1.407(6)C(2)–N(2) 1.343(5) N(2)–C(3) 1.333(6)C(3)–C(4) 1.402(6) C(4)–C(5) 1.441(6)C(5)–N(3) 1.343(6) C(5)–N(6) 1.350(5)N(3)–N(4) 1.353(5) N(4)–N(5) 1.298(5)N(5)–N(6) 1.377(6) N(11)–C(11) 1.341(6)N(11)–C(14) 1.367(5) C(11)–C(12) 1.388(7)C(12)–N(12) 1.346(6) N(12)–C(13) 1.362(6)C(13)–C(14) 1.390(7) C(14)–C(15) 1.452(7)C(15)–N(16) 1.324(5) C(15)–N(13) 1.346(6)N(13)–N(14) 1.350(5) N(14)–N(15) 1.325(5)N(15)–N(16) 1.357(6)

N(13)–Cu(1)–N(3) 170.5(2) N(13)–Cu(1)–N(11) 81.5(2)N(3)–Cu(1)–N(11) 97.7(2) N(13)–Cu(1)–N(1) 97.8(2)N(3)–Cu(1)–N(1) 81.1(2) N(11)–Cu(1)–N(1) 168.3(2)N(13)–Cu(1)–O(1) 96.22(14) N(3)–Cu(1)–O(1) 93.3(2)N(11)–Cu(1)–O(1) 96.11(14) N(1)–Cu(1)–O(1) 95.55(14)C(1)–N(1)–C(4) 118.4(4) N(1)–C(1)–C(2) 119.4(4)N(2)–C(2)–C(1) 122.9(4) C(3)–N(2)–C(2) 116.7(4)N(2)–C(3)–C(4) 121.7(4) N(1)–C(4)–C(3) 120.8(4)N(1)–C(4)–C(5) 113.6(4) C(3)–C(4)–C(5) 125.5(4)N(3)–C(5)–N(6) 110.7(4) N(3)–C(5)–C(4) 118.2(4)N(6)–C(5)–C(4) 131.1(4) C(5)–N(3)–N(4) 106.1(3)N(5)–N(4)–N(3) 109.1(4) N(4)–N(5)–N(6) 110.2(4)C(5)–N(6)–N(5) 104.0(3) C(11)–N(11)–C(14) 117.8(4)N(11)–C(11)–C(12) 120.9(4) N(12)–C(12)–C(11) 122.3(5)C(12)–N(12)–C(13) 117.0(4) N(12)–C(13)–C(14) 121.1(4)N(11)–C(14)–C(13) 120.9(4) N(11)–C(14)–C(15) 113.5(4)C(13)–C(14)–C(15) 125.5(4) N(16)–C(15)–N(13) 111.8(4)N(16)–C(15)–C(14) 130.6(4) N(13)–C(15)–C(14) 117.5(4)C(15)–N(13)–N(14) 105.6(3) N(15)–N(14)–N(13) 107.8(4)N(14)–N(15)–N(16) 110.4(4) C(15)–N(16)–N(15) 104.4(4)

M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540 1533

Lewis acid catalyst. This gave deep blue crystals of[Cu(pyztz)2(H2O)] (1), green crystals of [Cu(pyztz)2(H2O2)](2a), orange crystals of [Co(pyztz)2(H2O)2] (2b) and bluecrystals of [Cu(pyztz)2(H2O)2](H2O) (3).

It is well-known that the tetrazole ring formation viathe [2+3] cycloaddition of 4-cyanopyridine and azidetakes place under hydrothermal conditions so it is nota-ble that the tetrazole rings were formed at room temper-ature. The cycloaddition reaction was probablyaccelerated by the presence of the M(II) salt as a Lewisacid catalyst.

Table 3Selected bond lengths (A) and angles (�) for (2a)

Cu(1)–N(3) 1.996(2) Cu(1)–N(1) 2.078(2)Cu(1)–O(1) 2.316(2) N(1)–C(1) 1.338(3)N(1)–C(4) 1.348(3) C(1)–C(2) 1.403(4)C(2)–N(2) 1.332(4) N(2)–C(3) 1.340(4)C(3)–C(4) 1.395(4) C(4)–C(5A) 1.459(4)C(5)–N(6) 1.324(3) C(5)–N(3) 1.338(3)N(3)–N(4) 1.348(3) N(4)–N(5) 1.324(3)N(5)–N(6) 1.355(3)

N(3)–Cu(1)–N(1) 98.93(9) N(1)–Cu(1)–O(1) 92.15(8)N(3A)–Cu(1)–O(1A) 91.74(9) C(1)–N(1)–C(4) 117.1(2)N(1)–C(1)–C(2) 120.9(3) N(2)–C(2)–C(1) 122.2(3)C(2)–N(2)–C(3) 116.7(2) N(2)–C(3)–C(4) 121.7(3)N(1)–C(4)–C(3) 121.3(3) N(1)–C(4)–C(5A) 113.7(2)C(3)–C(4)–C(5A) 125.1(3) N(6)–C(5)–N(3) 111.8(2)N(6)–C(5)–C(4A) 129.4(2) N(3)–C(5)–C(4A) 118.8(2)C(5)–N(3)–N(4) 105.6(2) N(5)–N(4)–N(3) 108.2(2)N(4)–N(5)–N(6) 109.8(2) C(5)–N(6)–N(5) 104.7(2)

Symmetry code: (A) �x, �y + 1, �z.

Table 4Selected bond lengths (A) and angles (�) for (2b)

Co(1)–N(3) 2.103(4) Co(1)–N(1) 2.180(4)Co(1)–O(1) 2.059(3) N(1)–C(1) 1.342(6)N(1)–C(4) 1.343(6) C(1)–C(2) 1.384(7)C(2)–N(2) 1.335(7) N(2)–C(3) 1.332(6)C(3)–C(4) 1.384(7) C(4)–C(5A) 1.469(6)C(5)–N(6) 1.333(6) C(5)–N(3) 1.333(6)N(3)–N(4) 1.345(5) N(4)–N(5) 1.317(6)N(5)–N(6) 1.340(6)

N(3)–Co(1)–N(1) 101.46(15) N(1A)–Co(1)–O(1) 90.42(14)N(3)–Co(1)–O(1) 92.14(15) C(1)–N(1)–C(4) 115.9(4)N(1)–C(1)–C(2) 121.8(5) N(2)–C(2)–C(1) 122.1(5)C(2)–N(2)–C(3) 116.3(5) N(2)–C(3)–C(4) 122.1(5)N(1)–C(4)–C(3) 121.8(4) N(1)–C(4)–C(5A) 114.7(4)C(3)–C(4)–C(5A) 123.4(4) N(6)–C(5)–N(3) 111.7(4)N(6)–C(5)–C(4A) 127.6(4) N(3)–C(5)–C(4A) 120.6(4)C(5)–N(3)–N(4) 104.9(4) N(5)–N(4)–N(3) 108.9(4)N(4)–N(5)–N(6) 109.8(4) C(5)–N(6)–N(5) 104.6(4)

Symmetry code: (A) �x, �y, �z.

Table 5Selected bond distances (A) and angles (�) for (3)

Cu(1)–N(3) 1.989(3) Cu(1)–N(1) 2.044(3)Cu(1)–O(1A) 2.416(3) N(1)–C(1) 1.342(5)N(1)–C(4) 1.356(5) C(1)–C(2) 1.396(6)C(2)–N(2) 1.332(5) N(2)–C(3) 1.346(5)C(3)–C(4) 1.378(5) C(4)–C(5) 1.470(5)C(5)–N(6) 1.329(5) C(5)–N(3) 1.330(5)N(3)–N(4) 1.348(4) N(4)–N(5) 1.320(5)N(5)–N(6) 1.350(4)

N(3AS)–Cu(1)–N(1) 98.92(12) N(3)–Cu(1)–O(1A) 90.21(11)N(1)–Cu(1)–O(1) 91.74(11) C(1)–N(1)–C(4) 117.1(3)C(1)–N(1)–Cu(1) 129.0(3) C(4)–N(1)–Cu(1) 113.9(2)N(1)–C(1)–C(2) 120.4(4) N(2)–C(2)–C(1) 122.9(4)C(2)–N(2)–C(3) 116.3(4) N(2)–C(3)–C(4) 121.9(4)N(1)–C(4)–C(3) 121.5(3) N(1)–C(4)–C(5) 112.9(3)C(3)–C(4)–C(5) 125.7(3) N(6)–C(5)–N(3) 112.7(3)N(6)–C(5)–C(4) 129.2(3) N(3)–C(5)–C(4) 118.0(3)C(5)–N(3)–N(4) 105.2(3) C(5)–N(3)–Cu(1) 113.9(2)N(4)–N(3)–Cu(1) 140.9(3) N(5)–N(4)–N(3) 108.0(3)N(4)–N(5)–N(6) 110.7(3) C(5)–N(6)–N(5) 103.5(3)

Symmetry code: (A) �x + 1, �y, �z + 1.

Fig. 1. Perspective view of [Cu(pyztz)2(H2O)] (1).

Fig. 2. Packing plot of [Cu(pyztz)2(H2O)] (1). Broken lines indicatehydrogen bonds.

1534 M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540

3.1. Structures

A perspective view with atom labelling scheme ofcomplex 1 is given in Fig. 1, selected bond parametersare summarized in Table 2. The copper(II) ions arepenta-coordinated by nitrogen atoms N(1), N(3) N(11)and N(13) of two chelating pyztz ligands, which adoptthe basal sites, and oxygen atom O(1) of an aqua ligandat apical site. The CuN4O coordination polyhedron maybe described as a slightly distorted tetragonal pyramid(s = 0.04) [29]. The Cu–Npyz bonds [2.048(4) and2.052(4) A] are a little bit longer than the Cu–Ntet bonds[1.975(4) and 1.967(3) A], whereas the Cu(1)–O(1) bond is2.219(4) A. Cu(1) is located 0.186 A above the basal N4

plane. The chelating N–Cu–N bond angles are 81.1(2)�and 81.5(2)�, the other N–Cu–N bond angles are 97.7(2)�

and 97.8(2)�, whereas the N–Cu–O bond angles are in therange from 93.3(2)� to 96.22(14)�. The tetrazolato-ringsof the pyztz ligands are twisted by 3.2� and 4.2� from theirsixmembered pyrazine-rings. The mean planes of the twopyztz ligands have an acute angle of 14.1�. A packing viewof 1 is given in Fig. 2. The isolated polyhedra of 1 have aCu� � �Cu separation of 6.861(3) A, and are connected viahydrogen bonds of type O–H� � �N from O(1) to N(16)[�x,�y, 1 � z] and N(6) [1 � x, 1 � y,�z] to form a 1-Dsystem extented along [1,1,�1] with O� � �N separations of2.841(5) and 2.920(5) A, respectively. Within these chainsadjacent polyhedra are arranged head to tail in order toallow p–p-stacking interactions between neighbouring che-lating pyztz ligands.

The molecular structure of 2a, Fig. 3, has a centrosym-metric configuration, in which the octahedral Cu(II) ion iscoordinated by four equatorial nitrogen atoms from twopyztz ligands and axial oxygen atoms of coordinated watermolecules. As in 1, each pyztz ligand chelates to Cu throughone tetrazolato-nitrogen atom N1-site of the tetrazolato-ring and through the pyrazine nitrogen atom. The tetrazo-lato-ring is twisted by 5.1� from the sixmembered ring.Selected bond parameters are listed in Table 3. The

Fig. 3. Perspective view of [Cu(pyztz)2(H2O)2] (2a).

M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540 1535

distorted CuN4O2 octahedron has Cu–Npyz and Cu–Ntet

bond lengths of 2.078(2) and 1.996(2) A, respectively, anda Cu–O bond distance of 2.316(2) A. The water moleculeforms hydrogen bonds of type O–H� � �N from O(1) toN(4) [1 � x, 1 � y,�z] and N(6) [�1/2 + x, 1/2 � y, �1/2 + z] with O� � �N separations of 2.936(4) and 2.816(3) A,respectively, where two N atoms of the tetrazolato ringsin position 1 and 2 act as hydrogen bond acceptors to formcyclic tetrameric subunits. The shortest Cu� � �Cu separation

Fig. 4. (a) Perspective view of [Co(pyztz)2(H2O)2] (2b). (b) Packing plot of[Co(pyztz)2(H2O)2] (2b).

between Cu(II) polyhedra is 6.294(2) A, the basal CuN4

planes form acute angles of 21.6�. Compound 2b as shownin Fig. 4 is isostructural and selected bond parametersare listed in Table 4. The hydrogen bonding system in 2 dif-fers from that observed in the structure of corresponding[Mn(2-PTZ)2(H2O)2] complex, (2-PTZ = 5-(2-pyridyl)-tetrazolate anion) [22]. In this latter Mn complex eightintermolecular O–H� � �N(tetrazole) hydrogen bonds linkeach Mn complex to four other Mn complexes. In contrastto compounds 2a and 2b nitrogen atoms of the 2-PTZmoiety act as acceptors which correspond to N(5) andN(6) atoms of the present tetrazole ligands see Ref [22,Fig. 1b].

A perspective view of compound 3 is given in Fig. 5,selected bond parameters are summarized in Table 5.Although 3 has a similar centrosymmetric configurationas 2a, in which the octahedral Cu(II) ion is also coordi-nated by four equatorial nitrogen atoms from two pyztzligands and axial oxygen atoms of coordinated watermolecules, the bond parameters within the CuN4O2 coordi-nation polyhedron differ significantly. The Cu–Npyz andCu–Ntet bond lengths are shortened to 2.044(3) and1.989(3) A, respectively, whereas the axial Cu–O bonddistance is elongated to 2.416(3) A. The aqua ligands formhydrogen bonds of type O–H� � �N from O(1) to N(6)[1 � x, 1 � y, 1 � z] and N(5) [1/2 + x,�1/2 + y,z] to forma supramolecular network, with O� � �N separations of2.913(4) and 2.831(3) A, respectively. In addition, thedisordered lattice water molecule with split occupancy 0.5and related by a diad, form hydrogen bonds of typeO–H� � �O to apical O(1) atoms of adjacent Cu(II) polyhe-dra. The O� � �O separations are 2.790(13) and2.928(13) A. As a consequence of this additional latticewater molecule the packing of 3 is quite different comparedto 2a. The monomeric polyhedra have a V-type arrange-ment with acute angles of basal CuN4 planes of 49.8�.The shortest metal–metal distance is 7.334(2) A.

Bond lengths and bond angles of the five-membered tet-razolate rings in complexes 1–3 are very similar and agree

Fig. 5. Perspective view of [Cu(pyztz)2(H2O)2] Æ (H2O) (3).

Scheme 2.

Fig. 6. The three- and six-connected network in 2, the net topology is a rtl

or rutile net, the most common of all three- and six-connected nets.

1536 M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540

well with values reported in a series of bis-tetrazolate-dianions [30]. The N2–N3 bond opposite to C in position5 is significantly shorter [1.298(5)–1.325(5) A] than otherinteratomic distances within the heterocycle despite of thearomatic nature of the five-membered ring. In case of 5-phenyl tetrazolate anion (5-PhTZ) the deprotonation hadalso led to a noticeable elongation of the N2–N3 bondfrom 1.247 to 1.307(3) A, in excellent agreement with ab ini-

tio calculations [31].It is interesting to note that in case of the present com-

plexes 1–3, only one (in case of 1) and two (in case of 2a,b

and 3) out of four uncoordinated nitrogen donor atoms perpyztz molecule act as hydrogen bond acceptors. In case ofprevious reported complexes with 5-(4-pyridyl)tetrazolatoligands (4-PTZ) [21] all nitrogen donors are involved inhydrogen bonds. In fact, compound 1 can be described ashydrogen bond mismatched as it has nine possible hydro-gen bond acceptors but only two hydrogens can act as clas-sical donors. In 2, this ratio is 10:4 and in 3 11:6.Consequently, the most complex hydrogen bond patternis found in 3. This fact and the higher nitrogen contentcompared to the 4-PTZ ligand may also explain the ther-mal instability of the present compounds.

3.2. Network analysis

The analysis of network patterns as an aid in the under-standing of crystal structures was advocated already in themid 1950:ies by UK crystallographer Alexander Wells, [32]and recently network analysis of 3D-coordination poly-mers and Metal–Organic Frameworks have becomeincreasingly important [23,33]. However, as was shownalready by Wells, this analysis is relevant also for hydrogenbonded systems [24].

It should be emphasised that all structures do not form3D-networks, even if hydrogen bonding is considered, sofor example is compound 1 clearly well described as thepacking of 1D hydrogen bonded chains. Compound 2 onthe other hand is clearly hydrogen bonded in all threedimensions, and these bonds are few (compared to the totalnumber of atoms in the molecule) and well defined, thusthis structure is probably well described as a 3D-networkScheme 1.

Indeed, when we assign nodes and links in 2 accordingto Scheme 2 we get a three- and six-connected network,see Fig. 6. Close inspection of this net (visually and by cal-culating vertex symbols [34]) shows that the net topology is

Scheme 1.

a rtl- or rutile net, the most common of all three- and six-connected nets Scheme 3.

The situation in 3 is slightly more complicated as wehave introduced more possible hydrogen bond acceptorand donor sites. It appears, however, that this structurecan be described by the fsh-net, see Fig. 7.

Scheme 3.

Fig. 7. The four- and six-connected network in 3 has the fsh topology.

M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540 1537

Note that both nets are somewhat distorted from theideal nets, but they still have the same topology as the idealnets as they can be transformed into each other withoutbreaking any bonds.

3.3. Thermal analysis

Thermal decomposition analysis of the given tetrazolatecomplexes was performed under quite sensitive conditions;very small samples were taken (1.4–1.6 mg.) due to the highexplosion properties of such compounds. The only pub-lished thermal analysis data for pyridine tetrazolate com-

Table 6Thermal decomposition of 1, 2a, 2b, and 3

Complex DTG peak (�C) Temperature range (�C) De

[Cu(Pyztetz)2(H2O)] 121.73 105–127 H2

231.67 127–242 1 12

303.16 242–468 1 12

584.52 468–650 cyaCu

[Cu(Pyrztetz)2(H2O)2] 120.43 103–159 2H289.26 189–294 1 1

2

300.18 294–355 1 12

421.44 360–476 pyrCu

[Co(Pyrztetz)2(H2O)2] 212.82 150–225 2H357.87 225–381 tet399.58 381–427 tet558.97 427–570 2 p

Co

[Cu(Pyrztetz)2(H2O)2] Æ H2O 138.87 106–144 2H221.26 199–287 H2

314.72 292–342 2 t512.65 342–607 2 p

Cu

plexes were performed and tentatively assigned till 250 �C[21]. The DTA and DSC measurements of these complexesfailed as the samples were exploding even at low tempera-tures and lower masses less than 2.0 mg. It also gave somevapors which affects the sensor of the DSC instrument. Thestages of decomposition, temperature range, decomposi-tion product losses as well as the found and calculatedweight loss% of the complexes are given in Table 6. TheTG and DTG curves of complexes 1, 2a, 2b and 3,Fig. 8, show the decomposition steps.

The first step, almost in all complexes, represents theloss of water content, hydrated and coordinated water mol-ecules in the temperature range 103–280 �C. Although thetetrazolate group is a sensitive exploding group in thecomplexes, it decomposes slowly over a wide range oftemperature, perhaps overlapping with the loss of watermolecules or decomposition of the subsequently formedcyano-pyrazine group. Decomposition and liberation ofan azido group was found in the temperature range 154–355 �C. The third and fourth steps were generally thedecomposition of the cyano-pyrazine group, liberatingthe pyrazine moiety and leaving the cyano group on themetal atom which was further oxidized to give the final res-idue as a metal oxide.

3.4. Spectra

In the high energy region the room temperature IR spec-tra of the crystalline complexes 1, 2a, 2b and 3 exhibitstrong broad bands around 3000–3550 cm�1 correspondingto the coordinated water molecules to the Cu(II) ro Co(II)ions in the three complexes. Extensive hydrogen bonding of

composition product lost (formula weight) Weight loss (%)

Found (%) Calculated (%)

O 4.63 4.78N2 molecule 10.60 11.23N2 and cyano-pyrazine 37.75 39.14no-pyrazine group 26.14 27.96O residue 20.19 21.16

2O 9.50 9.14N2 molecule 9.11 10.71N2 and cyano-pyrazine 36.99 37.35azine group 19.37 20.10O residue 22.9 20.19

2O 9.40 9.24razolate group (in two steps) 17.35 17.74razolate group 17.41 17.74yrazine groups 38.80 41.14O residue 19.86 19.25

2O 8.88 8.74O 3.96 4.37etrazolato (3 N2 and 2 CN�) 32.99 33.04yrazine groups 34.07 38.40O Residue 17.9 19.31

Fig. 8. TG and DTG of complexes 1, 2a, 2b and 3.

1538 M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540

the types O–H� � �O and N–H� � �O are indicated by thepresence of broad medium strong bands centered around2400–2600 cm�1. The absence of any bands in the 2200–1750 cm�1 region confirms ring formation to the tetrazo-late ligand by the 1,3-dipolar reaction of the azide groupwith the nitrile group on the pyrazine ring. Neither vibra-tions associated with mCN of the 2-cyanopyrazine

Table 7Vibrational frequencies (cm�1) in the IR and Raman spectra of complexes 1,

Complex 1 Complex 2a Complex

IR Raman IR Raman IR

3343 s,b 3466 m 3345 s,b 3301 m 3330 vs,b3260 s,b 3255 s 3077 vs,b3089 s 3085 s 3089 s 3090 s 2554 m2631 w 2448 m 2605 w 2773 m 2354 m1726 w 1728 w 2328 m1675 vs 1662 m,b 2063 s1631 vs 1608 vs 1635 m,b 1600 vs 1610 m1582 s 1553 m1534 s 1539 vs 1535 m 1535 vs 1532 m1428 vs 1430 m 1455 s 1447 s1380 vs 1375 m 1375 s 1371 s1299 vs 1300 s 1267 w 1300 m1235 m 1234 s 1225 s1180 vs 1180 vs 1168 vs1133 m 1133 s 1134 vs1071 s 1072 s 1072 vs1046 vs 1022 s 1046 vs 1019 s 1036 vs954 w 958 w 936 w863 s 865 s 864 s769 w 770 s737 m 759 s 759 m627 w,b 625 mb 681 w593 m 593 s 593 s504 m 505 m 478 s418 s 420 s 418 s394 w 396 w 386 s296 w 295 w 293 m

126 s 137 s�126 m �137 m

(expected week to medium band centered around2240 cm�1) nor strong bands associated with masN3 in the2150–2000 cm�1 region are present [35]. The vibration fre-quencies of the coordinated pyrazine tetrazolato ligandscould be tentatively assigned in agreement with recentlyreported metal pyridine tetrazolate [21,22]. In the farregion few bands around 296 cm�1 could tentatively be

2a, 2b and 3

2b Complex 3 Assignment

Raman IR Raman

3542 s,b mOH water3075 m 3287 s,b 3262 s

3187 s,b 3262 s mO� � �H–O2630 w 2610 m mN� � �H–O1728 w

1616 s 1610 m1597 vs 1585 s1532 vs 1534 m 1540 m1462 w 1427 vs

1377 vs1301 s

1373 w 1231 s 1214 m1163 vs1130 vs pyrazine

1165 w 1070 vs tetrazolate1044 vs vibrations

1085 m 940 w1036 m 866 vs

770 s765 s

755 w 645 w

638 w 507 s,b417 m387 m296 w 292 s M–L vibrations

144 m�292 m anti-Stoke

M.A.M. Abu-Youssef et al. / Polyhedron 26 (2007) 1531–1540 1539

assigned as a M–L vibration. The Raman spectra showsome anti-Stokes peaks around �126 m, �137 m and�292 m, cm�1 for complexes 1, 2a and 3 respectively.Results are summarized in Table 7.

The electronic spectrum of complex 1 exhibits the d–dtransitions as a relatively strong broad absorption bandaround 15000 cm�1 suggesting five-coordination geometryaround the central copper ion, along with a shoulder on thehigh frequency side at 24300 cm�1 which could be attrib-uted to the LMCT from the pyrazine tetrazolate ligandsto the central copper ion [36]. The spectra of penta-amincopper(II) complexes with square pyramidal geometry havebeen found to exhibit an intense absorption band in the17000–15000 cm�1 range [37]. The complexes 2a and 3show the LMCT absorption bands around 26000 cm�1

but the d–d transition bands are shifted to higher energy.It is found at 15600 cm�1 for complex 2a and at16500 cm�1 for complex 3. The cobalt(II) complex 2b

shows the LMCT absorption bands around 26595 cm�1

while the d–d transition bands are shifted to higher energy.It is found as a broad band around 20160 cm�1. Theseshifts could be interpreted as the effect of an increasedcf-splitting due to the existence of a sixth ligand and is con-sistent with the 6-fold coordination field for the coppercomplexes [38] and the cobalt complex [39].

4. Conclusions

The preparation of 5-(pyridyl)tetrazole M(II) complexesfrom azide ions and 4-cyanopyridine were achieved underexceptionally mild conditions. The compounds preparedform a series of pseudo-polymorphs with different numbersof water molecules present, going from a system with amassive over-representation of hydrogen bond acceptorsthrough a more balanced system as more water moleculesare added. It was shown that the structures showingextended hydrogen bonds in three-dimensions could read-ily be analysed using the concept of 3D-nets.

5. Supplementary material

CCDC 278952, 278953, 622096 and 278954 contain thesupplementary crystallographic data for 1, 2a, 2b and 3,respectively. These data can be obtained free of chargevia http://www.ccdc.ac.uk/conts/retrieving.html, or fromthe Cambridge Crystallographic Data Centre, 12 UnionRoad, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.

Ideal form of the fsh-net from the RCSR. (http://okee-ffe-ws1.la.asu.edu/RCSR/home.htm)

cell: 1.5601, 1.5601, 5.6062, 90, 90, 120space group: R-3 mnodes (vertices):0.0000, 0.0000, 0.4108 (4 connected)0.0000, 0.0000, 0.0000 (6 connected)

Acknowledgements

M.A.M. Abu-Youssef and A.A. Massoud thank theSIDA-Swedish Research Links program for Grant No.348-2002-6879. F.A. Mautner thanks Prof. Kratky, Prof.Belaj (Univ. Graz) and Dr. J. Baumgartner (TU-Graz)for assistance.

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