Coordination versatility of 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane: Co(II) and Ni(II) complexes Vibha Mishra a , Francesc Lloret b , Rabindranath Mukherjee a, * a Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India b Departament de Quı ´mica Inorga ` nica, Facultat de Quı ´mica de la Universitat de Vale `ncia, Dr Moliner, 46100 Burjassot (Vale `ncia), Spain Received 14 March 2006; received in revised form 10 May 2006; accepted 10 May 2006 Available online 17 May 2006 Abstract The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L 8 ) has afforded six-coordinate monomeric and dimeric complexes [(L 8 )Co II (H 2 O) 2 ][ClO 4 ] 2 (1), [(L 8 )Ni II (MeCN) 2 ][BPh 4 ] 2 (2), [(L 8 )Ni II (O 2 CMe)][BPh 4 ](3), and ½ðL 8 Þ 2 Co II 2 ðl-O 2 CMeÞ 2 ½BPh 4  2 ð4Þ. The crystal structures of 1, 2 Æ MeCN, 3, and 4 revealed that the ligand L 8 is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing addi- tional coordination by two trans-H 2 O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral Co II N 2 ðpyridylÞN 0 2 ðpyrazoleÞO 2 ðwaterÞ, Ni II N 2 ðpyridylÞN 0 2 ðpyrazoleÞN 00 2 ðacetonitrileÞ, and Ni II N 2 ðpyridylÞN 0 2 ðpyrazoleÞO 0 2 ðacetateÞ coordination. The angles between the two CoN 2 /NiN 2 planes span a wide range 23.539(1)° (1), 76.934(8)° (2), and 69.874(14)° (3). In contrast, complex 4 is a bis-l-1,3-acetato-bridged (syn–anti coordination mode) dicobalt(II) complex [CoCo separation: 4.797(8) A ˚ ] in which L 8 provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L 8 . Absorption spectral studies (MeCN solution) have been done for all the com- plexes. Complexes 1–3 are uniformly high-spin. Temperature-dependent (2–300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling ð b H ¼JS 1  S 2 Þ between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: D (axial splitting param- eter) = 765(5) cm 1 , k (spin-orbit coupling) = 120(3) cm 1 , k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m 1 . Ó 2006 Elsevier B.V. All rights reserved. Keywords: Cobalt(II) and nickel(II) complexes; N-Tetradentate/bridging bidentate ligand; Crystal structure; syn–anti Acetate coordination mode; Fer- romagnetic exchange coupling in dicobalt(II) complex 1. Introduction The coordination chemistry of pyrazole-derived chelat- ing ligands [1], in addition to well known tris(pyraz- olyl)borates [2], has vigorously developed. As part of our general interest in the synthesis of coordination complexes of new chelating ligands with interesting properties (identi- fication of steric effect due to the presence of methyl substituents near donor site [3]; temperature- and light- induced spin-equilibria in Fe(II) compounds [4,5]; forma- tion of supramolecular architectures via primarily C– HCl hydrogen-bonding interaction [6], hydrolysis of ethyl acetate due to nucleophilic attack of Cu(II)-coordi- nated hydroxide ion [7]), we have studied the coordination behavior of non-planar bi- and tri-dentate mononucleating (L 1 –L 6 ) or bridging monodentate (L 7 ) pyrazole-based het- erocyclic ligands to control the stereochemistry at metal(II) centers [3–9]. The coordination chemistry of the ligand 1,3- bis[3-(2-pyridyl)pyrazol-1-yl]-propane (L 8 ), designed by linking two mixed-heterocycle synthon/ligand 3-(2-pyr- idyl)pyrazole [7,10–17] fragments by a propyl spacer, act- ing as a tetradentate mononucleating ligand towards Ag I and M II ions [M = Fe, Cu, Zn or Pb] was developed by Ward and co-workers [17]. Anticipating its potential to 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.05.005 * Corresponding author. Tel./fax: +91 512 2597437. E-mail address: rnm@iitk.ac.in (R. Mukherjee). www.elsevier.com/locate/ica Inorganica Chimica Acta 359 (2006) 4053–4062