Study on a pyrazine-modulated tetrapyridyltriamide and its complexes: Synthesis, structure and properties Wen-Zhen Wang a,b , Rayyat Huseyn Ismayilov a,b , Gene-Hsiang Lee a , Yuh-Sheng Wen b , Shie-Ming Peng a,b, * a Department of Chemistry, National Taiwan University, Taipei, Taiwan, ROC b Institute of Chemistry, Academia Sinica, Taipei, Taiwan, ROC article info Article history: Received 15 December 2009 Received in revised form 16 March 2010 Accepted 16 March 2010 Available online 25 March 2010 Keywords: Pyrazine-modulated oligo-a-pyridylamino ligand Copper complex Cobalt complex Hydrogen bonds Supramolecular networks abstract A pyrazine-modulated oligo-a-pyridylamine ligand H 3 pzpz and its mononuclear copper(II) and cobalt(II) complexes have been synthesized and structurally characterized. The protonated ligand cation 1 exhibits an anti-anti-anti-anti-syn-anti conformation. H 3 pzpz can be a quadridentate ligand and coordinates to metal atoms with all-anti mode in both copper and cobalt mononuclear complexes. The copper(II) ion in 2 is five-coordinated in tetragonal pyramid geometry with one of the perchlorate anions being weakly coordinated in the apex position. The cobalt(II) ion in 3 and 4 is six-coordinated in octahedron geometry. Extensive hydrogen bonds are formed, and construct the complexes 1 and 2 into 2D networks and 3 and 4 into 3D networks. X-band EPR spectra of 2 showed well-resolved hyperfine structures resulting from the two paramagnetic isotopes 63 Cu and 65 Cu, yielding g = 2.16 and A 0 = 67  10 4 cm 1 . Complexes 3 and 4 showed spin–orbital coupling and zero-field splitting that is reflected in the magnetic properties. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The variety of coordination mode of multidentate ligands is a fascinating topic. Oligo-a-pyridylamine ligands (Scheme 1) have attracted increasing attention over the past two decades owing to their capability to support linear metal strings and leading to metal string complexes, also called ‘‘Extended Metal Atom Chain complexes” (EMACs) [1,2]. Oligo-a-pyridylamido ligands coordi- nate to metal atoms in a variety of ways. In EMACs the supporting ligands are coordinated to metal in all-syn form, whereas all-anti form style was observed in mononuclear complexes [1–7]. The free ligands exhibit double helical structure, and the dimers are paired via hydrogen bonds between –NH groups [8]. To expand the cate- gory and number of metal atoms in EMACs, recently we have developed a series of modulated oligo-a-pyridylamido ligands. Among them pyrazine-modulated ligands, by graft pyrazine in- stead of pyridine ring(s) in oligo-a-pyridylamido ligands, have suc- cessfully resulted in heptacobalt and nonachromium EMACs which are the longest cobalt(II) and chromium(II) EMAC molecules ob- tained to-date (Scheme 2) [9,10]. Furthermore, by providing more donor nitrogen atoms in aromatic ring(s), the pyrazine ligands ex- hibit various coordination forms and are especially versatile in the construction of coordination polymers. 2D coordination polymers are obtained with two-pyrazine modulated ligands di(2-pyra- zyl)amine (Hdpza) and N,N 0 -di(pyrazin-2-yl)pyridine-2,6-diamine (H 2 dpzpda). Three-pyrazine modulated ligand N,N 0 -di(pyrazin-2- yl)pyrazine-2,6-diamine (H 2 tpzda) resulted in 1D polymers, but constructed 3D polymers with further addition of metal ions [4,11]. Here we focus on a tuning ligand from tetrapyridyltriamine (H 3 tetra) to N 2 -(pyrazin-2-yl)-N 6 -(6-(pyrazin-2-ylamino)pyridin- 2-yl)pyridine-2,6-diamine (H 3 pzpz). Its heptametal EMACs [M 7 (pzpz) 4 X 2 ] (M = Co(II), Cr(II), Ni(II); X = Cl, NCS) have been suc- cessfully synthesized and reported [5,10]. In this paper we report the result on protonated ligand [H 4 pzpz]ClO 4 (1), its copper (II) complex [Cu(H 3 pzpz)(ClO 4 )]ClO 4 (2) and cobalt (II) complexes [Co(H 3 pzpz)(H 2 O) 2 ](ClO 4 ) 2 (3) and [Co(H 3 pzpz)(NCS) 2 ](4). Com- plexes 2–4 provide promising building blocks to construct coordi- nation polymers. 2. Experimental 2.1. Materials and measurements All reagents and solvents were obtained from commercial sources and were used without further purification unless other- wise noted. Caution! Perchlorate salts are potentially explosive and should only be used in small quantities and handled with the necessary precautions. 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.03.051 * Corresponding author at: Department of Chemistry, National Taiwan Univer- sity, Taipei, Taiwan, ROC. Tel.: +886 2 3366 1655; fax: +886 2 8369 3765. E-mail address: smpeng@ntu.edu.tw (S.-M. Peng). Journal of Molecular Structure 973 (2010) 116–123 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc