supplementary materials

Oligo-α-pyridylamine ligands are very useful in the synthesis of metal string complexes, which are also known as extended metal atom chains (EMACs). EMACs are invaluable for acquiring a fundamental understanding of metal-metal bonds (Kiehl et al., 2004) and for potential applications such as molecular electronic devices. These oligo-α-pyridylamine ligands contain pyridyl and amine groups, and can result in the formation of double helical structures in nonpolar solvents due to hydrogen bonding (Leung et al., 2002). After deprotonation of oligo-α-pyridylamine ligands, the resulting anions can stabilize the linear metal cores. Activation of the H atom was observed in some EMACs. Recently we designed a series of modulated oligo-a-pyridylamino ligands, by including one or more of the nitrogen-rich aromatic rings such as pyrazine, pyrimidine and naphthyridine instead of pyridine rings to the ligands. The modification of ligands significantly improved the reactivity leading to the EMAC, and resulted in complexes with very different redox properties (Wang et al., 2008). Furthermore, by providing more donor nitrogen atoms in aromatic rings, the pyrazine ligands exhibit more coordination forms and are especially versatile in the construction of coordination polymers with potential applications in gas storage, catalysis, magnetism, luminescence, etc. due to their ability to form multidimensional frameworks through multiple metal-binding sites. (Ismayilov et al., 2007; Wang et al., 2007, 2008). Some interesting phenomena were also observed, e.g. the observation of disassembly of ligands during the preparation of EMACs. In this paper we describe a compound (I) from the decomposition of pyrazine-modulated N²-(pyrazin-2-yl)-N⁶– (6-(pyrazin-2-ylamino)pyridin-2-yl)pyridine-2,6-diamine (H₃pzpz) relating to the preparation of heptacobalt complexes (Wang et al., 2007).

The crystal structure of [C₄H₁₀NO]₂[CoCl₄] shown in Fig. 1 consists of two protonated tetrahydro-1,4-oxazine(morpholine) cations [C₄H₁₀NO]⁺ and a [CoCl₄]^2- dianion, the compound [C₄H₁₀NO]₂[CoCl₄] is a hybrid ionic inorganic-organic compound of Y₂X type. The Co^II ion is in a tetrahedral coordination geometry. The Co—Cl bond distances are in the range 2.2583 (8) - 2.2818 (8)Å with an average of 2.2675 (8)Å (The Co—Cl in CoCl₂ is 2.43 Å). The bond angles between Co—Cl are in the range 106.01 (3) - 113.73 (3)° with an average of 109.43 (3)°, which is very close to the ideal tetrahedral angle value of 109.28° (Fastje & Möller, 2009; Szklarz et al., 2009; Wu et al., 1997).

The cations are six-membered heterocycle rings, protonated tetrahydro- 1,4-oxazine, and exhibit chair-shaped conformations. All bond angles in the rings are in the range 108.8 (3) - 111.9 (2)° with an average of 110.4 (3)°, which is well consistent with a sp³ hybrid orbital angle. The nitrogen atom in tetrahydro-1,4-oxazine was protonated owing to the low basicity of tetrahydro-1,4-oxazine (pK_a = 8.4) due to the inductive effect of oxygen atom. The average C—C, C—N and C—O bond distances exhibit a typical value of single bonds, which are 1.503 (4), 1.490 (4) and 1.419 (4) Å, respectively.

Extensive hydrogen bonds between chloride atoms Cl(1), Cl(2) and Cl(3) in the [CoCl₄]^2- dianion and nitrogen and oxygen atoms N(1), N(2), O(1) and O(2) in both tetrahydro-1,4-oxazine cations were observed (Table 1). [CoCl₄]^2- dianions were paired through the hydrogen bonds between Cl(1), Cl(2) and N(1) atoms, resulting in an 8-membered ring N(1)···Cl(1)—Co—Cl(2)···N(1)···Cl(1)—Co—Cl(2) (Fig. 2) which were further linked to a 2-D sheet extending in the bc plane through hydrogen bonds between Cl(3) and N(2) atoms. A group of weak hydrogen bonds involving carbon atoms were observed between layers, which build the title compound (I) into a 3-D network (Fig. 3).