## 1 Introduction  
The coordination chemistry of iron(III) compounds with oxido-bridged species is valuable to synthetic chemists [1] namely due of their applications in biological systems, such as in storage and transport of dioxygen [2], phosphate ester hydrolysis [3], DNA synthesis [4], etc. Moreover, oxido-bridged dinuclear iron(III) units are also present at the active site of various non-heme metalloenzymes, such as hemerythrin, methane monooxygenase (MMO), ribonucleotide reductase, etc. [5]. Several oxido- [6], hydroxido- [7], alkoxido- [8], peroxidido- [9], or carboxylato-bridged [10] iron(III) complexes or coordination polymers have been reported by various research groups, which show interesting applications in areas of magnetism, catalysis, biology, electrochemistry, etc. [11]. On the other hand, pyrazine-based carboxylate ligands are important building blocks for the construction of various complexes and coordination polymers due to their versatile metal-binding and hydrogen-bonding capabilities [12]. 2-Pyrazinecarboxylic is illustrative of such behaviors [13]; moreover, by introducing substituents into the pyrazine ring, we can modify its coordination and hydrogen bonding properties. In this context, we have chosen an amine-substituted pyrazine carboxylate ligand, namely 3-aminopyrazine-2-carboxylic acid (HL), which has a good propensity for the formation of coordination and hydrogen bonds, as well as for \(\pi\)-\(\pi\) stacking interactions. It is known to form complexes with s-block [14], d-block [15], and f-block [16] metal ions. Moreover, our group has also reported several Sn(II), Pb(II), and Fe(III) metal complexes and coordination polymers based on such a ligand, and studied their polymorphic and catalytic activity towards some organic transformations [17; 18; 19]. Although a few oxido and methoxido iron complexes are known [9; 20], no example of oxido- or methoxo-bridged Fe(III) complexes with 3-aminopyrazine-2-carboxylic acid has been reported. Thus, the synthesis and study of complexes of this type constitute the general aim of the current work. The oxidation of alcohols to carbonyl compounds is one of the significant reactions in organic chemistry, and many metal-based homogeneous catalysts have been developed [21]. However, most of these systems required harsh reaction conditions, metal and solvent toxicity, high cost, or high reagent load or produced unwanted waste. To remove the harmful wastes, the development of catalytic oxidation procedures which involve green methods is a matter of current interest [22] and, in this context, microwave-assisted solvent-free oxidation of alcohols using environmentally suitable and effective catalyst, which can operate under mild conditions, are of a particular interest [23]. Besides that, iron is mostly used in many oxidation reactions, such as epoxidation [24], sulfoxidation [25], hydroxylation [26], etc. Alcohol oxidations are also catalyzed by iron complexes, and examples have been reported by our group, namely concerning the oxidations of secondary alcohols and cycloalkanes under microwave (MW) irradiation [27; 28]. Besides, the dichloro hydrotris (pyrazol-1-yl)methane iron(II) complex, heterogenized on carbon materials or zeolites or dispersed in ionic liquids, in the presence of 2-pyrazinecarboxylic acid, is an active, selective, and recyclable catalyst for oxidation of cyclohexane [29]. In addition, 2-pyrazinecarboxylic acid is an additive in the oxidation of alkanes catalyzed by iron(III) complexes [30]. Thus, heterogeneous catalytic systems based on substituted pyrazinecarboxylic acid-Fe(III) species should be promising for an efficient, clean, and safe alcohol oxidation reaction. Hence, we report herein the synthesis and structural characterization of a set of iron(III) complexes, viz.