Noncovalent interactions are of key importance in numerous chemical and biological processes and materials science [1]. Among different noncovalent interactions which are basis of supramolecular chemistry, those involving lone pair…π-systems (lp…π) are of great importance and interest in both chemistry and biology. Noncovalent interactions involving π-hole donors are incomparably less studied than those of σ-hole species. Among different π-hole donors are coordinated nitrate [2], acetonitrile [3], isocyanides [4-5], and carbonyl [6] ligands in their complexes in which the latter studied significantly.
The occurrence of such interaction was firstly noticed by Bürgi et al. during the structural study of (S)-methadone, in which the nucleophilic dimethylamine segment moves within close proximity of the carbonyl group [7]. Right after observation of such significant structural feature, they proposed a geometrical reaction coordinates on the basis of a survey on structural analyses of compounds containing nucleophilic and electrophilic centers which showed a trend for mapping the reaction coordinates through a minimum energy pathway, the so called Bürgi-Dunitz trajectory [8]. Since the proposing such interactions, most of the studies were focused on biomolecules and organic compounds. The first systematic CSD and computational studies of carbonyl…carbonyl interactions in organic compounds and first-row transition metal complexes were reported by Allen, Raithby and co-workers in 1998 and 2006, respectively [9]. In 2011 and 2012, Zukerman-Schpector et al., highlighted the importance of the intermolecular metal-carbonyl…π(aryl) interactions as a supramolecular synthon for the stabilization of transition metal carbonyl crystal structures [10]. Notably, its role in the construction of supramolecular assembly in metal complexes especially with M—CO…π*(aryl), M—CO…π*(C≡O) interactions, and peripheral
Proposed systems to study:
Scheme 1. Proposed Re(CO)3 complexes bearing mixed N- and O-donor ligands.

carbonyl…π*(C≡O), was unnoticed until the first papers by Echeverría [11]. On the other hand, Mooibroek et al., also studied the potential of coordinated nitrate anions, acetonitrile, and carbonyl ligands as π-hole donor for n → π* in their crystal structures thorough analysis of the CSD. It has been emphasised that intramolecular M—CO…π* interactions are prevalent in their structures and stabilize precise internal molecular conformations through maximizing the overlap between the donor and acceptor π*-orbitals involved in such interaction which is also very important in catalysis. It can also provide a measure of consolidation to their crystal structures and lead to supramolecular architectures in spite of their inherently weak nature. To this effects, the study of metal carbonyls complexes on the basis of participation in an n → π* interaction similarly to their organic counterparts and their roles in catalysis are of much interest. Similar to coordinated carbonyl ligand, it has been proven by Boyarskiy and Kukushkin [4-5] that the isocyanide (R−N≡C) or acetonitrile (CH3−C≡N) ligands, could be π-hole donor through coordination to a metal center. Therefore, it has been much interest recently on the structural and computational studies of non-covalent interactions in different axially coordinated ligands in Re(CO)3-core metal complexes. To this effects, the study of metal complexes bearing coordinated ligands providing π-hole is of great interest on the basis of participation in intra- and inter-molecular interactions such as n→π* and π→π*. Therefore, in continuation of our interest in intra- and intermolecular n→π* interactions in metal complexes [12-16], herein, we propose synthesis, full structural and computational studies of new Re(CO)3 complexes bearing mixed nitrogen and oxygen donor ligands along with the coordinated halogen and other axially coordinated ligands such as trifluoroacetate and trifluoromethanesulfonate (Scheme 1). The project is a planned and coordinated collaborative research work that is performed by the international team of experienced scientists. The implementation of this joint project will allow broadening the research scope of the collaboration and will give a chance to prepare furthermore ambitious projects with larger funding.
[1] J. M. Lehn, Supramolecular Chemistry: Concepts and Perspectives; Wiely VCH, Weinheim, 1st edn, 1995. [2] T. J. Mooibroek, CrystEngComm, 2017, 19, 4485-4488. [3] A. van der Werve, Y. R. van Dijk & T. J. Mooibroek, Chem. Commun., 2018, 54, 10742-10745. [4] S. A. Katkova, A. S. Mikherdov, M. A. Kinzhalov, A. S. Novikov, A. A. Zolotarev, V. P. Boyarskiy, V. Yu. Kukushkin, Chemistry – A European Journal 25 (36), 8590-8598. [5] A. S. Mikherdov, M. A. Kinzhalov, A. S. Novikov, V. P. Boyarskiy, I. A. Boyarskaya, Inorganic Chemistry 57 (11), 6722–6733. [6] M. T. Doppert, H. van Overeem, T. J. Mooibroek, Chem. Commun., 2018, 54, 12049–12052. [7] H. B. Bürgi, J. D. Dunitz & E. Shefter, Nature New Bio. 1973, 95, 5065-5067. [8] H. B. Bürgi, J. D. Dunitz, J. M. Lehn & G. Wipff, Tetrahedron, 1973, 30, 1563-1572. [9] H. A. Sparkes, P. R. Raithby, E. Clot, G. P. Shields, J. A. Chisholm & F. H. Allen, CrystEngComm, 2006, 8, 563-570. [10] (a) J. Zukerman-Schpector, I. Haiduc & E. R. T. Tiekink, Chem. Commun., 2011, 47, 12682–12684; (b) J. Zukerman-Schpector, I. Haidu & E. R. T. Tiekink, Adv. Organomet. Chem., 2012, 60, 49–92. [11] J. Echeverría, Chem. Comm. 2018, 54 (24), 3061–3064. [12] R. Kia, M. Hosseini, A. Abdolrahimi & M. Mahmoudi, CrystEngComm, 2019, 21, 5222-5226. [13] R. Kia, S. Mahmoudi & P. R. Raithby, CrystEngComm, 2019, 21, 77–93. [14] R. Kia & A. Kalaghchi, Acta Cryst., 2020, B76, 417-426. [15] R. Kia & A. Kalaghchi, Crystals, 2020, 10(4), 267-279. [16] R. Kia, H. Shojaei, V. P. Boyarskeiy & A. S. Mikherdov, CrysEngComm, 2023, 25, 1803-1816.