title: Iodide and triiodide anion complexes involving anion-π interactions with a tetrazine-based receptor.
abstract: Protonated forms of the tetrazine ligand L2 (3,6-bis(morpholin-4-ylethyl)-1,2,4,5-tetrazine) interact with iodide in aqueous solution forming relatively stable complexes (ΔG° = -11.6(4) kJ mol-1for HL2++ I-= (HL2)I and ΔG° = -13.4(2) kJ mol-1for H2L22++ I-= [(H2L2)I]+). When solutions of [(H2L2)I]+are left in contact with air, crystals of the oxidation product (H2L2)2(I3)3I·4H2O are formed. Unfortunately, the low solubility of I3-complexes prevents the determination of their stability constants. The crystal structures of H2L2I2·H2O (1), H2L2(I3)2·2H2O (2) and (H2L2)2(I3)3I·4H2O (3) were determined by means of X-ray diffraction analyses. In all crystal structures, it was found that the interaction between I-and I3-with H2L22+is dominated by anion interactions with the π electron density of the receptor. Only in the case of 1, the iodide anions involved in close anion-π interactions with the ligand tetrazine ring form an additional H-bond with the protonated morpholine nitrogen of an adjacent ligand molecule. Conversely, in crystals of 2 and 3 there are alternate segregated planes which contain only protonated ligands hydrogen-bonded to cocrystallized water molecules or I3-and I-forming infinite two-dimensional networks established through short interhalogen contacts, making these crystalline products good candidates to behave as solid conductors. In the solid complexes, the triiodide anion displays both end-on and side-on interaction modes with the tetrazine ring, in agreement with density functional theory calculations indicating a preference for the alignment of the I3-molecular axis with the molecular axis of the ligand. Further information about geometries and structures of triiodide anions in 2 and 3 was acquired by the analysis of their Raman spectra.
authors.affiliation: Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 3, 50019, Sesto Fiorentino, Italy. antonio.bianchi@unifi.it.
authors.forename: Matteo
authors.identifier: http://orcid.org/0000-0002-9780-7542
authors.initials: M
authors.lastname: Savastano
authors.affiliation: Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 3, 50019, Sesto Fiorentino, Italy. antonio.bianchi@unifi.it.
authors.forename: Carla
authors.identifier: http://orcid.org/0000-0003-4602-0405
authors.initials: C
authors.lastname: Bazzicalupi
authors.affiliation: Department of Inorganic and Organic Chemistry, University of Jaén 23071, Jaén, Spain. mmelgui@ujaen.es.
authors.forename: Celeste
authors.identifier: http://orcid.org/0000-0001-8455-9837
authors.initials: C
authors.lastname: García
authors.affiliation: Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 3, 50019, Sesto Fiorentino, Italy. antonio.bianchi@unifi.it.
authors.forename: Cristina
authors.identifier: http://orcid.org/0000-0002-3112-6680
authors.initials: C
authors.lastname: Gellini
authors.affiliation: Department of Inorganic and Organic Chemistry, University of Jaén 23071, Jaén, Spain. mmelgui@ujaen.es.
authors.forename: María Dolores
authors.identifier: http://orcid.org/0000-0002-4107-4474
authors.initials: MD
authors.lastname: López de la Torre
authors.affiliation: Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 3, 50019, Sesto Fiorentino, Italy. antonio.bianchi@unifi.it.
authors.forename: Palma
authors.identifier: http://orcid.org/0000-0003-4629-8933
authors.initials: P
authors.lastname: Mariani
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan. fabio@che.tohoku.ac.jp.
authors.forename: Fabio
authors.identifier: http://orcid.org/0000-0003-3165-4456
authors.initials: F
authors.lastname: Pichierri
authors.affiliation: Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 3, 50019, Sesto Fiorentino, Italy. antonio.bianchi@unifi.it.
authors.forename: Antonio
authors.identifier: http://orcid.org/0000-0002-1082-3911
authors.initials: A
authors.lastname: Bianchi
authors.affiliation: Department of Inorganic and Organic Chemistry, University of Jaén 23071, Jaén, Spain. mmelgui@ujaen.es.
authors.forename: Manuel
authors.identifier: http://orcid.org/0000-0002-2210-9547
authors.initials: M
authors.lastname: Melguizo