Probing solvents effects on the absorption spectrum of oxo-centered carbonyl-triruthenium clusters Natália Marcomini Perez a , Gabrielle Yumi Higashijima a , Vania Martins Ramos b , Ana Paula de Lima Batista a,⇑,1 , Sofia Nikolaou a,⇑,2 a Departamento de Química, Laboratório de Atividade Biológica e Química Supramolecular de Compostos de Coordenação (LABiQSC 2 ), Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14040-901 RibeirãoPreto-SP, Brazil b Departamento de Química, Laboratório Computacional de Espectroscopia e Cinética, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14040-901 Ribeirão Preto-SP, Brazil article info Article history: Received 9 October 2020 Accepted 25 November 2020 Available online 1 December 2020 Keywords: Solvatochromism Multiparametric analysis Ruthenium complexes charge transfer bands Density functional theory Natural transition orbitals abstract In this work, we describe a combined experimental and theoretical study focused on the solvatochromic effects of eight different solvents on the UV absorption spectrum of three distinct oxo-centered carbonyl- triruthenium clusters of general formula [Ru 3 O(CH 3 COO) 6 (CO)(L) 2 ], where L= (1) 2,6-dimethylpyrazine (dmpz), (2) pyridine (py), and (3) 4-aminopyridine (ampy). Due to the nature of the ancillary ligands, the charge transfer (CT) absorption band of each complex have a different shift as the solvent polarity/ polarizability increases. These shifts have been rationalized using a combined Density Functional/ Time-Dependent Density Functional theory and two popular solvatochromic scales: the Catalán and the Kamlet–Taft models. According to the Kamlet–Taft method, the ability of the solvent to donate a pro- ton in a solvent–solute hydrogen bond is more essential on describing the solvatochromic properties of 3 than 1, being also more relevant than solvent polarity. The employed solvatochromic scales also corrob- orate the preferential solvation behavior of these complexes. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction Oxo-carboxylate-bridged polynuclear metal complexes are known as essential structures for chemical, biological and thera- peutic purposes [1–8]. For instance, oxo-centered triruthenium complexes of the type [Ru 3 O(CH 3 COO) 6 (L) 3 ] n , where L is a solvent molecule or a N-heterocyclic ligand, have been explored as cata- lysts [9], electroactive systems [10,11], drug candidates [12–14], monomeric motifs to build supramolecular systems [15], among others. Since the discovery that carbon monoxide is a biological signal- ing species which participates in various regulatory and patho- genic physiological processes [16–20], there is a growing interest in a class of molecules called photoCORMs, the photo CO releasing molecules [21,22]. The carbonyl-triruthenium oxo clusters [Ru 3 O (CH 3 COO) 6 (L) 2 (CO)] 0 (L¼ N-heterocyclic ligands) match this definition because they can deliver carbon monoxide by light irra- diation [23–25]. Their electronic structure, which has as main characteristic the valence localization, is usually modulated by varying the ancillary L ligands [23–30]. Of particular interest to this work is the fact that the electronic structure of metal carbonyl complexes, in general, are also susceptible to their solvent medium [31–34]. Solvatochromic shifts observed in electronic absorption spectra usually help to unveil the nature of coordination compounds tran- sitions, since charge transfer bands are typically very sensitive to solvent variation, while ligand-field and intra-ligand (IL) bands are less [35–37]. This dependence is useful to tailor the photo- chemical and photophysical properties of molecular systems [38,39]. While the oxo-centered carbonyl-triruthenium clusters elec- tronic properties concerning different ligands have been described so far [23,26,40], a more detailed study exploring the solvent influ- ences is still lacking. In this context, through a combined experi- mental and theoretical study, the present work investigates three [Ru 3 O(CH 3 COO) 6 (L) 2 (CO)] 0 clusters, with L = (1) 2,6 – dimethylpyr- azine (dmpz), (2) pyridine (py), and (3) 4-aminopyridine (ampy) Fig. 1. These three compounds were specifically chosen because these N-heterocyclic ligands have different natures and structures, which influence the electronic characteristics and chemical behav- https://doi.org/10.1016/j.poly.2020.114944 0277-5387/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: aplima@iq.usp.br (A.P. de Lima Batista), sofia@ffclrp.usp.br (S. Nikolaou). 1 ORCID 0000-0003-2444-6069. 2 ORCID 0000-0002-9675-6106. Polyhedron 194 (2021) 114944 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly