Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica Research paper Trapping Ag(I) ions by a Pd8 metallacrown molecule to form an unusual nonanuclear AgPd8 cation ☆ Fernando B. Calleja a , Miguel Cortijo a , Josefna Perles b , Santiago Herrero a, ⁎ , Reyes Jiménez-Aparicio a, ⁎ a Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain b Laboratorio de Difracción de Rayos X de Monocristal, Servicio Interdepartamental de Investigación (SiDI), Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain ARTICLEINFO Keywords: Metallacrown Macrocyclic efect Palladium clusters ABSTRACT The {[Pd(µ-SC 6 F 5 )(µ-dppm)Pd](µ-SC 6 F 5 )} 4 (dppm = methanediylbis(diphenylphosphane)) (Pd8) metallacrown traps Ag(I) cations giving {Ag[Pd(µ 3 -SC 6 F 5 )(µ-dppm)Pd] 4 (µ-SC 6 F 5 ) 4 }(X) (X = SO 3 CF 3 − (AgPd8a), SbF 6 − (AgPd8b) and ClO 4 − (AgPd8c)) and {Ag[Pd(µ 3 -SC 6 F 5 )(µ-dppm)Pd] 4 (µ-SC 6 F 5 ) 4 } 2 [Pt(C 6 F 5 ) 4 ](AgPd8d). The insertion of silver increases signifcantly the stability of the cluster that is stable in solution even in the presence of light, because of the macrocyclic efect. 1. Introduction Metallacrowns (MCs) have attracted much attention since 1989 when Lah and Pecoraro [1] reported the structure of {Mn II [Mn III (salicylhydroximate) 4 ](acetate) 2 (DMF) 6 }·2DMF. These cyclic complexes have been considered as inorganic analogues of or- ganic crown ethers because of their ability to bind metals in their central pockets [2–4]. Unless there is a signifcant steric strain, MCs can trap metal ions increasing the stability of the system by reducing the electron repulsion between the donor atoms in the central cavity. MCs display aesthetically fascinating structures and ofer a great potential in many diferent areas. Their structures are very useful in the design of single-molecule magnets having 3d and 4f ions in a predictable geo- metry [5–8]. Numerous studies of reactions catalyzed by MCs [9–11] have been carried out inspired by the role that many multinuclear 3d complexes have in biological processes. Moreover, several lanthanide- encapsulated MCs have shown remarkable luminescent properties [12–15]. MCs have also been employed to build two- and three-di- mensional structures [16–18], as recognition agents [3,4,19–22] or even in CO 2 capture by [CrF(O 2 C t Bu) 2 ] 8 [23]. Some years ago the synthesis, crystal structure and reactivity of the Pd8 MC were reported by Usón’s group [24-26]. The structure of this octanuclear compound can be described as four metal–metal bonded Pd I (µ-SC 6 F 5 )(µ-dppm)Pd I fragments bridged by four SC 6 F 5 − ligands. Pd8 is stable in solid state but it decomposes when dissolved. However, fast reactions with neutral ligands such as tertiary phosphines and CO were investigated obtaining dinuclear complexes in which the Pd I (μ- SC 6 F 5 )(μ-dppm)Pd I fragment was kept [25]. Interestingly, ab initio calculations showed that Pd–Pd bond in these complexes arises mainly from the interactions of palladium sp orbitals, contrary to the pre- viously accepted d–d formulation [25]. In another related work, Pd8 was employed as starting material to prepare [Ag 2 Pd 2 (SC 6 F 5 ) 2 (SO 3 CF 3 ) (dppm) 3 ](SO 3 CF 3 )·CH 2 Cl 2 that contains Pd I (μ-SC 6 F 5 )(μ-dppm)Pd I frag- ments and displays Pd I -Ag I interactions [24]. The size of the central cavity and the presence of four sulphur atoms of the SC 6 F 5 − ligands defning a pseudotetrahedral hole, make Pd8 an excellent candidate to trap metal ions keeping its MC structure. Particularly, it seems very appropriate to trap Ag(I) ions since the dis- tance from the geometric centre of Pd8 to the four closest sulphur atoms is 2.596 Å, similar to the Ag(I)–S distances found in other com- pounds in which four aromatic thiolate ligands are coordinated to a silver ion [27–30]. On the other hand, only two structures have been reported containing four Au(I)–S bonds with aromatic thiolates having distances in the range of 2.340–2.357 Å [31] Similar complexes with Cu (I) also display shorter Cu(I)–S distances compared to the Ag(I)–S ones [32-35]. In principle, one can expect from the sulphur atom in SC 6 F 5 − a low tendency to bridge three metal centres due to the presence of electron withdrawing groups in the aromatic part of the ligands. However, two structures containing μ 3 -SC 6 F 5 moieties have been al- ready reported [36,37]. https://doi.org/10.1016/j.ica.2018.12.049 Received 25 October 2018; Received in revised form 11 December 2018; Accepted 31 December 2018 ☆ In memory of Miguel A. Usón and R. Usón who originally conceived this work. ⁎ Corresponding authors. E-mail addresses: sherrero@ucm.es (S. Herrero), reyesja@ucm.es (R. Jiménez-Aparicio). Inorganica Chimica Acta 488 (2019) 56–61 Available online 02 January 2019 0020-1693/ © 2019 Elsevier B.V. All rights reserved. T