molecules Article A New Synthetic Methodology in the Preparation of Bimetallic Chalcogenide Clusters via Cluster-to-Cluster Transformations Yu-Jie Zhong 1, Jian-Hong Liao 1 , Tzu-Hao Chiu 1, Yuh-Sheng Wen 2 and C. W. Liu 1,* 1 Department of Chemistry, National Dong Hwa University, Hualien 974301, Taiwan; [email protected] (Y.-J.Z.); [email protected] (J.-H.L.); [email protected] (T.-H.C.) 2 Institute of Chemistry, Academia Sinica, Taipei 11528, Taiwan; [email protected] * Correspondence: [email protected]; Tel.: +886-3-890-3607 i Abstract: A decanuclear silver chalcogenide cluster, [Ag10(Se){Se2P(O Pr)2}8](2) was isolated from a i hydride-encapsulated silver diisopropyl diselenophosphates, [Ag7(H){Se2P(O Pr)2}6], under thermal condition. The time-dependent NMR spectroscopy showed that 2 was generated at the first three hours and the hydrido silver cluster was completely consumed after thirty-six hours. This method il- lustrated as cluster-to-cluster transformations can be applied to prepare selenide-centered decanuclear i i bimetallic clusters, [CuxAg10-x(Se){Se2P(O Pr)2}8] (x = 0–7, 3), via heating [CuxAg7−x(H){Se2P(O Pr)2}6] (x = 1–6) at 60 ◦C. Compositions of 3 were accurately confirmed by the ESI mass spectrometry. While i the crystal 2 revealed two un-identical [Ag10(Se){Se2P(O Pr)2}8] structures in the asymmetric unit, a i i co-crystal of [Cu3Ag7(Se){Se2P(O Pr)2}8]0.6[Cu4Ag6(Se){Se2P(O Pr)2}8]0.4 ([3a]0.6[3b]0.4) was eventu- ally characterized by single-crystal X-ray diffraction. Even though compositions of 2,[3a]0.6[3b]0.4 1 2− Citation: Zhong, Y.-J.; Liao, J.-H.; and the previous published [Ag10(Se){Se2P(OEt)2}8]( ) are quite similar (10 metals, 1 Se , 8 ligands), Chiu, T.-H.; Wen, Y.-S.; Liu, C.W. A their metal core arrangements are completely different. These results show that different synthetic New Synthetic Methodology in the methods by using different starting reagents can affect the structure of the resulting products, leading Preparation of Bimetallic to polymorphism. Chalcogenide Clusters via Cluster-to-Cluster Transformations. Keywords: chalcogenide; hydride; silver; copper; inverse coordination Molecules 2021, 26, 5391. https:// doi.org/10.3390/molecules26175391 Academic Editor: Vladimir 1. Introduction A. Potapov In pursuit of metal chalcogenide clusters, Group 11 elements (Cu, Ag, Au) are fre- quently employed in the synthesis of novel clusters [1–4]. Silver chalcogenide clusters have Received: 10 August 2021 rich structural varieties which can be synthesized by many different approaches [5–11]. Accepted: 3 September 2021 Published: 5 September 2021 The primary strategy is the reaction of different Ag(I) precursors with highly reactive 2− 2− 2− silylated chalcogen reagents E(SiMe3)2 (E = S, Se, Te) [5], which can afford S /Se /Te Publisher’s Note: MDPI stays neutral in the construction of high-nuclearity silver chalcogenide clusters stabilized by phos- with regard to jurisdictional claims in phine, chalcogenolate, halide, carboxylate, or alkynyl ligands [6–11]. Under this guide- published maps and institutional affil- line, Fenske and his co-workers have structurally characterized many remarkable silver n t iations. chalcogenide clusters [6,7]. For example, [Ag114Se34(Se Bu)46(P Bu3)14], which contains a distorted cubic structure, was synthesized involving the reaction of C11H23CO2Ag, n t ◦ BuSeSiMe3 and P Bu3 at low temperature (<−20 C) [6]. Different diphosphine lig- ands (bis(diphenylphosphinol)propane, dppp) used in the previous reaction at −30 ◦C produce [Ag Se (SenBu) (dppp) ], which not only increases the cluster nuclearity Copyright: © 2021 by the authors. 172 40 92 4 Licensee MDPI, Basel, Switzerland. but also keeps similar cross sections of Ag2Se as that found in Ag114Se34 [6]. Another This article is an open access article mega cluster synthesized by the reaction of CF3CO2Ag, dppm, PhS(SiMe3) and S(SiMe3)2 ◦ distributed under the terms and at −40 C yielded [Ag70S20(PhS)28(dppm)10](CF3CO2)2 [7]. Compared with those gi- conditions of the Creative Commons ant silver chalcogenide clusters which are the kinetic products formed in different re- Attribution (CC BY) license (https:// action temperatures, smaller silver chalcogenide clusters encapsulated with a single 2− 2− creativecommons.org/licenses/by/ S /Se are rarely reported [12–22]. The as-synthesized chalcogenide anion can eas- 4.0/). ily insert in the metal clusters to achieve a high coordination number, i.e., µ8-Se in Molecules 2021, 26, 5391. https://doi.org/10.3390/molecules26175391 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x FOR PEER REVIEW 2 of 13 high coordination number, i.e., μ8-Se in [Ag8(Se){Se2P(OiPr)2}6] [15,16], μ9-Se in [Ag11(Se)(X)3{Se2P(OR)2}6] (X = I, Br; R = Et, iPr, 2Bu) [17,18], μ10-Se in [Ag10(Se){Se2P(OEt)2}8] [19] and μ12-S in [Cu12(S){S2CNR2}6{C≡CR’}4] [22]. These hyper-coordinated anions, which become the coordination center surrounded by an array of metal atoms, are examples of inverse coordination, an emerging concept coined by Ionel Haiduic [23,24]. Nevertheless, efficient controls on both the amount of chalcogenide generated in situ and the size of clusters remain challenging. Herein, we report a new synthetic pathway leading to the formation of M10(Se)L8 (L = diisopropyl diselenophosphate, dsep) via a cluster-to-cluster Molecules 2021, 26, 5391 transformation. In addition, intriguing structural isomers identified in the M10(Se) core2 of are 13 also presented. 2. Results and Discussion i i [Ag8(Se){Se2P(O Pr)2}6] [15,16], µ9-Se in [Ag11(Se)(X)3{Se2P(OR)2}6] (X = I, Br; R = Et, Pr, 22.1. Synthetic Strategy Bu) [17,18], µ10-Se in [Ag10(Se){Se2P(OEt)2}8][19] and µ12-S in [Cu12(S){S2CNR2}6{C≡CR’}4][22]. TheseIn hyper-coordinated our previous study, anions, a decanuclear which become silver the cluster, coordination [Ag10(Se){Se center2 surroundedP(OEt)2}]8 (1 by), was an arrayisolated of metal from atoms,the reaction are examples of [Ag(CH of inverse3CN)4]PF coordination,6 and NH4[Se an2P(OEt) emerging2] in concepta 1:1 molar coined ratio by at Ionel−20 °C Haiduic for 24 h [23 (Scheme,24]. Nevertheless, 1a) [19]. The efficient encapsul controlsated selenide on both anion the amount was generated of chalcogenide from the generatedslow decomposition in situ and theof dsep size ofligands. clusters Herein remain we challenging. introduced Herein, a new westrategy, report which a new is syn- in- spired by the thermal-induced self-redox reaction of [Ag7(H){S2P(OiPr)2}8] leading to the thetic pathway leading to the formation of M10(Se)L8 (L = diisopropyl diselenophosphate, dsep)generation via a cluster-to-clusterof a two-electron silver transformation. superatom, In[Ag addition,10{S2P(OiPr) intriguing2}8] [25]. In structural this work, isomers the Se- 7 2 i 2 8 identifiedanalogue inof the[Ag M(H){S10(Se)P(O corePr) are} also] [26] presented. as precursors under heating (Scheme 1b) can yield [Ag10(Se){Se2P(OEt)2}]8 (2). The composition of 2 (10 Ag+ + 1 Se2− + 8 dsep ligands) has been 2.characterized Results and by Discussion X-ray diffraction, which is the same as 1 but with a completely different 2.1.solid-state Synthetic structure. Strategy At 60 °C the cleavage of P-Se bond of dsep ligands occurs to generate Se, which can be reduced to Se2- by the interstitial hydride in [Ag7(H){Se2P(OiPr)2}8]. Unlike In our previous study, a decanuclear silver cluster, [Ag10(Se){Se2P(OEt)2}]8 (1), was isolatedthe reactions from theused reaction silylated of [Ag(CHchalcogen3CN) reagents4]PF6 and to generate NH4[Se2 considerableP(OEt)2] in a amount 1:1 molar of ratio chal- atcogenide−20 ◦C foranions, 24 h this (Scheme new1 methoda) [ 19]. can The control encapsulated the Se2 selenide− ratio in anion a relatively was generated small range from so thethat slow smaller decomposition size of metal of chalcoge dsep ligands.nide clusters Herein can we be introduced generated. a new strategy, which is i inspiredFollowing by the thermal-inducedthe same strategy, self-redox a diselenophosphate-stabilized reaction of [Ag7(H){S2P(O bimetallicPr)2}8] leadingCu/Ag hy- to i i i thedride, generation [CuxAg7-x of(H){Se a two-electron2P(O Pr)2}6 silver] (x = 1–6) superatom, [26] was [Ag used10{S instead2P(O Pr) of2 }[Ag8][257(H){Se]. In this2P(O work,Pr)2}8] i the(Scheme Se-analogue 1c), ofto [Ag form7(H){S 2aP(O selenide-centeredPr)2}8][26] as precursors decanuclear under heatingbimetallic (Scheme cluster,1b) i + 2− can[Cu yieldxAg10− [Agx(Se){Se10(Se){Se2P(O2Pr)P(OEt)2}8] (x2 }]= 80–7)(2). (3 The). This composition methodology of 2 provides(10 Ag a+ facile 1 Se route+ 8 to dsep pro- ligands)duce anion-encapsulated has been characterized heterometallic by X-ray cluste diffraction,rs via whicha cluster-to-cluster is the same astransformation.1 but with a completelyHowever, this different method solid-state cannot predict structure. the exac Att 60 position◦C the where cleavage the ofheterometals P-Se bond will of dsep pos- ligandssibly occupy. occurs Nevertheless, to generate Se, it whichopens canup many be reduced possibilities to Se2− toby generate the interstitial structural hydride isomers. in i [AgCompound7(H){Se2P(O 3, whichPr)2}8 the]. Unlike entirethe metal reactions core isused completely silylated different chalcogen from reagents that of to1 and generate 2, has considerablebeen structurally amount characterized of chalcogenide by XRD.