Lanthanide trifluoromethyltricyanoborates: Synthesis, crystal structures and thermal properties

Accepted Manuscript Title: Lanthanide trifluoromethyltricyanoborates: Synthesis, crystal structures and thermal properties Authors: Tatjana Ribbeck, Christoph Kerpen, Dominic L¨ow, Alexander E. Sedykh, Klaus Muller-Buschbaum, ¨ Nikolai V. Ignat’ev, Maik Finze PII: DOI: Reference:

S0022-1139(18)30446-9 https://doi.org/10.1016/j.jfluchem.2018.12.013 FLUOR 9275

To appear in:

FLUOR

Received date: Revised date: Accepted date:

5 November 2018 28 December 2018 29 December 2018

Please cite this article as: Ribbeck T, Kerpen C, L¨ow D, Sedykh AE, Muller¨ Buschbaum K, Ignat’ev NV, Finze M, Lanthanide trifluoromethyltricyanoborates: Synthesis, crystal structures and thermal properties, Journal of Fluorine Chemistry (2018), https://doi.org/10.1016/j.jfluchem.2018.12.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Lanthanide trifluoromethyltricyanoborates: Synthesis, crystal structures and thermal properties Tatjana Ribbecka,b, Christoph Kerpena,b, Dominic Löwa,b, Alexander E. Sedykha, Klaus Müller-Buschbauma, Nikolai V. Ignat’eva,c, Maik Finzea,b,*

für Anorganische Chemie, Institut für nachhaltige Chemie & Katalyse mit Bor

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aInstitut

(ICB), Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. Web: https://go.uniwue.de/finze-group. bInstitut

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E-mail: [email protected]

für nachhaltige Chemie & Katalyse mit Bor (ICB), Julius-Maximilians-

Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.

Merck KGaA, Frankfurter Straße 250, 64293, Darmstadt, Germany.

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cConsultant,

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Dedicated to Professor Erhard Kemnitz in recognition of the ACS Award on Creative

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Work in Fluorine Chemistry 2018.

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Graphical Abstract

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Highlights 

Synthesis of Brønsted acids with the perfluorinated cyanoborate anions [RFB(CN)3] (RF = CF3, C2F5) and metatheses with rare earth metal chlorides LnCl3 (Ln = La, Eu, Gd, Ho, Er).



Spectroscopic and structural characterization of rare earth metal cyanoborates of the type Ln[RFB(CN)3]3∙mH2O.



Investigation of thermal properties of the aforementioned coordination compounds. 1

Abstract Five lanthanide trifluoromethyltricyanoborates [La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a), [Ln{CF3B(CN)3}3(H2O)4] (Ln = Eu (3a), Gd (4a)), [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O (5a), and [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.34H2O (6a) have been synthesized in aqueous solution starting from LnCl3·nH2O and (H3O)[CF3B(CN)3] and characterized by single-crystal X-ray diffraction. The

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coordination number of the Ln3+ ions and the number of cyanoborate anions as well as

the number of water molecules coordinated depend on the size of the Ln3+ ion. All

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attempts to completely remove the water from 2a–6a resulted in decomposition. Surprisingly, the respective pentafluoroethyltricyanoborates are accessible as anhydrous compounds, for example [Gd{C2F5B(CN)3}3] (4b) that has been obtained

from GdCl3 and (H3O)[C2F5B(CN)3] in water. In addition, the syntheses of the starting

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compounds (H3O)[RFB(CN)3] (RF = CF3, C2F5) and the crystal structure of

perfluoroalkylborates;

Introduction

lanthanides;

coordination

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compounds

1.

cyanoborates;

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Keywords:

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(H3O)[CF3B(CN)3] are presented.

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Cyanoborate anions are widely used building blocks, for example for the design of low-viscosity room temperature ionic liquids (RTILs) with large electrochemical

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windows, as counterions for metal salts, and as ligands in coordination chemistry [1, 2]. Especially, salts of the tetracyanoborate anion [B(CN)4]– [3, 4] have been studied [1, 5-15] and some have been commercialized [2]. In addition to the homoleptic cyanoborate anion [B(CN)4]–, cyanoborate anions with substituents other than CN have

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been developed, which include the mixed substituted anions [BFn(CN)4–n]– (n = 1–3) [5, 16, 17], [BCln(CN)4–n]– (n = 1–3) [18], [BHn(CN)4–n]– (n = 1–3) [19-26], and [RFBFn(CN)3–n]– (RF = perfluoroalkyl [27], perfluoroaryl; n = 0–2 [25, 28]). These anions often result in similar interesting, sometimes even improved properties compared to the [B(CN)4]– anion. In recent years, studies on rare earth metal salts, complexes, and coordination polymers with cyanoborate anions have been published and interesting luminescence 2

properties have been reported [12, 15, 29-31]. In these coordination compounds, the cyanoborate

anion

either

acts

as

non-coordinating

counteranion,

e.g.

in

[Ln(H2O)8][B(CN)4]3∙nH2O (Ln = Tb, Dy, Tm, Lu, Y) [12], as terminal ligand, e.g. in [La(EtOH)3(H2O)2{B(CN)4}3]

[32],

or

as

bridging

ligand,

for

example

in

[Ln2{BH2(CN)2}9]·[Ln(CH3CN)9] (Ln = Ce, Eu, Tb) [31]. Best studied are mixed aquacyanoborate complexes of rare earth metal ions. These complexes were found to lose water at elevated temperatures and under reduced pressure. Surprisingly, even the

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anhydrous metal salts are accessible and the cyanoborate anions are stable against

the strongly Lewis-acidic Ln3+ ions. Noteworthy are the lanthanide coordination

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polymers [Ln{C2F5B(CN)3}3] (Ln = La, Eu, Ho), especially when taking the high fluoride

ion affinity of the Ln3+ ions into account that is the basis for Ln-mediated Caliphatic–F bond activation [33-35]. The borates [Ln{C2F5B(CN)3}3] (Ln = La, Eu, Ho) were synthesized from (H3O)[C2F5B(CN)3] and LnCl3·nH2O (n = 0, 6) in water followed by

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drying in vacuum [30]. Single crystals of [La{C2F5B(CN)3}3] were obtained by

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crystallization from the room temperature ionic liquid [EMIm][C2F5B(CN)3] (EMIm = 1ethyl-3-methylimidazolium) or via a ionothermal approach using the RTIL

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[EMIm][C2F5B(CN)3] as solvent and reagent [30].

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It is well documented in the literature that pentafluoroethyl groups bonded to boron are much more resistant with respect to fluoride ion abstraction than trifluoromethyl

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groups [36-40]. The reason for the comparably low thermal and chemical stability of B–CF3 units is the intermediate formation of difluorocarbene complexes followed by

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the irreversible loss of the CF2 ligand [36, 37, 41, 42]. This relatively low stability of the CF3 group is not limited to boron but well documented for E–CF3 compounds with E = Si [43-46], Sn [45, 47-51], Ge [49, 52, 53], Cd [54-56], and P [57, 58], as well. The

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related E–C2F5 molecules, e.g. with E = P [59] or group 14 elements [43, 59-67], reveal significantly higher thermal and chemical stabilities. Here, we report on first trifluoromethyltricyanoborate coordination polymers

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[La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a) and [Ln{CF3B(CN)3}3(H2O)4] (Ln = Eu (3a), Gd (4a)), as well as complex salts [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O (5a) and [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.34H2O (6a). All attempts to fully remove the water from 2a–6a resulted in decomposition, which is in contrast to the aforementioned pentafluoroethyl derivatives [Ln{C2F5B(CN)3}3] (Ln = La, Eu, Ho) [30] and to [Gd{C2F5B(CN)3}3] (4b), which is described in this contribution, for the first time.

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Furthermore, the syntheses of (H3O)[RFB(CN)3] (RF = CF3 (1a), C2F5 (1b)) and the crystal structure of (H3O)[CF3B(CN)3] (1) is discussed. 2.

Results and discussion

2.1.

Synthesis, thermal properties, and crystal structure of (H3O)[CF3B(CN)3] (1a)

The oxonium acids (H3O)[CF3B(CN)3] (1a) and (H3O)[C2F5B(CN)3] (1b) were obtained by extraction from solutions of the potassium salt of the respective

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perfluoroalkyltricyanoborate anion in hydrochloric acid using diethyl ether as shown in

Scheme 1. The syntheses are similar to the preparation of the related oxonium acids

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(H3O)[RB(CN)3] (R = H, F, CN) [68].

Both oxonium acids are solids at room temperature. The acid 1a was studied in

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more detail. It crystallizes in the hexagonal space group P63mc. Figure 1 shows a

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section of the two-dimensional layer that is a result of the N∙∙∙H–O hydrogen bonds. Each H3O+ cation forms hydrogen bonds to three [CF3B(CN)3] anions and vice versa

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to result in six-membered rings with chair conformation that are connected to result in

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a sheet structure. Similar structural motifs were found for (H3O)[BH(CN)3] [68] and (H3O)[B(CN)4] [10]. The F atoms of the CF3 group are not involved in any H bonding.

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The interatomic distances and angles given in Figure 1 are close to values reported for other oxonium acids of cyanoborate anions [10, 68]. The bond parameters of the

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[CF3B(CN)3]– anion are similar to those of K[CF3B(CN)3] [27].

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The oxonium acid 1a is stable up to 160 °C (DTA/TG, Figure 2). The related acids

(H3O)[B(CN)4], (H3O)[BF(CN)3], and (H3O)[BH(CN)3] possess lower thermal stabilities, up to 145, 125, and 110 °C, respectively [10, 68]. The thermal stability of 1a is

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unprecedented since trifluoromethyl borates are known to undergo decomposition via elimination of difluorocarbene CF2, in particular in presence of strong Lewis or Brønsted acids [36, 37, 41, 42]. Accordingly, the attempted synthesis of (H3O)[B(CF3)4] failed, and either the borane carbonyl (CF3)3BCO was formed [69], or the anion was fully disrupted [36, 37].

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2.2.

Syntheses, thermal properties, and crystal structures of

[La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a), [Ln{CF3B(CN)3}3(H2O)4] (Ln = Eu (3a), Gd (4a)), [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O (5a), [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.34H2O (6a), and [Gd{C2F5B(CN)3}3] (4b) 2.2.1. Syntheses The lanthanide cyanoborates 2a–6a were synthesized via metathesis starting from

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the Brønsted acid (H3O)[CF3B(CN)3] (1a) and the respective lanthanide chloride

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LnCl3∙nH2O (Ln = La, Gd, Ho, Er, n = 0; Ln = Eu, n = 6) as depicted in Scheme 2.

After removal of all volatiles and drying under reduced pressure, the salts [Ln{CF3B(CN)3}3]·nH2O were obtained with different water contents and in yields of 79–97%. Recrystallization from water afforded single crystals of mixed aqua-

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cyanoborate complexes 2a–6a, which have been studied by X-ray diffraction.

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The presence of water in the coordination compounds [Ln{CF3B(CN)3}3]·nH2O (n

A

= 6 (La and Eu), 4 (Gd), 5 (Ho), 7 (Er)) is evident from the results of the elemental analyses and IR spectra (Figures S1–S5 in the Supporting Information). The IR spectra

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show a sharp band for the (C≡N) stretching mode at 2267 cm1. The (OH) stretching modes of the water molecules are found in the range from 33233368 cm1.

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Furthermore, a broad band is recorded in the range of 2542–2561 cm1, which is assigned to O–H∙∙∙O hydrogen bonds [70].

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The reaction of GdCl3 with (H3O)[C2F5B(CN)3] (1b) gave [Gd{C2F5B(CN)3}3] with approximately two equivalents of water after brief drying in a vacuum, as evident from

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the elemental analysis and the IR spectrum depicted in Figure S6 in the Supporting Information. Unprecedentedly, recrystallization from water afforded [Gd{C2F5B(CN)3}3] (4b) as the anhydrous coordination compound (Scheme 3). Recently, we have reported on the related reactions of 1b with LnCl3 (Ln = La, Eu, Ho) that yielded

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anhydrous [La{C2F5B(CN)3}3] but [Ln{C2F5B(CN)3}3(H2O)2] (Ln = Eu, Ho) [30].

2.2.2. Single crystal X-ray diffraction [La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a) crystallizes in the monoclinic space group P21/n with Z = 4. The coordination environment of the lanthanum cation in the crystal 5

structure is depicted in Figure 3. The La3+ cation has a coordination number of nine with five anions and four molecules of water surrounding it. In the second coordination sphere, another molecule of water is located that has an occupation of only 0.28. One of the three crystallographically independent cyanoborate anions is coordinated exclusively to a single La3+ cation, whereas the other two anions interconnect two cations to form one-dimensional strands. These strands are connected via hydrogen

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bonds to give a supramolecular three-dimensional network.

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[Eu{CF3B(CN)3}3(H2O)4] (3a) and [Gd{CF3B(CN)3}3(H2O)4] (4a) are isostructural and crystallize in the orthorhombic space group Pnma with Z = 4. Similar to the crystal structure of 2a, the Eu3+ and Gd3+ ions in 3a and 4a have a coordination number of

nine with five anions and four water molecules bonded to the metal centers. Two of the

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three crystallographically independent [CF3B(CN)3] anions bridge two Ln3+ ions. The

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cyano groups of these two cyanoborate anions are not disordered whereas the CF 3 group and the third, non-coordinated CN group reveal disorder over two positions. The

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third [CF3B(CN)3] anion is bonded to a single Ln3+ ion via one CN group, only. This

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anion shows symmetry generated disorder over two positions with the exception of the nitrogen atom coordinated to the Ln3+ cation that is not disordered. In contrast to the

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structure of 2a, the bridging cyanoborate anions result in sheets, which are interconnected via hydrogen bonds to a three-dimensional network.

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Figure 3 shows the coordination polyhedron of the respective Ln3+ cation in the structures of 2a, 3a, and 4a that is a tricapped trigonal prism in all cases.

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[Ho{CF3B(CN)3}3(H2O)7]∙1.23H2O (5a) and [Er{CF3B(CN)3}3(H2O)7]∙1.34H2O (6a) both crystallize in the triclinic space group P¯ 1 ¯ with Z = 2 and similar cell dimensions. One of the three crystallographically independent [CF3B(CN)3]– ions is disordered over two positions in 5a and 6a. In addition, a second cyanoborate ion in 6a reveals partial

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disorder. The square antiprismatic coordination spheres of Ho3+ and Er3+ have only eight ligands that are composed of one cyanoborate ion and seven aqua ligands (Figure 4). Both remaining anions are coordinated via N∙∙∙H–O hydrogen bonds and are part of the second coordination sphere, only. In addition, the second coordination sphere contains disordered water molecules with partial occupation.

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[Gd{C2F5B(CN)3}3] forms a three-dimensional coordination polymer. It crystallizes in the hexagonal space group P63/m with Z = 2. Recently, we have reported the analogous coordination compound [La{C2F5B(CN)3}3] that crystallizes in the same space group [30]. Every cyanoborate ion interconnects three Gd3+ ions. Hence, the cations have the coordination number nine and the coordination polyhedron is a

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tricapped trigonal prism (Figure 5).

A comparison of the crystal structures of the [CF3B(CN)3]– containing coordination

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compounds 2a–6a shows that the coordination number and the number of aqua ligands depends on the ionic radius of the rare earth metal cation. The larger cations La3+, Eu3+, and Gd3+ have a coordination number of nine with five anions and four water

molecules in their coordination sphere, whereas the smaller cations Ho3+ and Er3+ have

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eight ligands, only, that are a single cyanoborate anion and seven aqua ligands. The

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preference of water with its O donor atom over the [CF3B(CN)3]– anion with its N donor atoms may reflect the increasing charge density of the smaller Ln3+ ions and, thus, an

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increased hardness according to the hard and soft acids and bases (HSAB) principle

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[71].

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As expected, comparison of the Ln3+∙∙∙N and Ln3+∙∙∙O distances of all coordination compounds reveals a trend of decreasing distances with decreasing ionic radius of the

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metal cation (Table 1). So, the lanthanum complex shows the largest and the erbium complex the smallest distances. This is in good accordance with other lanthanide cyanoborate complexes and in agreement to the different coordination numbers of the

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smaller rare earth metal cations [30]. The bond parameters of the cyanoborate anions [CF3B(CN)3]– and [C2F5B(CN)3]–

found in the coordination polymers and complexes 2a–6a and 4b, respectively, are

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similar and close to values reported for related salts and coordination compounds that have been described, earlier [27, 30].

2.2.3. Differential thermoanalysis (DTA) and thermogravimetry (TG) study on [Ln{CF3B(CN)3}3]·nH2O (n = 6 (La and Eu), 4 (Gd), 5 (Ho), 7 (Er))

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All five lanthanide coordination compounds with the [CF3B(CN)3]– anion that have been obtained after removal of the water under reduced pressure were analyzed by simultaneous differential thermoanalysis (DTA) and thermogravimetry (TG) in the range from 25 to 800 °C with a heating rate of 2 °C min–1 and under a gas flow of argon and nitrogen (20 mL min–1, each). The DTA curves of the coordination compounds [Ln{CF3B(CN)3}3]·nH2O (n = 6 (La and Eu), 4 (Gd), 5 (Ho), 7 (Er)) reveal two endothermic events at approximately 90–100 °C (Table 2) as exemplified by the DTA

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curve of [La{CF3B(CN)3}3]·6H2O (Figure 6). These events are accompanied by a mass

loss of 3–5%, which corresponds to release of 1–2 equivalents of water. The DTA and

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TG curves of [Ln{CF3B(CN)3}3]·nH2O (6 (Eu), 4 (Gd), 5 (Ho), 7 (Er)) are presented in

the Supporting Information (Figures S9–S12). At 160–170 °C a multi-step exothermic decomposition starts and at 800 °C circa 80% of the initial mass has been lost. It is thereby eminent, that the mass steps and signals in the heat flow subsequent to the

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release of water are corroborating with the signals observed for the acid 1a.

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Exothermic decomposition of [Ln{C2F5B(CN)3}3] was reported to start at 340 °C [30]. Hence, the related [CF3B(CN)3]– complexes are much less stable than their

Conclusions

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3.

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[C2F5B(CN)3]– counterparts.

First lanthanide trifluoromethyltricyanoborates were synthesized from the oxonium

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acid (H3O)[CF3B(CN)3] (1a) and the respective lanthanide trichloride in aqueous solution and structurally characterized. The coordination behavior of the metal ions in [La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a), [Ln{CF3B(CN)3}3(H2O)4] (Ln = Eu (3a), Gd (4a)), (5a),

[Er{CF3B(CN)3}(H2O)7]-

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[Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O

[CF3B(CN)3]2∙1.34H2O (6a), and [Gd{C2F5B(CN)3}3] (4b) depends on the size of the Ln3+ ion. In contrast to the aqua complexes 2a–6a, [Gd{C2F5B(CN)3}3] (4b) crystallizes as neat, anhydrous salt from water. The lanthanide trifluoromethyltricyanoborates are thermally less robust than the related lanthanide pentafluoroethyltricyanoborates [30], which is explained by the lower stability of B–CF3 compared to B–C2F5 derivatives, in general [36-42]. The lower

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stability of [Ln{CF3B(CN)3}3]·nH2O compared to [Ln{C2F5B(CN)3}3] is also reflected by the unsuccessful attempts to remove all water from [Ln{CF3B(CN)3}3]·nH2O, which resulted in decomposition as assessed by DTA/TG investigations. 4.

Experimental part

4.1. Materials and methods

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All standard chemicals were purchased from commercial sources. K[CF3B(CN)3] and K[C2F5B(CN)3] were synthesized according to literature procedures [27, 72] starting from K[CF3BF3] and K[C2F5BF3] [40, 73]. spectrometer operating at 1H: 400.1 MHz,

11B:

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NMR spectra were recorded at 25 °C in DMSO-d6 on a Bruker DPX 400 128.4 MHz,

19F:

376.5 MHz, and

13C:

125.8 MHz with deuterium lock. The NMR signals were referenced against TMS (1H and

13C),

BF3·OEt2 in CDCl3 with (11B) = 32.083974 MHz and CFCl3 with (19F) =

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94.094011 MHz as external standards [74]. 1H and 13C chemical shifts were calibrated

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against the residual proton signal or solvent signal, respectively, of DMSO-d6 at (1H)

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= 2.50 ppm and (13C) = 39.52 ppm [75]. IR spectra of the bulk compounds were recorded on a Bruker Alpha spectrometer equipped with an attenuated total reflection

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(ATR) module using a diamond-crystal with a resolution of 4 cm1 in the range of

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4000400 cm1 and scan rates of 1024. Elemental analyses (C, H, N) were performed with an ELEMENTAR Vario Micro Cube. Thermal properties were investigated by simultaneous DTA/TG using a NETZSCH STA-409. The samples (25–35 mg) of 1a

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and [Ln{CF3B(CN)3}3]·nH2O (6 (La and Eu), 4 (Gd), 5 (Ho), 7 (Er)) were investigated in an argon (Linde 5.0) / nitrogen (Linde 5.0) mixture with a gas flow of 40 mL min–1 and

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heated with a constant rate of 2 °C min–1 to a maximum temperature of 850 °C. 4.2.

Syntheses

4.2.1. Synthesis of (H3O)[CF3B(CN)3] (1a)

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K[CF3B(CN)3] (2.00 g, 10.1 mmol) was dissolved in aqueous HCl (10% v/v, 50 mL)

and stirred for 30 min at room temperature. The reaction mixture was extracted with diethyl ether (3 × 30 mL), the combined organic layers were dried with Na 2SO4, and the solvent was removed under reduced pressure. The remaining solid was dried in a vacuum. Yield: 94% (1.67 g, 9.4 mmol). 1H NMR (400.1 MHz, DMSO-d6):  4.21 (br, 3H, H3O). 11B NMR (128.4 MHz, DMSO-d6):  –32.1 (q, 2JF,B = 36.1 Hz, 1B). 19F NMR (376.5 MHz, DMSO-d6):  –64.7 (q, 2JF,B = 36.0 Hz, 3F).

13C{1H}

NMR (125.8 MHz, 9

DMSO-d6): 128.5 (q, coupling not resolved, 1C, CF3), 122.3 (q, 1JC,B = 66.2 Hz, 3C, CN). IR: 2540 (vbr, (OH)), 2268 cm1 ((C≡N)) (further broad bands are present in the range of 1900–1500 cm–1 that can be assigned to the H3O+ ion [76]). Elem. anal. calcd. for C4H3BNF3O: C, 27.16; H, 1.71; N, 23.76. Found: C, 27.17; H, 1.63; N, 24.05. Single crystals of (H3O)[CF3B(CN)3] (1a) were obtained from an aqueous solution. 4.2.2. Synthesis of (H3O)[C2F5B(CN)3] (1b)

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K[C2F5B(CN)3] (2.47 g, 10.0 mmol) was dissolved in aqueous HCl (10% v/v, 50 mL) and stirred for 30 min at room temperature. The reaction mixture was extracted

with diethyl ether (4 × 30 mL), the combined organic layers were dried with Na 2SO4,

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and the solvent was removed under reduced pressure. The remaining solid was dried

in a vacuum. Yield: 84% (1.91 g, 8.4 mmol). 1H NMR (400.1 MHz, DMSO-d6):  7.58 (br, 3H, H3O).

11B

NMR (128.4 MHz, DMSO-d6):  –31.9 (t, 2JF,B = 25.1 Hz, 1B).

19F

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NMR (376.5 MHz, DMSO-d6):  –81.0 (br s, 3F, CF3), –122.8 (s, 2JF,B = 25.0 Hz, 2F, CF2). IR: 2540 (vbr, (OH)), 2264 cm1 ((C≡N)) (further broad bands are present in

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the range of 1900–1500 cm–1 that can be assigned to the H3O+ ion [76]).

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[La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a)

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4.2.2. Preparation of [La{CF3B(CN)3}3]·6H2O and crystals of

(H3O)[CF3B(CN)3] (1a, 400 mg, 2.26 mmol) and LaCl3 (185 mg, 0.75 mmol) were

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dissolved in deionized water (15 mL) and stirred for two hours at room temperature. The solvent was removed under reduced pressure and the product was dried in a vacuum. Yield (according to the composition of the EA result): 86% (460 mg, 0.65 11B

NMR (128.4 MHz, DMSO-d6):  –32.1 (q, 2JF,B = 36.0 Hz, 3B).

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mmol).

(376.5 MHz, DMSO-d6):  –64.7 (q, 2JF,B = 36.0 Hz, 9F).

13C{1H}

19F

NMR

NMR (125.8 MHz,

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DMSO-d6):  128.8 (q, coupling not resolved, 3C, CF3), 122.8 (q, 1JC,B = 68.8 Hz, 9C, CN). IR: 3421 ((OH)), 2542 ((O∙∙∙H∙∙∙O)), 2267cm1 ((C≡N)). Elem. anal. calcd. for C12H12B3F9LaN9O6 (The water content of six molecules per formula unit was assessed

A

from the experimental EA data.): C, 20.00; H, 1.68; N, 17.49. Found: C, 19.17; H, 1.70; N,

18.02.

Recrystallization

from

water

resulted

in

single

crystals

of

[La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a). 4.2.3. Preparation of [Eu{CF3B(CN)3}3]·6H2O and crystals of [Eu{CF3B(CN)3}3(H2O)4] (3a) (H3O)[CF3B(CN)3] (1a, 400 mg, 2.26 mmol) and EuCl3∙6H2O (271 mg, 0.74 mmol) were dissolved in deionized water (15 mL) and stirred for two hours at room 10

temperature. The solvent was removed under reduced pressure and the product was dried in a vacuum. Yield (according to the composition of the EA result): 87% (479 mg, 0.65 mmol).

11B

NMR (128.4 MHz, DMSO-d6):  –32.0 (q, 2JF,B = 36.1 Hz, 3B).

NMR (376.5 MHz, DMSO-d6):  –64.7 (q, 2JF,B = 36.0 Hz, 9F).

13C{1H}

19F

NMR (125.8

MHz, DMSO-d6):  128.8 (q, coupling not resolved, 3C, CF3), 122.7 (q, 1JC,B = 69.8 Hz, 9C, CN). IR: 3323 ((OH)), 2561 ((O∙∙∙H∙∙∙O)), 2267 cm1 ((C≡N)). Elem. anal. calcd.

IP T

for C12H12B3F9EuN9O6 (The water content of six molecules per formula unit was calculated from the experimental EA data.): C, 19.65; H, 1.65; N, 17.18. Found: C, 19.48; H, 1.22; N, 16.39. Recrystallization from water afforded single crystals of the

SC R

coordination polymer [Eu{CF3B(CN)3}3(H2O)4] (3a).

4.2.4. Preparation of [Gd{CF3B(CN)3}3]·4H2O and crystals of [Gd{CF3B(CN)3}3(H2O)4] (4a)

U

(H3O)[CF3B(CN)3] (1a, 250 mg, 1.40 mmol) and GdCl3 (124 mg, 0.50 mmol) were dissolved in deionized water (15 mL) and stirred for two hours at room temperature.

19F

NMR (128.4 MHz, DMSO-d6):  –32.0

NMR (376.5 MHz, DMSO-d6):  –64.6 (q, 2JF,B = 36.0 Hz,

M

(q, 2JF,B = 36.0 Hz, 3B).

11B

A

vacuum. Yield: 97% (336 mg, 0.45 mmol).

N

The solvent was removed under reduced pressure and the product was dried in a

9F). 13C{1H} NMR (125.8 MHz, DMSO-d6):  128.5 (q, coupling not resolved, 3C, CF3),

ED

122.7 (q, 1JC,B = 68.8 Hz, 9C, CN). IR: 3328 ((OH)), 2543 ((O∙∙∙H∙∙∙O)), 2267 cm1 ((C≡N)). Elem. anal. calcd. for C12H8B3F9GdN9O4: C, 20.50; H, 1.15; N, 17.93. Found:

PT

C, 21.09; H, 1.33; N, 17.88. Recrystallization from water afforded single crystals of the coordination polymer [Gd{CF3B(CN)3}3(H2O)4] (4a).

CC E

4.2.5. Preparation of [Ho{CF3B(CN)3}3]·5H2O and crystals of [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O (5a) (H3O)[CF3B(CN)3] (1a, 400 mg, 2.26 mmol) and HoCl3 (204 mg, 0.75 mmol) were

dissolved in deionized water (15 mL) and stirred for two hours at room temperature.

A

The solvent was removed under reduced pressure and the product was dried in a vacuum. Yield: 79% (436 mg, 0.60 mmol). (q, 2JF,B = 35.5 Hz, 3B).

19F

11B

NMR (128.4 MHz, DMSO-d6):  –32.0

NMR (376.5 MHz, DMSO-d6):  –64.5 (q, 2JF,B = 35.8 Hz,

9F). 13C{1H} NMR (125.8 MHz, DMSO-d6):  129.0 (q, coupling not resolved, 3C, CF3), 122.8 (q, 1JC,B = 68.1 Hz, 9C, CN). IR: 3368 ((OH)), 2548 ((O∙∙∙H∙∙∙O)), 2267 cm1 ((C≡N)). Elem. anal. calcd. for C12H10B3F9HoN9O5 (The water content of only five molecules per formula unit was calculated from the experimental EA data.): C, 18.85; 11

H, 1.85; N, 16.49% Found: C, 20.04; H, 1.42; N, 16.58. Recrystallization from water yielded single crystals of the complex [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O (5a). 4.2.6. Preparation of [Er{CF3B(CN)3}3]·7H2O and crystals of [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.34H2O (6a) (H3O)[CF3B(CN)3] (1a, 250 mg, 1.40 mmol) and ErCl3 (129 mg, 0.50 mmol) were

IP T

dissolved in deionized water (15 mL) and stirred for two hours at room temperature. The solvent was removed under reduced pressure and the product was dried in a vacuum. Yield: 97% (347 mg, 0.45 mmol). 19F

NMR (128.4 MHz, DMSO-d6):  –32.0

NMR (376.5 MHz, DMSO-d6):  –64.7 (br,

SC R

(q, br, coupling not resolved, 3B).

11B

coupling not resolved, 9F). 13C{1H} NMR (125.8 MHz, DMSO-d6):  128.2 (q, coupling not resolved, 3C, CF3), 122.8 (q, 1JC,B = 68.3 Hz, 9C, CN). IR: 3328 ((OH)), 3267

U

((OH)), 2549 ((O∙∙∙H∙∙∙O)), 2267 cm1 ((C≡N)). Elem. anal. calcd. for

N

C12H14B3F9ErN9O7 (The water content of seven molecules per formula unit was assessed from the experimental EA data.): C, 18.79; H, 1.84; N, 16.44. Found: C, H,

1.84;

N,

14.70.

Single

crystals

A

19.03;

of

[Er{CF3B(CN)3}(H2O)7]-

M

[CF3B(CN)3]2∙1.34H2O (6a) crystallized from an aqueous solution. 4.2.7. Preparation of [Gd{C2F5B(CN)3}3]·2H2O and crystals of [Gd{C2F5B(CN)3}3] (4b)

ED

(H3O)[C2F5B(CN)3] (1b, 250 mg, 1.10 mmol) and GdCl3 (96 mg, 0.37 mmol) were dissolved in water (15 mL) and stirred for two hours at room temperature. The solvent

PT

was removed under reduced pressure and the product was briefly dried in a vacuum. Yield: 95% (286 mg, 0.35 mmol). 11B NMR (128.4 MHz, DMSO-d6):  –32.0 (s, br, 3B). NMR (376.5 MHz, DMSO-d6):  –81.1 (q, 9F, CF3), –122.9 (s, 6F, CF2).

13C{1H}

CC E

19F

NMR (125.8 MHz, DMSO-d6):  122.6 (q, 1JC,B = 67.5 Hz, 9C, CN). The signals of the pentafluoroethyl group were not observed. Most likely because of the complex couplings. IR: 3345 ((OH)), 3260 ((OH)), 2572 ((O∙∙∙H∙∙∙O)), 2266 cm1 ((C≡N)).

A

Elem. anal. calcd. for C15H4B3F9GdN9O2 (The water content of two molecules per formula unit was assessed from the experimental EA data. The presence of water is evident from the IR spectrum, as well.): C, 22.05; H, 0.49; N, 15.43. Found: C, 23.06; H, 0.91; N, 14.77. Recrystallization from water yielded single crystals of the anhydrous coordination polymer [Gd{C2F5B(CN)3}3] (4b). 4.3.

X-ray diffraction

12

Colorless crystals of (H3O)[CF3B(CN)3] (1a), [La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a), [Ln{CF3B(CN)3}3(H2O)4]

(Ln

=

Eu

(3a),

Gd

(4a)),

[Ho{CF3B(CN)3}(H2O)7]-

[CF3B(CN)3]2∙1.23H2O (5a), [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.34H2O (6a), and [Gd{C2F5B(CN)3}3] (4b) were obtained from aqueous solutions by slow evaporation of the solvent. The crystals were studied on a Bruker X8-Apex II diffractometer with a CCD area detector and a multi-layer mirror using Mo-Kα radiation (λ = 0.71073 Å) at 100 K. The structures were solved via intrinsic methods (SHELXT) [77] and the

IP T

refinement is based on full-matrix least-squares calculations on F2 (SHELXL) [78, 79].

The positions of the H atoms that are involved in H bonding were located from ∆F-

SC R

synthesis. The positions of most of the other H atoms were placed on calculated

positions. All atoms except for the hydrogen were refined anisotropically. Some restraints had to be applied to some atoms to ensure a stable and meaningful refinement of the (partially) disordered cyanoborate anions and water molecules.

U

All calculations were performed with the ShelXle graphical interface [80]. Molecular

N

structure diagrams were drawn with the program Diamond 4.4.1 [81]. Crystallographic

A

data have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications. Copies of the data can be obtained free of charge via

Acknowledgments

ED

M

www.ccdc.cam.ac.uk/data_request/cif.

The authors gratefully acknowledge the Deutsche Forschungsgemeinschaft (DFG)

PT

for generous support within the priority program SPP1708 (FI-1628/4-2 and MU1562/8-2) and the Studienstiftung des Deutschen Volkes for a PhD scholarship for A.

CC E

E. Sedykh.

A

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A

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17

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Figure captions

Figure 1. A sequence of the two-dimensional layer of (H3O)[CF3B(CN)3] (1a) in the crystal (displacement ellipsoids are depicted at the 50% probability level). Selected

U

interatomic distances [Å] and angles (°): B–CCF 1.630(8), B–CCN 1.591(4), C–F 1.343(3), C≡N 1.140(4), O–H 0.96(3), N∙∙∙H 1.67(4), N···O 2.622(3), CCN–B–CCN

N

109.69(15) and 109.73(15), CCF–B–CCN 109.22(13), B–C≡N 179.2(3), B–C–F

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PT

ED

M

A

112.74(10), F–C–F 106.01(11), H–O–H 114(2), O–H···N 172(2).

Figure 2. Differential thermal analysis (DTA) curve (red) and thermogravimetry (TG)

A

curve (black) of 1a (heating rate: 2 °C min–1 in a constant flow of an Ar/N2 mixture).

18

IP T SC R U N A M ED PT CC E

Figure 3. Coordination spheres of the Ln3+ ions in the crystal structures of [La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a, top), [Eu{CF3B(CN)3}3(H2O)4] (3a, middle), and

A

[Gd{CF3B(CN)3}3(H2O)4] (4a, bottom) (displacement ellipsoids are depicted at the 50% probability level; any disorder of the [CF3B(CN)3]– ions are omitted for clarity). An enlarged picture can be found in the Supporting Information.

19

IP T SC R U N

A

Figure 4. Coordination spheres of the Ln3+ ions in the crystal structures of

M

[Ho{CF3B(CN)3}3(H2O)7]∙1.23H2O (5a, left) and [Er{CF3B(CN)3}3(H2O)7]∙1.34H2O (6a, right) (displacement ellipsoids are depicted at the 50% probability level; any disorder

ED

of the [CF3B(CN)3]– ions and H2O molecules are omitted for clarity). An enlarged

A

CC E

PT

picture can be found in the Supporting Information.

20

Figure 5. Coordination spheres of the Gd3+ ion in the crystal structures of [Gd{C2F5B(CN)3}3] (4b) (displacement ellipsoids are depicted at the 50% probability

SC R

IP T

level). Again, an enlarged picture can be found in the Supporting Information.

U

Figure 6. Differential thermal analysis (DTA) curve (red) and thermogravimetry (TG)

A

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PT

ED

M

A

N

curve (black) of [La{CF3B(CN)3}3]·6H2O (heating rate: 2 °C min–1).

21

Scheme captions

K[RFB(CN)3]

HCl(aq) (10% v/v), Et2O

(H3O)[RFB(CN)3]

removal of Et2O

(RF = CF3: 1a (94%), C2F5: 2a (84%))

recrystallization

H2O

2a–6a

[Ln{CF3B(CN)3}3]·nH2O

r.t., 1.5 h

from water

(79–97%)

SC R

LnCl3·nH2O + 3 (H3O)[CF3B(CN)3]

IP T

Scheme 1. Syntheses of the oxonium acids 1a and 1b.

Ln = La (2a), Eu (3a), Gd (4a), Ho (5a), Er (6a)

U

n = 0, 6; m (assessed from the elemental analyses) = 4 (Gd), 5 (Ho), 6 (La, Eu), 7 (Er) composition of the single crystals:

5a: [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2·1.23H2O

3a: [Eu{CF3B(CN)3}3(H2O)4]

6a: [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2·1.34H2O

A

N

2a: [La{CF3B(CN)3}3(H2O)4]·0.28H2O

recrystallization

H2O

[Gd{C2F5B(CN)3}3]·2H2O

r.t., 1.5 h

[Gd{C2F5B(CN)3}3] from water

(95%)

(4b)

PT

GdCl3 + 3 (H3O)[C2F5B(CN)3]

ED

Scheme 2. Synthesis of 2a–6a.

M

4a: [Gd{CF3B(CN)3}3(H2O)4]

A

CC E

Scheme 3. Synthesis of 4b.

22

Table Table 1. Selected interatomic distances [Å] and angles [°] in the crystal structures of [La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a), [Eu{CF3B(CN)3}3(H2O)4] (3a), [Gd{CF3B(CN)3}3(H2O)4] (4a), [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O (5a), [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.34H2O (6a), and [Gd{C2F5B(CN)3}3] (4b). 4a

5a

6a

4b 2.517(4)

Ln∙∙∙Nmin

2.645(3)

2.540(2)

2.527(3)

Ln∙∙∙Nmax

2.681(3)

2.562(2)

2.546(4)

Ln∙∙∙Omin

2.493(2)

2.396(2)

2.383(2)

2.327(4)

2.312(3)

-

Ln∙∙∙Omax

2.532(3)

2.490(2)

2.487(3)

2.354(4)

2.342(3)

-

C≡Na

1.137(4)

1.142(3)

1.142(4)

1.138(9)

1.138(4)

1.147(5)

BCCNa

1.591(5)

1.593(3)

1.594(5)

1.584(9)

1.587(6)

1.590(6)

BCCF3a

1.611(6)

1.620(6)

1.617(14)

1.601(10)

1.610(6)

BCCF2a

-

-

-

CCF2CCF3a

-

-

-

CFa

1.348(5)

1.345(14)

1.348(15)

1.330(9)

1.35(2)

1.336(5)

Ln-N-Ca

164.5(3)

172.0(4)

170.1(2)

174.6(5)

174.8(3)

171.5(5)

N-C-Ba

177.1(4)

175.1(3)

176.9(9)

177.2(7)

177.6(11)

179.0(5)

C-B-Ca

109.7(3)

109.2(3)

109.1(3)

109.5(5)

110.5(3)

108.1(4)

B-C-Fa

112.5(3)

112.0(6)

114.6(6)

114.0(15)

109.7(3)

-

106.7(4)

-

F-C-Fa

106.1(3)

115.0(8) -

104.7(9)

N

A -

104.7(11)

2.530(4)

-

SC R

-

2.473(3)

IP T

2.480(5)

-

-

-

1.655(9)

-

-

1.519(9)

105.4(7)

105.5(2)

107.7(4)

PT

C-C-F

Mean value.

M

ED

a

a

3a

U

2a

CC E

Table 2. Onset temperature [°C] of the first endothermic (loss of water) and exothermic event (decomposition) of the DTA/TG study on 2a–6a. compound

Tdec (exothermic)

90

170

[Eu{CF3B(CN)3}3]·6H2O

90

170

[Gd{CF3B(CN)3}3]·4H2O

100

165

[Ho{CF3B(CN)3}3]·5H2O

95

165

[Er{CF3B(CN)3}3]·7H2O

100

170

A

[La{CF3B(CN)3}3]·6H2O

T(H2O release) (endothermic)

23

I N U SC R

Table 3. Crystallographic data of (H3O)[CF3B(CN)3] (1a), [La{CF3B(CN)3}3(H2O)4]∙0.28H2O (2a), [Eu{CF3B(CN)3}3(H2O)4] (3a), [Gd{CF3B(CN)3}3(H2O)4] (4a), [Ho{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.23H2O (5a), [Er{CF3B(CN)3}(H2O)7][CF3B(CN)3]2∙1.34H2O (6a), and [Gd{C2F5B(CN)3}3] (4b). 1a

2a

1874719

1874720

C4H3BF3N3O

C12H8.56B3LaF9N9O4.28 C12H8B3EuF9N9O4 C12H8B3GdF9N9O4

C12H16.46B3HoF9N9O8.23 C12H16.69B3ErF9N9O8.34 C15B3F15GdN9

Molar mass [g mol ]

176.90

689.64

Temperature [K]

100

100

Color

colorless

colorless

Crystal system

hexagonal

monoclinic

Space group

P63mc

a [Å]

8.754(2)

b [Å] c [Å]

5.886(1)

PT

 [°]  [°]  [°] 3

5a

6a

4b

1874721

1874724

1874722

1874725

1874723

702.95

786.83

791.22

780.92

100

100

100

100

100

colorless

colorless

colorless

colorless

Colorless

orthorhombic

orthorhombic

triclinic

triclinic

hexagonal

P21/n

Pnma

Pnma

P¯ 1 ¯

P¯ 1 ¯

P63/m

11.8809(8)

19.548(2)

19.501(1)

9.1159(5)

9.0979(9)

12.936(2)

17.0959(10)

14.912(1)

14.8800(8)

11.8179(8)

11.773(1)

12.5380(7)

9.0527(7)

9.0422(6)

14.444(1)

14.489(2)

92.334(2)

92.473(3)

91.160(2)

91.402(3)

107.081(2)

106.805(3)

92.850(3)

8.184(1)

390.6(2)

2543.5(3)

2638.8(4)

2623.8(3)

1485.4(2)

1483.1(3)

1185.9(4)

2

4

4

4

2

2

2

ber [Mg·m ]

1.504

1.801

1.756

1.780

1.759

1.771

2.187

 [mm ]

0.154

1.784

2.476

2.627

2.770

2.937

2.941

F(000) [e]

Z

CC E

Volume [Å ]

4a

697.66

ED

–1

A

Empirical formula

M

CCDC number

3a

–3

–1

1323

1336

1340

761

765

734

1489

30210

27375

40892

18658

26063

8425

Independent reflections

322

5429

2941

2919

6342

6405

915

R(int)

0.0516

0.0732

0.0461

0.0783

0.0612

0.0475

0.1158

Data/restraints/parameters 322/1/31

5429/15/384

2941/45/284

2919/51/275

6342/71/486

6405/95/588

915/0/75

R1 [I > 2(I)]

0.0363

0.0324

0.0196

0.0252

0.0477

0.0287

0.0344

0.0882

0.0604

0.0482

0.0674

0.1030

0.0594

0.0671

1.174

1.019

1.072

1.023

1.058

1.032

1.054

0.671/–0.905

0.808/–0.834

1.341/–1.807

0.749/–0.885

1.090/–0.868

A

176

Reflections collected

a

wR2 (all reflections) Goodness-of-fit

b

c

Largest diff. peak/hole

0.438/–0.163 0.549/–0.615

24

I N U SC R

R1 = (Fo− Fc)/Fo. Rw = [w(Fo2 − Fc2)2/wFo2]1/2, w = [2(Fo) + (aP)2 + bP]−1, P = (max(0,Fo2)+2Fc2)/3); 1a: a = 0.0494, b = 0; 2a: a = 0.0142, b = 2.6362; 3a: a = 0.0229, b = 1.7092; 4a: a = 0.0429, b = 0; 5a: a = 0.0385, b = 3.9121; 6a: a = 0.0222, b = 1.4224; 4b: a = 0.0226, b = 0.7511. c Goodness-of-fit S = w(Fo2 − Fc2)2/(m − n); (m: reflections, n: variables). a

A

CC E

PT

ED

M

A

b

25