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Supporting Information for Angew. Chem. Int. Ed. 200460478 © Wiley-VCH 2004 Supporting Information for Angew. Chem. Int. Ed. 200460478 © Wiley-VCH 2004 69451 Weinheim, Germany [Yb3N(Dpa)6][Yb(Dpa)3], das erste molekulare Nitrid eines Selten-Erd- ** Elementes mit einer Yb3N-Einheit Catharina C. Quitmann und Klaus Müller-Buschbaum* ** − (Dpa = dipyridylamide anion, (C5H4N)2N ) Experimental As described in the manuscript, [Yb3N(Dpa)6][Yb(Dpa)3] (Dpa = dipyridylamide anion − (C5H4N)2N ) is obtained via a combination of the low temperature oxidation of ytterbium metal with 2,2’-dipyridylamide in liquid ammonia and a subsequent temperature program in an evacuated ampoule. Liquid ammonia is capable of solvating electrons and already dissolves both europium and ytterbium at normal pressure. The formation of an electride is only an intermediate, which is followed by the immediate reaction with the amine ligand, producing hydrogen. This process is accompanied by a colour change of the solution from deep blue to green and yellow. It has to be stressed, that the crystalline product obtained from the temper process is not necessarily the initial reaction product obtained from liquid ammonia. Instead it is most likely that homoleptic ammonia complexes of ytterbium are formed first, which decompose upon the removal of ammonia. Furthermore non-coordinating ammonia solvate molecules will be released from the product at this stage. In contrast the nitride ion centring the triangular Yb3N 3- unit is a result of the ammonolysis of NH3 to N and survives both the removal of ammonia as well as the subsequent heating in evacuated ampoules, which is necessary to obtain a crystalline product suitable for the single crystal X-ray diffraction. Investigations whether the monomeric units also present in [Yb3N(Dpa)6][Yb(Dpa)3] might be a decomposition product of triangular units are under way. All manipulations were carried out under inert atmospheric conditions using glove box, ampoule as well as vacuum line techniques. The IR spectra were recorded using a BRUKER 1 FTIR-IS66V-S spectrometer, the Raman spectrum using a BRUKER FRA 106-S spectrometer. For MIR investigations KBr pellets, and PE pellets for FIR were used under vacuum. The EDX analysis was carried out using an ECON IVPV9900-26 EDAX- International Inc. instrument. Analysis: C90H72N28Yb4, C: 47.8 (calc: 48.30), H: 3.5 (calc: 3.24), N: 18.0 (calc: 17.52) % Investigations on the nitride character In order to confirm the nitride character of the Yb3N unit MIR, Far IR, Raman spectroscopical and EDX investigations were carried out. In comparison to the nitride free homoleptic dipyridylamide [Yb2(Dpa)6] as well as the free ligand [Yb3N(Dpa)6][Yb(Dpa)3] exhibits -1 additional vibration bands at 828 and 692 cm (IR), which can be assigned to the νasym of Yb- N(nitride). Because [Yb3N(Dpa)6][Yb(Dpa)3] gave no Raman spectrum the νsym expected at -1 about 230 cm could not be observed. Unfortunately as [Yb3N(Dpa)6][Yb(Dpa)3] is the first molecular nitride of a rare earth element, no comparable rare earth examples can be found. Thus only a comparison to heavy transition metal vibrations can be drawn.[1] In addition, an EDX analysis was carried out to rule out oxygen impurities or the presence of oxide anions instead of the nitride. Though a surface method, which consequently should give a rather higher oxygen content considering the air and moisture sensitivity of the compound, no oxygen was found in the analysis. Given that the percentage of content of elements with a low mass assigned in the EDX analysis are usually too high this gives further evidence to the absence of oxygen. The nitrogen content is located in the shoulder of the carbon signal. 2 Int keV Figure 1: The result of the EDX analysis of [Yb3N(Dpa)6][Yb(Dpa)3]. The combination of the high yield and the analysis methods described together with the necessity of electron neutrality excludes a presence of oxide anions on the positions of the nitride ions. Beyond that the formation of an electride solution in liquid ammonia makes the presence of oxygen containing compounds unlikely throughout the whole synthesis. As a result [Yb3N(Dpa)6][Yb(Dpa)3] is considered to be the first molecular nitride of a rare earth element. In addition, the product is a nitrido amide taking the surrounding Dpa amide ligands into account. Crystal Structure The crystal structure of [Yb3N(Dpa)6][Yb(Dpa)3] contains two different uncharged molecular units. Though the cell constants indicate a higher symmetry, only the positions of the ytterbium atoms as well as the nitride ion obey the symmetry R3. The positions of the other ligand atoms enforce a transition down to the triclinic space group P1. Whereas the triangular units [Yb3N(Dpa)6] with Yb1-3 exhibit complete ordering (Figure 2) both monomers [Yb(Dpa)3] suffer from disorder phenomena due to the ytterbium atoms being positioned on a centre of symmetry. The ratio Yb/Dpa of 1:3 results in all ligand atom positions being only half occupied. The ligands share common atom positions but in a different manner for Yb4 and Yb5. However no indication for an acentric setup in the space 3 group P1 was found. A possible hemihedric twinning was checked and can be excluded. In order to check possible twinnings resulting in a wrong metric and unit cell powder diffraction was used. The compound was investigated in sealed capillaries on a STOE STADI P transmission diffractometer (Cu Kα1 radiation λ = 1.540598 Å, focussed single crystal germanium monochromator). The diffraction pattern of the powder sample was compared with a simulated diffractogram. Indexing of the powder diffractogram gave no other reasonable unit cell and symmetry than the single crystal X-ray investigation. Thus the pseudo hexagonal metric of [Yb3N(Dpa)6][Yb(Dpa)3] may be explained by the triangular [Yb3N(Dpa)6] units only, whilst the monomeric units can take two different positions between the triangular units with no distinct far ordering. Figure 3 shows the van-der-Waals spheres of the atoms of [Yb3N(Dpa)6][Yb(Dpa)3]. Figure 4 illustrates the crystal structure depicting the same view of the unit cell of [Yb3N(Dpa)6][Yb(Dpa)3] without van-der-Waals spheres. Like for the homoleptic “high temperature” reaction products of the metal based redox reactions giving amides, [Yb3N(Dpa)6][Yb(Dpa)3] does not show a tendency for the formation of an “ate”-complex as seen for many alkaline based solvent reactions of the rare earth elements.[2] Discussing the coordination spheres of the ytterbium atoms the Yb3N triangle is surrounded by dipyridylamides, that coordinate the Yb atoms in a strained 1,3-chelating mode and µ1 to another Yb atom. All nitrogen atoms participate in the coordination sphere. Contrary the homoleptic rare earth dipyridylamides show strained 1,3-chelates only at the edges of the coordination polyhedra. Double 1,3-1,3 double chelates are linking between the metal centers. Both examples enlarge the strained, single 1,3-chelate coordination of aminopyridinato- complexes.[3] Whereas the 1,3-1,3-double-chelating mode is rarely observed in transition metal chemistry, a single, wide 1,5-chelate is favoured instead.[4] Examples of the coordination mode described here are rare but present e.g. in the complexes [V2(dpa)4] or [4d] [V2(dpa)3Cl2]*2CH2Cl2. Because the nitride ion almost lies within the plane of the ytterbium atoms the Yb-N distances in this unit are particularly short, ranging from 207(1) to 209(1) pm. The Yb-N distances to the dpa ligands lie in the range of 240(2) to 250(2) pm and [5] are in the expected region and comparable to those in [Yb2(dpa)6], in which the 1,3-1,3- double-chelating dpa ligands show Yb-N distances of 238 to 258 pm. The ytterbium atoms in the unit [Yb3N(dpa)6] are further coordinated by seven N-atoms giving a distorted pentagonal bipyramid. Thereby the C.N. of this molecular unit is smaller than in the other [8, 11] dipyridylamides [Ln2(dpa)6], Ln = Sc, La – Yb, that exhibit a C.N. of eight or ten, as 4 well as in common multi-chelating ligand systems like the phthalocyanates with a C.N. of eight. [6] The second molecular units of [Yb3N(dpa)6][Yb(dpa)3] consist of homoleptic monomers of the formula [Yb(dpa)3]. Hence the structures of both units do not correspond with the dimeric structure of the homoleptic dipyridylamides of the rare earth elements. [5] In the monomeric units the dpa ligands exhibit only the single 1,3-chelating coordination of the Yb-atoms [5] comparable to the end-on coordinating dpa ligands in [Yb2(Dpa)6] as well as in aminipyridinato-complexes [9] that have no additional ring at their disposal. The Yb-N distances in the [Yb(dpa)3] units lie in a wide region, ranging from 227(2) to 270(2) pm. The Yb atoms show a C.N. of six For all information concerning the crystallographic data, please contact the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223336033 or e-mail: [email protected]) by pointing out the CCDC-No. 232899. [1] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 3rd Edition, Wiley VCH, 1978, p. 301. [2] R. Kempe, Angew. Chem. Int. Ed. Engl. 2000, 39, 468-498; Angew. Chem. 2000, 112, 478-504. [3] a) R. Kempe, H. Noss, T. Irrgang, J. Organomet. Chem. 2002, 647, 12-20; b) A. Spangenberg, P. Arndt, R. Kempe, Angew. Chem. 1998, 110, 824-827; Angew.
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