Synthesis and properties of homoleptic 2,2′-bipyridyl complexes of rare-earth elements. Crystal and molecular structures of the complexes Ln(N2C10H8)4 (Ln=Sm, Eu, Yb, or Lu) and the ionic complex [Lu(N2C10H8)4][Li(THF)4]

Abstract

Honaolcpiic 2.2 '-btpyrid,vl comptc,~c~ t~l laulh:midcs (Ln), I..lt~bp.,. i4. ~vcrc prepared by the reactions of iodides Lnl2(TH t=) 2 {Ln = Sin. ELI, Im, or Yb), t.nl ~(lHFh ~[.n := La. (7c. Pr, Nd, Gd. or Tb). or bis(irimcthylsilyl.bamidc,, L~q N(SiMc~)2I 3 {I..n = D3,. t lo, Er, or I.u) with bipyridyllitllium it~ tclrahydrofura~l (IHF) or 1.2-dinlciho\ycthanc ill ihc presence of frcc 2,2 "-bipyridmc. The IR and ESR spectral data. the magnclic sust:cpiibditic',, and Ihe resells of X-ray diffraction analysis illdic;ltc ihat the conlplcxes of ;ill clclncilis ol the tanlhanidc series, t.,xccpt 10r the" ctlropitlli/complc\, cllnlalll Ell <~ C/lliOlls glP, d atliOillC bpv tigand>. ACCOl'dillg tO tile X-fdV dil/rclctioll dcliil, the c,,>ordhlalitUl l~olyhcdra ahotll the Sin :.llld [:.tl :lloms :ire tribes. Key words: rare-torah clenaci~ts, 2.2 "-bip.,,ridinc. comptc'xcs, ,,;ifticltlfc. magliclic: 0ropcrtics.Recently, wc i3ave initiated a scries of studies aimed at the SVllthesis o( complexes of rare-earth cletllellts with the chelating 2,2"-bipyridyl (bpy) ligartd This ligar~d po.,,-sesscs both a-donor (four-electron N-donor) ae, d =-acceptor properties. Successive reduction of the ligand allows one to prcpare its mollO-and dianionic lorms. Bigyridyl complexes of many mctals are known. In the ease of d-block elements, the ligaud acts to a greater cxtcllt as at1 n-donor and the LUMO of the ligand ietllaiils unoccupied, whereas clectropositi,,e metals can lorm comple~,es both with nl(.mo-and dJallions, Pre~i-otlsly, we have prepared various complexes of rare-earth clcments with bpy'-radical anions. Among them, three types can be distinguished: (a) the mixed bpy-DAD complex of samarium ISm~:~(DAD-' )(DAD-)(bpy~ ~DAD = BuINCHCHNBtH): I (b) the aniollic complcxes J Li(TH F)4J+[Ln(bp.v)nl-iLn = Sin, Tb, Tin, Yb, or De. n = 3 or 4), which were synthesizect by the reactions of iodides with Li(bpy) in TI-IF: z and (c) the mixed iodinc-bpy complexes of ytterbium(n), vi:.. Ybl(bpy)(DME)~, 3 and lanthanum(Ill), viz,, Lal2(bpy)~DME) 2 aud Lal_,(-bpy)~l'DME), 4 which were lormed in the reactions of the corresponding iodinenaphthalene complexes [YbI(DME)_,I2(bI-Ct0H~i) or ll.alz(fHt:)zJ_~(.u-Cj0H ,) with one or two equivalents of bpy. Recently, 5 we have reported the syHthcsis and X-ray diffraction study of the first complex of latlthanidc with the bipyridyl diarti<m, [Yb~bpy)(TI4 F)2I ~ (the scc(md metal complex of this type known to date), which wa~, prepared by reduction of 2,2"-bipyridinc (biPy) with an excess of CI!~HsYb(THF): in "IHF. When wc ~tartcd thix work, onl.~ coNtr:ldietory data de, the sxnthesis of tctrakis(bipyrid.vt) complexes of conlposhion Lrltbpyl 4 ILn = Eu or Yb: 6 Ln = Nd or Cc 7) werc a,,ailable in the literature. The [_li(bpy) 4 complexes iLia --Eu or u were prepared ~ by tile reactions of soh.llions of the correspouding metals m liquid ammonia ",,vitb free 2,2"-bipyridine. Based on the results of magllctic nleasurcmetlts, it was su.ggcsted ~ lhat these complexes contain the Eu +2 or Yb +2 cations and the b...

[U(bipy)4]: A Mistaken Case of U0?

“…Thus, based upon the structural evidence alone, 1 is best described not as U 0 but as U IV ligated by four radical bipy monoanions in the form [U IV (bipy .− ) 4 ]. Notably, this structure differs from the related lanthanide complexes wherein [Ln III (bipy 2− )(bipy .− )(bipy 0 )] is predominant across the series and more in‐line with [M(bipy .− ) 3 ] (M=Sc, Ti, Y) found amongst the early d‐elements …”

“…Even in complexes containing redox‐limited metals, such as the lanthanides, canonical oxidation state assignments can be nontrivial . For instance, in the [Lu(bipy) 4 ] complex, magnetic data support either [Lu 0 (bipy 0 ) 4 ] or [Lu III (bipy 2− )(bipy .− )(bipy 0 ) 2 ] form with an EPR value ( g =2.0014) suggestive of the latter . In homoleptic transition‐metal complexes of the type [M(bipy) 3 ], redox activity of both metal and ligand make formal oxidation state assignments difficult as shown by Wieghardt et al .…”

“…Crystals of 2 ⋅0.5 C 7 H 8 (Figure ), grown from THF/C 7 H 8 mixtures, show a non‐interacting cation/anion pair within the P space group where the uranium retains its distorted cubic coordination geometry, differing from dodecahedral lutetium in [Li(THF) 4 ][Lu III (bipy −. ) 4 ] . As with 1 , the [U(bipy) 4 ] − fragment occupies a crystallographically independent position that allows for the localized charge assignment of each bipy ligand.…”

“…[11] For instance, in the [Lu(bipy) 4 ]c omplex, magnetic data supporte ither [Lu 0 (bipy 0 ) 4 ]o r[Lu III (bipy 2À )(bipyC À )(bipy 0 ) 2 ]f orm with an EPR value (g = 2.0014) suggestive of the latter. [12] In homoleptic transition-metal complexeso ft he type [M(bipy) 3 ],[a] Prof.…”

“…Crystalso f2·0.5 C 7 H 8 (Figure 2), grown from THF/C 7 H 8 mixtures, show an on-interacting cation/anionp air within the P1 space group where the uraniumr etains its distorted cubic coordination geometry,d iffering from dodecahedrall utetium in [Li(THF) 4 ][Lu III (bipy À C) 4 ]. [12] As with 1,t he [U(bipy) 4 ] À fragment occupies ac rystallographically independentp ositiont hat allows for the localized chargea ssignment of each bipy ligand. Inspection of the C py ÀC py metric parameters reveals two distinct charge states corresponding to bipy À C (1.422(5), 1.439 (5) ) andb ipy 2À (1.379(8), 1.384 (7) ) in 2.C onsistent with this, the UÀN bipy distances of the bipy À C ligands ( 2.53 (avg)) are longert han the analogous distances of the two bipy 2À ligands (2.47 ( avg)).…”