User:Praseodymium-141/Lanthanide compounds 2
When in the form of
The low probability of the 4f electrons existing at the outer region of the atom or ion permits little effective overlap between the
Many of these features make lanthanide complexes effective
Despite this, the use of lanthanide coordination complexes as
Ln(III) compounds
The trivalent lanthanides mostly form ionic salts. The trivalent ions are
Compounds in other oxidation states
The most common divalent derivatives of the lanthanides are for Eu(II), which achieves a favorable f7 configuration. Divalent halide derivatives are known for all of the lanthanides. They are either conventional salts or are Ln(III) "
Hydrides
Chemical element | La | Ce | Pr | Nd | Pm | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Atomic number | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 |
Metal lattice (RT) | dhcp | fcc | dhcp | dhcp | dhcp | r | bcc | hcp | hcp | hcp | hcp | hcp | hcp | hcp | hcp |
Dihydride[19] | LaH2+x | CeH2+x | PrH2+x | NdH2+x | SmH2+x | EuH2 o "salt like" |
GdH2+x | TbH2+x | DyH2+x | HoH2+x | ErH2+x | TmH2+x | YbH2+x o, fcc "salt like" |
LuH2+x | |
Structure | CaF2 | CaF2 | CaF2 | CaF2 | CaF2 | CaF2 | *PbCl2[20] | CaF2 | CaF2 | CaF2 | CaF2 | CaF2 | CaF2 | CaF2 | |
metal sub lattice | fcc | fcc | fcc | fcc | fcc | fcc | o | fcc | fcc | fcc | fcc | fcc | fcc | o fcc | fcc |
Trihydride[19] | LaH3−x | CeH3−x | PrH3−x | NdH3−x | SmH3−x | EuH3−x[21] | GdH3−x | TbH3−x | DyH3−x | HoH3−x | ErH3−x | TmH3−x | LuH3−x | ||
metal sub lattice | fcc | fcc | fcc | hcp | hcp | hcp | fcc | hcp | hcp | hcp | hcp | hcp | hcp | hcp | hcp |
Trihydride properties transparent insulators (color where recorded) |
red | bronze to grey[22] | PrH3−x fcc | NdH3−x hcp | golden greenish[23] | EuH3−x fcc | GdH3−x hcp | TbH3−x hcp | DyH3−x hcp | HoH3−x hcp | ErH3−x hcp | TmH3−x hcp | LuH3−x hcp |
Lanthanide metals react exothermically with hydrogen to form LnH2, dihydrides.[19] With the exception of Eu and Yb, which resemble the Ba and Ca hydrides (non-conducting, transparent salt-like compounds),they form black pyrophoric, conducting compounds[24] where the metal sub-lattice is face centred cubic and the H atoms occupy tetrahedral sites.[19] Further hydrogenation produces a trihydride which is non-stoichiometric, non-conducting, more salt like. The formation of trihydride is associated with and increase in 8–10% volume and this is linked to greater localization of charge on the hydrogen atoms which become more anionic (H− hydride anion) in character.[19]
Halides
Chemical element | La | Ce | Pr | Nd | Pm | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Atomic number | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 |
Tetrafluoride | CeF4 | PrF4 | NdF4 | TbF4 | DyF4 | ||||||||||
Color m.p. °C | white dec | white dec | white dec | ||||||||||||
Structure C.N. | UF4 8 | UF4 8 | UF4 8 | ||||||||||||
Trifluoride | LaF3 |
CeF3 | PrF3 | NdF3 | PmF3 | SmF3 | EuF3 | GdF3 | TbF3 | DyF3 | HoF3 | ErF3 | TmF3 | YbF3 | LuF3 |
Color m.p. °C | white 1493[28] | white 1430 | green 1395 | violet 1374 | green 1399 | white 1306 | white 1276 | white 1231 | white 1172 | green 1154 | pink 1143 | pink 1140 | white 1158 | white 1157 | white 1182 |
Structure C.N. | LaF3 9 | LaF3 9 | LaF3 9 | LaF3 9 | LaF3 9 | YF3 8 | YF3 8 | YF3 8 | YF3 8 | YF3 8 | YF3 8 | YF3 8 | YF3 8 | YF3 8 | YF3 8 |
Trichloride | LaCl3 | CeCl3 | PrCl3 | NdCl3 | PmCl3 | SmCl3 | EuCl3 | GdCl3 | TbCl3 | DyCl3 | HoCl3 | ErCl3 | TmCl3 | YbCl3 | LuCl3 |
Color m.p. °C | white 858 | white 817 | green 786 | mauve 758 | green 786 | yellow 682 | yellow dec | white 602 | white 582 | white 647 | yellow 720 | violet 776 | yellow 824 | white 865 | white 925 |
Structure C.N. | UCl3 9 | UCl3 9 | UCl3 9 | UCl3 9 | UCl3 9 | UCl3 9 | UCl3 9 | UCl3 9 | PuBr3 8 | PuBr3 8 | YCl3 6 | YCl3 6 | YCl3 6 | YCl3 6 | YCl3 6 |
Tribromide | LaBr3 | CeBr3 | PrBr3 | NdBr3 | PmBr3 | SmBr3 | EuBr3 | GdBr3 | TbBr3 | DyBr3 | HoBr3 | ErBr3 | TmBr3 | YbBr3 | LuBr3 |
Color m.p. °C | white 783 | white 733 | green 691 | violet 682 | green 693 | yellow 640 | grey dec | white 770 | white 828 | white 879 | yellow 919 | violet 923 | white 954 | white dec | white 1025 |
Structure C.N. | UCl3 9 | UCl3 9 | UCl3 9 | PuBr3 8 | PuBr3 8 | PuBr3 8 | PuBr3 8 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 |
Triiodide | LaI3 | CeI3 | PrI3 | NdI3 | PmI3 | SmI3 | EuI3 | GdI3 | TbI3 | DyI3 | HoI3 | ErI3 | TmI3 | YbI3 | LuI3 |
Color m.p. °C | yellow 766 | green 738 | green 784 | green 737 | orange 850 | dec. | yellow 925 | 957 | green 978 | yellow 994 | violet 1015 | yellow 1021 | white dec | brown 1050 | |
Structure C.N. | PuBr3 8 | PuBr3 8 | PuBr3 8 | PuBr3 8 | BiI3 6 | BiI3 6 | BiI3 6 | BiI3 6 | BiI3 6 | BiI3 6 | BiI3 6 | BiI3 6 | BiI3 6 | BiI3 6 | |
Difluoride | SmF2 | EuF2 | TmF2 | YbF2 | |||||||||||
Color m.p. °C | purple 1417 | yellow 1416 | grey | ||||||||||||
Structure C.N. | CaF2 8 | CaF2 8 | CaF2 8 | ||||||||||||
Dichloride | NdCl2 | SmCl2 | EuCl2 | DyCl2 | TmCl2 | YbCl2 | |||||||||
Color m.p. °C | green 841 | brown 859 | white 731 | black dec. | green 718 | green 720 | |||||||||
Structure C.N. | PbCl2 9 | PbCl2 9 | PbCl2 9 | SrBr2 | SrI2 7 | SrI2 7 | |||||||||
Dibromide | NdBr2 | SmBr2 | EuBr2 | DyBr2 | TmBr2 | YbBr2 | |||||||||
Color m.p. °C | green 725 | brown 669 | white 731 | black | green | yellow 673 | |||||||||
Structure C.N. | PbCl2 9 | SrBr2 8 | SrBr2 8 | SrI2 7 | SrI2 7 | SrI2 7 | |||||||||
Diiodide | LaI2 metallic |
CeI2 metallic |
PrI2 metallic |
NdI2 high pressure metallic |
SmI2 | EuI2 | GdI2 metallic |
DyI2 | TmI2 | YbI2 | |||||
Color m.p. °C | bronze 808 | bronze 758 | violet 562 | green 520 | green 580 | bronze 831 | purple 721 | black 756 | yellow 780 | Lu | |||||
Structure C.N. | CuTi2 8 | CuTi2 8 | CuTi2 8 | SrBr2 8 CuTi2 8 |
EuI2 7 | EuI2 7 | 2H-MoS2 6 | CdI2 6 | CdI2 6 | ||||||
Ln7I12 | La7I12 | Pr7I12 | Tb7I12 | ||||||||||||
Sesquichloride | La2Cl3 | Gd2Cl3 | Tb2Cl3 | Er2Cl3 | Tm2Cl3 | Lu2Cl3 | |||||||||
Structure | Gd2Cl3 | Gd2Cl3 | |||||||||||||
Sesquibromide | Gd2Br3 | Tb2Br3 | |||||||||||||
Structure | Gd2Cl3 | Gd2Cl3 | |||||||||||||
Monoiodide | LaI[29] | ||||||||||||||
Structure | NiAs type |
The only tetrahalides known are the tetrafluorides of cerium, praseodymium, terbium, neodymium and dysprosium, the last two known only under matrix isolation conditions.[25][30] All of the lanthanides form trihalides with fluorine, chlorine, bromine and iodine. They are all high melting and predominantly ionic in nature.[25] The fluorides are only slightly soluble in water and are not sensitive to air, and this contrasts with the other halides which are air sensitive, readily soluble in water and react at high temperature to form oxohalides.[31]
The trihalides were important as pure metal can be prepared from them.[25] In the gas phase the trihalides are planar or approximately planar, the lighter lanthanides have a lower % of dimers, the heavier lanthanides a higher proportion. The dimers have a similar structure to Al2Cl6.[32]
Some of the dihalides are conducting while the rest are insulators. The conducting forms can be considered as LnIII electride compounds where the electron is delocalised into a conduction band, Ln3+ (X−)2(e−). All of the diiodides have relatively short metal-metal separations.
The sesquihalides Ln2X3 and the Ln7I12 compounds listed in the table contain metal
LaI is the only known monohalide. Prepared from the reaction of LaI3 and La metal, it has a NiAs type structure and can be formulated La3+ (I−)(e−)2.[29]
Oxides and hydroxides
All of the lanthanides form sesquioxides, Ln2O3. The lighter (larger) lanthanides adopt a hexagonal 7-coordinate structure while the heavier/smaller ones adopt a cubic 6-coordinate "C-M2O3" structure.[27] All of the sesquioxides are basic, and absorb water and carbon dioxide from air to form carbonates, hydroxides and hydroxycarbonates.[33] They dissolve in acids to form salts.[34]
Cerium forms a stoichiometric dioxide, CeO2, where cerium has an oxidation state of +4. CeO2 is basic and dissolves with difficulty in acid to form Ce4+ solutions, from which CeIV salts can be isolated, for example the hydrated nitrate Ce(NO3)4.5H2O. CeO2 is used as an oxidation catalyst in catalytic converters.[34] Praseodymium and terbium form non-stoichiometric oxides containing LnIV,[34] although more extreme reaction conditions can produce stoichiometric (or near stoichiometric) PrO2 and TbO2.[25]
Europium and ytterbium form salt-like monoxides, EuO and YbO, which have a rock salt structure.[34] EuO is ferromagnetic at low temperatures,[25] and is a semiconductor with possible applications in spintronics.[35] A mixed EuII/EuIII oxide Eu3O4 can be produced by reducing Eu2O3 in a stream of hydrogen.[33] Neodymium and samarium also form monoxides, but these are shiny conducting solids,[25] although the existence of samarium monoxide is considered dubious.[33]
All of the lanthanides form hydroxides, Ln(OH)3. With the exception of lutetium hydroxide, which has a cubic structure, they have the hexagonal UCl3 structure.[33] The hydroxides can be precipitated from solutions of LnIII.[34] They can also be formed by the reaction of the sesquioxide, Ln2O3, with water, but although this reaction is thermodynamically favorable it is kinetically slow for the heavier members of the series.[33] Fajans' rules indicate that the smaller Ln3+ ions will be more polarizing and their salts correspondingly less ionic. The hydroxides of the heavier lanthanides become less basic, for example Yb(OH)3 and Lu(OH)3 are still basic hydroxides but will dissolve in hot concentrated NaOH.[25]
Chalcogenides
All of the lanthanides form Ln2Q3 (Q= S, Se, Te).[34] The sesquisulfides can be produced by reaction of the elements or (with the exception of Eu2S3) sulfidizing the oxide (Ln2O3) with H2S.[34] The sesquisulfides, Ln2S3 generally lose sulfur when heated and can form a range of compositions between Ln2S3 and Ln3S4. The sesquisulfides are insulators but some of the Ln3S4 are metallic conductors (e.g. Ce3S4) formulated (Ln3+)3 (S2−)4 (e−), while others (e.g. Eu3S4 and Sm3S4) are semiconductors.[34] Structurally the sesquisulfides adopt structures that vary according to the size of the Ln metal. The lighter and larger lanthanides favoring 7-coordinate metal atoms, the heaviest and smallest lanthanides (Yb and Lu) favoring 6 coordination and the rest structures with a mixture of 6 and 7 coordination.[34]
Polymorphism is common amongst the sesquisulfides.[36] The colors of the sesquisulfides vary metal to metal and depend on the polymorphic form. The colors of the γ-sesquisulfides are La2S3, white/yellow; Ce2S3, dark red; Pr2S3, green; Nd2S3, light green; Gd2S3, sand; Tb2S3, light yellow and Dy2S3, orange.[37] The shade of γ-Ce2S3 can be varied by doping with Na or Ca with hues ranging from dark red to yellow,[26][37] and Ce2S3 based pigments are used commercially and are seen as low toxicity substitutes for cadmium based pigments.[37]
All of the lanthanides form monochalcogenides, LnQ, (Q= S, Se, Te).[34] The majority of the monochalcogenides are conducting, indicating a formulation LnIIIQ2−(e-) where the electron is in conduction bands. The exceptions are SmQ, EuQ and YbQ which are semiconductors or insulators but exhibit a pressure induced transition to a conducting state.[36] Compounds LnQ2 are known but these do not contain LnIV but are LnIII compounds containing polychalcogenide anions.[38]
Oxysulfides Ln2O2S are well known, they all have the same structure with 7-coordinate Ln atoms, and 3 sulfur and 4 oxygen atoms as near neighbours.[39] Doping these with other lanthanide elements produces phosphors. As an example, gadolinium oxysulfide, Gd2O2S doped with Tb3+ produces visible photons when irradiated with high energy X-rays and is used as a scintillator in flat panel detectors.[40] When mischmetal, an alloy of lanthanide metals, is added to molten steel to remove oxygen and sulfur, stable oxysulfides are produced that form an immiscible solid.[34]
Pnictides
All of the lanthanides form a mononitride, LnN, with the rock salt structure. The mononitrides have attracted interest because of their unusual physical properties. SmN and EuN are reported as being "
The other pnictides phosphorus, arsenic, antimony and bismuth also react with the lanthanide metals to form monopnictides, LnQ, where Q = P, As, Sb or Bi. Additionally a range of other compounds can be produced with varying stoichiometries, such as LnP2, LnP5, LnP7, Ln3As, Ln5As3 and LnAs2.[43]
Carbides
Carbides of varying stoichiometries are known for the lanthanides. Non-stoichiometry is common. All of the lanthanides form LnC2 and Ln2C3 which both contain C2 units. The dicarbides with exception of EuC2, are metallic conductors with the calcium carbide structure and can be formulated as Ln3+C22−(e–). The C-C bond length is longer than that in CaC2, which contains the C22− anion, indicating that the antibonding orbitals of the C22− anion are involved in the conduction band. These dicarbides hydrolyse to form hydrogen and a mixture of hydrocarbons.[44] EuC2 and to a lesser extent YbC2 hydrolyse differently producing a higher percentage of acetylene (ethyne).[45] The sesquicarbides, Ln2C3 can be formulated as Ln4(C2)3.
These compounds adopt the Pu2C3 structure[26] which has been described as having C22− anions in bisphenoid holes formed by eight near Ln neighbours.[46] The lengthening of the C-C bond is less marked in the sesquicarbides than in the dicarbides, with the exception of Ce2C3.[44] Other carbon rich stoichiometries are known for some lanthanides. Ln3C4 (Ho-Lu) containing C, C2 and C3 units;[47] Ln4C7 (Ho-Lu) contain C atoms and C3 units[48] and Ln4C5 (Gd-Ho) containing C and C2 units.[49] Metal rich carbides contain interstitial C atoms and no C2 or C3 units. These are Ln4C3 (Tb and Lu); Ln2C (Dy, Ho, Tm)[50][51] and Ln3C[26] (Sm-Lu).
Borides
All of the lanthanides form a number of borides. The "higher" borides (LnBx where x > 12) are insulators/semiconductors whereas the lower borides are typically conducting. The lower borides have stoichiometries of LnB2, LnB4, LnB6 and LnB12.[52] Applications in the field of spintronics are being investigated.[35] The range of borides formed by the lanthanides can be compared to those formed by the transition metals. The boron rich borides are typical of the lanthanides (and groups 1–3) whereas for the transition metals tend to form metal rich, "lower" borides.[53] The lanthanide borides are typically grouped together with the group 3 metals with which they share many similarities of reactivity, stoichiometry and structure. Collectively these are then termed the rare earth borides.[52]
Many methods of producing lanthanide borides have been used, amongst them are direct reaction of the elements; the reduction of Ln2O3 with boron; reduction of boron oxide, B2O3, and Ln2O3 together with carbon; reduction of metal oxide with boron carbide, B4C.[52][53][54][55] Producing high purity samples has proved to be difficult.[55] Single crystals of the higher borides have been grown in a low melting metal (e.g. Sn, Cu, Al).[52]
Diborides, LnB2, have been reported for Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. All have the same, AlB2, structure containing a graphitic layer of boron atoms. Low temperature ferromagnetic transitions for Tb, Dy, Ho and Er. TmB2 is ferromagnetic at 7.2 K.[26]
Tetraborides, LnB4 have been reported for all of the lanthanides except EuB4, all have the same UB4 structure. The structure has a boron sub-lattice consists of chains of octahedral B6 clusters linked by boron atoms. The unit cell decreases in size successively from LaB4 to LuB4. The tetraborides of the lighter lanthanides melt with decomposition to LnB6.[55] Attempts to make EuB4 have failed.[54] The LnB4 are good conductors[52] and typically antiferromagnetic.[26]
Hexaborides, LnB6 have been reported for all of the lanthanides. They all have the CaB6 structure, containing B6 clusters. They are non-stoichiometric due to cation defects. The hexaborides of the lighter lanthanides (La – Sm) melt without decomposition, EuB6 decomposes to boron and metal and the heavier lanthanides decompose to LnB4 with exception of YbB6 which decomposes forming YbB12. The stability has in part been correlated to differences in volatility between the lanthanide metals.[55] In EuB6 and YbB6 the metals have an oxidation state of +2 whereas in the rest of the lanthanide hexaborides it is +3. This rationalises the differences in conductivity, the extra electrons in the LnIII hexaborides entering conduction bands. EuB6 is a semiconductor and the rest are good conductors.[26][55] LaB6 and CeB6 are thermionic emitters, used, for example, in scanning electron microscopes.[56]
Dodecaborides, LnB12, are formed by the heavier smaller lanthanides, but not by the lighter larger metals, La – Eu. With the exception YbB12 (where Yb takes an intermediate valence and is a Kondo insulator), the dodecaborides are all metallic compounds. They all have the UB12 structure containing a 3 dimensional framework of cubooctahedral B12 clusters.[52]
The higher boride LnB66 is known for all lanthanide metals. The composition is approximate as the compounds are non-stoichiometric.[52] They all have similar complex structure with over 1600 atoms in the unit cell. The boron cubic sub lattice contains super icosahedra made up of a central B12 icosahedra surrounded by 12 others, B12(B12)12.[52] Other complex higher borides LnB50 (Tb, Dy, Ho Er Tm Lu) and LnB25 are known (Gd, Tb, Dy, Ho, Er) and these contain boron icosahedra in the boron framework.[52]
Organometallic compounds
Lanthanide-carbon
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