Polyhedron Vol[ 06\ No[ 10\ pp[ 2666Ð2673\ 0887Þ 0887 Elsevier Science Ltd\ Pergamon All rights reserved[ Printed in Great Britain9166Ð4276:87 ,08[99¦9[99PII] SS916!6427"68#79907!44

Unusual coordination modes of multidentateligands^ crystal structure of

ð"""tmhd#2Y##1"hmteta#Łðtmhd � ButCOCHCOBut

andhmteta � Me1N"CH1CH1NMe#1CH1CH1NMe1Ł

Ian Baxter\a Simon R[ Drake\b Michael B[ Hursthouse\a� John McAleese\b

K[ M[ Abdul Malik\a D[ Michael P[ Mingos\b David J[ Otwayb\$ and John C[Plakatourasb

a Department of Chemistry\ University of Wales Cardi}\ P[O[ Box 801\ Park Place\ Cardi}\ CF0 2TB\U[K[

b Department of Chemistry\ Imperial College of Science\ Technology and Medicine\ South Kensington\London SW6 1AY\ U[K[

"Received 02 March 0887^ accepted 3 May 0887#

Abstract*The reaction of the hydrated lanthanide metal b!diketonate complexes ðLn"tmhd#2"H1O#Ł"tmhd�ButCOCHCOBut# with hexamethyltriethylenetetramine "hmteta�Me1N"CH1CH1NMe#1CH1CH1

NMe1# in n!hexane at room temperature yields the anhydrous\ bridged dimeric complexes\ð""tmhd#2Ln#1"hmteta#Ł\ where Ln�Gd 0 or Y 1[ An X!ray study of 1 shows that only three of the four possiblenitrogen atoms of the hmteta ligand are utilised in bonding to the yttrium centres[ The complexes are air andmoisture stable\ and more importantly both have good volatility\ thermal stability\ and mass transportproperties as demonstrated by sublimation\ di}erential scanning calorimetry "DSC# and thermal gravimetricanalysis "TGA#\ thus making them potential precursors for MOCVD application[ Þ 0887 Published by ElsevierScience Ltd[ All rights reserved

Keywords] gadolinium^ yttrium^ hmteta^ b!diketonate^ crystal structure

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INTRODUCTION

Metal alkoxides and b!diketonates have attracted alarge amount of interest because they are suitable asprecursors for electronic and ceramic materials ð0Ð7Ł[Metal oxides are of technological importance as solidoxide electrolytes\ e[g[ Y9[0Zr9[8O0[84 "at 799>C# orCe9[8Gd9[0O0[84 "at ca[ 499>C# ð8Ð00Ł[

Low temperature chemical vapour deposition

� Author to whom correspondence should be addressed[Tel[] ¦33!0111!763957^ Fax] ¦33!0111!763918^ E!mail]hursthouseÝcardi}[ac[uk[

$ E!mail] d[j[otwayÝic[ac[uk

2666

"LPCVD# routes to a wide range of metal oxide _lmshave been previously studied ð01\ 02Ł[ Our plan was touse either bulky or chelating alkoxide\ or b!diketonateligands\ thereby facilitating simple cleavage pathwaysand a}ord a reduction in the carbonaceous content ofthe _lms produced[ The rational behind this techniqueis based on studies by Bradley\ who demonstrated thedramatic e}ect of branching in the alkyl chain of aseries of Ta and Nb alkoxides ð03Ð06Ł[ Small changesin the molecular architecture of the ligands will alterphysical properties such as oligomerisation\ volatility\and mass transport ð8\ 07Ł[ It is an important require!ment when designing the molecular precursors thatsu.cient coordinative saturation is incorporated intoboth ligand and chelate\ such that low molecular mass

I[ Baxter et al[2667

volatile species will result which are air and moisturestable[ This approach is highly ~exible since LÐL maybe varied with the use of either O or N functionalisedchelates[

Herein we report that the reactions ofðLn"tmhd#2"H1O#Ł "Ln�Gd or Y# with hmteta to yieldthe dimeric bridged complexes ð""tmhd#2Ln#1

"hmteta#Ł\ where Ln is Gd 0 or Y 1[ The results of thecrystal structural studies for 1 are also described[

EXPERIMENTAL

General procedures and techniques

The complexes described are air and moisture stablebut were routinely prepared under nitrogen using tho!roughly degassed and dry solvents[ The startingmaterials Gd"tmhd#2=H1O and Y"tmhd#2=H1O wereobtained from Inorgtech[ Details of procedures andinstruments used were the same as described earlierð08Ł[

Synthesis of ð""tmhd#2Gd#1"hmteta#Ł 0

To a suspension of Gd"tmhd#2=H1O "9[202 g\9[4 mmol# in n!hexane "19 ml#\ hmteta "9[07 ml\0 mmol# was added[ The resulting suspension was stir!red until all starting material had dissolved over ca[34 min[ The resulting solution was then stripped todryness to yield a colourless oil[ The ~ask was turnedto spread the oil all over the surface and then wasclamped\ and the product crystallized in two days[Yield] 9[23 g\ 82)[ M[P[] 006Ð010>C[ Anal[] FoundC\ 46[97^ H\ 7[52^ N\ 2[47^ C67H033Gd1N3O01 requiresC\ 45[85^ H\ 7[73^ N\ 2[30)[ The complex sublimedintact between 004Ð049>C at 4×09−2 Torr\ m[p[ ofthe sublimed product] 014Ð017>C[ IR "Nujol\ n\ cm−0#]0478 "ms#\ 0464 "ms#\ 0426 "m#\ 0494 "m#\ 0301 "m#\0246 "m#\ 0170 "w#\ 0133 "w#\ 0113 "w#\ 0073 "w#\ 0026"w#\ 0980 "w#\ 0921 "w#\ 0906 "w#\ 846 "w#\ 820 "w#\757 "w#\ 681 "w#\ 647"w#\ 626 "w#\ 612 "w#\ 599 "w#\366 "w#[ "Hexachlorobutadiene\ n\ cm−0#] 1850 "s#\1890 "m\ sh#\ 0478 "vs#\ 0451 "vs#\ 0427 "s#\ 0494 "vs#\0369 "m#\ 0341 "s#\ 0302 "vs#\ 0277 "s#\ 0247 "s#\ 0170"w#\ 0133 "m#\ 0114 "m#\ 0020 "ms#\ 0958 "w#\ 0906"w#\ 659 "m#\ 626 "w#\ 599 "mw#[ UV:visible "n!hexanesolution\ l in nm#] 295\ 292\ 290\ 186\ 183189\ 176\ 173\ 171\ 179\ 166\ 164\ 161\ 155\ 159\ 109\194\ 087\ 084[ Mass spectrum] "EI¦^ m:u¦#\695 ðGd"tmhd#2Ł¦ "7)#\ 538 ðGd"tmhd#1"ButCOCHCOH#Ł¦ "40)#\ 412 ðGd"tmhd#1Ł¦ "099)#\353 ðGd"tmhd#"ButCOCHCOH#Ł¦ "8)#[

Synthesis of ð""tmhd#2Y#1"hmteta#Ł 1

Y"tmhd#2"H1O# "9[61 g\ 0[98 mmol# was dissolvedin n!hexane "09 ml# in a ~ame dried Schlenk[ To theclear colourless solution\ hmteta "9[18 ml\ 0[98 mmol#

was added and stirred for 0 h[ The solvent was thenremoved in vacuo and the Schlenk kept under vacuumat 54>C for 29 min[ On cooling to room temperature\the Schlenk was turned to spread the oil over its sur!face and then clamped on its side[ Large colourlessblocks crystallised over a period of 1 days with theSchlenk being turned every 13 h to spread the oil andinduce further crystallization[ Yield] 9[65 g\ 81)\m[p[] 098Ð001>C[ Anal[] Found\ C\ 50[42^ H\ 8[40^C67H033O01N3Y1 requires C\ 51[04^ H\ 8[45)[ Thecompound sublimes intact between 89Ð009>C at4×09−2 Torr forming crystals on the cold _nger andsome microcrystalline powder on the sides of thevessel[ The m[p[ of the sublimed solid was 009Ð002>C[IR "Nujol\ n cm−0#] 1616 "vw#\ 0598 "m#\ 0489 "m#\0465 "vs#\ 0429 "m#\ 0495 "s#\ 0306 "s#\ 0295 "w#\ 0134"w#\ 0115 "w#\ 0079 "w#\ 0030 "w#\ 0908 "vw#\ 851 "vw#\682 "vw#\ 648 "vw#\ 612 "w#\ 366 "vw#^ "hex!achlorobutadiene\ n cm−0#] 1851 "vs#\ 1891 "m#\ 1754"m#\ 0598 "s#\ 0489 "vs#\ 0428 "s#\ 0495 "vs#\ 0368 "m#\0341 "s#\ 0306 "vs#\ 0277 "s#\ 0248 "s#\ 0175 "vw#\ 0134"w#\ 0115 "m#\ 0068 "m#\ 0030 "m#\ 0915 "w#\ 594 "vw#\365 "w#[ 0H NMR "C5D5\ 169 MHz\ 19>C#] d 0[19 "s\097H\ CH2#\ 1[10 "s\ 5H\ NCH2#\ 1[23 "s\ 01H\N"CH2#1#\ 1[48 "d\ 01H\ NCH1#\ 4[75 "s\ 5H\ CH#[02C"0H# NMR "C5D5\ 56[83 MHz\ 19>C#] d 17[25 "s\CH2#\ 39[21 "s\ C"CH2#2#\ 31[44 "s\ NCH2#\ 34[49 "s\N"CH2#1#\ 43[86\ 44[56\ 46[38 "s\ NCH1#\ 89[62 "s\CH#\ 087[67 "s\ CO#[ Mass spectrum] "EI¦^ m:u¦#\ 527ðY"tmhd#2Ł¦ "01)#\ 470 ðY"tmhd#1"ButCOCHCOH#Ł¦

"53)#\ 344 ðY"tmhd#1Ł¦ "099)#\ 286 ðY"tmhd#"ButCOCHCOH#Ł¦ "5)#\ 161 ðY"tmhd#Ł¦ "2)#[

X!ray crystallo`raphy for ð"Y"tmhd#2#1"hmteta#Ł 1

Crystal data C67H027N3O01Y1\ Mr 0490[63\ triclinic\a�09[163"3#\ b�10[912"8#\ c�10[309"8# A� \a�57[47"1#\ b�75[08"2#\ g�71[82"2#>\ U�3160"2#A� 2\ space group P0¹ "No[ 1#\ Z�1\ m"MoÐKa#�03[96 cm−0\ l�9[60958 A� \ T�049 K\ crystalsize 9[19×9[04×9[02 mm[

Crystallographic measurements were made using aDelft instruments FAST TV area detector di}ract!ometer equipped with a rotating anode "Mo# gen!erator by following previously described proceduresð19Ł[ Total data "0[86¾u¾14[59>^ −00¾h¾8\−12¾k¾12\ −13¾l¾03# collected 02851\ 01912unique "Rint�9[9654#[ The crystal was weaklydi}racting and relatively few data were observed\ butthe structure was successfully solved by directmethods "SHELXS75# ð10Ł and di}erence synthesis\and re_ned on F1 by full!matrix least!squares"SHELXL82# ð11Ł[ Absorption e}ects were ignored[All nonhydrogen atoms were anisotropic[ The hydro!gen atoms were included in calculated positions "rid!ing model# with Uiso tied to the Ueq of the parentatoms[ One of the t!butyl groups ðpivot atom C"01#Łwas orientationally disordered\ and its three methylgroups were re_ned each with partial occupancies

Unusual coordination modes of multidentate ligands 2668

"9[57 and 9[21#[ Final R0 "on F\ 0445 data withFo×3s"Fo#Ł�9[9503\ wR1 "on F1\ all 01912 data\ 813parameters#�9[1678\ w�0:ðs1"Fo

1#Ł[ Sources of scat!tering factors as in Ref[ ð11Ł[ The diagram was drawnwith SNOOPI ð12Ł[ The calculations were done on aPentium 199 MHz personal computer[ Full details ofcrystallographic results have been deposited withCambridge Crystallographic Data Centre\ Ref[ No[CCDC!090004[

RESULTS AND DISCUSSION

Synthesis

A range of synthetic routes has been used for thepreparation of metal alkoxides or b!diketonates ð13Ð22Ł[ There are several features that may be noted forthe synthesis of such materials\ i[e[ "a# the syntheticstrategy of using a preformed metal b!diketonate"either anhydrous or a hydrate# leads to water freeproducts ð22Ł\ "b# the coordinative saturation of themetal centre by the multidentate chelate and b!dike!tonates leads to air and moisture stable precursors ofknown stoichiometry and is thus highly ~exible sinceLÐL may be varied with the use of either O! or N!functionalised chelates\ "c# The designed synthesis ofvolatile molecular metal organics is possible withouthaving to use sterically hindered ligands[ The mul!tidendate amine "LÐL# forces the complex into amolecular regime\ thereby removing the possible inter!actions between the monomers and increasing thevolatility and mass transport properties of the com!plexes[

Physical properties

Compounds 0 and 1 are both highly soluble in arange of organic solvents[ This pronounced solubilityeven in nonpolar aliphatic hydrocarbon solvents "i[e[n!hexane# is most likely to be due to the coordinativesaturation of the metal atoms in these complexes[Another important property is their excellent stabilityto both air and moisture[

Both 0 and 1 show a signi_cant drop "ca[ 59>C# intheir melting points on complexation with the amineligand[ Complex 0 melts at 006Ð010>C\ whereas theparent compound Gd"tmhd#2=H1O melts at 069Ð061>C[ It sublimes intact between 004Ð049>C at4×09−2 torr over 0[4 h[ The large colourless crystalsobtained for compound 1 melt cleanly at 098Ð001>Ccompared with 059Ð054>C for ðY"tmhd#2"H1O#Ł and66Ð70>C for ð""tmhd#2Y#1"triglyme#Ł "triglyme�MeOCH1OCH1OCH1OMe# ð22Ł[ Compound 1 sub!limes intact between 89Ð009>C at 4×09−2 Torr over0 h forming crystals on the cold _nger and some micro!crystalline powder on the sides of the vessel[

Infrared spectra

The infrared bands for 0 and 1 "experimental sec!tion# are comparable with those in other hydratedand anhydrous b!diketonates ð07\ 23Ł[ The only realdi}erence from the spectra of the parent compounds isthe presence of the amine n"CÐN# stretch at 0039 cm−0^this is a shift of ca[ 29 cm−0 over the free ligand andindicative of coordinated amine with relatively weakMÐN bonding[

NMR spectra

The 0H and 02C"0H# NMR spectra of 1 were runin C5D5 but due to large paramagnetic NMR shift ofthe Gd2¦ metal nucleus no spectra could be obtainedfor 0[ The 0H NMR spectrum of 1 in C5D5 shows boththe tmhd and hmteta ligands as well resolved peaks[The hmteta protons are split into three groups^ singletsfor 5H "ÐNCH2# and 01H "ÐN"CH2#1# and a doubletfor 01H "ÐNCH1Ð#[ Integration for the complex givesa tmhd]hmteta ratio of 5]0[ The 02C"0H# NMR spec!tra reveals only one environment for the tmhd andamine ligand\ suggesting that either the complex existsin solution as a symmetrically bonded dimer or a rapidexchange process is occurring[

Mass spectrometry

In the mass spectra for complexes 0 and 1 the high!est molecular mass ions observed for these complexesare due to the ðLn"tmhd#2Ł¦ species at 694 and 527amu respectively[ Other intense peaks are noted in theexperimental\ in particular ðLn"tmhd#1Ł¦ at 412 and344 amu\ and below this breakup of the tmhd groups isalso seen[ The isotope patterns of the metal containingcomplexes are consistent with those obtained from thenatural abundance patterns or by computer simu!lation[ The m:z ratios relate to the isotopes of greatestnatural abundance\ e[g[ 046Gd and 78Y[

The above data suggest that in the vapour phaseunder high vacuum conditions "09−7 Torr# these com!plexes dissociate to form the oligomeric donor!Lewisbase free complexes\ Ln1"tmhd#5[ Such behaviour isstill an important observation since the materials maybe used under atmospheric conditions very e}ectivelyor at low vacuum "ca[ 09−2 Torr# conditions as molec!ular precursors for Ln1O2\ or other ternary oxidessuch as YBa1Cu2O6−x[ The fact that the Lewis base"amine# is not coordinated to the metals under theconditions used here has been noted previously forlanthanide complexes ð24\ 25Ł[

TGA:DSC studies

Both the hydrated starting materials and the aminestabilised products were subjected to thermal analysis[The results show that the addition of an amine ligand

I[ Baxter et al[2679

to the hydrated species removes any coordinatedwater and more importantly it signi_cantly reducesthe decomposition point with respect to the parenthydrate compounds[ The TGA and DSC plots for 1

are shown in Fig[ 0[The DSC of 0 shows two distinct endotherms over

the range 099Ð299>C[ The _rst\ centred at 027[66>C"−7[50 mcal:mg#\ corresponds to the melting point ofthe compound[ The second\ broad peak\ centred at129[57>C "−23[04 mcal:mg#\ correlates well with itscomplete\ intact sublimation observed in the TGAplot between 079 and 179>C[ A very small residue of1[64) is probably due to a small amount of car!bonaceous material left[

The DSC of 1 shows an endotherm between 009Ð024>C "−6[27 mcal:mg# corresponding to the meltingpoint\ and two more endotherms ð065Ð134>C"−3[75 mcal:mg# and 134Ð179>CŁ due to sublimation

Fig[ 0[ The DSC and TGA plot for ð""tmhd#2Y#1"hmteta#Ł "1#[

of the complex into the vapour phase[ The TGA plotis consistent with these observations^ namely a sub!limation of 86[3) of the complex over the range 049Ð179>C leaving a _nal residue of 1)[

X!ray structure of ð"Y"tmhd#2#1"hmteta#Ł 1

A single crystal structural study of complex 1 wasundertaken to unambiguously identify its structuralcomposition and to determine whether all of thepotential N!donor sites were bound to the yttriummetal centres[ The solid state structure of 1 is shownin Fig[ 1 and selected bond lengths and angles aregiven in Table 0[

The structure is a dimer based on two Y"tmhd#2units linked by a hmteta ligand in an unusual bondingmode[ The amine ligand acts simultaneously as a che!

Unusual coordination modes of multidentate ligands 2670

Fig[ 1[ X!ray structure of ð""tmhd#2Y#1"hmteta#Ł 1^ the tert!butyl methyl groups are omitted for clarity[ Thermal ellip!

soids are drawn at 49) probability level[

late ðto Y"1#Ł\ terminal ligand ðto Y"0#Ł and as a bridg!ing ligand via the central ethylene bridges[ This modeof bonding of the potentially tetradentate hmtetaligand appears to be unique^ such ligands are normallyfound to form two chelates involving all the four nitro!gen atoms as observed in ðBa"hfpd#1"hmteta#Ł"hfpd�0\0\0\4\4\4!hexafluoropentane!1\3!dionate#ð21Ł[ The binuclear structure observed for 1 does notpermit utilisation of all the four potential nitrogenbinding sites and this raises the question why the situ!ation is di}erent from the related triglyme bridgedcomplex ð"Y"tmhd#2#1"triglyme#Ł ð22Ł in which all thefour oxygen atoms are involved in bonding with themetal atoms[

The environments of the two metal centres\ Y"0#and Y"1#\ illustrated in Fig[ 2\ are signi_cantly di}er!ent and may be explained by the asymmetric bridgingof the amine ligand[ Y"0# is bonded to six oxygensfrom three chelating tmhd ligands and one nitrogenfrom the bridging hmteta ligand[ This atom is seven

coordinate with a geometry best described as distortedmonocapped trigonal prismatic[ Two of the tmhdligands are chelated along the edges of a square face ofthe trigonal prism\ whereas the third tmhd is chelatingfrom the capping atom to an apex of the prism[ Theremaining apical site of the prism is occupied by onenitrogen atom from the amine ligand[ The coor!dination around Y"1# consists of six oxygens fromthree chelating tmhd ligands\ as well as two nitrogensfrom the hmteta ligand forming a 4!memberedchelate[ Y"1# is thus eight coordinate with a squareantiprismatic geometry[ The chelation of the ligandsaround this metal is interesting in that two tmhdligands are chelating along the edges of square faceswhereas the third tmhd and the hmteta ligands chelatebetween the two square faces[ It is to be noted thatyttrium resembles the lanthanide elements in mostrespects and can easily accommodate a high coor!dination number such as eight[ In fact octa!coor!dination is a common feature observed in di}erentyttrium complexes with b!diketonate and alkoxideligands\ and examples include species with variousdegrees of oligomerisation\ e[g[ ðY"pd#2"H1O#1Ł=H1O"monomer# "pd�pentane!0\2!dionate# ð26Ł\ð""tmhd#2Y#1"triglyme#Ł "dimer# ð22Ł\ ðY1"pd#3"O1

CCH2#1"H1O#1Ł "dimer# ð27Ł and ðY2"pd#3"OCH1CH1OMe#4Ł "trimer# ð28Ł[ The geometry aboutyttrium in all these complexes is distorted square anti!prismatic[ There are\ however\ examples of lowercoordination numbers for yttrium\ e[g[\ the hexa!coor!dinated oxide Y1O2 and the hepta!coordinatedmethoxyethoxide {{Y"OC1H3OMe#2||[ The last com!pound was shown to be a centrosymmetric cyclicdecamer ð"Y"OC1H3OMe#2#09Ł ð39Ł\ in which all the_ve unique yttrium atoms have pentagonal bipyr!amidal geometry[ This compound also appears to bethe highest oligomer structurally characterised forhomoleptic metal alkoxides[

The Y"1#ÐN bond lengths are quite asymmetricð1[551"7#\ 1[605"7# A� Ł\ with the terminal NMe1 groupbinding closer to the metal centre[ In contrast\ theY"0#ÐN bond length involving only the terminal nitro!gen from the other NMe1 group at 1[597"7# A� is muchshorter[ These di}erences in the YÐN bond lengthscan be explained by the di}ering coordination num!bers for the two yttrium atoms and also by the stericfactors[ The bonding of hmteta in the present com!pound has no immediately accessible comparison inLnÐN chemistry\ but may be contrasted with that inthe barium compound ðBa"hfpd#1"hmteta#Ł ð22Ł[ In thiscompound\ which is monomeric\ all four nitrogenatoms of hmteta are bonded to barium forming twonearly symmetrical chelate rings ðBaÐN distance1[852"2#Ð2[911"09# A� Ł\ with quite acute NÐBaÐN che!late angles\ 51[0"2# and 50[3"2#>[ The hmteta ligandcan bind to barium in this way because the largerradius of Ba1¦ "0[38 A� # supports the higher coor!dination number compared with Y2¦ "0[93 A� # ð30Ł[

The YÐO bond lengths involving the b!diketonateligands lie in the range 1[100"5#Ð1[227"6#\ average

I[ Baxter et al[2671

Table 0[ Selected bond lengths "A� # and angles "># for ð""tmhd#2Y#1"hmteta#Ł 1

Y"0#ÐO"5# 1[100"5# Y"0#ÐO"1# 1[120"6#Y"0#ÐO"3# 1[126"5# Y"0#ÐO"0# 1[159"6#Y"0#ÐO"4# 1[159"6# Y"0#ÐO"2# 1[204"6#Y"0#ÐN"0# 1[597"7# Y"1#ÐO"00# 1[124"6#Y"1#ÐO"8# 1[135"5# Y"1#ÐO"03# 1[179"6#Y"1#ÐO"02# 1[173"6# Y"1#ÐO"01# 1[185"7#Y"1#ÐO"09# 1[227"6# Y"1#ÐN"3# 1[551"7#Y"1#ÐN"2# 1[606"7#

O"5#ÐY"0#ÐO"1# 79[0"2# O"5#ÐY"0#ÐO"3# 88[2"1#O"1#ÐY"0#ÐO"3# 66[1"2# O"5#ÐY"0#ÐO"0# 003[8"2#O"1#ÐY"0#ÐO"0# 62[9"1# O"3#ÐY"0#ÐO"0# 017[8"1#O"5#ÐY"0#ÐO"4# 63[7"2# O"1#ÐY"0#ÐO"4# 017[7"2#O"3#ÐY"0#ÐO"4# 049[9"2# O"0#ÐY"0#ÐO"4# 67[3"2#O"5#ÐY"0#ÐO"2# 72[2"2# O"1#ÐY"0#ÐO"2# 032[3"1#O"3#ÐY"0#ÐO"2# 62[5"1# O"0#ÐY"0#ÐO"2# 032[3"1#O"4#ÐY"0#ÐO"2# 65[3"2# O"5#ÐY"0#ÐN"0# 051[7"2#O"1#ÐY"0#ÐN"0# 005[2"2# O"3#ÐY"0#ÐN"0# 79[4"2#O"0#ÐY"0#ÐN"0# 66[9"2# O"4#ÐY"0#ÐN"0# 85[6"2#O"2#ÐY"0#ÐN"0# 79[0"2# O"00#ÐY"1#ÐO"8# 76[0"2#O"00#ÐY"1#ÐO"03# 049[5"2# O"8#ÐY"1#ÐO"03# 63[8"2#O"00#ÐY"1#ÐO"02# 096[6"2# O"8#ÐY"1#ÐO"02# 039[6"2#O"03#ÐY"1#ÐO"02# 64[2"2# O"00#ÐY"1#ÐO"01# 63[1"2#O"8#ÐY"1#ÐO"01# 65[5"2# O"03#ÐY"1#ÐO"01# 68[0"2#O"02#ÐY"1#ÐO"01# 62[0"2# O"00#ÐY"1#ÐO"09# 68[6"2#O"8#ÐY"1#ÐO"09# 62[9"2# O"03#ÐY"1#ÐO"09# 004[5"2#O"02#ÐY"1#ÐO"09# 033[2"2# O"01#ÐY"1#ÐO"09# 039[5"2#O"00#ÐY"1#ÐN"3# 025[7"2# O"8#ÐY"1#ÐN"3# 005[9"2#O"03#ÐY"1#ÐN"3# 61[5"2# O"02#ÐY"1#ÐN"3# 67[0"2#O"01#ÐY"1#ÐN"3# 032[6"2# O"09#ÐY"1#ÐN"3# 62[7"2#O"00#ÐY"1#ÐN"2# 61[7"2# O"8#ÐY"1#ÐN"2# 034[0"2#O"03#ÐY"1#ÐN"2# 022[5"2# O"02#ÐY"1#ÐN"2# 62[6"2#O"01#ÐY"1#ÐN"2# 011[1"2# O"09#ÐY"1#ÐN"2# 64[4"2#N"3#ÐY"1#ÐN"2# 56[8"2#

Fig[ 2[ The coordination sphere around ð""tmhd#2Y#1"hmteta#Ł 1[

1[155 A� \ and are close to the values in other complexesð22\ 26Ð28\ 31Ł[ Close examination of the individualYÐO distances in 1 indicate that only one tmhd ligandðcontaining O"02# and O"03# and chelated to Y"1#Ł is

nearly symmetric whilst the remaining _ve tmhdligands are chelated quite asymmetrically[ Not unex!pectedly\ the Y"1#ÐO distances ð1[124"6#Ð1[227"6#\average 1[17 A� Ł are in general longer than the Y"0#ÐO

Unusual coordination modes of multidentate ligands 2672

distances ð1[100"5#Ð1[203"6#\ average 1[14 A� Ł re~ectingthe greater steric crowding around Y"1#[

The geometry parameters involving the hmteta andtmhd ligands are as expected[ The hmteta chelate isnonplanar with a relative l conformation[ The OC2Oskeletons of one tmhd ligand chelated to Y"1# showssigni_cant deviations from planarity ðatomic devi!ations −9[978Ð9[011"1# A� Ł whilst the other tmhdligands chelated to Y"I# and Y"1# are almost planarðatomic deviations ¾9[92"1# A� Ł[ The six!memberedM"O1C2# chelates are also nonplanar with fold anglesof 6[8Ð10[6"2#> about the O===O axes[ These defor!mations observed in coordinated tmhd ligands maybe attributed to steric factors and re~ect the ~exiblenature of such ligands[

CONCLUSION

Recent developments in organo!lanthanide chem!istry have shown that the chemistry of these metalsmay be controlled by varying the steric environmentaround the metal[ We have applied the above strategyto a range of lanthanides\ including Y\ Tb\ Pr\ Eu andGd\ e[g[ ð""tmhd#2Y#1"triglyme#Ł is a dimeric air stablehighly volatile precursor ð21Ł[ This technique worksbecause the lanthanide complexes are hard acidswhich are coordinatively unsaturated\ and will reactwith multidendate Lewis bases which will {{plug|| vac!ant coordination sites and even displace water fromhydrated species\ as for yttrium above[ Given that wecan use either O or N functionalised chelating ligands\we are now in a position to tailor the coordinationenvironment of the metal quite speci_cally[

Acknowled`ementsWe thank the EPSRC "D[J[O[\ M[B[H[\K[M[A[M[ and J[C[P[#\ the CASE sponsor Inorgtech\ andfor the STA equipment\ the Leverhulme Trust "J[M[#\ theRoyal Society "for an inert atmosphere glove!box and otherancillary equipment# and B[P[ for endowing D[M[P[M[|schair[

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