Hydrothermal synthesis and characterization of an unusual polyoxovanadium borate cluster: structure of Rb4[(VO)6{ {B10O16(OH)6} }2] · 0.5H2O

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Pergamon PII] S9166Ð4276"86#99284Ð0

Polyhedron Vol[ 06\ No[ 05\ pp[ 1488Ð1594\ 0887 Þ 0887 Elsevier Science Ltd All rights reserved[ Printed in Great Britain 9166Ð4276:87 ,08[99¦9[99

Hydrothermal synthesis and characterization of an unusual polyoxovanadium borate cluster] structure of Rb3ð"VO#5" B09O05"OH#5# 1Ł = 9[4H1O Christopher J[ Warren\a\$ Job T[ Rijssenbeek\a David J[ Rose\b Robert C[ Haushaltera$ and Jon Zubietab a

NEC Research Institute\ 3 Independence Way\ Princeton\ NJ 97439\ U[S[A[

b

Department of Chemistry\ Syracuse University\ Syracuse\ NY 02133\ U[S[A[ "Received 05 June 0886^ accepted 13 September 0886#

Abstract*The hydrothermal reaction of RbVO2\ "NH3#1B3O6 = 3H1O\ ethylenediamine "en#\ and H1O in a mole ratio of 0]7]1]024 heated at 069>C for 4 days produces pale green crystals of the novel polyoxovanadium borate cluster compound Rb3ð"VO#5"B09O05"OH#5#1Ł = 9[4H1O "0# which contains ðV5B19O27"OH#01Ł3− clusters\ each cluster comprising a nearly hexagonal ring of six trans!edge!sharing VO4 square pyramids capped on each side by a B09O05"OH#57− triangle[ The ðV5B19O27"OH#01Ł3− clusters are separated in the solid state by Rb¦ cations[ Magnetic susceptibility and valence sum calculations indicate that all six of the vanadium atoms in the cluster are in the 3¦ oxidation state[ Þ 0887 Elsevier Science Ltd[ All rights reserved[ Þ 0887 Elsevier Science Ltd[ All rights reserved Keywords] hydrothermal synthesis^ polyoxovanadium borates^ polyoxometalates^ X!ray structures[ ———————————————————————————————————————————————

INTRODUCTION The chemistry of polyoxometalates incorporates a rich and diverse agglomeration of compounds unique in their topological and electronic properties\ making them applicable in _elds ranging from analytical and clinical chemistry\ to catalysis "including pho! tocatalysis#\ biochemistry "electron transport inhi! bition#\ medicine "antitumoral and antiviral#\ and solid state devices ð0Ł[ Metal!metal interactions in the oxo clusters range from very weak "virtually none# to very strong "metal!metal bonding# and can be con! trolled by choice of metal "2d\ 3d\ 4d#\ electron popu! lation "degree of reduction#\ and extent of protonation[ It has been observed that mixed!valence vanadates\ in particular\ show highly variable capacit! ies for unpaired electrons\ and many form clusters

Author to whom correspondence should be addressed[ $Current mailing address] SymyX Technologies\ 2099 Central Expressway\ Santa Clara\ CA 84940\ U[S[A[

containing highly symmetrical core assemblies of VOx units that can adopt quasi!spherical structures ð1Ł[ Although the chemistry of the polyoxovanadates "a subset of the polyoxometalates# is very diverse\ only a few structural motifs\ which are based largely on edge and corner sharing VO4 square pyramids\ are actually observed ð2Ł[ The polyoxovanadium borates "a subset of the polyoxovanadates# remain largely unexplored\ and although a large number of borate mineral structures are known ð3Ł\ synthetically pre! pared and structurally characterized examples are rare ð4Ł[ Having recently isolated the polyoxovana! dium borates "enH#"enH1#3ð"VO#01B06O27"OH#7Ł = H1O "en  ethylenediamine# and "enH1#4ð"VO#01O5 "B2O5"OH##5Ł = H1O ð5Ł\ which were prepared by hydrothermal synthetic techniques\ we were encour! aged to further explore this potentially rich and struc! turally diverse system[ We report herein the synthesis of a novel polyoxovanadium borate cluster species\ Rb3ð"VO#5"B09O05"OH#5#1Ł = 9[4H1O "0#\ containing a hexavanadate core and polyborate ligands of unpre! cedented structure[

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General Compound "0# was prepared by the hydrothermal reaction of RbVO2 "9[003 g# "NH3#1B3O6 = 3H1O "0[29 g#\ ethylenediamine "9[963 g#\ and H1O in a 0]7]1]024 molar ratio heated at 069>C for 4 days[ The syntheses were conducted in 12 mL poly! tetra~uoroethylene!lined acid digestion bombs _lled to ca[ 7) at room temperature[ In all cases\ the borate was added _rst\ followed by the vanadium source\ water\ and _nally the amine[ This preparation gave a nearly single phase of pale green plate!shaped crystals of Rb3ð"VO#5"B09O05"OH#5#1Ł = 9[4H1O "0# which were isolated in approximately 34) yield with a minor phase "ca[ 0Ð1)# of orange crystals[ An X!ray struc! tural analysis of the orange crystals revealed that they contained the previously characterized ð"VO#01O5"B2O5"OH##5Ł09− cluster ð5Ł[ The role of the ethylenediamine "en# in the preparation is currently under investigation as this species appears to be needed in the syntheses "perhaps to adjust the pH of the reactions which are typically in the 7Ð8 range# although it is not incorporated in the _nal structure[ Indeed\ experiments using equimolar amounts of 0\2! diaminopropane "DAP# in place of en resulted in nearly the same yield of "0#\ but if neither en nor DAP are used\ no crystals are obtained ð6Ł[ Crystallo`raphy A single crystal of "0# having approximate dimen! sions of 9[06×9[01×9[00 mm was mounted on a glass _ber[ A total of 03\196 re~ections were collected on a Siemens SMART system equipped with a CCD detec! tor at 182 K in the u range of 1[97> to 17[14>\ of which 4289 "Rint9[9345# were considered observed ð"Ir2[9s "I#Ł and 4273 were used in the _nal re_ne! ment[ The structure was solved by direct methods and re_ned by full!matrix least!squares on F1 using SHELXTL[ All of the non!hydrogen atoms were re_ned with anisotropic displacement parameters[ The Rb¦ atoms were disordered and re_ned with 49) occupancy factors[ The _nal cycle of least!squares using 310 variable parameters converged with R"Rw#9[9255"9[9361# and a goodness!of!_t value of 0[910[ The largest "smallest# peak in the _nal di}erence  −2[ Further details of the map was 9[836"−9[471# eA X!ray structural analysis are given in Table 0\ and some selected bond lengths and angles are given in Table 1[ A complete listing of atomic coordinates\ thermal parameters and Fobs:Fcalc values have been deposited at the Cambridge Crystallographic Data Centre[ Ma`netic Susceptibility Magnetic susceptibility measurements were done on a Quantum Design MPMS SQUID magnetometer[

Table 0[ Crystallographic Data for Rb3ð"VO#5 "B09O05"OH#5#1Ł = 9[4H1O Formula FW Crystal Color\ Habit # a"A # b"A # c"A b">#  2# V"A Z Space Group Dcalc"g¾cm−2# m "mm−0# Crystal Size "mm# u range for Data Collection "># No[ of Data Collected Data Ir2s"I# No[ of Variables Final R:Rw

Rb3V5B19O49[4H6 0567[17 Green\ Plate 00[8821"2# 01[63379"09# 03[8403"1# 84[6219"09# 1162[74"3# 1 P 10:n "No[03# 1[341 4[463 9[06x9[01x9[00 1[97 to 17[14 03196 4289 319 9[9255:9[93461

The data from 099 to 299 K were _t to the CurieÐ Weiss law and gave an e}ective moment per vanadium atom of 0[60 mB[ This agrees well with the theoretical value of 0[62 mB for a free spin d 0 "V3¦# system[ RESULTS AND DISCUSSION clusters in Rb3ð"VO#5 The V5B19O49 "B09O05"OH#5#1Ł = 9[4H1O "0# can be visualized most easily as being composed of a nearly hexagonal ring of six trans!edge!sharing VO4 square pyramids "Fig[ 0# capped on each side by a B09O05"OH#57− triangle "Fig[ 1#[ All six of the terminal vanadyl "V1O# groups in this hexagonal vanadate\ whose toroid structure is unprecedented among polyoxometalate species\ radi! ate outwardly from the cluster\ and have VÐO bond  [ The distances ranging from 0[501"1#Ð0[513"1# A B09O05"OH#57− caps are composed of three fused B2O4"OH#23− FBB|s "fundamental building blocks# ð7Ł that share oxygen atoms with a central tetrahedral BO3 group[ This tetrahedral BO3 group possesses a terminal BÐO− bond that is collinear with the pseudo 2¹ axis of the cluster\ and the two B09O05"OH#57− caps are related by twofold symmetry about one of the three two!fold axes bisecting the vanadium ring[ Of the six!OH groups that radiate out from the triangular B09O05"OH#57− units\ three are bonded to trigonal planar boron atoms and have BÐO bond distances  \ while the other ranging from 0[274"3#Ð0[267"3# A three "which were identi_ed using valence bond cal! culations# ð8Ł are shared between adjacent tetrahedral boron atoms having BÐO bond distances ranging from  [ The central tetrahedral BO3 0[314"3#Ð0[328"3# A group has three internal BÐO bond distances of  \ and a signi_cantly 0[384"3#\ 0[382"3#\ and 0[377"3# A  shorter terminal BÐO bond distance of 0[313"3# A

Hydrothermal synthesis and characterization of an unusual polyoxovanadium borate cluster

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 # and Bond Angles "># in Rb3ð"VO#5"B09O05"OH#5#1Ł = 9[4H1O Table 1[ Selected Bond Lengths "A V"0#ÐO"0# V"0#ÐO"3# V"0#ÐO"7# V"0#ÐV"1# V"1#ÐO"7# V"1#ÐO"00# V"1#ÐV"2# V"2#ÐO"02#(0 V"2#ÐO"3#(0 V"2#ÐV"0#(0 O"3#ÐV"2#(0 O"4#ÐB"0# O"5#ÐB"0# O"6#ÐB"5#(0 O"7#ÐB"1# O"8#ÐB"2# O"09#ÐB"7# O"00#ÐB"2# O"01#ÐB"2# O"02#ÐV"2#(0 O"03#ÐB"4# O"04#ÐB"8# O"05#ÐB"3# O"06#ÐB"4# O"07#ÐB"5# O"08#ÐB"4# O"10#ÐB"6# O"11#ÐB"6# O"13#ÐB"8# B"2#ÐO"05#(0 B"5#ÐO"6#(0 B"09#ÐO"6#(0

0[501"1# 0[852"1# 0[857"1# 2[9647"6# 0[837"1# 0[845"1# 2[9028"6# 0[840"1# 0[859"1# 2[9370"6# 0[859"1# 0[323"3# 0[342"3# 0[421"3# 0[346"3# 0[415"3# 0[244"3# 0[370"3# 0[369"3# 0[840"1# 0[415"3# 0[248"3# 0[322"3# 0[363"3# 0[324"3# 0[353"3# 0[257"3# 0[274"3# 0[267"3# 0[328"3# 0[421"3# 0[382"3#

V"0#ÐO"02# V"0#ÐO"06# V"0#ÐV"2#(0 V"1#ÐO"1# V"1#ÐO"19# V"1#ÐO"06# V"2#ÐO"2# V"2#ÐO"19# V"2#ÐO"00# O"3#ÐB"0# O"4#ÐB"1# O"5#ÐB"6# O"6#ÐB"09#(0 O"6#ÐB"0# O"8#ÐB"09#(0 O"8#ÐB"1# O"09#ÐB"1# O"01#ÐB"7# O"02#ÐB"3# O"03#ÐB"09# O"03#ÐB"3# O"04#ÐB"3# O"05#ÐB"2#(0 O"07#ÐB"4# O"08#ÐB"8# O"19#ÐB"5# O"10#ÐB"5#(0 O"12#ÐB"7# O"14#ÐB"09# B"5#ÐO"10#(0 B"09#ÐO"8#(0

0[833"1# 0[856"1# 2[9370"6# 0[513"1# 0[841"1# 0[859"1# 0[519"1# 0[844"1# 0[860"1# 0[355"3# 0[314"3# 0[246"3# 0[382"3# 0[425"3# 0[376"3# 0[431"3# 0[353"3# 0[255"3# 0[356"3# 0[384"3# 0[418"3# 0[358"3# 0[328"3# 0[318"3# 0[260"3# 0[366"3# 0[352"3# 0[273"4# 0[313"3# 0[352"3# 0[376"3#

O"0#ÐV"0#ÐO"02# O"02#ÐV"0#ÐO"3# O"02#ÐV"0#ÐO"06# O"0#ÐV"0#ÐO"7# O"3#ÐV"0#ÐO"7# O"0#ÐV"0#ÐV"2#(0 O"3#ÐV"0#ÐV"2#(0 O"7#ÐV"0#ÐV"2#(0 O"02#ÐV"0#ÐV"1# O"06#ÐV"0#ÐV"1# V"2#(0ÐV"0#ÐV"1# O"1#ÐV"1#ÐO"19# O"1#ÐV"1#ÐO"00# O"19#ÐV"1#ÐO"00# O"7#ÐV"1#ÐO"06# O"00#ÐV"1#ÐO"06# O"7#ÐV"1#ÐV"2# O"00#ÐV"1#ÐV"2# O"1#ÐV"1#ÐV"0# O"19#ÐV"1#ÐV"0# O"06#ÐV"1#ÐV"0# O"2#ÐV"2#ÐO"02#(0 O"02#(0ÐV"2#ÐO"19# O"02#(0ÐV"2#ÐO"3#(0 O"2#ÐV"2#ÐO"00# O"19#ÐV"2#ÐO"00# O"2#ÐV"2#ÐV"1# O"19#ÐV"2#ÐV"1# O"00#ÐV"2#ÐV"1# O"02#(0ÐV"2#ÐV"0#(0

095[75"00# 66[92"8# 80[56"8# 000[76"00# 89[73"8# 007[61"8# 27[87"5# 006[05"5# 006[37"6# 27[24"5# 010[05"1# 097[31"00# 097[16"00# 67[80"8# 65[36"8# 031[11"8# 006[17"6# 39[93"5# 019[29"8# 005[94"6# 27[42"5# 098[63"00# 039[20"8# 65[82"8# 098[58"00# 67[37"8# 010[55"8# 28[37"5# 28[58"5# 27[30"5#

O"0#ÐV"0#ÐO"3# O"0#ÐV"0#ÐO"06# O"3#ÐV"0#ÐO"06# O"02#ÐV"0#ÐO "7# O"06#ÐV"0#ÐO"7# O"02#ÐV"0#ÐV"2#(0 O"06#ÐV"0#ÐV"2#(0 O"0#ÐV"0#ÐV"1# O"3#ÐV"0#ÐV"1# O"7#ÐV"0#ÐV"1# O"1#ÐV"1#ÐO"7# O"7#ÐV"1#ÐO"19# O"7#ÐV"1#ÐO"00# O"1#ÐV"1#ÐO"06# O"19#ÐV"1#ÐO"06# O"1#ÐV"1#ÐV"2# O"19#ÐV"1#ÐV"2# O"06#ÐV"1#ÐV"2# O"7#ÐV"1#ÐV"0# O"00#ÐV"1#ÐV"0# V"2#ÐV"1#ÐV"0# O"2#ÐV"2#ÐO"19# O"2#ÐV"2#ÐO"3#(0 O"19#ÐV"2#ÐO"3#(0 O"02#(0ÐV"2#ÐO"00# O"3#(0ÐV"2#ÐO"00# O"02#(0ÐV"2#ÐV"1# O"3#(0ÐV"2#ÐV"1# O"2#ÐV"2#ÐV"0#(0 O"19#ÐV"2#ÐV"0#(0

009[93"00# 096[27"00# 031[46"8# 030[14"8# 64[71"8# 27[46"5# 007[05"6# 019[94"g# 006[25"6# 27[99"5# 098[70"00# 030[61"8# 89[83"8# 098[41"00# 78[10"8# 008[79"8# 28[45"5# 005[91"6# 27[36"5# 006[32"6# 008[78"1# 098[84"00# 097[19"00# 89[47"8# 77[45"8# 031[95"8# 003[63"6# 005[81 "6# 008[30"8# 005[44"6# continued

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C[ J[ Warren et al[ Table 1*continued[ O"3#(0ÐV"2#ÐV"0#(0 V"1#ÐV"2#ÐV"0# (0 B"0#ÐO"3#ÐV"0# B"1#ÐO"4#ÐB"0# B"09#(0ÐO"6#ÐB"5#(0 B"5#(0ÐO"6#ÐB"0# B"1#ÐO"7#ÐV"0# B"09#(0ÐO"8#ÐB"2# B"2#ÐO "8#ÐB "1# B"2#ÐO"00#ÐV"1# V"1#ÐO"00#ÐV"2# B"3#ÐO"02#ÐV"0# V"0#ÐO"02#ÐV"2#(0 B"09#ÐO"03#ÐB"3# B"4#ÐO"04#ÐB"3# B"4#ÐO"06#ÐV"1# V"1#ÐO"06#ÐV"0# B"8#ÐO"08#ÐB"4# B"5#ÐO"19#ÐV"2# B"6#ÐO"10#ÐB"5#(0 O"4#ÐB"0#ÐO"3# O"4#ÐB"0#ÐO"6# O"3#ÐB"0#ÐO"6# O"4#ÐB"1#ÐO"09# O"4#ÐB"1#ÐO"8# O"09#ÐB"1#ÐO"8# O"05#(0ÐB"2#ÐO"00# O"05#(0ÐB"2#ÐO"8# O"00#ÐB"2#ÐO"8# O"05#ÐB"3#ÐO"04# O"05#ÐB"3#ÐO"03# O"04#ÐB"3#ÐO"03# O"07#ÐB"4#ÐO"06# O"07#ÐB"4#ÐO"03# O"06#ÐB"4#ÐO"03# O"07#ÐB"5#ÐO"19# O"07#ÐB"5#ÐO"6#(0 O"19#ÐB"5#ÐO"6#(0 O"5#ÐB"6#ÐO"11# O"09#ÐB"7#ÐO"01# O"01#ÐB"7#ÐO"12# O"04#ÐB"8#ÐO"13# O"14#ÐB"09#ÐO"8#(0 O"8#(0ÐB"09#ÐO"6#(0 O"8#(0ÐB"09#ÐO"03#

28[93"5# 007[81"1# 013[3"1# 006[5"1# 011[4"1# 003[6"1# 014[0"1# 011[1"1# 004[2 "1# 017[0 "1# 099[16"8# 015[8"1# 092[90"09# 010[5"1# 010[4"2# 015[4"1# 092[00"09# 010[0"2# 017[9"1# 019[8"2# 001[2"2# 097[8"1# 096[9"1# 009[0"1# 097[3"1# 096[9"1# 000[2"1# 097[2"1# 097[1"1# 000[6 "1# 097[4"1# 096[3"1# 001[3 "2# 098[7"1# 096[4"1# 001[0"1# 097[4"1# 096[4"1# 008[3"2# 013[2"2# 005[2 "2# 006[0"2# 098[6"2# 095[4"1# 096[5"1#

O"00#ÐV"2#ÐV"0#(0 B "0#ÐO"3#ÐV"2# (0 V"2#(0ÐO"3#ÐV"0# B"6#ÐO"5#ÐB"0# B"09#(0ÐO"6#ÐB"0# B"1#ÐO"7#ÐV"1# V"1#ÐO"7#ÐV"0# B"09#(0ÐO"8#ÐB"1# B"7#ÐO"09#ÐB"1# B"2#ÐO"00#ÐV"2# B"7#ÐO"01#ÐB"2# B"3#Ð"02#ÐV"2#(0 B"09#ÐO"03#ÐB"4# B"4#ÐO"03#ÐB"3# B"3#ÐO"05#ÐB"2#(0 B"4#ÐO"06#ÐV"0# B "4#ÐO"07#ÐB"5# B"5#ÐO"19#ÐV"1# V"1#ÐO"19#ÐV"2# O"4#ÐB"0#ÐO"5# O"5#ÐB"0#ÐO"3# O"5#ÐB"0#ÐO"6# O"4#ÐB"1#ÐO"7# O"7#ÐB"1#ÐO"09# O"7#ÐB"1#ÐO"8# O"05#(0ÐB"2#ÐO"01# O"01#ÐB"2#ÐO"00# O"01#ÐB"2#ÐO"8# O"05#ÐB"3#ÐO"02# O"02#ÐB"3#ÐO "04# O"02#ÐB"3#ÐO"03# O"07#ÐB"4#ÐO"08# O"08#ÐB"4#ÐO "06# O"08#ÐB"4#ÐO"03# O"07#ÐB"5#ÐO"10#(0 O"10#(0ÐB"5#ÐO"19# O"10#(0ÐB"5#ÐO"6#(0 O"5#ÐB"6#ÐO"10# O"10#ÐB"6#ÐO"11# O"09#ÐB"7#ÐO"12# O"04#ÐB"8#ÐO "08# O"08#ÐB"8#ÐO"13# O"14#ÐB"09#ÐO"6#(0 O"14#ÐB"09#ÐO"03# O"6#(0ÐB"09#ÐO"03#

004[55"6# 018[9 "1# 090[87"09# 010[1"2# 011[0"1# 017[1 "1# 092[42 "09# 011[4"1# 011[1 "2# 015[6 "1# 019[6"2# 016[3"1# 010[2"1# 006[0"1# 005[8"1# 016[0"1# 004[6 "1# 015[3"1# 099[85"09# 097[4"1# 000[8"2# 097[0"1# 001[1"2# 000[1"1# 096[6"1# 000[2"2# 098[5"1# 097[9"1# 001[0"1# 098[2"2# 096[6"1# 009[7"2# 097[5"1# 096[4"1# 009[9"1# 098[8"2# 097[6"1# 013[3"2# 005[1"2# 008[3"2# 013[0"2# 007[7"2# 002[8"2# 001[5"2# 095[0"1#

Symmetry transformations used to generate equivalent atoms] (0 −x\ −y¦0\ −z[

"which is consistent with its assignment as an O− group#[ The assignment of the O− group to the central tetrahedral boron atom "and not one of the trigonal boron atoms# is also reasonable given the fact that one would expect an oxygen atom bonded to a tetrahedral boron to be more acidic than an oxygen atom bonded to a corresponding trigonal boron[ This assignment is also consistent with valence bond calculations ð8Ł\ and the charge balancing requirements of the cluster[ As can be seen in Figs 2 and 3\ the ð"VO#5"B09O05"OH#5#1Ł3− cluster\ as a whole\ displays approximate 2¹ symmetry about an axis running

through the center of the vanadium ring perpendicular to the plane of the six vanadium atoms[ The cluster  "VÐV# at the has an approximate diameter of 5 A  "OÐO of the vanadium ring and a height of 4[8 A nearest oxygens of the central boron in each cap#[ Unlike the previously characterized V01B06O47 and V01B07O59 clusters ð5Ł\ which contain ethylenediamine template molecules and water molecules that reside between the clusters\ the intercluster space in "0# is _lled only with Rb¦ cations\ and the intracluster space contains electron density corresponding to a partially occupied water molecule[ In comparing the structures

Hydrothermal synthesis and characterization of an unusual polyoxovanadium borate cluster

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Fig[ 0[ A polyhedral representation of the hexagonal ring of six trans!edge!sharing VO4 square pyramids present in the structure of "0#[

of these unusual polyoxovanadate borate clusters\ it is interesting to note that each has a very speci_c polyborate ligand which is associated with a very spec! i_c vanadate moiety[ The V01B07O59 cluster\ for example\ comprises a puckered B07O25"OH#5 ring sandwiched between two triangular rings of six alter! nating cis and trans edge!sharing vanadium atoms[ The V01B06O47 cluster\ on the other hand\ comprises a contorted vanadium oxide ring in which two semi! circles of _ve trans edge!sharing VO4 square pyramids interpenetrate forming clefts which are occupied by B7O06"OH#3 and B8O07"OH3#"enH# chains[ Obviously\

Fig[ 1[ Two views of the B09O05"OH#57− triangular polyborate caps that are present in the structure of "0#[ The central tetrahedral boron atom has a BÐO− bond which is collinear with the pseudo 2¹ axis of the cluster\ while the other six tetrahedral boron atoms have oxygen atoms pointing in the opposite direction that are part of the hexavanadate ring[

Fig[ 2[ Two views of the structure of the ðV5B19O27"OH#01Ł3− cluster in Rb3ð"VO#5"B09O05"OH#5#1Ł = 9[4H1O "0#[

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Fig[ 3[ ORTEP view of the structure of the ðV5B19O27"OH#01Ł3− cluster in Rb3ð"VO#5"B09O05"OH#5#1Ł = 9[4H1O "0# showing the 49) probability thermal ellipsoids and atomic numbering scheme[

very sensitive relationships exist between the polyb! orate and vanadate moieties\ and these relationships are clearly dependent on synthetic conditions which will require further study[ The ¦3 oxidation state of the vanadium atoms in "0# satis_es the charge requirements of the cluster and has been con_rmed by valence bond calculations ð8Ł[ This oxidation state has also been veri_ed by magnetic susceptibility experiments[ The pale green color of the crystals also suggests that "0# contains only VIV\ and not mixed VIV:VV sites as are observed in the orange or dark red compounds containing V01B06O47 and V01B07O59\ respectively[ The facile\ high yield\ synthesis of this and other structurally and compositionally unprecedented vanadium borate clusters ð6Ł continues to point to hydrothermal synthesis as a particularly useful\ and increasingly important\ method for preparation of new compounds[ Acknowled`ements*The work at Syracuse University was supported by NSF Grant CHE8506121[ We thank Chris D[W[ Jones for performing the magnetic susceptibility measurements[

REFERENCES 0[ "a# Pope\ M[ T[\ Heteropoly and Isopoly Oxome!

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