JournalofSolidStateChemistry170(2003)227–231 A 2 VNb 6 Cl 18 (A=Rb,In,Tl):synthesis,crystalstructure andmagneticpropertiesofanewseriesofquaternaryniobium chlorideclustercompounds ThirumalaiDuraisamy, a JeremyS.Qualls, b andAbdessadekLachgar a, * a Department of Chemistry, Wake Forest University, Box 7486, Reynolds Station, Winston-Salem, NC 27109, USA b Department of Physics, Wake Forest University, Winston-Salem, NC 27109, USA Received5March2002;receivedinrevisedform12September2002;accepted25September2002 Abstract Anewseriesofquaternaryniobiumchlorideclustercompoundscorrespondingtothegeneralformula, A 2 VNb 6 Cl 18 (A=Rb,Tl orIn),hasbeenpreparedinsealedquartztubesfromamixturecontainingNbCl 5 ,Nb,VCl 3 andRbCl,orInorTlmetalbysolid state reactions at 7501C. The structure of Tl 2 VNb 6 Cl 18 was determined using single-crystal X-ray diffraction: Crystal data: rhombohedral, R % 3(No.148), a ¼ 9:1122ð17Þ; c ¼ 25:178ð7Þ A ˚ , V ¼ 1810:5ð7Þ A ˚ 3 and Z=3.Thefull-matrixleast-squaresrefinement against F 2 converged to R 1 ¼ 0:0515; wR 2 ¼ 0:1104 (all data). The structure consists of discrete octahedral cluster units, [Nb 6 Cl i 12 Cl a 6 ] 4 linked by V 2+ and A + cations, located in a 6-coordinated octahedral and 12-coordinated anticubeoctahedral chlorideenvironment,respectively.Theintra-clusterbondlengthsindicate16valenceelectronspercluster.Magneticsusceptibility studies show paramagnetic behavior with a magnetic moment of 3.37 m B per formula unit. Electrical resistivity measurements indicateasemiconductingbehavior. r 2002PublishedbyElsevierScience(USA). Keywords: Cluster;Crystalstructure;Magneticproperties;Niobium;Chloride;Vanadium 1. Introduction Investigationsofmetal-richniobiumhalidescontain- ing Nb 6 octahedral clusters led to the discovery of a number of original structure types in which the [Nb 6 X 18 ] n (X=Cl or Br) anionic cluster constitutes the basic building block [1–4]. In most compounds obtainedthroughsolid-statehigh-temperaturesynthesis theclusterunitisstablewith16valenceelectrons(VEC) available for metal–metal bonding. The anionic cluster unitcanbestabilizedusingacombinationof(+1)metal cationsasinK 4 Nb 6 Cl 18 [5], A 2 Li 2 Nb 6 Cl 18 (A=InorTl) [6] andK 2 SrNb 6 Cl 18 [7].Perrinetal.preparedanumber of niobium chloride cluster compounds corresponding to the general formula A x LnNb 6 Cl 18 (A=alkali and Ln=lanthanide) (x ¼ 0; 1; 2) [8–11], wherein the [Nb 6 Cl 18 ] 4 anionic chloride units are stabilized by a combination of lanthanide and monovalent metal cations.Thesecompoundscrystallizeintherhombohe- dral crystal system (space group R % 3) except for CsLnNb 6 Cl 18 , which crystallizes in the trigonal crystal system(spacegroup P % 31c).Theseries LnNb 6 Cl 18 [9,11] is based on cluster units containing 15 electrons in metal–metal bonding states leading to paramagnetic behavior. Our work in this field has focused on the investigation of halides and oxyhalides containing transition metals as counter-ions and led to the discovery of Rb 2 Cu 2 Nb 6 Cl 18 [12] which contains Cu(I), K 2 MnNb 6 Cl 18 [13] which contains Mn(II), the series ATiNb 6 Cl 18 (A=K, Rb, Cs, In, Tl) [14], which contains Ti(III) and a number of low-dimensional oxychlorides containing Ti(III) as counter-ion [15–19]. In this paper, we report the synthesis of the new reduced niobium chloride cluster compound series with the general formula A 2 VNb 6 Cl 18 (A =Rb, Tl or In) containing vanadium counter-cations and alkali metals or group 13 cations. The crystal structureofTl 2 VNb 6 Cl 18 anditsmagneticpropertiesare discussed. *Correspondingauthor.Fax:336-758-4656. E-mail address: lachgar@wfu.edu(A.Lachgar). 0022-4596/03/$-seefrontmatter r 2002PublishedbyElsevierScience(USA). PII:S0022-4596(02)00054-3