Structural investigation of R2Mo4O15 (R=La, Nd, Sm), and polymorphs of the R2Mo4O15 (R=rare earth) family

Details Structural investigation of R2Mo4O15 (R=La, Nd, Sm), and polymorphs of the R2Mo4O15 (R=rare earth) family Structural investigation of R2Mo4O15 (R=La, Nd, Sm), and polymorphs of the R2Mo4O15 (R=rare earth) family

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jssch.173..407n&link_type=abstract

Journal of Solid State Chemistry, Volume 173, Issue 2, p. 407-417.

Computer Science

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Scientific paper

Pyrolysis of rare earth (R) polyoxomolybdate, [R2(H2O)12Mo8O27].xH2O (R=La, Nd and Sm), at 750°C for 2-8h results in crystallization of R2Mo4O15 compounds. β-La2Mo4O15 crystallizes together with an α-form in monoclinic P21/a (No. 14), /a=13.8893(5), /b=13.0757(4), /c=20.0927(8)Å, /β=95.199(2)°, /V=3634.1(2)Å3, /Z=12, R1(I>2σ(I))=0.048, Rw (all data)=0.116. The structure is built up with {LaOn} (/n=9, 10) and {MoOn'} (/n'=4-6) polyhedral units. The {LaOn} units are polymerized into a linear {La6O39}∞ chain, while the {MoOn} are connected together to form {Mo4O15} and {Mo7O26} groups. The structure can be related to the /α-form by partial rearrangement of O atoms and small shifts of La and Mo atoms. The R2Mo4O15 (R=Nd and Sm) compounds are isomorphous with the previously reported R=Eu and Gd analogs, crystallizing in triclinic, /P1¯ (No. 2), /a=9.4989(5) and 9.4076(7), /b=11.0088(7) and 10.9583(8), /c=11.5665(6) and 11.5234(8)Å, /α=104.141(3) and 104.225(3), /β=109.838(3) and 109.603(3), /γ=108.912(3) and 108.999(3)°, /V=987.3(1) and 970.5(1)Å3, /Z=3, R1(I>2σ(I))=0.028 and 0.030, Rw (all data)= 0.079 and 0.094, respectively. The crystal structure is composed of {RO8} and {MoOn'} (/n'=4-6) polyhedral units. The molybdate units are condensed to give a corrugated {Mo4O17}∞ chain. The square-antiprismatic {RO8} units share their trigonal and square faces, forming {R2O13} and {R2O12} groups, respectively. A very short R⋯R distance (3.557(6)Å for R=Nd; 3.4956(6)Å for R=Sm) is achieved in the latter unusual {R2O12} group. A common cationic arrangement was found in all the structures in the R2Mo4O15 family: a R-R pair with the shortest separation and surrounding 12 Mo atoms. The symmetry of the cationic arrangement was reduced with an increase of atomic number of R, viz. La>Ce, Pr>Nd-Gd~Tb, Ho.

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