ANION-ANION INTERACTIONS INVOLVING THE [MO3SE13](2-) CLUSTER - SYNTHESES AND CHARACTERIZATION OF (ME(4)N)(2)MO3SE13, K2MO3SE12.5O0.5, AND K6MO6SE27-CENTER-DOT-6H(2)O

The hydrothermal reaction of MoO3, Na2Se2 and Me(4)NCl (molar ratio, 1 :3:2) at 135 degrees C for 3 days gave dark red needles of (Me(4)N)(2) Mo3Se13 (I); the reaction of MoO3 and K2Se2 (molar ratio of 1:2 for on e month and 1:3-5 for 3 days) at 135 degrees C gave black needle-like crystals of K2Mo3Se12.5O0.5 (II) and black chunky crystals of K6Mo6-Se -27. 6H(2)O (III) respectively. The structures were determined by sing le crystal X-ray diffraction techniques. Compound I crystallizes in th e trigonal space group P3(i)m (No. 157), Z = 1, a = 11.578(1) Angstrom , c = 6.110(2) Angstrom, V = 709.4(3) Angstrom(3). d(calc) = 3.42 g/cm (3), mu = 177.99 cm(-1). Number of data measured: 992. Number of uniqu e data: 502. Number of data having I > 3.0 sigma(I): 438. Number of va riables = 49. R/R(w) = 6.0/7.5%. Compound II crystallizes in the monoc linic space group Cm (No. 8), Z = 2, a = 11.874(3) Angstrom, b = 16.83 4(3) Angstrom, c = 5.820(3) Angstrom, beta = 116.65(2)degrees, V = 104 0(1) Angstrom(3), d(calc) = 4.45 g/cm(3). mu = 246.64 cm(-1). Number o f data measured: 997. Number of unique data: 951. Number of data havin g I > 3.0 sigma(I): 849. Number of variables = 89. R/R(w) = 4.3/5.3%. III crystallizes in the monoclinic space group P2(1)/n (No. 14), Z = 4 , a = 10.21(2) Angstrom, b = 17.84(1) Angstrom, c = 27.04(2) Angstrom, beta = 98.8(1)degrees, V = 4868(21) Angstrom(3), d(calc) = 4.15 g/cm( 3). mu = 219.98 cm(-1). Number of data measured: 8706. Number of uniqu e data: 7920. Number of data having I > 3.0 sigma(I): 3520. Number of variables = 391. The [Mo3Se13](2-) in I and [Mo3Se12.5O0.5](2-) in II are isostructural with [Mo3S13](2-), while III is the cocrystallizatio n of two K2Mo3Se13 clusters and one K2Se. The anions of I and II are t he same except that the triply bridging Se site is partially occupied by O atoms in II. Solid state IR and UV/vis spectra are reported. The [Mo3Se13](2-) cluster has been found to possess significant affinity f or anionic species, and this has been manifested in all currently know n compounds containing this trinuclear cluster. The new compounds repo rted in this paper also exhibit clearly defined anion-anion weakly bon ding interactions. Extended Huckel calculations were performed to expl ain the unusual [Mo3Se13](2-). Se2- interactions in these compounds. T he calculations show that the Se atoms (of the bridging Se-2(2-)), whi ch form the points of interaction of the cluster with the anionic spec ies, are weakly positively charged.