INTERPLAY OF STRUCTURAL FLEXIBILITY AND CRYSTAL PACKING IN A SERIES OF PARAMAGNETIC CYCLOPENTADIENYL DITHIOLENE MO AND W COMPLEXES - EVIDENCE FOR MOLECULAR SPIN LADDERS/

Mixed cyclopentadienyl/dithiolene complexes of general formula [Cp2MIV (dithiolene)] with M=Mo. W and dmit(2-) (2-thioxo-1,3-dithiole-4,5-dit hiolate), dmid(2-) (2-oxo-1,3-dithiole-4,5-dithiolate), and dsit(2-) ( 2-thioxo-1,3-dithiole-4,5-diselenolate) as dithiolene ligand are oxidi zed to the six corresponding 1:1 charge-transfer salts with TCNQF(4) ( tetrafluorotelracyanoquinodimethane), and their X-ray crystal structur es are described. The structural flexibility of these complexes is evi dent in the large variations of the folding angle of the MQ(2)C(2) pla ne (M = Mo or W, Q = S in dmid(2-) and dmit(2-), Q = Se in dsit(2-)) a long the Q-Q hinge in the [Cp2M(dithiolene)](+.) cations, and is ratio nalized thanks to an extended Huckel molecular orbital fragment analys is. In the solid, TCNQF(4)(-.) radical anions are strongly dimerized i nto diamagnetic [TCNQF(4)](2)(2-) moieties, while the [Cp2M(dithiolene )](+.) cations form head-to-tail dimers whose structure depends on the nature of the metal and the dithiolene ligand. These dimers organize in the solid state into various one-dimensional supramolecular structu res, from quasi-regular chains to spin ladders, taking full advantage of the minute differences introduced between the different complexes ( Mo vs. W,O vs. S vs. Se in the dithiolene ligands). [Cp2Mo(dmid)][TCNQ F(4)] and [Cp2W(dmid)] [TCNQF(4)] are isostructural, the [Cp2M(dmid)]( +.) cations (M=Mo, W) form dimers held together by dmid/dmid overlap i ntel actions, and they interact with each other to give spin ladders, as confirmed by the analysis of the magnetic susceptibility temperatur e dependence. Albeit isostructural, the Mo and W spin ladders exhibit different spin gaps, reflecting the differences between intermolecular overlaps. Two phases were obtained from [Cp2Mo(dmit)] and TCNQF(4), v ery thin needles of a 2:1 phase, [Cp2Mo(dmit)](2)[TCNQF(4)], and a sol vent-containing 1:1 phase, shown to be [Cp2Mo(dmit)] [TCNQF(4)][CH2Cl2 ](0.33) by X-ray crystal structure determination. In the latter minor phase, [Cp2Mo(dmit)](+.) forms head-to-tail dimers which interact with each other in a ladderlike motif, In [Cp2W(dmit) ][TCNQF(4)]. lateral S ... S interactions lead to the formation of weak dimers, which also interact with each other in a ladder-type structure. as confirmed by analysis of the magnetic susceptibility temperature dependence. [Cp2Mo (dsit)][TCNQF(4)] and [Cp2W(dsit)][TCNQF(4)] are isostructural: [Cp2M( dsit)](+.) cations (M=Mo, W) are organized into antiferromagnetic chai ns in which Cp/dsit overlap interactions alternate with lateral chalco gen/ chalcogen (Se, S) interactions.