The application of 1 H, 2 H, and 13 C solid-state NMR spectroscopy to polycrystalline paramagnetic sandwich compounds was tested for chromocene (Cp 2 Cr), deuteriated chromocene (Cp 2 Cr-d 10 ), and decamethylchromocene (Cp* 2 Cr).

To shed light on the interaction in molecule-based magnetic materials, the decamethylmetallocenium hexafluorophosphates, [(C(5)Me(5))(2)M](+) [PF(6)](-) with M = Cr, Mn, Fe, Co, and Ni, as well as the tetracyanoethenides, [(C(5)Me(5))(2)M](+) [TCNE](-) with M = Cr, Mn, Fe, and Co, have been investigated in the solid state by using (1)H, (13)C, (19)F, and (31)P NMR spectroscopy under magic angle spinning (MAS). The isotropic (13)C and (1)H NMR signals cover ranges of about 1300 and 500 ppm, respectively. From the shift anisotropies of the ring carbon signal of the [(C(5)Me(5))(2)M](+) cations, the total unpaired electron spin density in the ligand pi orbitals has been calculated; it amounts up to 36% (M = Ni) and is negative for M = Cr, Mn, and Fe. The radical anion of [(C(5)Me(5))(2)M](+) [TCNE](-) shifts the (13)C NMR signals of all [(C(5)Me(5))(2)M](+) cations to high frequency, which establishes transfer of positive spin density from the anions to the cations. The (19)F and (31)P NMR signals of the paramagnetic salts [(C(5)Me(5))(2)M](+) [PF(6)](-) are shifted up to 13.5 ppm relative to diamagnetic [(C(5)Me(5))(2)Co](+) [PF(6)](-). The signs of these shifts are the same as those of the pi spin density in [(C(5)Me(5))(2)M](+). After consideration of interionic ligand- and metal-centered dipolar shifts, this establishes cation-anion spin delocalization. The mixed crystals [(C(5)Me(5))(2)M(x)Co(1-x)](+)[PF(6)](-) have been prepared for M = Cr and Ni. They are isostructural with [(C(5)Me(5))(2)Co](+) [PF(6)](-) whose single-crystal structure has been determined by X-ray diffraction. The (13)C, (19)F, and (31)P MAS NMR spectra of the mixed crystals show that the respective two closest paramagnetic ions in the lattice delocalize spin density to [(C(5)Me(5))(2)Co](+), [(C(5)Me(5))(2)Ni](+), and [PF(6)](-). In [(C(5)Me(5))(2)M](+), about 10(-4) au per carbon atom are transferred.

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Se,NBr,, a planar molecule shaped liked dividers, was formed by the reaction of SeBr, with N(SiMe,), , which reduced the selenium to the trivalent state. Under the same conditions, Se,NCI, was obtained by the reaction of SeCI, with N(SiMe,),, retaining the tetravalent state of selenium. The molecule is formed by two edge-sharing pseudotrigonal bipyramids with selenium as their central atoms. Se,NCI, reacts with PPh,CI to form the Se,NCI, ion by the addition of a CIion to only one of the two selenium atoms, resulting in pseudooctahedral coordination of this atom. Ab initio calculations for all the compounds reported confirm the experimentally determined structures.

To probe the sign of the unpaired spin density on the ligands of metallocenes neutral and cationic derivatives which contained the isodicyclopentadienyl (Isodicp) ligand have been synthesized. The resulting compounds have the composition (Isodicp)2M [M = Fe (3), V (4), Cr (5), Ni (7)], and the corresponding salts are (Isodicp)2M+PF6 - (M+ = Fe+) (3 +PF6 -), Cr+ (5 +PF6 -), Co+ (6 +PF6 -), Ni+ (7 +PF6 -). While the exo,exo-, exo,endo-, and endo,endo-isomers (a, b, and c, respectively) are conceivable, 4a, 5a, 5a +PF6 -, 7, and 7a +PF6 - have been isolated as the only isomers. By contrast, mixtures of 3a and 3b, 3a +PF6 - and 3b +PF6 -, as well as 6a +PF6 -, 6b +PF6 -, and 6c +PF6 - have been obtained; 3a and 3a +PF6 - could be separated by crystallization. Metal-dependent ligand exchange is proposed to be responsible for the isomer distribution. All compounds have been investigated by 1H and 13C NMR spectroscopy. The diamagnetic species 3a, 3b, 6a +PF6 -, and 6b +PF6 - served as NMR standards for the neutral and cationic paramagnetic species, respectively. X-ray crystal structure analyses of 3a +PF6 - and 5a +PF6 - provided similar geometrical data which were used to calculate the dipolar signal shifts and subsequently the contact shifts (δ con) of all paramagnetic compounds. The two different carbons which are separated from the Cp ring by two bonds (β carbons) have been used as probes for the spin sign. From the difference of their δ con values negative spin could be established in the ligand π orbitals of the vanadocene, chromocene, chromocenium ion, and ferrocenium ion; for the nickelocene and nickelocenium ion the spin was positive. This method proved to be most reliable, because the perturbation by σ spin delocalization could be strongly reduced. The spin-carrying orbitals were analyzed on the basis of MO calculations.