The synthesis and characterization of the complexes of Cu(I), Ag(I), Cu(II), and Co(II) ions with 1,2,5-selenadiazolopyridine (psd) is reported. The following complexes have been prepared: [Cu(2)(psd)(3)(CH(3)CN)(2)](2+)2(PF(6)(-)); [(CuCl)(2)(psd)(3)]; [Cu(2)(psd)(6)](2+)2(ClO(4))(-); [Ag(2)(psd)(2)](2+)2(NO(3))(-); [Ag(2)(psd)(2)](2+)2(CF(3)COO)(-); [Cu(psd)(2)(H(2)O)(3)](2+)2(ClO(4))(-)·(psd)(2); [Cu(psd)(4)(H(2)O)](2+)2(ClO(4))(-)·(CHCl(3)); [Cu(psd)(2)(H(2)O)(3)](2+)2(NO(3))(-)·(H(2)O)·(psd)(2), and [Co(psd)(2)(H(2)O)(4)](2+)2(ClO(4))(-)·(psd)(2). The electronic structure of ligand psd, in particular the bond order of Se-N bonds, has been probed by X-ray diffraction, (77)Se NMR, and computational studies. A detailed analysis of the crystal structures of the ligand and the complexes revealed interesting supramolecular assembly. The assembly was further facilitated by the presence of neutral ligands for some complexes (Cu(II) and Co(II)). The molecular structure of the ligand showed that it was present as a dimer in the solid state where the monomers were linked by strong secondary bonding Se···N interactions. The crystal structures of Cu(I) and Ag(I) complexes revealed the dinuclear nature with characteristic metallophilic interactions [M···M] (M = Cu, Ag), while the Cu(II) and Co(II) complexes were mononuclear. The presence of M···M interactions has been further probed by Atoms in Molecules (AIM) calculations. The paramagnetic Cu(II) and Co(II) complexes have been characterized by UV-vis, ESI spectroscopy, and room temperature magnetic measurements.

Pinacolyltellurium(IV) dihalides, (t-BuCOCH 2 ) 2 TeX 2 (X ) Br (1b), I (1c)) and Ar(t-BuCOCH 2 )TeCl 2 (Ar ) 1-C 10 H 7 (Np) (2a), 2,4,6-Me 3 C 6 H 2 (Mes) (3a)), are readily prepared at room temperature by the oxidative insertion of elemental tellurium into the C sp 3 -Br or -I bond of the R-halopinacolone and by the reaction of ArTeCl 3 with the pinacolone t-BuCOCH 3 . The bromides Np(t-BuCOCH 2 )TeBr 2 (2b) and Mes(t-BuCOCH 2 )TeBr 2 (3b) can be prepared by the addition of bromine to the telluride Ar(t-BuCOCH 2 )-Te or of R-bromopinacolone to ArTeBr. Variable-temperature 1 H and 13 C NMR of the separate signals for the o-Me groups in 3a,b indicate a very high barrier to rotation about the Te-C(aryl) bond. Crystal diffraction data for 1c, 2a-c, and 3b show that intramolecular 1,4-Te‚‚‚O(C) secondary bonding interactions (SBIs) are retained even in the presence of bulky aryl groups and intermolecular Te‚‚‚X SBIs are subject to electronic population and steric congestion around the Te(IV) center in the solid state.

Electrophilic substitution of acylmethanes (methyl ketones), RCOCH3 (R = i-Pr, 1; Et, 2; Me, 3) with aryltellurium trichlorides, ArTeCl3 (Ar = 1-C10H7, Np, A; 2,4,6-Me3C6H2, Mes, B; 4-MeOC6H4, Anisyl, C) under mild conditions affords the corresponding acylmethyl(aryl)tellurium dichlorides (RCOCH2)ArTeCl2. Reduction of the dichlorides, gives tellurides, (i-PrCOCH2)ArTe, 1A-1C, which give the corresponding dihalides, (i-PrCOCH2)ArTeX2 (X = Cl, 1Aa-1Ca; Br, 1Ab-1Cb; I, 1Ac-1Cc) when reacted in situ with SO2Cl2, Br2 or I2. The unsymmetric tellurides are labile towards disproportionation and attempts to obtain them lead to the isolation of Ar2Te2 except in the case of (i-PrCOCH2)MesTe (1B), which represents an interesting example of a kinetically stable aryl(alkyl)telluride. All the dihalomesityltellurium(IV) derivatives show separate 1H and 13C NMR signals for the ortho methyls irrespective of the sizes of R and X ligands. The telluride, 1B with free rotation about Te-C(mesityl) bond shows, like the unsymmetric diorganotellurium(IV) dihalides, only one 125Te NMR signal. The 1,4-chelating behavior of the acyl ligand among diorganotellurium(IV) compounds is inferred from the X-ray diffraction data for 1Aa, 1Ac, 1Ba, 1Bb, 1cA and 1Cc which are indicative of the presence of intramolecular Te...O secondary bonding interactions (SBIs) at least in the solid state. As a consequence, steric repulsion in case of the mesityltellurium(IV) derivatives, 1Ba and 1Bb, reaches the threshold so as to cause loss of two-fold rotational symmetry of the mesityl group about the Te-C(mesityl) bond axis. Intermolecular C-HO...O H-bonding interactions appears to stabilize such an orientation of the aryl ligand at least in the solid state.