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The synthesis and characterization of a series of digermynes and distannynes stabilized by terphenyl ligands are described. The ligands are based on the Ar 0 (Ar 0 ¼ C 6 H 3 -2,6(C 6 H 3 -2,6-i Pr 2 ) 2 ) or Ar* (Ar* ¼ C 6 H 3 -2,6(C 6 H 2 -2,4,6-i Pr 3 ) 2 ) platforms which were modified at the meta or para positions of their central aryl rings to yield 4-X-Ar 0 (4-X-Ar 0 ¼ 4-X-C 6 H 2 -2,6(C 6 H 3 -2,6-i Pr 2 ) 2 , X ¼ H, F, Cl, OMe, t Bu, SiMe 3 , GeMe 3 ) and 3,5-i Pr 2 -Ar 0 or Ar* and 3,5-i Pr 2 -Ar*. The compounds were synthesized by reduction of the terphenyl germanium(II) or tin(II) halide precursors with a variety of reducing agents. The precursors were obtained by the reaction of one equivalent of the lithium terphenyl with GeCl 2 dioxane or SnCl 2 . For germanium, their X-ray crystal structures showed them to be either Ge-Ge bonded dimers with trans-pyramidal geometries or V-shaped monomers. In contrast, the terphenyl tin halides had no tin-tin bonding but existed either as halide bridged dimers or V-shaped monomers. Reduction with a variety of reducing agents afforded the digermynes ArGeGeAr (Ar ¼ 4-Cl-Ar 0 , 4-SiMe 3 -Ar 0 or 3,5-i Pr 2 -Ar*) or the distannynes ArSnSnAr (Ar ¼ 4-F-Ar 0 , 4-Cl-Ar 0 , 4-MeO-Ar 0 , 4-t Bu-Ar 0 , 4-SiMe 3 -Ar 0 , 4-GeMe 3 -Ar 0 , 3,5-i Pr 2 -Ar 0 , 3,5-i Pr 2 -Ar*), which were characterized structurally and spectroscopically. The digermynes display planar trans-bent core geometries with Ge-Ge distances near 2.26A and bending angles near 128 consistent with Ge-Ge multiple bonding. In contrast, the distannynes had either multiple bonded geometries with Sn-Sn distances that averaged 2.65A and an average bending angle near 123.8 , or single bonded geometries with a Sn-Sn bond length near 3.06 A and a bending angle near 98 . The 3,5-i Pr 2 -Ar*SnSnAr*-3,5-i Pr 2 species had an intermediate structure with a longer multiple bond near 2.73A and a variable torsion angle (14-28 ) between the tin coordination planes. M€ ossbauer data for the multiple and single bonded species displayed similar isomer shifts but had different quadrupole splittings.Scheme 1 Single bonded or multiple bonded trans-bent geometry of RMMR (M ¼ Si, Ge, Sn, Pb; R ¼ terphenyl or silyl substituents)

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New Pt(II) and Pd(II) complexes with donor-acceptor Schiff bases are conveniently prepared in only two steps. The complexes efficiently absorb in the red part of the spectrum (ε > 10(5) M(-1) cm(-1)) and show moderate to strong room-temperature phosphorescence in the near-infrared (NIR) region. Particularly, Pt(II) complexes possess phosphorescence quantum yields (Φ) of ~10%, but the emission of the respective Pd(II) complexes is less efficient (Φ ≈ 1%-2%). The complexes exhibit solvatochromic behavior, in which the absorption and emission spectra shift bathochromically in polar solvents. The Pt(II) complexes are embedded in polystyrene to produce oxygen-sensing materials. The Pd(II) and Pt(II) complexes are demonstrated to be efficient sensitizers in triplet-triplet annihilation-based upconversion systems.

Stabilization of the central atom in an oxidation state of zero through coordination of neutral ligands is a common bonding motif in transition-metal chemistry. However, the stabilization of main-group elements in an oxidation state of zero by neutral ligands is rare. Herein, we report that the transamination reaction of the DAMPY ligand system (DAMPY=2,6-[ArNH-CH2 ]2 (NC5 H3 ) (Ar=C6 H3 -2,6-iPr2 )) with Sn[N(SiMe3 )2 ]2 produces the DIMPYSn complex (DIMPY=(2,6-[ArNCH]2 (NC5 H3 )) with the Sn atom in a formal oxidation state of zero. This is the first example of a tin compound stabilized in a formal oxidation state of zero by only one donor molecule. Furthermore, three related low-valent Sn(II) complexes, including a [DIMPYSn(II) Cl](+) [SnCl3 ](-) ion pair, a bisstannylene DAMPY{Sn(II) [N(SiMe3 )2 ]2 }2 , and the enamine complex MeDIMPYSn(II) , were isolated. Experimental results and the conclusions drawn are also supported by theoretical studies at the density functional level of theory and (119) Sn Mössbauer spectroscopy.