First Halogen Anion-Bridged (MMX)_<i>n</i>-Type One-Dimensional Coordination Polymer Built upon d¹⁰−d¹⁰ Dimers

The complex [Ag2(PhPPy2)2(NCCH3)2](ClO4)2 [PhPPy2 = bis(2-pyridyl)phenylphosphine] reacts with NH4Cl to form an insoluble one-dimensional polymer of the type (MMX)n, {[Ag2(PhPPy2)2Cl](ClO4)}n. The binuclear unit, Ag2(PhPPy2)22+, exhibits two PhPPy2 tridentate ligands bridging the two Ag atoms in a head-to-tail fashion with C2h symmetry, and the Ag···Ag distance [3.0942(11) Å, X-ray] suggests argentophilic interactions. Each Ag center adopts a distorted trigonal-bipyramidal geometry, coordinated by one P atom and two pyridyl arms at the equatorial positions and interacting with one Cl ion and one Ag ion at the axial positions. The short Ag−Cl bond length [2.5791(7) Å] indicates the presence of some covalent character. The solid-state absorption bands spread all the way to 600 nm have been interpreted by means of density functional theory (DFT) and time-dependent DFT (B3LYP), and the lowest-energy excited states are assigned to metal/halide-to-pyridyl charge transfer, consistent with the d10 electronic configuration of Ag. The calculated oscillator strengths are low because of the poor molecular orbital overlaps in the charge-transfer components. The novel material exhibits a luminescence band centered at about ∼520 nm.