The recent discovery that tertiary phosphanes PR 3 can act as bridging ligands [1] (A, Figure 1) was a breakthrough in coordination chemistry, [2] since binucleating ligands potentially allow the synthesis of di-and polynuclear complexes that are of great interest in many fields, such as catalysis, bioinorganic chemistry, and materials sciences.[3] Up to now, only two types of binuclear compounds bearing symmetrically bridging phosphanes are known (Rh I [1] (C) and Pd I [4] homodimers (D), Figure 1). In order to establish phosphanes as versatile binucleating ligands, it is necessary to show that they can effectively stabilize other dinuclear fragments, and that they possess properties typical of well-established bridging ligands. [3] In this paper we describe the synthesis and characterization in the solid state of the first heterobimetallic complex and the first copper(i) homodimers bearing bridging phosphane ligands. Furthermore, we show that there is a continuum between symmetrically bridging (A) and semibridging (B) [5] coordination modes ( Figure 1), a key structural feature analogous to that observed for CO, [6] which is the archetypal bridging ligand.We have synthesized a heteronuclear Pd-Pt analog of complex D 1 (Figure 1) by a stepwise method, which allows the sequential introduction of the metal centers.[4b] Treatment of Pt II complex 1 with Pd 0 , 2,5-bis(2-pyridyl)phosphole (2), [7] and two equivalents of AgOTf gave derivative 3, which was isolated as an air-stable red powder (69 % yield, Scheme 1).High-resolution mass spectrometry data and elemental analyses are consistent with the proposed formula. Between room temperature and 173 K, the 31 P{ 1 H} NMR spectrum of 3 consists of a sharp singlet at d = 49.9 ppm ( 1 J P,Pt = 2113.5 Hz). As expected, two sets of signals are present for the pyridyl groups in the 13 C{ 1 H} NMR spectrum. [8] It is noteworthy that heterobimetallic 3 is stable in CH 2 Cl 2 solution for days; no signals corresponding to the Pd I dimer D 1 ( 31 P{ 1 H} NMR: d = 69.9 ppm) or to the corresponding, hitherto-unknown Pt I dimer are observed.The proposed structure of 3 was confirmed by an X-ray diffraction study (Figure 2).[8] The dication of 3 contains two square-planar metal centers capped by two 2,5-bis(2-pyridyl)phosphole ligands acting as six-electron m-1kN:1,2kP:2kN donors. The geometric parameters of the 2,5-bis(2-pyridyl)-phosphole ligands are almost identical for 3 and the corresponding homometallic Pd I dimer D 1 .[4] The metal-metal distance in 3 (2.7851 (9) ) is fairly long compared to typical Pd I ÀPt I single bond lengths, [9] but is similar to that measured for the dipalladium complexes D (2.767(1)-2.787(1) ).[4] The dication of 3 has a crystallographic center of symmetry at the midpoint of the metal-metal bond, which induces an equal occupancy of the Pd and Pt atoms at the two metal positions.[10] The metal-nitrogen bond lengths in 3 and D 1 are essentially equal, although the geometry of the M 2 P 2 core differs: for the homobimetallic complex D 1 the P ato...

A new highly solid-state luminescent phase of a previously reported weakly luminescent Cu I 8 Pd II 1 dicationic assembly is reported revealing the high geometrical versatility of this moiety that importantly alters its luminescent properties. This very minor new species B c is based on a different conformer scaffold than the one encountered in the previously reported B o form and, essentially differs from B o by displaying shorter Cu I -Cu I intermetallic distances. DFT calculations allow concluding that the predominance in the solidstate of the weakly luminescent and less stable B o phase is due to the extra stability induced by a larger number of intermolecular non-covalent π-CH interactions in its crystalline packing and not by the intrinsic stability of the Cu I 8 Pd II 1 dicationic moiety. Calculations also revealed that a more stable conformation B calc is expected in vacuum, which bears a different distribution of Cu I -Cu I intermetallic distances than the dications in B o and B c phases. Taking into account that the geometrical alterations are associated to drastic changes of luminescence properties, this confer to the Cu I 8 Pd II 1 assembly high potentiality as stimuli-sensitive luminescent materials. Indeed, by applying mechanical or thermal stress to samples of B o phase, new phases B g and B m , respectively, were obtained. Alterations of the solid-state photophysical properties of these new species compared to those recorded for B o are reported together with a combined experimental and computed study of the structures/properties relationships observed in these phases.