Unusual triplet-triplet annihilation in a 3D copper(i) chloride coordination polymer

From Short-Bite Ligand Assembled Ribbons to Nanosized Networks in Cu(I) Coordination Polymers Built Upon Bis(benzylthio)alkanes (BzS(CH2)nSBz; n = 1-9)

With the objective to establish a correlation between the spacer distance and halide dependence on the structural features of coordination polymers (CPs) assembled by the reaction between CuX salts (X = Cl, Br, I) and dithioether ligands BzS(CH₂)_nSBz (n = 1-9; Bz = benzyl), a series of 26 compounds have been prepared and structurally investigated. A particular attention has been devoted to the design of networks with extremely long and flexible methylene spacer units between the SBz donor sites. Under identical conditions, CuI and CuBr react with BzSCH₂Bz (L1) affording respectively the one-dimensional (1D) CPs {Cu(μ₂-I)₂Cu}(μ-L1)₂]_n (CP1) and {Cu(μ₂-Br)₂Cu}(μ-L1)₂] (CP2), which incorporate Cu(μ₂-X)₂Cu rhomboids as secondary building units (SBUs). The hitherto unknown architecture of two-dimensional (2D) layers obtained with CuCl (CP3) differs from that of CP1 and CP2, which bear inorganic -Cl-Cu-Cl-Cu-Cl- chains interconnected through bridging L1 ligands, thus forming a 2D architecture. The crystallographic characterization of a 1D CP obtained by reacting CuI with 1,3-bis(benzylthio)propane (L2) reveals that [{Cu(μ₂-I)₂Cu}(μ-L2)₂]_n (CP4) contains conventional Cu₂I₂ rhomboids as SBUs. In contrast, unusual isostructural CPs [{Cu(μ₂-X)}(μ₂-L2)]_n (CP5) and (CP6) are obtained with CuX when X = Br and Cl, respectively, in which the isolated Cu atoms are bridged by a single μ₂-Br or μ₂-Cl ion giving rise to infinite [Cu(μ₂-X)Cu]_n ribbons. The crystal structure of the strongly luminescent three-dimensional (3D) polymer [{Cu₄(μ₃-I)₃(μ₄-I)(μ-L3)_1.5]_n (CP7) issued from reacting 2 equiv of CuI with BzS(CH₂)₄SBz (L3) has been redetermined. CP7 features unusual [(Cu₄I₃)(μ₄-I)]_n arrays securing the 3D connectivity. In contrast, mixing CuI with an excess of L3 provides the nonemissive material [{Cu(μ₂-I)₂Cu}(μ-L3)₂]_n (CP8). Treatment of CuBr and CuCl with L3 leads to [{Cu(μ₂-Br)₂Cu}(μ-L3)₂]_n (CP9) and the 0D complex [{Cu(μ₂-Cl)₂Cu}(μ-L3)₂] (D1), respectively. The crystallographic particularity for CP9 is the coexistence of two topological isomers within the unit cell. The first one, CP9-1D, consists of simple 1D ribbons running along the a axis of the unit cell. The second topological isomer, CP9-2D, also consists of [Cu(μ₂-Br)₂Cu] SBUs, but these are interconnected in a 2D manner forming 2D sheets placed perpendicular to the 1D ribbons. Four 2D CPs, namely, [{Cu₄(μ₃-I)₄}(μ-L4)₂]_n (CP10), [{Cu(μ₂-I)₂Cu}(μ-L4)₂]_n (CP11), [{Cu(μ₂-Br)₂Cu}(μ-L4)₂]_n (CP12), and [{Cu(μ₂-Cl)₂Cu}(μ-L4)₂]_n (CP13), stem from the self-assembly process of CuX with BzS(CH₂)₆SBz (L4). A similar series of 2D materials comprising [{Cu₄(μ₃-I)₄}(μ-L5)₂]_n (CP14), [{Cu(μ₂-I)₂Cu}(μ-L5)₂]_n (CP15), [{Cu(μ₂-Br)₂Cu}(μ-L5)₂]_n (CP16), and [{Cu(μ₂-Cl)₂Cu}(μ-L5)₂]_n (CP17) result from the coordination of BzS(CH₂)₇SBz (L5) on CuX. Ligation of CuX with the long-chain ligand BzS(CH₂)₈SBz (L6) allows for the X-ray characterization of the luminescent 2D [{Cu₄(μ₃-I)₄}(μ-L6)₂]_n (CP18) and the isostructural 1D series [{Cu(μ₂-X)₂Cu}(μ-L6)₂]_n CP19 (X = I), CP20 (X = Br) and CP21(X = Cl). Noteworthy, BzS(CH₂)₉SBz (L7) bearing a very flexible nine-atom chain generated the crystalline materials 2D [{Cu₄(μ₃-I)₄}(μ-L7)₂]_n (CP22) and the isostructural 1D series [{Cu(μ₂-X)₂Cu}(μ-L6)₂]_n CP23 (X = I), CP24 (X = Br), and CP25 (X = Cl), featuring nanometric separations between the cubane- or rhomboid-SBUs. This comparative study reveals that the outcome of the reaction of CuX with the shorter ligands BzS(CH₂)_nSBz (n = 1-4) is not predictable. However, with more flexible spacer chains BzS(CH₂)_nSBz (n = 6-9), a clear structural pattern can be established. Using a 1:1 CuX-to-ligand ratio, [{Cu(μ₂-X)₂Cu}(μ-L4-7)₂] CPs are always formed, irrespectively of L4-L7. Employing a 2:1 CuX-to-ligand ratio, only CuI is able to form networks incorporating Cu₄(μ₃-I)₄ clusters as SBUs. All attempts to construct polynuclear cluster using CuBr and CuCl failed. The materials have been furthermore analyzed by powder X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis, and the photophysical properties of the emissive materials have been studied.