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).

Abstract

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.