Halogen bond in crystal engineering : structural studies on crystals with neutral ruthenium centered complexes and 1-(4-pyridyl)-4-thiopyridine zwitterion as halogen bond acceptors

Abstract

This work focuses on using both ruthenium complexes and a newly synthesized organic zwitterion as halogen bond (XB) acceptors to construct a series of crystal structures and to investigate the selectivity of halogen bond. p-Diiodotetrafluorobenzene (p-DITFB) was used as the halogen bond donor to co-crystalize with [Ru(bpy)(CO)2X2] (X=Cl, Br, I), yielding a series of crystals 1-3. The strength of X…I in 1-3 follows the order of Ru-Cl>Ru-Br>Ru-I, indicating electrostatic nature of the XBs. Isomorphic [Ru(bpy)(CO)2Cl2]•p-DITFB (1) and [Ru(bpy)(CO)2Br2]•p-DITFB (2), with both halido ligands involved in XB, form zig-zag chains, which expand into 3D network with solvent accommodating voids. [Ru(bpy)(CO)2I2]•p-DITFB (3) forms linear chains with only one of the two iodo ligands involved in XB. The neighboring linear chains are further linked together via F…O interaction to form 3D networks. The XB preference for S over N in the sulfur coordinated thiocyanate ligand of [Ru(bpy)(CO)2(S-NCS)2] was studied with I2 as XB donor. The computational analysis results, which demonstrate no major energy differences between SCN…I and NCS…I system, suggest the pivotal role of packing effect. Moreover, because of the narrower energy gap between HOMO and LUMO in [Ru(bpy)(CO)2(S-NCS)2]•2I2 than in [Ru(bpy)(CO)2(S-NCS)2]•I2 (4), the singly interacting adduct (4) was the only experimentally obtained structure, regardless of the amount of I2 used. A new bidentate XB acceptor, 1-(4-pyridyl)-thiopyridine (PTP), incorporating both bidentate sp3-S and monodentate sp2-N, has been synthesized. Three crystals (5-7) were obtained from co-crystalizing the PTP with p-diiodobenzene (DIB), p-DITFB, and iodopentafluorobenzene (IPFB), respectively. The structure of 5-7 demonstrate the selectivity of XB between S and N as well. All the results from this study prove that XB is a viable tool in constructing extended metal networks with [Ru(bpy)(CO)2X2], and, however, indicate that all the other intermolecular interactions, along with XB, also exert unneglectable impact on the crystal formation.