Iron cyclopentadienyl carbonyl-halide and -chalcogenolate complexes CpFe(CO)₂X (X = Cl, Br, I, TePh, SPh) readily afford cocrystals with the bidentate halogen bond donor 1,4-diiodotetrafluorobenzene (p-DITFB) under slow evaporation or vapor diffusion conditions. The same microcrystalline [CpFe(CO)₂TePh](p-DITFB) product instantly precipitates upon mixing p-DITFB and CpFe(CO)₂TePh in hexane solution. Supramolecular [CpFe(CO)₂X(p-DITFB)]_n chains in the cocrystals are assembled by halogen bonds (XB) between the electrophilic area of iodine atoms of p-DITFB and the nucleophilic area of X in CpFe(CO)_nX. The 5–10 cm⁻¹ hypsochromic shift of the CO stretching bands in the IR spectra of [CpFe(CO)₂X(p-DITFB)] cocrystals is explained by the pronounced electron-withdrawing effect of halogen bonding (XB), as supported by DFT calculations. The observed influence of the nature of the XB acceptor (X) on the XB geometry is described in terms of hybridization and electrostatic surface potential (ESP) mapping.

A number of stannylene complexes with different M: Sn ratios were obtained using various metals and substituents at the tin atom. The structures of the complexes were examined. A reaction of CpMn(CO)₂THF with (Ph₄As)⁺(SnCl₃)⁻ gave the ionic complex [Ph₄As]⁺[CpMn(CO)₂SnCl₃]⁻ (I). The action of C₆F₅MgBr on the complex C₅H₅Mn(CO)(NO)SnCl₃ produced C₅H₅Mn(CO)(NO)Sn(C₆F₅)₃ (II). Replacement of the Cl ions in the complex [CpFe(CO)₂]₂SnCl₂ by phenylacetylenide groups gave rise to the neutral complex [CpFe(CO)₂]₂Sn(C≡CPh)₂ (III). A reaction of (Dppm)PtCl₂ (Dppm is 1,1-bis(diphenylphosphino)methane) with SnCl₂ · 2H₂O in the presence of diglyme yielded the ionic complex [η³-CH₃O(CH₂)₂O(CH₂)₂OCH₃)SnCl]⁺[(η ²-Dppm)Pt(SnCl₃)₃]⁻ (IV). Transmetalation in a reaction of [(Dppe)₂CoCl][SnCl₃] · PhBr (Dppe is 1,2-bis(diphenylphosphino)ethane) with (Dcpd)PtCl₂ (Dcpd is dicyclopentadiene) in the presence of SnCl₂ afforded the ionic complex [Pt(Dppe)₂]₃[Pt(SnCl₃)₅]₂ (V). Structures I–V were identified by X-ray diffraction. In these structures, the formally single bonds between the atoms of transition metals M (Mn, Fe, and Pt) and Main Group heavy elements (Sn and P) having vacant d orbitals are appreciably shortened. The M-Sn bond length in complexes II and III are virtually independent of the substituents at the tin atom and the Pt-Sn bond length in complexes IV and V is virtually independent of the Pt: Sn ratio.

The supramolecular arrangement of 4-cyanopyridine (4CNpy) in its native crystal form and its co-crystals with halogen bond (XB) donors is discussed in terms of long-range synthon aufbau modules (LSAMs) and energy frameworks. Dissociations of 2D zigzag chains of parent 4CNpy into 1D dimers observed in its co-crystals are in good agreement with the aufbau model. Its co-formers, XB donors 1,4-I₂(CF₂)₄, C₂I₂, 1,3- and 1,4-I₂C₆F₄ (m- and p-DITFB), provide equal energy of I⋯N XBs, but perfluorinated iodo-alkane 1,4-I₂(CF₂)₄ and diiodoacetylene C₂I₂ cannot achieve the same strength of homomolecular aggregation as π–π stacking in columnar DITFB modules. As a result, DITFBs form I⋯N XBs with both N_py and N_CN nitrogen atoms of 4CNpy, while 1,4-I₂(CF₂)₄ and C₂I₂ only with the N_py atom. This is not a particular case of 4CNpy co-crystals, but in general, DITFB appears to be a more effective XB donor co-former than C₂I₂, 1,4-I₂(CF₂)_n and other iodo-XB donors, which has similar potential to an iodine atom but lacks homomolecular aggregation. In supramolecular reactions of p-DITFB with (η⁶-Ar)RuX₂(4CNpy) (Ar = p-cymene, X = Cl, I) bearing N_py-coordinated 4CNpy, the former gives definite preference to the XBs with the halogen atoms, but not to the CN group of the 4CNpy ligand.

A carboxylate⋯iodine supramolecular heterosynthon can be reliably applied in cocrystal engineering, using metal carboxylates as building blocks. Analysis of the energy framework of the exemplary paddlewheel crystal [Cu(OAc)₂MeOH]₂ indicates a robust 1D chain and even 2D layer long-range synthon modules, which can be intactly transferred into cocrystals. However, this approach allows the identification of a “weak link” – i.e. layers where the C–H⋯OC hydrogen bonds between ([Cu(OAc)₂(MeOH)]₂)_n polymeric chains will be subject to substitution by I⋯OC halogen bonds during interaction with halogen bond donor co-formers. In contrast to the O–H⋯OC/C–H⋯OC catemeric crystals of pure acetic acid, the crystal design exercise based on the I⋯OC(carboxyl) supramolecular synthon afforded a 1 : 1 cocrystal of 1,4-C₆F₄I₂ and CH₃COOH, where the discrete centrosymmetric dimers of acetic acid are stabilized by I⋯OC(carboxyl) halogen bonds.

Each PdO₄ plane of Pd₃(OAc)₆ behaved as a 5-center nucleophile (O lone pairs and the d_z²-Pd^II orbital) that interacts with π-donating arenes to afford highly polar circular stacking, where organics wrapped inorganics.