A short, unsupported Cu(i)⋯Cu(i) interaction, 2.65 Å, in a dinuclear guanidine chloride complex

Abstract

The reaction of CuCl with the neutral guanidine Hhpp ligand (1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) yields two crystalline polymorphs of the neutral dimer, bis(1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) dichloro-di-copper(I) with the shortest distance known for a bridging unsupported copper(I)-copper(I) interaction.

Cuprophilic Interactions in and between Molecular Entities

“…As cuprophilic interactions are weak forces, the unsupported Cu I –Cu I interactions in aggregates are usually accompanied by other forces, such as packing in crystal lattices, hydrogen bonding, anion–cation columbic attractions, or π–π stacking interactions between supporting ligands etc., which render the weak Cu I –Cu I interactions not always readily discernible. In light of the impact that metallophilic interactions may have on macroscopic properties of bulk materials, it is thus of critical importance for corroborating cuprophilic interactions by spectroscopic investigations, such as absorption and vibration spectroscopy, in addition to X‐ray crystallography . In this regard, more efforts to prepare and characterize neutral Cu I ‐containing “monomers” and their aggregates are necessary.…”

“…Formation of these mononuclear complexes was initially attributed to the presence of the NH functionality of HPPH, which build interactions with the halido ligands. However, by changing the stoichiometry of the ratio of HPPH to CuCl to 1:1, Fackler, Jr. et al. were able to characterize the dimer [Cu(HPPH)Cl] 2 ( 124 ).…”

“…By comparing the Raman spectra of the dimeric 126 and 127 , monomeric 107 and 108 , and the supporting ligands, the stretching frequency of the unsupported Cu–Cu interactions in 126 and 127 were located at =204 cm −1 . Noteworthy is that the lack of secondary interactions, such as face‐to‐face π–π interactions or hydrogen bonding, in 126 and 127 indicates that the formation of these two dimers was mainly driven by the unsupported cuprophilic interactions.…”

Aurophilicity: The Effect of the Neutral Ligand L on [{ClAuL}2] Systems

“…The experimental examples with potential Cu I ···Cu I interactions tend to have one or several bridges between the copper atoms, see references [12,[35][36][37]. (For one unbridged Cu···Cu of 265 pm, see work by Chiarella et al [38] ) As quoted by van Koten, [35] a simple model for such a bridging was proposed by Mason and Mingos. [39] For a DFT analysis of the possible threecenter, two-electron (3c-2e) bonding, see work by Karagiannis and Tsipis.…”

Structural Diversity of Copper(I)–N‐Heterocyclic Carbene Complexes; Ligand Tuning Facilitates Isolation of the First Structurally Characterised Copper(I)–NHC Containing a Copper(I)–Alkene Interaction

“…Cuprophilic interactions in complexes lacking a bidentate ligand are less common than their argentophilic and aurophilic analogues, though some examples have been described in the literature. [29][30][31][32] It is evident from the solid state structure that distortion of the C-Cu-Br bonds (to 169.8° and 167.7°) away from linearity occurs, presumably as a result of the cuprophilic interaction. The Cu-C bond lengths of 1.91 and 1.92 Å are within the usual range for copper(I)-NHC complexes, as are the Cu-Br bond lengths (both 2.28 Å).…”