Unprecedented Large Temperature Dependence of Silver(I)–Silver(I) Distances in Some N-Heterocyclic Carbene Silver(I) Complex Salts

Abstract

Six examples from a series of complex salts containing bis(1,3-dialkylimidazol-2-ylidene)silver(I) cations (with dialkyl = dimethyl, diethyl, methyl, ethyl, diisopropyl) with [PF 6 ] − , [SbF 6 ] − , [ClO 4 ] − , or [AgBr 2 ] − anions, respectively, were prepared in high yields and characterized by elemental analysis, 1 H and 13 C NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction experiments reveal unprecedentedly large contractions of the metallophilic Ag(I)−Ag(I) distances in the solid-state structures upon cooling. In the salt containing diisopropylsubstituted ligands and [PF 6 ] − anions, a contraction from 3.498(8) to 3.180(2) Å was observed on cooling from 293(1) to 100(1) K. Photochemical measurements show strong hypsochromic shifts of the emission maxima upon cooling, underlining the metallophilic-based nature of the emission bands. Ab initio calculations show that the strong temperature dependence of the observed Ag−Ag distances can be attributed to some extent to both the shallowness and the anharmonicity of the intermetallic interaction potential. The Ag−Ag interaction potentials are found to be attractive only when relativity is accounted for in the calculations.

Cobaltocenium Carboxylate Transition Metal Complexes: Synthesis, Structure, Reactivity, and Cytotoxicity

“…This situation is observed in all common silver carboxylates, where similar Ag–Ag distances typically in the range of 2.7–3.0 Å are present 11. Commonly such weak d 10 ‐d 10 interactions are called argentophilic behavior that has been supported by theoretical calculations on various levels11,12 as well as by Raman11 and luminescence data 12. It is interesting to note that the zwitterionic cobaltocenium carboxylate and regular uninegative carboxylate ligands behave quite similarly in terms of argentophilicity, however, this is mostly the consequence of the geometric constraints of the carboxylate donor moieties.…”

Through‐Space Spin Coupling in a Silver(II) Porphyrin Dimer upon Stepwise Oxidations: AgII⋅⋅⋅AgII, AgII⋅⋅⋅AgIII, and AgIII⋅⋅⋅AgIIIMetallophilic Interactions

“…[1][2][3] Heavier d 8 transition-metal ions are considered to have a closed shell and have been shownt ob ei nvolved in metallophilic interactions. There are severalreports of argentophilic interactions with silver(I); [5] however,d ue to the open-shell configuration, no evidenceo fs uch interactions for silver(II) is claimed [2a] and only recently [6] we have shown evidence of Ag···Ag interactions with Ag III .S of ar,t here is no systematic investigation to estimatet he structure and energy characteristics of metallophilic interactions in Ag II /Ag II (d 9 /d 9 ), Ag III /Ag III (d 8 /d 8 ), and also mixed-valent Ag II /Ag III (d 9 /d 8 )c omplexes,w hich have been demonstrated in the presents tudy.…”

Direct X‐Ray Scattering Evidence for Metal–Metal Interactions in Solution at the Molecular Level

“…X-ray diffraction measurements at different temperatures (100-298 K) show that the geometry of the [Ag 2 (bisNHC) 2 ] 2+ ions are not significantly affected by temperature. [15] Theg eometry of the Uconformer 2a ( Figure 2a)i s almost identical to that of the cation of 1,e xcept for the side arms. [19] For 2a,t he dihedral ("open-book") angle is 73.38(5)8 8 and the separation between the silver atoms (Ag1 À Ag2) has adistance of 3.4431 (3) , whereas for 1 these values measured 73.38 (7) 8 8 and 3.4512(5) .…”