Distortion of ethyne on coordination to silver acetylide, C2H2⋅⋅⋅AgCCH, characterised by broadband rotational spectroscopy and ab initio calculations

Abstract

The rotational spectra of six isotopologues of a complex of ethyne and silver acetylide, C2H2⋅⋅⋅AgCCH, are measured by both chirped-pulse and Fabry-Perot cavity versions of Fourier-transform microwave spectroscopy. The complex is generated through laser ablation of a silver target in the presence of a gas sample containing 1% C2H2, 1% SF6, and 98% Ar undergoing supersonic expansion. Rotational, A0, B0, C0, and centrifugal distortion ΔJ and ΔJK constants are determined for all isotopologues of C2H2⋅⋅⋅AgCCH studied. The geometry is planar, C2v and T-shaped in which the C2H2 sub-unit comprises the bar of the "T" and binds to the metal atom through its π electrons. In the r0 geometry, the distance of the Ag atom from the centre of the triple bond in C2H2 is 2.2104(10) Å. The r(HC≡CH) parameter representing the bond distance separating the two carbon atoms and the angle, ∠(CCH), each defined within the C2H2 sub-unit, are determined to be 1.2200(24) Å and 186.0(5)°, respectively. This distortion of the linear geometry of C2H2 involves the hydrogen atoms moving away from the silver atom within the complex. The results thus reveal that the geometry of C2H2 changes measurably on coordination to AgCCH. A value of 59(4) N m(-1) is determined for the intermolecular force constant, kσ, confirming that the complex is significantly more strongly bound than hydrogen and halogen-bonded analogues. Ab initio calculations of the re geometry at the CCSD(T)(F12(*))/ACVTZ level of theory are consistent with the experimental results. The spectra of the (107)Ag(13)C(13)CH and (109)Ag(13)C(13)CH isotopologues of free silver acetylide are also measured for the first time allowing the geometry of the AgCCH monomer to be examined in greater detail than previously.

Distortions of ethyne when complexed with a cuprous or argentous halide: the rotational spectrum of C2H2⋯CuF

“…Similar distortions have now been observed in the series of molecules C 2 H 2 ···CuF, C 2 H 2 ···AgCl, 4 C 2 H 2 ···AgCCH, 5 and C 2 H 2 ···CuCl, 6 each of which has the planar T-shaped, C 2v geometry with the metal atom adjacent to the ethyne π bond (see Fig. 1 ).…”

Chemistry in Laser-Induced Plasmas: Formation of M–C≡C–Cl (M = Ag or Cu) and their Characterization by Rotational Spectroscopy

“…The geometry of the 2 ∑ ground state of the CCCl radical has r (C–C) = 1.267 Å, r (C–Cl) =1.634 Å, and ∠CCCl = 156.9°. The first and third of these lie midway between the corresponding values in ethyne and ethene (see ref ( 18 ) for the r 0 geometries of HC≡CH and CH 2 =CH 2 ), while r (C–Cl) = 1.634 Å is very similar to the corresponding distance determined here for both Ag–C≡C–Cl and Cu–C≡C–Cl. This suggests a structure for CCCl with 2.5 C–C bonds.…”

“…Although correlation problems prevent fitting of zero-point principal moments of inertia to determine independently all three distances r (M–C), r (C≡C), and r (C–Cl) necessary to define the r 0 geometry of the linear molecules M–C≡C–Cl (M = Ag or Cu), some progress is possible as follows. We assume that, for Ag–C≡C–Cl, r (C≡C) lies within 0.02 Å of the equilibrium value 1.2219 Å calculated at the CCSD(T)/aug-cc-pV5Z level of theory (a reasonable assumption given the high level of theory and the fact that the difference 18 , 19 between r 0 and r e for the short, stiff triple bond in acetylene is 0.003 Å). The values that result from fitting the other two distances to all six observed zero-point principal moments of inertia (using the program STRFIT of Kisiel 20 ) are then r (Ag–C) = 2.015(14) Å and r (C–Cl) = 1.635(6) Å, where the errors quoted reflect the range of values implied by the assumed range ±0.02 Å in r (C≡C).…”

A perspective on chemistry in transient plasma from broadband rotational spectroscopy

“…An example arises from recent experiments that characterised the geometry of the C 2 H 2 Á Á ÁAgCCH complex. 47 Natural samples of many common metals, including silver, are comprised of more than one naturally-abundant isotope leading to distinctive and characteristic patterns of transitions in spectra. Such distinctive patterns are of considerable value in facilitating the assignment of spectra whose molecular carriers are initially unknown and unpredicted.…”