Experimental and Theoretical Studies of Metal Cation−Pyridine Complexes Containing Cu and Ag

Abstract

Photodissociative experiments were performed on Cu+−C5H5N and Ag+−C5H5N complexes in the gas phase. The dissociative ligand-to-metal charge-transfer fragments, pyridine+, were observed for both complexes. Photodissociation spectra were recorded as a function of laser wavelength. Two continuous, structureless bands were investigated in each complex. Because of the low-energy 2D state of the Cu atom, the Cu+−pyridine dissociative process is more complicated. Several possible mechanisms for this process have been discussed. The binding energies were determined experimentally to be 65.5 and 45.2 kcal/mol for Cu+−pyridine and Ag+−pyridine, respectively. M+−C5H5N (M = Cu or Ag) complexes also were studied theoretically using the HF, MP2, and B3LYP methods. All complexes under study show C 2 v symmetry. The binding energies predicted from the theoretical calculations were less than the experimental values, which were derived from the onset of the charge-transfer appearance combined with the IP (ionization potential). The complexes containing Cu+ and Ag+ are characterized predominantly by electrostatic interactions.

Infrared Spectrum of the Ag+–(Pyridine)2 Ionic Complex: Probing Interactions in Artificial Metal‐Mediated Base Pairing

“…[90] These values are in fact slightly lower than the reliable experimental value of (204 AE 16) kJ mol À1 determined by mass spectrometry monitoring equilibria of ion-molecule reactions. [64,90] Interestingly, the Ag + ÀPy(p) isomer was not identified as a local minimum in previous calculations for Ag + ÀPy [62] and the related Cu + ÀPy dimer. [91] However, calculations for Au + ÀPy yielded a shallow local Au + ÀPy(p) minimum at the MP2/6-31G(d,p) level, [33] similar to the one obtained herein for Ag + ÀPy at the MP2 and B3LYP levels (Figure 1 c) ÀPy 2 isomer in the IRMPD spectrum.…”

“…[60,61] Thus, it may be expected that the isolated Ag + ÀPy 2 complex adopts a linear PyÀAg + ÀPy configuration. Isolated complexes of metal ions with Py have been the subject of quantum chemical studies, [33,36,37,62] mass spectrometry, [35,63,64] and electronic spectroscopy. [33,36,62,65,66] Interestingly, mass spectra of Ag + ÀPy n clusters generated by laser ablation in a supersonic expansion do not show any magic numbers according to the expected strong preference for the formation of Ag + ÀPy 2 .…”

“…[50] This observation indicates that the interaction of Py with more than one Ag atom on the surface is preferentially through p bonding, whereas it changes to s bonding when interacting with a single Ag atom. [49,50] Although Ag the HF, MP2, and B3LYP levels, respectively, using the 6-31G(d,p) basis set, [62] whereas D 0 = 203 kJ mol À1 was derived at the B3LYP/6-31 + + G(d,p) level. [43] Our calculations at the MP2 and B3LYP levels using the aug-cc-pVDZ basis yield values of D 0 = 182 and 219 kJ mol À1 (Table 2).…”

“…[43] Our calculations at the MP2 and B3LYP levels using the aug-cc-pVDZ basis yield values of D 0 = 182 and 219 kJ mol À1 (Table 2). An upper limit for the experimental dissociation energy is obtained from the onset of the UV photodissociation spectrum as D 0 189.1 kJ mol À1 , [62,65] which suggests that the B3LYP level with larger basis sets might slightly overestimate the interaction. On the other hand, binding energies derived from photodissociation thresholds are not always reliable.…”

Ligands of biologically active compounds in the nanochemistry of silver and gold (A review)

“…Quantum-chemical investigation [106] of the supramolecular complexes (DPyEt) n (AgNO 3 ) m showed that one silver atom coordinates four ligands, and the attachment of a second atom provides an additional energy gain. Yang et al [107] established that the reversibility of binding in response to variations of the parameters of medium is more typical of silver than of copper, which is related to the fact that the binding energy in the latter case is almost one and a half times greater than that in the former one: 45.2 kcal versus 65.5 kcal.…”