title: Mononuclear and polynuclear copper(I) complexes with a new N,N',S-donor ligand and with structural analogies to the copper thionein core.
abstract: The N,N',S-donor ligand 4-methoxy-3,5-dimethyl-2-((3-(2-(methylthio)phenyl)-1H-pyrazol-1-yl)methyl)pyridine (L) was prepared from 2-(chloromethyl)-4-methoxy-3,5-dimethylpyridine hydrochloride and 3-(2-(methylthio)phenyl)-1H-pyrazole. The Cu(I) complexes [Cu2(L)2CH3CN][Cu(L)CH3CN](BF4)3 (1), [Cu(L)PPh3]BF4 (2), and [Cu6(L)2(C6F5S)6] (3) were prepared and characterized by X-ray crystallography (PPh3=triphenylphosphine, C6F5S-=pentafluorothiophenolate). The unit cell of compound 1 consists of cocrystallized mononuclear and dinuclear entities in which all of the copper atoms exhibit distorted tetrahedral coordination. Compound 2 is monomeric with L bound in the kappa3-N,N',S mode and a PPh3 molecule that completes the coordination environment. Compound 2 presents a fluxional behavior in CDCl3 solution due to the boat inversion of the six-membered N,N' chelate ring (DeltaH=+43.6(3) kJ mol(-1), DeltaS=-16(1) J mol(-1) K(-1)). Crystallization of 3 in acetonitrile leads to a polynuclear structure that contains a CH3CN molecule coordinated to one of the copper atoms: [Cu6(L)2(C6F5S)6CH3CN] (3a). The core of 3a partially resembles a {Cu4S6} adamantane-like moiety, the only difference being that the Cu-NCCH3 interaction leads to the opening of the cluster by disrupting a Cu-Cu interaction. Part of this assembly is found in the yeast metallothionein copper(I)-cysteinate core whose crystal structure has recently been reported. Two additional [Cu(L)]+ peripheral moieties interact with the cluster by means of bridging thiolates. ESI-mass spectrometry, conductivity measurements, and 1H/19F pulsed gradient spin echo (PGSE) NMR experiments suggest that 3a dissociates in acetonitrile solution: 3a+CH3CN-->[Cu4(C6F5S)6]2-+2[Cu(L)CH3CN]+. The stability of the cluster with respect to the hypothetical mononuclear species, [Cu(L)(C6F5S)], is confirmed by DFT calculations (B3LYP), which illustrate the exergonic character of the reaction: 6[Cu(L')(C6H5S)]-->[Cu6(L')2(C6H5S)6]+4L' (DeltaG298=-58.6 kJ mol(-1), where L' and C6H5S- are simplified models for L and C6F5S-, respectively). The energetics pertinent to the ionic dissociation of the cluster in acetonitrile is computed using the polarizable continuum model (PCM) approach.
authors.affiliation: Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Università degli Studi di Parma, v.le G.P. Usberti 17/a, I 43100 Parma, Italy.
authors.forename: Marcello
authors.initials: M
authors.lastname: Gennari
authors.forename: Maurizio
authors.initials: M
authors.lastname: Lanfranchi
authors.forename: Roberto
authors.initials: R
authors.lastname: Cammi
authors.forename: Maria Angela
authors.initials: MA
authors.lastname: Pellinghelli
authors.forename: Luciano
authors.initials: L
authors.lastname: Marchiò
mesh_terms: D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008668:Metallothionein / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; C007121:copper thionein; D003300:Copper; D008668:Metallothionein