Synthesis, characterization, and photoinduced CO-release reactivity of a Pb(II) ﬂavonolate complex: Comparisons to Group 12 analogs Katarzyna Grubel a , Sushma L. Saraf a , Stacey N. Anderson a , Brynna J. Laughlin b , Rhett C. Smith b , Atta M. Arif c , Lisa M. Berreau a,⇑ a Department of Chemistry & Biochemistry, Utah State University, Logan, UT 84322-0300, USA b Department of Chemistry, Clemson University, Clemson, SC 29634, USA c Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA article info Article history: Received 1 May 2013 Received in revised form 11 July 2013 Accepted 18 July 2013 Available online 27 July 2013 Keywords: Lead compounds Photochemistry Carbon monoxide Flavonol Zinc compounds Catalysis abstract The synthesis, characterization, and photoinduced CO-release reactivity of [(6-Ph 2 TPA)Pb(3-Hﬂ)]ClO 4 (1; 6-Ph 2 TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; 3-Hﬂ = anion of 3- hydroxyﬂavone) is reported and compared with Group 12 analogues ([(6-Ph 2 TPA)M(3-Hﬂ)]ClO 4 (M = Hg(II) (2), Cd(II) (3), Zn(II) (4)). The Pb(II) complex exhibits unique features within this group of complexes in terms of its structural and spectroscopic features involving the coordinated ﬂavonolate ligand. Similar to the Group 12 compounds, irradiation of 1 at 300 nm in an O 2 -containing environment results in the quantitative release of CO and the formation of a Pb(II) O-benzoylsalicylate (O-bs, depside) complex via a photoinduced dioxygenase-type reaction. Comparison of the quantum yield for the reac- tion of the Pb(II) ﬂavonolate complex (U = 0.21(6)) versus the reactions of the structurally-related Group 12 metal complexes (6-Ph 2 TPA)M(3-Hﬂ)]ClO 4 (M = Hg(II) (2, U = 0.31(2)), Cd(II) (3, U = 0.28(2)), Zn(II) (4), U = 0. 09(1)) revealed that ﬂavonolate complexes of a heavy metal ion (Cd(II), Hg(II), Pb(II)) exhibit a higher reaction quantum yield than the Zn(II) derivative. Both Pb(II) and Zn(II) ﬂavonolate complexes were found to be catalysts for the oxidative photoinduced degradation of 3-hydroxyﬂavone. The com- bined results of these investigations suggest that metal contaminants typically present in soil, including toxic heavy metal ions, might facilitate the oxidative decomposition of plant-derived ﬂavonols via pho- toinduced reactions. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Lead is a widespread environmental contaminant, with soil being cited as a major point of deposition of this toxic metal ion [1–3]. As an approach toward investigating the inﬂuence of toxic Pb(II) on the photochemistry of plant-derived humic substances in soil, Cornard and co-workers recently reported studies of the photochemistry of Pb(II)–ﬂavonolate species, [Pb(3-Hﬂ)] + (3-Hﬂ = 3-hydroxyﬂavonolate) [4–6]. To date, however, the struc- tural characterization of a Pb(II) ﬂavonolate complex has not been reported. Thus, information about the coordination properties of Pb(II) versus other heavy metal ions (e.g. Hg(II), Cd(II)) with ﬂavo- nols is lacking. Additionally, there is currently a signiﬁcant gap in understanding of how Pb(II) coordination, versus that of other bio- logically relevant metal ions (e.g. Zn(II)), inﬂuences photochemical reactions that could occur in nature [7]. Spectroscopic studies of the anions of 3-hydroxyﬂavone (3-HﬂH) and quercetin (Fig. 1(b)) in the presence of Pb(II) have suggested the formation of 1:1 cationic species of the formula [Pb(3-Hﬂ)] + (Fig. 1(a)) and [Pb(quercetin)] + (Fig. 1(b)), with coordination of the metal ion at the 3-hydroxy-4-pyrone chelate motif. A similar 1:1 Pb(II)–ﬂavonolate interaction has been proposed to occur in a ruthe- nium acetylide ﬂuorescent chemosensor that includes a 3-hydrox- yﬂavonol appendage for metal coordination (Fig. 1(c)) [8]. We note that a complex of the formulation Pb(3-Hﬂ) 2 2H 2 O(Fig. 1(d)) has been reported based on elemental analysis and spectroscopic data, but was not characterized by X-ray crystallography [9]. As part of our ongoing studies of divalent metal ﬂavonolate complexes [10–12], in this contribution we report the synthesis and ﬁrst structural characterization of a mononuclear Pb(II) 3-hydroxyﬂ- avonolate complex, [(6-Ph 2 TPA)Pb(3-Hﬂ)]ClO 4 (1, 6-Ph 2 TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; 3-Hﬂ = anion of 3-hydroxyﬂavone). The structural and spectroscopic properties of this compound, as well as its photoinduced CO-release 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2013.07.029 ⇑ Corresponding author. Address: Department of Chemistry & Biochemistry, Utah State University, 0300 Old Main Hill, Logan, UT 84322-0300, USA. Tel.: +1 435 797 1625; fax: +1 435 797 3390. E-mail addresses: grubelk@gmail.com (K. Grubel), sushmasaraf4@gmail.com (S.L. Saraf), snanderson@aggiemail.usu.edu (S.N. Anderson), BrynnaL@clemson.edu (B.J. Laughlin), Rhett@clemson.edu (R.C. Smith), arif@chem.utah.edu (A.M. Arif), lisa.berreau@usu.edu (L.M. Berreau). Inorganica Chimica Acta 407 (2013) 91–97 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica