Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

Abstract

The syntheses, structures, and photophysical properties of two new zinc(II) complexes bearing the tridentate N,N′‐dimethyl‐N,N′‐dipyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) ligand are presented. Structural investigations through single‐crystal X‐ray diffractometry, NMR spectroscopy, and density functional theory calculations revealed a diverse coordination behavior that depends on the counterion. Spectroscopic (UV/Vis and emission spectroscopy) and theoretical techniques (DFT and time‐dependent DFT calculations) were employed to explore the photophysical properties of the complexes.

Structure and Electronic Properties of an Expanded Terpyridine Complex of Nickel(II) [Ni(ddpd)2](BF4)2

“…Single crystals suitable for X‐ray diffraction were obtained from diffusion of ethyl ether into a concentrated solution of 1 (BF 4 ) 2 in MeCN. 1 (BF 4 ) 2 crystallizes as [Ni(ddpd) 2 ](BF 4 ) 2 · 2MeCN in the orthorhombic space group Fddd , isostructural to homoleptic mer ‐[ M (ddpd) 2 ](BF 4 ) 2 · 2MeCN ( M = Fe, Co, Zn) The NiN 6 coordination arrangement corresponds to a slightly compressed octahedron with four longer Ni–N bonds to the peripheral pyridine rings [Ni1–N1: 2.0923(15) Å] and two slightly shorter bonds to the central pyridine rings [Ni1–N2: 2.058(2) Å] (Figure a).…”

“…The quasireversible electrochemical oxidation of 1 2+ to nickel(III) in acetonitrile/[ n Bu 4 N][PF 6 ] occurs at E 1/2 = 1.22 V, followed by an irreversible oxidation at E p = 1.71 V vs. ferrocene (Figure S1, Supporting Information). The latter process is ligand centered . Electrochemical reduction of 1 2+ is irreversible (–2.03 V).…”

“…Compared to five‐membered chelate rings, the larger flexibility of six‐membered chelates enables an energetically less favored cis ‐facial coordination in [Co(ddpd) 2 ] 2+ in addition to the thermodynamically preferred meridional isomer , . The equilibration of octahedral [Zn(ddpd) 2 ] 2+ complexes with trigonal‐bipyramidal ZnCl 2 (ddpd) and tetrahedral [ZnCl 4 ] 2– in the presence of chloride ions demonstrates the coordination diversity of d 10 ions in the absence of ligand field stabilization . A remaining gap in the series of 3d n ‐metal(II) bis(ddpd) complexes with n = 6–10 is [Ni(ddpd) 2 ] 2+ ( 1 2+ ), a 3d 8 ‐metal polypyridine complex.…”

Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes

“…The ligand ddpd is fluorescent in solution (λ max = 398 nm; Φ = 8.0%, τ = 3.0 ns in CH 3 CN; λ max = 410 nm in acid-free CH 2 Cl 2 ) [49,50]. In acidic CH 2 Cl 2 or in the intentional presence of acid, the emission band shifts to 395 nm (τ = 4.0 ns) [49]. In contrast, protonation of tpy in CH 3 CN shifts its emission band from 340 nm to 412 nm (25.6 ns) [51].…”

Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex

“…[20,36,37] Af urther aspect is to reduce excited state distortion, especially large trigonal twists. [16,17] Similar to the mainly meridionally coordinating tridentate ligand ddpd, [3,6,[38][39][40][41][42][43] the tripodal ligand 1,1,1-tris(pyrid-2yl)ethane (tpe) [44] forms 6-membered chelate rings with nearly 908 8 bite angles with transition metal complexes. [45,46] Te tradentate tpe analogues [47] were successfully employed in several MCl 2 (L) complexes.…”