Dimerization of Paramagnetic Trinuclear Complexes by Coordination Geometry Changes Showing Mixed Valency and Significant Antiferromagnetic Coupling through −Pt···Pt– Bonds

Abstract

Paramagnetic trinuclear complexes, trans-[Pt 2 M-(piam) 4 (NH 3 ) 4 ](ClO 4 ) x (t-M; piam = pivalamidate, M = Mn, Fe, Co, Ni, and Cu, x = 2 or 3), aligned as Pt−M−Pt were successfully synthesized and characterized. The dihedral angles between the Pt and M coordination planes in t-M are approximately parallel, showing straight metal−metal bonds with distances of approximately 2.6 Å. Except for t-Fe, the trinuclear complexes are dimerized with close contact (approximately 3.9 Å) between the end Pt atoms to form Pt−M−Pt•••Pt−M−Pt alignments with high-spin M(+2) containing five (t-Mn), three (t-Co), two (t-Ni), and one (t-Cu) unpaired electrons localized on M atoms. Several physical measurements and calculations revealed that the dimerized structures were maintained in MeCN, where cyclic voltammograms for t-M exhibited two-step oxidation and reduction attributed to Pt−Mvia mixed-valent states. Magnetic susceptibility measurements for t-M showed antiferromagnetic interaction, t-Mn: J = −0.9 cm −1 , t-Co: J = −3.5 cm −1 , t-Ni: J = −7.3 cm −1 , and t-Cu: J = 0.0 cm −1 , between the two M centers with distances of 9.0 Å through Pt•••Pt bonds.

Structure and redox behaviour of a paramagnetic Rh–Pt–Cu–Pt–Rh heterometallic-extended metal-atom chain

“…The unbridged Pt–Cu distances (3.14655(12) Å) in 2 are similar to those found in 3 (3.1632(11) and 3.0472(9) Å), 39 but are longer than the bridged Pt–Cu distances in cis -[Pt 2 Cu(piam) 4 (NH 3 ) 4 ](PF 6 ) 2 (2.6870(6) Å) 45 and trans -[Pt 2 Cu(piam) 4 (NH 3 ) 4 ](ClO 4 ) 2 (2.6495(5) and 2.6575(5) Å). 46 The Rh–Pt distances (2.7328(2) Å) in 2 are slightly longer than those in 1 (2.7289(8) Å) and 3 (2.7197(5) and 2.7092(5) Å). 39…”

“…The average g value (g av = 2.07) is smaller than g av = 2.12 (g ∥ = 2.191, g ⊥ = 2.082) in trans-[Pt 2 Cu (NHCOCH 3 ) 4 (NH 3 ) 4 ](ClO 4 ) 2 , 47 g av = 2.16 (g ∥ = 2.347, g ⊥ = 2.065) in cis-[Pt 2 Cu( piam) 4 (NH 3 ) 4 ](PF 6 ) 2 , 45 and g av = 2.16 (g ∥ = 2.35, g ⊥ = 2.07) in trans-[Pt 2 Cu( piam) 4 (NH 3 ) 4 ](ClO 4 ) 2 . 46 Based on these EPR parameters, the unpaired electron density, α 2 , in the d-orbital of Cu(+2) is estimated using the following equation: 48…”

“…According to this equation, α 2 = 0.68 for 2, which is smaller than α 2 = 0.82 for cis-[Pt 2 Cu( piam) 4 (NH 3 ) 4 ](PF 6 ) 2 , 45 and larger than α 2 = 0.42 for trans-[Pt 2 Cu(piam) 4 (NH 3 ) 4 ](ClO 4 ) 2 . 46 The pentanuclear backbone of 2 is maintained upon solvation in MeCN. The intense absorption at 334 nm for 0.025 mM 2 in MeCN (Fig.…”

“…The average g value ( g av = 2.07) is smaller than g av = 2.12 ( g ∥ = 2.191, g ⊥ = 2.082) in trans -[Pt 2 Cu(NHCOCH 3 ) 4 (NH 3 ) 4 ](ClO 4 ) 2 , 47 g av = 2.16 ( g ∥ = 2.347, g ⊥ = 2.065) in cis -[Pt 2 Cu(piam) 4 (NH 3 ) 4 ](PF 6 ) 2 , 45 and g av = 2.16 ( g ∥ = 2.35, g ⊥ = 2.07) in trans -[Pt 2 Cu(piam) 4 (NH 3 ) 4 ](ClO 4 ) 2 . 46 Based on these EPR parameters, the unpaired electron density, α 2 , in the d-orbital of Cu(+2) is estimated using the following equation: 48 α 2 = ( A ∥ / P ) + ( g ∥ − 2) + (3/7)( g ⊥ − 2) + 0.04,where P = 0.036 cm −1 , and A ∥ is the hyperfine term. According to this equation, α 2 = 0.68 for 2 , which is smaller than α 2 = 0.82 for cis -[Pt 2 Cu(piam) 4 (NH 3 ) 4 ](PF 6 ) 2 , 45 and larger than α 2 = 0.42 for trans -[Pt 2 Cu(piam) 4 (NH 3 ) 4 ](ClO 4 ) 2 .…”

Metal–Metal BondUmpolungin Heterometallic Extended Metal Atom Chains

“…Bond polarity is a fundamental property of chemical systems, with donor–acceptor interactions at the heart of acid–base reactions, − organic chemistry, , inorganic solid state chemistry, − and coordination chemistry. − For example, the modern lexicon of coordination chemistry now contains X-, L-, or Z-type ligands, which indirectly describes the polarity of a metal–ligand bond by identifying the donor and acceptor involved in the interaction. − Reversal of expected bond polarity, or umpolung , is also an important concept with impacts in organic synthesis, − catalysis, ,− frustrated Lewis pairs, , and bonding in main group chemistry. − Another area in which bond polarity plays an important but underappreciated role is in coordination compounds containing heterometallic metal–metal bonds. The recent explosion of interest in heterometallic compounds − has produced a number of systematic series that illustrate how polarity impacts heterometallic bonding generally. Bond polarity is most commonly assessed using electronegativity, χ, and we use here the Allred–Rochow definition, in which χ is effectually proportional to effective nuclear charge, Z eff , according to the following equation Here, e is the electron charge, r is the atomic radius, and a is a constant that brings the Allred–Rochow scale in line with Pauling’s electronegativity scale.…”