Syntheses, structures and magnetism of linear tri- and tetra-copper chains containing anions of N,N′-bis(pyrimidine-2-yl)formamidine

Abstract

Reaction of Kpmf (pmf(-) = anion of N,N'-bis(pyrimidyl-2-yl)formamidine, Hpmf) with divalent copper salt CuX2 afforded the linear trinuclear complexes of the type [Cu3(pmf)4](X)2 (X = BF4, 1; NO3, 2; ClO4, 3), while reaction of Kpmf with monovalent copper salt CuX gave the linear tetranuclear complexes of the type Cu4(pmf)4X2 (X = Cl, 4; Br, 5). The copper atoms of complexes 1-5 are helically bridged by four pmf(-) ligands, resulting in three different coordination modes for the pmf(-) ligands. In complexes 1-3, one pmf(-) ligand adopts a new coordination mode with the two amine nitrogen atoms chelating to the central copper atom, while the other three feature chelation by one pyrimidyl and one adjacent amine nitrogen atoms. The Cu(II)...Cu(II) distances are 2.729(2) and 2.825(2) A for 1, 2.762(1) and 2.832(1) A for 2 and 2.732(1) and 2.827(1) A for 3. In complexes 4 and 5, the pmf(-) ligands are coordinated to the copper atoms in tetradentate fashion with each nitrogen atom coordinating to one Cu atom. The Cu...Cu distances are 2.580(1) and 2.549(1) A for 4 and 2.582(1) and 2.561(1) A for 5. Antiferromagnetic interactions between the copper ions are observed with calculated g and J values of 2.03(1) and -188(2) cm(-1) for 1, 2.09(1) and -268(3) cm(-1) for 2, and 2.09(1) and -486(2) cm(-1) for 5. By comparing the magnetic data it can be shown that the bonding mode of the pmf(-) ligand is one of the important factors in determining the strengths of the Cu...Cu interactions in linear trinuclear and tetranuclear copper complexes.

Linear Copper Complex Arrays as Versatile Molecular Strings: Syntheses, Structures, Luminescence, and Magnetism

“…The mixed-valent neutral complexes 57 and 58,r eported by Chen et al,e xhibit substantially larger Cu II in ···Cu II in' separations [2.525(2)-2.580(2) ]a nd also somewhat larger Cu I out ···Cu II in distances [2.518(2)-2.525(2) ]i nc omparison to 56. [50] These tetranuclear chain complexess how strong antiferromagnetic coupling behavior as well, as evidenced by temperature-dependent magnetic susceptibility measurements. As eries of unique pentacopper(chain) complexes that exclusively contain cupric ions, 59-62,w as described by Ta nase and co-workers( Scheme 4).…”

“…Strong antiferromagnetic coupling was also observed for the closely related complexes 53 and 54. [50] The trinuclearc upric array 55 exhibitss ubstantially larger Cu II ···Cu II distances within the almostl inear metal chain. [51] At emperature-dependent magnetic susceptibilitys tudy revealed antiferromagnetic coupling between the paramagnetic Cu II centers andareduced effective magnetic momentat3 00 K( m eff = 1.4 m B ).…”

“…Although no tetranuclearc uprica ssembly with intermetallic distances below the sum of two copper van der Waals radii has been reported to date,afew examples of corresponding mixed-valent Cu I /Cu II chain complexes are known ( Figure 12). [23,50] Compound 56 wasi nitially obtained from the reactiono f[ Li(dphip)] with Cu II Cl 2 in low yields, presumably by partial reduction of Cu II Cl 2 through the lithium salt of the ligand.T his is conclusive, since the authors also obtained the completely reduced trinuclear cuprous complex [Cu 3 (dphip) 2 ](CuCl 2 )( 6,F igure 4, section2.2) as as econd reaction product.…”

Highly Luminescent Linear Complex Arrays of up to Eight Cuprous Centers

“…All of them show either as trictly linear or slightlyb ent arrangemento ff our copper centers in the solid state andt hey are predominantly ionic. [25,[27][28][29][30][31] Our approach originates from an ew multinucleating ligand whoseb asic design is well established in the form of bis(amidines)l inked to alkylenea nd aryleneb ackbones. [17,[32][33][34] These ligands have attracted considerable attention in lanthanide and in Group 4a nd 6c omplex chemistry,a lso with related catalytic applicationst hat include asymmetricc atalysis.…”

Hg(II) Coordination Polymers Based on N,N’-bis(pyridine-4-yl)formamidine

“…The coordination chemistry of metal complexes containing neutral formamidine and anionic formamidinate ligands has been investigated extensively in recent years [10]. Mononuclear and polynuclear complexes have been reported [10,11,12,13]. These types of ligands could be improved by having different directions of donor sites to construct coordination polymers with higher dimensionality [14,15].…”