Magneto‐Structural Studies on Two Bis‐μ‐Methoxido‐Bridged Dicopper(II) Complexes Supported by Subtly Different m‐Xylyl‐Based Terminal N₃ Donor Binucleating Ligands

Reactions of L XYL17 or L XYL18 (L XYL17 = α , α′ ‐bis[((1‐methyl‐2‐benzimidazolyl)methyl)‐ N ‐(6‐methyl‐2‐pyridylmethyl)‐amino]‐ m ‐xylene; L XYL18 = α , α′ ‐bis[((1‐methyl‐2‐benzimi‐dazolyl)‐methyl)‐ N ‐(2‐pyridylethyl)‐amino]‐ m ‐xylene) with [Cu(MeCN) 4 ](ClO 4 ) in CH 2 Cl 2 at 298 K, subsequent exposure to dioxygen, and work‐up from MeCN–MeOH, led to [Cu II 2 (L XYL17 )(μ‐OMe) 2 ](ClO 4 ) 2 •0·5H 2 O ( 1 ) and [Cu II 2 (L XYL18 )(μ‐OMe) 2 ](ClO 4 ) 2 •0.5MeCN ( 2 ). Structural characterization revealed their bis(methoxido)‐bridged binuclear copper(II) structure. The well‐known ring‐hydroxylation of the xylyl‐spacer has not been observed here. In both 1 and 2 , each copper(II) center is terminally coordinated by a common N‐methyl‐benzimidazolyl nitrogen and a tertiary amine nitrogen; in 1 , an additional terminal coordination is provided by a 6‐methyl‐2‐pyridylmethyl nitrogen, generating a five‐membered and in 2 it is by a 2‐pyridylethyl nitrogen, generating a six‐membered chelate ring. The binuclear copper(II) complexes have Cu … Cu separation of 3.0239(16) Å ( 1 ) and 3.0022(17) Å ( 2 ). The geometry around the two Cu(II) centers is almost ideal square‐pyramidal in 1 ( τ values: 0.05 and 0.015) and slightly distorted in 2 ( τ values: 0.23 and 0.243). Magnetic susceptibility measurements (100–300 K) on 1 and 2 reveal strong antiferromagnetic coupling J = –916(10) cm –1 for 1 and J = –820(10) cm –1 for 2 . The differential magnetic coupling is fine‐tuned by structural differences exerted by two subtly different non‐Schiff base m ‐xylyl‐based terminal N 3 ligands.