Synthesis and crystal structure of trichromium metal string complex

The synthesis, crystal structures and molecular packing of the three trichromium metal string complexes [Cr ₃(dpa) ₄Cl(OC ₂H ₅)]OH·C ₂H ₅OC ₂H ₅·2.5H ₂O (1), [Cr ₃(dpa) ₄(OH) ₂]ClO ₄·3H ₂O (2) and [Cr ₃(dpa) ₄F ₂Na(H ₂O)BF ₄]BF ₄·CH ₃OH (3) (dpa ^-=bis(2- pyridyl)amido) have been studied. The crystal structure data for 1: C ₄₆H ₅₄ClCr ₃N ₁₂O _5.5, monoclinic, P2 ₁/c, a=19.9998(4) , b=15.9756(3) , c=16.9943(3) , β=114.0548(8)°, Z=4, R ₁=0.0791, wR ₂=0.1927; for 2: C ₄₀H ₄₀ClCr ₃N ₁₂O ₉, orthogonal, Pna2 ₁, a=18.3373(2) , b=16.8220(2) , c=14.0268(2) , Z=4, R ₁=0.0683, wR ₂=0.1804; for 3: C ₄₁H ₃₈B ₂Cr ₃F ₁₀N ₁₂NaO ₂, monoclinic, P2 ₁/n, a=12.3902(1) , b=16.2081(2) , c=23.4119(3) , β=98.8725(6)°, Z=4, R ₁=0.0670, wR ₂=0.1568. The structure data were collected using graphite monochromated molybdenum Kα radiation and refined using full-matrix least square techniques on F ². The magnetic property of complex 1 was carried out on polycrystalline samples with a SQUID magnetometer. The IR, FAB-MS mass spectra of all complexes were also measured. In the three complexes, trichromium metal string complexes can be considered as mini-1D asymmetrically chains since the distance between the two axial ligands is around 1 nm. The types of hydrogen bonding in three complexes are C-H⋯O, C-H⋯Cl, C-H⋯F and O-H⋯O). 1 and 2 have a one-dimensional double-chain structures. 1 is a rare example of three-dimensional novel sandwich structure. In 3, one of the axial ligand, F ^- acts as a bridge ligand to link the sodium ion to the Cr ₃ axis with a bond angle of Cr(1)-F(1)-Na in 169.90(13)°. It can be considered as a metal string complex with an extra long axis.