Syntheses, Crystal Structures and Spectroscopic Studies of Bis[1‐methyl‐3‐(methoxycarbonylmethyl)‐benzimidazolium]²⁺ [CuBr₄]²⁻ and [ZnBr₄]²⁻ Compounds

Abstract

X‐ray diffraction structure of two new bis [1‐methyl‐3‐(methoxycarbonylmethyl) benzimidazolium]2+ [CuBr4]2− and [ZnBr4]2− compounds has been determined. Zn‐crystal is monoclinic with perfect Td symmetry of the ZnBr4 tetrahedron, whereas the Cu‐compound is orthorhombic with D2d symmetry of CuBr4 tetrahedron. The difference in these structures is described as due to the static Jahn‐Teller effect. Vibrational spectroscopy (1800–3200 cm−1) identified hydrogen bond network. NIR‐UV‐Vis spectra (5000–50000 cm−1) are dominated by ligand‐to‐metal bands with d‐d transition contribution. EPR results (Q‐band) analyzed in terms of the MO‐theory showed a very strong delocalization of unpaired electron density on ligands accompanied by the Cu(II) 4pz orbital contribution. This effect is partially compensated by charge transfer transitions to the EPR g‐factor.

Crystal Chemistry, Optic and Magnetic Characterizations of a New Copper Based Material Templated by Hexahydrodiazepine

“…A multipeak Gaussian fitting was used to characterize the possible electronic transitions within the title compound (Figure ). The bands observed around 1000 nm are characteristic of d–d transitions within the halidocuprate­(II) complex in its pseudotetrahedral D 2 d geometry . The bands at 910 and 1089 nm are assigned to the crystal field transitions from the a 1 (d z 2 ) and e (d xz ; d yz ) orbitals to the highest energy level b 2 (d x 2 – y 2 ), respectively .…”

“…26 , 27 With Br2i–Cu1–Br2 and Br1–Cu1–Br1i angles of 124.87(8) and 138.44(8)°, respectively, the tetrahedral [CuBr 4 ] 2– ion is strongly distorted and has D 2 d symmetry. 28 This expected distortion is due to the Jahn–Teller effect. The C–C and N–C distances range from 1.448(19) to 1.512(16) Å and from 1.473(10) to 1.490 (12) Å, respectively ( Table S1 ).…”

“…The bands observed around 1000 nm are characteristic of d–d transitions within the halidocuprate(II) complex in its pseudotetrahedral D 2 d geometry. 28 The bands at 910 and 1089 nm are assigned to the crystal field transitions from the a 1 (d z 2 ) and e (d xz ; d yz ) orbitals to the highest energy level b 2 (d x 2 – y 2 ), respectively. 36 The bands located at 264, 380, 508, and 631 nm are due to the ligand–metal charge transfer (LMCT) from p-orbitals of the Br – ligand to d-orbitals of Cu 2+ (b 2 (d x 2 – y 2 )).…”

“…In the inorganic anion, the central Cu 2+ cation is coordinated by four Br – anions and forms a [CuBr 4 ] 2– distorted tetrahedron (see Figure b). The inorganic part is constituted by an isolated [CuBr 4 ] 2– tetrahedron with the Cu–Br bond distances varying from 2.3697(10) to 2.4049(11) Å and the Br–Cu–Br angles ranging from 99.34(3) to 138.44(8)° (Table S2), which are comparable to those found in similar structures. , With Br2i–Cu1–Br2 and Br1–Cu1–Br1i angles of 124.87(8) and 138.44(8)°, respectively, the tetrahedral [CuBr 4 ] 2– ion is strongly distorted and has D 2 d symmetry . This expected distortion is due to the Jahn–Teller effect.…”