Crystal Structure of [11,14,17,110,51,54,57,510-Octaaza-1,5(1,4)-dicyclododecana-3,7(1,3)-dibenzenacyclooctaphane]zinc(II) tetrakis(nitrate), [m,m-bis(ZnII-cyclen)](NO3)4

Abstract

1,4,7,10-Tetraazacyclododecane, cyclen, is a macrocyclic (12-membered) tetraamine, and its ZnII complexes have been utilized as biological probes.1 Fujioka et al. reported a ZnII complex of the dinuclear cyclen derivative, m,m-bis(ZnIIcyclen), for recognizing the malonate dianion (CCDC744746).2 Although the crystal structure of a macrocyclic dimer for malonate/m,m-bis(ZnII-cyclen) complex of 1:1 stoichiometry has been revealed, the monomer crystal structure of its monomer is not reported. The malonate bridges may affect the structure in the macrocyclic dimer. Here, to elucidate the structural difference between the monomer and the malonate-bridged dimer, we describe the monomer crystal structure of m,mbis(ZnII-cyclen) comprising a nitrate. The systematic name of m,m-bis(ZnII-cyclen) is [11,14,17,110,51, 54,57,510-octaaza-1,5(1,4)-dicyclododecana-3,7(1,3)-dibenzenacyclooctaphane]zinc(II)tetrakis(nitrate), and the chemical structure is provided in Fig. 1. The complex was prepared according to a method previously reported by Fujioka et al.2 Crystals suitable for X-ray structure analysis were obtained upon recrystallization with water. A preliminary examination was performed, and data were collected on a Rigaku XtaLAB Synergy-i diffractometer (Rigaku Co., Tokyo, Japan) using graphite-monochromated Cu-Kα radiation at 93.15 K. Crystal data and details regarding data collection are provided in Table 1. The initial structure was solved using an intrinsic phasing method with SHELXT-2018/3.3 All non-hydrogen atoms were refined using the full-matrix least-squares method on F2 by utilizing SHEXL-2018/3.4 All hydrogen atoms were located using a geometrical calculation, and were not refined. All calculations were performed using Olex2 crystallographic software.5 Crystallographic data were deposited to the Cambridge Crystallographic Data Center (CCDC 2041868). An ORTEP drawing of the cationic part is shown in Fig. 2, and selected bond lengths and angles are provided in Table 2. The title complex is related by a crystallographic two-fold axis along the a-axis at the center of the cavity of m,m-bis(ZnIIcyclen). The coordination geometry around the central ZnII atom, Zn1, is a distorted square pyramidal with τ 6 = 0.009 [τ = (β – α)/60, where β = N1–Zn1–N3, 137.86(10)° and α = N2– Zn1–N4i, 137.30(10)°; for an ideal square pyramid, τ = 0, whereas, for an ideal trigonal pyramid, τ = 1]. Four nitrogen atoms (N1, N2, N3, and N4i) from the cyclen unit comprise the basal plane. The apical position is occupied by an oxygen atom, O1, of the nitrate anion. Of the four nitrates, two are coordinated to the respective ZnII, one is hydrogen bonded to N3–H3, and the other is located above the cavity of m,m-bis(ZnII-cyclen). 2021 © The Japan Society for Analytical Chemistry