Structural relationship of various squarates

Abstract

This work illustrates the structural relationship between three types of metal squarates as well as the ligand in its acid form and in its monoanion salt. Squaric acid, H2C404, is known to have a polymeric layer structure with planar molecules connected through intermolecular hydrogen bonds. The interlayer distance is only 2.649A. The crystal of H2NMe2[H3(C404)2] is found to contain columns of [H3(C404)2-] repeating units, again connected by intermolecular hydrogen bonds. Within the repeated unit, there is a symmetric hydrogen bond connected to two HC404 moieties. A new type of metal squarate with M(HCaOa)2(H20)4 [_M : MnU~ Fe n both belong to space group P1, Z-1, a = 5.194 (3), b = 7.454(2), c = 8.901(2)A, u = 67.07(2), /3 = 77.26(3), y = 74.46(4) °, for Mn u] is shown to have a layer-type structure, where all [HC404] units are bonded into infinite chains via symmetric hydrogen bonds, each (HC404)22-ligand bridging two metal ions (#-2) in a trans fashion. The structurally most well understood metal squarate M(CaOa)(H20)4 (M = Mn u, Fe u, Co u, Ni il and Zn u, space group C2/c, Z = 4) is again a polymeric chain with C4042serving as a bridging ligand between two metal ions (#-2) in trans positions. A threedimensional polymeric structure is found to have the formula M(C404)(H20)2, where C40 ]-is a bridging ligand between four metal ions (#-4). Due to the slight difference in packing, there are two structure types in this category: one is in space group R3 [M = Fe u, a = 11.440 (2), c = 14.504 (3) A,oZ = 9], the other is in Pn3n [M = Co u, a = 16.255 (3)A, Z = 24]. The structural relationship between all these structures relies heavily on the understanding of intra-and intermole-, cular hydrogen bonds. The interesting building blocks of each compound will be illustrated. There are tunnels of various sizes in all these structures.

Hydrothermal Synthesis and Structural Characterization of Two pH‐Controlled Cd–Squarate Coordination Frameworks, [Cd2(C4O4)2.5(H2O)4]·(dpaH)·1.5(H2O) and [Cd(C4O4)(dpa)(OH2)] (dpa = 2,2′‐dipyridylamine)

“…Two Cd ions are linked together through two bridging water molecules to form a [Cd(dpa)(H 2 O)] 2 4+ dimeric fragment (see Figure 5 [a] bonds fall in the same range, analogous to those in the [Cd(C 4 O 4 )(H 2 O) 2 ] complex. [10] The Cd···Cd separations along the µ 2 -O water and µ 1,2 -C 4 O 4 2-bridges are 3.670(1) and 7.672(1) Å, respectively. It should be noted that adjacent ladders are displaced by half a repeating unit along the a and c axes.…”

“…The second one (C5-C8) also adopts a µ 1,2,3 -bridging mode [12] to link Cd(1) with Cd(3) (5.918 [a] Cd (1) (14) ii 82.42 (9) O ( and 6.057 Å) and Cd(1) with Cd(1) (8.434 Å), respectively. The last one (C9-C10) adopts a µ 1,2,3,4 -bridging mode [10] ( Figure 2) to link Cd(2) with Cd(3) (2 × 5.854 and 2 × 6.088 Å), Cd(2) with Cd(2) (8.434 Å) and Cd(3)···Cd(3) (8.457 Å), respectively. To the best of our knowledge, compound 1 is the first coordination framework consisting of a Cd/squarate system with hybrid µ 1,2,3 -and µ 1,2,3,4 -bridging modes of squarates.…”

“…A very strong band centered at around 1500 cm -1 is attributed to the vibrational modes of a combination of C-O and C-C stretching motions; the assignment of which is in agreement with the characteristic of the (CO) n 2-salts. [26] [10] It is important to note that the squarate ligand (C 4 O 4 2-), acting as a bridging ligand with two different bridging modes, plays a key role in the construction of a novel 2D anionic framework. Three crystallographically distinct squarate ligands are found: the first one (C1-C4) adopts a µ 1,2,3 -bridging mode [12] (Figure 2) to link Cd(1) with Cd(2) (5.926 and 6.065 Å) and Cd(1) with Cd(1) (8.457 Å), respectively.…”

“…[10][11][12][13][14][15][16][17] Many squaratebridged metal complexes with µ 1,2 -or µ 1,3 -bridging modes incorporating different nitrogen-based, flexible ligands have been structurally characterized [18][19][20][21][22][23][24] and showed interesting magnetic behavior. [25] In this contribution, we report the hydrothermal syntheses, structures and thermal stability of two novel Cd-squarate coordination frameworks,…”

Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

“…Squarate acts as a bridge between two or more metal atoms in mono-or polydentate coordination modes when acting as a ligand towards first row transition metal ions [8,9]. It coordinates to Fe(II), Fe(III), Ni(II) and Cu(II) complexes in a l-1,3 fashion, giving binuclear [10][11][12] and chain structures [13,14], whereas the l-1,2 coordination mode has been reported for binuclear and chain complexes of Cu(II) and Pd(II) [15,16]. It is also observed that the squarate anion, with Cu(II) and Ni(II), acts as a tetramonodentate ligand and forms polynuclear compounds [17].…”