Abstract:
A series of five new complexes incorporating N-(aminopropyl)-diethanolamine, H2apdea, has been
synthesized and characterized by employing elemental, thermal, magnetic, spectroscopic and single
crystal X-ray techniques. The reaction of transition metal salts with H2apdea under ambient conditions
affords mono-, di- or tetranuclear complexes with the compositions [Ni(H2apdea)(SCN)2]0.5H2O (1),
[Co2(Hapdea)(apdea)(SCN)2]NO31.5H2O (2), [Co2(Hapdea)(apdea)(H2O)2]3NO3H2O (3), [Cu2(Hapdea)2(H2O)2]-
2NO32H2O (4) and [Zn4(apdea)2(OCOCH3)2(SCN)2]2MeOH (5). Single crystal X-ray crystallography of 1–5
confirms that the ligand binds to the metal ions in neutral form (H2apdea) in 1, in mono- as well as dianionic
form (Hapdea and apdea2) in 2 and 3, in monoanionic form (Hapdea) in 4, and in dianionic form
(apdea2) in 5. Spectral data and crystal structures confirm the distorted octahedral (1–3), square pyramidal
(4) and tetrahedral as well as TBP geometries (5) around the metal ions. While 2 and 3 are dinuclear Co(III)
systems, the tetranuclear zinc cluster (5) shows interesting structural features with the first example of both
two tetrahedral and two TBP Zn(II) centers present in the same molecule. As a result of non-covalent
interactions, 1 forms a 2D sheet while 2–5 exist as 3D supramolecular assemblies. A 2D sheet structure is
formed due to the presence of SH interactions in 1 (O–HS = 2.518 Å, N–HS = 2.727 Å). Intermolecular
OH and SH contacts (C–HO = 2.595 Å, C–HS = 2.894 Å, N–HO = 2.123 and 2.403 Å) along
with other H-bonding interactions in 2 generate a 3D supramolecular assembly. Coexistence of a cyclic
octamer of oxygen and nitrogen atoms also helps consolidate the architecture in 2. The OH contacts,
i.e., O–HO, C–HO and N–HO interactions, play an important role in the aggregation of molecular
entities of 3 and 4 to form a 3D supramolecular network. In the case of 5, interactions between the two
tetranuclear (Zn4) clusters i.e., N–HC (2.795 Å) and N–HO (2.229 Å) and the interactions formed via
lattice solvent molecules (C–HO = 2.495 Å, O–HO = 2.003 Å, O–HC = 2.741 Å) generate a robust 3D
supramolecular network. The selected supramolecular interactions (like OH and SH) are further explored
using Hirshfeld surface analyses, and electrostatic potential (ESP) and deformation density (DD) calculations
