Due to the paramagnetic nature of manganese(II) complexes and their tendency to adopt d 5 high-spin configurations with commonly 5 unpaired electrons , standard 1 H-NMR measurements do not provide insightful information on the purity and structural identity of Mn II+ compounds. As a result, Evans method NMR was used to investigate the effective magnetic moment (μeff in Bohr magneton μB) which provide evidence on the number of unpaired electrons, electronic configuration and hence the structure of the complexes in solution. Table shows the values determined for the effective magnetic moment of compound I-VII. The investigated values range between 5.0 μB and 5.5 μB. Even if the theoretical magnetic moment for 5 unpaired electrons is expected to be around 5.9 μB, the high magnetic moment found is far away from the theoretical value for one potential unpaired electron of 1.7 μB for the respective low spin complex and exhibit similar values to other experimentally determined Mn II+ high spin complexes. The deviation found compared to the theoretical values arises from contributions of the orbital angular magnetic moment. Although this analysis confirms the high spin state of the synthesized complexes, it does not help to identify the geometry of the coordination sphere as even for tetrahedral or also for octahedral coordination, 5 unpaired electrons are expected. The solid-state crystalline structures of the complexes were analyzed to gain a detailed understanding on the bonding situation. A selected set of crystal structures are presented in Figure , while the structure for compound VII can be found in the SI. Compound III could not be measured due to decomposition during the crystal picking prior to the measurement. An overview of selected structural parameters is provided in Table , while detailed crystallographic data are provided in the SI and deposited in the CCDC database. Nearly all compounds crystallize in a dinuclear state, while only the tert-butyl derivate of the acetamidinates (II) is mononuclear, that could be attributed to the steric bulk of the side chain and their repulsion towards the methyl group on the backbone (C2) which suppresses the ligand bridging required for dimerization. All the structures exhibit similar Mn-N bond distances in the range between 2.12 Å and 2.19 Å. The dinuclear as well as the mononuclear complexes were found to exhibit distorted tetrahedral coordination spheres with τ4 values of 0.54 and 0.76 -0.81 for the mononuclear and dinuclear structures, respectively. Given that the geometry index equals one for tetrahedral (τ4 = 1) and zero square planar (τ4 = 0) structures, the mononuclear structure showed a much higher degree of distortion than the dinuclear structures. This implied dimerization occurs to reduce geometrical tension around the central atoms. The compounds crystallized in a monoclinic crystal system, except compound V. Interestingly, it was found to crystalize in an orthorhombic crystal system and favored another mode of dinuclear arrangement in which the bridging guanidinate ligands formed in a z-shaped step. The dihedral angle (ω) in the backbone of the ligands (Figure ) was identified as an indicator that reflected the effects of alternating coordination on the ligands themselves: Generally, the delocalized π-electrons in the backbone of these ligands ensure a high rigidity and therefore a low dihedral angle. For the chelating amidinate ligands (I-III) it was found to be in the range between 4.1° and 30.5°. For compounds I and IV, ω exhibited small values of 35.5° and 36.6° for the bridging ligands, too. This reflects the π-electron delocalization and is in accordance with the backbone bond lengths of around 1.33 Å, which ranges between the common values for C-N double and single bonds. Contrastingly, for the guanidinates compound V and VII, much higher values of ω between 74.7° and 99.4° were found. The illustrated resonance structure of guanidinates (Figure ) between a delocalized monoanionic and a localized monoanionic structure can be used to explain this phenomenon. With higher steric demand of R, the tetrahedral coordination was observed to be accompanied by a higher torsion of the side chain and therefore a higher dihedral angle ω. Consequently, the delocalization of the π-electrons decreases and increases the electron density in the C-N amide bond of the guanidinate. In the extreme case, this phenomenon can result even in carbodiimide de-insertion , which can be a potential reason for the unsuccessful synthesis of compound VI. A further structural difference between the dinuclear amidinates (I&IV) and the dinuclear guanidinates (V&VII) was evident in the much higher Mn-Mn interatomic distances. The smallest distance found for the amidinates (I-IV) is 3.08 Å, while for the guanidinates (V&VII) a value of 4.40 was found, which may have originated from the strong distortion of the bridging ligand. Nevertheless, even the smallest Mn-Mn distance of 3.08 Å is out of the range of known Mn-Mn interactions. Even though a general structural similarity of the all-nitrogen coordinated compounds could be found, the distortion and strain within the guanidinate ligand systems in comparison to the other compounds might indicate a lower stability of these compounds comparing it with the amidinates, which is discussed in detail in the following sections.