Metal‐4,4′‐azobis(3,5‐dimethyl‐1H‐pyrazole) Complexes with Seven‐ and Nine‐membered Hydrogen‐bonded Rings Originating from the Pyrrolic NH Function

Abstract

The metal complexes [Cu(NO 3 ) 2 (H 2 O) 2 (H 2 azbpz) 2 ]·2H 2 O (1) and [Ni(H 2 O) 4 (H 2 azbpz) 2 ](NO 3 ) 2 ·2H 2 O (2) of 4,4Ј-azobis(3,5-dimethyl-1H-pyrazole) (H 2 azbpz) incorporate the bipyrazole as a monodentate ligand and are associated into supramolecular architectures by hydrogen bonds and azo-pz π interactions in the solid state. In 1 a cis configuration is integrated and the NH function adjacent to the metalcoordinating nitrogen atom gives rise to a seven-membered anionassisted hydrogen-bonded ring around the central metal atom bringing the NH function in endo-position to the azo-bridge. The interplay of * Prof. Dr. C. Janiak E-Mail: janiak@uni-duesseldorf.de [a]

Solid-State Landscape of 4,4′-Azobis(3,5-dimethyl-1H-pyrazole) with the Isolation of Conformer-Dependent Polymorphs

“…4,4′-Azobis­(3,5-dimethyl-1 H -pyrazole) (H 2 azbpz) (Chart ) was first synthesized by Hüttel et al in 1955 via a Mills condensation reaction, and its crystal habit was described as flat golden prisms . We synthesized H 2 azbpz via a Japp–Klingemann reaction from 4-amino­(3,5-dimethyl-1 H -pyrazole) (Scheme S1, Supporting Information) following a procedure published by us recently, where we utilized H 2 azbpz as a pyrazole-pyrazolate ligand (Hazbpz – ) in a two-dimensional zinc­(II) coordination polymer and in its neutral form in supramolecular architectures of monomeric metal-complexes. , …”

“…The conformer designation is 4,4′-{a/s},{a/s}-E, where a/s is a shortening of ap/sp, which refers to the antiperiplanar and synperiplanar configuration at the C(4)–N and C(4′)–N′ bonds respectively, and E is the configuration at the azo double bond. Note that the 4,4′-s,a-E and 4,4′-a,s-E forms cannot be distinguished in the solid state unless there is an additional element of orientation, e.g., a coordinating metal atom …”

“…37 We synthesized H 2 azbpz via a Japp− Klingemann reaction from 4-amino(3,5-dimethyl-1H-pyrazole) (Scheme S1, Supporting Information) following a procedure published by us recently, where we utilized H 2 azbpz as a pyrazole-pyrazolate ligand (Hazbpz − ) in a two-dimensional zinc(II) coordination polymer and in its neutral form in supramolecular architectures of monomeric metal-complexes. 36,38 Regarding the solid-state structures of azobenzene-compounds, sometimes a conformational disorder associated with a pedal motion of the azo-group has been observed. 25,39 and the solid-state structures of ortho-and meta-substituted azobenzene-compounds have been studied accordingly, with examples being available where conformational disorder was observed showing both conformers in one crystal structure (cf.…”

Supporting coordination through hydrogen bonding in lanthanide complexes of 7-azaindole-N-oxide

“…6 Where hydrogen bonding is desired alongside coordination bonding, pyrazole is a useful building block which combines a coordinating imine-like nitrogen atom directly attached to a pyrrole-like hydrogen bond donor. 7 N-H pyrazoles and indazoles have been widely used in engineering coordination polymers and MOFs supported by intra-or intermolecular hydrogen bonding, 8 with N-H⋯O contacts in particular playing a key role in mixed-ligand networks. 9 Beyond 1,2-diazoles however, endocyclic N-H donor functionality adjacent to a heterocyclic coordination site and with a sufficiently high pK a to remain protonated under typical reaction and crystallisation conditions is less common.…”