Nitric oxide is a well-known mammalian signaling molecule most recognized for its vasodilation effect. However, its one electron reduced and protonated analogue HNO is not as well studied. HNO has been found to have its own unique chemical biology such as targeting thiols and direct reaction with FeIII-hemes. HNO is also a myocardial inotrope (increases heart muscle strength) and its plasma marker is calcitonin gene-related peptide (CGRP). Unfortunately, HNO undergoes rapid dimerization to N2O and H2O, thus necessitating the need for HNO donors. The current donors have limitations such as co-releasing other reactive nitrogen species (RNS), short half-lives, or non-biological HNO release. One approach to making a better HNO-donor is metal-nitroxyls (M-HNO/M-NO–) as these complexes are often critical intermediates in the global nitrogen cycle. Described herein is the synthesis and characterization of a family of {CoNO}8/9 complexes with a LN4 tetradentate supporting ligand for the facile release of HNO.