A "stable complex" refers to a situation or relationship that is secure and unlikely to change or become unsettled. It implies a state of durability, strength, and reliability. Full definition
It forms stable complexes with copper, manganese, and zinc. (chiro.org)
«A plant can only uptake about 20 percent of the nutrients applied through soil, with the remainder either forming stable complexes with soil constituents or being washed away with water, causing runoff. (sciencedaily.com)
Fructosamines are stable complexes of carbohydrates and proteins. (2ndchance.info)