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Personal life and family

Haber met Clara Immerwahr in Breslau in 1889, while he was serving his required year in the military. Clara was the daughter of a chemist who owned a sugar factory, and was the first woman to earn a PhD (in chemistry) at the University of Breslau. She converted from Judaism to Christianity in 1897, several years before she and Haber became engaged. They were married on 3 August 1901; their son Hermann was born on 1 June 1902.

Clara was a women's rights activist and according to some accounts, a pacifist. Intelligent and a perfectionist, she became increasingly depressed after her marriage and the resulting loss of her career. On 2 May 1915, following an argument with Haber, Clara committed suicide in their garden by shooting herself in the heart with his service revolver. She did not die immediately, and was found by her 12-year-old son, Hermann, who had heard the shot.

Her reasons for suicide remain the subject of speculation. There were multiple stresses in the marriage, and it has been suggested that she opposed Haber's work in chemical warfare. According to this view, her suicide may have been in part a response to Haber's having personally overseen the first successful use of chlorine gas during the Second Battle of Ypres, resulting in over 67,000 casualties. Haber left within days for the Eastern Front to oversee gas release against the Russian Army. Originally buried in Dahlem, Clara's remains were later transferred at her husband's request to Basel, where she is buried next to him.

Haber married his second wife, Charlotte Nathan, on 25 October 1917 in Berlin. When out travelling, Fritz was staying at the Adlon Hotel which was near the Deutscher Klub. At this establishment, Fritz met Nathan, who was one of the secretaries and sparked his interest with her accomplishments despite not having extensive experience or education. On the day that he met her, it had been raining and she gave him an umbrella to use to which he replied "I lay the umbrella into your arms and myself and my thanks at your feet". She replied "I'd rather like the contrary". They began seeing each other and he would soon propose to her. Charlotte rejected the proposal at first due to their large age difference but eventually, she agreed. Charlotte, like Clara, converted from Judaism to Christianity before marrying Haber. The couple had two children, Eva-Charlotte and Ludwig Fritz ("Lutz"). Again, however, there were conflicts, and the couple were divorced as of 6 December 1927.

Haber and Clara's son, Hermann Haber, lived in France until 1941, but was unable to obtain French citizenship. When Germany invaded France during World War II, Hermann and his wife and three daughters escaped internment on a French ship travelling from Marseilles to the Caribbean. From there, they obtained visas allowing them to immigrate to the United States. Hermann's wife Margarethe died after the end of the war, and Hermann committed suicide in 1946. His oldest daughter, Claire, committed suicide in 1949; also a chemist, she had been told her research into an antidote for the effects of chlorine gas was being set aside, as work on the atomic bomb was taking precedence.

Fritz Haber's other son, Ludwig Fritz Haber (1921–2004), became an eminent British economist and wrote a history of chemical warfare in World War I, The Poisonous Cloud (1986). Hermann's daughter Eva lived in Kenya for many years, returning to England in the 1950s. She died in 2015, leaving three children, five grandchildren, and eight great-grandchildren. Several members of Haber's extended family died in Nazi concentration camps, including his half-sister Frieda's daughter, Hilde Glücksmann, her husband, and their two children.